One-dimensional anodic TiO2nanotubes coated by atomic layer deposition:Towards advanced applications

Applied Ma e ials Today 14 (2019) 1–20 Con en s lis s a ailable a ScienceDi ec Applied Ma e ials Today j ou na l h o mepage: www.else ie .com/loca e/apm One-dimensional anodic TiO2nano ubes coa ed by a omic laye deposi ion: Towa ds ad anced applica ions Filip D o aka, Raul Zazpea,b, Milos K bala, Hanna Sophaa,b, Jan P ik yla, Siowwoon Ngb, Ludek H omadkoa, Filip Bu esc, Jan M. Macaka,b,∗ aCen e o Ma e ials and Nano echnologies, Facul y o Chemical Technology, Uni e si y o Pa dubice, Nam. Cs. Legii 565, 53002 Pa dubice, Czech Republic bCen al Eu opean Ins i u e o Technology, B no Uni e si y o Technology, Pu kyno a 123, 612 00 B no, Czech Republic cIns i u e o O ganic Chemis y and Technology, Facul y o Chemical Technology, Uni e si y o Pa dubice, S uden ska 573, 53210 Pa dubice, Czech Republic a i c l e i n o A icle his o y: Recei ed 21 Sep embe 2018 Recei ed in e ised o m 11 Oc obe 2018 Accep ed 2 No embe 2018 Keywo ds: A omic laye deposi ion TiO2nano ube Coa ings Func ionaliza ion Aspec a io a b s a c A omic laye deposi ion (ALD) ep esen s a unique deposi ion echnique ha allows o coa uni o mly a - ious high aspec a io (HAR) po ous nanos uc u es, in addi ion o i s adi ional ole o coa fla subs a es (e.g. Si wa e s). Sel -o ganized anodic TiO2nano ube (TNT) laye s belong among he mos in es iga ed ino ganic nanos uc u es. They possess highly unc ional ma e ials wi h p omising applica ion po en ial ac oss many echnological fields. He ein, we e iew he u iliza ion o ALD o he unc ionaliza ion o anodic TNT laye s by seconda y ma e ials o ad ance hei physicochemical and pho oelec ochemical p ope ies. Fi s , he applica ion o ALD o unc ionaliza ion o po ous aluminium oxide, which ep esen undamen al HAR nanos uc u e, is b iefly in oduced. Then he main expe imen al pa ame e s go e n- ing he uni o mi y and he con o mali y o ALD coa ing wi hin HAR nanos uc u es a e discussed. Finally, he e iew ocuses on he use o ALD o deposi seconda y ma e ials in o TNT laye s o a ious pu poses — he in oduc ion o pionee ing s udies is ollowed by pa icula examples o ALD based unc ional- iza ions o coa ed TNT laye s o op imized isible-ligh abso p ion, cha ge sepa a ion and passi a ion, (pho o)ca alysis, s abili y, gas sensing, and ene gy s o age. © 2018 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4.0/). Con en s 1. In oduc ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. ALD in o po ous aluminium oxide — o e iew . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Aspec s o ALD in o high aspec a io nanos uc u es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. ALD in o TiO2nano ube laye s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. Pionee ing e o s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4.2. Ligh abso p ion and pho oelec ochemical con e sion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4.3. Cha ge sepa a ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.4. Pho oca alysis and elec oca alysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.5. S abili y and imp o ed physical p ope ies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 4.6. Gas sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 4.7. Ene gy s o age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Acknowledgemen s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Re e ences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Abb e ia ions: AAO, anodic aluminium oxide; ALD, a omic laye deposi ion; CBD, chemical ba h deposi ion; DSSC, dye-sensi ized sola cell; EDX, ene gy-dispe si e X- ay spec oscopy; EOR, e hanol oxida ion eac ion; FTIR, Fou ie ans o m in a ed spec oscopy; HAADF, high-angle annula da k-field; (H)AR, (high) aspec a io; IPCE, inciden pho on o elec on con e sion e ficiency; MB, me hylene blue; MC, Mon e Ca lo; PEC, pho oelec ochemical; QCM, qua z c ys al mic obalance; QD, quan um do s; SEM, scanning elec on mic oscope; SILAR, successi e ionic laye adso p ion and eac ion; (S)TEM, (scanning) ansmission elec on mic oscope; TMA, ime hylaluminium; TNT, TiO2nano ube; UV, ul a iole spec al ange; is, isible spec al ange; XRR, X- ay eflec i i y. ∗Co esponding au ho . E-mail add ess: [email p o ec ed] (J.M. Macak). h ps://doi.o g/10.1016/j.apm .2018.11.005 2352-9407/© 2018 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY-NC-ND license (h p://c ea i ecommons.o g/licenses/by-nc-nd/4. 0/). 2 F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 1. In oduc ion Ti anium dioxide (TiO2) ep esen s a ascina ing and highly unc ional ma e ial. Un il now, TiO2has ound i s main comme cial applica ions in pigmen s, ood indus y and cosme ics. Pionee - ing obse a ion o pho oca aly ic decomposi ion o wa e a TiO2 elec ode in 1970s [1] launched he emendous in e es in he de elopmen o applica ions o TiO2in sola ene gy con e sion, ene gy s o age, and pho o-assis ed bio emedia ion, which ep e- sen essen ial componen s o he concep o enewable ene gy sou ces and o sus ainable en i onmen [2]. These applica ions also ake he ad an ages o TiO2 o be a low cos ma e ial wi h an ex emely low pho oco osion a e. Addi ionally, hanks o inhe - en biocompa ibili y, low oxici y, and high chemical s abili y o TiO2, eme gence o biomedical applica ions o TiO2, including pho- odynamic he apy o cance ea men , d ug deli e y sys ems, cell imaging, biosenso s, and gene ic enginee ing has also aken place [3]. TiO2is a wide band gap (3.0–3.2 eV) n- ype semiconduc o and hus i abso bs ligh only in he UV spec al ange. Gene ally, he ma e ial p ope ies can be uned by nanos uc u ing, ealized by a g adual dec ease o he cha ac e is ic size o applied ma e ials down o he nanome e scale [4]. Nanos uc u ing o ma e ials esul s in an ex emely inc eased su ace o olume a io wi h sig- nifican impac on ma e ial physicochemical p ope ies, including ligh abso p ion. Since many applica ions o TiO2a e o g ea ex en influenced by he su ace o TiO2[5], nanos uc u ing o TiO2 ep- esen an impo an s ep o i s e ficien and flexible u iliza ion in a ious applica ions. P obably he mos p ominen u iliza ion o nanos uc u ed TiO2 is ep esen ed by he u iliza ion o TiO2nanopa icles in he dye- sensi ized sola cell (DSSC), in oduced by O’Regan and G ä zel [6] and by he ecen u iliza ion in pe o ski e sola cells [7,8]. Ano he class o nanos uc u ed TiO2is p esen ed by 1-D nanos uc u ed ma e ials such as nanowi es, nano ods, nanobel s, and nano ubes [9]. 1-D nanoma e ials sha e wi h nanopa icles (0-D ma e ials) he high su ace a ea and p omo ional size quan um confinemen e ec s, bu ha e one dimensions ou side he nanoscale, ypically po e dep h o leng h (applies o ube, ods, wi es, fib es). 1-D nano- ma e ials o e be e unidi ec ional cha ge/ eac an /ion anspo p ope ies and be e mechanical in eg i y. TiO2nano ube (TNT) laye s p epa ed by anodiza ion o Ti ep esen a e y popula ype o 1-D ma e ial wi h he key ad an ages o acile g ow h, sel - o de ing, well-con olled geome y, scalabili y, high su ace a ea, di ec con ac o me al-suppo , and sui abili y o coa ing by sec- onda y ma e ials [10–12]. The impo an cha ac e is ic pa ame e o TNT laye s is hei aspec a io (AR), which is he a io be ween leng h and diame e o TNT. In gene al, he highe AR o e s he la ge su ace a ea which enhances he benefi s o he nano ube s uc u es. Ano he impo an aspec o TNT laye s is hei s uc- u al a iabili y – hey a e amo phous in he as-anodized s a e, bu can be con e ed, depending on he empe a u e, in o ana ase, u ile o hei mix u es [11] wi h la ge flexibili y owa ds applica- ions. Las , bu no leas , hey possess e y good adhesion o he unde lying Ti subs a es, howe e , upon specific ea men s, hey can be de ached in o ee-s anding memb anes [13,14] o nano ube powde s [15]. To add ess complex unc ionali ies o TNT laye s in applica ions, i is beneficial o combine hem wi h seconda y ma e ials. In o de o keep ad an ages o he high su ace nano ubula geome y, i is necessa y o coa he en i e su ace o nano ubes. The mos o en used app oaches o fill/coa he nano ube laye s, such as elec ode- posi ion [16–19], chemical ba h deposi ion [20–22], spincoa ing [23,24], o spu e ing [25–27], a e able o uni o mly coa TNTs laye s wi h specific dimensions (p edominan ly wi h a low AR). The a omic laye deposi ion (ALD) ep esen s he only deposi ion Fig. 1. Illus a ion o u iliza ion o ALD o ad anced unc ionaliza ion o TNT laye s. echnique able o coa uni o mly highly po ous nanos uc u es o i ually any size [28]. ALD is an es ablished deposi ion echnique based on sequen- ial sel -limi ed adso p ion o apou s o compa ible p ecu so s on su aces leading o he o ma ion o equi ed coa ings. The sel - limi ed adso p ion is he key aspec o ALD making i di e en om o he deposi ion echniques. Unde op imized condi ions ( em- pe a u e, p essu e, and exposi ion ime), he p ecu so molecules a e adso bed all o e he su ace in jus one monolaye – u he adso p ion o p ecu so molecules on he al eady occupied su ace si es is no allowed. No ma e o he geome y o he subs a e, he coa ings p epa ed by ALD ha e unp eceden ed con o mi y all o e he su ace and hei hickness is con ollable on he a omic le el [29]. As illus a ed in Fig. 1, ALD coa ings can help o une/enhance many p ope ies o TNT laye s, such as ligh abso p ion, sepa a ion o pho ogene a ed elec on-hole pai s, pho oca aly ic and elec o- ca aly ic p ope ies, chemical, he mal, and mechanical s abili y, gas sensing, and ene gy s o age. In pa icula , ALD is sui able o e y hin coa ings while i is only o a limi ed ex en ( om he poin o bo h high p ecu so cos s and high ime demands) usable o he g ow h o hick coa ings (> ens o nanome e s). The es ic ed empe a u e window o sel -limi ed egime o ALD deposi ion and high in es men cos s o he ools/p ecu so s ep esen main d aw- back o nowadays ALDs, bu hese a e o e come s ep by s ep by con inuous ad ancemen s in he ALD echnology and also ma ke compe i ion. Recen ly, he usabili y o ALD o unc ional coa ings o nanos uc u es owa ds ene gy/ligh -d i en applica ions has been ho oughly e iewed [29–40]. In his e iew, we add ess he u i- liza ion o ALD o ailo he unc ionali y o anodic TNT laye s o imp o ed pe o mance o ealize new ypes o de ices o a ious pu poses. Fi s , we b iefly summa ize he exis ing li e a u e on ALD deposi ion in o model 1-D ma e ial – po ous anodic aluminium oxide (AAO) – and in oduce specific heo e ical ea u es o ALD coa ing o HAR (HAR) nanos uc u es; nex we ocus on he u iliza- ion o ALD o unc ionaliza ion o anodic TNT laye s. We in oduce pionee ing s udies o ALD in o anodic TNT laye s and finally we ol- low by he desc ip ion o he u iliza ion o ALD o imp o ed ligh abso p ion, cha ge sepa a ion, (pho o)ca aly ic p ope ies, s abil- i y (mechanical, he mal, and chemical), gas sensing, and ene gy s o age o ALD modified TNT laye s. F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 3 2. ALD in o po ous aluminium oxide — o e iew Pionee ing s udies o u iliza ion o ALD o unc ional coa ing o 1-D HAR nanos uc u es by seconda y ma e ials we e pe o med on po ous anodic aluminium oxide (AAO) – a well-es ablished sel -o de ed 1-D ma e ial [41,42]. Po ous AAO is cha ac e ized by i s mechanical, chemical, and he mal s abili y, nanoscale po e diame e s, high su ace-a ea a io and low cos ab ica ion. These p ope ies a ac ed a conside able in e es o a wide numbe o applica ions in ca alysis, molecula sepa a ion, elec onics and pho- onics, (bio)senso s, ene gy s o age and con e sion, d ug deli e y, and empla ed syn hesis among o he s e iewed by Md Jani e al. [43]. Po ous AAO can be ab ica ed ia elec ochemical anodiza ion o aluminium. The applica ion o app op ia ed p ocessing pa ame e s du ing he anodiza ion (e.g. applied ol age, elec oly e concen- a ion, e c.) allows a e y good con ol o he po e size, he in e -po e dis ance, he hickness o he po ous laye and he o e all AR o he po es. The inhe en high su ace a ea and AR makes po ous AAO a pa icula ly appealing nanoscale empla e o in es iga ions o he kine ics and mechanisms o he su ace chemical eac ions ha he a omic laye deposi ion (ALD) me hod is based on. In pa icula , Fou ie ans o m in a ed spec oscopy (FTIR) was employed o s udy he bina y chemical eac ions o deposi SiO2and Al2O3using po ous AAO as a suppo [44–47]. ALD p ope ies as sub-nanome e hickness con ol and uni o - mi y o he deposi ed ma e ial in o he po es we e exploi ed in u n, o sh ink he po e diame e o po ous AAO. The educ ion o he po e diame e o molecula dimensions by he deposi ion o Al2O3, TiO2and SiO2d ama ically imp o ed he gas sepa a ion p ope ies o he po ous AAO [48,49]. Elam e al. used ul ahigh AR (AR ≈ 5000) po ous AAO o a comp ehensi e s udy on uni o mi y o ALD coa ing o HAR s uc u es [50], which will be discussed in de ail in he nex sec ion. ALD enables o deposi a whole ange o ma e ials in o AAO as demons a ed ex ensi ely in li e a u e. Johansson e al. fi s pe o med and demons a ed ALD o a me allic compound ia he deposi ion o coppe nanopa icles in o po ous AAO. The ein, homogeneous pa icle size and pa icle dis ibu- ion along he po es we e demons a ed [51]. Following wo ks epo ed on he deposi ion o di e en me als in o po ous AAO using ALD, such as Pd [52], Ni and Co [53,54], Ru [55], P /I [56], Ag [57], and P [58]. Also, he deposi ion o sulfides [59], ni ides [60], a wide numbe o di e en oxides as Al2O3[61–63], TiO2 [57,62–68], Ta2O5[66], Fe2O3[53,54,63,69], SiO2[63,70–73], ZnO [63,74–78], SnO2[79], Co3O4[80], oge he wi h he e ojunc ions TiO2/Sb2S3/CuSCN(no ALD) [81] and NiO/Sb2S3[82], mul ilaye ed s uc u es as SiO2/Fe2O3/SiO2[83,84], Fe3O4/Z O2/Fe3O4[85], and Au−CoxFe3−xO4co e–shell nanowi es [86] ha e been epo ed. The success ul u iliza ion o ALD o build-up o unc ional nanos- uc u es on AAO empla es o unable magne ism [69] and pho o ol aic de ices [81] is illus a ed in Fig. 2. Po ous AAO has se ed as an excellen subs a e o e alua e he abili y o no el p ecu so s o coa /infil a e HAR subs a es [59,70,79,80]. The ALD sub-nanome e hickness con ol allowed fine- uning o po e diame e s [61–63,71,72] and e alua e he impac o educed po e diame e on he single-molecule sens- ing p ope ies [61], he memb ane sepa a ion p ope ies [63,71], and he ionic anspo h ough he nanopo ous memb anes [72]. The deposi ion o seconda y ma e ials enabled he unc ionaliza- ion o po ous AAO as di e en senso s [52,56,58,68], anode o Li ion ba e ies [67] and pho oanode o dye-sensi ized sola cells [74,81,82]. Excep hese applica ions, aking he unique ALD p op- e ies o con o mal deposi ion and he wide ange o ma e ials ha can be deposi ed, po ous AAO has been in ensi ely exploi ed as a empla e o he syn hesis o di e en nanos uc u es. Nano ubula s uc u es o di e en na u e we e epo ed, such as TiN nano ubes Fig. 2. Illus a ion o unc ional nanos uc u es based on empla es o po ous AAO u ilizing ALD. (a)–(c) Mic og aphs (SEM and TEM) o ALD deposi ed i on oxide nano- ubes o unable magne ic p ope ies, adop ed om [69]. (d) ALD deposi ed TiO2 (g een) and Sb2S3( ed) wi h (no ALD) CuSCN (yellow) in AAO o in eg a ion in o pho o ol aic de ice, ep oduced om [81]. (Fo in e p e a ion o he e e ences o colou in his figu e legend, he eade is e e ed o he web e sion o his a icle.) (exhibi ing good duc ili y [60]), ZnO nano ubes (wi h supe io pho- oluminescence cha ac e is ics [76]), o e omagne ic nano ubes composed o Ni and Co [53,54] and Fe2O3[53,54,69] shown in Fig. 2a. Single wall TNTs [64,66] and Ag loaded TiO2nano ubes [57], whe ein an enhanced pho oca aly ic ac i i y compa ed o unloaded TNTs was e ealed, and hie a chical mul iwall TNTs, ab ica ed ia deposi ion o al e na ing TiO2/Al2O3nanolamina es ollowed by we e ching o sac ificial Al2O3laye [65], ha e been also epo ed. The ALD benefi s we e also applied o he ab ica ion o mul i- laye ed nano ubes, such as TiO2/Sb2S3/CuSCN o applica ion in solid s a e sola cells [81] illus a ed in Fig. 2d, and SiO2/Fe2O3/SiO2 [83,84] o Fe3O4/Z O2/Fe3O4[85], whose magne ic p ope ies we e explo ed and hei po en ial applica ions o eseen. Po ous AAO also assis ed he ab ica ion o Ru nanowi e a ays as a pla o m o senso de ices [55] and ZnO nano ods [75,76], and ALD coa ed po ous AAO ollowed by elec odeposi ion enabled he ab ica- ion o complex nanos uc u es as TiO2-coa ed Ni nanowi e a ays [64], Ta2O5-coa ed Ni nano ods [66], and Au–Co e i e nanowi es [86]. Likewise, po ous AAO has been p oposed as sui able pla o m o di e en heal h and en i onmen al applica ions – see Re . [87] and e e ences he ein. In pa icula , ALD ZnO coa ed po ous AAO exhibi ed encou aging an imic obial ac i i y wi h po en ial de ma- ological applica ions [77,78]. The u iliza ion o ALD o coa ing po ous AAO has p o ided a e y s ong mo i a ion case o all o he high-aspec 1-D nanos- uc u es, including nanopo es [88], nano ubes [89,90], nano ods [91], nanowi es [92], and b anching nanos uc u es [93,94] o a - ious ma e ials, o be p ocessed in a simila ashion. Among hose, TNT laye s o med by anodiza ion main ain o e on posi ion and 4 F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 p omise o be ea ed by ALD, due o acile p epa a ion and high unc ionali y o TiO2compa ed o o he ma e ials. 3. Aspec s o ALD in o high aspec a io nanos uc u es In o de o design an ALD p ocess, leading o con o mal coa ings o HAR nanos uc u es, i is necessa y o unde s and he kine ics and chemis y o ha pa icula ALD p ocess on he undamen al le el. Nume ous heo e ical s udies we e de o ed o he desc ip- ion o ALD su ace chemis y and kine ics. A comp ehensi e e iew on heo e ical aspec s o ALD is beyond he scope o his e iew. Ins ead, in his sec ion we wan o ocus on impo an heo e i- cal aspec s go e ning ALD in HAR nanos uc u es. The desc ip ion o he ALD p ocess in he HAR nanos uc u es was heo e ically add essed by nume ous models: a simple kine ic model [95], a kine ic model coupled wi h Langmui adso p ion [96], Mon e Ca lo (MC) based simula ions in molecula [50,97–102], Knudsen and di - usi e [103] gas flow egimes, and nume ic o analy ic solu ions o Bol zmann anspo equa ion coupled wi h Langmui adso p ion models [104–108]. Al hough he s udies used di e en heo e ical amewo ks, he common idea desc ibing he pa ame e s leading o he con o mal coa ing o HAR nanos uc u es allows o d aw gene al quali a i e o e iew, as ollows. One o he key aspec s o achie ing con o mal and uni o m coa ings is o each he sa u a ion egime o on ALD deposi ion. This si ua ion occu s when he p ecu so molecules fill (chemiso b on) all a ailable adso p ion posi ions o he subs a e su ace wi hin e e y ALD cycle (leading o he sa u a ion co e age). The co e- sponding sa u a ing exposu e dose (mul iplica ion o sa u a ion exposu e ime and p essu e o p ecu so molecules) depends on he su ace a ea (numbe o a ailable adso p ion posi ions [109]), he su ace eac ion p obabili y (su ace s icking coe ficien ), he di usion a e, and he ecombina ion loss p obabili y (in case o plasma ALD p ocesses) o p ecu so molecules. Fig. 3 illus a es he e olu ion o s ep co e age p ofiles o HAR nanos uc u e unde cha ac e is ic deposi ion egimes o ALD discussed below. The ligh blue a ea oge he wi h a ows indica e he e olu ion o s ep co - e age p ofile o HAR nanos uc u e (black a ea). Black dashed lines ep esen comple e co e age p ofile unde sa u a ed egime o ALD. Depending on he su ace eac ion p obabili y o p ecu so s and he aspec a io (AR) o nanos uc u e, he o ma ion o sa u a ed Fig. 3. The illus a ion o e olu ion o s ep co e age p ofiles (ligh blue) o HAR nanos uc u e (black) by ALD unde a ious p ocess egimes. Ligh blue a ea and a ows indica e e olu ion o s ep co e age wi h inc easing ALD exposu e dose. Dashed black lines ep esen co e age p ofiles unde sa u a ed egime condi ions (sa u a ion exposu e dose). (a) The eac ion-limi ed, (b) he di usion-limi ed, and (c) he ecombina ion-limi ed egimes o ALD deposi ion. (Fo in e p e a ion o he e e ences o colou in his figu e legend, he eade is e e ed o he web e sion o his a icle.) co e age du ing ALD deposi ion in o HAR s uc u es can be lim- i ed ei he by he di usion o he eac ion abili y o p ecu so s [50]. The so-called eac ion-limi ed egime akes place o low su - ace eac ion p obabili y o p ecu so molecules as compa ed o he di usion p obabili y o a gi en AR. This co esponds o he si ua- ion when he exposu e ime and p essu e in combina ion wi h he su ficien di usion a e allow p ecu so molecules o each e e y adso p ion posi ion a ailable wi hin he po e/ ench and he only pa ame e go e ning he co e age is he su ace eac ion p oba- bili y. The sa u a ing exposu e dose is no a ec ed by he po ous na u e o subs a e o be coa ed and nea ly equals o he sa u a - ing dose o plana su aces wi h he equi alen su ace a ea [100]. The co esponding s ep co e age p ofile o he po e/ ench e ol es almos uni o mly wi h inc easing exposu e as i is schema ically illus a ed in Fig. 3a. E en unsa u a ed co e age wi hin one cycle o ALD can lead o he g ow h o uni o m coa ings o HAR nanos- uc u es. This is simila o chemical apo deposi ion whe e he con o mali y inc eases o low eac ion p obabili ies as a esul o educed deple ion o p ecu so s along he ia [110]. On he o he hand, he di usion-limi ed egime occu s when he eac ion p obabili y (s icking coe ficien ) o p ecu so molecules is much la ge han hei di usion p obabili y o each bo om o an HAR nanos uc u e. The p ecu so molecules chemiso b on he a ailable su ace si es successi ely om he en ance-opening o he nanos uc u e and he p ecu so co e age p ofile e ol es in he on -like manne wi h he inc easing exposu e as depic ed in Fig. 3b. The sa u a ing exposu e dose app oxima ely scales wi h second powe o AR [50,95]. The g adien o he co e age p ofile wi hin he on is s ep-like o eac ion p obabili y o 100% and i g adually smoo hens wi h dec easing eac ion p obabili y [97]. In he case o plasma ALD p ocesses, he sa u a ion exposu e dose is s ongly a ec ed by he ecombina ion p obabili y o he p ecu so s, e.g. he wall ecombina ion o plasma adicals o ozone [100,101]. P ecu so molecules a he end o unde go ecombi- na ion hen o each bo om o HAR. The co e age p ofiles in ecombina ion-limi ed egimes a e complex and no uni o m, as i is d awn in Fig. 3c, and he o ma ion o sa u a ion co e age is possible only o he limi ed AR wi h significan sa u a ion doses [100,106,111,112]. Repea ed ALD cycles (wi h cons an exposu e ime) lead o he g ow h o hicke coa ing and consequen ly o change o cha ac- e is ic dimension/ adius o opening o HAR nanos uc u e. As a consequence, when he hickness o coa ing is compa able o adius o he opening o po e), he esul ing hickness p ofile is a ec ed as he di usion becomes mo e limi ed. Fo such cases, he expo- su e ime h oughou epea ed ALD cycles needs o be p ope ly scaled in o de o achie e he uni o m hickness o he final coa ing [107]. Gene ally, he wo ks in oduced abo e show examples o se o expe imen al pa ame e s go e ning he uni o mi y o ALD coa - ing wi hin HAR nanos uc u es. The de e mina ion o he su ficien sa u a ion dose o p ecu so wi hin one ALD cycle is c i ical o he success ul ALD o uni o m coa ings o HAR nanos uc u es. In he eali y, he ALD p ocess is influenced by many expe imen al pa ame e s depending on ype o p ecu so , subs a e ma e ial, ALD p ocess pa ame e s, and/o ALD eac o design. The esul s o simula ion models o ALD deposi ion ep esen quali a i e suppo o expe imen al de e mina ion o pa ame e s leading o sa u a ed egime o ALD deposi ions, which need o be pe o med and op i- mized o each sys em and coa ing ma e ial indi idually. 4. ALD in o TiO2nano ube laye s Anodic TiO2nano ubes, p epa ed by he anodiza ion o Ti, go in o he o e on o 1-D nanos uc u ed ino ganic ma e ials F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 5 since he de elopmen o o ganic based elec oly es (such as e hy- lene glycol o glyce ol), which allowed g ow h o HAR TNT laye s [10,113,114]. The abili y o p epa e HAR TNT laye s ep esen s a key s ep o success ul applica ions o TNT laye s. The nex impo an s ep in he de elopmen o TNT-based applica ions is hei ailo - ing by seconda y ma e ials, which ep esen s a a ge inhe en ly sui able o ALD u iliza ion. 4.1. Pionee ing e o s The fi s wo ks de o ed o coa ing o anodized TNT laye s by ALD ha e been ocused on sensi iza ion o TNT laye s by In2S3 o sola ene gy con e sion [115] and on he ole o Al2O3, Ta2O5, and TiO2ALD coa ings on elec ic p ope ies o coa ed TNT laye s [116]. The wo k o Sa ka e al. [111] p esen s an ex ensi e expe - imen al s udy o ALD g ow h o In2S3applied p ac ically on he coa ing o TNT laye s wi h AR o ≈62. The ALD has been pe o med by u iliza ion o indium(III) ace ylace ona e (In(acac)3) and H2S p ecu so s. The au ho s pe o med ho ough analysis o In2S3ALD p ocess on fla subs a es fi s . Qua z c ys al mic obalance (QCM), X- ay eflec i i y (XRR), and FTIR we e used in o de o moni o mass gains du ing each eac an cycles, o measu e he g ow h pe cycle and i s empe a u e dependence, o e i y he sel -limi ed su ace chemis y o u ilized p ecu so s, and o iden i y su ace species o med du ing sequen ial su ace eac ions. The e ified ALD p ocess pa ame e s wi h inc eased exposu e imes we e u i- lized o sensi iza ion o HAR TNT laye s by 5 nm hick In2S3ALD coa ing (Fig. 4a). Un o una ely, de ailed SEM o TEM in es iga ions o p o e he uni o mi y o ALD coa ing o TNT laye we e miss- ing in ha pape . The p ominen e ec o he In2S3coa ing on he pho oelec ochemical (PEC) p ope ies o he TNT laye s is illus- a ed in Fig. 4b. The In2S3coa ed TNT laye s exhibi ed a educed op ical band gap o 2.07 eV and eached 10% ex e nal quan um e fi- ciency o pho on ene gy >2.5 eV while he uncoa ed TNT laye was gene ally pho o-inac i e o pho on ene gy <3.0 eV. The obse ed quan um e ficiency was significan ly below he heo e ically p e- dic ed maximum quan um e ficiency (≈70%). The limi ed quan um e ficiency was a ibu ed o ecombina ion losses and cha ge col- lec ion/injec ions p ocesses. The wo k o Tupala e al. [116] p esen s ALD coa ings o TNT laye s wi h AR o ≈10 by selec ed me al oxides: Al2O3, Ta2O5, and TiO2. TNT laye s we e p epa ed by anodiza ion o Ti hin lay- e s e apo a ed on ITO conduc i e glass. The TNT laye s p epa ed on anspa en conduc i e suppo a e a e y sui able ma e ial o sola ene gy applica ions (e.g. pe o ski e sola cells [8]) and hei unc ionaliza ion is an impo an echnological s ep. The ALD was pe o med wi h es ablished p ecu so s: ime hylaluminium (TMA, Al(CH3)3), an alum pen oxide (Ta(OE )5), and i anium e aisop opoxide (Ti(OiP )4) in combina ion wi h wa e . The a ge hickness o he coa ing was 5 nm. The example o TiO2coa ed TNT laye s is shown in Fig. 4c. TNT laye s coa ed by ALD we e shown o ha e highe elec ic conduc i i ies (ac oss he laye ) compa ed o hei uncoa ed coun e pa s, as shown in Fig. 4d. Despi e bo h hese pionee ing wo ks clea ly demons a ed he unc ionali y o ALD coa ed TNT laye s, hey did no p o ide any di ec e idence o uni o mi y o ALD coa ings wi hin he TNT laye s (such as SEM and TEM images). The ollow up wo k o Macak e al. [117] p esen ed in e es ingly imp o ed ligh apping p ope ies o plasma ALD In2O3coa ed TNT laye s wi h AR up o ≈80 oge he wi h mic oscopic e idence o he p esence o he In2O3coa ing. The ALD deposi ed In2O3was ound o success ully coa he en i e TNT in e io s wi h g adually dec easing hickness o he coa ing om 30 o 5 nm om op o he bo om o he TNT laye (wi h AR ≈ 80, and laye hickness o ≈8 ␮m), espec i ely. The obse ed hickness g adien o In2O3 esul ed om a limi a ion o plasma assis ed ALD Fig. 4. Pionee ing ALD coa ings o TNT laye s. (a) The In2S3coa ing o TNT laye s and (b) co esponding quan um e ficiency. (c) The TiO2coa ed TNT laye and (d) he cu en densi y h ough he TNT laye modified by a ious me al oxide coa ings. (a) and (b) we e ep oduced om [115] and (c) and (d) we e ep oduced om [116]. 6 F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 Fig. 5. ALD Al2O3coa ing o TNT laye s wi h aspec a io o 180: (a) Influence o exposu e ime o TMA p ecu so du ing one ALD cycle on uni o mi y o hickness o Al2O3 coa ing wi hin TNT laye ; (b–e) Illus a ion o uni o m hickness o Al2O3coa ing o 5 s TMA exposu e ime as e ealed by SEM inspec ion h ough ou di e en dep h le els – op, nea - op, middle, and bo om, espec i ely. Rep oduced om [118]. o coa uni o mly HAR nanos uc u es due o he limi ed li e ime o plasma-gene a ed adicals and ecombina ion e ec s. Con a y, u ilizing he he mal ALD p ocess, Zazpe e al. [118] epo ed uni o m ALD deposi ion o Al2O3coa ings wi hin TNT lay- e s wi h a high AR o ≈180. The con o mali y o ALD Al2O3coa ings wi h a ious exposu e imes o TMA p ecu so was inspec ed by SEM a di e en dep h le els o he TNT laye s (and suppo ed by in si u QCM measu emen s and STEM in es iga ions). Wi h an inc easing exposu e ime o TMA, he ALD coa ing was ound o be uni o m down o he deepes le els o TNT laye s, as shown in Fig. 5a. Op imal exposu e ime led o uni o m coa ings wi hin he en i e TNT laye s, as demons a ed by SEM images measu ed a ou di e en dep h le els o he coa ed TNT laye s, shown in Fig. 5b–e. The obse ed esul s co espond o di usion limi ed egime o ALD g ow h, as in oduced in [50] and discussed in he p e ious sec ion. These pionee ing wo ks p esen he success ul u iliza ion o ALD o coa ing o TNT laye s by seconda y ma e ials wi h ad anced unc ionali ies, ele an o sola ene gy con e sion and o he op o- elec onic applica ions. Ob ained esul s clea ly demons a e ha he ul a- hin ALD coa ing is able o significan ly al e he unc- ionali y o TNT laye s and p o e ha ALD is he mos sui able and p ac ical echnique o ailo p ope ies o HAR nanos uc u es. Table 1 p esen s a comple e lis o epo s u ilizing ALD o coa - ing HAR anodic TNT laye s. In he ollowing ex , hese epo s will be in oduced in hema ically selec ed sec ions, as illus a ed in Fig. 1. 4.2. Ligh abso p ion and pho oelec ochemical con e sion While he TiO2e ficien ly abso bs ligh in he UV spec al ange, he main limi a ion o sola -ligh -d i en applica ions o TiO2is i s ela i ely la ge in insic band gap (3.2 eV o ana ase and 3.0 eV o u ile) which does no allow ligh abso p ion wi hin he isible-ligh spec al ange. Besides a dye sensi iza ion [119] o a me al/non-me al doping [120–124], an al e na i e way o imp o e isible-ligh pho oelec ochemical (PEC) pe o mance o TiO2is he modifica ion o TiO2by a sui able na ow band gap semiconduc o . The pho oexci a ion connec ed wi h he e ec i e cha ge sepa a ion leading o he elec on injec ion o he TiO2conduc ion band can significan ly enhance he isible-ligh pho o esponse o TiO2based he e os uc u es, such as nanopa icula e and nano ubula laye s. In o de o abso b mos o he inciden ligh , he ange o hick- nesses o he compac abso be laye s should be on he mic oscale. Thus, he ALD does no quali y i sel as mos sui able deposi ion echnique a fi s glance o his pu pose, since i is echnique sui - able o p oduc ion o coa ings wi h hickness on he nanome e scale. Howe e , he si ua ion is diame ically di e en in he case when HAR nanos uc u es a e used as subs a es. Only a ew ens o nm hick abso be laye (o e en less) a e e ec i e enough o e fi- cien sola ene gy ha es ing, as a esul o emendously inc eased specific su ace a ea o he HAR nanos uc u e, allowing o each he e ec i e abso p ion mass o sensi ize wi h compa ably hinne coa ings han o plana subs a es, and he mul iple ligh sca e ing e en s, p olonging significan ly op ical pa h in HAR nanoma e ials [125–127]. Mo eo e , a low hickness o abso be laye is also c i - ical o he educ ion o cha ge ecombina ion losses du ing cha ge ans e h ough he ma e ial. The leng h-scale o e ec i e cha ge sepa a ion is cha ac e ized by he size o he deple ion laye . On he nanome e scale, he ALD se es as an excellen ool o deposi- ion o uni o m coa ings wi h minimum amoun o de ec s, which ep esen s undamen al building block o highly e ficien TiO2 nanoma e ials o be used o sola ene gy con e sion applica ions. The fi s wo k u ilizing ALD o coa TNT laye s by seconda y isible-ligh abso bing ma e ial was ca ied ou by Sa ka e al. [115], as discussed in he p e ious sec ion. The ollowing wo k was pe o med by Huang e al. [128], who deposi ed Co3O4in o TNT laye s wi h AR o e 100. The ALD was pe o med u ilizing bis(cyclopen adienyl)cobal (II) (Co(Cp)2) and O3as ALD p ecu - so s. The hickness o he coa ing was anging up o 20 nm and i was e ified by SEM and by he calib a ion on e e ence Si wa e . ALD Co3O4coa ed TNT laye s we e explo ed o he isible-ligh (>420 nm) induced pho ocu en gene a ion. The bes pho ocu en esponse was obse ed o TNT laye s coa ed by Co3O4wi h a hick- ness o 4 nm. The co esponding PEC pe o mances o he 4 nm ALD Co3O4/TNT laye , a e e ence Co3O4/TNT laye coa ed by imp egna- ion me hod, and a e e ence blank TNT laye a e shown in Fig. 6a and b. The enhanced PEC pe o mance o ALD Co3O4/TNT laye s was a ibu ed o he a ou able band alignmen o Co3O4/TNT laye s as e ealed by XPS, shown in Fig. 6c, and o he ALD echnique used, p o iding uni o m Co3O4coa ing o con olled hickness and wi h minimal amoun o de ec s, which main ained he la ge open su - ace a ea o TNT laye s and minimized cha ge ecombina ion losses. Howe e , i is wo h o no e ha he epo ed absolu e alues o he pho ocon e sion e ficiency (Fig. 6b) we e ex emely low. A significan ly p onounced posi i e e ec on he isible-ligh pho o esponse can be expec ed, when CdS is u ilized as a ligh F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 7 Table 1 Summa y o ALD coa ings on TNT laye s oge he wi h he in o ma ion abou geome y o TNT laye s (* di e ence be ween inne and ou e ube diame e aken in o accoun ). Ma e ial Yea L (␮m) D (nm) AR Re e ence ALD uni o mi y Al2O32016 20 110 182 [118] Ligh abso p ion In2S32010 4 65 62 [115] Co3O42015 10 85 118 [128] CdS 2017 0.6 95–56–35 6; 11; 17 [134] CdS 2018 1–130 80–230 13–897 [125] MoSeOx2017 5 230 22 [135] Cha ge sepa a ion Al2O32014 23 100 230 [139] Al2O32014 x 97 x [140] Al2O3+ QD 2016 1.7 120 14 [141] TiO2, Al2O3, ZnO + QD 2017 1.7 110 15 [142] ZnO 2014 4.5 120 38 (*60) [143] ZnO 2014 0.5 60 8 [144,145] ZnO + QD 2016 2.4 97 25 [146] ZnO 2016 0.5 60 8 [147] ZnO + P3HT 2017 0.5 60 8 [148] TiO22017 5 230 22 [149] (Pho o)ca alysis Ti, Al, Zn, Sn, Cu, W 2014 7.5 95 79 [175] Pd 2015 1 70 14 [172] SnO2+ Pd 2017 1 70 14 [179] P 2018 7 100 70 [173] P 2018 1–5–20 80–230–110 13–22–181 [174] S abili y and physical p ope ies Al2O3, TiO2, Ta2O52012 1 100 10 [116] In2O32015 0.5–2–8 80–80–100 6–25–80 [117] Al2O32017 20 110 182 [181] Gas sensing ZnO 2017 5 230 22 [185] Ene gy s o age ZnO Al2O32013 2 100 20 [200] Al2O32017 5 230 22 [201] L = ube leng h; D = inne ube diame e . abso be wi h TiO2[129]. CdS is p edominan ly deposi ed in he o m o quan um do s (QD) by con en ional echniques such as chemical ba h deposi ion [20,130], successi e ionic laye adso p ion (SILAR) [21,131], o elec odeposi ion [132], which can gene ally p o ide deco a ion o HAR nanos uc u es wi h much mo e limi ed uni o mi y han ALD. The expec ed e ficiency o CdS sensi ized TNT laye s scales wi h he o al su ace a ea o TNT laye as long as he TNT laye can be uni o mly coa ed by sensi ize (and di usion leng h o cha ge ca ie s is long enough o each collec ing elec odes [133]). A di ec way o inc ease su ace a ea (AR) o TNT laye s is (i) o dec ease he diame e o nano ubes (inc ease hei a eal densi y) o (ii) o inc ease he o e all hickness o TNT laye s. The nex wo wo ks well desc ibe cases (i) and (ii). K bal e al. [134] epo ed downscaling he ube diame e o ALD CdS sensi ized TNT laye s o e ficien PEC ene gy con e sion. TNT laye s wi h hickness o 600 nm and wi h di e en a e age ube diame e s o 35, 56, and 96 nm – ea u ing a ious su ace a eas (52, 29, and 23 cm2/cm2, espec i ely) – we e coa ed by 6 nm hick CdS laye s by ALD (using dime hylcadmium and H2S as p e- cu so s). The co esponding mo phology o CdS coa ed TNT laye s wi h a ious ube diame e s, cap u ed by SEM, is shown in Fig. 7a–c. The ob ained inciden pho on o con e sion e ficiencies (IPCE) a e shown in Fig. 7d, espec i ely. The CdS coa ing o TNT laye s led o he s ong enhancemen o hei pho o esponse in he isible-ligh spec al ange. The pho o esponse ose wi h he dec easing TNT laye ube diame e (inc easing su ace a ea). The composi e ALD CdS/TNT laye wi h he smalles ube diame e ≈ 35 nm (la ges su ace a ea ≈ 52 cm2/cm2) exhibi ed IPCE abo e 50% up o 470 nm wi h he pho o esponse onse a ound 520 nm (co esponding wi h he band gap o CdS ≈ 2.4 eV). In a ollow up s udy, Zazpe e al. [125] p esen ed on he upscaling o he hickness o ALD CdS coa ed TNT laye s. Ul a HAR TNT laye s wi h hicknesses be ween 1 ␮m and 130 ␮m (AR up o 900) we e coa ed by ALD CdS wi h hicknesses be ween 2 nm and 10 nm. The e idence o 10 nm CdS coa ing o a ac ion o TNT laye ea u ed by HAADF STEM image and STEM/EDX elemen al mapping wi h co esponding line p ofiles is depic ed in Fig. 7e–g, espec i ely. The u iliza ion o CdS coa ed ul a HAR TNT laye s esul ed fi s o all in o a supe io PEC pe o mance, as demons a ed by high IPCE alues o a ound 70%. In addi ion, i esul ed in an appa en shi o he onse o isible-ligh pho o esponse o CdS-TNT laye s up o 675 nm (≈1.8 eV, significan ly below he band gap o CdS) while he IPCE a ound 70% was kep in he ange om 300 o 600 nm, as i is shown in Fig. 7h. The unexpec edly significan shi o he onse o pho o esponse was a ibu ed o he ad an ageous geome y o he ul a HAR TNT laye s gi ing ise o mul iple ligh -sca e ing e ec s, which ex emely p olong he op ical pa h o ligh wi hin nanos uc- u e as illus a ed in Fig. 7i and he e o e enhances he p obabili y o cap u ing ligh by sub-band gap ansi ions in con o mal and uni o m ALD CdS coa ings. The ob ained esul s clea ly demon- s a e he p ofi abili y o ALD o ligh ha es ing applica ions o e ec i ely u ilize he deposi ed ma e ial in o m o a uni o m ul a- hin coa ing, pe ec ly adop ing a la ge su ace/in e ace a ea o he suppo nanos uc u e, using TNT laye as a model example. The imp o ed pho o esponse o ALD coa ed TNT laye s was also p esen ed by Ng e al. [135], who deposi ed molybdenum oxyse- lenide (MoSexOy) coa ing u ilizing Mo(CO)6and (CH3Si)2Se ALD p ecu so s. The op imal hickness o he MoSexOycoa ing o max- imal pho ocu en gene a ion and pho oca aly ic deg ada ion o model dye (me hylene blue (MB)) was ound o be wi hin he ange o 2–5 nm. The s udy ep esen s a undamen al s ep o u u e ai- lo ed deposi ion o ansi ion me al dichalcogenides, such as MoSe2 [136], in o TNT laye s by ALD. 4.3. Cha ge sepa a ion Gene ally, one o he key limi ing ac o s o he pe o mance o sola cell de ices is he ecombina ion o pho ogene a ed cha ge ca ie s. Main cha ge ecombina ion cen es a e ep esen ed by de ec s, ap s a es and cha ge impu i ies a su aces and in e aces, 8 F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 Fig. 6. PEC pe o mance o 4 nm hick Co3O4coa ing o TNT laye s by ALD. (a) The pho ocu en densi y and (b) pho ocon e sion e ficiency o Co3O4/TNT laye he - e os uc u e upon isible-ligh illumina ion (>420 nm, 100 mW/cm2). (c) Illus a ion o band alignmen wi hin he he e os uc u e as de e mined by XPS. Rep oduced om [128]. e.g. Ti3+ in e s i ials gi ing ise o Ti 3d s a es below conduc ion band edge in TiO2[137,138]. Fo HAR nanos uc u es (which a e also high su ace a ea ma e ials), he p e en ion o ecombina ion a su aces/in e aces is o u mos impo ance. One way o sup- p ess he ecombina ion on su ace de ec s is o p epa e su aces wi h lowes possible concen a ion o su ace de ec s. This can be ealized ei he by op imiza ion o he g ow h condi ions o ha pa - icula ma e ial i sel o by deposi ion o an o e laye o a sui able de ec -deple ed ma e ial – passi a ion laye – which passi a es he su ace de ec s o an unde lying ma e ial. Howe e , such an o e - laye should no al e he p ope ies o he unde lying ma e ial and should be e y hin no o limi he cha ge ans e h ough he laye i sel . The cha ge ecombina ion a he in e aces can be sup- p essed by a combina ion o compa ible ma e ials, o ming a high quali y in e ace wi h low amoun o de ec s and wi h an inhe en ene gy ba ie o he back ans e o elec ons o holes. ALD, being inhe en ly ideal o he deposi ion o con o mal and uni o m coa - ings wi h minimal amoun o de ec s and hickness con olled on he nanome e scale, ep esen s e y p omising echnique o he g ow h o blocking/passi a ing laye s. The c edi o ALD is eflec ed by a high numbe o ecen s udies u ilizing ALD o deposi ion o blocking laye s. Fo he case o TNT laye s, he ALD was u ilized o he deposi ion o Al2O3[139–142], ZnO [142–148], and TiO2[142,149] hin coa ings as blocking laye s in o de o imp o e he PEC pe o mance o TNT laye s. In addi- ion, he same ma e ials we e also u ilized as blocking laye s in mesopo ous TiO2laye s used in DSSC [150–154]. Wide band gap and almos ideal ALD g ow h make Al2O3a p o o ypical ma e ial o a blocking laye deposi ed by ALD. ALD g ow h o Al2O3is usually ealized using TMA and wa e as p e- cu so s. Gui e al. [140] coa ed TNT laye s by Al2O3by 10–200 ALD cycles a 100–400 ◦C empe a u e ange in o de o enhance he PEC wa e spli ing by he su ace passi a ion o TNT laye s. The bes PEC pe o mance was obse ed o Al2O3coa ing by 25 cycles (2.6 nm) a 200 ◦C yielding 1.8 imes highe pho ocu en densi y han ba e TNT laye s. Kim e al. [139] coa ed TNT laye s wi h AR o ≈230 by ul a hin Al2O3coa ings wi h hickness o 0.1–0.6 nm (deposi ed by 1–6 ALD cycles) a 200 ◦C and subsequen ly sensi- ized hem wi h N-719 u henium based dye. The s udy showed ha al eady a e one ALD cycle, he Al2O3coa ing led o an inc ease o open ci cui ol age and p olonged he elec on li e imes. In con- as , Al2O3coa ings deposi ed by mo e han wo ALD cycles was ound o educe he pho ocu en densi y as a esul o an inc ease o he ene gy ba ie o he injec ion o elec ons om he dye o he TiO2conduc ion band. Zeng e al. [141] examined he ole o ALD Al2O3o e laye s wi h a ious hicknesses on PEC pe o mance o coa ed CdS and PbS QD sensi ized TNT laye s. The Al2O3o e laye s we e deposi ed by 3–100 ALD cycles. The op imal hickness lead- ing o imp o ed cha ge collec ion e ficiency was ound o be 1.5 nm (achie ed by 30 ALD cycles) yielding 1.6 imes highe pho ocu en densi y han o ba e QD sensi ized TNT laye s. Fo he illus a ion o p ope ies o Al2O3ALD coa ing o TNT laye s, he s uc u e o 30 ALD cycles Al2O3coa ed QD-TNT laye s and PEC e ficiency wi h model o beneficial in e ace band alignmen o ALD Al2O3coa ed QD-TNT laye s a e shown in Fig. 8a–c. Fundamen al mechanisms behind he passi a ion e ec o Al2O3o e laye s can be lea ned om he field o silicon sola cells [155]. Al2O3coa ings help o educe he su ace/in e ace ecombi- na ion a e by (i) passi a ion o su ace/in e ace de ec s, so-called chemical passi a ion which is ealized by hyd ogen inco po a ed na u ally in bulk Al2O3[156] and (ii) by significan educ ion o he concen a ion o one ype o cha ge ca ie a he su ace/in e ace by an elec ic field deno ed as field e ec passi a ion, ha s ems om he inhe en accumula ion o nega i e cha ge in Al2O3nea he in e ace, connec ed o de ec s in o m o Al acancies and O in e s i ials [157]. The highe is he empe a u e o ALD p ocess, he lowe amoun o hyd ogen is ound in Al2O3, esul ing in less e ec- i e chemical passi a ion [158]. The op imal empe a u e ange o Al2O3ALD deposi ion is ound o be be ween 150 and 250 ◦C. The pos -deposi ion annealing o Al2O3imp o es he passi a ion e ec wi h onse abo e 300 ◦C as i p omo es di usion o H owa ds he in e ace and also inc eases he nega i e cha ge accumula ed in Al2O3. The hickness also a ec s he passi a ion capabili y o Al2O3. The chemical passi a ion s a s o be limi ed o coa ings hinne han 5 nm, while he field e ec passi a ion emains down o 2 nm. On he o he hand, inc eased hickness o he passi a ion laye limi s i s cha ge ans e p ope ies. The ade-o be ween F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 9 Fig. 7. ALD coa ing o TNT laye s by CdS ligh -abso be laye o imp o ed isible-ligh pho o esponse. (a–c) SEM images o 6 nm CdS coa ed TNT laye s wi h a e age ube diame e s 35 nm, 56 nm, and 95 nm, espec i ely, scale ba 100 nm. (d) IPCE o TNT laye s wi h a ious nano ube diame e sensi ized by 6 nm hick ALD CdS coa ing upon illumina ion wi h a monoch oma ized ligh sou ce (e) High angle annula da k field (HAADF) STEM image and ( ) STEM/EDX elemen al map o ac ion o nano ube coa ed by 10 nm hick CdS o e laye , he g een a ows ma k he co esponding elemen al line p ofiles shown in (g). (h) IPCE o TNT laye s wi h a ious hicknesses sensi ized by 5 nm hick ALD CdS coa ing. (i) Illus a ion o mul iple ligh sca e ing e ec s p olonging he op ical pa h o ligh in TNT laye and acili a ing e ficien ligh ha es ing. (a–d) Rep oduced om [134] and (e–i) ep oduced om [125]. he passi a ion and cha ge ans e p ope ies yields op imal Al2O3 hicknesses o a ound 2 nm employed as capping passi a ion laye [155]. The abo e discussed esul s clea ly demons a e he unique- ness o ALD o ailo he coa ings o HAR nanos uc u es on a omic le el and ul ahigh p ecision, non- easible o al e na i e deposi- ion echniques. In an analogous way o Al2O3, se e al wo ks add essed o which ex en he PEC pe o mance o TNT laye s based pho oan- odes can benefi om he seconda y coa ing by hin ZnO o e laye , deposi ed by ALD. ZnO ep esen s a di ec band gap semiconduc- o wi h he band gap alue (3.4 eV) close o TiO2, which is known o p omo e e ficiency o DSSC [159]. Jeong e al. [143] coa ed TNT laye s by 10 nm hick ZnO (using 50 ALD cycles) and sensi ized i by N719 dye. The ZnO coa ing was ound o o m a pa icula e-like deco a ion o TNT laye s inc easing he su ace a ea o he pho oan- ode. The sho ci cui pho ocu en densi y imp o ed om 3.98 o 4.31 mA/cm2. Co espondingly, he e ficiency imp o ed om 1.23 o 1.42% by ZnO coa ing. The posi i e e ec o he ZnO coa ing was a ibu ed o he inc eased su ace a ea o ZnO coa ed TNT laye s and o he high isoelec ic poin o ZnO o ming an inhe en ly posi- i e cha ge a he ZnO/elec oly e in e ace, acili a ing an e ficien dye adso p ion. Mo eo e , he di e ence o TiO2and ZnO isoelec ic poin s caused a nega i e shi o he TiO2conduc ion band, esul ing in an inc eased ene gy le el di e ence wi h he liquid elec oly e leading o an inc eased open ci cui ol age. In se e al s udies, Cai e al. [144,145,147,148] inspec ed he e ec o 2, 5, and 10 nm hick ZnO coa ing (deposi ed by 10, 25, and 50 ALD cycles) on he PEC pe o mance o ZnO/TNT lay- e s and o unc ionalized poly(3-hexyl hiophene)/ZnO/TNT laye s. The bes PEC pe o mance was e ealed o 2 nm hick ZnO film (10 ALD cycles). The pho ocu en densi y ose by a ac o o 1.6 and he esul s o impedance spec oscopy poin ed o he imp o ed cha ge sepa a ion ea u ed by lowe ed cha ge- ans e esis ance, nega i e shi o fla band po en ial, and longe elec on li e imes. The addi ionally poly(3-hexyl hiophene) unc ionalized ZnO/TNT laye s showed inc eased ligh abso p ion and p omo ed pho oluminescence quenching as a ma k o sup essed adia i e ecombina ion o pho ogene a ed cha ge ca ie s [148]. Zeng e al. [146] deposi ed a hin ZnO laye by ALD as an in e - laye o PbS and CdS QD sensi ized TNT laye s. The au ho s u ilized TNT laye s wi h a ious hicknesses (1.5–2.8 ␮m) and coa ed hem by ALD ZnO wi h hickness be ween 0.7 and 10.5 nm (5, 10, 30, and 70 ZnO ALD cycles). The ALD ZnO/TNT laye s we e a e wa ds loaded by CdS/PbS QD using SILAR echnique. Illus a i e SEM and TEM images o TNT laye coa ed by ALD ZnO (30 ALD cycles equi a- len o hickness o 4.5 nm) and deco a ed by PbS/CdS QD a e shown in Fig. 8d and e. The obse ed inc ease o he ligh abso p ion and he PEC pe o mance a e ZnO coa ing was mos p onounced o he 2.4 ␮m hick TNT laye s wi h CdS/PbS QD loaded o e coa ing o 10 ALD cycles o ZnO (1.5 nm hick) esul ing in he maximum 16 F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 [15] R. Kupcik, P. Rehulka, Z. Bilko a, H. Sopha, J.M. Macak, New in e ace o pu ifica ion o p o eins: one-dimensional TiO2nano ubes deco a ed by Fe3O4nanopa icles, ACS Appl. Ma e . In e aces 9 (2017) 28233–28242, h p://dx.doi.o g/10.1021/acsami.7b08445. [16] J.M. Macak, B.G. Gong, M. Hueppe, P. Schmuki, Filling o TiO2nano ubes by sel -doping and elec odeposi ion, Ad . Ma e . 19 (2007) 3027–3031, h p:// dx.doi.o g/10.1002/adma.200602549. [17] J.M. Macak, C. Zoll ank, B.J. Rod iguez, H. Tsuchiya, M. Alexe, P. G eil, P. Schmuki, O de ed e oelec ic lead i ana e nanocellula s uc u e by con e sion o anodic TiO2nano ubes, Ad . Ma e . 21 (2009) 3121–3125, h p://dx.doi.o g/10.1002/adma.200900587. [18] D. Fang, K. Huang, S. Liu, D. Qin, High densi y coppe nanowi e a ays deposi ion inside o de ed i ania po es by elec odeposi ion, Elec ochem. Commun. 11 (2009) 901–904, h p://dx.doi.o g/10.1016/j.elecom.2009.02. 023. [19] L. Assaud, V. He esanu, M. Hanbücken, L. San inacci, Fab ica ion o p/n he e ojunc ions by elec ochemical deposi ion o Cu2O on o TiO2nano ubes, C.R. Chem. 16 (2013) 89–95, h p://dx.doi.o g/10.1016/j.c ci.2012.11.004. [20] W.-T. Sun, Y. Yu, H.-Y. Pan, X.-F. Gao, Q. Chen, L.-M. Peng, CdS quan um do s sensi ized TiO2nano ube-a ay pho oelec odes, J. Am. Chem. Soc. 130 (2008) 1124–1125, h p://dx.doi.o g/10.1021/ja0777741. [21] D.R. Bake , P.V. Kama , Pho osensi iza ion o TiO2nanos uc u es wi h CdS quan um do s: pa icula e e sus ubula suppo a chi ec u es, Ad . Func . Ma e . 19 (2009) 805–811, h p://dx.doi.o g/10.1002/ad m.200801173. [22] Q. Wang, J. Qiao, S. Gao, Fab ica ion o ZnxIn1 − xS quan um do -sensi ized TiO2nano ube a ays and hei pho oelec ochemical p ope ies, Ma e . Le . 131 (2014) 354–357, h p://dx.doi.o g/10.1016/j.ma le .2014.05.142. [23] J.M. Macak, T. Kohou ek, L. Wang, R. Be anek, Fas and obus infil a ion o unc ional ma e ial inside i ania nano ube laye s: case s udy o a chalcogenide glass sensi ize , Nanoscale 5 (2013) 9541, h p://dx.doi.o g/10. 1039/c3n 03014h. [24] S.H. Ju, S. Han, J.S. Kim, The g ow h and mo phology o coppe ph halocyanine on TiO2nano ube a ays, J. Ind. Eng. Chem. 19 (2013) 272–278, h p://dx.doi.o g/10.1016/j.jiec.2012.08.011. [25] J.E. Yoo, K. Lee, M. Al oma e, E. Selli, P. Schmuki, Sel -o ganized a ays o single-me al ca alys pa icles in TiO2ca i ies: a highly e ficien pho oca aly ic sys em, Angew. Chem. In . Ed. 52 (2013) 7514–7517, h p:// dx.doi.o g/10.1002/anie.201302525. [26] N.T. Nguyen, J. Yoo, M. Al oma e, P. Schmuki, “Suspended” P nanopa icles o e TiO2nano ubes o enhanced pho oca aly ic H2e olu ion, Chem. Commun. 50 (2014) 9653–9656, h p://dx.doi.o g/10.1039/C4CC04087B. [27] J. Yoo, K. Lee, P. Schmuki, Templa ing using sel -aligned TiO2nano ube s umps: highly o de ed me al and polyme bumped a ays, ChemElec oChem 1 (2014) 64–66, h p://dx.doi.o g/10.1002/celc. 201300133. [28] S.M. Geo ge, A omic laye deposi ion: an o e iew, Chem. Re . 110 (2010) 111–131, h p://dx.doi.o g/10.1021/c 900056b. [29] C. De a e nie , J. Dendoo en, S. Pulin hana hu S ee, K.F. Ludwig, J.A. Ma ens, Tailo ing nanopo ous ma e ials by a omic laye deposi ion, Chem. Soc. Re . 40 (2011) 5242, h p://dx.doi.o g/10.1039/c1cs15091j. [30] D.H. Kim, M.D. Losego, Q. Peng, G.N. Pa sons, A omic laye deposi ion o sensi ized sola cells: ecen p og ess and p ospec s, Ad . Ma e . In e aces 3 (2016) 1600354, h p://dx.doi.o g/10.1002/admi.201600354. [31] J.A. an Del , D. Ga cia-Alonso, W.M.M. Kessels, A omic laye deposi ion o pho o ol aics: applica ions and p ospec s o sola cell manu ac u ing, Semicond. Sci. Technol. 27 (2012) 074002, h p://dx.doi.o g/10.1088/0268- 1242/27/7/074002. [32] W. Niu, X. Li, S.K. Ka u u i, D.W. Fam, H. Fan, S. Sh es ha, L.H. Wong, A.I.Y. Tok, Applica ions o a omic laye deposi ion in sola cells, Nano echnology 26 (2015) 064001, h p://dx.doi.o g/10.1088/0957-4484/26/6/064001. [33] T. Wang, Z. Luo, C. Li, J. Gong, Con ollable ab ica ion o nanos uc u ed ma e ials o pho oelec ochemical wa e spli ing ia a omic laye deposi ion, Chem. Soc. Re . 43 (2014) 7469–7484, h p://dx.doi.o g/10. 1039/C3CS60370A. [34] C. Ma ichy, M. Bechelany, N. Pinna, A omic laye deposi ion o nanos uc u ed ma e ials o ene gy and en i onmen al applica ions, Ad . Ma e . 24 (2012) 1017–1032, h p://dx.doi.o g/10.1002/adma.201104129. [35] B. Ahmed, C. Xia, H.N. Alsha ee , Elec ode su ace enginee ing by a omic laye deposi ion: a p omising pa hway owa d be e ene gy s o age, Nano Today 11 (2016) 250–271, h p://dx.doi.o g/10.1016/j.nan od.2016.04.004. [36] C. Bae, H. Shin, K. Nielsch, Su ace modifica ion and ab ica ion o 3D nanos uc u es by a omic laye deposi ion, MRS Bull. 36 (2011) 887–897, h p://dx.doi.o g/10.1557/m s.2011.264. [37] F.-X. Xiao, J. Miao, H.B. Tao, S.-F. Hung, H.-Y. Wang, H. Bin Yang, J. Chen, R. Chen, B. Liu, One-dimensional hyb id nanos uc u es o he e ogeneous pho oca alysis and pho oelec oca alysis, Small 11 (2015) 2115–2131, h p://dx.doi.o g/10.1002/smll.201402420. [38] C. Guan, J. Wang, Recen de elopmen o ad anced elec ode ma e ials by a omic laye deposi ion o elec ochemical ene gy s o age, Ad . Sci. 3 (2016) 1500405, h p://dx.doi.o g/10.1002/ad s.201500405. [39] A.F. Palms om, P.K. San a, S.F. Ben , A omic laye deposi ion in nanos uc u ed pho o ol aics: uning op ical, elec onic and su ace p ope ies, Nanoscale 7 (2015) 12266–12283, h p://dx.doi.o g/10.1039/ C5NR02080H. [40] X. Meng, X. Wang, D. Geng, C. Ozgi -Akgun, N. Schneide , J.W. Elam, A omic laye deposi ion o nanoma e ials syn hesis and unc ionaliza ion in ene gy echnology, Ma e . Ho iz. 4 (2017) 133–154, h p://dx.doi.o g/10.1039/ C6MH00521G. [41] F. Kelle , M.S. Hun e , D.L. Robinson, S uc u al ea u es o oxide coa ings on aluminum, J. Elec ochem. Soc. 100 (1953) 411, h p://dx.doi.o g/10.1149/1. 2781142. [42] G.E. Thompson, R.C. Fu neaux, G.C. Wood, J.A. Richa dson, J.S. Goode, Nuclea ion and g ow h o po ous anodic films on aluminium, Na u e 272 (1978) 433–435, h p://dx.doi.o g/10.1038/272433a0. [43] A.M. Md Jani, D. Losic, N.H. Voelcke , Nanopo ous anodic aluminium oxide: ad ances in su ace enginee ing and eme ging applica ions, P og. Ma e . Sci. 58 (2013) 636–704, h p://dx.doi.o g/10.1016/j.pma sci.2013.01.002. [44] S.M. Geo ge, O. Sneh, A.C. Dillon, M.L. Wise, A.W. O , L.A. Okada, J.D. Way, A omic laye con olled deposi ion o SiO2and Al2O3using ABAB. . . bina y eac ion sequence chemis y, Appl. Su . Sci. 82–83 (1994) 460–467, h p:// dx.doi.o g/10.1016/0169-4332(94)90259-3. [45] A.C.C. Dillon, A.W. O , J.D.D. Way, S.M. Geo ge, Su ace chemis y o Al2O3 deposi ion using Al(CH3)3and H2O in a bina y eac ion sequence, Su . Sci. 322 (1995) 230–242, h p://dx.doi.o g/10.1016/0039-6028(95)90033-0. [46] A.W. O , K.C. McCa ley, J.W. Klaus, J.D. Way, S.M. Geo ge, A omic laye con olled deposi ion o Al2O3films using bina y eac ion sequence chemis y, Appl. Su . Sci. 107 (1996) 128–136, h p://dx.doi.o g/10.1016/ S0169-4332(96)00503-X. [47] A.W. O , J.W. Klaus, J.M. Johnson, S.M. Geo ge, K.C. McCa ley, J.D. Way, Modifica ion o po ous alumina memb anes using Al2O3a omic laye con olled deposi ion, Chem. Ma e . 9 (1997) 707–714, h p://dx.doi.o g/10. 1021/cm960377x. [48] B.S. Be land, I.P. Ga land, A.W. O , S.M. Geo ge, In si u moni o ing o a omic laye con olled po e educ ion in alumina ubula memb anes using sequen ial su ace eac ions, Chem. Ma e . 10 (1998) 3941–3950, h p://dx. doi.o g/10.1021/cm980384g. [49] M. a Came on, I.P. Ga land, J. a Smi h, S.F. Diaz, S.M. Geo ge, A omic laye deposi ion o SiO2and TiO2in alumina ubula memb anes: po e educ ion and e ec o su ace species on gas anspo , Langmui 16 (2000) 7435–7444, h p://dx.doi.o g/10.1021/la9916981. [50] J.W. Elam, D. Rou ke i ch, P.P. Ma dilo ich, S.M. Geo ge, Con o mal coa ing on ul ahigh-aspec - a io nanopo es o anodic alumina by a omic laye deposi ion, Chem. Ma e . 15 (2003) 3507–3517, h p://dx.doi.o g/10.1021/ cm0303080. [51] A. Johansson, T. Tö ndahl, L.M. O osson, M. Boman, J.-O. Ca lsson, Coppe nanopa icles deposi ed inside he po es o anodized aluminium oxide using a omic laye deposi ion, Ma e . Sci. Eng. C 23 (2003) 823–826, h p://dx.doi. o g/10.1016/j.msec.2003.09.139. [52] J.W. Elam, A. Zino e , C.Y. Han, H.H. Wang, U. Welp, J.N. H yn, M.J. Pellin, A omic laye deposi ion o palladium films on Al2O3su aces, Thin Solid Films 515 (2006) 1664–1673, h p://dx.doi.o g/10.1016/j. s .2006.05.049. [53] M. Daub, M. Knez, U. Goesele, K. Nielsch, Fe omagne ic nano ubes by a omic laye deposi ion in anodic alumina memb anes, J. Appl. Phys. 101 (2007) 09J111, h p://dx.doi.o g/10.1063/1.2712057. [54] K. Nielsch, J. Bachmann, M. Daub, J. Jing, M. Knez, U. Gösele, S. Ba h, S. Ma hu , J. Esc ig, D. Al bi , Fe omagne ic nanos uc u es by a omic laye deposi ion: om hin films owa ds co e–shell nano ubes, ECS T ans. (2007) 139–148, h p://dx.doi.o g/10.1149/1.2779078. [55] W.-H. Kim, S.-J. Pa k, J.-Y. Son, H. Kim, Ru nanos uc u e ab ica ion using an anodic aluminum oxide nano empla e and highly con o mal Ru a omic laye deposi ion, Nano echnology 19 (2008) 045302, h p://dx.doi.o g/10.1088/ 0957-4484/19/04/045302. [56] D.J. Coms ock, S.T. Ch is ensen, J.W. Elam, M.J. Pellin, M.C. He sam, Tuning he composi ion and nanos uc u e o P /I films ia anodized aluminum oxide empla ed a omic laye deposi ion, Ad . Func . Ma e . 20 (2010) 3099–3105, h p://dx.doi.o g/10.1002/ad m.201000389. [57] Y.-C. Liang, C.-C. Wang, C.-C. Kei, Y.-C. Hsueh, W.-H. Cho, T.-P. Pe ng, Pho oca alysis o Ag-loaded TiO2nano ube a ays o med by a omic laye deposi ion, J. Phys. Chem. C 115 (2011) 9498–9502, h p://dx.doi.o g/10. 1021/jp202111p. [58] A. Vaish, S. K uege , M. Dimi iou, C. Majk zak, D.J. Vande ah, L. Chen, K. Gaw isch, Enhancing he pla inum a omic laye deposi ion infil a ion dep h inside anodic alumina nanopo ous memb ane, J. Vac. Sci. Technol. A: Vac. Su . Film 33 (2015) 01A148, h p://dx.doi.o g/10.1116/1.4904398. [59] V. Po e, M. Ri ala, M. Leskelä, A omic laye deposi ion o i anium disulfide hin films, Chem. Vap. Deposi ion 13 (2007) 163–168, h p://dx.doi.o g/10. 1002/c de.200606530. [60] J. Yoon, S. Kim, K. No, Highly o de ed and well aligned TiN nano ube a ays ab ica ed ia empla e-assis ed a omic laye deposi ion, Ma e . Le . 87 (2012) 124–126, h p://dx.doi.o g/10.1016/j.ma le .2012.07.081. [61] P. Chen, T. Mi sui, D.B. Fa me , J. Golo chenko, R.G. Go don, D. B an on, A omic laye deposi ion o fine- une he su ace p ope ies and diame e s o ab ica ed nanopo es, Nano Le . 4 (2004) 1333–1337, h p://dx.doi.o g/10. 1021/nl0494001. [62] G. Xiong, J.W. Elam, H. Feng, C.Y. Han, H.-H. Wang, L.E. I on, L.a. Cu iss, M.J. Pellin, M. Kung, H. Kung, P.C. S ai , E ec o a omic laye deposi ion coa ings on he su ace s uc u e o anodic aluminum oxide memb anes, J. Phys. Chem. B 109 (2005) 14059–14063, h p://dx.doi.o g/10.1021/jp0503415. [63] V. Vega, L. Gelde, A.S. González, V.M. P ida, B. He nando, J. Bena en e, Di usi e anspo h ough su ace unc ionalized nanopo ous alumina memb anes by a omic laye deposi ion o me al oxides, J. Ind. Eng. Chem. 52 (2017) 66–72, h p://dx.doi.o g/10.1016/j.jiec.2017.03.025. F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 17 [64] M. Kemell, V. Po e, J. Tupala, M. Ri ala, M. Leskelä, A omic laye deposi ion o nanos uc u ed TiO2pho oca alys s ia empla e app oach, Chem. Ma e . 19 (2007) 1816–1820, h p://dx.doi.o g/10.1021/cm062576e. [65] C. Bae, Y. Yoon, H. Yoo, D. Han, J. Cho, B.H. Lee, M.M. Sung, M. Lee, J. Kim, H. Shin, Con olled ab ica ion o mul iwall ana ase TiO2nano ubula a chi ec u es, Chem. Ma e . 21 (2009) 2574–2576, h p://dx.doi.o g/10. 1021/cm803112p. [66] M. Kemell, E. Hä könen, V. Po e, M. Ri ala, M. Leskelä, Ta2O5- and TiO2-based nanos uc u es made by a omic laye deposi ion, Nano echnology 21 (2010) 035301, h p://dx.doi.o g/10.1088/0957-4484/21/3/035301. [67] S.K. Panda, Y. Yoon, H.S. Jung, W.-S. Yoon, H. Shin, Nanoscale size e ec o i ania (ana ase) nano ubes wi h uni o m wall hickness as high pe o mance anode o li hium-ion seconda y ba e y, J. Powe Sou ces 204 (2012) 162–167, h p://dx.doi.o g/10.1016/j.jpowsou .2011.12.048. [68] J. Lee, D.H. Kim, S.-H. Hong, J.Y. Jho, A hyd ogen gas senso employing e ically aligned TiO2nano ube a ays p epa ed by empla e-assis ed me hod, Sens. Ac ua o s B: Chem. 160 (2011) 1494–1498, h p://dx.doi.o g/ 10.1016/j.snb.2011.08.001. [69] J. Bachmann, J. Jing, M. Knez, S. Ba h, H. Shen, S. Ma hu , U. Gösele, K. Nielsch, U. G?sele, K. Nielsch, O de ed i on oxide nano ube a ays o con olled geome y and unable magne ism by a omic laye deposi ion, J. Am. Chem. Soc. 129 (2007) 9554–9555, h p://dx.doi.o g/10.1021/ ja072465w. [70] J. Bachmann, R. Zie old, Y.T. Chong, R. Haue , C. S u m, R. Schmid -G und, B. Rheinlände , M. G undmann, U. Gösele, K. Nielsch, A p ac ical, sel -ca aly ic, a omic laye deposi ion o silicon dioxide, Angew. Chem. In . Ed. 47 (2008) 6177–6179, h p://dx.doi.o g/10.1002/anie.200800245. [71] L. Velleman, G. T iani, P.J. E ans, J.G. Shap e , D. Losic, S uc u al and chemical modifica ion o po ous alumina memb anes, Mic opo ous Mesopo ous Ma e . 126 (2009) 87–94, h p://dx.doi.o g/10.1016/j. mic omeso.2009.05.024. [72] V. Rome o, V. Vega, J. Ga cía, R. Zie old, K. Nielsch, V.M. P ida, B. He nando, J. Bena en e, Changes in mo phology and ionic anspo induced by ALD SiO2 coa ing o nanopo ous alumina memb anes, ACS Appl. Ma e . In e aces. 5 (2013) 3556–3564, h p://dx.doi.o g/10.1021/am400300 . [73] C. Bae, H. Kim, Y. Yang, H. Yoo, J.M. Mon e o Mo eno, J. Bachmann, K. Nielsch, H. Shin, Rapid, con o mal gas-phase o ma ion o silica (SiO2) nano ubes om wa e condensa es, Nanoscale 5 (2013) 5825, h p://dx.doi. o g/10.1039/c3n 00906h. [74] A.B.F. Ma inson, J.W. Elam, J.T. Hupp, M.J. Pellin, ZnO nano ube based dye-sensi ized sola cells, Nano Le . 7 (2007) 2183–2187, h p://dx.doi.o g/ 10.1021/nl070160+. [75] C.-J. Yang, S.-M. Wang, S.-W. Liang, Y.-H. Chang, C. Chen, J.-M. Shieh, Low- empe a u e g ow h o ZnO nano ods in anodic aluminum oxide on Si subs a e by a omic laye deposi ion, Appl. Phys. Le . 90 (2007) 033104, h p://dx.doi.o g/10.1063/1.2431786. [76] Y.-H. Chang, S.-M. Wang, C.-M. Liu, C. Chen, Fab ica ion and cha ac e is ics o sel -aligned ZnO nano ube and nano od a ays on Si subs a es by a omic laye deposi ion, J. Elec ochem. Soc. 157 (2010) K236, h p://dx.doi.o g/10. 1149/1.3489953. [77] R.J. Na ayan, S.P. Adiga, M.J. Pellin, L.A. Cu iss, S. S a slien, B. Chisholm, N.A. Mon ei o-Ri ie e, R.L. B igmon, J.W. Elam, A omic laye deposi ion o nanopo ous bioma e ials, Ma e . Today 13 (2010) 60–64, h p://dx.doi.o g/ 10.1016/S1369-7021(10)70035-3. [78] S.A. Skoog, M.R. Baya i, P.E. Pe ochenko, S. S a slien, J. Daniels, N. Cilz, D.J. Coms ock, J.W. Elam, R.J. Na ayan, An ibac e ial ac i i y o zinc oxide-coa ed nanopo ous alumina, Ma e . Sci. Eng. B 177 (2012) 992–998, h p://dx.doi. o g/10.1016/j.mseb.2012.04.024. [79] J.W. Elam, D.A. Bake , A.J. H yn, A.B.F. Ma inson, M.J. Pellin, J.T. Hupp, A omic laye deposi ion o in oxide films using e akis(dime hylamino) in, J. Vac. Sci. Technol. A: Vac. Su . Film 26 (2008) 244–252, h p://dx.doi.o g/ 10.1116/1.2835087. [80] M. Diskus, O. Nilsen, H. Fjell åg, Thin films o cobal oxide deposi ed on high aspec a io suppo s by a omic laye deposi ion, Chem. Vap. Deposi ion 17 (2011) 135–140, h p://dx.doi.o g/10.1002/c de.201006891. [81] Y. Wu, L. Assaud, C. K yschi, B. Capon, C. De a e nie , L. San inacci, J. Bachmann, An imony sulfide as a ligh abso be in highly o de ed, coaxial nanocylind ical a ays: p epa a ion and in eg a ion in o a pho o ol aic de ice, J. Ma e . Chem. A 3 (2015) 5971–5981, h p://dx.doi.o g/10.1039/ C5TA00111K. [82] M.K.S. Ba , L. Assaud, Y. Wu, C. La on, P. Pa en , J. Bachmann, L. San inacci, Enginee ing a h ee-dimensional, pho oelec ochemically ac i e p-NiO/i-Sb2S3junc ion by a omic laye deposi ion, Elec ochim. Ac a 179 (2015) 504–511, h p://dx.doi.o g/10.1016/j.elec ac a.2015.07.016. [83] K. Pi zschel, J.M.M. Mo eno, J. Esc ig, O. Alb ech , K. Nielsch, J. Bachmann, Con olled in oduc ion o diame e modula ions in a ayed magne ic i on oxide nano ubes, ACS Nano 3 (2009) 3463–3468, h p://dx.doi.o g/10.1021/ nn900909q. [84] R. Zie old, Z. Wu, J. Biskupek, U. Kaise , J. Bachmann, C.E. K ill, K. Nielsch, Magne ic, mul ilaye ed nano ubes o low aspec a ios o liquid suspensions, Ad . Func . Ma e . 21 (2011) 226–232, h p://dx.doi.o g/10. 1002/ad m.201001395. [85] K. Pi zschel, J. Bachmann, J.M. Mon e o-Mo eno, J. Esc ig, D. Gö li z, K. Nielsch, Re e sal modes and magne os a ic in e ac ions in Fe3O4/Z O2/Fe3O4mul ilaye nano ubes, Nano echnology 23 (2012) 495718, h p://dx.doi.o g/10.1088/0957-4484/23/49/495718. [86] G. A melles, A. Cebollada, A. Ga cía-Ma ín, J.M. Mon e o-Mo eno, M. Waleczek, K. Nielsch, Magne o-op ical p ope ies o co e–shell magne o-plasmonic Au–CoxFe3−xO4nanowi es, Langmui 28 (2012) 9127–9130, h p://dx.doi.o g/10.1021/la300431a. [87] R.J. Na ayan, S.P. Adiga, M.J. Pellin, L. a Cu iss, A.J. H yn, S. S a slien, B. Chisholm, C.-C. Shih, C.-M. Shih, S.-J. Lin, Y.-Y. Su, C. Jin, J. Zhang, N. a Mon ei o-Ri ie e, J.W. Elam, A omic laye deposi ion-based unc ionaliza ion o ma e ials o medical and en i onmen al heal h applica ions, Philos. T ans. R. Soc. A: Ma h. Phys. Eng. Sci. 368 (2010) 2033–2064, h p://dx.doi.o g/10.1098/ s a.2010.0011. [88] S.J. Ku, G.C. Jo, C.H. Bak, S.M. Kim, Y.R. Shin, K.H. Kim, S.H. Kwon, J.-B. Kim, Highly o de ed ees anding i anium oxide nano ube a ays using Si-con aining block copolyme li hog aphy and a omic laye deposi ion, Nano echnology 24 (2013) 085301, h p://dx.doi.o g/10.1088/0957-4484/ 24/8/085301. [89] C. Gue a-Nu˜ nez, Y. Zhang, M. Li, V. Chawla, R. E ni, J. Michle , H.G. Pa k, I. U ke, Mo phology and c ys allini y con ol o ul a hin TiO2laye s deposi ed on ca bon nano ubes by empe a u e-s ep a omic laye deposi ion, Nanoscale 7 (2015) 10622–10633, h p://dx.doi.o g/10.1039/C5NR02106E. [90] X.L. Li, C. Li, Y. Zhang, D.P. Chu, W.I. Milne, H.J. Fan, A omic laye deposi ion o ZnO on mul i-walled ca bon nano ubes and i s use o syn hesis o CNT-ZnO he e os uc u es, Nanoscale Res. Le . 5 (2010) 1836–1840, h p:// dx.doi.o g/10.1007/s11671-010-9721-z. [91] R. Pie uszka, B.S. Wi kowski, G. Luka, L. Wachnicki, S. Gie al owska, K. Kopalko, E. Zielony, P. Bieganski, E. Placzek-Popko, M. Godlewski, Pho o ol aic p ope ies o ZnO nano ods/p- ype Si he e ojunc ion s uc u es, Beils ein J. Nano echnol. 5 (2014) 173–179, h p://dx.doi.o g/10. 3762/bjnano.5.17. [92] M.E. Edley, S. Li, G.W. Guglie a, H. Majidi, J.B. Bax e , Ul a as cha ge ca ie dynamics in ex emely hin abso be (ETA) sola cells consis ing o CdSe-coa ed ZnO nanowi es, J. Phys. Chem. C 120 (2016) 19504–19512, h p://dx.doi.o g/10.1021/acs.jpcc.6b03974. [93] A. Ka ga , K. Sun, Y. Jing, C. Choi, H. Jeong, G.Y. Jung, S. Jin, D. Wang, 3D b anched nanowi e pho oelec ochemical elec odes o e ficien sola wa e spli ing, ACS Nano 7 (2013) 9407–9415, h p://dx.doi.o g/10.1021/ nn404170y. [94] K. Yuan, Q. Cao, X. Li, H.Y. Chen, Y. Deng, Y.Y. Wang, W. Luo, H.L. Lu, D.W. Zhang, Syn hesis o WO3@ZnWO4@ZnO–ZnO hie a chical nanocac us a ays o e ficien pho oelec ochemical wa e spli ing, Nano Ene gy 41 (2017) 543–551, h p://dx.doi.o g/10.1016/j.nanoen.2017.09.053. [95] R.G. Go don, D. Hausmann, E. Kim, J. Shepa d, A kine ic model o s ep co e age by a omic laye deposi ion in na ow holes o enches, Chem. Vap. Deposi ion 9 (2003) 73–78, h p://dx.doi.o g/10.1002/c de.200390005. [96] J.-Y. Kim, J.-H. Ahn, S.-W. Kang, J.-H. Kim, S ep co e age modeling o hin films in a omic laye deposi ion, J. Appl. Phys. 101 (2007) 073502, h p://dx. doi.o g/10.1063/1.2714685. [97] J. Dendoo en, D. Deduy sche, J. Musschoo , R.L. Vanmei haeghe, C. De a e nie , Modeling he con o mali y o a omic laye deposi ion: he e ec o s icking p obabili y, J. Elec ochem. Soc. 156 (2009) P63, h p://dx. doi.o g/10.1149/1.3072694. [98] M. Rose, J.W. Ba ha, Me hod o de e mine he s icking coe ficien o p ecu so molecules in a omic laye deposi ion, Appl. Su . Sci. 255 (2009) 6620–6623, h p://dx.doi.o g/10.1016/j.apsusc.2009.02.055. [99] R.A. Adomai is, De elopmen o a mul iscale model o an a omic laye deposi ion p ocess, J. C ys . G ow h 312 (2010) 1449–1452, h p://dx.doi. o g/10.1016/j.jc ysg o.2009.12.041. [100] H.C.M. Knoops, E. Lange eis, M.C.M. an de Sanden, W.M.M. Kessels, Con o mali y o plasma-assis ed ALD: physical p ocesses and modeling, J. Elec ochem. Soc. 157 (2010) G241, h p://dx.doi.o g/10.1149/1.3491381. [101] A. Yanguas-Gil, J.W. Elam, A Ma ko chain app oach o simula e a omic laye deposi ion chemis y and anspo inside nanos uc u ed subs a es, Theo . Chem. Acc. 133 (2014) 1–13, h p://dx.doi.o g/10.1007/s00214-014-1465-x. [102] V. C eme s, F. Geenen, C. De a e nie , J. Dendoo en, Mon e Ca lo simula ions o a omic laye deposi ion on 3D la ge su ace a ea s uc u es: Requi ed p ecu so exposu e o pilla - e sus hole- ype s uc u es, J. Vac. Sci. Technol. A: Vac. Su . Film 35 (2017) 01B115, h p://dx.doi.o g/10.1116/ 1.4968201. [103] M.C. Schwille, J. Ba h, T. Schössle , F. Schön, J.W. Ba ha, M. Oe el, Simula ion app oach o a omic laye deposi ion in la ge 3D s uc u es, Modell. Simul. Ma e . Sci. Eng. 25 (2017) 035008, h p://dx.doi.o g/10.1088/ 1361-651X/aa5 9d. [104] M.K. Gobbe , V. P asad, T.S. Cale, Modeling and simula ion o a omic laye deposi ion a he ea u e scale, J. Vac. Sci. Technol. B: Mic oelec on. Nanom. S uc . 20 (2002) 1031, h p://dx.doi.o g/10.1116/1.1481754. [105] A. Yanguas-Gil, J.W. Elam, Simple model o a omic laye deposi ion p ecu so eac ion and anspo in a iscous-flow ubula eac o , J. Vac. Sci. Technol. A: Vac. Su . Film 30 (2012) 01A159, h p://dx.doi.o g/10.1116/1. 3670396. [106] A. Yanguas-Gil, J.W. Elam, Sel -limi ed eac ion–di usion in nanos uc u ed subs a es: su ace co e age dynamics and analy ic app oxima ions o ALD sa u a ion imes, Chem. Vap. Deposi ion 18 (2012) 46–52, h p://dx.doi.o g/ 10.1002/c de.201106938. [107] N. Yazdani, V. Chawla, E. Edwa ds, V. Wood, H.G. Pa k, I. U ke, Modeling and op imiza ion o a omic laye deposi ion p ocesses on e ically aligned ca bon nano ubes, Beils ein J. Nano echnol. 5 (2014) 234–244, h p://dx.doi. o g/10.3762/bjnano.5.25. 18 F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 [108] T. Keu e , N.H. Menzle , G. Maue , F. Vondahlen, R. Vaßen, H.P. Buchk eme , Modeling p ecu so di usion and eac ion o a omic laye deposi ion in po ous s uc u es, J. Vac. Sci. Technol. A: Vac. Su . Film 33 (2015) 01A104, h p://dx.doi.o g/10.1116/1.4892385. [109] R.L. Puu unen, G ow h pe cycle in a omic laye deposi ion: a heo e ical model, Chem. Vap. Deposi ion 9 (2003) 249–257, h p://dx.doi.o g/10.1002/ c de.200306265. [110] A. Yanguas-Gil, N. Kuma , Y. Yang, J.R. Abelson, Highly con o mal film g ow h by chemical apo deposi ion. II. Con o mali y enhancemen h ough g ow h inhibi ion, J. Vac. Sci. Technol. A: Vac. Su . Film 27 (2009) 1244–1248, h p://dx.doi.o g/10.1116/1.3207746. [111] H.C.M. Knoops, J.W. Elam, J.A. Libe a, W.M.M. Kessels, Su ace loss in ozone-based a omic laye deposi ion p ocesses, Chem. Ma e . 23 (2011) 2381–2387, h p://dx.doi.o g/10.1021/cm2001144. [112] J. Dendoo en, D. Deduy sche, J. Musschoo , R.L. Vanmei haeghe, C. De a e nie , Con o mali y o Al2O3and AlN deposi ed by plasma-enhanced a omic laye deposi ion, J. Elec ochem. Soc. 157 (2010) G111, h p://dx.doi. o g/10.1149/1.3301664. [113] J.M. Macak, H. Tsuchiya, L. Ta ei a, S. Aldabe ge o a, P. Schmuki, Smoo h anodic TiO2nano ubes, Angew. Chem. In . Ed. 44 (2005) 7463–7465, h p:// dx.doi.o g/10.1002/anie.200502781. [114] J.M. Macak, P. Schmuki, Anodic g ow h o sel -o ganized anodic TiO2 nano ubes in iscous elec oly es, Elec ochim. Ac a 52 (2006) 1258–1264, h p://dx.doi.o g/10.1016/j.elec ac a.2006.07.021. [115] S.K. Sa ka , J.Y. Kim, D.N. Golds ein, N.R. Neale, K. Zhu, C.M. Ellio , A.J. F ank, S.M. Geo ge, In2S3a omic laye deposi ion and i s applica ion as a sensi ize on TiO2nano ube a ays o sola ene gy con e sion, J. Phys. Chem. C 114 (2010) 8032–8039, h p://dx.doi.o g/10.1021/jp9086943. [116] J. Tupala, M. Kemell, E. Hä könen, M. Ri ala, M. Leskelä, P epa a ion o egula ly s uc u ed nano ubula TiO2 hin films on ITO and hei modifica ion wi h hin ALD-g own laye s, Nano echnology 23 (2012) 125707, h p://dx.doi.o g/10.1088/0957-4484/23/12/125707. [117] J.M. Macak, J. P ik yl, H. Sopha, L. S izik, An i eflec ion In2O3coa ings o sel -o ganized TiO2nano ube laye s p epa ed by a omic laye deposi ion, Phys. S a us Solidi Rapid Res. Le . 9 (2015) 516–520, h p://dx.doi.o g/10. 1002/pss 201510245. [118] R. Zazpe, M. Knau , H. Sopha, L. H omadko, M. Albe , J. P ik yl, V. Gä ne o á, J.W. Ba ha, J.M. Macak, A omic laye deposi ion o coa ing o high aspec a io TiO2nano ube laye s, Langmui 32 (2016) 10551–10558, h p://dx.doi.o g/10.1021/acs.langmui .6b03119. [119] A. Hag eld , G. Boschloo, L. Sun, L. Kloo, H. Pe e sson, Dye-sensi ized sola cells, Chem. Re . 110 (2010) 6595–6663, h p://dx.doi.o g/10.1021/ c 900356p. [120] T. Ohno, F. Tanigawa, K. Fujiha a, S. Izumi, M. Ma sumu a, Pho oca aly ic oxida ion o wa e by isible ligh using u henium-doped i anium dioxide powde , J. Pho ochem. Pho obiol. A: Chem. 127 (1999) 107–110, h p://dx. doi.o g/10.1016/S1010-6030(99)00128-8. [121] R. Asahi, T. Mo ikawa, T. Ohwaki, K. Aoki, Y. Taga, Visible-ligh pho oca alysis in ni ogen-doped i anium oxides, Science (80-) 293 (2001) 269–271, h p://dx.doi.o g/10.1126/science.1061051. [122] C. Bu da, Y. Lou, X. Chen, A.C.S. Samia, J. S ou , J.L. Gole, Enhanced ni ogen doping in TiO2nanopa icles, Nano Le . 3 (2003) 1049–1051, h p://dx.doi. o g/10.1021/nl034332o. [123] M. Anpo, S. Dohshi, M. Ki ano, Y. Hu, M. Takeuchi, M. Ma suoka, The p epa a ion and cha ac e iza ion o highly e ficien i anium oxide-based pho o unc ional ma e ials, Annu. Re . Ma e . Res. 35 (2005) 1–27, h p://dx. doi.o g/10.1146/annu e .ma sci.35.100303.121340. [124] S. Sak hi el, H. Kisch, Dayligh pho oca alysis by ca bon-modified i anium dioxide, Angew. Chem. In . Ed. 42 (2003) 4908–4911, h p://dx.doi.o g/10. 1002/anie.200351577. [125] R. Zazpe, H. Sopha, J. P ik yl, M. K bal, J. Mis ik, F. D o ak, L. H omadko, J.M. Macak, A 1D conical nano ubula TiO2/CdS he e os uc u e wi h supe io pho on- o-elec on con e sion, Nanoscale 10 (2018) 16601–16612, h p:// dx.doi.o g/10.1039/C8NR02418A. [126] E. Rabino ich, G. Hodes, E ec i e bandgap lowe ing o CdS deposi ed by successi e ionic laye adso p ion and eac ion, J. Phys. Chem. C 117 (2013) 1611–1620, h p://dx.doi.o g/10.1021/jp3105453. [127] M.V. Malashchonak, A.V. Mazanik, O.V. Ko olik, E.A. S el so , A.I. Kulak, Influence o wide band gap oxide subs a es on he pho oelec ochemical p ope ies and s uc u al diso de o CdS nanopa icles g own by he successi e ionic laye adso p ion and eac ion (SILAR) me hod, Beils ein J. Nano echnol. 6 (2015) 2252–2262, h p://dx.doi.o g/10.3762/bjnano.6.231. [128] B. Huang, W. Yang, Y. Wen, B. Shan, R. Chen, Co3O4-modified TiO2nano ube a ays ia a omic laye deposi ion o imp o ed isible-ligh pho oelec ochemical pe o mance, ACS Appl. Ma e . In e aces 7 (2015) 422–431, h p://dx.doi.o g/10.1021/am506392y. [129] H.K. Jun, M.A. Ca eem, A.K. A o , Quan um do -sensi ized sola cells-pe spec i e and ecen de elopmen s: a e iew o Cd chalcogenide quan um do s as sensi ize s, Renew. Sus ain. Ene gy Re . 22 (2013) 148–167, h p://dx.doi.o g/10.1016/j. se .2013.01.030. [130] Y. Yu, J. Ren, M. Meng, Pho oca aly ic hyd ogen e olu ion on g aphene quan um do s ancho ed TiO2nano ubes-a ay, In . J. Hyd ogen Ene gy 38 (2013) 12266–12272, h p://dx.doi.o g/10.1016/j.ijhydene.2013.07.039. [131] Y. Zhu, Y. Wang, Z. Chen, L. Qin, L. Yang, L. Zhu, P. Tang, T. Gao, Y. Huang, Z. Sha, G. Tang, Visible ligh induced pho oca alysis on CdS quan um do s deco a ed TiO2nano ube a ays, Appl. Ca al. A: Gen. 498 (2015) 159–166, h p://dx.doi.o g/10.1016/j.apca a.2015.03.035. [132] Y. Liu, H. Zhou, B. Zhou, J. Li, H. Chen, J. Wang, J. Bai, W. Shangguan, W. Cai, Highly s able CdS-modified sho TiO2nano ube a ay elec ode o e ficien isible-ligh hyd ogen gene a ion, In . J. Hyd ogen Ene gy 36 (2011) 167–174, h p://dx.doi.o g/10.1016/j.ijhydene.2010.09.089. [133] J.R. Jennings, A. Ghico , L.M. Pe e , P. Schmuki, A.B. Walke , Dye-sensi ized sola cells based on o ien ed TiO2nano ube a ays: anspo , apping, and ans e o elec ons, J. Am. Chem. Soc. 130 (2008) 13364–13372, h p://dx. doi.o g/10.1021/ja804852z. [134] M. K bal, J. P ik yl, R. Zazpe, H. Sopha, J.M. Macak, CdS-coa ed TiO2nano ube laye s: downscaling ube diame e owa ds e ficien he e os uc u ed pho oelec ochemical con e sion, Nanoscale 9 (2017) 7755–7759, h p://dx. doi.o g/10.1039/C7NR02841E. [135] S. Ng, M. K bal, R. Zazpe, J. P ik yl, J. Cha o , F. D oˇ ák, L. S izik, S. Slang, H. Sopha, Y. Kos o, V. Ma olin, F.K. Yam, F. Bu es, J.M. Macak, MoSexOy-coa ed 1D TiO2nano ube laye s: e ficien in e ace o ligh -d i en applica ions, Ad . Ma e . In e aces 1701146 (2017) 1701146, h p://dx.doi.o g/10.1002/ admi.201701146. [136] M. K bal, J. P ik yl, R. Zazpe, F. D o ak, F. Bu es, J.M. Macak, 2D MoSe2 s uc u es p epa ed by a omic laye deposi ion, Phys. S a us Solidi Rapid Res. Le . 1800023 (2018) 4–7, h p://dx.doi.o g/10.1002/pss .201800023. [137] A. Hag eld , M. G ä zel, Ligh -induced edox eac ions in nanoc ys alline sys ems, Chem. Re . 95 (1995) 49–68, h p://dx.doi.o g/10.1021/ c 00033a003. [138] S. Wend , P.T. Sp unge , E. Li a, G.K.H. Madsen, Z. Li, J. Hansen, J. Ma hiesen, A. Blekinge-Rasmussen, E. Lægsgaa d, B. Hamme , F. Besenbache , The ole o in e s i ial si es in he Ti3d de ec s a e in he band gap o i ania, Science (80-) 320 (2008) 1755–1759, h p://dx.doi.o g/10.1126/science.1159846. [139] J.-Y. Kim, K.-H. Lee, J. Shin, S.H. Pa k, J.S. Kang, K.S. Han, M.M. Sung, N. Pinna, Y.-E. Sung, Highly o de ed and e ically o ien ed TiO2/Al2O3nano ube elec odes o applica ion in dye-sensi ized sola cells, Nano echnology 25 (2014) 504003, h p://dx.doi.o g/10.1088/0957-4484/25/50/504003. [140] Q. Gui, Z. Xu, H. Zhang, C. Cheng, X. Zhu, M. Yin, Y. Song, L. Lu, X. Chen, D. Li, Enhanced pho oelec ochemical wa e spli ing pe o mance o anodic TiO2 nano ube a ays by su ace passi a ion, ACS Appl. Ma e . In e aces 6 (2014) 17053–17058, h p://dx.doi.o g/10.1021/am504662w. [141] M. Zeng, X. Peng, J. Liao, G. Wang, Y. Li, J. Li, Y. Qin, J. Wilson, A. Song, S. Lin, Enhanced pho oelec ochemical pe o mance o quan um do -sensi ized TiO2nano ube a ays wi h Al2O3o e coa ing by a omic laye deposi ion, Phys. Chem. Chem. Phys. 18 (2016) 17404–17413, h p://dx.doi.o g/10. 1039/C6CP01299J. [142] Q. Zhou, J. Zhou, M. Zeng, G. Wang, Y. Chen, S. Lin, Pho oelec ochemical pe o mance o quan um do -sensi ized TiO2nano ube a ays: a s udy o su ace modifica ion by a omic laye deposi ion coa ing, Nanoscale Res. Le . 12 (2017) 261, h p://dx.doi.o g/10.1186/s11671-017-2036-6. [143] J.-S. Jeong, B.-H. Choe, J.-H. Lee, J.-J. Lee, W.-Y. Choi, ZnO-coa ed TiO2 nano ube a ays o a pho oelec ode in dye-sensi ized sola cells, J. Elec on. Ma e . 43 (2014) 375–380, h p://dx.doi.o g/10.1007/s11664-013-2908-1. [144] H. Cai, Q. Yang, Z. Hu, Z. Duan, Q. You, J. Sun, N. Xu, J. Wu, Enhanced pho oelec ochemical ac i i y o e ically aligned ZnO-coa ed TiO2 nano ubes, Appl. Phys. Le . 104 (2014) 053114, h p://dx.doi.o g/10.1063/1. 4863852. [145] H. Cai, Q. You, Z. Hu, Z. Duan, Y. Cui, J. Sun, N. Xu, J. Wu, Fab ica ion and co ela ion be ween pho oluminescence and pho oelec ochemical p ope ies o e ically aligned ZnO coa ed TiO2nano ube a ays, Sol. Ene gy Ma e . Sol. Cells 123 (2014) 233–238, h p://dx.doi.o g/10.1016/j.solma . 2014.01.033. [146] M. Zeng, X. Zeng, X. Peng, Z. Zhu, J. Liao, K. Liu, G. Wang, S. Lin, Imp o ing pho oelec ochemical pe o mance on quan um do s co-sensi ized TiO2 nano ube a ays using ZnO ene gy ba ie by a omic laye deposi ion, Appl. Su . Sci. 388 (2016) 352–358, h p://dx.doi.o g/10.1016/j.apsusc.2015.12. 169. [147] H. Cai, P. Liang, Z. Hu, L. Shi, X. Yang, J. Sun, N. Xu, J. Wu, Enhanced pho oelec ochemical ac i i y o ZnO-coa ed TiO2nano ubes and i s dependence on ZnO coa ing hickness, Nanoscale Res. Le . 11 (2016) 1–11, h p://dx.doi.o g/10.1186/s11671-016-1309-9. [148] H. Cai, X. Yang, W. Zhang, H. Li, Y. Qiu, N. Xu, J. Wu, J. Sun, Enhanced ligh abso p ion and quenched pho oluminescence esul ing in pho oac i e poly(3-hexyl- hiophene)-co e ed ZnO/TiO2nano ubes o high ligh ha es ing e ficiency, Sol. Ene gy Ma e . Sol. Cells 162 (2017) 47–54, h p:// dx.doi.o g/10.1016/j.solma .2016.12.040. [149] H. Sopha, M. K bal, S. Ng, J. P ik yl, R. Zazpe, F.K. Yam, J.M. Macak, Highly e ficien pho oelec ochemical and pho oca aly ic anodic TiO2nano ube laye s wi h addi ional TiO2coa ing, Appl. Ma e . Today 9 (2017) 104–110, h p://dx.doi.o g/10.1016/j.apm .2017.06.002. [150] K. Yu, X. Lin, G. Lu, Z. Wen, C. Yuan, J. Chen, Op imized CdS quan um do -sensi ized sola cell pe o mance h ough a omic laye deposi ion o ul a hin TiO2coa ing, RSC Ad . 2 (2012) 7843, h p://dx.doi.o g/10.1039/ c2 a20979a. [151] C.Y. Jiang, W.L. Koh, M.Y. Leung, S.Y. Chiam, J.S. Wu, J. Zhang, Low empe a u e p ocessing solid-s a e dye sensi ized sola cells, Appl. Phys. Le . 100 (2012), h p://dx.doi.o g/10.1063/1.3693399. [152] D.H. Kim, M. Wood oo , K. Lee, G.N. Pa sons, A omic laye deposi ion o high pe o mance ul a hin TiO2blocking laye s o dye-sensi ized sola cells, F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 19 ChemSusChem 6 (2013) 1014–1020, h p://dx.doi.o g/10.1002/cssc. 201300067. [153] L. Ka an, N. Té eaul , T. Moehl, M. G ä zel, Elec ochemical cha ac e iza ion o TiO2blocking laye s o dye-sensi ized sola cells, J. Phys. Chem. C 118 (2014) 16408–16418, h p://dx.doi.o g/10.1021/jp4103614. [154] J.-H. Yum, T. Moehl, J. Yoon, A.K. Chandi an, F. Kessle , P. G a ia, M. G ä zel, Towa d highe pho o ol age: e ec o blocking laye on cobal bipy idine py azole complexes as edox shu le o dye-sensi ized sola cells, J. Phys. Chem. C 118 (2014) 16799–16805, h p://dx.doi.o g/10.1021/jp412777. [155] G. Dingemans, W.M.M. Kessels, S a us and p ospec s o Al2O3-based su ace passi a ion schemes o silicon sola cells, J. Vac. Sci. Technol. A: Vac. Su . Film 30 (2012) 040802, h p://dx.doi.o g/10.1116/1.4728205. [156] G. Dingemans, W. Beye , M.C.M. Van De Sanden, W.M.M. Kessels, Hyd ogen induced passi a ion o Si in e aces by Al2O3films and SiO2/Al2O3s acks, Appl. Phys. Le . 97 (2010) 2008–2011, h p://dx.doi.o g/10.1063/1.3497014. [157] B. Hoex, J.J.H. Gielis, M.C.M. an de Sanden, W.M.M. Kessels, On he c-Si su ace passi a ion mechanism by he nega i e-cha ge-dielec ic Al2O3, J. Appl. Phys. 104 (2008) 113703, h p://dx.doi.o g/10.1063/1.3021091. [158] G. Dingemans, M.C.M. an de Sanden, W.M.M. Kessels, Influence o he deposi ion empe a u e on he c-Si su ace passi a ion by Al2O3films syn hesized by ALD and PECVD, Elec ochem. Solid-S a e Le . 13 (2010) H76, h p://dx.doi.o g/10.1149/1.3276040. [159] S.J. Roh, R.S. Mane, S.K. Min, W.J. Lee, C.D. Lokhande, S.H. Han, Achie emen o 4.51% con e sion e ficiency using ZnO ecombina ion ba ie laye in TiO2 based dye-sensi ized sola cells, Appl. Phys. Le . 89 (2006) 1–4, h p://dx. doi.o g/10.1063/1.2410240. [160] A.K. Chandi an, M. Abdi-Jalebi, M.K. Nazee uddin, M. G ä zel, Analysis o elec on ans e p ope ies o ZnO and TiO2pho oanodes o dye-sensi ized sola cells, ACS Nano 8 (2014) 2261–2268, h p://dx.doi.o g/10.1021/ nn405535j. [161] Y. Hwang, C. Hahn, B. Liu, P. Yang, Pho oelec ochemical p ope ies o TiO2 nanowi e a ays: a s udy o he dependence on leng h and a omic laye deposi ion coa ing, ACS Nano 6 (2012) 5060–5069, h p://dx.doi.o g/10. 1021/nn300679d. [162] S.S. Mali, C.S. Shim, H.K. Pa k, J. Heo, P.S. Pa il, C.K. Hong, Ul a hin a omic laye deposi ed TiO2 o su ace passi a ion o hyd o he mally g own 1D TiO2nano od a ays o e ficien solid-s a e pe o ski e sola cells, Chem. Ma e . 27 (2015) 1541–1551, h p://dx.doi.o g/10.1021/cm504558g. [163] S. So, I. Hwang, P. Schmuki, Hie a chical DSSC s uc u es based on “single walled” TiO2nano ube a ays each a back-side illumina ion sola ligh con e sion e ficiency o 8%, Ene gy En i on. Sci. 8 (2015) 849–854, h p:// dx.doi.o g/10.1039/C4EE03729D. [164] I. Hwang, S. So, M. Mokh a , A. Alsheh i, S.A. Al-Thabai i, A. Maza e, P. Schmuki, Single-walled TiO2nano ubes: enhanced ca ie - anspo p ope ies by TiCl4 ea men , Chem. Eu . J. 21 (2015) 9204–9208, h p://dx. doi.o g/10.1002/chem.201500730. [165] N.T. Nguyen, I. Hwang, T. Kondo, T. Yanagishi a, H. Masuda, P. Schmuki, Op imizing TiO2nano ube mo phology o enhanced pho oca aly ic H2 e olu ion using single-walled and highly o de ed TiO2nano ubes deco a ed wi h dewe ed Au nanopa icles, Elec ochem. Commun. 79 (2017) 46–50, h p://dx.doi.o g/10.1016/j.elecom.2017.04.016. [166] M. Mo ola, H. Sopha, M. K bal, L. H omádko, G. Plesch, J.M. Macák, Compa ison o pho oelec ochemical pe o mance o anodic single- and double-walled TiO2nano ube laye s, Elec ochem. Commun. (2018). [167] J. Schneide , M. Ma suoka, M. Takeuchi, J. Zhang, Y. Ho iuchi, M. Anpo, D.W. Bahnemann, Unde s anding TiO2pho oca alysis: mechanisms and ma e ials, Chem. Re . 114 (2014) 9919–9986, h p://dx.doi.o g/10.1021/ c 5001892. [168] I. Pa amasi am, H. Jha, N. Liu, P. Schmuki, A e iew o pho oca alysis using sel -o ganized TiO2nano ubes and o he o de ed oxide nanos uc u es, Small 8 (2012) 3073–3103, h p://dx.doi.o g/10.1002/smll.201200564. [169] J.M. Macak, P.J. Ba czuk, H. Tsuchiya, M.Z. Nowakowska, A. Ghico , M. Chojak, S. Baue , S. Vi anen, P.J. Kulesza, P. Schmuki, Sel -o ganized nano ubula TiO2ma ix as suppo o dispe sed P /Ru nanopa icles: enhancemen o he elec oca aly ic oxida ion o me hanol, Elec ochem. Commun. 7 (2005) 1417–1422, h p://dx.doi.o g/10.1016/j.elecom.2005.09. 031. [170] Y.Y. Song, Z. Da Gao, J.H. Wang, X.H. Xia, R. Lynch, Mul is age colo ing elec och omic de ice based on TiO2nano ube a ays modified wi h WO3 nanopa icles, Ad . Func . Ma e . 21 (2011) 1941–1946, h p://dx.doi.o g/10. 1002/ad m.201002258. [171] C.W. Lai, S. S eekan an, Inco po a ion o WO3species in o TiO2nano ubes ia we imp egna ion and hei wa e -spli ing pe o mance, Elec ochim. Ac a 87 (2013) 294–302, h p://dx.doi.o g/10.1016/j.elec ac a.2012.09.022. [172] L. Assaud, N. B azeau, M.K.S. Ba , M. Hanbücken, S. N ais, E.A. Ba ano a, L. San inacci, A omic laye deposi ion o Pd nanopa icles on TiO2nano ubes o e hanol elec ooxida ion: syn hesis and elec ochemical p ope ies, ACS Appl. Ma e . In e aces 7 (2015) 24533–24542, h p://dx.doi.o g/10.1021/ acsami.5b06056. [173] J. Yoo, R. Zazpe, G. Cha, J. P ik yl, I. Hwang, J.M. Macak, P. Schmuki, Uni o m ALD deposi ion o P nanopa icles wi hin 1D anodic TiO2nano ubes o pho oca aly ic H2gene a ion, Elec ochem. Commun. 86 (2018) 6–11, h p://dx.doi.o g/10.1016/j.elecom.2017.10.017. [174] V.C. Ani ha, R. Zazpe, M. K bal, J. Yoo, H. Sopha, J. P ik yl, G. Cha, S. Slang, P. Schmuki, J.M. Macak, Anodic TiO2nano ubes deco a ed by P nanopa icles using ALD: an e ficien elec oca alys o me hanol oxida ion, J. Ca al. 365 (2018) 86–93, h p://dx.doi.o g/10.1016/j.jca .2018.06.017. [175] I. Tu ke ych, S. Kosa , Y. Pihosh, K. Mawa a i, T. Ki amo i, J. Ye, K. Shimamu a, Syne gis ic e ec be ween TiO2and ubiqui ous me al oxides on pho oca aly ic ac i i y o composi e nanos uc u es, Nippon Se amikkusu Kyokai Gakuju su Ronbunshi/J. Ce am. Soc. Japan 122 (2014) 393–397, h p://dx.doi.o g/10.2109/jce sj2.122.393. [176] M. Nolan, Su ace modifica ion o TiO2wi h me al oxide nanoclus e s: a ou e o composi e pho oca aly ic ma e ials, Chem. Commun. 47 (2011) 8617, h p://dx.doi.o g/10.1039/c1cc13243a. [177] H. Tong, N. Umezawa, J. Ye, Visible ligh pho oac i i y om a bonding assembly o i anium oxide nanoc ys als, Chem. Commun. 47 (2011) 4219, h p://dx.doi.o g/10.1039/c0cc05699e. [178] S.J. Taus e , S ong me al–suppo in e ac ions, Acc. Chem. Res. 20 (1987) 389–394, h p://dx.doi.o g/10.1021/a 00143a001. [179] M.K.S. Ba , L. Assaud, N. B azeau, M. Hanbücken, S. N ais, L. San inacci, E.A. Ba ano a, Enhancemen o Pd ca aly ic ac i i y owa d e hanol elec ooxida ion by a omic laye deposi ion o SnO2on o TiO2nano ubes, J. Phys. Chem. C 121 (2017) 17727–17736, h p://dx.doi.o g/10.1021/acs.jpcc. 7b05799. [180] H. Liu, C. Song, L. Zhang, J. Zhang, H. Wang, D.P. Wilkinson, A e iew o anode ca alysis in he di ec me hanol uel cell, J. Powe Sou ces 155 (2006) 95–110, h p://dx.doi.o g/10.1016/j.jpowsou .2006.01.030. [181] R. Zazpe, J. P ik yl, V. Gä ne o a, K. Nech ilo a, L. Benes, L. S izik, A. Jäge , M. Bosund, H. Sopha, J.M. Macak, A omic laye deposi ion Al2O3coa ings significan ly imp o e he mal, chemical, and mechanical s abili y o anodic TiO2nano ube laye s, Langmui 33 (2017) 3208–3216, h p://dx.doi.o g/10. 1021/acs.langmui .7b00187. [182] M.M. A a a , B. Dinan, S.A. Akba , A.S.M.A. Haseeb, Gas senso s based on one dimensional nanos uc u ed me al-oxides: a e iew, Senso s (Swi ze land) 12 (2012) 7207–7258, h p://dx.doi.o g/10.3390/s120607207. [183] O.K. Va ghese, D. Gong, M. Paulose, K.G. Ong, C.A. G imes, Hyd ogen sensing using i ania nano ubes, Sens. Ac ua o s B: Chem. 93 (2003) 338–344, h p://dx.doi.o g/10.1016/S0925-4005(03)00222-3. [184] C. Ma ichy, N. Pinna, A omic laye deposi ion o ma e ials o gas sensing applica ions, Ad . Ma e . In e aces 3 (2016), h p://dx.doi.o g/10.1002/ admi.201600335. [185] S. Ng, P. Kube sk´ y, M. K bal, J. P ik yl, V. Gä ne o á, D. Mo a co á, H. Sopha, R. Zazpe, F.K. Yam, A. Jäge , L. H omádko, L. Beneˇ s, A. Hamᡠcek, J.M. Macak, ZnO coa ed anodic 1D TiO2nano ube laye s: e ficien pho o-elec ochemical and gas sensing he e ojunc ion, Ad . Eng. Ma e . 20 (2018) 1700589, h p://dx.doi.o g/10.1002/adem.201700589. [186] J. Bao, I. Shalish, Z. Su, R. Gu wi z, F. Capasso, X. Wang, Z. Ren, Pho oinduced oxygen elease and pe sis en pho oconduc i i y in ZnO nanowi es, Nanoscale Res. Le . 6 (2011) 1–7, h p://dx.doi.o g/10.1186/1556-276X-6- 404. [187] C.C. Li, Z.F. Du, L.M. Li, H.C. Yu, Q. Wan, T.H. Wang, Su ace-deple ion con olled gas sensing o ZnO nano ods g own a oom empe a u e, Appl. Phys. Le . 91 (2007) 032101, h p://dx.doi.o g/10.1063/1.2752541. [188] C. Liu, E.I. Gille e, X. Chen, A.J. Pea se, A.C. Kozen, M.A. Sch oede , K.E. G ego czyk, S.B. Lee, G.W. Rublo , An all-in-one nanopo e ba e y a ay, Na . Nano echnol. 9 (2014) 1031–1039, h p://dx.doi.o g/10.1038/nnano. 2014247. [189] F. Bonino, L. Busani, M. Lazza i, M. Mans e a, B. Ri ol a, B. Sc osa i, Ana ase as a ca hode ma e ial in li hium—o ganic elec oly e echa geable ba e ies, J. Powe Sou ces 6 (1981) 261–270, h p://dx.doi.o g/10.1016/0378- 7753(81)80031-6. [190] S.Y. Huang, L. Ka an, I. Exna , M. G ä zel, Rocking chai li hium ba e y based on nanoc ys alline TiO2(ana ase), J. Elec ochem. Soc. 142 (1995) L142, h p://dx.doi.o g/10.1149/1.2048726. [191] L. Ka an, M. G ä zel, J. Ra housk´ y, A. Zukal, Nanoc ys alline TiO2(ana ase) elec odes: su ace mo phology, adso p ion, and elec ochemical p ope ies, J. Elec ochem. Soc. 143 (1996) 394, h p://dx.doi.o g/10.1149/1.1836455. [192] T. Djenizian, I. Hanzu, P. Knau h, Nanos uc u ed nega i e elec odes based on i ania o Li-ion mic oba e ies, J. Ma e . Chem. 21 (2011) 9925, h p:// dx.doi.o g/10.1039/c0jm04205 . [193] P.G. B uce, B. Sc osa i, J.-M. Ta ascon, Nanoma e ials o echa geable li hium ba e ies, Angew. Chem. In . Ed. 47 (2008) 2930–2946, h p://dx.doi. o g/10.1002/anie.200702505. [194] G.F. O iz, I. Hanzu, T. Djenizian, P. La ela, J.L. Ti ado, P. Knau h, Al e na i e Li-ion ba e y elec ode based on sel -o ganized i ania nano ubes, Chem. Ma e . 21 (2009) 63–67, h p://dx.doi.o g/10.1021/cm801670u. [195] N.A. Kye ema eng, Sel -o ganised TiO2nano ubes o 2D o 3D Li-ion mic oba e ies, ChemElec oChem 1 (2014) 1442–1466, h p://dx.doi.o g/ 10.1002/celc.201402109. [196] J.B. Goodenough, Y. Kim, Challenges o echa geable Li ba e ies, Chem. Ma e . 22 (2010) 587–603, h p://dx.doi.o g/10.1021/cm901452z. [197] K. Leung, Y. Qi, K.R. Za adil, Y.S. Jung, A.C. Dillon, A.S. Ca anagh, S.-H. Lee, S.M. Geo ge, Using a omic laye deposi ion o hinde sol en decomposi ion in li hium ion ba e ies: fi s -p inciples modeling and expe imen al s udies, J. Am. Chem. Soc. 133 (2011) 14741–14754, h p://dx.doi.o g/10.1021/ ja205119g. [198] T. Dobbelae e, F. Ma elae , J. Dendoo en, P. Ve eecken, C. De a e nie , Plasma-enhanced a omic laye deposi ion o i on phospha e as a posi i e elec ode o 3D li hium-ion mic oba e ies, Chem. Ma e . 28 (2016) 3435–3445, h p://dx.doi.o g/10.1021/acs.chemma e .6b00853. 20 F. D o ak e al. / Applied Ma e ials Today 14 (2019) 1–20 [199] M. Ku epeli, S. Deng, F. Ma elae , D.J. Co , P. Ve eecken, J. Dendoo en, C. De a e nie , S. Bals, He e ogeneous TiO2/V2O5/ca bon nano ube elec odes o li hium-ion ba e ies, ACS Appl. Ma e . In e aces 9 (2017) 8055–8064, h p://dx.doi.o g/10.1021/acsami.6b12759. [200] R. Li, Z. Xie, H. Lu, D.W. Zhang, A. Yu, Fab ica ion o ZnO@TiO2co e–shell nano ube a ays as h ee-dimensional anode ma e ial o li hium ion ba e ies, In . J. Elec ochem. Sci. 8 (2013) 11118–11124 h p://www. elec ochemsci.o g/pape s/ ol8/80911118.pd . [201] H. Sopha, G.D. Salian, R. Zazpe, J. P ik yl, L. H omadko, T. Djenizian, J.M. Macak, ALD Al2O3-coa ed TiO2nano ube laye s as anodes o li hium-ion ba e ies, ACS Omega 2 (2017) 2749–2756, h p://dx.doi.o g/10.1021/ acsomega.7b00463.