ORIGINAL RESEARCH
published: 17 June 2020
doi: 10.3389/ chem.2020.00520
F on ie s in Chemis y | www. on ie sin.o g 1June 2020 | Volume 8 | A icle 520
Edi ed by:
Guido Mula,
Uni e si y o Caglia i, I aly
Re iewed by:
Zhenmeng Peng,
Uni e si y o Ak on, Uni ed S a es
Robe o Paolesse,
Uni e si y o Rome To Ve ga a, I aly
*Co espondence:
Zineb Saghi
[email p o ec ed]
Angel Ba anco
[email p o ec ed]
Ana Bo as
[email p o ec ed]
Special y sec ion:
This a icle was submi ed o
Nanoscience,
a sec ion o he jou nal
F on ie s in Chemis y
Recei ed: 21 Feb ua y 2020
Accep ed: 19 May 2020
Published: 17 June 2020
Ci a ion:
Ob e o JM, Filippin AN, Alcai e M,
Sanchez-Valencia JR, Jacob M,
Ma ei C, Apa icio FJ,
Macias-Mon e o M, Rojas TC,
Espinos JP, Saghi Z, Ba anco A and
Bo as A (2020) Suppo ed Po ous
Nanos uc u es De eloped by Plasma
P ocessing o Me al Ph halocyanines
and Po phy ins. F on . Chem. 8:520.
doi: 10.3389/ chem.2020.00520
Suppo ed Po ous Nanos uc u es
De eloped by Plasma P ocessing o
Me al Ph halocyanines and
Po phy ins
Jose M. Ob e o1, Alejand o N. Filippin1, Ma ia Alcai e1, Juan R. Sanchez-Valencia1,2,
Ma in Jacob3, Cons an in Ma ei3, F ancisco J. Apa icio1, Manuel Macias-Mon e o1,4,
Te esa C. Rojas1, Juan P. Espinos1, Zineb Saghi3*, Angel Ba anco 1*and Ana Bo as1*
1Nano echnology on Su aces and Plasma Labo a o y, Ma e ials Science Ins i u e o Se ille (ICMS, CSIC-US), Se ille, Spain,
2Depa amen o de Física A ómica, Molecula y Nuclea , Uni e sidad de Se illa, Se ille, Spain, 3Uni e si é G enoble Alpes,
CEA, LETI, G enoble, F ance, 4Ins i u o de Óp ica Daza Baldés (CSIC), Mad id, Spain
The la ge a ea scalable ab ica ion o suppo ed po ous me al and me al oxide
nanoma e ials is acknowledged as one o he g ea es challenges o hei e en ual
implemen a ion in on-de ice applica ions. In his wo k, we will p esen a comp ehensi e
e ision and he la es esul s ega ding he pionee ing use o comme cially a ailable
me al ph halocyanines and po phy ins as solid p ecu so s o he plasma-assis ed
deposi ion o po ous me al and me al oxide ilms and h ee-dimensional nanos uc u es
(hie a chical nanowi es and nano ubes). The mos ad anced ea u es o his me hod
elay on i s ample gene al cha ac e om he poin o iew o he po ous ma e ial
composi ion and mic os uc u e, mild deposi ion and p ocessing empe a u e and ene gy
cons ic ions and, inally, i s s aigh o wa d compa ibili y wi h he di ec deposi ion o he
po ous nanoma e ials on p ocessable subs a es and de ice-a chi ec u es. Thus, aking
ad an age o he a ie y in he composi ion o comme cially a ailable me al po phy ins
and ph halocyanines, we p esen he de elopmen o me al and me al oxides laye s
including P , CuO, Fe2O3, TiO2, and ZnO wi h mo phologies anging om nanopa icles
o nanocolumna ilms. In addi ion, we combine his me hod wi h he ab ica ion by
low-p essu e apo anspo o single-c ys alline o ganic nanowi es o he o ma ion o
hie a chical hyb id o ganic@me al/me al-oxide and @me al/me al-oxide nano ubes. We
ca y ou a ho ough cha ac e iza ion o he ilms and nanowi es using SEM, TEM, FIB
3D, and elec on omog aphy. The la es wo echniques a e e ealed as c i ical o he
elucida ion o he inne po osi y o he laye s.
Keywo ds: suppo ed po ous nanoma e ials, po ous hin ilms, plasma deposi ion, nanowi es, nano ubes,
ph halocyanine, 3D cha ac e iza ion, elec on omog aphy
INTRODUCTION
The syn hesis o nanos uc u ed po ous me al and me al oxide nanoma e ials has become
impe a i e o he de elopmen o unc ional and ca aly ic applica ions because o hei unable
physical and chemical p ope ies, high su ace a ea and ad an ageous use as he hos ma e ial in he
no el hyb id and he e os uc u ed sys ems (Mo is and Whea ley, 2008; Shiju and Gulian s, 2009;
Kim and Nai , 2013; Zhu e al., 2015; Wang e al., 2017; Jin and Madu ai ee an, 2019). T adi ionally,
Ob e o e al. 3D Po ous Nanos uc u es
much mo e a en ion has been in es ed in he colloidal syn hesis
o po ous ma e ials in he o m o powde s and me allo ganic
amewo ks han in he syn hesis o suppo ed nanopo ous ilms
and low dimensional nanoma e ials (Mo is and Whea ley, 2008;
Shiju and Gulian s, 2009; Dhakshinamoo hy and Ga cia, 2012;
Kim and Nai , 2013; Zhu e al., 2015; Zhao e al., 2016; Wang
e al., 2017; Jin and Madu ai ee an, 2019). Howe e , du ing he
las decade, he in e es in he con olled deposi ion o me al
and me al oxide (MOs) po ous nanosys ems has been os e ed
by he ad anced and eme gen applica ions in a eas, such as
pho onics, pho o ol aics, ene gy ha es ing and s o age, sma
su aces and nanosenso s (Rome o-Gómez e al., 2010; Sánchez-
Valencia e al., 2010; Ce o olini e al., 2011; Sun e al., 2012; Zhang
e al., 2012; Da e and Malpani, 2014; Wu e al., 2014a,b; Ba anco
e al., 2016; Sk e al., 2016; Fe ando-Villalba e al., 2018; Rami ez-
Gu ie ez e al., 2019; Luo e al., 2020). A common ea u e o hese
applica ions is he need o he on-base g ow h o he po ous
nanoma e ial om a p ocessable subs a e, such as anspa en
conduc ing oxides (TCOs), o on-de ice a chi ec u e, such as
in e digi a ed elec odes (Rome o-Gómez e al., 2010; Sánchez-
Valencia e al., 2010; Ce o olini e al., 2011; Sun e al., 2012;
Zhang e al., 2012; Da e and Malpani, 2014; Wu e al., 2014a,b;
Ba anco e al., 2016; Sk e al., 2016; Fe ando-Villalba e al., 2018;
Rami ez-Gu ie ez e al., 2019; Luo e al., 2020). In consequence,
he numbe o publica ions de o ed o he unable deposi ion
o me al and me al oxide po ous sys ems including chemical
solu ion me hods, elec odeposi ion o elec ospinning, and
acuum phase as physical apo deposi ion and chemical apo
deposi ion has eno mously inc eased (Hodes, 2007; Je ónimo
e al., 2007; Rome o-Gómez e al., 2010; Sánchez-Valencia e al.,
2010; Ce o olini e al., 2011; Kim and Ro hschild, 2011; Sun
e al., 2012; Zhang e al., 2012; Pal and Bhaumik, 2013; Da e and
Malpani, 2014; Lee and Pa k, 2014; Sun and Xu, 2014; Wu e al.,
2014a,b; Malg as e al., 2015; Ba anco e al., 2016; Sk e al., 2016;
Xue e al., 2017; Fe ando-Villalba e al., 2018; Liu e al., 2018;
Coll and Napa i, 2019; Coll e al., 2019; Rami ez-Gu ie ez e al.,
2019; Luo e al., 2020; Siebe e al., 2020). In he case o acuum
phase app oaches, he me hodologies p e iously de eloped o
he syn hesis o highly compac ilms, such as he mal, elec on-
beam o ion-assis ed e apo a ion, magne on spu e ing, a omic
laye deposi ion (ALD), and plasma enhanced chemical apo
deposi ion (PECVD) ha e been ho oughly modi ied and
expanded o p oduce mic opo ous and mesopo ous laye s
(Rome o-Gómez e al., 2010; Sánchez-Valencia e al., 2010;
Bo as e al., 2012; Ba anco e al., 2016; Coll and Napa i, 2019;
Coll e al., 2019). S a egies, such as deposi ion in glancing angle
condi ions (Ba anco e al., 2016) o he use o sac i icial so
and ha d empla es (Pal and Bhaumik, 2013; Lee and Pa k,
2014; Sun and Xu, 2014; Malg as e al., 2015) ha e allowed he
ab ica ion o me al and me al oxide laye s endowed wi h unde -
design po osi y, mic os uc u e and s uc u e as well as wi h
s ic con ol on he chemical bulk and su ace composi ion, and
unc ionaliza ion. Thus, he ad an ages o he use o acuum
deposi ion me hods elay on bo h, he s ic con ol on he
chemical composi ion o he esul ing ma e ial, and he di ec
la ge scale and indus ial implemen a ion o hese echniques.
Vacuum phase deposi ion me hods a e he e o e applied in many
ields because o hei low byp oduc s yield, sol en less na u e,
s aigh o wa d au oma iza ion and compa ibili y wi h mul i-
s ep deposi ion p ocedu es and oll- o- oll ab ica ion (Bo as
e al., 2012; Ba anco e al., 2016; Coll and Napa i, 2019; Coll
e al., 2019; Tian e al., 2019). In he conc e e case o plasma-based
app oaches, such as PECVD, Plasma assis ed ALD o magne on
spu e ing, i is wo h o men ion ha he ene gy balance is as well
posi i e. Hence, he subs a e empe a u es o ob ain high-quali y
ma e ials, including c ys alline sys ems and low dimensional
nanos uc u es, emain wi hin a mild ange (Ba anco e al.,
2016; Joseph e al., 2018; B andenbu g e al., 2019; Chiang
e al., 2019; Os iko , 2019; Tian e al., 2019; Wel mann e al.,
2019). This makes he plasma-assis ed me hods e y a ac i e
o he de elopmen o po ous laye s on empe a u e sensi i e
subs a es and in applica ions in ended o an e icien payback
pe iod, which is he case in mic oelec onics, pho o ol aic, op ic,
and au omo i e indus ies, among o he s (Joseph e al., 2018;
B andenbu g e al., 2019; Chiang e al., 2019; Os iko , 2019;
Tian e al., 2019; Wel mann e al., 2019). In his a icle, we
will summa ize ou la es esul s ega ding he de elopmen o
a hyb id he mal e apo a ion, plasma deposi ion and e ching
app oach o he o ma ion o me al and me al oxide po ous
laye s using ph halocyanine and po phy in molecules as solid
me al p ecu so s (see Scheme 1A) o he chemical s uc u e o
some o he molecules es ed in his a icle). This p ocedu e
e ol es om he Remo e Plasma Assis ed Vacuum Deposi ion
(RPAVD) me hod p e iously in ended o he ab ica ion o
o ganic (polyme -like) laye s om unc ional o ganic molecules
(see Scheme 1B) (Ba anco and G oening, 2006; Apa icio e al.,
2011, 2012, 2014, 2016; Idígo as e al., 2018; Alcai e e al.,
2019a). In addi ion o he al eady men ioned ea u es o he
acuum and plasma deposi ion app oaches, he use o me al
ph halocyanines and po phy ins as solid p ecu so s may su pass
adi ionally applied o ganome allic liquids and apo s in se e al
aspec s, among hem: (i) hey can be s aigh o wa dly handled
in acuum due o hei low sublima ion empe a u es and high
s abili y, (ii) hei use is ha mless in compa ison wi h s anda d
o ganome allic p ecu so s (low oxici y, non-in lammable solid
ma e ial), (iii) hese a e al eady comme cially a ailable molecules
wi h ela i ely acile p oduc ion in high olume, (i ) he e is
an ample a ie y ega ding he me al ca ions wi h a mul i ude
o a ailable ansi ion me als; ( ) ab ica ion o mul ilaye s
o doped nanopo ous oxides a e achie able by sequen ial o
simul aneous p ocessing o po phy ins and ph halocyanines wi h
di e en me al ca ions and o pe iphe ic ligands and inally, ( i)
his me hod is ex ensible o o he sublimable unc ional me al
complexes (Alcai e e al., 2011, 2016; Filippin e al., 2017a).
An addi ional ad an age o he use o hese molecules deals
wi h hei applica ion as building blocks o he o ma ion o low
dimensional o ganic nanos uc u es h ough sel -assembly. The
assembly mechanism is d i en by sup amolecula in e ac ions,
such as an de Waals o ces (Bo as e al., 2008, 2010; B iseno
e al., 2008a,b; Zhang e al., 2014; Zong e al., 2019; Mi abi o
e al., 2020). These molecules possess an ex ensi e ne wo k
o delocalized elec ons, he so-called π-elec ons, which allow
hem o unde go a oma ic-a oma ic in e ac ions and s ack
one o e he o he h ough π-s acking. The sel -assembly in
F on ie s in Chemis y | www. on ie sin.o g 2June 2020 | Volume 8 | A icle 520
Ob e o e al. 3D Po ous Nanos uc u es
SCHEME 1 | (A) Chemical s uc u e o some o he me al ph halocyanines and po phy ins es ed in his a icle. (B) Schema ic ep esen a ion o he emo e
plasma-assis ed acuum deposi ion p ocess (RPAVD) and he so plasma e ching p ocess (SPE).
highly π-conjuga ed plana sys ems is mainly domina ed by
hese π-πin e ac ions, bu i is la gely a ec ed by he ype
o subs i uen s and cen al me al ca ion which can lead o
di e en nanos uc u ed mo i s, such as ubes, ods, shee s,
nanowi es, e c. In his a icle, we will p o i om his ea u e
o go a s ep o wa d and ab ica e suppo ed po ous co e@shell
nanowi es and nano ubes. Wi h his aim, we will ex end a so -
empla e me hodology based on he use o single-c ys alline
o ganic nanowi es as suppo ed one-dimensional and h ee-
dimensional empla es.
The cha ac e iza ion o hese po ous sys ems is no an easy
ask since he adi ional echniques as N2iso he ms ail in he
elucida ion o po e-size dis ibu ions. This is mainly due o he
ac ha he usual amoun o ma e ial o med o on-su ace o
on-de ice pu poses does no each he minimum weigh limi
o hese me hods. O he app oaches as op ical iso he ms using
UV-Vis o ellipsome y spec oscopies and oom empe a u e
iso he ms p o ided by a qua z c ys al mic obalance (QCM) ha e
been exploi ed du ing he las yea s (Bo as e al., 2007b, 2012).
Howe e , hese app oaches equi e high op ical quali y, which
hinde s hei applica ion in sca e ing media, as 3D nanowi es,
o hei combina ion wi h addi ional es ing as Ru he o d
Backsca e ing Spec oscopy (RBS) o de e mine he ma e ial
densi y (Bo ás e al., 2006). Des uc i e and non-des uc i e
in es iga ion o he 3D po osi y and po e size dis ibu ion
in hin ilms and low dimensional nanos uc u es can be
conduc ed using di e en o ms o omog aphy. A om p obe
omog aphy (APT) p o ides 3D in o ma ion abou he s uc u e
and composi ion o ma e ials wi h sub-nanome e esolu ion.
Fo nanopo ous ma e ials o be analyzed by APT, i is essen ial
o ill he po es in o de o ob ain compac ma e ials. This was
success ully achie ed by elec on beam induced deposi ion o
nanopo ous gold wi h po e diame e o 50 nm (P ei e e al.,
2015), and by elec ochemical illing o nanopo ous silicon
wi h po e diame e o 10 nm (Mou on e al., 2017). Elec on
omog aphy (ET) u ilizes a ansmission elec on mic oscope
(TEM) o he acquisi ion o a se o p ojec ions a di e en il
angles, o e as wide a il ange as possible. The 3D objec is hen
econs uc ed a e alignmen o he il se ies, wi h a esolu ion
in he nanome e ange. ET has played a c i ical ole in he
s udy o ca alys ma e ials (e.g., F ied ich e al., 2009), po ous
hin ilms (e.g., Bie mans e al., 2010; Mula e al., 2017), and
nanowi es (e.g., Fe ando-Villalba e al., 2018), bu has a ield o
iew limi ed o ew hund eds o nanome e s. Fo la ge olumes,
ocused ion beam (FIB) milling combined wi h scanning elec on
mic oscopy (SEM) p o ides 3D econs uc ions wi h a oxel size
o ∼10nm, al hough 3 nm is achie able, as epo ed in Can oni
e al. (2010), and a ield o iew o ew mic ons. Applied o
po ous s uc u es, such as solid oxide uel cells (Iwai e al.,
2010; Sabha wal e al., 2017), his echnique (FIB-3D) gi es
in aluable in o ma ion abou he mic os uc u al p ope ies o
he ma e ials, and he olumes gene a ed can se e as models o
he es ima ion o anspo p ope ies. FIB-3D, howe e , equi es
he imp egna ion o he po es wi h epoxy esin, which can
induce changes in he s uc u e, as sugges ed in Sabha wal e al.
(2017). Fo simila ields o iew, nanoscale X- ay compu e ized
omog aphy (nano-CT) p oduces 3D econs uc ions a ∼50 nm
spa ial esolu ion and in a non-des uc i e way, making i
in e es ing o in-si u s udies. Compa ed o FIB-3D, nano-CT
does no equi e epoxy imp egna ion, bu he acquisi ion ime is
longe . A mo e in-dep h compa ison o he wo echniques can be
ound in Wa go e al. (2013). In his wo k, we used FIB-3D o he
analysis o a suppo ed nanopo ous oxide hin ilm and elec on
omog aphy o he 3D econs uc ion o an isola ed TiO2po ous
F on ie s in Chemis y | www. on ie sin.o g 3June 2020 | Volume 8 | A icle 520
Ob e o e al. 3D Po ous Nanos uc u es
nano ube. These 3D cha ac e iza ions we e complemen ed by
classical SEM (plana and c oss-sec ion iews), and 2D TEM,
STEM, and EDX.
RESULTS AND DISCUSSION
Remo e Plasma-Assis ed Vacuum
Deposi ion o Po ous Me al Oxide Thin
Films
The RPAVD me hodology has been de eloped in ecen yea s
o he o ma ion o mul i unc ional nanocomposi e o ganic
ilms showing an enhanced pe o mance in applica ions, such
as UV and gas senso s, lasing media, hyd ophobic coa ings,
and encapsula ion o agile ma e (Ba anco and G oening,
2006; Apa icio e al., 2011, 2012, 2014, 2016; Idígo as e al.,
2018; Alcai e e al., 2019a). In s anda d ope a ion condi ions,
he RPAVD me hod consis s o he he mal e apo a ion o he
p ecu so molecules in he a e glow egion o a mic owa e
plasma suppo ed by elec on cyclo on esonance (ECR), i.e., in
a downs eam con igu a ion (see Scheme 1B). The subs a es a e
placed acing he e apo a ion sou ce and back o a mic owa e
plasma discha ge. The deposi ion is ca ied ou wi h he
subs a es a oom empe a u e and in he p esence o A as
plasma gas. In ou p e ious a icles, we ha e ocused on he
applica ion o his me hod o he de elopmen o laye s ab ica ed
wi h o ganic unc ional ma e ials as la onols, pe ylenes,
hodamines, and adaman ane (Ba anco and G oening, 2006;
Apa icio e al., 2011, 2012, 2014, 2016; Idígo as e al., 2018;
Alcai e e al., 2019a). He ein, we include wo modi ica ions,
on one hand, he use o me al conjuga ed molecules, me al
po phy ins and ph halocyanines, and on he o he , he use
o oxygen- ich plasmas and plasma e ching pos - ea men s.
The use o me allo ganic molecules will pa e he way o he
de elopmen o me al and me al oxide laye s, meanwhile, he
applica ion o oxygen plasma p ocedu es will allow he o ma ion
FIGURE 1 | Plana iew and c oss-sec ion SEM mic og aphs o ep esen a i e samples as labeled (see also Table 1 a he Expe imen al Sec ion): (a,b) plana and
c oss-sec ions co esponding o he di ec sublima ion o ZnPc molecules wi h he subs a e a oom empe a u e; (c) Plana iew o a CuPc sublima ed sample wi h
he subs a e empe a u e a 200◦C; (d) C oss-sec ion o a sample Remo e plasma assis ed acuum deposi ed sample o P OEP using A plasma; (e–g) plana (le )
and c oss-sec ion ( igh ) iews o ZnPc, CuPc, and P OEP molecules deposi ed by RPAVD-O2;(h,i) Plana and c oss-sec ion iews o he ZnPc deposi ion a glancing
angles suppo ed by emo e oxygen plasma.
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Ob e o e al. 3D Po ous Nanos uc u es
o columna oxide laye s. Figu e 1 ga he s di e en c oss-sec ion
and no mal iew SEM mic og aphs o ep esen a i e samples
p epa ed by his me hod (Table 1 in he Expe imen al Sec ion
includes he de ailed expe imen al condi ions). Samples labeled
as SUBL we e ab ica ed by he di ec sublima ion o he
molecules wi hou plasma ac i a ion (panels a-c), RPAVD-A
we e deposi ed applying a emo e A plasma (d) and RPAVD-O2
combining A and O2as plasma gases (e-i). All he expe imen s
we e ca ied ou wi h he subs a es a oom empe a u e excep
he example in panel (c). Pa ame e s, such as he deposi ion
a e, hickness, subs a e geome y, and plasma powe we e
uned o show an o e iew o he e sa ili y o he me hod.
Thicknesses and g ow h a es we e moni o ed by a QCM and
se led in he ange be ween 200 and 600 nm and 0.4 and 0.8 Å/s,
espec i ely. The mic os uc u es o he samples bo h in c oss-
sec ion and plana iew a e ob iously di e en . The he mal
e apo a ion condi ions p oduce a polyc ys alline con o ma ion
(Bo as e al., 2010) wi h andomly o ien ed g ains o med by he
me allic complex molecules. The A plasma-assis ed deposi ion
gene a es smoo h samples wi h almos inapp eciable ea u es a
he nanoscale. This is in good ag eemen wi h p e ious esul s
ega ding he RPAVD deposi ion o o ganic unc ional molecules
showing oo mean squa e oughness in he o de o 0.5 nm (in 1
×1µm) o ilms se e al hund ed nanome e s hick (Idígo as
e al., 2018; Alcai e e al., 2019a). The RPAVD-O2condi ions
yield in all he cases a nanocolumna mo phology. These
columns p esen na ow diame e and leng h size dis ibu ions,
gi ing ise o highly homogeneous samples wi h well-de ined
ea u es. The condi ions selec ed in Figu e 1 p oduce samples
wi h column wid hs in he o de o 65 nm o bo h CuPc and
P OEP p ecu so s, panels ( ) and (g), co esponden ly. The
columns p esen homogeneous hicknesses and wid hs om
op o bo om. Howe e , i is impo an o add ess ha he
nanocolumna o ma ion is p eceded by a con inuous laye . The
hickness o his laye anges om 75 (g) o 130 nm ( ). This
esul migh be in conco dance wi h p e ious epo s in he
li e a u e abou he plasma enhanced chemical apo deposi ion
(PECVD) o nanocolumna hin ilms (Bo as e al., 2007a,b,
2012). These a icles demons a e ha he e en ual o ma ion
o he columns depends on bo h he shadowing e ec s (also
depending on he s icking coe icien o he ad-species) and he
oughness o he su ace, in he way ha a minimum oughness
h eshold is equi ed o de elop he ini ial shadowing mechanism
esponsible o he g ow h o his ype o mo phology (Coll
e al., 2019). Highe s icking coe icien s a e indeed ela ed o
he applica ion o O2plasmas whe e he ad-species a e easily
oxidized a he su ace o he g owing ilms in compa ison
wi h A plasmas, usually de e mined by a p onounced di usion-
enhanced mechanism (Bo as e al., 2007b). This also explains
ha he in e media e ilm is hinne o highe powe plasmas
(600 W, panel g) han o he lowe (300 W, panel ). I is
also wo h men ioning ha in ou pa icula case, he sel -
shadowing e ec s a e ba ely a ec ing he g ow h o he columns
since hey p esen a homogeneous diame e along hei leng h
and no he cha ac e is ical hicke ips (Bo as e al., 2007a,b).
I is impo an o s ess he ein ha he exploi a ion o he
shadowing mechanism o gene a e unde design nanocolumna
TABLE 1 | Expe imen al condi ions selec ed o he syn hesis o hyb id and me al
oxide laye s by RPAVD.
Sample Gas
plasma
Deposi ion
a e [Å/s]
Powe
[W]
P essu e
[mba ]
ZnPc RPAVD-O2O20.4 300 3·10−2
ZnPc RPAVD-O2-GLAD O20.4 300 1·10−3
CuPc RPAVD-O2O20.4 300 3·10−2
F16CuPc RPAVD-O2O20.4 150 3·10−2
P OEP-RPAVD-A A 0.4 300 3·10−2
P OEP RPAVD-O2A /O20.4 600 3·10−2
ClFePc RPAVD-O2O20.4 600 3·10−2
laye s had been ma ked du ing he las wo decades by he leading
ole o he glancing angle ab ica ion me hods mos ly based
on physical apo deposi ion (PVD) app oaches, as he mal
and e-beam assis ed deposi ion and magne on spu e ing. In
ac , e y ew epo s ha e appea ed ega ding he glancing
angle deposi ion by CVD o PECVD me hods (Ba anco e al.,
2016). In PVD glancing angle u oblique angle deposi ions
(GLAD o OAD), he di ec ionali y o he p ecu so apo
is well-de ined wi h espec o he g owing su ace and he
simple il ing o o a ion o he subs a es wi h espec o a
punc ual sou ce o p ecu so p o ide a ple ho a o possible
mo phologies, om e ical o il ed columns, including zig-zag
and sculp u ed samples o o ganic, me al, me al oxide hyb id
and he e os uc u ed composi ion, amo phous and c ys alline
mic os uc u es (Ba anco e al., 2016). Thus, his app oach
has been success ully applied in ields de ined by on-su ace
o on-de ices s a egies like op ics, pho onics, mic o luidics,
pho o ol aics, magne ism and nanosenso s, and he ela ionship
be ween mic os uc u e, po osi y and enhanced p ope ies has
been ho oughly analyzed. In his a icle, we p esen he esul s o
he i s se o explo a o y expe imen s combining he RPAVD-
O2condi ions wi h he il ing o he subs a e wi h espec o
he p ecu so e apo a ion sou ces (Figu es 1h,i). This sample
was deposi ed unde he e y same condi ions (0.4 A/s, 300 W,
O2plasma) as sample in panel (e) bu wi h he subs a e
o ming an angle ß ∼80◦wi h espec o he e apo a ion lux
and unde educed O2p essu e, i.e., 1 ×10−2compa ed o
3×10−2mba (see Expe imen al Sec ion). The c oss-sec ion
image depic s he cha ac e is ic il ed nanocolumna o ma ion
o he samples deposi ed unde glancing angle condi ions,
wi h he columns o ming an angle α∼23 ±2◦(Ba anco
e al., 2016) The wid h o he nanocolumns is hinne o
he RPAVD-O2-GLAD (34 ±5 nm) han o he equi alen
RPAVD-O2condi ions (52 ±5nm). This image also shows
he ini ial g anula egion a he in e ace wi h he subs a e
which unde hese condi ions eaches up o 200 nm. The no mal
iew image co obo a es he il ed alignmen o he sample bu
does no p esen he budling e ec s (i.e., he agglome a ion
o he ips o he columns in a de e mined di ec ion) o en
p esen ed by GLAD laye s (Ba anco e al., 2016). Al hough
al eady men ioned, hese a e p elimina y expe imen s ha
pa e he way o an al e na i e plasma-based glancing angle
deposi ion app oach.
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Ob e o e al. 3D Po ous Nanos uc u es
I is well-known ha he RPAVD-A p ocedu e p o ides he
o ma ion o nanocomposi e laye s whe e he o ganic molecules
appea embedded in a polyme ic ma ix consis ing o he
molecula agmen s o med a e he in e ac ion o he p ecu so
molecules wi h he plasma species (Ba anco and G oening,
2006; Apa icio e al., 2011, 2012, 2014, 2016; Idígo as e al.,
2018; Alcai e e al., 2019a). This s iking ea u e has allowed he
ab ica ion o solid, non-soluble and he mally s able laye s wi h
unable p ope ies om molecula unc ions o plasma-polyme s.
Figu es 2,3and Table S1 (see also Alcai e e al., 2011, 2016;
Filippin e al., 2017a), ga he he UV-Vis ansmi ance spec a
and X-Ray Pho oelec on Spec oscopy (XPS) esul s aiming o
he elucida ion o he chemical composi ion o he samples,
compa ing di ec sublima ion, RPADVD-A , and RPAVD-
O2condi ions. The ansmi ance spec a o he sublima ed
ph halocyanine samples in Figu es 2A,B esemble hose o
he molecules (ZnPc and F16CuPc, espec i ely) wi h he
cha ac e is ic Q and So e abso p ion bands in he 600–800
and 300–400 nm co esponden ly. XPS esul s also indica e ha
he sublima ed samples p esen he s oichiome y equi alen
o he molecules (see Figu e 3 and Table S1). On he o he
hand, in good ag eemen wi h p e ious esul s o he applica ion
o RPAVD-A , he spec a o he RPAVD-A samples con ains
bands co esponding o in ege embedded molecules along
wi h small moie ies o med a e pa ial plasma agmen a ion
o he molecule. This is also no iceable in he XPS esul s:
o example, he spec um o P 4 o he sample p epa ed
unde such condi ions appea s a binding ene gies co esponding
o P in o he P OEP molecule (Filippin e al., 2017a) (see
Figu e 3B and Table S1). These in ege molecules a e embedded
in he c osslinked ma ix o med by agmen ed molecules. On
he o he hand, he RPAVD-O2condi ions lead o a di e en
si ua ion: samples p epa ed a no mal incidence angle a e
anspa en in he isible ange wi h he di e ence in he
abso p ion edge and anspa ency depending on he molecule
and he sample hickness (see also Filippin e al., 2017a). The
decon olu ion o he P 4 peaks in Figu e 3C is compa ible
wi h he p esence o P coming om he P OEP molecules
as well ha in P O and P O2. This esul indica es ha he
RPAVD-O2me hod yields, in ac , hyb id laye s con aining
in ege molecules, oxidized agmen s, and c osslinked molecula
agmen s. Finally, he samples p epa ed unde RPAVD-O2
GLAD condi ions p esen in addi ion sligh abso p ion bands
co esponding wi h he o iginal molecule. This migh indica e
he weak oxida ion o he molecules unde such expe imen al
pa ame e s and i is in good ag eemen wi h he p esence o hick
con inuous laye s a he in e ace o he subs a es p e ious o he
o ma ion o il ed nanocolumns.
The ul ima e con e sion in o me al o me al oxides o
he hyb id laye s can be achie ed by pos -p ocessing wi h
so plasma e ching (SPE) in he same eac o (Alcai e e al.,
2011, 2016; Filippin e al., 2017a) (see Scheme 1B) unde
di e en combina ions o oxygen and a gon gases in he plasma
and o empe a u es anging om RT o 180◦C as ga he ed
in Figu e 4. Sublima ed and RPAVD-O2samples e ain hei
columna mic os uc u e a e he SPE ea men s, which in
addi ion p oduce h ee isible e ec s on he nanos uc u es: he
FIGURE 2 | (A-C) UV-Vis T ansmi ance spec a compa ing samples p epa ed
unde di e en expe imen al condi ions as labeled.
agg ega ion o he nanocolumns leading o an inc ease o o e all
sample po osi y as he columns end o o m bundles, educ ion
in he hickness when compa ed wi h he as-g own laye s and ise
o he su ace oughness o such columns due o he o ma ion
o me al nanopa icles (Figu es 4a–g). The inc emen in he
empe a u e o he subs a es and plasma e ching ime inc eases
he size o he bundles and he dis ance be ween hem (see
panels b-c and Filippin e al., 2017a). P OEP samples deposi ed
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Ob e o e al. 3D Po ous Nanos uc u es
FIGURE 3 | P 4 peaks ob ained by XPS o he P OEP samples deposi ed unde di ec sublima ion (A), RPAVD-A (B) and RPAVD-O2 (C). E olu ion o he N 1 s (D),
Cu 2p (E) and O 1s (F) peaks o he CuPc-SUBL sample a e so -plasma e ching ea men s o di e en du a ions.
unde A plasma (RPAVD-A in Figu es 4h,i), ha o iginally
consis o con inuous and a he compac laye s, expe ience a
di e en ans o ma ion a e SPE ea men : he mic os uc u e
is con e ed in o a po ous in e connec ed ne wo k.
FIB-3D was pe o med on a sample ab ica ed by a simila
p ocess using ClTiPc as p ecu so , a e epoxy imp egna ion
and ca bon coa ing (Figu e 5). The ield o iew chosen o
his expe imen was 6 ×1.5 ×4µm3, wi h a pixel size o
4nm. Figu e 5 shows he oxel ende ing o a sub olume and
selec ed slices h ough he econs uc ion. This econs uc ion
p o ides an insigh iew o he highly po ous sys ems gene a ed
a e a comple e pos - ea men wi h po es showing a b oad
size dis ibu ion and diame e s in he ange be ween 150 and
10 nm in bo h he con inuous and columna coun e pa o
he samples. The po osi y es ima ed o he bo om laye is ca.
56%. I is impo an o s ess he ein ha his alue migh be
unde es ima ed since he pixel size is in he limi o esolu ion
o he smalle po es, as we will discuss in he second sec ion. The
su ace chemical composi ion o he as-g own samples and a e
se e al pos - ea men s was e alua ed by means o ex si u XPS
(see Figu es 3D–F and Table S1). Auge pa ame e s es ima ed
o he CuPc as-g own and pos - ea ed samples co espond o
α(Cu) =1850.85eV (SUBL), 1851.05 eV (SPE 10 min), and
1851.00 eV (SPE 40 min). The las wo alues a e compa ible
wi h he o ma ion o CuO wi h small pa icle size (Espinos
e al., 2002). In b ie , he su ace concen a ion o ca bon and
ni ogen dec eases, and he oxygen a ises, o ZnPc, CuPc,
F16CuPc, ClTiPc, ClFePc, and P OEP hin ilms a e he so -
plasma e ching pos - ea men compa ed wi h he as-g own ones
as expec ed. The amoun o oxygen also has a s ong dependence
on he oxide s oichiome y and he amoun o subs a e [Si(100)]
unco e ed and also oxidized unde he plasma ea men . In
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Ob e o e al. 3D Po ous Nanos uc u es
FIGURE 4 | (a-i) Plana iew and c oss-sec ion SEM mic og aphs ep esen a i e o he so -plasma e ching esul s as labeled.
all he cases, we ha e achie ed he comple e con e sion o he
co esponding me al oxide a e so -plasma e ching ea men s
o di e en du a ions and empe a u es below 180◦C. Table S1
p obe ha ZnO, TiO2, CuO, and Fe2O3oxides can be e en ually
o med. In he pa icula case o P OEP, i is also possible o o m
me al pa icles and laye s a e u he annealing unde A and
H2a mosphe e (Filippin e al., 2017a).
De elopmen o Hyb id, Me al, and Me al
Oxide Co e@Shell Nanowi es and
Nano ubes
In his sec ion, we will show he ex ension o he esul s abo e o a
so - empla e me hod o he ab ica ion o co e@shell nanowi es
and nano ubes. Such a me hod has been de eloped du ing he
las yea s o he syn hesis o suppo ed and on-de ice nanowi es
and nano ubes wi h applica ions as supe hyd ophobic and an i-
eezing su aces, nanoscale wa eguides, nanosenso s, exci onic
sola cell pho oelec odes, and piezoelec ic nanogene a o s
(Bo as e al., 2009; Macias-Mon e o e al., 2013, 2017;
Filippin e al., 2017b, 2019; Alcai e e al., 2019b). Scheme 2
p esen s he main s eps o he ab ica ion o hese hie a chical
nanos uc u es. The ounda ion o he me hodology is he
o ma ion o single-c ys al o ganic nanowi es by low-p essu e
apo anspo o physical apo deposi ion on subs a es
p e iously deco a ed wi h nuclea ion cen e s. Me al and me al
oxide hin ilms and nanopa icles deposi ed on a subs a e as
well as polyme ic and o ganic su aces ha e been demons a ed
as sui able nuclea ion cen e s o he o ma ion o small-molecule
o ganic nanowi es. In ou p e ious a icles (Bo as e al., 2008,
2009, 2010; Macias-Mon e o e al., 2013, 2017; Filippin e al.,
2017b, 2019; Alcai e e al., 2019b) we ha e op imized he p ocess
o Au, Ag, ITO, ZnO, TiO2, SiO2, PDMS, and o ganic subs a es
(S ep i) and molecules as me al -po phy ins, -ph halocyanines
and pe ylenes wo king as he nanowi es building blocks (S ep ii).
Scheme 2 igh shows SEM images o he di e en s eps du ing
he o ma ion o he co e@shell nanowi es. Panel (b) shows a
op- iew image o he ONWs e ealing squa ed mo phology
and ex emely la su aces. The main pa ame e s con olling he
o ma ion o o ganic nanowi es om e apo able molecules a e
he subs a e su ace oughness and mic os uc u e, empe a u e
o he subs a e in ela ion o he sublima ion empe a u e o
he molecules, p essu e, g ow h a e and hickness (Bo as e al.,
2008, 2010). These NWs ac as 1D o 3D (Bo as e al., 2009;
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Ob e o e al. 3D Po ous Nanos uc u es
FIGURE 5 | FIB-3D o a sample ab ica ed using RPAVD-O2and so plasma e ching o ClTiPc. (a) Voxel ende ing o he 3D econs uc ion. (b) A sub olume was
selec ed [inse in (a)] o he segmen a ion o he po es (displayed in g een) and he po osi y es ima ion. (e) is an xy slice h ough he olume. (c,d) a e xz slices a he y
posi ions * and ** indica ed in (e). Scaleba : 500 nm.
Filippin e al., 2017b) so - empla e, compa ible wi h acuum
and plasma deposi ion o laye s, p e e ably when he deposi ion
me hod yields he g ow h o con o mal shells, as in he case o
PECVD o ino ganic and RPAVD o o ganic laye s. Panel (c)
in Scheme 2 shows a i s insigh o he RPAVD-O2o a me al
ph halocyanine molecule on as-g own o ganic nanowi es. The
esul is he o ma ion o a high densi y o hyb id co e@shell
nanowi es wi h a shell mo phology and composi ion essembling
hose o he hin ilm coun e pa . Figu es 6a–d show SEM
and TEM mic og aphs o se e al co e@shell nanowi es o med
by RPAVD-O2. In gene al, his syn hesis p ocess leads o he
deco a ion o he ONWs wi h adially dis ibu ed nanocolumns
o med wi h simila aspec s bu smalle han hose p esen ed
on la subs a es (see Figu es 6b–d). The column wid h
on ONWs is abou 50% smalle han on a la silicon
subs a e. The shell o ma ion is usually con o mal o he ONW
ac ing as 1D suppo wi h nanocolumns adially dis ibu ed
om he co e (see Scheme 2c,Figu es 6a–d) gi ing ise o
highly con o mal and hie a chical 3D nanos uc u es. Howe e ,
shadowing e ec s a e qui e no iceable when wo king in glancing
angle condi ions (Figu e 6e) o wi h long and il ed o ganic
nanowi es (Figu es 6 ,g). Thus, Figu es 6e,7show he ZnPc
RPAVD-O2-GLAD o ma ion on he ONWs and demons a e
he di e ence in hicknesses be ween he nanocolumns o med
on he side o he ONW acing owa d he di ec ion o he
a i ing p ecu so species. TEM (Figu e 7a), HAADF-STEM
(Figu es 7b,c) mic og aphs, and EDX maps (Figu es 7d–g)
con i ms he XPS and UV-Vis spec oscopy esul s discussed
abo e on he o ma ion o small ZnO pa icles unde RPAVD-
O2-GLAD condi ions co-exis ing wi h ZnPc a he same ime
ha e eals he po osi y o he indi idual columns. The p esence
o a ZnO shell is e ealed by EDX, while he inne pa o he
column seems o be mainly coming om he o ganic coun e pa
o he molecule.
I is also in e es ing o add ess ha in he p e ious examples
he plasma condi ions du ing he RPAVD-O2p ocess ha e been
selec ed o keep pa o he o ganic nanowi e as he sca old o
he shell. Ne e heless, he o ganic co e can be easily emo ed
by annealing a mild empe a u es du ing he o ma ion o
he shell o in a pos -p ocessing s ep as i is shown in he
STEM mic og aph in Figu e 6d. The emo al o he o ganic
co e lea es squa e o ec angula inne ubes wi h ex emely
la walls (Filippin e al., 2017b; Macias-Mon e o e al., 2017).
In addi ion, in conco dance wi h he esul s ega ding he hin
ilm coun e pa s, once he hyb id co e@shell nanowi es a e
o med, we can apply he so -plasma e ching pos -p ocessing
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