Full Leng h A icle
Magne on spu e ed ß-Ti coa ings o biomedical applica ion: A HiPIMS
app oach o imp o e co osion esis ance and mechanical beha io
Juan Ca los S´
anchez-L´
opez
a,*
, Vanda Godinho
a,b
, Ca men L´
opez-San os
a,c
, Paula Na a o
b,d
,
Luisa Ma leny Rod íguez-Albelo
b
, Mi iam S´
anchez-P´
e ez
a
, Emilio Jim´
enez-Piqu´
e
e
,
Yadi To es
b
a
Ins i u o de Ciencia de Ma e iales de Se illa (ICMS), CSIC-US, A da. Am´
e ico Vespucio 49, E-41092 Se illa, Spain
b
Depa amen o de Ingenie ía y Ciencia de Los Ma e iales y del T anspo e, Uni e sidad de Se illa, Escuela Poli ´
ecnica Supe io , Vi gen de ´
A ica 7, E-41011 Se illa,
Spain
c
Depa amen o de Física Aplicada I, Escuela Poli ´
ecnica Supe io , Uni e sidad de Se illa, Vi gen de ´
A ica 7, E-41011 Se illa, Spain
d
Ins i u o de Mic oelec ´
onica de Se illa, IMSE-CNM, A da. Am´
e ico Vespucio 28, 41092 Se illa, Spain
e
Cen e o S uc u al In eg i y, Reliabili y, and Mic omechanics o Ma e ials (CIEFMA), Depa men o Ma e ials Science and Enginee ing, Uni e si a Poli `
ecnica de
Ca alunya (UPC) - Ba celonaTECH, 08019, Ba celona, Spain
ARTICLE INFO
Keywo ds:
TNZT
Magne on spu e ing
Mechanical p ope ies
We ing
Su ace chemis y
Elec ical impedance
ABSTRACT
This wo k p esen s he su ace modi ica ion o comme cially pu e Ti specimens (c.p.-Ti) p epa ed by con en-
ional powde me allu gy by deposi ing a hin ilm o a ß-Ti alloy (Ti-35Nb-7Z -5Ta, w . %, TNZT). Two ypes o
pulsed echnologies: con en ional (p-DC) and high-powe impulse magne on spu e ing (HiPIMS), wi h and
wi hou bias assis ance (−60 V) unde simila powe condi ions (250 W) we e applied on i anium specimens and
silicon subs a es leading o di e en ilm mo phologies and unc ional p ope ies. Mic os uc u al, X- ay
di ac ion, nanoinden a ion, su ace we ing, XPS and elec ochemical impedance measu emen s we e done o
cha ac e ize hei unc ionali y. All he coa ings p esen ed a educed Young’s Modulus (E ≤80GPa) compa ed o
he bulk Ti, ep esen ing a educ ion o mo e han 30 %. This dec ease can signi ican ly con ibu e o he
educ ion o he s ess-shielding e ec , mi iga ing he isk o implan loosening and ailu e. The ha dness alues
o TNZT coa ings, sligh ly lowe han c.p.-Ti subs a e, ange om 4.1 o 4.7 GPa. XPS analysis shows a
passi a ion laye o TiO
2
, Nb
2
O
5
, and Z O
2
, which o e s high impedance and excellen co osion esis ance. The
bes comp omise be ween mechanical and co osion p ope ies is achie ed wi h he HiPIMS echnology, hanks
o i s compac ilm mic os uc u e wi h high elec ical esis ance, despi e i s limi ed hickness o abou 1
μ
m.
1. In oduc ion
Ti anium (Ti) and i s alloys ha e eme ged as a p e e ed choice o
o hopedic and den al implan s o e he las ew decades [1,2]. This
p e e ence elies on he combina ion o adequa e p ope ies, including
excellen biocompa ibili y, high co osion esis ance, and sui able me-
chanical p ope ies when compa ed o o he ma e ials. Al hough Ti
implan s combine nume ous ad an ages wi h high success a es, s ill
5–10 % esul in ailu e [3], which conside ing he high numbe o
implan s placed e e y yea is deemed unaccep able.
The e a e h ee main easons o Ti implan s ailu e. Fi s ly, he
s ess-shielding phenomenon, caused by he subs an ial dispa i y in
s i ness be ween he implan and he bone, leads o bone eso p ion and
inc eases he isk o ac u e o he adjacen bone. Secondly, p oblems
associa ed wi h excessi e mechanical loads o a igue ailu es esul ing
om inapp op ia e ma e ial selec ion o implan design. Thi dly, he
co osion esis ance o Ti implan s s ill equi es imp o emen . The
co osion esis ance o i anium is mainly asc ibed o he spon aneous
o ma ion o a e y hin (2–5 nm) amo phous laye o i anium dioxide
(TiO
2
), which is c ucial o he biocompa ibili y o Ti implan s. This
passi a ion laye se es as a ba ie , con e ing Ti and i s alloys in o bio-
ine ma e ials, he eby minimizing he elease o ions om he implan
in o he su ounding issues and p e en ing ad e se eac ions in he
body. Howe e , when exposed o agg essi e biological media and sub-
jec ed o epe i i e o a ying loads, hese oxide laye s, which usually
con ain many de ec s, can be comp omised [4].
* Co esponding au ho a : Ins i u o de Ciencia de Ma e iales de Se illa (CSIC-Uni . Se illa), A da. Am´
e ico Vespucio 49, E-41092 Se illa, Spain.
E-mail add ess: [email p o ec ed] (J.C. S´
anchez-L´
opez).
Con en s lis s a ailable a ScienceDi ec
Applied Su ace Science
jou nal homepage: www.else ie .com/loca e/apsusc
h ps://doi.o g/10.1016/j.apsusc.2024.161366
Recei ed 4 July 2024; Recei ed in e ised o m 16 Sep embe 2024; Accep ed 26 Sep embe 2024
Applied Su ace Science 680 (2025) 161366
A ailable online 27 Sep embe 2024
0169-4332/© 2024 The Au ho s. Published by Else ie B.V. 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/ ).
Hence, he de elopmen o ma e ials wi h app op ia e biomechan-
ical beha io , such as low compliance, good ibological esis ance, and
bio unc ional cha ac e is ics like co osion esis ance and bone
ing ow h. This is pa icula ly impo an o implan applica ions whe e
a high s eng h and a igue esis ance o he implan s uc u e a e
equi ed oge he wi h low elas ic modulus and be e biocompa ibili y
close o he bone is desi ed. β-Ti alloys, wi h Young’s Modulus (E) alling
wi hin he ange o 50–95 GPa [1,5,6] a e p omising candida es o a oid
he s ess shielding phenomenon, as hei modulus is close o ha o
co ical bone. In pa icula , β-Ti alloy wi h chemical composi ion o Ti-
35Nb-7Z -5Ta (in w .%), he ea e e e ed o as TNZT, exhibi s one o
he lowes E among β-Ti alloys, a ound 55 GPa [6]. Mo eo e , he
passi a ion laye o med on hese alloys includes Z O
2
and Nb
2
O
5
,
imp o ing he co osion esis ance p ope ies when compa ed o ha
o med on pu e Ti [6–9]. Addi ionally, alloying elemen s wi h low
elec ochemical eac ion po en ials, such as Ta, Nb, and Z could lead o
he educ ion o he anode ac i i y and imp o emen o passi e p op-
e ies [8].
Howe e , TNZT alloy p esen s ela i ely low s eng h and poo wea
beha io , limi ing i s applica ion as implan ma e ial [5,6]. Fo bulk
alloy ma e ials, di e en echniques we e applied o inc ease he
s eng h o hese alloys, ei he by inclusion o o he alloy elemen s
[10,11], se e e plas ic de o ma ion [12] o ageing ea men s [13].
Su ace modi ica ion echniques can be used o cus omize he
implan design o mee he speci ic medical equi emen s o each si u-
a ion. In ou p e ious wo k [14], we in oduced he employ o magne-
on spu e ing-based echniques o modi y he su ace o Ti implan s
manu ac u ed h ough con en ional powde me allu gy wi h a Ti-6Al-
4V coa ing, esul ing in imp o ed mechanical p ope ies. Plasma-
based me hods such as magne on spu e ing no only allow o he
g ow h o c ys alline ma e ials a oom empe a u e unde non-
equilib ium condi ions bu also p o ide con ol o e he deposi ion
pa ame e s, enabling he c ea ion o di e en su ace nanos uc u es
ha could enhance os eoblas ma u a ion, inc ease bone- o-implan
con ac and imp o e he implan success a es. This s udy employed
he high-powe impulse magne on spu e ing echnique (HiPIMS),
which is widely ecognized as an ad an ageous a ian o achie ing
imp o ed mechanical, ibological, and an i-co osi e p ope ies
[15,16]. This echnique has been shown o yield supe io esul s when
compa ed wi h DC magne on spu e ing [14–16]. The high-ene gy
pulses deli e ed o he a ge ma e ial du ing he spu e ing p ocess
esul in a dense and mo e adhe en coa ing on he implan able o
wi hs and handling and i s inse ion in he pa ien body as well as
gua an ee a good pe o mance in se ice [14].
In his wo k, we explo e a simila app oach o ailo he su ace o Ti
implan s deposi ing a β-Ti alloy (TNZT) wi h he aim o dec easing he
misma ch be ween he bone and he implan , imp o ing osseoin eg a-
ion. Addi ionally, alloying Ti wi h Nb, Z , and Ta a oids he po en ial
d awbacks associa ed wi h oxici y om elemen s such as Al and V, wi h
excellen mechanical p ope ies and wo kabili y [1,6]. In his wo k, we
in es iga e he abili y o high plasma ioniza ion o HiPIMS echnique
and ion ene gy ( ia subs a e biasing) on he mo phology, we abili y
and mechanical p ope ies o TNZT coa ings. In addi ion, elec ical
impedance measu emen s a e pe o med o semi-quan i a i ely e alua e
po en ial changes in he coa ings, which can be ela ed o he co osion
esis ance o he su aces and any al e a ions ha may occu a he
implan /bone in e ace. The achie ed unc ionali y o he coa ing is
compa ed wi h an analogous one deposi ed ia con en ional DC
spu e ing in pulsed mode, designed o p e en a c o ma ion. The
combina ion o su ace ailo ing and a p omising bioma e ial like TNZT
could play a c ucial ole in in luencing and modula ing cell-su ace in-
e ac ions, he eby enhancing he coa ing’s po en ial o biomedical
applica ion.
2. Expe imen al
2.1. Thin ilm deposi ion
The TNZT coa ings we e ab ica ed ia magne on spu e ing (MS)
om a comme cial 2 inches diame e by 3 mm- hickness a ge wi h he
ollowing nominal chemical composi ion (Ti 53 w %, Nb 35 w %, Z 7
w %, Ta 5 w %) p o ided by Pho on Expo . The subs a es we e i a-
nium cylinde s (diame e 12 mm; heigh 5 mm) p epa ed om
comme cially pu e Ti −g ade IV (c.p.-Ti) h ough con en ional powde
me allu gy. The p ocedu e ollowed o he p epa a ion o he i anium
specimens is u he desc ibed in [14]. Replica coa ings, deposi ed
simul aneously on silicon (100) subs a es we e also employed o
mic os uc u al and chemical analysis. The p essu e o he acuum
chambe was ≈1x10
−4
Pa p io o syn hesis. Then a gon was ed in o he
chambe a a low a e o 25 sccm un il he p essu e eached 0.75 Pa,
se ing as spu e ing gas. A ci cula 2 inches balanced magne on was
used, p o iding a o al a ea o 20.27 cm
2
. The powe applied o he
magne on head was 250 W using h ee di e en me hodologies: pulsed
di ec cu en (p-DC), HiPIMS, and HiPIMS wi h simul aneous biasing o
he subs a es a −60 V. ENI DC-pulsed and HiPIMS Sol ix equipmen
we e used as powe sou ces. The o a y sample holde (30 .p.m.) was
hea ed a 250 ◦C du ing ilm deposi ion (du a ion: 150 min). The dis-
ance be ween he subs a e and he a ge was consis en ly main ained
a 10 cm o each deposi ion. The ime cha ac e is ics o he pulses a e
summa ized in Table 1. The ope a ion du y cycle ep esen s he on/o
ime a io o he pulses and ypically a e less han 10 % in HiPIMS
p ocesses. This ensu es an ul ahigh peak powe densi y and a highe
ioniza ion pe cen age o spu e ed species [16]. Wi h an a e age spu -
e ing powe o 250 W, he ol age du ing pulses was measu ed a 625 V,
and he peak cu en was app oxima ely 25 A. The co esponding peak
powe densi y and peak cu en densi y we e es ima ed o be a ound
0.77 kW/cm
2
and 1.2 A/cm
2
, espec i ely. The bias ol age (nega i e
a e age alue o 60 V) was applied wi h he p-DC sou ce using he same
pulse ea u es ( equency 250 kHz; du a ion 496 ns).
2.2. Phase composi ion, mic os uc u al and mechanical cha ac e iza ion
o coa ings
X- ay di ac ion analysis (XRD) was employed o s udy he c ys al-
line phase composi ion o he coa ings, he uncoa ed Ti subs a es, along
wi h he a ge ma e ial u ilized o he spu e ing deposi ion. The
equipmen employed was an X’Pe P o PANALYTICAL di ac ome e
wi h Cu K
α
adia ion a 1◦o incidence angle. The a e age c ys alline
domain sizes we e es ima ed using he Debye-Sche e o mula based on
he (110) and (211) e lec ions.
X- ay pho oemission spec oscopy (XPS) was used o in es iga e he
composi ion and chemical s a e o he coa ings su ace, wi h a PHOIBOS
100 spec ome e , wo king wi h he Mg K
α
adia ion as exci a ion
sou ce. The pass ene gy was se a 50 eV o he su ey spec a, and 30
eV o he high ene gy esolu ion spec a o he de ec ed elemen s. An
ionic spu e ing wi h A
+
ions (2 keV, 5 min, 10
-6
mba ) o
Table 1
Pulse pa ame e s used and deposi ion a es o each sample p epa a ion.
Spu e ing me hodology Pulse cha ac e is ics Du y Cycle Deposi ion a e (nm/min)
p-DC 250 kHz; 496 ns 88 % 19.3
HiPIMS 500 Hz; 40 µs 2 % 7.6
HiPIMSþbias (─60 V) 500 Hz; 40 µs 2 % 7.7
J.C. S´
anchez-L´
opez e al. Applied Su ace Science 680 (2025) 161366
2
app oxima ely 1.0 µA was made o emo e pa ially he su ace
con amina ion. The spec a we e calib a ed using he binding ene gy
(BE) o he main oxide componen o Ti 2p peak a ibu able o TiO
2
phase a 458.6 eV.
Scanning elec on mic oscopy (SEM) was conduc ed using a SEM-
FEG Hi achi S4800 mic oscope wi h an ene gy-dispe si e X- ay (EDX)
de ec o . Mo phological cha ac e iza ion and chemical analysis we e
pe o med a 5 and 20 kV, espec i ely. The coa ed i anium specimens
we e di ec ly obse ed o op analysis while silicon wa e s (100) we e
used o c oss-sec ion analysis. Se e al SEM images unde wen image
analysis o asce ain he equi alen diame e (Deq) o columna s uc-
u es and po es, and shape ac o (F ), calcula ed by he o mula F =
4
π
A/PE
2
, whe e A ep esen s he a ea o columns/po es, and PE s ands
o he expe imen al pe ime e o pseudoellip ic columns/po es. Image-
P oPlus 6.2 so wa e (Mediacibe nec ic, Be hesda, MD, USA) was
employed o image analysis measu emen s.
Op ical in e e ome y was employed o de e mine he ilm su ace
oughness (Sa and Sq) on silicon coa ed subs a es using a S-Neox 090
mic oscope om Senso a a 50×magni ica ion. The analyzed a ea
co esponds o app oxima ely 300
μ
m
2
.
We abili y was assessed h ough s a ic con ac angle (CA) mea-
su emen s acqui ed using an OCA 20 Da aphysics ins umen . Mea-
su emen s we e done wi h milli-Q wa e (1–2
μ
L, 3 eplicas, 72.8 mN/m)
and bo ine albumin se um om Sigma Ald ich (5
μ
L, 1 es , 50.0 mN/m
[17]), on coa ed c.p.-Ti subs a es. The measu ed alues we e compa ed
wi h hose ob ained o an uncoa ed and coa ed c.p.-Ti specimen wi h
he biomedical alloy Ti6Al4V[14].
Nanoinden a ion expe imen s we e ca ied ou using an MTS nano-
inden e XP wi h a Be ko ich diamond ip a a cons an s ain a e o
0.05 s
−1
. A ma ix o 4 ×4 inden a ions was d awn o each coa ing and
he esul s we e analyzed by he Oli e and Pha me hod [18]. A used
silica s anda d was used o calib a ion. Film ha dness alue was es i-
ma ed a 10 % o he hickness o he coa ing and he elas ic modulus
was es ima ed by ex apola ion o ze o pene a ion dep h, acco ding o
ISO 14577. Measu emen s we e done u ilizing he con inuous s i ness
measu emen (CSM) op ion, enabling he calcula ion o bo h p ope ies
du ing loading pe iod ela i e o he pene a ion dep h.
The in luence o he in es iga ed TNZT coa ings on he elec ical
impedance o he c.p.-Ti cylinde s was e alua ed using a Hewle -
Packa d 4395A (Agilen Technologies) equipmen and me hodology
desc ibed in ea lie wo ks [14,19]. A ß-Ti bulk TNZT alloy was also
p epa ed and measu ed in simila way o compa ison pu poses. To
place he samples in he analyze , he de ice ea u es a e ac able
accesso y, he HP19042 module, which was used o secu e each sample
while measu emen s we e conduc ed. The con ac a ea o he ou pu
po is 12 mm
2
. Once he HP 4395A is calib a ed, ix u e compensa ion
Table 2
Chemical composi ion o he a ge ma e ial and deposi ed coa ings by EDX analysis a 20 kV. Nominal composi ion o he a ge is Ti53Nb35Z 7Ta5.
Ti Nb Z Ta Nb/Ti Z /Ti Ta/Ti
w .% (a .%) w .% (a .%) w .% (a .%) w .% (a .%) w .% (a .%) w .% (a .%) w .% (a .%)
Ta ge 55.3
(71.9)
34.0
(22.8)
5.0
(3.4)
5.7
(2.0)
0.61
(0.32)
0.09
(0.05)
0.10
(0.03)
p-DC 59.6
(75.0)
29.6
(19.2)
6.7
(4.4)
4.1
(1.4)
0.50
(0.26)
0.11
(0.06)
0.07
(0.02)
HiPIMS 57.3
(73.0)
32.6
(21.4)
6.4
(4.3)
3.7
(1.2)
0.57
(0.29)
0.11
(0.06)
0.06
(0.02)
HiPIMSþbias 55.9
(71.9)
33.9
(22.5)
6.4
(4.3)
3.7
(1.3)
0.61
(0.31)
0.11
(0.06)
0.07
(0.02)
Fig. 1. XRD scans o he h ee TNZT ilms unde he h ee di e en syn hesis condi ions (p-DC, HiPIMS and HiPIMS+bias) compa ed o hose o he used TNZT
a ge and he uncoa ed c.p.-Ti subs a e. The posi ions o he cubic [c-Ti (□) (PDF #44–1288), c-Nb (
○) (PDF #2–1108), c-Ta (×) (PDF #1–1309)], and hexagonal
c ys alline e e ences [h-Ti (✰) (PDF #44–1294)] a e also included.
J.C. S´
anchez-L´
opez e al. Applied Su ace Science 680 (2025) 161366
3
is pe o med o calib a e i along wi h he HP19042 o elimina e e o s
occu ing be ween he elec ode o he es ix u e and he ou pu po o
he impedance es ki . Elec ical impedance measu emen s we e pe -
o med unde d y condi ions in he ambien en i onmen , as he de ice
does no equi e speci ic condi ions o measu emen s. The equency
anged be ween 100 MHz and 500 MHz This ange was speci ically
chosen due o he absence o no able di e ences obse ed among he
cu es ob ained o each coa ed disc a lowe equencies. The imped-
ance measu emen s we e pe o med h ee imes o e e y sample, he
mean alue was hen calcula ed and g aphically ep esen ed.
3. Resul s and Discussion
The chemical composi ion o he coa ings was ob ained by EDX
analysis on h ee silicon coa ed specimens and compa ed o ha ob-
ained o he a ge ma e ial. The esul s a e ou lined in Table 2,
exp essed in w .% (wi h co esponding alues in a . % p o ided in
pa en hesis).
The composi ion o he coa ings closely ep oduces he a ge
composi ion wi h sligh di e ences. The mos signi ican ea u e co e-
sponds o he Nb/Ti a io, which inc eases om 0.50 o 0.57 (in w .%)
when changing om p-DC o HiPIMS, and eaching 0.61 in he
HiPIMS+bias, ep oducing he alue measu ed o he a ge . Rega ding
Z and Ta elemen s, he di e ences we e no signi ican based on he
deposi ion mode.
The c ys alline s uc u e o he coa ings was es ablished by g azing
angle XRD a 1◦o incidence angle. Fig. 1 depic s he di ac og ams
ob ained o he h ee spu e ing condi ions oge he wi h hose co e-
sponding o he ini ial TNZT alloyed a ge and he uncoa ed Ti spec-
imen. The di ac ion pa e ns o he TNZT ilms ag ee wi h cubic
i anium (in con as o he hexagonal phase o he c.p.-Ti subs a e)
whose posi ions a e sligh ly shi ed owa ds highe angles due o he
p esence o Ta, wi h lowe la ice pa ame e (a
0
=0.3298 s. 0.3306 nm
o Ti). No e idence o hexagonal phases o i anium o zi conium is
obse ed, con i ming ha a e spu e ing he cubic o m (ß-phase) o
Table 3
Coa ing hickness gi en by SEM c oss-sec ion, su ace oughness alues by op-
ical in e e ome y and c ys alli e size calcula ed by XRD da a om peaks (110)
and (211).
Coa ing
hickness
Sa C ys al size
(110)
C ys al size
(211)
(nm) (nm) (nm) (nm)
p-DC 2900 10.2 ±
1.2
54 52
HiPIMS 1140 3.0 ±
0.5
68 21
HiPIMSþbias 1150 2.7 ±
0.8
22 12
Fig. 2. C oss-sec ion (le column) and op ( igh column) mic og aphs ob ained by SEM o he h ee TNZT coa ings deposi ed on silicon subs a es and c.p.-Ti
specimens, espec i ely.
J.C. S´
anchez-L´
opez e al. Applied Su ace Science 680 (2025) 161366
4
he ini ial a ge alloy is main ained in he h ee coa ings. Ne e heless,
he c ys allog aphic o ien a ions a e modi ied om a p edominan
(110) g ow h owa ds (211) in he TNZT hin ilms. The poly-
c ys allini y, cha ac e ized by a mo e andom o ien a ion, is enhanced
in he p-DC compa ed o HiPIMS, whe e he occu ences o he (200) and
(220) o ien a ions a e e y mino , al hough i migh be in luenced by i s
highe hickness. Addi ionally, he e is a no iceable peak b oadening,
pa icula ly e iden when HiPIMS and biasing o he subs a es a e
u ilized simul aneously. The de e mina ion o he peak b oadening,
using he FWHM da a o (110) and (211) e lec ions, allows he es i-
ma ion o he c ys alline domain sizes. The alues a e summa ized in
Table 3 and con i m ha unde condi ions o high ion bomba dmen ,
achie ed combining HiPIMS discha ges and subs a e biasing [16,20],
he c ys al sizes a e minimized. Speci ically, when employing a gon as
spu e ing gas, Ti is an elemen cha ac e ized by a high ioniza ion e i-
ciency due o a ela i ely la ge elec on impac ioniza ion c oss-sec ion
and a low ioniza ion po en ial. Bohlma k and cowo ke s [21,22]
demons a ed he highe ionic con ibu ion and b oad ene gy dis ibu-
ion in he HiPIMS s. DC plasmas. They ound ha he ionic con ibu-
ion o Ti exceeded 90 % (compa ed o 8 % in DC), and app oxima ely
hal o he ionized Ti had ene gies highe han 20 eV, in con as o
app oxima ely 2 eV in DC spu e ing discha ge.
Fig. 2 summa izes c oss and op sec ions SEM mic og aphs o he
h ee TNZT coa ings. The c oss-sec ion images we e ob ained om sil-
icon coa ed samples a e clea age while he op- iews we e cap u ed
om he coa ed c.p.-Ti cylinde s. The ea u es ob ained on bo h ype o
subs a es a e consis en , con i ming ha he ilm mo phology is inde-
penden o he na u e o he subs a e, depending mainly on he depo-
si ion pa ame e s.
The measu ed hickness alues a e 2900, 1140, and 1150 nm o he
ilms deposi ed wi h p–DC, HiPIMS and HiPIMS+bias, espec i ely. The
dec ease in hickness o HiPIMS samples is consis en wi h he educ ion
o deposi ion a es achie ed by his echnology in compa ison o p–DC
[23] and consis en wi h ou p e ious esul s [24]. This educ ion elies
on he dec ease o ope a ion ime (du y cycle dec eased om 88 % in p-
DC o 2 % in HiPIMS), and he back–a ac ion o he la ge p opo ion
o posi i ely cha ged ions om he a ge p esen in HiPIMS discha ges
[25]. The ilm g ow h is clea ly columna in p-DC bu he ilm mic o-
s uc u e e ol es o ain-like in he HiPIMS samples. This ype o
mic os uc u e is ypical o me allic glass-like beha io [26]. Despi e he
la ge hickness o he p-DC sample, we can conclude ha he columna
s uc u e wi h e y well-de ined bo de s is al eady isible a a hickness
compa able o ha o HiPIMS samples. As commen ed p e iously, he
highe ion densi y achie ed in he HiPIMS plasma a o ed a dense ilm
mo phology, while in p-DC less ene ge ic condi ions esul ed in a
mic os uc u e cha ac e ized by shadowing e ec s, leading o an open
in e columna mo phology [16]. The addi ional subs a e bias acili a es
he accele a ion o A
+
ions a highe ene gies con ibu ing also o
densi y he ilm su ace and o educe he deposi ion a e [24]. The op
iew o he samples clea ly illus a es his end, wi h a ma ked educ-
ion o he open po osi y a he column bounda ies when changing o
HiPIMS condi ions. Fu he su ace smoo hing is achie ed wi h he
assis ance o nega i e bias al hough he column shape becomes mo e
i egula . The bigge s uc u es co espond o pilla s o med by a ious
subuni s (mino columns), which coalesce unde he in luence o addi-
ional ion bomba dmen .
Image analysis ca ied ou on hese mic og aphs allows o de e mine
he a e age columna size and he po e size dis ibu ion. The es ima ed
in e columna po osi ies we e ound o be 4, 2, 0.3 % (co esponding
equi alen po e diame e 16, 10 and 1.5 nm) o p-DC, HiPIMS and
HiPIMS+bias, espec i ely. These esul s highligh he inc easing
compac ion s uc u es ob ained unde mo e ene ge ic condi ions.
De ailed esul s a e summa ized in suppo ing in o ma ion, including
his og ams (Fig. S1a) and image analysis (Fig. S1b). Using a ious op
iew mic og aphs, he equi alen column diame e s we e es ima ed o
be 150 nm o p-DC, 95 nm o HiPIMS and 154 nm o HiPIMS+bias.
These alues a e p obably o e es ima ed due o he high deg ee o
coalescence and su ace smoo hening in luenced by ion bomba dmen ,
making di icul o e alua e accu a ely he size o columns. A ending o
he op iew (c . Fig. 2, igh column), i becomes e iden ha he
Fig. 3. A e age su ace oughness measu ed by in e e ome ic analysis on he
silicon coa ed samples.
Fig. 4. Elas ic modulus (a) and ha dness alues (b) o he di e en coa ings (p-
DC, HiPIMS and HiPIMS+bias) deposi ed on silicon compa ed o he uncoa ed
c.p.-Ti subs a e.
J.C. S´
anchez-L´
opez e al. Applied Su ace Science 680 (2025) 161366
5
column shape o he HiPIMS+bias sample is mo e he e ogeneous,
al e na ing la ge ea u es wi h mino ones. The esul is a mosaic-like
pa e n whose space be ween iles is minimized esul ing in smoo he
su ace o e all. The es ima ion o su ace oughness by means o in e -
e ome ic mic oscopy analysis con i med his esul . Fig. 3 summa izes
he mean alues (Sa and Sq) e ealing a ma ked s ep down when an-
si ioning om p-DC o HiPIMS, om 10 o ≤3 nm, al hough a ce ain
con ibu ion om he la ge hickness o p-DC sample canno be dis-
ega ded. The 2D and 3D images used o his analysis can be ound in
supplemen a y ma e ial (Figu e S2).
The mechanical p ope ies o he di e en coa ings we e assessed by
nanoinden a ion, and he esul ing elas ic modulus (E) and ha dness (H)
alues a e compa a i ely included in Fig. 4a and 4b, espec i ely,
oge he wi h he uncoa ed subs a e ma e ial (c.p.-Ti). The g aphics
show an ini ial egime whe e bo h H and E alues a e lowe han hose o
he p is ine subs a e. This egime aligns wi h he 10 % ule o humb
commonly used o assessing he mechanical p ope ies, minimizing he
in luence o he subs a e. Thus, he elas ic moduli o he h ee coa ings
ob ained by ex apola ion o ze o a e simila (80 ±5 GPa). This ep e-
sen s a educ ion o mo e han 30 % o Young’s modulus o he c.p.-Ti
specimen (120 ±5 GPa), which would con ibu e o dec ease he
s ess shielding phenomena be ween he Ti implan and he bone.
Mo eo e , compa ing his esul wi h ou p e ious wo k [14], he use o
his TiNbZ Ta alloyed a ge p o es o be ad an ageous compa ed o
TiAlV coa ings, p epa ed by he same spu e ing deposi ion echnique
[3]. The educ ion in elas ic modulus alues, in ha case, a ied
be ween 8–20 % [14] compa ed o he alues p esen ed by he Ti sub-
s a e, depending on whe he he p-DC o HiPIMS mode was used. This
end is coinciden wi h he wo k o Co dei o e al. whose alues we e
102, 139 and 82 GPa po c.p.-Ti, TiAlV and TNZT, espec i ely [27]. In
e ms o ha dness, he de eloped coa ings exhibi alues ha a e com-
pa able o he alues epo ed o TNZT alloys [28,29], and sligh ly
lowe han pu e i anium su ace, ( anging om 4.1 o 4.7 ±0.1 GPa),
wi h he highes alues co esponding as expec ed o he ilm p oduced
using HiPIMS and bias assis ance.
An impo an pa ame e o be conside ed o he implan ’s li e ime is
i s wea esis ance. The ma e ial esis ance o ab asion, a igue and
adhesion o ces a e di ec ly de e mined by he mechanical p ope ies
while co osi e wea is also condi ioned by he elec ochemical
beha io . Thus, he o ma ion o he Nb oxide con aining passi a ion
laye on β-Ti alloys has been epo ed as a posi i e ac o o imp o e
wea esis ance [30].
Table 4 summa izes he measu ed mechanical p ope ies, H/E and
H
3
/E
2
alues o he di e en coa ings s. he uncoa ed i anium spec-
imen. The H/E a io co ela es wi h elas ic s ain o ailu e and wea
esis ance, and he H
3
/E
2
a io is connec ed o he esis ance agains
plas ic de o ma ion [31]. In he case o he coa ings p epa ed in his
wo k, H/E a ied be ween 0.05 and 0.06, and H
3
/E
2
om 0.011 o
0.016. These alues a e compa able o hose ound in he li e a u e o
β-Ti alloys and Ti6Al4V alloys subjec ed o lase ea men s o imp o e
wea esis ance [28,32] and ep esen s a signi ican imp o emen in
espec o c.p.-Ti., pa icula ly in he case o HiPIMS deposi ion wi h bias
assis ance (H/E =0.06; H
3
/E
2
=0.016).
Ano he c ucial pa ame e con ibu ing o he success o an implan
is he su ace we abili y. Hyd ophilic i anium-based implan su aces
acili a e imp o ed cell adhesion while hyd ophobic su aces a e
commonly known o he epellen esponse o bac e ia adhesion.
Howe e , when he ma e ial is wo king o long- e m o e en unde
cycling in physiological en i onmen s, su ace we abili y h ough he
in e ac ion wi h wa e may no be a good e e ence. In his wo k,
we abili y has been e alua ed bo h in wa e and bo ine se um media.
The coa ings de eloped using di e en deposi ion echniques exhibi a
qui e simila su ace esponse o he in e ac ion wi h liquids o di e en
na u e as p esen ed in Fig. 5. We abili y o he coa ings using milli-Q
wa e d ople s esul s in compa able WCA alues a ound 80◦, as
Table 4
Values o Young’s modulus (E), ha dness (H), and he a ios H/E and H
3
/E
2
measu ed by nanoinden a ion o he coa ings deposi ed ia p-DC, HiPIMS and
HiPIMS+bias, and he ba e subs a e (c.p.-Ti).
E (GPa) H (GPa) H/E H
3
/E
2
p-DC 80 ±5 4.1 ±0.1 0.05 0.011
HiPIMS 80 ±5 4.1 ±0.1 0.05 0.011
HiPIMSþbias 80 ±5 4.7 ±0.1 0.06 0.016
c.p.-Ti 120 ±5 5.1 ±0.1 0.04 0.009
No e: The H alues we e es ima ed a ≈300 nm o p-DC samples and ≈100 nm
o HiPIMS samples, ollowing he 10 % ule o humb. E alues we e de e mined
by ex apola ing he linea po ion o he cu e o ze o nm.
Fig. 5. Measu ed con ac angles on he su aces coa ed by TNTZ using wa e and bo ine albumin se um as we ing agen s. The uncoa ed c.p.-Ti is also included
as e e ence.
J.C. S´
anchez-L´
opez e al. Applied Su ace Science 680 (2025) 161366
6
shown in Fig. 5a, being ela i ely lowe in he case o he HiPIMS+bias
deposi ion. This quasi-hyd ophobic s a e, compa ed wi h he ma ked
hyd ophilic esponse o he uncoa ed c.p.-Ti implan (WCA o 48◦), is
consis en wi h p e ious indings ob ained wi h he same ab ica ion
echniques o Ti6Al4V coa ings [14]. When he TNZT su aces a e
we ed wi h d ople s o a biological medium simula ing luid, such as
bo ine se um albumin p o ein (Fig. 5b), he measu ed con ac angles
a ied mo e signi ican ly depending on he echnique. They anged om
62◦ o he coa ing ab ica ed wi h he p-DC mode o a ound 75◦ o
HiPIMS deposi ion, ega dless o whe he bias is applied o no . This
esul indica es ha he we ing p ope ies o TNZT coa ings p epa ed by
HiPIMS ha e li le e ec on changing he subs a e’s a ini y o we ing
wi h bo ine se um while he p-DC su ace (wi h highe a e age ough-
ness) imp o es his a ini y. This is unlike Ti6Al4V coa ings in ou p e-
ious wo k, which p esen ed highe con ac angle alues [14]. Coa ings
wi h lowe su ace ension would align wi h p esen ing some esis ance
o bac e ia in e ac ion and inhibi ing h ombus o ma ion by p e en ing
pla ele accumula ion [33,34]. Thus, by dis ega ding he di e ences
ha may a ise om he chemical na u e de eloped using p-DC o
HiPIMS echniques (as discussed in he nex sec ion), i becomes
appa en ha he less ough su ace wi h ewe de ec s p oduced by
HiPIMS seems o induce a sligh ly mo e hyd ophilic and less p o ein-
philic cha ac e , sugges ing be e bio- and hemo-compa ible beha io
[35].
Addi ionally, su ace chemis y signi ican ly in luences he in-
e ac ions be ween su aces and hei en i onmen , a ec ing bio and
wea esponse. Analysis o he su ace chemical composi ion by XPS is
summa ized in Table 5, including bo h he ini ial da a and a e A
+
e ching o in es iga e benea h he ou e mos su ace egion. The mos
signi ican conclusion is he high con ibu ion o oxygen (mo e han 50
a .%) which is no emo ed a e mild A
+
bomba dmen whils ca bon
con en ends o dec ease. This is indica i e o he o ma ion o a su ace
oxide laye by ou di usion o he me als o ming he TNZT alloy, mainly
Ti, Nb and Z as expec ed [27]. The low a omic concen a ion o Ta (<2
a .% as measu ed by EDX) along wi h he high oxide co e age o med
h ough he majo elemen s p esen in he alloy ende ed his elemen
unde ec able. Compa ing he Nb/Ti and Z /Ti among he h ee coa ings,
di e ences in he ou wa d di usion o me als a e no iceable depending
on he ype o spu e ing p ocess. Thus, he highes alues a e ob ained
o he sample p epa ed by HiPIMS wi h bias assis ance, indica ing
en ichmen in Nb and Z in he passi a ion laye . Compa ing wi h he
bulk a omic Nb/Ti and Z /Ti a ios measu ed by EDX (c . Table 2, a .%),
he e is a clea inc eased ou di usion o Z (a ac o be ween 2.5 and 5)
o he h ee coa ings, and Nb o he HiPIMS+bias sample ( ac o 1.5 o
2). These chemical a ia ions should be conside ed oge he wi h he
na u e o he o med oxide on he co osion and biocompa ibili y o he
su aces.
XPS su ey analysis was he e o e conduc ed a he Ti 2p, Z 3d and
Nb 3d pho oelec on peaks o es ablish he oxida ion s a e o hese el-
emen s in he ou e mos laye o he h ee coa ings. Fig. 6 exhibi s he
high- esolu ion Ti 2p, Z 3d and Nb 3d pho opeak double s o p-DC,
HiPIMS and HiPIMS+bias, bo h in he ini ial s a e and a e A
+
e ching.
No me al–me al bonding was iden i ied in none o he deposi ed coa -
ings and he binding ene gy posi ions align wi h oxidized s a es in all
cases. Fig. 6a shows he main componen o XPS Ti 2p peak cen ed a
458.6 eV o binding ene gy. This alue is ypical o i anium bonded o
Table 5
A omic composi ion o TNZT su ace coa ings ab ica ed by p-DC, HiPIMS and
HiPIMS+bias be o e and a e a mild A
+
e ching ea men .
Ini ial
% a . (TNZT) C O Ti Z Nb N Nb/Ti Z /Ti
p-DC 32.0 48.3 13.9 2.4 3.4 −0.24 0.17
HiPIMS 32.2 47.8 12.9 2.4 3.3 1.4 0.26 0.19
HiPIMSþbias 41.1 44.1 7.6 2.0 3.4 1.8 0.45 0.26
A e A
+
spu e ing
% a . (TNZT) C O Ti Z Nb N Nb/Ti Z /Ti
p-DC 28.7 48.8 15.7 3.9 2.9 −0.18 0.25
HiPIMS 25.0 52.9 14.9 2.3 4.0 1.0 0.27 0.15
HiPIMSþbias 9.4 63.7 12.4 3.7 7.7 3.3 0.62 0.30
Fig. 6. XPS high ene gy esol ed spec a o he di e en coa ings (p-DC,
HiPIMS and HiPIMS+bias): a) Ti 2p, b) Nb 3d and c) Z 3d.
J.C. S´
anchez-L´
opez e al. Applied Su ace Science 680 (2025) 161366
7
oxygen in TiO
2
phase. This assignmen is u he suppo ed wi h he
co esponding O 1 s pho oelec on peaks shown in Fig. S3a om he
suppo ing in o ma ion. Compa ing hese oxygen signals (Fig. S3a) in
he as-deposi ed s a e wi h hose ob ained wi h Ti6Al4V su aces [14], i
is e iden ha he hyd oxide componen is no p esen in his case. O he
sub-oxidized i anium species, such as Ti
2
O
3
, appea jus below he
ou e mos su ace egion as a b oad con ibu ion a lowe binding en-
e gies (o e 456.2 eV) o he HiPIMS+bias sample, as well as o a lesse
ex en , o he p-DC one [36]. The p esence o Ti
3+
in he non-
s oichiome ic TiO
2
s uc u e gene a es oxygen acancies in o de o
achie e he elec oneu ali y, which in luence nega i ely he co osion
p ope ies. Howe e , i is epo ed ha he p esence o Nb in he TNZT
alloys helps o dec ease he con en o hese anionic acancies,
imp o ing he passi a ion cha ac e is ics o he oxide ilm [37]. Mo e-
o e , he adii simila i y o Ti and Nb ions con ibu es ha he
eplacemen in he c ys al la ice does no gene a e poin de ec s, which
also a ou he co osion a e. Fig. 6b p esen s he main con ibu ion o
he Z 3d egion cen ed a 182.3 eV. This binding ene gy is sligh ly
lowe han hose ypically epo ed o Z O
2
species [27]. A compa able
pa e n is obse ed in he posi ion o he main peak o he Nb 3d
pho oelec on peak (207.0 eV), which is loca ed a ene gies sligh ly
below ha co esponding o Nb
2
O
5
(BE ~ 207.3 eV) [38,39]. These
chemical species a e s able a e he ion bomba dmen cleaning excep
o he case o he HiPIMS+bias me hod, which displays a wide XPS
signal in he Nb 3d peak (Fig. 6c), which ex ends o lowe binding en-
e gies in ol ing sub-oxidized con ibu ions (NbO
x
a ound 203.9 eV)
[40]. As a esul , simila o he obse a ions in he analysis o he i a-
nium spec um, he HiPIMS+bias condi ions a ou ed he p esence o
sub-s oichiome ic Nb oxides benea h he opmos laye , non- eaching
he maximum oxida ion s a e and mos he modynamically s able
Nb
2
O
5
phase.
In summa y, he assembly o XPS esul s a e indica i e o he o -
ma ion o a passi a ion oxide laye wi h TiO
2
as p edominan phase,
conside ing i s a omic concen a ion in he alloy, which is nea ly h ee
imes highe han he alues co esponding o he o he elemen s.
Addi ionally, he Z and Nb con en s a e inc eased in he oxide laye in
espec o hei a io in he bulk alloy composi ion. S able su ace
oxida ion h ough he gene a ion o a mix u e o TiO
2
, Nb
2
O
5
, Z O
2
and
Ta
2
O
5
laye has been p e iously epo ed like biocompa ible [28] and
co osion esis ance [6–9] when compa ed o Ti o TiAlV alloys used o
o hopedic implan s. Ne e heless, he p esence o anion acancies,
poin de ec s and non-s oichiome ic unde ce ain syn hesis condi ions
may induce changes in he elec ochemical beha iou as we will discuss
nex .
Elec ical impedance spec oscopy (EIS) measu emen s we e pe -
o med o semi-quan i a i ely e alua e po en ial changes in he elec-
ochemical p ope ies o he su aces de e mining he bio-co osion
esis ance [41,42].Fig. 7 illus a es a schema ic ep esen a ion o he
elec ical impedance measu emen s, conside ing he sys em c.p.-Ti
subs a e +TNZT coa ing as se ies esis o s in a ci cui . Fig. 8 shows
he elec ical impedance alues |Z| o he ba e i anium subs a e and
he e ec o he di e en TNZT coa ings a equencies om 100 o 500
MHz. P e ious wo ks ha e also u ilized a simila ange o equencies in
EIS o e alua e he po osi y in implan s [41], o s udy he cellula
g ow h on po ous Ti implan s [42] o o co ela e he changes in he
impedance alues wi h he mechanical p ope ies o co ical o abec-
ula bones [43]. A hese equencies, i is possible o de ec a ia ions in
biological ma e ials in he so-called γ– egion [44], in pa icula on he
aqueous con en o biological species and small molecules.
As expec ed, he impedance alues a e highe in he coa ed discs, as
illus a ed in Fig. 8a, and exhibi a linea dependence wi h he e-
quency, a ying om app oxima ely 150 o 500 mΩ[19,41]. These
alues a e compa able o a ully dense bulk β−TNZT alloy, included in
he same g aph o compa ison pu poses, despi e o hei limi ed
hickness (1 o 3
μ
m). This demons a es ha he coa ings we a e
ob aining a e qui e dense and achie e consis en chemical composi ions,
esul ing in simila alues o elec ical impedance. Howe e , he di -
e ences among he di e en β-Ti coa ings and he ba e Ti implan
become mo e appa en a highe equency alues, when he e ec s o
he mic os uc u e and chemical composi ion a e mo e ele an , as has
been obse ed in p e ious wo ks [19,41].
To be e e alua e he di e ences in impedance p ope ies o he
TNZT coa ings, he impedance alue o he ba e Ti subs a e we e i s ly
emo ed om he o iginal measu emen s (Fig. 8b). Then hese alues
we e no malized by di iding hem by he co esponding coa ing hick-
ness (Fig. 8c). Upon emo ing he e ec o he hick c.p.-Ti subs a e, a
signi ican dec ease in impedance alues is obse ed. Once no malized
by he coa ing hickness, e y high impedance alues a e obse ed (c .
Fig. 8c). These da a ea men s enable a mo e ho ough e alua ion o he
coa ings’beha io . The esul s indica e ha p-DC deposi ed coa ing
shows he lowes impedance alues, whe eas he HiPIMS deposi ed
TNZT coa ings demons a e signi ican ly highe impedance, mul iplying
by a ac o o 4 o 7 depending on he p ocess and es ing equency.
On he o he hand, in Fig. 8d, he elec ical impedance esul s a e
no malized by he elec ical impedance esponse o he i anium sub-
s a e, yielding a no malized impedance a io. In his ype o esul s
analysis p o ocol, he e ec o equency on elec ical impedance mea-
su emen s is dis ega ded, deno ing he same beha io o he coa ings in
all anges o measu ed equencies. In Fig. 8 , he impedance alues a e
also di iding by he coa ing hicknesses o ob ain he elec ical esis-
ance by leng h uni . Once again, highe alues o impedance a e
obse ed o he HiPIMS coa ings.
The e is a di ec ela ionship be ween he su ace s a e and he
elec ical p ope ies o he coa ed implan s, o in o he wo ds be ween
elec ical impedance esul s and co osion esis ance. The XPS su ace
analysis p o ed he o ma ion o a su ace p o ec i e passi a ion laye
comp ising a mix u e o Ti, Nb and Z oxides, se ing o p e en he
co osion in biological media. Besides, he high alues o WCA angles
measu ed on TNZT coa ings, a ound 80◦ s. 50◦in he case o c.p.-Ti,
helps o educe su ace we ing phenomena, he eby inhibi ing co o-
si e mechanisms. These expe imen al e idences jus i y he inc eased
elec ical impedance alues o ß-coa ed Ti specimens. Howe e , o he
ac o s as ilm mic os uc u e, oxide ype, oxide s oichiome y and oxide
a io inside he passi a ion laye mus be conside ed o ully explain he
dis inc beha io depending on he me hod o syn hesis employed. Thus,
p-DC coa ing p esen s he lowes impedance alues, which can be
Fig. 7. Scheme o elec ical impedance measu emen s conside ing he sys em c.p.-Ti subs a e +TNZT coa ing as in se ies esis o s in a ci cui (M.S.: magne-
on spu e ing).
J.C. S´
anchez-L´
opez e al. Applied Su ace Science 680 (2025) 161366
8
ela ed o he columna mic os uc u e wi h high in e columna
po osi y, in opposi ion o he dense mo phology obse ed in he
HiPIMS samples. The open s uc u e easies he access o he oxygen o
he i anium subs a e, and he e o e he beha io demons a ed by he
p-DC is mo e simila o ha o ba e c.p.-Ti. Be ween he HiPIMS samples,
a sligh ly poo e beha io is ound i simul aneous bias ol age is
applied o he subs a e. The inc eased Nb and Z di usion in he
passi a ion laye and he p esence o suboxides NbO
x
and Ti
2
O
3
may
accoun o his dec ease in co osion esis ance as p e iously epo ed
in non-s oichiome ic and poin de ec s oxides [37,45].
4. Conclusions
In his wo k, a β-Ti alloy composed was deposi ed by magne on
spu e ing o Ti–35Nb–7Z –5Ta (w . %) on c.p.-Ti specimens p epa ed
by con en ional powde me allu gy o implan applica ions. Pulsed
magne on spu e ing echnologies (p-DC and HiPIMS, wi h and wi hou
bias assis ance) unde simila powe condi ions we e applied leading o
di e en ilm mo phologies and unc ional p ope ies (mechanical,
su ace chemis y and co osion esis ance). All he coa ings p esen ed a
educed Young’s Modulus (≤80GPa) compa ed o he c.p.-Ti specimen,
ep esen ing a educ ion o E o mo e han 30 %. This dec ease can
Fig. 8. a) Elec ical impedance measu emen s (|Z|) o he ba e c.p.-Ti subs a e s. TNZT coa ed c.p.-Ti subs a es. A ully dense bulk ß-TNZT alloy (FD TZNT) is
included o compa ison pu poses; b) Elec ical impedance alues o he TNZT coa ings a e sub ac ion o ba e c.p.-Ti subs a e, |Z
C
|=|Z|-|Z
c.p.-Ti
|; c) No malized
alues o impedance o he TNZT coa ings conside ing he coa ing hickness ( ), |Z
C/
|=|Z
C
|/ ; d) No malized impedance a ios conside ing he impedance o he
ba e c.p.-Ti subs a e, |Z
N
|=|Z|/|Z
c.p.-Ti
|; e) No malized impedance a ios o he TNZT a e sub ac ion o he ba e c.p.-Ti con ibu ion, |Z
NC
|=|Z
N
|-1; ) No malized
impedance a ios o he TNZT coa ings by he coa ing hickness, |Z
NC/
|=|Z
NC
|/ .
J.C. S´
anchez-L´
opez e al. Applied Su ace Science 680 (2025) 161366
9
