Colo ed semi- anspa en Cu-Si oxide hin ilms
p epa ed by magne on spu e ing
J. Gil-Ros a,1,* F. Yube o,1 R. Fe nández,4 T. Vilajoana,2 P. A ús,2 J. C. Dü s ele ,2
J. Co ino,1 I. O ega,3 and A. R. González-Elipe1
1Ins i u o de Ciencia de Ma e iales de Se illa (CSIC – U. Se illa), C/ Amé ico Vespucio 49, E-41092 Se illa, Spain
2INDO (A . Alcalde Ba nils), 72. 08174 San Cuga del Vallès, Spain
3Cen o Nacional de Acele edado es (CSIC-U. Se illa), Tomas Alba Edison 7, E-41092 Se illa, Spain
4Dep . o Physical Me allu gy, Cen o Nacional de In es igaciones Me alú gicas (CENIM) CSIC, A . G ego io del
Amo 8, E-28040 Mad id, Spain
*gil os [email protected]
Abs ac : Colo ed semi- anspa en Cu-Si oxide hin ilms ha e been
p epa ed by eac i e magne on spu e ing om a single ca hode o coppe -
silicon composi ion. Thin ilms o di e en composi ion and op ical
esponse we e ob ained by changing p ocess pa ame e s like he ela i e
amoun o coppe in he a ge and he O2/A mix u e o he eac i e plasma
gas. The ilm cha ac e is ics we e analyzed by se e al echniques. Thei
op ical p ope ies ( e ac i e index, abso p ion coe icien , colo ) ha e been
co ela ed wi h he p ocess pa ame e s used in he ilm p epa a ion as well
as wi h he ilm s oichiome y and chemis y.
©2011 Op ical Socie y o Ame ica
OCIS codes: (310.6860) Thin ilms, op ical p ope ies; (310.1860) Deposi ion and ab ica ion;
(310.3840) Ma e ials and p ocess cha ac e iza ion; (330.4460) Oph halmic op ics and de ices.
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1. In oduc ion
Colo ed hin ilms ha e been p epa ed by a a ie y o me hods including physical apo
e apo a ion, magne on spu e ing o plasma enhanced chemical apou deposi ion (PECVD)
[1–7]. In mos cases, he ilms no only p esen a gi en colo bu also a ce ain glow because
o he highly e lec ing cha ac e o hei su aces. In many cases, hese hin ilms also p esen
a good elec ical conduc i i y. Wi hin his ype o ma e ials we can quo e he ni ides,
oxini ides, ca bides and ni oca bides o he elemen s o he i s ansi ion se ies [8]. In
compa ison wi h he huge numbe o wo ks on his opic a ailable in he li e a u e, he e a e
e y ew epo s on he p epa a ion o colo ed oxide hin ilms which show some abso p ion
in he isible egion o he elec omagne ic spec a. These ilms can ind applica ion in
impo an indus ial sec o s ela ed o deco a i e coa ings o oph halmic indus y due o hei
aes he ic aspec and o he unc ional p ope ies.
A ypical way o ailo he op ical p ope ies o oxide hin ilm ma e ials, pa icula ly hei
colo , is o adjus he ela i e concen a ion o wo single oxides mixed in a single phase. The
ange o a ia ion o he op ical cha ac e is ics o he ilms achie ed in his way can be e y
wide i he wo oxides mixed oge he ha e a he di e en e ac i e index and ex inc ion
coe icien . This idea is ela ed o he common use o ansi ion me al oxides o colo glasses,
adi ionally employed in s ained-glass windows and o he hand-c a glasses [3,4,9–12].
Howe e , con ol o he op ical pe o mance ( e ac i e index, abso p ion, colo ) in hin
ilms o educed hickness aces impo an p oblems ela ed wi h he adjus men o he
concen a ion o he colo ing ca ion and he uning o hei chemis y, pa icula ly i he
deposi ion p ocess occu s a low empe a u e and no pos -deposi ion ea men is easible
because o he he mal s abili y o he subs a e. Fo example, his is he case o oph halmic
and o he op ical applica ions based on polyme ic lenses. In his ega d, i is pa icula ly
con enien ha he colo ed ca ion o be inco po a ed is ully compa ible wi h SiO2 o o he
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anspa en oxides used as s anda d low index ma e ials in an i e lec i e o dielec ic mi o
coa ings o as an isc a ching coa ings.
In his pape , we epo on semi- anspa en coa ings based on mixed Cu-Si oxide hin
ilms p epa ed by eac i e magne on spu e ing, whe e coppe is he colo ing ca ion and
silicon, in 4 + oxida ion s a e, de ines he hos anspa en ma ix. The inco po a ion o coppe
in silica e glasses is a well known p ocedu e o colo hem. Fo example, he cha ac e is ic
uby colo is achie ed by inco po a ion o me allic Cu colloidal pa icles in anspa en silica
o sodium silica e ma ix [9,10]. I is also well known ha glasses wi h eddish colo can be
ob ained by he inco po a ion o Cu2+ ions and CuO clus e s in hese anspa en ma ices
[3,4,9,12]. Thus, a c ucial impo an poin o he cha ac e iza ion o he p epa ed Cu-Si oxide
hin ilms has been o dis inguish whe he he cons i uen oxides o m a andomly dis ibu ed
mixed phase (solid solu ion o he oxide phases) o seg ega e in o sepa a ed phases, and o
which ex en he local elec onic s uc u e a ound he wo ca ions is dependen on mixing.
Ano he impo an issue om a echnological poin o iew is he in si u con ol o he
deposi ion p ocess. In his espec , we ha e cha ac e ized he plasma discha ge used in he
deposi ion p ocess by Op ical Emission Spec oscopy (OES). Special e o has been de o ed
o co ela e he cha ac e is ics o he p ocess plasma wi h he inal p ope ies o he ilms.
Finally, in o ma ion abou he local elec onic s uc u e o he ilms has been also gained by
means o X- ay Pho oelec on Spec oscopy (XPS) and Fou ie T ans o m In a ed (FTIR)
spec oscopies.
2. Expe imen al
2.1 Sample p epa a ion
Mixed Cu-Si oxide hin ilms we e p epa ed by eac i e magne on spu e ing. Silicon a ge s
o 2 inches diame e we e used as he sou ce o silicon. Coppe was supplied by Cu s ips
(0.25 mm hickness, 1.4 mm wide om Good ellow) w apped o he Si a ge along i s
diame e . Samples we e p epa ed wi h 1, 2, 3 and 5 s ips. As e idenced by he e osion ack
o med in he a ge , spu e ing mainly occu ed in a ci cum e ence o ~20 mm o adius (i.e.,
~125 mm ci cum e ence leng h). The a ea a io o he spu e ed coppe s ips was abou 3, 6,
9, and 15% o he o al a ge a ea o he expe imen al si ua ions used o he p epa a ion o
he ilms. A indus ial scale his app oach could be subs i u ed by one in which a ge s o Si-
Cu alloys o mix u es a e used o assu e au oma ic ep oducibili y o esul s. Samples wi h
di e en op ical pe o mances we e also p epa ed by a ying he O2/A a io in he p ocess
gas mix u e. The O2/A gas mix u e was se wi h mass low con olle s. The oxygen mass
low ΦO2 was a ied be ween 4 o 25 sccm, while he a gon mass low ΦA was a ied
be ween 40 and 10 sccm. Thus, he mass low a io ΦO2/ΦA was a ied be ween 0.1 and 2.5.
The base p essu e in he deposi ion chambe was 2x10−6 mba and he wo king p essu e was
se cons an o 5x10−3 mba . The magne on head (GENCOA, 5 cm diame e a ge s) was
powe ed wi h a pulsed DC sou ce (MPS15 om Milko Angelo Consul ing L d). A pulse
equency o 80 kHz and a du y cycle o 40% we e used, wi h applied powe s anging
be ween 100 and 300 W. The sample holde was pola ized wi h −100 V. The a ge -sample
dis ance was also a ied be ween 50 o 100 mm. In hese condi ions, he sample empe a u e
du ing ilm g ow h was always below 373 K.
The eac i e plasmas used o deposi ion o he hin ilms we e cha ac e ized by Op ical
Emission Spec oscopy (OES). The emission spec um was analyzed using a 0.5 m CVI
Digik om DK480 monoch oma o (CVI Lase Co po a ion, Albuque que, NM), wi h wo
1200 g oo es/mm g a ings, 200/600 blaze. Wa eleng h selec i e il e s may be used o
elimina e he unwan ed adia ion. In he expe imen s, he spec al esolu ion was o 0.2 nm,
and spec al sensi i i y anging om 200 o 900 nm (Hamama su R928 pho o ube). The ligh
was collec ed by an op ical ibe which was ixed o he monoch oma o and posi ioned nea
he middle plane be ween he anode and he ca hode using a acuum eed h ough wi h a
collima ing lens in he plasma chambe .
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2.2 Thin ilm cha ac e iza ion
Thin ilm mic os uc u e was analyzed wi h a Hi achi S4800 ield emission scanning elec on
mic oscopy (SEM). C oss sec ional and plana iews o hin ilms p epa ed on Si(100) wa e s
we e aken o cha ac e ize he mic os uc u e and o assess he ilm hicknesses.
Elemen al dep h p o iling was pe o med by means o Ru he o d Backsca e ing
Spec ome y (RBS) a he 3 MeV andem ion accele a o o he Cen o Nacional de
Acele ado es o Se ille. The RBS spec a we e analyzed wi h he SRIM so wa e [13].
Chemical cha ac e iza ion by X- ay Pho oelec on Spec oscopy (XPS) was ca ied ou
wi h a PHOIBOS 5MCD elec on analyze using unmonoc oma ised Al-Kα adia ion. P io o
he XPS cha ac e iza ion a mild O2+ (1 keV, sample cu en 1 μA /cm2, 20 min) spu e ing was
pe o med o all he samples o emo e he ad en i ious ca bon con amina ion.
Fou ie T ans o m In a ed spec oscopy (FT-IR) in ansmission mode was pe o med in
a Nicole 510 appa a us o hin ilms p epa ed on polished undoped Si(100) wa e s o
iden i y he ype o bonding and local s uc u al a angemen a ound each me al ca ion.
Op ical cha ac e iza ion o he ilms was pe o med by ansmission and e lec ion UV-
VIS in a Pe kin-Elme Lambda 12 spec ome e . Re ac i e index and ex inc ion coe icien
we e ob ained by leas squa ed i o he simula ion o he ansmi ed and e lec ed spec a.
Colo coo dina es we e e alua ed acco ding o s anda d heo y [14].
3. Resul s
3.1 Analysis o he deposi ion p ocess
OES analysis o he magne on plasma discha ge has been ca ied ou in si u, du ing hin ilm
g ow h, as a unc ion o p ocess pa ame e s. As a gene al beha io , all emi ed lines inc ease
in in ensi y when he magne on powe is inc eased. Mo e in e es ing is he pe o mance o a
ixed powe . Figu e 1 shows a se ies o OES spec a, eco ded in he 315-425 nm ange, using
a se ies o s anda d condi ions ( ixed magne on powe o 100 W, o al p essu e o 5x10−3
mba , a ge -sample dis ance o 10 cm, and 3 Cu s ips in he a ge and se e al Φ
O2/ΦA
a ios) du ing he deposi ion p ocesses. The s onges lines in hese spec a can be easily
asc ibed o Cu-I (I324, I327) and A -I (I416, I420) emissions [15]. We obse e ha hese emission
lines inc ease in in ensi y as he amoun o A in he plasma discha ge inc eases ( o ixed
powe and p essu e). The inse in Fig. 1 shows he in ensi y a io be ween hese Cu and A
lines. When ΦO2/ΦA ≥ 1 he a io be ween he Cu and A emissions ICu/IA (ICu = I324 + I327; IA
= I416 + I420) emains cons an . Howe e , i inc eases up o a ac o 2 o ΦO2/ΦA = 0.1.
Fig. 1. OES spec a co esponding o se e al ΦO2/ΦA a ios o he p ocess plasma discha ge, as
indica ed. Bands a e assigned o di e en species acco ding o [15]. Inse : In ensi y a ios o he
s onges Cu (I324 + I327) and A (I416 + I420) emission lines in he plasma discha ge as a unc ion
o he gas low a io Φ
O2/ΦA co esponding o a Si a ge wi h 3 Cu s ips, 100 W applied
powe and 5x10−3 mba o al p essu e in he eac ion chambe .
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Rega ding he deposi ion a e d , i is ound ha i diminishes when he sample- a ge
dis ance inc eases (5-10 cm ange), and inc eases wi h he powe supplied o he magne on
(100-300 W) and numbe o Cu s ips in he a ge . Fo example, o 100 W powe , a sample
a ge dis ance o 10 cm, and ΦO2/ΦA = 1.0, d inc eases om 3.2 nm/min o no Cu s ip
(deposi ion o pu e SiO2) o 5.2 nm/min o 5 s ips. I also a ies wi h he mass low a io
ΦO2/ΦA used du ing he deposi ion p ocess. Thus, o 100 W, 10 cm sample- a ge dis ance
and 3 Cu s ips, i inc eases om 3.8 nm/min o 9.8 nm/min when ΦO2/ΦA dec eases om 2.5
o 0.1. Table 1 collec s a su ey o p epa a ion condi ions and he co esponding deposi ion
a es.
3.2 Elemen al composi ion and dep h analysis
The in-dep h composi ion o he ilms was s udied by RBS. Figu e 2 shows ypical RBS in-
dep h composi ion spec a and hei i ing wi h he SRIM so wa e. The analysis
demons a es ha , in all cases, coppe dis ibu es homogeneously in dep h and ha he coppe
con en a ies depending on he deposi ion condi ions. Besides, no signi ican su ace
seg ega ion o any o he wo cons i uen ca ion is obse ed. Table 1 summa izes he ela i e
s oichiome y xCu (xCu = [Cu]/([Si] + [Cu]), ob ained o se e al p epa a ion condi ions. The
epo ed alues show ha he Cu con en in he ilms is clea ly dependen on he numbe o
Cu s ips w apped o he Si a ge , a ying be ween 0.16, 0.39, and 0.68 when using 1, 3 and 5
Cu s ips w apped o he Si ca hode, espec i ely. On he o he hand, xCu is no signi ican ly
a ec ed by ΦO2/ΦA .
Fig. 2. Expe imen al and i ed RBS spec a o wo selec ed mixed Cu-Si oxide hin ilms. The
spec a demons a e a homogenous in-dep h dis ibu ion o Cu and Si a oms.
The su ace composi ion o he samples was also analyzed by s anda d XPS. Gene al XPS
spec a showed ha all he ilms p epa ed we e composed o O, Si and Cu and e y low
amoun o C a oms (below 2 a omic pe cen ), p obably due o ad en i ious ca bon. Rega ding
he ela i e xCu alues de ined abo e, bo h XPS and RBS echniques ag eed in he
quan i ica ion wi hin 5 a omic %, hus con i ming ha no su ace seg ega ion o any o he
cons i uen s was p esen .
3.3 Mic os uc u e and bonding s uc u e o he ilms
Figu e 3 shows ypical SEM c oss sec ion images ob ained o he Si-Cu oxide ilms. They
appea la and ea u eless, wi hou any de ined g ain s uc u e. The s uc u e o he ilms was
also assessed by means o s anda d B agg-B en ano X- ay di ac ion analysis. No di ac ion
e lec ions we e de ec ed, con i ming he amo phous cha ac e o he s uc u e o he ilms.
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Fig. 3. SEM c oss sec ion mic og aph o a ypical Cu-Si oxide hin ilm.
In o ma ion abou he bonding en i onmen a ound Si and Cu a oms was ob ained by FT-IR
analysis. Figu e 4 shows a se ies o FT-IR spec a o selec ed samples. We obse e ha he
s e ching mode co esponding o Si-O-Si ib a ion, ha appea s a abou 1065 cm−1 o pu e
SiO2 ilms, shi s o lowe wa enumbe s ( o ~1055 cm−1) as he amoun o Cu in he ilm
inc eases. A he same ime a new band a ~925 cm−1 de elops in he spec a. This la e band
is a clea indica ion o Si-O-Cu bond o ma ion [16]. Fo ilms wi h 50% Cu he Si-O-Si band
has nea ly disappea ed, indica ing ha he e is no seg ega ion o a pu e SiO2 phase in he
ilms. No e also ha a b oad band a abou 450-650 cm−1 de elops when he amoun o Cu in
he ilms inc eases. Howe e , he ypical bands o Cu-O-Cu s e ching modes in ei he Cu2O
(a 615 cm−1) o CuO (480 and 529 cm−1) a e no obse ed in he spec a [17,18]. This
con i ms he absence o any signi ican phase seg ega ion o hese oxides, and he e o e ha
he ilms can be desc ibed as a solid solu ion o silicon and coppe oxides.
Fig. 4. FT-IR spec a o a se ies o Cu-Si oxide hin ilms wi h inc easing numbe o Cu s ips
in he Si ca hode and p epa ed wi h 3 s ips and inc easing alues o ΦO2/ΦA o he p ocess
gas.
3.4 Chemical s a e analysis and local bonding s uc u e
Figu e 5 shows a se ies o Cu 2p spec a ob ained o se e al Cu-Si mixed oxide samples. The
e olu ion in he shape o he spec a can be a ionalized by a p og essi e change in he
ela i e con en o coppe a oms wi h ei he Cu+ o Cu2+ oxida ion s a es [19,20]. We obse e
ha i a ies om a si ua ion wi h mos ly Cu2+ o ilms p epa ed wi h one coppe s ip and
ΦO2/ΦA = 1.0 o pu e Cu+ o he ilms p epa ed wi h h ee coppe s ips and ΦO2/ΦA = 0.1
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(i.e., he minimum amoun o O2 in he eac i e gas ha wa an ies ull oxida ion o silicon o
Si4+). The pa i ion be ween hese wo oxida ion s a es can be deduced by linea combina ion
o he spec a o co esponding o pu e Cu2+ and Cu+ s a es. The [Cu+]/([Cu+] + [Cu2+]) a ios
ob ained in his way a e epo ed in Table 1 o he di e en p epa a ion condi ions. In gene al
we ob ain ha , o a ixed Cu con en in he Cu-Si a ge , he amoun o coppe a oms in he
Cu + oxida ion s a e which a e inco po a ed in he Cu-Si mixed oxide hin ilm inc eases o
lowe ΦO2/ΦA a ios. Howe e , p ecise quan i ica ion o he ilm chemis y based only on his
echnique has o be aken wi h ca e, since we ha e obse ed ha he su ace cleaning
p ocedu e (mild O2+ spu e ing) ends o educe he Cu2+ species o Cu+ a he sample su ace.
Table 1. Su ey o Expe imen al Condi ions and P ope ies Ob ained o Mixed Si-Cu
Oxides P epa ed by Reac i e Magne on Spu e ing
# Cu
s ips
Φ
O2
/Φ
A
(sccm)
d
(nm/min)
[Cu]/
([Cu] + [Si])
[Cu+]/
([Cu
+
] + [Cu
2+
])
n550 k550
0
10/10
13
0
-
1.46
<0.005
1
10/10
18
0.16
0
1.64
0.020
2
10/10
24
0.27
0.20
1.76
0.030
3
10/10
27
0.39
0.35
1.83
0.062
5
10/10
35
0.68
0.48
2.12
0.15
3
4/40
7
0.38
1
1.81
0.063
3
25/10
25
0.40
0.36
1.82
0.058
Fu he in o ma ion o he chemical na u e and local elec onic s uc u e a ound he wo
cons i uen ca ions o he mixed oxide hin ilms can be gained h ough he Si and Cu Auge
pa ame e s [21–23]. The Auge pa ame e is a local p obe ha can be co ela ed o: i) changes
in he chemical na u e (i.e., oxida ion s a e) o he emi e a om and ii) a ia ion in he ex a-
a omic elaxa ion ene gy when, o a ixed oxida ion s a e, he local en i onmen o a ca ion
changes.
Auge pa ame e s o Si αSi and Cu αCu ha e been e alua ed in he usual way [21,22]
αSi = BE(Si 2p) + KE(Si KLL)
αCu = BE(Cu 2p3/2) + KE(Cu L3VV)
whe e BE(Si 2p) and BE(Cu 2p3/2) a e he binding ene gies o he Si 2p and Cu 2p3/2 signals
and KE(Si KLL) and KE(Cu L3VV) a e he kine ic ene gies o he Si KLL and Cu L3VV
Auge emissions, espec i ely.
Figu e 6 (le ) shows ha αSi a ies linea ly be ween 1712.2 o 1712.6 eV as he Cu
pe cen age inc eases in he Si-Cu-O ma ix. As a e e ence, he αSi o pu e SiO2 samples
(p epa ed wi hou Cu) appea s a 1711.4 eV. No e ha o all s udied samples, silicon a oms
a e always p esen as Si4+ species. The e o e, he inc ease o αSi as he amoun o Cu in he
ilms inc eases indica es ha he pho oholes c ea ed a he Si si es elax easie (mo e ene gy is
eleased by pola iza ion o he nea by ma ix) as he amoun o coppe in he ilms inc eases.
The e o e, he p obabili y ha Cu is he second neighbo h ough he de elopmen o Si-O-Cu
bond s uc u es inc eases wi h inc easing Cu con en in he ilms. This esul poin s again o
lack o phase seg ega ion, yielding as a esul a con inuous e olu ion in he Auge pa ame e
o Si4+ species om he pu e SiO2 ma ix o Si dilu ed in a mos ly CuOx ma ix o he
samples wi h highes xCu alues.
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Fig. 5. Cu 2p pho oemission spec a o Cu-Si oxide hin ilms p epa ed wi h di e en
expe imen al p ocess pa ame e s.
The opposi e beha io is obse ed o αCu. The in e p e a ion o he e olu ion o αCu wi h
he ilms composi ion is no so s aigh o wa d, as bo h he oxida ion s a e (Cu+, Cu2+) and he
pola iza ion e ec s a y simul aneously. Figu e 6 ( igh ) shows he e olu ion o αCu wi h he
ela i e amoun o Cu+ species in he samples, as de e mined by XPS. Since he epo ed
Auge pa ame e o Cu+ species in Cu2O is 1849.2 eV and Cu2+ species in CuO is 1851.6 eV
(see Fig. 6 ( igh )), i is likely ha changes in αCu a e a consequence o bo h he p esence o
di e en oxida ion s a es in he ilms and he in luence o he di e en pola iza ion o he
en i onmen [20].
Fig. 6. Silicon Auge pa ame e αSi (le ) and Cu Auge pa ame e s αCu ( igh ) as a unc ion o
he composi ion o he Cu-Si oxide hin ilms.
3.5 Op ical p ope ies
Figu e 7 shows ansmission UV-Vis spec a o se e al ilms p epa ed on glass wi h 100 wa s
as magne on powe . I shows a se ies o spec a o samples p epa ed wi h a ixed a io
ΦO2/ΦA = 1.0 and a ying he numbe o Cu s ips w apped o he a ge , as well as spec a o
samples p epa ed wi h se e al Cu s ips and di e en mass low a io Φ
O2/ΦA . The
hicknesses o hese samples a e abou 0.2 mic ons. I is appa en ha he o e all abso p ion o
he ilms inc eases wi h he numbe o Cu s ips in he ca hode and o lowe ΦO2/ΦA alues,
i.e., wi h he pe cen age o Cu in he ilms (see Table 1). I is obse ed a cons an weak
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abso p ion abo e 0.6 mic ons. This abso p ion inc eases o sho e wa eleng hs. The
h eshold a abou 0.3 mic ons co esponds o he abso p ion o he glass used in his s udy.
Fig. 7. UV-Vis ansmission spec a o a se ies o Cu-Si oxide hin ilms p epa ed unde se e al
p epa a ion condi ions (see legend).
The e ac i e index and ex inc ion coe icien o Cu-Si oxide ma e ials was e alua ed by
simula ion o ansmission and e lec ion UV-Vis spec a o he ilms, conside ing a
homogeneous single laye and a Fo ohui-Bloome model o he complex e ac i e index [24].
The esul s o his analysis o he se ies o samples shown in Fig. 7 is epo ed in Fig. 8.
Re ac i e index o pu e SiO2 (p epa ed wi hou Cu s ips and ΦO2/ΦA = 1.0) is also included
o comple eness. Table 1 collec s he e ac i e index alues a 550 nm (n550) o hese ilms.
I is ound ha he e ac i e index o he Cu-Si oxide ilms inc eases wi h he Cu con en in
he ilms. Thus, o ΦO2/ΦA = 1.0 and xCu = 0.16, 0.27, 0.37, and 0.68 we ob ain ha n550 =
1.64, 1.76, 1.83, and 2.12, espec i ely. Besides, o a ixed Cu/Si s oichiome y, i is ound
ha lowe ing he ΦO2/ΦA a io, he e ac i e index u he inc eases. Acco ding o he
p e ious chemical quan i ica ion, his inc ease o e ac i e index is co ela ed wi h he
inc ease o Cu+ species in he ilms.
Fig. 8. Re ac i e index (le ) and ex inc ion coe icien ( igh ) o a se ies o Cu-Si oxide hin
ilms o a ΦO2/ΦA a io o 1.0 and di e en numbe o s ips in he ca hode and o 3 s ipes
and di e en alues o he ΦO2/ΦA a io.
A his poin i is con enien o co ela e he ob ained esul s wi h da a epo ed in he
li e a u e o single SiO2, Cu2O o CuO oxides. I is well known ha he e ac i e index o
SiO2 is abou 1.45. Re ac i e indices o cup ous oxide hin ilms [6,17,18,25–27], cup ic
oxide [17,18,27] and mix u es o hem [28] ha e been epo ed in he li e a u e. F om he
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