In luence o hickness and coa ings mo phology in he an imic obial pe o mance
o zinc oxide coa ings.
P. Ca alho1, P. Sampaio2, J. O. Ca nei o1, C.Vaz2, J. P. Espinós3, V. Teixei a1
1 Depa men o Physics, Uni e si y o Minho, Campus de Azu ém, 4800-058 Guima aes, Po ugal
2 CBMA, Uni e si y o Minho, Campus de Gual a , 4700 B aga, Po ugal
3 Ins i u o de Ciencia de Ma e iales de Se illa, CSIC-Uni e si y o Se illa, A da. Amé ico Vespucio 49,
41092 Se illa, Spain
Abs ac
In his esea ch wo k, he p oduc ion o undoped and sil e (Ag) doped zinc oxide (ZnO) hin
ilms o ood packaging applica ions was de eloped. The main goal was o de e mine he
in luence o coa ings mo phology and hickness on he an imic obial pe o mance o he
p oduced samples. The ZnO based hin ilms we e deposi ed on PET (Polye hylene
e eph hala e) by means o DC eac i e magne on spu e ing. The hin ilms we e cha ac e ized
by op ical spec oscopy, X-Ray Di ac ion (XRD), X- ay pho oelec on spec oscopy (XPS)
and Scanning Elec on Mic oscopy (SEM). The an imic obial pe o mance o he undoped and
Ag-doped ZnO hin ilms was also e alua ed. The esul s a ained ha e shown ha all he
deposi ed zinc oxide and Ag-doped ZnO coa ings p esen columna mo phology wi h V-shaped
columns. The inc ease o ZnO coa ings hickness un il 200nm inc eases he ac i e su ace a ea
o he columns. The hinne samples (50 and 100 nm) p esen a less p onounced an ibac e ial
ac i i y han he hickes ones (200-600nm). Rega ding Ag-doped ZnO hin ilms, i was
e i ied ha inc easing he sil e con en dec eases he g ow h a e o E. coli. and dec eases he
amoun o bac e ia cells p esen a he end o he expe imen .
Keywo ds: ZnO hin ilms, an imic obial ac i i y, ood packaging
1. In oduc ion
Mo e na u al, sa e and highe quali y consumable p oduc s ha e been seen as a
ma ke demand o huge impo ance in wha conce ns he Food Packaging Indus y.
Foodbo ne illnesses and dea h is ising wo ldwide, pa icula ly in de eloped
coun ies[
1
]. Indeed, da a om he Foodbo ne Diseases Ac i e Su eillance Ne wo k
(Food Ne ) s a es ha compa ing 2007 wi h 2004-2006, he es ima ed occu ence o
in ec ions caused by Campylobac e , Lis e ia, Salmonella, Shigella, Vib io, and
Ye sinia did no diminished significan ly, and abo e all, he incidence o
C yp ospo idium in ec ions e en inc eased by 44% [
2
]. A he same ime, oodbo ne
illness-ou b eaks c ea e emendous social and economic bu dens b inging he ea o
he e-eme gence o in ec ions diseases. Fu he mo e, he de elopmen o an ibio ic
esis ance con inues o d aw public a en ion o ood sa e y [
3
,
4
]. The combina ion o he
sup a-men ioned easons wi h he cu en awa eness o en i onmen al conse a ion and
p o ec ion has empowe ed he de elopmen o edible coa ings and films om
biodeg adable ma e ials o main ain he quali y o bo h esh and p ocessed ood [
5
].
Sil e -based hin ilms [
6
,
7
,
8
] and zinc oxide nanopa icles [
9
,
10
,
11
,
12
,
13
,
14
,
15
] ha e
eme ged as p omising candida es o ac i e ood packaging sys ems, pa icula ly due o
hei an ibac e ial ac i i y. Howe e , due o he lack o knowledge ega ding he
in e ac ions o nano-sized ma e ials a he molecula and physiological le els and hei
po en ial e ec s on human body, a majo conce n ela ed o sa e y o nanopa icles o
consume ’s heal h is aising [
16
,
17
,
18
,
19
]. Ti anium dioxide (TiO2) has been used as a sel -
cleaning and sel -s e ilizing ma e ial o coa di e en ools, including sani a y wa e,
ood ablewa e and cooking wa e [
20
,
21
]. The an imic obial e ec s o TiO2 a e ac i a ed
by i s pho oca aly ic beha iou , which is o ally dependen on ul a iole and/o isible
ligh i adia ion. Howe e , o ood packaging indus y his is a huge d awback since
he an imic obial ac i i y will only be e ec i e in i adia ed packages. An al e na i e o
o e come his limi a ion could be he use o Zinc oxide (ZnO). ZnO p esen s
an imic obial ac i i y, can ac as a pe mea ion ba ie coa ing [
22
] and is Gene ally
Recognized as Sa e ma e ial (GRAS) by he U.S. Food and D ug Adminis a ion
(21CFR182.8991). In his sense, he de elopmen o zinc oxide hin ilms can be
conside ed o g ea added alue o ood packaging indus y. The e a e a limi ed amoun
o scien i ic publica ions a ailable desc ibing he in e ac ion be ween ZnO nanopa icles
and bac e ial cells and as a he au ho s knowledge he e is no epo ed wo k
conce ning he an imic obial ac i i y o zinc oxide coa ings deposi ed by means o
eac i e magne on spu e ing. In his sense, he main goal o his esea ch wo k is o
e alua e he an imic obial ac i i y o zinc oxide hin ilms and s udy he in luence o
coa ing hickness, mo phology and sil e con en in he an imic obial ac i i y. I s
applicabili y o ood packaging sys ems will also be discussed.
To he au ho ’s knowledge, his wo k is he i s o s udy he in luence o hickness
and coa ings mo phology on he an imic obial ac i i y, con ibu ing o he knowledge o
impo an physical a iable in he hin ilms p oduc ion.
2. Ma e ials and Me hods
2.1. Thin ilms p oduc ion and cha ac e iza ion
Zinc oxide hin ilms we e deposi ed on Polye hylene Te eph hala e (PET)
subs a es om Good elow and silicon (Si) subs a es om Silllicon Ma e ials by
eac i e DC magne on spu e ing (Ad anced Ene gy Pinnacle Plus, 5K, DC Pulsed).
The ilms deposi ed on PET we e used o he e alua ion o he op ical p ope ies and
he an imic obial ac i i y and he ones deposi ed on Si we e used o s uc u al,
mo phological and composi ional cha ac e iza ion. I was used a ci cula zinc a ge
(Φ=75mm) wi h a pu i y o 99,9% and a hickness o 4mm acqui ed om Good ellow
Be o e deposi ion he spu e ing chambe was pumped down o 10-3 Pa. A gas
a mosphe e composed by a gon (A , wo king gas) and oxygen (O2, eac i e gas) was
used in he deposi ion p ocesses. The A and O2 lows we e kep cons an a 70 sccm
(s anda d cubic cen ime e pe minu e) and 18 sccm, espec i ely. Each deposi ion was
ca ied ou wi h a wo king p essu e o 0.6 Pa, a cu en o 0.35 A and a a ge /subs a e
dis ance o 80 mm. P io o each deposi ion he zinc a ge was p e-spu e ed du ing 5
minu es. All o he deposi ion pa ame e s we e kep cons an and he deposi ions we e
pe o med a oom empe a u e (40 ºC measu ed inside he chambe ).
X- ay di ac ion (Philips PW 1710 X- ay di ac ome e ) analysis was used o
in es iga e he c ys allog aphic s uc u e o ZnO hin ilms. The hickness and
mo phology o ZnO hin ilms we e ob ained by he obse a ion o he c oss sec ion o
he ac u ed hin ilms by SEM (NanoSEM-FEINOVA 200). The op ical ansmi ance
was measu ed by isible spec oscopy (Shimadzu UV-310PC scanning
spec opho ome e ). The chemical cha ac e iza ion was by using a XPS spec ome e
(12 kV, 20 mA) om VG (ESCALAB 210). An unmonoc oma ized Mg K (1253.6
eV) sou ce was used du ing he measu emen s. Fo all he zinc oxide coa ings, he
binding ene gies o he XPS spec a we e calib a ed by using o Zn 2p3/2 a 1022.2 eV
and he spec a we e acqui ed a oom empe a u e. All he coa ings we e spu e ing
cleaned wi h A + un il a s a iona y composi ion was achie ed. A his s age, no ca bon
esul ing om supe icial con amina ion was obse ed.
2.2. Thin ilms an imic obial ac i i y
In his esea ch wo k, he Esche ichia coli was he bac e ia species chosen and i
was ob ained om he Cen e o Molecula and En i onmen al Biology (CBMA),
Depa men o Biology, Uni e si y o Minho. A p e-cul u e was p epa ed o each
indi idual ba ch expe imen . One colony o E. coli s ain HB101 was picked and loop
inocula ed in o a 125-ml E lenmeye flask, con aining 20 ml o Lu ia Be ani (LB) b o h
(10 g/L yp one, 10 g/L NaCl, and 5 g/L yeas ex ac ). This p e-cul u e was incuba ed
a 37°C, o 12 o 15h. On he day a e , cells we e ans e ed in o di e en 250-ml
E lenmeye flasks con aining 50 ml o LB b o h medium a a s a ing op ical densi y
(OD) o 0.1 measu ed a a wa eleng h o 640 nm. A coa ed PET ci cula sample
(diame e o 6 cm), p e iously s e ilized wi h 70% e hanol o 1 hou and insed in
s e ile wa e , was deposi ed on he bo om o he lask. Flasks we e hen shaken a 80
pm in a empe a u e-con olled incuba o a 37 °C, and he OD was moni o ed e e y
hou . OD measu emen s we e made using a Spec onic 20 ins umen a 640 nm and he
backg ound ( u bidi y due o g ow h medium) was elimina ed by aking blank eadings.
The specific g ow h a e (μ) was calcula ed om he exponen ial phase, acco ding o he
ollowing equa ion:











1
2
12
ln
1
OD
OD
μ
(1)
whe e OD1 and OD2 a e he op ical densi ies co esponding o ime ins an s 1 and 2,
espec i ely. The gene a ion ime ( g) can be calcula ed acco ding o he equa ion:
μ
g
2ln

(2)

3. Resul s and discussion
3.1. Thin ilms s uc u e and mo phology
The p oduced ZnO hin ilms in his esea ch wo k a e highly anspa en ,
p esen ing a ansmi ance o abou 80% in he isible egion o he elec omagne ic
spec um. The emainde 20%, is los by e lec ion a he ai /ZnO in e ace, by
dispe sion and by abso p ion o ligh in he subs a e.
In o de o s udy he in luence o he coa ing hickness and mo phology in i s
an imic obial ac i i y, he hickness was con olled by changing he deposi ion ime.
Wi h his me hodology i was obse ed ha he ilm hicknesses anged om 50 o 600
nm. X- ay di ac ion analyses we e pe o med in ep esen a i e samples and he
measu emen s we e done be ween 20º and 70º () o all hin ilms. Fig. 1 shows he
undoped zinc oxide X-Ray Di ac ion pa e ns o he hin ilms ha ing 50, 200 and 600
nm hicknesses.
Fig. 1 XRD pa e ns o ZnO hin ilms wi h 50, 200 and 600 nm hickness, deposi ed in
PET subs a e.
In XRD pa e ns i is obse ed he p esence o he (002) di ac ion peak o he ZnO
wu zi e s uc u e (JPCDS36-1451[
23
]) in all he samples, indica ing a p e e en ial
o ien a ion o he c-axis pe pendicula o he subs a e, as p e iously epo ed by o he s
au ho s[
24
,
25
,
26
]. Some au ho s co ela e he p e e en ial o ien a ion wi h he
minimiza ion o in e nal s ess and su ace ene gy [
27
,
28
,
29
] and o he s [
30
] epo ed ha
c-o ien a ion maybe esul om he highes a omic densi y ound along (002) plane. In
Figu e 1 i is also possible o obse e ha , as expec ed, he inc ease o he coa ings
hickness induces an inc ease o di ac ion peak in ensi y. The dec ease o ull wid h a
hal maximum also sugges s an inc ease o g ain size wi h he hickness.
Fig. 2 shows he SEM mic og aphs o he undoped ZnO samples c oss-sec ions;
he g ains ex end om he subs a e o he op o he ilm. The ypical mo phology can
be iden i ied as a Zone 1 ilm o he modi ied s uc u e zone model [
31
] wi h ypically
low compac ness.
Fig. 2. SEM mic og aphs p esen ing he hin ilms c oss-sec ions wi h di e en
hickness deposi ed in Si subs a e: a) 50nm; b)200nm; c) 300nm and d) 600nm.
The hinne coa ings, 50 and 100 nm (no showed he e) p esen a mo e compac
mo phology in compa ison wi h he hickes ones. I is possible o obse e ha he
inc ease o coa ings hickness induces he o ma ion o less compac coa ings, wi h well
de ine and sepa a ed columns (Fig. 2). F om his igu e i is can also be iden i ied an
inc ease o columns wid h wi h he inc ease o coa ings hickness. F om he p esen ed
a)
b)
c)
d)
esul s i is also possible o conclude ha a ace plane can be obse ed in he uppe
egion o he hickes coa ings (300-600 nm). The a ained esul s a e in ag eemen wi h
he ones epo ed by J. W. Shin e al. [
32
] ha deposi ed ZnO coa ings a oom
empe a u e on Si subs a es. These au ho s explained he o ma ion o ace planes as
being a consequence o he lowe di usion a e o he a oms on he ZnO su ace du ing
column’s g ow h he deposi ion a e.
To be e unde s and he mo phology o hese coa ings, op iew SEM
mic og aphs o ZnO samples wi h di e en hickness we e aken and a e shown in Fig.
3.
Fig. 3. Top- iew SEM mic og aphs o ZnO hin ilms wi h di e en hickness deposi ed
in Si subs a e: a) 50nm; b)200nm; c) 300nm and d) 600nm.
a)
b)
c)
d)
Fig. 7. XPS Zn2p (le ) and Ag3d ( igh ) spec a o sil e doped ZnO ilms and
undoped ZnO. All coa ings we e deposi ed on Si subs a e.
The Zn2p3/2 co e line, (calib a ed a 1022.2 eV[
60
] o binding ene gy) exhibi s a small
asymme y in he igh side, indica ing ha zinc could p esen mo e han one oxida ion
s a e. The XPS spec a o Ag3d3/2 peak (Fig. 7) shows binding ene gies in he ange
368.6-369.2eV o he h ee doped samples. The e olu ion o he binding ene gy o
Ag3d3/2 wi h he chemical s a e o sil e is anomalous, since i dec eases wi h he
oxida ion s a e o his elemen . The epo ed sil e compound wi h he highes binding
ene gy is AlAg2 (368.7 eV), and he one wi h he lowes is AgF2 (367.7 eV). Binding
ene gies o pu e Ag, Ag2O, and AgO bulk samples a e 368.22, 367.8, and 367.4 eV,
espec i ely[
61
,
62
,
63
,
64
,
65
,
66
,
67
,
68
]. I is e iden ha he peak Ag3d5/2 in Ag doped ZnO
samples a e loca ed a ene gies a abo e bulk me allic sil e (+1 eV) and e en abo e
ha o bulk AlAg2 (+0.5 eV). Un o una ely, since he su ace concen a ion o sil e in
doped ilms is e y low, i is no possible o de ec p ope ly in hese samples he
AgMVV Auge signals and, consequen ly, he alue o he modi ied Auge pa ame e

o sil e , which is so use ul o de e mine he chemical s a e o his elemen , canno be
ob ained.
We can imagine wo di e en hypo hesis ha could explain he high binding
ene gy alues ob ained o Ag3d3/2 peaks in ZnO(Ag) ilms. One, ha sil e is o ming
small me al clus e s s ongly in e ac ing wi h ZnO suppo , since i has been widely
discussed in he li e a u e ha he binding ene gy o small me allic pa icles is usually
shi ed o lowe binding ene gy [
69
]. Fo ins ance, a shi o 0.4 eV was obse ed o
sil e deposi ed on g aphi e[
70
], shi s o +0.6 eV [
71
] and +0.9 eV [
72
] ha e been
epo ed o sil e on Al2O3, while shi s o +0.6 and +1.2 eV ha e been epo ed o
sil e deposi ed on TiO2 a 300K and 100K, espec i ely [
73
]. These shi s ha e been
a ibu ed o bo h ini ial and inal s a e ac o s a ec ing he pho oemission p ocess.
Ini ial s a e e ec s a e hose a ec ing he ene gy o he ini ial s a e, as o ins ance, he
me al-subs a e in e ac ion, he mean coo dina ion o he a oms in he clus e s and hei
geome y [
74
,
75
]. Final s a e e ec s a e hose a ec ing he elaxa ion o sc eening o he
pho ohole, as he Coulombic po en ial o he dielec ic cons an o he subs a es [
76
,
77
].
The binding ene gy shi obse ed in ou samples, up o +1.0 eV, would be in he uppe
limi o he ange ound o small sil e clus e s on Al2O3 and TiO2. To e i y he
alidi y o his hypo hesis, we ha e ca ied ou an expe imen in ou labo a o y whe e
inc easing amoun s o pu e sil e a e condensed unde ul a high acuum on ZnO ilms,
om a ac ion o a monolaye o many monolaye s. No e ha , ega dless o he g ow h
mechanism ollowed by sil e deposi ing on ZnO (laye by laye o h ee dimensional
island g ow h), he mean pa icle size will inc eases when he deposi ed amoun
inc eases. The esul o his expe imen is illus a ed in Fig. 8, whe e he e olu ion o
Ag3d spec um is displayed as a unc ion o he nominal hickness o deposi ed sil e ,
and in Fig. 9, whe e he e olu ion o he Ag3d5/2 peak binding ene gy is plo e sus he
same a iable. As can be seen, when deposi ed on ZnO, he binding ene gy o e y
small sil e agg ega es only shi up o +0.6 eV in espec o ha one o bulk sil e ,
which is qui e lowe han he expe imen al binding ene gy alue ound o Ag doped
ZnO ilms.
380 376 372 368 364 360
Ag3d
In ensi y (a.u.)
Binding Ene gy (eV)
136.0
60.4
30.5
15.2
6.7
4.3
3.2
2.2
1.6
0.7
0.1
Ag/ZnO nominal hickness (A)
Fig. 8. E olu ion o Ag3d spec um o g owing amoun s o me al sil e deposi ed
unde UHV on ZnO. The nominal hickness o deposi ed sil e , assuming a laye o
laye g ow h mode, is exp essed in Angs oms.
020 40 60 80 100 120 140
368.2
368.4
368.6
368.8
369.0
369.2
Ag3d5/2 Binding Ene gy
Ag nominal hickness ()
Ag/ZnO
Fig. 9. E olu ion o he Ag3d5/2 binding ene gy o sil e o deposi s o sil e on ZnO
wi h g owing nominal hickness.
A second possible hypo hesis o explain he high binding ene gy ound o
sil e in Ag/ZnO, is ha me al Ag pa icles a e doped wi h me al Zn, gi ing ise o he
o ma ion o an in e me allic compound, whe e he binding ene gy o Ag3d3/2 signal
could be highe han ha o pu e sil e , as epo ed o AlAg2. Since he pe cen age o
sil e doping he ZnO ilms is e y low, he de ec ion o he Zn species linked o he
sil e a oms is ully hidden by hose Zn a oms loca ed in he ZnO phase. Mo eo e ,
me al Zn species canno be dis inguish om Zn+2 ca ions by XPS on he basis o he
main p ima y pho oelec on signals (Zn2p), because bo h chemical species gene a es
jus he e y same spec um. Fo una ely, he elucida ion o he chemical s a e o Zn can
be made e ec i ely by XPS by de e mining he alue o he modi ied Auge
pa ame e [
78
]. Fo ha pu pose, bo h ZnL3M45M45 and Zn2p3/2 pho oemission signals
mus be measu ed, since he alue o he Zn modi ied Auge pa ame e , ´, is equal o
he sum o he binding ene gy o he Zn2p3/2 pho oelec on peak and he kine ic ene gy
o he ZnL3M45M45 Auge line.
In o de o u he s udy his second hypo hesis, one ilm o Zn con aining a
small amoun o Ag, was deposi ed by magne on spu e ing om me allic Zn and Ag
a ge s, and analyzed by XPS. The objec i e was o ob ain a e e ence sample o Ag
doped wi h me allic Zn, and compa e i s Ag3d3/2 binding ene gy wi h he one o he
case o Ag doped ZnO ilms.
In spi e o being p epa ed om pu e Zn and Ag a ge s, he ilm o Ag doped Zn,
when examined by XPS, only showed di alen zinc a he su ace, cha ac e ized by a
modi ied Auge pa ame e o ~2010.0 eV, e y likely as a consequence o he co osion
o his me al du ing i s exposi ion o he a mosphe e o he labo a o y. Howe e , and as
expec ed, he spu e ing cleaning o i s su ace, by bomba dmen wi h A + ions,
g adually emo e he al e ed laye , and a s a iona y s a e is eached in i s composi ion
a e a ea men o 120 min, ea men long enough o emo e a ound ~12 nm. The
e olu ion o he su ace composi ion o his ilm by he ion e ching ea men is nea ly
no iceable by he dec ease in he O/Zn a omic a io and by he changes in he shape o
ZnL3M45M45 Auge line, whe e a new peak a 991.8 eV o kine ic ene gy, due o Zn(0),
ises wi h he spu e ing ea men . In Fig. 10, he spec al egion o ZnL3M45M45 signal
is shown o his sample a he s a iona y s a e, whe e he peaks o Zn(0) and Zn(+2)
a e labeled and he alues o he espec i e modi ied Auge pa ame e s calcula ed.
980 985 990 995 1000
a e 120minA +
´=2013.83eV
Zn0
991.65
In ensi y (a.u.)
Kine ic Ene gy (eV)
ZnL3M45M45
987.25
Zn+2
´=2009.43eV
Fig. 10- Pho oemission spec um o he ZnL3M45M45 Auge line o he Zn(Ag) sample
a e su ace cleaning by spu e ing wi h A + ions o 2.5 keV o 120 min.
As he mo phology o his coa ing is highly columna , e en a he s a iona y s a e he
collec ed XPS signal p esen s he con ibu ion o he co oded la e al su ace o he
columns.
Fig. 11Fig. 11 shows he Zn2p and Ag3d pho oemission signals o his sil e
doped zinc ilm a he o iginal s a e (su ace co oded) and a he s a iona y s a e a e
spu e ing. As can be seen, Zn2p3/2 peak appea s in bo h si ua ions a a ound 1022.20 eV
o binding ene gy, while Ag3d5/2 peak shi s wi h he spu e ing ea men om 368.64
o 369.47 eV. The in ensi ies o bo h Zn and Ag signals inc ease wi h his ea men , as
a esul o he emo al o su ace con aminan s and, e y likely, he p e e en ial
spu e ing o oxygen. Ob iously, he binding ene gy o he Ag3d5/2 peak, 369.47 eV, is
so high ha i canno be asc ibed o pu e me allic sil e , al hough consis ing o e y
small pa icles. Since i inc eases simul aneously wi h he de ec ion o me allic zinc, he
o ma ion o a Zn-Ag bond is he mos p obable explana ion o his high alue o
binding ene gy. In o he wo ds, while he p esence o e y small agg ega es o sil e

( i s hypo hesis) could only accoun o a binding ene gy shi o up o +0.6 eV, he
doping o hese pa icles wi h Zn (second hypo hesis) could explain by i sel he whole
expe imen al shi and e en u he .
1028 1024 1020 1016
o iginal
a e 120minA +
In ensi y (a.u.)
Binding Ene gy (eV)
Zn2p1022.20
a)
380 376 372 368 364 360
In ensi y (a.u.)
Binding Ene gy (eV)
o iginal
a e 120minA +
Ag3d5/2
369.5
b)
Fig. 11. XPS Zn2p (a)) and Ag3d (b)) spec a o sil e doped zinc ilm a he o iginal
s a e and a e 120 min o su ace e ching wi h A + ions o 2.5 keV .
Fig. 12 shows he op and c oss sec ion mic og aphs o he sil e doped ZnO
hin ilms.
Fig. 12. Top- iew and c oss sec ion SEM mic og aphs o sil e doped ZnO hin ilms;
a) and b) ZnO(Ag)-1 sample, c) and d) ZnO(Ag)-3 sample.
F om he p e ious igu e i is possible o obse e ha he p esence o sil e
induces a change in he ZnO coa ings mo phology in compa ison wi h Fig. 2b. Fo he
samples wi h e y low sil e con en , ZnO(Ag)-1 and 2 (no showed he e), he shape o
he columns change om ci cula pilla -like mo phology (see Fig. 2) o iangula
mo phology (see Fig. 12), main aining a V shape o m in he c oss sec ion iew. I is
impo an o no e ha hese samples do no show a c ys alline p e e en ial g ow h, in
con as wi h he undoped zinc oxide samples. The sample wi h he highes sil e
con en p esen s a columna mo phology wi h a ci cula shape, simila o he undoped
samples, bu wi h a much less dense mo phology, whe e he space be ween columns is
clea ed obse ed. Once mo e ime, he ci cula columna mo phology is ela ed o a
200 000x –ZnO(Ag)-1 200 000x –ZnO(Ag)-1
200 000x –ZnO(Ag)-3
200 000x –ZnO(Ag)-3
a)
b)
c)
d)
p e e en ial o ien a ion o he c-axis pe pendicula o he subs a e su ace (see Fig. 6).
This esul sugges s ha he di e en c ys alline g ow h ela ed wi h he p esence o
sil e could induce mo phology changes in he coa ings. L.N. Wang, e al. [
79
] epo ed
ha Ag doping could cause mo phological changes in he ZnO hin ilms. The au ho s
obse ed ha he p esence o sil e induces he o ma ion o a po ous mo phology.
The an ibac e ial ac i i ies o undoped and Ag-doped ZnO hin ilms agains E.
coli a e depic ed in Fig.7.
a) b)
Fig. 13. An ibac e ial ac i i ies o undoped and Ag- doped ZnO hin ilms agains E.
coli. a) Op ical densi y (OD) a 640 nm o e ime o incuba e bac e ia cells wi h
di e en Ag con en The con ol g ow h was assessed using non coa ed PET wi h he
same a ea; b) gene a ion ime o E. coli. bac e ia.
F om he p e ious plo (Fig. 13) i is possible o obse e an enhancemen o
an ibac e ial ac i i y wi h he inc ease o sil e con en in he zinc oxide based coa ings.
Wi h he inc ease o sil e con en he e is a dec ease o E. coli. g ow h a e (see, Fig.
13.a) and 7.b)), a dec eased amoun o bac e ia cells p esen a he end o he
expe imen . On he o he hand o he sample ha ing he highes Ag/Zn a omic a io o
0.04 i is obse ed a comple e g ow h inhibi ion (see, Fig. 13.a).
The an ibac e ial mechanism o ZnO is s ill unde in es iga ion. Two majo
mechanisms ha e been sugges ed: (1) he elease o Zn2+ ions om he coa ing [
80
] and
(2) he gene a ion o hyd ogen pe oxide as well as adical oxygen species om ZnO
su ace[
81
,
82
,
83
,
84
,
85
,
86
].
Suga man [
87
] sugges ed ha zinc ions binds o he memb anes o
mic oo ganisms, ex ending he lag phase o he g ow h cycle and inc easing he
gene a ion ime o he mic oo ganisms [
88
]. O he s au ho s [
89
,
90
,
91
], obse ed ha Zn2+
ions do no ha e much an ibac e ial ac i i y up o a concen a ion o 7.3x10-5 M, he
same o de o magni ude o he solubili y o ZnO in he solu ion. This may be consis en
wi h he p edic ion ha E. coli can me abolize Zn2+ as an oligoelemen [
92
]. This
sugges s ha hese ions a e no p ima ily esponsible o he an ibac e ial ac i i y o
ZnO. The same au ho s claimed ha he an imic obial dominan mechanism should
esul om Radical Oxygen Species (ROS) gene a ion and hei subsequen in e ac ion
wi h cell.
Rega ding he gene a ion o highly eac i e species, such as OH adicals,
H2O2 and O22−, Naga ajan Padma a hy and co au ho s[
93
] explained as ollows: ZnO
wi h de ec s can be ac i a ed by bo h UV and isible ligh , which will induce elec on-
hole pai s (e-/h+) gene a ion. Wa e molecules can spon aneously dissocia e in o OH-
and H3O+ species. Dissol ed oxygen molecules a e ans o med o supe oxide adical
anions 
, ha in u n will eac wi h H3O+ o gene a e (HO2) adicals, which upon
subsequen collision wi h elec ons p oduce hyd ogen pe oxide anions (HO2-). Then,
hey hen eac wi h H3O+ o p oduce H2O2 molecules. Howe e , ligh is needed o
p oduce pho oca aly ic ROS. Since in he p esen wo k he E. coli. A- Bac e ia cells
we e incuba ed in da k condi ions, he gene a ion o (ROS) canno be explained by a
pho oca aly ic mechanism. By ano he hand, Ken Hi o a e al.[
94
] and J. Sawai e al.[
95
]
obse ed he gene a ion o OH adicals om ZnO ce amics in da k condi ions. Bo h
au ho s did no explain he o ma ion mechanism o hese adicals.
72
K.Lou, T.P.S .Clai , X.Lai and D.W.Goodman. J.Phys.Chem. B, 104 (2000) 3050-
3057.
73
K.Lou, T.P.S .Clai , X.Lai and D.W.Goodman. J.Phys.Chem. B, 104 (2000) 3050-
3057.
74
M.G.Mason, Physical Re iew B, 27(2) (1983) 748-762.
75
P.S.Bagus, C.R.B undle, G.Pacchioni, F.Pa megiani, Su . Sci. Rep. 19 (1993) 265.
76
G.K. We heim, S.B.DiCenzo, D.N.E.Buchanan, Physical Re iew B 33 (1986,)5384
77
W.F.J . Egelho , G.G.Tibbe s, Physical Re iew B, 19 (1979) 5028.
78
C.D.Wagne , Fa aday Discuss. Chemical Soc., 60 (1975) 291.
79
L. N. Wang, L.Z.Hu, H.Q.Zhang, Y.Qiu,Y.Lang, G.Q.Liu,J.Y.Ji, J.X.Ma,Z.W.Zhao,
Ma e ials Science in Semiconduc o P ocessing 14 (3-4) (2011) 274.
80
M. Heinlaan, A. I ask, I. Blino a, H.C. Dubou guie , A. Kah u, Chemosphe e 71
(2008) 1308–16.
81
S.J. Chen, Y.C. Liu, C.L. Shao, R. Mu, Y.M. Lu, J.Y. Zhang, Ad Ma e 17 (2005)
586-90.
82
J. Sawai, S. Shoji, H. Iga ashi, A. Hashimo o, T. Kokugan, M. Shimizu, J Fe men
Bioeng 86 (1998) 521–2.
83
J. Sawai, S. Shoji, H. Iga ashi, A. Hashimo o, T. Kokugan, M. Shimizu, H. Kojima,
Fe men . Bioeng. 86 (1998) 521–522.
84
R. B ayne , R. Fe a i-Iliou, N. B i ois, S. Djedia , M.F. Benede i, F. Fie e , Nano
Le 6 (2006) 866–70.
85
T. Xu, CS. Xie, P og O g Coa 46 (2003) 297–301.
86
J. Sawai, S. Shoji, H. Iga ashi, A. Hashimo o, T. Kokugan, M. Shimizu, H. Kojima, J.
Fe men . Bioeng. 86 (1998) 521–522.
87
B. Suga man, Re . In ec . (1983) 138-147.
88
L.L. Radke, B.L. Hahn, D.K. Wagne , P.G. Sohnle, Clinical Immun. And Immuno.
Pa hol. 73(3) (1994) 344-349.
89
J. Sawai, Jou nal o Mic obiological Me hods 54 (2003) 177– 182.
90
Lingling Zhang, Yunhong Jiang, Yulong Ding, Nikolaos Daskalakis, La s Jeuken,
Malcolm Po ey, Alex J. O’Neill, Da id W. Yo k, J Nanopa Res 12 (2010) 1625–
1636.
91
Guy Apple o , Ana Lipo sky, Rachel D o , Nina Pe kas, Yeshayahu Ni zan, Rachel
Luba , Aha on Gedanken, Ad . Func . Ma e . 19 (2009) 842–852.

92
M. Roselli, A. Finamo e, I. Ga aguso, M.S. B i i, E. Menghe i J. Nu . 133 (2003)
4077-4082.
93
Naga ajan Padma a hy, Rajagopalan Vijaya agha an, Sci. Technol. Ad . Ma e . 9
(2008) 035004.
94
Ken Hi o a, Maiko Sugimo o, Masaki Ka o, Kazuhiko Tsukagoshi, Too u Tanigawa,
Hi oshi Sugimo o, Ce amics In e na ional 36 (2010) 497–506.
95
J. Sawai, E.Kawada, F.Kanou, H. Iga ashi., A. Hashimo o, , T. Kbkugan, , M.
Shimizu, J. Chem. Eng. Japan, 29 (1996) 627-633.
96
J. M. Schie holz, L. J. Lucas, A. Rump, G. Pul e e , jou nal o Hospi al In ec ion 40
(I 998) 257-262.
97
J. M. Schie holz, L. J. Lucasj, A. Rump, G. Pul e e , jou nal o Hospi al In ec ion 40
(I 998): 257.
98
K. Modak, C. Fox, Biochem Pha m 22 (1973) 2392-2404.
99
J. M. Schie holz, L. J. Lucas, A. Rump, G. Pul e e , jou nal o Hospi al In ec ion 40
(I 998) 257-262.
100
J.A. Spada o, T.J. Be ge , S.D. Ba anco, S.E. Chapin, R.O. Becke , Mic ob. Agen s
Chemo he . 6 (1974) 637.
101
Q.L. Feng, J. Wu, G.Q. Chen, F.Z. Cui, T.M. Kim, J.O. Kim, J. Biomed. Ma e . Res.
52 (2000) 662.