Research Article Influence of Annealing on Properties of...

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2013 Article ID 146382 8 pageshttpdxdoiorg1011552013146382

Research ArticleInfluence of Annealing on Properties of Spray Deposited ZnOThin Films

Kalyani Nadarajah Ching Yern Chee and Chou Yong Tan

Department of Mechanical Engineering Faculty of Engineering University of Malaya Lembah Pantai50603 Kuala Lumpur Malaysia

Correspondence should be addressed to Ching Yern Chee chingycumedumy

Received 8 August 2013 Revised 18 October 2013 Accepted 21 October 2013

Academic Editor Mengnan Qu

Copyright copy 2013 Kalyani Nadarajah et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Zinc Oxide (ZnO) thin films were deposited on glass substrates via the spray pyrolysis technique The films were subsequentlyannealed in ambient air from 300∘C to 500∘C The morphology and structural properties of the thin films were studied by fieldemission scanning electron microscope (FESEM) atomic force microscopy (AFM) and X-ray diffractometry (XRD) techniquesElectrical resistivity of the thin films was measured using a data acquisition unit The optical properties of the films werecharacterized by UV-vis spectroscopy and photoluminescence (PL) technique X-ray diffraction data showed that the films weregrown in the (002) direction with a hexagonal wurtzite structure The average grain size ranged from 15 to 27 nm Increasingannealing temperatures resulted in larger grain sizes and higher crystallinity with the surface roughness of annealed films beingmore than twice if compared to unannealed film The electrical resistivity of the films decreased with the increasing annealingtemperatureTheUV and visible band emissions were observed in the photoluminescence spectra due to exciton and defect-relatedemissions respectively The transmission values of the films were as high as 90 within the visible range (400ndash700 nm)

1 Introduction

Currently ZnO nanomaterials are being applied in electron-ics photonics catalysis lighting and chemical sensing Itis well known that ZnO exhibits many favorable propertiessuch as high chemical stability wide bandgap of 337 eVhigh exciton binding energy of 60meV and abundancein nature and is also regarded as nontoxic [1 2] High-quality ZnO films aremainly fabricated by using physical andchemical methods The physical methods include sputtering[3] molecular beam epitaxy [4] and laser ablation [5] whilethe chemical method includes spray pyrolysis [6] chemicalvapor deposition (CVD) [7] sol-gel [8] spin coating [9] dipcoating [10] and electrodeposition [11] Most of the methodsmentioned in the literature are not ideally suited for largearea coatings However the spray pyrolysis method is oneof the best methods to produce large area coatings basedon the previous studies [3ndash11] Additionally it is simplehas low temperature deposition is cost-effective has goodadhesion between films and substrate and demonstrates

uniform particle distribution high purity and excellentoptical properties [12] Some of the main factors affecting theproperties of the film that uses spray pyrolysis technique arechemical solution (chemical composition concentration)the distance between the substrate and atomizer interac-tion during film deposition spray temperatures substratehomogeneity annealing conditions and spray rates [13]The spray pyrolysis method is efficient in producing thinfilm multilayer film thick film and porous film on aninexpensive substrate [12] Several oxides such as ZnO [14]CdO [15] TiO

2[16] SnO

2[17] NiO [18] and Bi

2O3[19]

have been deposited using a spray pyrolysis method Thistechnique involves a wateralcohol solution of metal saltssprayed onto a heated substrate followed by allowing it todecompose into an oxide film The formation of oxide dueto the decomposition reaction is thermodynamically feasibleand leaves no residue on other reactants The substratetemperature strongly affects film morphology By increasingthe temperature the filmrsquos morphology can be changedfrom a cracked to a porous structure [20] The types and

2 Journal of Nanomaterials

Hot plate

Atomizer

Substrate holderSubstrate

IR thermometerAir brush

Figure 1 Schematic diagram of spray pyrolysis experimental setup

concentrations of precursor and additive elements are othervital variables that influence the properties and structure [21]The unannealed spray deposited film has high resistivity lowroughness and less transparency due to its low crystallinityand the presence of organic residues [22ndash24] The propertiesof the unannealed film can be enhanced due to the thermalannealing plasma treatment and laser treatment [25 26] Ofthese options the thermal annealing is one of the simplestand effective ways to treat the spray deposited films Thethermal annealing temperatures time and various gaseousenvironments influence films and structural defects in thematerials During the thermal annealing process dislocationsand other structural defects in the material adsorption ordecomposition are retained on the surface therefore thestructure and the stoichiometric ratio of the material arealtered [27] Oxygen interstitials zinc interstitials oxygenvacancies zinc vacancies and excess oxygen are commondefects found in deposited ZnO films Zinc interstitial andoxygen vacancies are the most common defects [28 29]

Nunes et al [30 31] reported the deposition of ZnO thinfilms using zinc acetate as a precursor Their work reportedthe structural optical and electrical properties of undopedand doped ZnO thin films under different conditions Yoonand Cho [32] demonstrated the synthesis of ZnO thin filmsusing a zinc acetate dihydrate as a precursor Their workreported on the effects of different substrate temperaturesand heat treatments on the luminescence properties of ZnOfilm Ayouchi et al [33] also synthesized ZnO thin filmsusing zinc acetate precursor and described the effects ofsubstrate temperature and the physical properties of ZnOthin films Despite our knowledge of various influenceson film structure the effects of annealing temperature onthe ZnO films prepared by spray pyrolysis are unknownIn this study the effects of annealing on the structuralmorphological electrical optical and photoluminescencebehavior of ZnO films are investigated

2 Experimental

21 Sample Preparation The ZnO thin films were depositedon glass and Si substrates using spray pyrolysis techniquesThe substrates were ultrasonically cleaned in methanol andacetone for 20 minutes and then immersed into 01M HClfor 12 hours to remove the ionic contamination and metalresidues These substrates were rinsed with deionized waterand dried in ambient air prior to the deposition 01M zincacetate (Zn (C

2H3O2)2999purity SigmaAldrich) was used

as a precursor A 2mL acetic acid was added to the ethanolto assist in the complete dissolution of the zinc acetate Aschematic diagram of the spray pyrolysis system is illustratedin Figure 1 The precursor solution was atomized into fineuniform droplets on the heated substrate using the spraygun which is connected with nitrogen gas The substrate washeated to 250∘C during the deposition processThe outlet gaspressure was kept constant at 30 psi The distance betweenthe substrate and target was kept at 100mm and spray ratewas 30 sec After spraying the deposited films were annealedin ambient air from 300∘C to 500∘C for 120 minutes Theannealing temperature was conducted until 500∘C in thisstudy since further increase of the temperature would causethe bending of the soda-lime glass substrate

22 Characterization of Film The morphologies of thefilm and grain size were studied with a Zeiss Ultra-60field emission scanning electron microscopy (FESEM) Theroughness and surface morphology were evaluated using anAmbios 4500 model atomic force microscope (AFM) Filmcrystallinity was characterized by Bruker X-ray diffraction(XRD) with CuK120572 radiation The electrical resistivity of thefilm was measured using data acquisition unit The filmthickness was measured using KLA Tencor surface profileThe crystalline quality of the filmwas studied using RenishawinVia Raman spectroscope with a He-Cd laser at 325 nm

Journal of Nanomaterials 3

100 nm

(a)

100 nm

(b)

100 nm

(c)

100 nm

(d)

Figure 2 FESEM images of ZnO thin film deposited on Si substrate (a) unannealed (b) annealed at 300∘C (c) annealed at 400∘C and (d)annealed at 500∘C

Optical transmission spectra were characterized using adouble beam UV-vis spectrophotometer (Cary 50) in thewavelength range of 300ndash800 nm

3 Results and Discussion

31 Surface Morphology Study of Films by FESEM Figure 2illustrates the surface morphologies of the films before andafter annealing (300∘C and 500∘C) process It appears thatthe grain size andmorphology of the films improved with theincreasing annealing temperatures The FESEM micrographshows that the unannealed films are not compact and havevery small crystallites on Si substrate which occur due toincomplete intermediate products from the spray pyrolysistechnique The well-defined round shapes of the grains areobserved in the film at an annealing temperature of 300∘CA 30 nm average grain size of ZnO films is achieved whenthe annealing temperature reaches 500∘C The grain sizeincreases with the increase in the annealing temperaturesdue to reduction of grain boundaries in ZnO thin film [34]

32 AFM Morphology Study of Films Figures 3(a) to 3(c)show the AFM images with the corresponding rms valueof unannealed and annealed ZnO thin films grown on Sisubstrates For the unannealed films (Figure 3(a)) the resultexhibits less elongated grains over the surface Figures 3(b)

and 3(c) display fine grains that exhibit greatly improvedvertical alignment (nanotips-like morphology) than theunannealed filmswhich is consistentwith the FESEMresultsThe surface roughness of the ZnO film is determined usingAFM software The rms roughness value can be estimatedusing the following formula [35]

119877 (rms) = (sum119873

119868=1

(119885119894minus 119885avg)

2

119873)

12

(1)

where 119873 is the number of points 119885119894is the 119894th point of

Z and 119885avg is the average value of the 119885 The unannealedfilm roughness is 21 nm After being annealed at 300∘C400∘C and 500∘C the filmrsquos roughness increased to 43 nm54 nm and 56 nm respectively The measurements of sam-ples revealed that the average roughness of annealed filmsincreased compared to that of the unannealed film As aresult of this the annealing temperature enhances elongatedgrains over the surface of the film which leads to the slightincrease of surface roughness Tong et al [36] have reportedthat an increase of roughness is suitable for the growth of ZnOnanowires on ZnO thin films

33 Structural Studies of Films The phase composition ofZnO thin films is determined using XRD at room temper-ature with monochromatic CuK120572 (120582 = 015406 nm) The


9661 nm(120583

m)

(120583m)

0

2

4

6

8

02

46

8

908070605040302010

0(nm)

(a)

(120583m

)

(120583m)

8824 nm

0

2

4

6

8

02

46

810

80

70

60

50

40

30

20

10

0(nm)

(b)

(120583m

)

(120583m)

550 nm

0

2

4

6

8

02

46

8

60

50

40

30

20

10

0(nm)

(c)

(120583m

)

(120583m)

7959 nm

0

2

4

6

8

02

46

8

80

70

60

50

40

30

20

10

0(nm)

(d)

Figure 3 AFM images of ZnO thin film deposited on Si substrate (a) unannealed (b) annealed at 300∘C (c) annealed at 400∘C and (d)annealed at 500∘C

30 35 40 45 50 55 60 65 70

(112)(103)(110)(102)

(101)

(002)

(100)

(d)

(c)

(b)

(a)

Inte

nsity

(au

)

2120579 (deg)

Figure 4 XRD pattern of ZnO thin film on Si substrate (a)unannealed (b) annealed at 300∘C (c) annealed at 400∘C and (d)annealed at 500∘C

intensity data is collected over a range of 2120579 from 30∘ to 70∘with a scan rate of 003 degs The XRD spectra of the spraypyrolysis deposited unannealed and annealedZnOfilms on Sisubstrate are illustrated in Figure 4 ZnOdiffraction peaks areindexed as (100) (101) (002) (102) (110) (103) and (112)for corresponding peak positions of 31766∘ 34419∘ 36251∘47536∘ 56591∘ 62852∘ and 67942∘ These diffraction peaksrsquoposition and intensities quantities are well matched with theJoint Committee on Powder Diffraction Standards (JCPDS)card no 067454 The patterns observed from the XRDmeasurements show that the films possess the hexagonalwurtzite structure and a space group P6

3mcThe unannealed

film shows lower diffraction peak intensities compared tothat of the annealed film The diffraction peaks intensitiesincrease with the increasing annealing temperatures Thusthe 500∘C annealed film shows a strong preferential growthorientation along the (002) planeThe diffraction peaks of thefilm become more intense when the annealing temperatureincreases which in turn leads to increase in the grain size aswell as the enhancement of crystallinity The full width halfmaxima (FWHM) values decrease with increasing annealing


250 300 350 400 450 500 550 6000

051

152

253

354

455

556

Resis

tivity

(ohm

s cm

)

Annealing temperature (∘C)

Figure 5 Electrical resistivity variation of ZnO thin film on glasssubstrate as a function of annealing temperatures

temperatures The grain size (D) can be computed using thefollowing Scherrerrsquos formula [37]

119863 =094120582

120573 cos 120579 (2)

where 120573 is FWHM 120582 is wavelength of X-ray and 120579 isBraggrsquos diffraction angle Furthermore the average grainsizes are estimated to be around 15 20 22 and 27 nm forunannealed and 300∘C 400∘C and 500∘C annealed filmsrespectively The decrease of FWHM with the increase ofannealing temperature can be attributed to the increase ofgrain sizes This correlates with the findings reported byprevious researchers [24 38]

34 Electrical Resistivity Study of Films Figure 5 illustratesthe electrical resistivity of ZnO thin films as a function ofannealing temperatures The electrical resistivity is greatlyinfluenced by the annealing temperatures It is observed thatthe resistivity of the film decreases dramatically up to 400∘Cand again decreases slowly afterward This might be dueto either an increase in the mobility andor increase of thecarriers The increase of annealing temperature is attributedto larger grain sizes thus leading to the increase of mobilitychange that has been reported in the literature [39] At roomtemperature there are very small numbers of charge carriersthat are available in ZnO The electronically active carriersincrease when the temperature increases thereby leading toan excess carrier in the conduction band This increase incarriers occurs due to thermal excitation giving rise to theconductivity of the films Similar results have been reportedin the literature [40] The resistivity of the 500∘C annealedfilm is measured to be 081Ω cm

35 Photoluminescence Studies of Films The room temper-ature photoluminescence (PL) spectra of unannealed andannealed ZnO thin films on glass substrate are illustrated inFigure 6 There are three peaks positions that are observed

350 400 450 500 550 600 650 700

300 400 500Unannealed

Inte

nsity

(au

)

(d)

(c)

(b)

(a)

Wavelength (nm)

Inte

nsity

(au

)


Figure 6The photoluminescence spectra of ZnO thin film on glasssubstrate (a) unannealed (b) annealed at 300∘C (c) annealed at400∘C and (d) annealed at 500∘CThe inset shows the intensity vari-ation of near band edge emission at different annealed temperatures

from the spectra For unannealed films the PL spectrumconsists of three emission bands a strong UV emission bandat sim382 nm (325 eV) yellow band at sim603 nm (206 eV)and orange-red band at sim672 nm (185 eV) respectively Theband emission occurring in the UV range is due to excitonicrecombination while the band emission existing at the visibleemission band is due to the recombination of deep-levelholes and electrons [41] All of the deep-level emissionsare correlated to the defects arising during the growth ofcrystallites and are related to the change of crystallinity due tozinc interstitials zinc vacancies oxygen interstitials oxygenvacancies and dislocations [42] Previous works [43 44]reported that the yellow-orange emission originated fromoxygen interstitials in ZnO while the orange-red emissioncould be related to excess oxygen on the ZnO surface Fromthe spectra it is observed that the PL peak intensity increaseswith the increasing annealing temperature The increase ofthe visible emissions of the ZnO film is due to the increaseof the oxygen interstitials and excess oxygen concentrations[45] by the increase of annealing temperature The UV peakposition is red shifted from 325 eV (for unannealed film)to 322 eV (for 500∘C annealed film) The red shift can beexplained by the quantum confinement theory which statesthat the energy bandgap of a semiconductor decreases withincreasing grain sizes [46] However after annealing theyellow emission is improved with a blue shift towards awavelength of 594 nm Fujihara et al [47] and Chen et al[48] have also reported a blue shift in their studies

The inset of Figure 6 shows the UV portion of the PLemission centered at 385 nm as a function of annealingtemperatures The intensity of UV-PL peak increases withthe increasing annealing temperature as shown in the insetof Figure 6 The increase in the UV portion of the PLemission is due to the removal of microstructural defects andhomogenization of the films


350 400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

70

80

90

100

300 350 400 450 500220

230

240

250

260

270

280

290

Unannealed

Thic

knes

s (nm

)

Wavelength (nm)

Tran

smiss

ion

()


(d)(c)

(b)(a)

Figure 7 The transmission spectra of ZnO thin film on glasssubstrate (a) unannealed (b) annealed at 300∘C (c) annealed at400∘C and (d) annealed at 500∘C The inset shows the filmsthickness variation of different annealed temperatures

36 Transmission Studies of ZnO Thin Films The opticaltransmission of ZnO films is carried out using a doublebeam spectrophotometer in the wavelength range from 300to 800 nm Figure 7 shows optical transmission spectra ofboth unannealed and annealed ZnO thin films The averagetransmittance values are directly related to the thickness offilms The inset in Figure 7 illustrates the average thicknessvariation of the films with the increase of annealing temper-atures The thickness of unannealed film is 2822 nm Afterannealing at 300∘C 400∘C and 500∘C the film thicknessdecreases to 2686 nm 2506 nm and 2284 nm respectivelyThe relationship between the optical transmission and thick-ness is given by the Beer-Lambert equation as follows [49]

119879 =119868

119868119900

= 119890(minus120572119905)

(3)

where 119868 is the transmitted intensity at a particularwavelength119868119900is the incident light intensity120572 is the absorption coefficient

and 119905 is the film thickness The equation shows that theoptical transmission of the ZnO films will decrease inverselyproportional to the film thickness The optical transmissionis inversely proportional to the thickness of the films Thetransmission in the visible region of the unannealed filmis approximately 80 The visible transmission of the ZnOfilms increases from 90 to 92 when annealing tempera-ture increased from 300∘C to 400∘C The transmission filmapproaches to 96 when the annealing temperature reached500∘C A very steep absorption edge near 370 nm is observedfor both unannealed and annealed films indicating highcrystal quality which could enhance luminescent efficiencyThe transmission of films increases in tandemwith annealingtemperatures due to the increase in grain sizes structuralhomogeneity and crystallinity The same observation hasbeen reported by previous researchers [50 51] Jayatissaet al [52] have demonstrated that the transmission of ZnO

films can be improved by annealing which could lead tothe reaction of oxygen with ZnO It suggests that ambientconditions annealing would greatly influence the opticaltransmission of ZnO films This is especially valuable for theapplications as a front electrode and window materials insolar cell

4 Conclusions

ZnO thin films were prepared by spray pyrolysis methodand it was thermally annealed at different temperatures Thestructural electrical and optical properties of the ZnO thinfilms were characterized using XRD AFM data acquisitionunit and UV-vis spectrophotometer The grain size of thefilms increases with the increase of annealing temperaturesThe XRD diffractogram revealed that the thermal annealedfilm at 500∘C possesses good crystalline hexagonal wurtzitestructure with a preferred plane orientation along (002)The grain size estimated from FESEM analysis is in goodagreement with XRD data The PL emission of the samplesshows a narrow emission centered at 385 nmand a broad peakemission located at 594 nm and 672 nmThe ZnO films showan increase of transmission with the increase of annealingtemperature In particular ZnO film annealed at 500∘Cachieves high light transmission of 96 in the visible rangewith low electrical resistivity of 082Ω cm These propertiesrender that the ZnO film is attractive to optoelectronic deviceapplications

Acknowledgment

The authors acknowledge financial support from the Uni-versity Malaya Postgraduate Research Grant of nos PV033-2012A CG013-2013 CG07-2013 RP011A-13AET FP030-2013A and ER014-2012A

References

[1] J-H Lee K-H Ko and B-O Park ldquoElectrical and opticalproperties of ZnO transparent conducting films by the sol-gelmethodrdquo Journal of Crystal Growth vol 247 no 1-2 pp 119ndash1252003

[2] R Konenkamp K Boedecker M C Lux-Steiner et al ldquoThinfilm semiconductor deposition on free-standingZnOcolumnsrdquoApplied Physics Letters vol 77 no 16 pp 2575ndash2577 2000

[3] S Eisermann J Sann A Polity and B K Meyer ldquoSputterdeposition of ZnO thin films at high substrate temperaturesrdquoThin Solid Films vol 517 no 20 pp 5805ndash5807 2009

[4] D C Look D C Reynolds C W Litton R L Jones D BEason and G Cantwell ldquoCharacterization of homoepitaxial p-type ZnO grown by molecular beam epitaxyrdquo Applied PhysicsLetters vol 81 no 10 pp 1830ndash1832 2002

[5] MHiramatsu K Imaeda N Horio andMNawata ldquoTranspar-ent conducting ZnO thin films prepared by XeCl excimer laserablationrdquo Journal of Vacuum Science and Technology A vol 16no 2 pp 669ndash673 1998

[6] R Ayouchi D Leinen F Martın M Gabas E Dalchieleand J R Ramos-Barrado ldquoPreparation and characterization oftransparent ZnO thin films obtained by spray pyrolysisrdquo ThinSolid Films vol 426 no 1-2 pp 68ndash77 2003


[7] S Fay U Kroll C Bucher E Vallat-Sauvain and A Shah ldquoLowpressure chemical vapour deposition of ZnO layers for thin-film solar cells temperature-induced morphological changesrdquoSolar Energy Materials and Solar Cells vol 86 no 3 pp 385ndash397 2005

[8] D Bao H Gu and A Kuang ldquoSol-gel-derived c-axis orientedZnO thin filmsrdquo Thin Solid Films vol 312 no 1-2 pp 37ndash391998

[9] G Srinivasan N Gopalakrishnan Y S Yu R Kesavamoorthyand J Kumar ldquoInfluence of post-deposition annealing on thestructural and optical properties of ZnO thin films prepared bysol-gel and spin-coating methodrdquo Superlattices and Microstruc-tures vol 43 no 2 pp 112ndash119 2008

[10] C J Brinker G C Frye A J Hurd and C S AshleyldquoFundamentals of sol-gel dip coatingrdquoThin Solid Films vol 201no 1 pp 97ndash108 1991

[11] E A Dalchiele P Giorgi R EMarotti et al ldquoElectrodepositionof ZnO thin films on n-Si(100)rdquo Solar Energy Materials andSolar Cells vol 70 no 3 pp 245ndash254 2001

[12] D Perednis and L J Gauckler ldquoThin filmdeposition using spraypyrolysisrdquo Journal of Electroceramics vol 14 no 2 pp 103ndash1112005

[13] G Korotcenkov V Brinzari J Schwank and A CerneavschildquoPossibilities of aerosol technology for deposition of SnO

2

-based films with improved gas sensing characteristicsrdquo Mate-rials Science and Engineering C vol 19 no 1-2 pp 73ndash77 2002

[14] M Krunks and E Mellikov ldquoZinc oxide thin films by the spraypyrolysis methodrdquoThin Solid Films vol 270 no 1-2 pp 33ndash361995

[15] O Vigil F Cruz A Morales-Acevedo G Contreras-Puente LVaillant and G Santana ldquoStructural and optical properties ofannealed CdO thin films prepared by spray pyrolysisrdquoMaterialsChemistry and Physics vol 68 no 1ndash3 pp 249ndash252 2001

[16] C Natarajan N Fukunaga and G Nogami ldquoTitanium dioxidethin film deposited by spray pyrolysis of aqueous solutionrdquoThinSolid Films vol 322 no 1-2 pp 6ndash8 1998

[17] V Brinzari G Korotcenkov and V Golovanov ldquoFactors influ-encing the gas sensing characteristics of tin dioxide filmsdeposited by spray pyrolysis understanding and possibilities ofcontrolrdquoThin Solid Films vol 391 no 2 pp 167ndash175 2001

[18] P S Patil and L D Kadam ldquoPreparation and characterization ofspray pyrolyzed nickel oxide (NiO) thin filmsrdquo Applied SurfaceScience vol 199 no 1ndash4 pp 211ndash221 2002

[19] T P Gujar V R Shinde and C D Lokhande ldquoSpray pyrolysedbismuth oxide thin films and their characterizationrdquo MaterialsResearch Bulletin vol 41 no 8 pp 1558ndash1564 2006

[20] C Chen E M Kelder P J J M van der Put and J SchoonmanldquoMorphology control of thin LiCoO

2

films fabricated usingthe electrostatic spray deposition (ESD) techniquerdquo Journal ofMaterials Chemistry vol 6 no 5 pp 765ndash771 1996

[21] S Golshahi S M Rozati R Martins and E Fortunato ldquoP-typeZnO thin film deposited by spray pyrolysis technique the effectof solution concentrationrdquo Thin Solid Films vol 518 no 4 pp1149ndash1152 2009

[22] S Salam M Islam M Alam et al ldquoThe effect of processingconditions on the structural morphology and physical proper-ties of ZnO and CdS thin films produced via sol-gel synthesisand chemical bath deposition techniquesrdquo Advances in NaturalSciences Nanoscience and Nanotechnology vol 2 no 4 ArticleID 045001 2011

[23] X Zhu E Defay M Aıd et al ldquoPreferential growth andenhanced dielectric properties of Ba

07

Sr03

TiO3

thin films withpre annealed Pt bottom electroderdquo Journal of Applied Physics Dvol 46 Article ID 105301 2013

[24] J Karamdel C F Dee and B Y Majlis ldquoEffects of annealingconditions on the surface morphology and crystallinity ofsputtered ZnO nano filmsrdquo Sains Malaysiana vol 40 no 3 pp209ndash213 2011

[25] J Yang J Bei and S Wang ldquoEnhanced cell affinity of poly(DL-lactide) by combining plasma treatment with collagenanchoragerdquo Biomaterials vol 23 no 12 pp 2607ndash2614 2002

[26] B D Ahn S H Oh C H Lee G H Kim H J Kim and SY Lee ldquoInfluence of thermal annealing ambient on Ga-dopedZnO thin filmsrdquo Journal of Crystal Growth vol 309 no 2 pp128ndash133 2007

[27] L Wang Y Pu W Fang et al ldquoEffect of high-temperatureannealing on the structural and optical properties of ZnOfilmsrdquoThin Solid Films vol 491 no 1-2 pp 323ndash327 2005

[28] H S Kang J S Kang J W Kim and S Y Lee ldquoAnnealing effecton the property of ultraviolet and green emissions of ZnO thinfilmsrdquo Journal of Applied Physics vol 95 no 3 pp 1246ndash12502004

[29] P Sagar P K Shishodia R M Mehra H Okada A Wakaharaand A Yoshida ldquoPhotoluminescence and absorption in sol-gel-derived ZnO filmsrdquo Journal of Luminescence vol 126 no 2 pp800ndash806 2007

[30] P Nunes E Fortunato and R Martins ldquoInfluence of the post-treatment on the properties of ZnO thin filmsrdquoThin Solid Filmsvol 383 no 1-2 pp 277ndash280 2001

[31] P Nunes B Fernandes E Fortunato P Vilarinho and RMartins ldquoPerformances presented by zinc oxide thin filmsdeposited by spray pyrolysisrdquo Thin Solid Films vol 337 no 1-2 pp 176ndash179 1999

[32] K H Yoon and J Y Cho ldquoPhotoluminescence characteristicsof zinc oxide thin films prepared by spray pyrolysis techniquerdquoMaterials Research Bulletin vol 35 no 1 pp 39ndash46 2000

[33] R Ayouchi F Martin D Leinen and J R Ramos-BarradoldquoGrowth of pure ZnO thin films prepared by chemical spraypyrolysis on siliconrdquo Journal of Crystal Growth vol 247 no 3-4pp 497ndash504 2003

[34] P Uthirakumar and C-H Hong ldquoEffect of annealing temper-ature and pH on morphology and optical property of highlydispersible ZnO nanoparticlesrdquoMaterials Characterization vol60 no 11 pp 1305ndash1310 2009

[35] C Periasamy R Prakash and P Chakrabarti ldquoEffect of postannealing on structural and optical properties of ZnO thin filmsdeposited by vacuum coating techniquerdquo Journal of MaterialsScience Materials in Electronics vol 21 no 3 pp 309ndash315 2010

[36] Y Tong Y Liu L Dong et al ldquoGrowth of ZnO nanostructureswith different morphologies by using hydrothermal techniquerdquoJournal of Physical Chemistry B vol 110 no 41 pp 20263ndash202672006

[37] Q Humayun M Kashif and U Hashim ldquoArea-selective ZnOthin film deposition on variable microgap electrodes and theirimpact on UV sensingrdquo Journal of Nanomaterials vol 2013Article ID 301674 5 pages 2013

[38] Z B Fang Z J Yan Y S Tan X Q Liu and Y Y Wang ldquoInflu-ence of post-annealing treatment on the structure properties ofZnO filmsrdquo Applied Surface Science vol 241 no 3-4 pp 303ndash308 2005


[39] M Rusop K Uma T Soga and T Jimbo ldquoPost-growthannealing of zinc oxide thin films pulsed laser deposited underenhanced oxygen pressure on quartz and silicon substratesrdquoMaterials Science and Engineering B vol 127 no 2-3 pp 150ndash153 2006

[40] N H Al-Hardan M J Abdullah A Abdul Aziz H Ahmadand L Y Low ldquoZnO thin films for VOC sensing applicationsrdquoVacuum vol 85 no 1 pp 101ndash106 2010

[41] R Hong H Qi J Huang H He Z Fan and J Shao ldquoInfluenceof oxygen partial pressure on the structure and photolumines-cence of direct current reactive magnetron sputtering ZnO thinfilmsrdquoThin Solid Films vol 473 no 1 pp 58ndash62 2005

[42] A B Djurisic W C H Choy V A L Roy et al ldquoPhotolumi-nescence and electron paramagnetic resonance of ZnO tetrapodstructuresrdquo Advanced Functional Materials vol 14 no 9 pp856ndash864 2004

[43] W Q Peng S C Qu G W Cong and Z G Wang ldquoStructureand visible luminescence of ZnO nanoparticlesrdquo MaterialsScience in Semiconductor Processing vol 9 no 1ndash3 pp 156ndash1592006

[44] B PanigrahyM Aslam D SMisraM Ghosh andD BahadurldquoDefect-related emissions andmagnetization properties of ZnONanorodsrdquo Advanced Functional Materials vol 20 no 7 pp1161ndash1165 2010

[45] A B Djurisic Y H Leung K H Tam et al ldquoDefect emissionsin ZnO nanostructuresrdquo Nanotechnology vol 18 no 9 ArticleID 095702 2007

[46] S Cho J Ma Y Kim Y Sun G K LWong and J B KettersonldquoPhotoluminescence and ultraviolet lasing of polycrystallineZnO thin films prepared by the oxidation of the metallic ZnrdquoApplied Physics Letters vol 75 no 18 pp 2761ndash2763 1999

[47] S Fujihara Y Ogawa and A Kasai ldquoTunable visible photo-luminescence from ZnO thin films through Mg-doping andannealingrdquo Chemistry of Materials vol 16 no 15 pp 2965ndash2968 2004

[48] S Chen Z Zhao B Z Tang and H S Kwok ldquoGrowthmethods enhanced photoluminescence high hydrophobicityand light scattering of 4 41015840-bis(1 2 2-triphenylvinyl)biphenylnanowiresrdquo Organic Electronics vol 13 pp 1996ndash2002 2012

[49] V S Reddy K Das A Dhar and S K Ray ldquoThe effect ofsubstrate temperature on the properties of ITO thin films forOLED applicationsrdquo Semiconductor Science andTechnology vol21 no 12 pp 1747ndash1752 2006

[50] A L Mercado C E Allmond J G Hoekstra and J M Fitz-Gerald ldquoPulsed laser deposition vs matrix assisted pulsed laserevaporation for growth of biodegradable polymer thin filmsrdquoApplied Physics A vol 81 no 3 pp 591ndash599 2005

[51] R Jones and D Fried ldquoAttenuation of 1310-nm and 1550-nmlaser light through sound dental enamelrdquo in Lasers in DentistryVIII vol 4610 ofProceedings of SPIE pp 187ndash190 San Jose CalifUSA January 2002

[52] A H Jayatissa S-T Cheng and T Gupta ldquoAnnealing effect onthe formation of nanocrystals in thermally evaporated tungstenoxide thin filmsrdquoMaterials Science and Engineering B vol 109no 1ndash3 pp 269ndash275 2004

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Journal ofNanomaterials


Hot plate

Atomizer

Substrate holderSubstrate

IR thermometerAir brush

Figure 1 Schematic diagram of spray pyrolysis experimental setup

concentrations of precursor and additive elements are othervital variables that influence the properties and structure [21]The unannealed spray deposited film has high resistivity lowroughness and less transparency due to its low crystallinityand the presence of organic residues [22ndash24] The propertiesof the unannealed film can be enhanced due to the thermalannealing plasma treatment and laser treatment [25 26] Ofthese options the thermal annealing is one of the simplestand effective ways to treat the spray deposited films Thethermal annealing temperatures time and various gaseousenvironments influence films and structural defects in thematerials During the thermal annealing process dislocationsand other structural defects in the material adsorption ordecomposition are retained on the surface therefore thestructure and the stoichiometric ratio of the material arealtered [27] Oxygen interstitials zinc interstitials oxygenvacancies zinc vacancies and excess oxygen are commondefects found in deposited ZnO films Zinc interstitial andoxygen vacancies are the most common defects [28 29]

Nunes et al [30 31] reported the deposition of ZnO thinfilms using zinc acetate as a precursor Their work reportedthe structural optical and electrical properties of undopedand doped ZnO thin films under different conditions Yoonand Cho [32] demonstrated the synthesis of ZnO thin filmsusing a zinc acetate dihydrate as a precursor Their workreported on the effects of different substrate temperaturesand heat treatments on the luminescence properties of ZnOfilm Ayouchi et al [33] also synthesized ZnO thin filmsusing zinc acetate precursor and described the effects ofsubstrate temperature and the physical properties of ZnOthin films Despite our knowledge of various influenceson film structure the effects of annealing temperature onthe ZnO films prepared by spray pyrolysis are unknownIn this study the effects of annealing on the structuralmorphological electrical optical and photoluminescencebehavior of ZnO films are investigated

2 Experimental

21 Sample Preparation The ZnO thin films were depositedon glass and Si substrates using spray pyrolysis techniquesThe substrates were ultrasonically cleaned in methanol andacetone for 20 minutes and then immersed into 01M HClfor 12 hours to remove the ionic contamination and metalresidues These substrates were rinsed with deionized waterand dried in ambient air prior to the deposition 01M zincacetate (Zn (C

2H3O2)2999purity SigmaAldrich) was used

as a precursor A 2mL acetic acid was added to the ethanolto assist in the complete dissolution of the zinc acetate Aschematic diagram of the spray pyrolysis system is illustratedin Figure 1 The precursor solution was atomized into fineuniform droplets on the heated substrate using the spraygun which is connected with nitrogen gas The substrate washeated to 250∘C during the deposition processThe outlet gaspressure was kept constant at 30 psi The distance betweenthe substrate and target was kept at 100mm and spray ratewas 30 sec After spraying the deposited films were annealedin ambient air from 300∘C to 500∘C for 120 minutes Theannealing temperature was conducted until 500∘C in thisstudy since further increase of the temperature would causethe bending of the soda-lime glass substrate

22 Characterization of Film The morphologies of thefilm and grain size were studied with a Zeiss Ultra-60field emission scanning electron microscopy (FESEM) Theroughness and surface morphology were evaluated using anAmbios 4500 model atomic force microscope (AFM) Filmcrystallinity was characterized by Bruker X-ray diffraction(XRD) with CuK120572 radiation The electrical resistivity of thefilm was measured using data acquisition unit The filmthickness was measured using KLA Tencor surface profileThe crystalline quality of the filmwas studied using RenishawinVia Raman spectroscope with a He-Cd laser at 325 nm


100 nm

(a)

100 nm

(b)

100 nm

(c)

100 nm

(d)







119877 (rms) = (sum119873

119868=1

(119885119894minus 119885avg)

2

119873)

12

(1)





9661 nm(120583

m)

(120583m)

0

2

4

6

8

02

46

8

908070605040302010

0(nm)

(a)

(120583m

)

(120583m)

8824 nm

0

2

4

6

8

02

46

810

80

70

60

50

40

30

20

10

0(nm)

(b)

(120583m

)

(120583m)

550 nm

0

2

4

6

8

02

46

8

60

50

40

30

20

10

0(nm)

(c)

(120583m

)

(120583m)

7959 nm

0

2

4

6

8

02

46

8

80

70

60

50

40

30

20

10

0(nm)

(d)


30 35 40 45 50 55 60 65 70

(112)(103)(110)(102)

(101)

(002)

(100)

(d)

(c)

(b)

(a)

Inte

nsity

(au

)

2120579 (deg)



3mcThe unannealed



250 300 350 400 450 500 550 6000

051

152

253

354

455

556

Resis

tivity

(ohm

s cm

)




119863 =094120582

120573 cos 120579 (2)




350 400 450 500 550 600 650 700


Inte

nsity

(au

)

(d)

(c)

(b)

(a)

Wavelength (nm)

Inte

nsity

(au

)






350 400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

70

80

90

100

300 350 400 450 500220

230

240

250

260

270

280

290

Unannealed

Thic

knes

s (nm

)

Wavelength (nm)

Tran

smiss

ion

()


(d)(c)

(b)(a)



119879 =119868

119868119900

= 119890(minus120572119905)

(3)




4 Conclusions


Acknowledgment


References















2









2





07

Sr03

TiO3







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




100 nm

(a)

100 nm

(b)

100 nm

(c)

100 nm

(d)







119877 (rms) = (sum119873

119868=1

(119885119894minus 119885avg)

2

119873)

12

(1)





9661 nm(120583

m)

(120583m)

0

2

4

6

8

02

46

8

908070605040302010

0(nm)

(a)

(120583m

)

(120583m)

8824 nm

0

2

4

6

8

02

46

810

80

70

60

50

40

30

20

10

0(nm)

(b)

(120583m

)

(120583m)

550 nm

0

2

4

6

8

02

46

8

60

50

40

30

20

10

0(nm)

(c)

(120583m

)

(120583m)

7959 nm

0

2

4

6

8

02

46

8

80

70

60

50

40

30

20

10

0(nm)

(d)


30 35 40 45 50 55 60 65 70

(112)(103)(110)(102)

(101)

(002)

(100)

(d)

(c)

(b)

(a)

Inte

nsity

(au

)

2120579 (deg)



3mcThe unannealed



250 300 350 400 450 500 550 6000

051

152

253

354

455

556

Resis

tivity

(ohm

s cm

)




119863 =094120582

120573 cos 120579 (2)




350 400 450 500 550 600 650 700


Inte

nsity

(au

)

(d)

(c)

(b)

(a)

Wavelength (nm)

Inte

nsity

(au

)






350 400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

70

80

90

100

300 350 400 450 500220

230

240

250

260

270

280

290

Unannealed

Thic

knes

s (nm

)

Wavelength (nm)

Tran

smiss

ion

()


(d)(c)

(b)(a)



119879 =119868

119868119900

= 119890(minus120572119905)

(3)




4 Conclusions


Acknowledgment


References















2









2





07

Sr03

TiO3







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




9661 nm(120583

m)

(120583m)

0

2

4

6

8

02

46

8

908070605040302010

0(nm)

(a)

(120583m

)

(120583m)

8824 nm

0

2

4

6

8

02

46

810

80

70

60

50

40

30

20

10

0(nm)

(b)

(120583m

)

(120583m)

550 nm

0

2

4

6

8

02

46

8

60

50

40

30

20

10

0(nm)

(c)

(120583m

)

(120583m)

7959 nm

0

2

4

6

8

02

46

8

80

70

60

50

40

30

20

10

0(nm)

(d)


30 35 40 45 50 55 60 65 70

(112)(103)(110)(102)

(101)

(002)

(100)

(d)

(c)

(b)

(a)

Inte

nsity

(au

)

2120579 (deg)



3mcThe unannealed



250 300 350 400 450 500 550 6000

051

152

253

354

455

556

Resis

tivity

(ohm

s cm

)




119863 =094120582

120573 cos 120579 (2)




350 400 450 500 550 600 650 700


Inte

nsity

(au

)

(d)

(c)

(b)

(a)

Wavelength (nm)

Inte

nsity

(au

)






350 400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

70

80

90

100

300 350 400 450 500220

230

240

250

260

270

280

290

Unannealed

Thic

knes

s (nm

)

Wavelength (nm)

Tran

smiss

ion

()


(d)(c)

(b)(a)



119879 =119868

119868119900

= 119890(minus120572119905)

(3)




4 Conclusions


Acknowledgment


References















2









2





07

Sr03

TiO3







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




250 300 350 400 450 500 550 6000

051

152

253

354

455

556

Resis

tivity

(ohm

s cm

)




119863 =094120582

120573 cos 120579 (2)




350 400 450 500 550 600 650 700


Inte

nsity

(au

)

(d)

(c)

(b)

(a)

Wavelength (nm)

Inte

nsity

(au

)






350 400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

70

80

90

100

300 350 400 450 500220

230

240

250

260

270

280

290

Unannealed

Thic

knes

s (nm

)

Wavelength (nm)

Tran

smiss

ion

()


(d)(c)

(b)(a)



119879 =119868

119868119900

= 119890(minus120572119905)

(3)




4 Conclusions


Acknowledgment


References















2









2





07

Sr03

TiO3







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




350 400 450 500 550 600 650 700 750 8000

10

20

30

40

50

60

70

80

90

100

300 350 400 450 500220

230

240

250

260

270

280

290

Unannealed

Thic

knes

s (nm

)

Wavelength (nm)

Tran

smiss

ion

()


(d)(c)

(b)(a)



119879 =119868

119868119900

= 119890(minus120572119905)

(3)




4 Conclusions


Acknowledgment


References















2









2





07

Sr03

TiO3







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials











2









2





07

Sr03

TiO3







































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials

























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Research Article Influence of Annealing on Properties of...

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