STRUCTURAL AND ELECTRICAL PROPERTIES OF ANNEALED NICKEL OXIDE (NiO) THIN FILMS PREPARED BY CHEMICAL BATH DEPOSITION

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1 Journl of Ovonic Reserch Vol. 9, No. 1, Jnury Ferury 2013, p STRUCTURAL AND ELECTRICAL PROPERTIES OF ANNEALED NICKEL OXIDE (NiO) THIN FILMS PREPARED BY CHEMICAL BATH DEPOSITION J. C. OSUWA *, G. I. ONYEJIUWA Deprtment of Physics, Michel Okpr university of Agriclture, Umudike PMB 7267, Ai Stte, Nigeri Nickel oxide (NiO) thin films prepred y chemicl th deposition t room temperture of 30 o C were nneled in n oven t tempertures of 100 o C, C nd 300 o C. Structurl nd electricl properties of the thermlly treted thin film smples were chrcterized using Scnning Electron microscope (SEM), X-Ry Diffrction (XRD), Energy Dispersive Spectroscopy (EDS) nd Surfce Profiler. The results show tht the NiO thin film thickness decresed with nneling temperture from 1.40 μm for s grown smple to 0.75 μm for smple nneled t 300 o C. The sheet resistnce nd resistivity of the NiO thin films lso decresed with nneling temperture while the electricl conductivity incresed from 6.50 x 10-4 Ω -1 m -1 for s grown smple to x10-4 Ω -1 m -1 for the smple nneled t 300 o C. SEM microgrphs nd the XRD ptterns reveled incresing morphosity of the NiO thin films with increse in nneling temperture, while the EDS reveled wide rnge of inclusions in the elementl composition with the presence of luminum, silicon, mgnesium, etc nd their ovious effects on the properties of the NiO thin films. (Received Jnury 7, 2013; Accepted Jnury 30, 2013) Keywords: Nickel oxide, scnning electron microscope (SEM), morphosity, conductivity. 1. Introduction Nickel oxide (NiO) is trnsition metl oxide with excellent chemicl nd therml stility [1, 7]. It hs potentil pplictions in such res s electro-chromic disply devices, ntiferromgnetic lyers, solr therml sorer nd s cthode mteril for lkline tteries [2-5]. Some other interesting electronic properties of NiO thin film include its wide nd gp rnge of ev [6] nd its p-type conductivity which mke it fvourle mteril for electronic device pplictions [7-8]. Thin films of NiO cn e deposited y vrious chemicl nd physicl methods like chemicl th deposition/solution growth technique, rective sputtering, vcuum evportion technique etc [9-12]. In this work, chemicl th deposition hs een used nd the effects of nneling on the structurl nd electricl properties of the deposited NiO thin films hve een nlyzed. * Corresponding uthor: josuw70@gmil.com

2 10 2. Experimentl detils 2.1 Deposition of Nickel oxide (NiO) thin films All chemicls used for the deposition of NiO thin films were of nlyticl grde nd ll the solutions were prepred in de-ionized wter. The nickel oxide thin films were prepred from queous solutions of nickel sulphte (NiS 4 ) in 1 percent polyvinyl lcohol (PVA). Ammoni solution NH 3 ws used s complexing gent during deposition. Glss slides were used s the sustrte for the chemicl th deposition of nickel oxide thin films. Before deposition, the glss sustrtes were degresed in n qu regi which is comintion of hydrochloric cid (HCl) nd nitric cid (HNO 3 ) for 48hours. Then, clensed with distilled wter for nother few minutes nd dried in ir. The mixture of Hydrochloric cid (HCl) nd Nitric cid (HNO 3 ) provide solute oxidtion of hlides on the sustrte therey providing nucletion surfce on which the film is grfted. The clensed glss sustrtes were then inserted verticlly into the eker contining the rection th. The rection th hs synthetic fom covering which prtly covered the top of the eker consisting the th. The film growth rection ths were composed of 40mls of 0.5M of nickel sulphte/1% PVA solution, 10ml of molr concentrtion of NH 3, ph of 11 nd 50ml of distilled wter. Ech deposition ws mde for 48hours. The mixture ws stirred thoroughly using glss rod t ech stge to otin homogeneous solutions into 100ml eker. Ech th ws mde up to 100mls with distilled wter. The th ws left undistured for 48 hours t room temperture. The deposited thin films were nneled in n oven t different tempertures. Smple K 1, ws nneled t 100 o C, smple K 2, 200 C, nd smplek 3, 300 o C ech for 1hr, while smple k is s grown. 2.2 Chrcteriztion of structurl nd electricl properties of Nickel oxide (NiO) thin films The chrcteriztion of the NiO thin film smples ws done t Shed Science nd Technologicl Complex (SHESTCO), Gwgwld, Auj. All the smples were nlyzed nd the XRD ptterns were otined with X pertpro PANnlyticl diffrctometer, using CuKα rdition (500nm) in the 2θ scnning mode. Mximum crystllite sizes of the films could not e otined s ll the films were morphous nd thus could not e estimted using Sherrer s formul. The specimen surfce ws scnned with n electron em nd the reflected or ck scttered em of electrons ws collected nd displyed on screen. The surfce ws not electriclly conductive, thus, very thin metllic surfce coting is pplied. The smples microstructures were photogrphed t mgnifiction of1000x. Further ttchment to the SEM which enled qulittive nlysis of the elementl composition of very smll loclized surfce re of the NiO thin films known s EDS ws lso nlyzed A surfce profiler (Veeco Dektk 150) ws used to determine the NiO thin film thickness. The informtion gotten ws represented grphiclly nd the film thickness ws determined y reding the width of the grph in ngstrom nd converted to micrometer (µm) for the purpose of using the vlue for electricl resistivity clcultions. The electricl resistnce of the deposited thin film ws mesured using the Vnder Puw Four Point Proe method. The sheet resistnce R s of the film smple is given y (Ie nd Mgenu, 1997); where the constnt K = nd the resistivity of the smple ecomes where t = film thickness nd conductivity, σ E is 1/ρ. R S = K(V/I) 2.1 ρ = t x R S 2.2

3 11 3. Results nd discussion Fig. 3.1 (,,c) show the SEM microgrphs of the NiO thin films nneled t different tempertures nd scnned t (1000X) mgnifiction. The microgrphs exhiit scnty non well crystllized grins which incresed in morphosity with increse in nneling temperture [13 ]. Also oserved, is the occurrence of surfce defects in the form of incresing crcks with increse in nneling temperture. c Fig. 3.1 SEM microgrphs of NiO thin films (x1000) nneled t () 100 o C () 200 o C nd (c) 300 o C. Fig. 3.2: EDS of glss/nio thin film nneled t () 100 o C nd () 300 o C

4 12 Brgg s ngle 2θ Brgg s ngle 2θ c d Brgg s ngle 2θ Brgg s ngle 2θ Fig. 3.3 XRD ptterns of NiO thin films nneled in n oven t () 100 o C () 200 o C (c) 300 o C nd (d) As grown. c d Fig. 3.4: Surfce Profile of NiO thin films nneled t () 100 o C () 200 o C (c) 300 o C nd (d) As grown. This could result from inclusions such s Aluminum during processing (fg. 3.2). Thus, preprtion of NiO thin films require gret cre to reduce surfce defects ssocited with inclusions [10]. Figures 3.3 (-d) show the XRD results with no oserved peks nd with the ppernce of smll humps t higher nneling tempertures. This could simply men tht the smples exhiit morphous glssy stte nd the ppernce of humps could indicte tht the nickel

5 oxide thin films hve gone under structurl relxtion nd phse trnsformtion t higher nneling tempertures [13]. Tle 3.1 shows vlues of the film thickness otined from the plots of the surfce profiler, fig.3.4 nd the clculted vlues of electricl properties of the nickel oxide thin films t different nneling tempertures. Figure 3.5 shows the grphicl representtion of the film thickness 13 Tle 3.1: Electricl Properties nd thickness of NiO thin films t different nneling tempertures Smple/Anneling Temperture ( 0 C) Thickness (µm) Resistnce R(Ω) Sheet Resis Tnce Rs(Ω) Resistivity (ρ) (x10 2 Ωm) K(As deposited) K1 (100) K2 (200) K3 (300) Conductivity σ E (x10-4 Ω -1 m -1 ) while the electricl resistivity nd conductivity s functions of the nneling temperture, re shown in fig. 3.6 (, ) respectively. Clerly, the thin film thickness decreses with increse in nneling temperture nd remins firly constnt for nneling temperture of more thn 200 o C while the resistivity decreses s the conductivity increses with increse in the nneling temperture. Film thickness (μm) Anneling Temperture (in 0 C) Fig. 3.5 Vrition of NiO film thickness with temperture

6 14 Resistivity (x10 2 Ωm) Anneling Temperture (in 0 C) () Conductivity (x10 4 m 1 Ω -1 ) Anneling Temperture (in 0 C) () Fig, 3.6: Vritions of electricl properties of NiO thin films with nneling temperture 4. Conclusion Nickel oxide thin films grown y chemicl th deposition hve een chrcterized for their structurl nd electricl properties t different nneling tempertures. The XRD nd SEM results show incresing morphosity of the thin films with nneling temperture. The film thickness decresed from 1.4 μm for s grown smple to 0.75 μm for the smple nneled t 300 o C. The resistivity nd sheet resistnce lso decresed with increse in nneling temperture while the electricl conductivity incresed from 6.50 x 10-4 Ω -1 m -1 for s grown smple to x 10-4 Ω -1 m -1 for the smple nneled t 300 o C. A vriety of inclusions mong them luminum nd silicon were lso detected. References [1] H. Chen, Y. Lu nd W. Hwng, Surfce nd Coting Technology, (2005) [2] A, Fuchs, M. Bogner, K. Shngl, R. Winter, T. Dell nd I. Eisele, Sens. Actutors B. Chem, 47, 145 (1998) [3] T. Miki, K. Yoshimur nd S. Tnemur, Jpn. J. Appl. Phys. 34,240m(1995) [4] A. Tomozw, F. Fujii, H. Torii nd R. Tkym, Jpn. J. Appl. Phys. 35,1328 (1996) [5] B. N. Wng, O. Y. Li, Z. I. Nie, Z. H. Wong, Q. Wei Journl of Culloid Interfce Science, 320, 254 (2005). [6] T. Minmi, H. Sti, S. Tkt nd T Ymd, Thin Solid Films c5 27 ( 1995)

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