Effect of Growth Temperature on Chemical …...chemical methods such as chemical vapour deposition (CVD), chemical bath deposition (CBD), electrodeposition, spray pyrolysis, SILAR

___________________________________________________________________________________________

*Corresponding author: Email: [email protected];

International Research Journal of Pure &Applied Chemistry

4(1): 97-107, 2014

SCIENCEDOMAIN internationalwww.sciencedomain.org

Effect of Growth Temperature on ChemicalSynthesis of PbS quantum dots

P. K. Kalita1*, B. Das1 and R. Devi1

1Department of Physics, Nanoscience Research Laboratory, Guwahati College,Guwahati-781 021, Assam, India.

Authors’ contributions

This work was carried out in collaboration between all authors. Author PKK designed thestudy, managed the analyses of the study and wrote the protocol as well as the manuscript.

Author BD had done the experimental and characterization work and author RD managedthe literature searches and made relevant discussion. All authors read and approved the

final manuscript.

Received 24th June 2013Accepted 13th August 2013

Published 11th October 2013

ABSTRACT

PbS quantum dots synthesized at room temperature through CBD technique show alarge blue shift of absorption edge due to formation of very small particle size of the orderof 2nm confirmed by HRTEM measurement. It exhibits a further blue shift whensynthesized in acidic medium (pH 5.5) whereas a red shift for those synthesized inalkaline medium (pH 9.5) on rise of growth temperature up to 355K. PVA is found to playa key role in determination of quantum confinement. At high bath temperature theadditional oxide phases that come into surface are also expected to influence theoptoelectronic properties. Photoluminescence clearly exhibits UV emission at 360nmalong with blue-green emissions at 470nm, 480nm, 490nm and 590nm owing to thedoubly and singly ionized oxygen defects. The electrical conductivity in PbSnanocomposites may be attributed to the carrier tunneling process across the potentialbarriers created primarily between the PbS and oxide nanoparticles. The IR spectroscopyreveals the presence of oxides in PbS nanocomposites.

Keywords: PbS; lead oxides; high temperature bath; hyperbolic band structure.

Original Research Article

International Research Journal of Pure & Applied Chemistry, 4(1): 97-107, 2014

98

1. INTRODUCTION

Lead chalcogenides PbS, PbSe and PbTe and their ternary compounds are of immenseinterest in recent years because of their diverse applications in different type of IR detectors,sensors and other IR electroluminescence devices [1-8]. Lead sulphide has a cubic rock saltstructure and a small band gap 0.41eV. Because of narrow band gap, it has large Bohr radii18nm and small effective mass of electron and hole. It also possesses high carrier mobility(0.44Cm2V-1S-1) and dielectric constant (17.3) [2,8]. These properties provide a third ordernonlinear optical response that makes PbS a suitable nanomaterial for optical and photonicdevice applications [3]. Lead sulphide also have the capability of showing the multipleexciton generation which in turn multiply can increase the photoconversion efficiency up to66% in solar cell [4,8]. As PbS shows strong quantum confinement, therefore there isenough scope for band gap engineering to develop noval nanomaterials suitable foroperating in visible to near infrared regions. Considerable efforts have been devoted todevelop the synthesis of PbS nanoparticles in a controllable manner. Most of the researchworkers use organic as well as inorganic polymers for making strong matrix to stabilize theparticles. Polymers offer an active and flexible medium for organizing nanoclusters. Thecovalent interaction arising from the surface functionality on the clusters and on the suitablegroup on the polymer surface can provide a stable environment for regular dispersion ofshape oriented nanoparticles. In most of the cases the metal is introduced for polymersupport by the reaction of polymer bound functionalities with suitable metal precursors. Metalprecursors can subsequently and conveniently be reduced by varying growth parameters toform either polymer supported nanoparticles or nanoparticles within the polymer. Theparticles embedded in those polymers forms various nanocomposite structures where theflexibility and easy processing can be profitably used for device fabrication. A variety ofchemical methods such as chemical vapour deposition (CVD), chemical bath deposition(CBD), electrodeposition, spray pyrolysis, SILAR etc have been employed for preparation ofPbS nanocrystals [2-6,9-14]. Among those the CBD technique is widely used because of itssimplicity, inexpensive and convenient for large area deposition [4,10-12,15]. However thereare also possibilities to form a variety of oxides because of presence of dissolved as well asatmospheric oxygen atoms if the synthesis is carried out in open environment. The differentoxide traces may co-exist with the prime product in general because of dissolution-precipitation reaction of metal hydroxide in the precursor solution. Hence the study of growthparameters mainly the deposition temperature and pH values along with the capping andsurfacent materials are of considerable interest to control the reaction mechanism to yieldstable and reproducible PbS nanostructures. In the present work PbS nanostructures areprepared through CBD route and a brief report on the effect of bath temperature and pH onthe structural and optical properties has been highlighted.

2. EXPERIMENTAL DETAILS

PbS nanostructures are synthesized through chemical bath deposition method. Equivolumeand equimolar (1M) solution of lead acetate and thiourea were taken for the synthesis. A 3%solution of poly vinyl alcohol (PVA) using as a capping agent was mixed with the lead saltsolution. The mixture solution was stirred under mild heating. Ammonia solution was thenadded to form clear metal complex. The pH values were varied from 5.5 (acidic) to 9.5(alkaline). Equal volume thiourea was the added drop by drop into that solution underconstant stirring to form the final precursor solution. The solubility product of PbS is verysmall. Hence the control precipitation of PbS in the reaction bath is a critical aspect. The


99

control of free Pb++ ions in the solution was done by using ammonia (NH4OH) as complexingagent. The reaction mechanism can be stated as follows [11]

NH2CSNH2 + OH- = CH2N2 + H2O + HS-

HS- + OH- = H2O + S-2

Pb2+ + S-2 = PbS

When the ionic product of Pb2+ and S-2 exceeds the solubility product of PbS, precipitation ofPbS occurs in the precursor solution. On the other hand if the concentration of Pb and OH-

ions in the solution exceeds some critical value, precipitation of PbO starts transformingPb(OH)2 into PbO nanocrystals.

Pb(OH)2 = PbO + H2O

In the present synthesis, lead oxide traces were also found with the PbS. Hence thesolubility of Pb(OH)2 which releases the Pb and OH- ions are expected to be dependentupon the bath temperature and pH of the solution.

For deposition of thin films of respective samples, the glass substrates were first keptovernight in dilute hydrochloric acid then those were washed by rubbing with tissue papersproperly under running distilled water. The substrates were washed several times withdeionized water and finally rinsed in very dilute sodium hydroxide solution. The substrateswere again rinsed with distilled water and dried. Thin films of PbS were allowed to cast onglass substrates by dip coating in the final matrix solution which was maintained at bathtemperature in the range 303K-355K. The structures of prepared PbS quantum dots werecharacterized by XRD (X-Ray Diffraction) and HRTEM (High Resolution TransmissionMicroscopy) whereas the optical properties were studied using UV-VIS absorption, PL(Photoluminescence) and IR (Infra Red) spectroscopy. The I (current)-V (voltage)measurements were done using a Aplab Picometer in gape type film geometry. A printedcircuit board having parallel copper films separated by 1mm was cleaned with sand papers,rubbed with acetone and rinsed with deionized water. The PbS/PVA colloidal film was castedupon two copper electrodes separated by 1mm to form a gape type configuration.

3. RESULTS AND DISCUSSION

3.1 XRD Studies

The X- ray diffraction traces of PbS thin films prepared in acidic and an alkaline medium aredepicted in Figs. 1 and 2. The diffractograms were recorded within the 2 range between 10ºto 80º through X-Ray Powder Diffractometer (Seifert XRD 3003) using Cu K radiation. Thetraces show that the all films are polycrystalline having cubic rock salt type structure which isconfirmed from standard data (ICDD-PDF No:01-072-487). The prominent peaks are foundat (2) 26.05º, 30.15º and 43.25º corresponding to (111), (200) and (220) planes. Rock salttype structure is quite common in chemically synthesized lead sulphide [5,7,9-12,14].

The XRD of room temperature grown PbS films clearly show a broad hump upon which thediffraction peaks appeared. The broad hump may be attributed to the existence of some ofamorphous phase together with that of crystalline structures. On increasing the temperature


100

of precursor solutions up to 355K, the hump completely disappeared and transforming thematerial into a fair crystalline structure irrespective of growth medium either acidic oralkaline. It is observed that the preferred crystal plane orientation are along (111) and (200)for room temperature grown films. The other preferred plane along (220) comes into surfaceafter heat treatment. The diffraction intensity (counts/sec) also increases with the rise oftemperature. However the respective peaks are broaden for films grown in acidic medium.But those become narrower in an alkaline medium along with the more numbers of chemicalbyproducts as a result of fast heterogeneous reaction. It is observed that the heterogeneouschemical reaction started on heat treatment of final matrix solution which is quiteunavoidable for synthesis in open air environment [15]. Because of the heterogeneousreaction of residual lead complex ions with oxygen atoms from atmosphere as well asdissolved oxygen, the lead oxides were formed. The XRD traces after heat treatmentindicate the formation of different prime phases of lead oxides viz: PbO2, Pb2O3, and PbO[16-22]. Lead di oxides have two structures orthorhombic α-PbO2 and tetragonal β-PbO2[16,18].

Fig. 1-3. XRD traces of PbS quantum dots synthesized in acidic (Fig. 1) and alkaline(Fig. 2) medium rising bath temperature from room temperature (300K) to 355K;

HRTEM image of a typical quantum dot (Fig. 3)

In the present case -PbO2 is expected as one of product that can be understood followingits prominent peak positions at 22º and 34º corresponding to orthorhombic crystal planes


101

(011) and (021) respectively. PbO2 is not a stable phase of lead oxide [18]. Therefore thepresences of co-existence of other oxide phases were also seen in the X- ray diffractogramson rise of growth temperature. The intensity and broadening of diffraction peakcorresponding to (2) at 14º for PbO become prominent than those other oxides onincreasing the ambient temperature up to 355K. This clearly signifies the transformation ofstable PbO nanostructures from other forms of oxides. PVA is amorphous in general.However it is expected to improve its crystallinity with the rise of temperature. The (2) at 20ºis therefore attributed to that of PVA [13].

The lattice constants for the synthesized PbS films were calculated and the average valuewas found to be 5.919A which is in good agreement with that of bulk 5.92A. Assumingoverall line broadening due to size, the average crystallite sizes (D) are estimated accordingto Debye-Scherrer formula [ 5,7,9-12]

D= k/ cos

where is the full with at half maximum (FWHM) of the most preferred prominent peak along(111) and K is a constant. The crystallite size are found to decrease from 13nm to 7nm forfilms deposited at pH 5.5 whereas it is in reverse order from 16nm to 24nm for thosedeposited at pH 9.5. This may be attributed to two competent physical processes viz;nanograin growth governed by capping agent PVA and the rate of reaction on rising thetemperature of precursor solution. In the acidic medium as the reaction rate is slow it canpromote the nanograin growth rather than Ostowald reipening [10]. The seed PbS particlesare better confined because of higher mobility of functional groups or ligands of polymer athigh temperature. The lead oxides as a result of heterogeneous oxidation reaction are alsoconfined to have nanosize particles because of that similar effect. Alkaline media cause fastchemical reaction which governs the grain growth mechanism and produces more byproducts as a result of oxidation. As the XRD technique is not sensitive enough to measureparticle size, the sizes are not consistent with that of measured from HRTEM (JEM 2100)image (Fig. 3) and optical absorption. The experiment clearly reveals that the synthesis inopen environment may be carried out at room temperature preferably in acidic medium toyield good reproducible PbS nanocomposites. However it is observed that if the synthesis iscarried out in nitrogen or other inert gas environment, better quality nanostructured PbS mayalso results even at high bath temperature in acidic medium.

3.2 Optical Studies

The absorption spectra of the prepared PbS were taken using a UV-VIS spectrophotometer(Hitachi U3210) as shown in Fig. 4a & 4b. It shows that all samples irrespective of theirgrowth condition exhibit a large blue shift of absorption edge. The absorption edges arefound to be within the range 284nm-291nm which implies an enhancement of band gap from0.41eV (bulk) to 4.44eV-4.55eV. This clearly indicates the occurrence of strong quantumconfinement in these synthesized PbS dots. Similar results are also found by other workers[1-2]. Considering the hyperbolic band structure of PbS, the particle size can be estimatedfrom the equation [1,6]

E=[ Eg2 + 2h2Eg (/R)2/m*]1/2

where E is the increment in band gap energy, m* = 0.085me effective mass and Eg is bulkband gap of PbS. The average particle size (2R) found from above is nearly 1.3nm which is


102

well agreement with the HRTEM measurement. However there is a small change of particlesize with the change of pH and growth temperature as shown in Table 1.

Table 1. Variation of absorption edge, band gap and particle size in fresh andannealed PbS quantum dots

pH 5.5 (acidic) 9.5 (alkaline)Temp. (K) Fresh (303K) Annealed (355K) Fresh (303K) Annealed (355K)a (nm) 289.6 285.6 284.4 291.2Eg (eV) 4.47 4.53 4.55 4.44D (nm) 1.34 1.32 1.31 1.35

HRTEM image (Fig. 3) shows spherical particles having average size about 2nm. Inchemical synthesis initial product molecules are called seeds which subsequently grow insize in a thermodynamically controlled manner to form nanocrystallites. Thesenanocrystallites exhibit the most of physical and chemical properties of the material.However the crystallites have a tendency to grow further in size and if the growthmechanism is not controlled, then due to Ostwald ripening and Van Der Waals interactionsbetween particles, they agglomerate to form bigger structures. Hence the particle sizedistribution is never uniform. Scherrer formula also measures the average crystal size ingeneral that is least of agglomerated particle size. The agglomeration can be arrested byeither stabilizing electrostatically or by inducing steric hindrances at appropriate stages in theprecipitation reaction to achieve size selective synthesis. In the present case the sterichindrance is expected to achieve by the adsorption of PVA molecules on the surface of theparticles. Most of the workers therefore suggest the hyperbolic band theory for a precisemeasurement of size [1-2,6]. The present results agree with the reported values of particlesize less than 2nm when band gap rises to around 4.5eV [1,4]. This suggests that there isstrong coulomb interaction between PbS quantum dots.

Fig. 4. Absorption spectra of fresh and annealed PbS quantum dots synthesized inacidic (a) and alkaline (b) medium


103

It is also seen from absorption spectra that the absorption edge of 289.6nm for fresh roomtemperature grown films in acidic medium is slightly further blue shifted to 285.6nm on riseof growth temperature up to 355K whereas those films grown in alkaline medium red shiftedfrom 284.4nm to 291.2nm. The observation is quite consistent with the respectivebroadening of XRD peaks. This type of reverse effect owing to simultaneous change of pHand growth temperature is not seen earlier. However, the symmetric extended absorptionpeak towards UV region may be attributed to the increase absorption at band-tail states ofPbS-PbO nanocomposites. The band-tail states are caused by the disorder/defects at thelead sulphide and oxide surfaces. A detail study is indeed necessary to understand thehomogeneous growth mechanism of PbS quantum dots governed by polymer cappedprecursor solution.

Fluorescence spectroscopy is a kind of electromagnetic spectroscopy which analysesfluorescence from a sample. The photoluminescence spectrum of PbS nanocompositesprepared in alkaline medium is shown in Fig. 5. A Hitachi f-2500 spectrophotometer with anexcitation wavelength 325nm was used for taking the spectrum. Photoluminescence clearlyexhibits UV emission at 360nm along with blue-green emission at 470nm, 480nm, 490nmand 590nm. The UV emission at 360nm is originated from excitonic recombinationcorresponding to blue shifted near band-gap emission of the PbS-PbO nanocomposites,while the other emission peaks are usually referred to as deep-level or trap- state emissions.It is noted that the UV emission PL peak is quite broad having higher FWHM and is redshifted with respect to that of absorption edge. This difference in transition energy ofemission and absorption spectrum is the stokes shift which reveals the existence of defectstates in the material.

Fig. 5. Photoluminescence spectrum of PbS dots prepared alkaline medium; Insetshows energy levels diagram

Native defects arise from positively charged oxygen vacancy (Vo) and lead interstitial (Pbi)which are electron compensated as well as oxygen interstitial (Oi) and lead vacancy (Vpb)which are hole compensated. Amongst these Vo is the most stable defect and acts as adominant donor species [19]. In the present work the strong blue emission at 470nmcorresponds to the doubly ionized oxygen vacancies in PbS-PbO nanocomposites. Otheremissions at 480nm and 490nm also result from the recombination of photogenerated holeswith the doubly ionized charge states of the oxygen defect [20]. The radiative recombination


104

of photo-generated holes and electrons occupying the singly ionized oxygen vacancies (Vo)may be the cause of that of green emissions at 590nm. An energy level diagram is given inInset of Fig. 5 where 3.49eV is the blue shifted band gap, 2.67eV and 2.13eV are the energylevels corresponding to doubly and singly ionized oxygen defects. Similar PL emissions at370nm, 473nm and 500nm was reported by A V Borhade et al. [20]

Fig. 6. Infrared spectra of PbS dots prepared in acidic (a) and alkaline (b) medium

The IR spectra of prepared PbS in acidic and alkaline medium are shown in Fig. 6. Spectrawere taken using a Perkin Elmer IR Spectrometer. It shows weak and medium Pb-S bondingfor 414cm-1, 424cm-1 and 473.5cm-1 . The spectra exhibit vibrational frequency 3445 cm-1 forOH stretching, 2920 for CH2 stretching, 1595 cm-1 corresponding to vinyl group of dispersedPVA matrix in the precursor solution [3,10]. It also shows 1160cm-1 and 1096 cm-1 means forimproved crystallinity with CO stretching. The spectra also clearly shows the appearance ofadditional vibrational harmonic frequencies 522.6cm-1, 668.6cm-1, 728.7cm-1, 767.9cm-1

which can be assigned to lead oxides[21]. These functional groups exist in all samplesirrespective of present growth conditions. Similar harmonics were also found by Pasha et al[22] in mixed phase PbO nanocrystals.

3.3 Electrical Measurements

The I (current)- V (voltage) characteristics of PbS films were studied in the operating voltagerange -100V to 100V. The curves were linear in the range -20V to 20V and became non-linear afterwards for higher applied bias as shown in the Fig. 7. Nonlinearity leads to arectifying nature at sufficient higher order bias. Linear region is attributed to the ohmicconduction whereas the nonlinearity may arise from different mechanism. Nonlinearbehaviour mainly arises due to thermally activated process, space charge limited conduction


105

(SCLC) process or tunneling effect [14,23-25]. Saraidarov et al studied [23] the I-Vcharacteristics of PbS hybrid films in sandwich type configuration and suggested that therectifying behaviour as a result of resonant tunneling process through the quantizedelectronic states in the conduction band of PbS nanocrystals. As the surface of quantum dotis very sensitive, the surface states dominantly determine the electronic properties. In thepresent work additional potential barriers are expected to form across the interfaces of PbSand those PbO nanoparticles.

Fig. 7. I-V characteristics at 300K (1) and 355K (2) of a typical PbS quantum dots filmprepared in acidic medium. Inset: Measurement technique (E-electrodes; F-film)

The surface states govern the potential barrier and introduce some series resistance in theconduction path. There also exist inter grain boundary barriers that contain grain boundarystates. All these imperfection states act as traps as well as recombination centres and playthe key role in determination of conduction processes. In the present case more number ofrecombination centres is predicted at the barrier of synthesized PbS-PbO nanocompositesand as a result those lower the conductivity. In addition there exist pores, discontinuity andother surface disorders especially in gap type film, which make conductivity becomes lessand as a result a high order of bias is usually required for conduction. At sufficient high biasthe enhancement of current and thereby the nonlinearity may be due to the carrier tunnelingprocess across the potential barriers created primarily between the PbS and oxidenanoparticles.

4. CONCLUSION

PbS nanocrystals are synthesized through chemical bath deposition. The synthesized PbSquantum dots are found to be polycrystalline having prominent planes oriented along (111),(200) and (220) in cubic rock salt type structure. The crystallinity is improved with the rise ofgrowth temperature. The UV-VIS spectra exhibit clear large blue shifts that enhance theband gap energy in the range 4.44eV-4.55eV. This indicates a strong quantum confinement.The average particle size measured from hyperbolic band theory is around 1.34nm which isconsistent with the HRTEM measurement. A rise of growth temperature cause a blue shift ofabsorption edge for PbS synthesized in acidic medium whereas it is red shifted for those in


106

alkaline medium. The optical properties are in well agreement with the respectivebroadening of XRD peaks. Photoluminescence shows band gap emission at 360nm. Astrong blue emission results at 470nm corresponds to the doubly ionized oxygen vacanciesand other a green emission at 590nm is attributed to singly ionized oxygen vacancies inPbS-PbO nanocomposites The IR spectroscopy show the relevant functional groups alongwith PbS stretching as well as the presence of lead oxides. The I-V characteristics showohmic conduction up to low applied bias +20V and thereafter nonlinear in the higher order ofapplied bias. Nonlinearity may be attributed to the tunneling of quantized electronic states inthe conduction bands of mainly PbS quantum dots and across the barriers formed by theinterfaces between PbS dots and lead oxide nanoparticles.

ACKNOWLEDGEMENTS

The authors sincerely thank Indian Institute of Technology, Guwahati and Department ofChemistry, Gauhati University for providing the XRD and optical characterization facilitiesrespectively.

COMPETING INTERESTS

Authors have declared that no competing interests exist.

REFERENCES

1. Lu SW, Schmidt HK. Nanostructures, optical properties and imaging application ofLead sulfide nanocomposite coating. Int J Appl Ceramic Tech. 2004;1(2):119-128.

2. Suresh Babu K, Vijayan C, Devanathan R, Strong quantum confinement effect inpolymer based PbS nanostructures prepared by ion exchange method. Mater. lett.2004;58:1223-1226.

3. Wise FW. Lead salt quantum dots: the limit of strong quantum confinement. Acc ChemRes. 2000;33:773-780

4. Askari M, Ghamsari MS. Anew colloidal techniques for the synthesis of Lead Sulfidenanoparticles. Scientia Iranica. 2003;10(3):357-360.

5. Mispa KJ, Subramanium P, Murugesan R. Microwave-assisted route for synthesis ofnanosized metal sulfides. Chalcogenide lett. 2010;7:335-340.

6. Zhang B, Li G, Zhang J, Zhang Y, Zhang L. Synthesis and characterization of PbSnanocrystals in water/C12E9/cyclohexane microemulsions. Nanotechnology.2003;14:443-446.

7. Bakueva L, Gorelikov I, Musikhin S, Zhao XS, Sargent EH, Kumacheva E. PbSQuantum dots with stable efficient luminescence in the near IR spectral range. Adv.Mater 2004;16(11):926-929.

8. Akhter J, Malik MA, O'Brien P, Wijayantha KGU, Dharmadasa R Hardman SJO, et al.A greener route to photo electrochemically active PbS nanoparticles. J Mater Chem.2010;20:2336-2344.

9. Bai H-J, Zhang Z-M. Microbial synthesis of semiconductor lead sulfide nanoparticlesusing immoblizied Rhodabacter sphaeroides. Mater Lett. 2009;63:764-766.

10. Kumar D, Agrawal G, Tripathi B, Vyas D, Kulshrestha V. Characterization of PbSnanoparticles synthesized by chemical bath deposition. J Alloys Compd.2009;484:463-466.


107

11. Jana S, Thapa R, Maity R, Chottopadhyay KK. Optical and dielectric properties of PVAcapped nanocrystalline PbS thin films synthesized by chemical bath deposition.Physica E. 2008;40:3121-3126.

12. Patil RS, Pathan HM, Gujar TP, Lokhande CD. Characterization of chemicallydeposited nanocrystalline PbS thin films. J Mater Sci. 2006;41:5723-5725.

13. Kalita PK. Structural and optical properties of chemically synthesised PbSe nanorods.Res J Mater Sci. 2013;1:26-30.

14. Atwa DMM, Azzouz IM, Badir Y. Optical structural and optoelectronic properties ofpulsed laser deposition PbS thin films. Appl Phys B. 2011;103:161-164.

15. Bhattacharyya B, Kalita PK, Datta P. Structral characterization of CdSe and ZnSenanoparticles AIP Conf. Proc. 2010;1276:124-130.

16. Singh DP, Srivastava ON. Synthesis of micron-sized hexagonal and flower likenanostructures of lead oxide (PbO2) by anodic oxidation of lead. Nano-Micro lett.2011;3(4):223-227

17. Wang H. Electrochemical perfomance of synthesis of nanostructured lead oxide. ModAppl Sci. 2010;4(4):116-121.

18. Choi YC, Kim J, Bu SD, Yun YJ. Synthesis of crystalline lead di-oxide nanowires andtheir electron-beam-induced phase transformation to oxygen deficient lead mono-oxide. J Kor Phys Soc. 2007;51(6):2045-2050.

19. Scanlon DO, Kehoe AB, Watson GW, Jones MO, David IF, Payne DJ, et al Nature ofband gap and origin of conductivity of PbO2 revealed by theory and experiment. PRL.2011;107:246402(5).

20. Borhade AB, Tope DR, Uphade BK. An efficient photocatalytic degradation of methylblue dye by using synthesised PbO nanoparticles. E-J Chem. 2012;9:705-715.

21. Wu ZJ. Theoretical study of PbS, PbO and their anions. Chem Phys Lett.2003;370:39-43.

22. Pasha SK, Chidambaram K, Vijyan N, Madhuri W. Structural and electrical propertiesof nanostructure lead oxide. Optoectronic and Adv. Mater-Rapid Comm. 2012;6:110-116.

23. Saraidarov T, Reisfeld R, Sashchiuk A, Lifshitz E. Nanocrystallites of lead su;fide inhybrid films prepared by sol-gel process. J Sol-gel Sci Tech. 2005;34:137-145.

24. Jiang P, Liu Z-F, Cai S-M. Single Electron tunneling in a single PbS nanocrystalsnucleated on 11-Mercaptoundecanoic acid self-assembled monolayer at roomtemperature. J Appl Phys. 2001;90(1):2039-2041.

25. Deen MJ, Paskal F. Electrical characterization of semiconductor materials anddevices-review. J Mater Sci. Mater Electron. 2006;17:549-575.

_________________________________________________________________________© 2014Kalita et al.; This is an Open Access article distributed under the terms of the Creative Commons AttributionLicense (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproductionin any medium, provided the original work is properly cited.

Peer-review history:The peer review history for this paper can be accessed here:

http://www.sciencedomain.org/review-history.php?iid=277&id=7&aid=2250

Documents

Effect of Growth Temperature on Chemical …...chemical methods such as chemical vapour deposition (CVD), chemical bath deposition (CBD), electrodeposition, spray pyrolysis, SILAR