Chemical, Structural and Optical Properties of ē-Beam Evaporated Tungsten Diselenide Polycrystalline Thin Film.docx

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1、Chemical, Structural and Optical Properties of e-Beam./. Nano- Electron. Phys. 4,03001 (2012)KyPHAl HAHO- TA E/lEKTPOHHOi 13HKI1Tom 4 N 3, 03001 (3cc) (2012)Chemical, Structural and Optical Properties of e-Beam Evaporated Tungsten DiselenidePolycrystalline Thin FilmMayur M. Patel z K.D. Patel, V.M.

2、Pathak, R. Srivastava*Department of Phy sics f Sardar Patel University, Vallabh Vidyanagar, 388 12(), Gujara, India(Received 18 June 2012; published online 29 October 2012)Polycrystalline thin films of tungsten diescline were prepared by using rarely reported technique ofelectron beam evaporation fo

3、r transition metal dichalcogenides. High purity (99.999 %) reacted compoundwas used as starting material for the preparation of WSe thin films. Various parameters and conditionsare outlined which were used for deposition of thin films. The prepared films were characterized usingEDAX spectrum, X-ray

4、diffraction, Electron diffraction, Scanning electron microscopy and optical absorp-tion spectroscopy methods. The as grown films were found to be partially transparent, uniform and welladherent. Uniformity was confirmed by SEM. WSe2 film was found in stoichiometric proportion. XRD pat-tern as well a

5、s TEM images revealed the fact that the deposited films are polycrystalline in nature havinghexagonal structure. From the study of optical absorption spectra it is found that the prepared films showdirect allowed transition with optical band gap of 1.89 eV. The results are in good agreement with the

6、 ear-lier published data of VVSe2 thin films deposited by different techniques.Keywords: e-Beam Evaporation, WSe2 Thin Films, Structural analysis, Optical Studies, SEMz TEM.PACS numbers: 68.55ajz 7390 + F03001-3physics.mayur(1. INTRODUCTIONThe various chalcogenide thin films like WSe2zM0Se2z WS2, Cd

7、Sz CdSez and SnSe have been preparedand characterized for structural, optical and electricalstudies by above mention technique l-9. Transitionmetal dichalcogenides like WSe2z M0Se2 etc. can beused to convert solar energy to electrical energy effi-ciently in the thin film structure 10. Tungstendisele

8、nide (WSe2) single cstals and thin films haveattractive properties like bandgap in the range of 1 一2 eV which is most suitable range of energy to tap so-lar spectrum for soalr cell applications. There havebeen several methods like chemical vapour deposition(CVD), R. F. Sputtering, Spray Pyrolysis, E

9、lectrodepo-sition, Solid reaction, Chemical bath deposition (CBD)etc. 1,11-14 which have been reported for the prepa-ration of polycrystalline thin films of tungstendiselenide.Present paper reports the results of our investiga-tions regarding deposition of WSe2 thin films usingelectron beam evaporat

10、ion technique and chemical,structural and optical characterization of preparedfilms. The preparative parameters like, vacuum condi-tion, deposition rate, thickness, deposition temperatureis reported in detailed in this paper.2. EXPERIMENTAL DETAILSThin films of 1732 A were deposited on chemicallyand

11、 ultrasonically cleaned glass substrates with thehelp of 3 kWatt 180 3beam source attached to a box-coater vacuum system (BC-300z Hindhivac-Banglore).All the gadgets of the vacuum chamber were firstcleaned by acetone.2.1 Substrate CleaningThe deposition was done on glass slides of4 inch 2 inch dimen

12、sions. These substrates werecleaned by ultrasonic vibrations followed by washingsuccessively with detergent and acetone.2.2 Source MaterialsAnalytical grade high purity reacted tungstendiselenide powder (99.999 %) was used to prepare thinfilms and it was placed in well cleaned water cooledcopper cru

13、cible.The cleaned substrates were fixed on the substrateholder and digital quartz crystal sensor was placed inclose vicinity to them for the in situ thickness meas-urements. The chamber was evacuated at a pressure of0.5 10 -5T0rr by the combination of rotary and diffu-sion pump. When vacuum of 1() -

14、6 Torr was attained inthe vacuum chamber, the emission current of filamentwas gradually raised to generate electron beam whichis accelerated toward the water cooled crucible with thehelp of magnetic field. The accelerated electrons losetheir energy by colliding to powdered source materialand generat

15、e heat to raise the temperature in excess ofthe melting point of WSe2. This allowed the evapora-tion of WSe2 material. The rate of deposition was keptbetween 1 - 3.5 As -1 till the final thickness of 1.732 kAof deposited films was attained.2.3 Characterization of WSe2 Thin FilmThe thickness of deposited thin films was measuredby in situ digital quartz crystal monitor (Hi-Tech DTM101). The JEOL JSM 5410 SEM with an Oxford LinkIsis-Energy Dispersive X-ray Spectrometer (EDS) wasused for the chemical characterization and electronmicroscopy. The X-ray diffraction analysis of WSe2