بررسي لايه نازك WS2 روي سطح (101)TiO2

چكيده انگليسي :

AbstractDensity Functional eory DFT is a computational quantum me anical modeling method is theory is one of the most successful theories in computational physics emistry andmaterials science DFT was used in this thesis e rst apter begins with a brief explanation of the main motivation to start this project T iO2 and W S2 compounds are two a ractive materials with unique properties whi havebeen studied and investigated in the previous decades e curiosity for investigation of thesesemiconductors in contact with ea other led us to start the project through the investigationof the surface contact between the two semiconductors T iO2 and W S2 semiconductors havebeen introduced in the rest of apter 1 and their signi cant properties and applications havealso been enumerated Chapter 2 addresses the primary calculations Kohn Sham and Pseudo Potential approa eshave brie y introduced at the beginning and the parameter optimization process for necessaryparameters have been explained La ice constants and energy cuto were optimized and theenergy volume diagram ed with respect to the Murnaghon equations of states e ingprocess resulted the equilibrium volume and the volume module of T iO2 bulk and repeatingthe same process for Ultra so and PAW pseudo potentials made the pseudo potentials judi cable Some electronic calculations of T iO2 bulk will be discussed at the end of apter 2 According to the main purpose of the project the T iO2 101 surface in the two di erentTitanium termination and Oxygen termination were simulated and the behavior of ea onewas investigated e T iO2 101 surface with Ti termination was osen for further calcu lations e next step in the simulation of T iO2 W S2 thin lm system is to place a W S2mono layer on the T iO2 101 surface e taking place process encountered with some con vergence problems and needed a suitable solution Some di erent suggestions were proposedand applied applying dipole correction taking place the W S2 layers step by step an S layer then a W layer and eventually an S layer on the T iO2 101 surface and relaxing W S2 con gurations before taking place on the surface A er examining all three propositions thesolution for the problem turned out to be the last option relaxing W S2 con gurations beforetaking place on the surface whi subsequently was used both manually and through US PEX structure predictor in order to nd the stable W S2 con gurations ereupon using thethird advice and the transition path calculations NEB method we found 8 di erent meta stable T iO2 W S2 con gurations whi were studied precisely First of all the stability ofthe con gurations was e ed whi all of them succeeded in the stability test e electrondensity of the con gurations was calculated and plo ed whi showed a metallic behavior inthe system erefore in order to correct the metallic behavior the conventional method forapplying strain was used and the obtained results were discussed e interface of T iO2 W S2 system has been explained in the nal apter as well e inter face investigations contain the relation between the con gurations stability and the geometryof the structures the relation between stability and bond lengths electron density and den sity of states DOS Hence a good sight about stability the bonds in the interface and theirqualities were a ieved Finally the transition paths between di erent con gurations and thepossibility for experimental synthesizebility of these con gurations were calculated and dis cussed Key words Density Functional eory ab initio calculations Titanium Dioxide T iO2 Tungsten Disul de

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بررسي لايه نازك WS2 روي سطح (101)TiO2

نظريه تابعي چگالي , محاسبات ابتدا به ساكن , مواد دوبعدي , TMDC ها , لايه نشاني , محاسبات مسير گذار (NEB)