Density functional investigation of nano-structures

Üzengi Aktürk, Olcay
In this thesis, we first investigate the physical properties of some metal atoms, molecules and their clusters. We then study the interaction of these with silicon and graphene surfaces. The adsorption of NH3 and H2S molecules on Au3Pt3 is also studied. We calculate the equilibrium atomic structures of metal clusters using density functional theory (DFT) up to eight atoms. The electronic structures of these free and adsorbed clusters are also calculated in detail. We find that the adsorption generally modifies the structure of the Au3Pt3 cluster and the adsorbate (NH3 and H2S ). We also study the site-dependent shapes of the Au8 cluster, associated adsorption energies, band structures and the corresponding charge distribution for the S i(100) asymmetric surface. We show that the electronic properties of the cluster and the substrate complex change with the location of the cluster on the surface. We study the AunPtn clusters on graphene surface. We observe that graphene can be metallic or semiconducting depending on the number of Au and Pt atoms in the cluster and the charge transfer between the cluster and the graphene. We have studied bismuth both as an adsorbate and substitutional dopant in graphene. We have shown that bismuth causes a weak p-type doping for the adsorption case within generalized gradient approximation (GGA), but it n-dopes graphene when it is substitutional and for the adsorption case within local density approximation (LDA). Our results are in agreement with recent angle-resolved photoemission results for the weak adsorption.


Design and production of antireflection coating for Ge, ZnSe and ZnS in 8-12 micrometer wavelength region
Üçer, Begüm; Parlak, Mehmet; Department of Physics (2009)
This thesis describes the works done during the design and deposition process of the antireflection coating for the materials commonly used as refractive optical elements in thermal imaging systems. These coatings are quite necessary to reduce reflection losses from the surface of the optics and stray light that directly affects the image quality. Germanium, zinc sulfide and zinc selenide were used as substrate material and their optical properties were investigated with infrared ellipsometry and FTIR. Anti...
Optical properties of silicon based amorphous thin films
Akaoğlu, Barış; Katırcıoğlu, Bayram; Department of Physics (2004)
Silicon based hydrogenated amorphous semiconducting (intrinsic and n/p doped a-Si:H and a-Si1-xCx:H) thin films have been deposited by plasma enhanced chemical vapor deposition (PECVD) system. In order to analyze the optical response of these amorphous films, intrinsic optical absorption mechanisms have resumed and spectral variations of absorption coefficient ?(E) are derived. The exponential variation of absorption coefficient for energies below the band edge is discussed in the frame of randomly distribu...
A continuum model for decoherence in 1D transport
Şenozan, Selma; Turgut, Sadi; Department of Physics (2005)
In this thesis we study the conductance of a one dimensional conductor in the presence of dephasing. Dephasing effects are modelled after generalizing Büttiker̕s dephasing model (Phys. Rev. B 33, 3020 (1986)) to a continuous one. Infinitely many electron reservoirs are coupled to the conductor as phase breakers and the method for calculating the conductance is presented. We investigate how this continuum decoherence effect the conductance of a wire, with single and double rectangular barriers.
Dynamic ion behavior in plasma source ion implantation
Bozkurt, Bilge; Bilikmen, Kadri Sinan; Department of Physics (2006)
The aim of this work is to analytically treat the dynamic ion behavior during the evolution of the ion matrix sheath, considering the industrial application plasma source ion implantation for both planar and cylindrical targets, and then to de-velop a code that simulates this dynamic ion behavior numerically. If the sepa-ration between the electrodes in a discharge tube is small, upon the application of a large potential between the electrodes, an ion matrix sheath is formed, which fills the whole inter-ele...
Development of atomic force microscopy system and kelvin probe microscopy system for use in semiconductor nanocrystal characterization
Bostancı, Umut; Turan, Raşit; Department of Physics (2007)
Atomic Force Microscopy (AFM) and Kelvin Probe Microscopy (KPM) are two surface characterization methods suitable for semiconductor nanocrystal applications. In this thesis work, an AFM system with KPM capability was developed and implemented. It was observed that, the effect of electrostatic interaction of the probe cantilever with the sample can be significantly reduced by using higher order resonant modes for Kelvin force detection. Germanium nanocrystals were grown on silicon substrate using different g...
Citation Formats
O. Üzengi Aktürk, “Density functional investigation of nano-structures,” Ph.D. - Doctoral Program, Middle East Technical University, 2010.