Browsing by Author "Cvetkov K."

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    Ab-Initio Molecular Dynamics Simulation of Graphene Sheet
    (2017-02-06) Kolev S.; Balchev I.; Cvetkov K.; Tinchev S.; Milenov T.
    The study of graphene is important because it is a promising material for a variety of applications in the electronic industry. In the present work, the properties of 2D periodic graphene sheet are studied with the use of ab initio molecular dynamics. DFT in the generalized gradient approximation is used in order to carry out the dynamical simulations. The PBE functional and DZVP-MOLOPT basis set are implemented in the CP2K/Quickstep package. A periodic box, consisting of 288 carbon atoms is chosen for the simulations. After geometry optimization it has dimensions 2964 x 2964 x 1500 pm and form angles of 90, 90, 60 degrees. The dynamical simulation is run for 1 ps in the NPT ensemble, at temperature T = 298.15 K. The radial distribution function shows a first peak at 142 pm, marking the bond length between carbon atoms. The density of states for the periodic systems is simulated as occupied orbitals represent the valence band and unoccupied ones the conduction band. The calculated bandgap, as expected is close to 0 eV.
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    Modeling approaches for electron beam lithography
    (2018-10-19) Koleva E.; Vutova K.; Asparuhova B.; Kostic I.; Cvetkov K.; Gerasimov V.
    In this paper, a study based on the mathematical modelling, applying different process simulation tools (CASINO, TREM, SELID) for characterization of PMMA resist and for the improvement of the resolution concerning the critical dimensions of nano-patterning by electron beam lithography (EBL) is presented. Data for important EBL characteristics (energy deposition function, proximity effect parameters, solubility rate, etc.) are obtained by applying different approaches (Monte Carlo methods, regression models, etc.).