Author : Naveen Gupta
Publisher :
ISBN 13 :
Total Pages : 142 pages
Book Rating : 4.:/5 (148 download)
Book Synopsis Realistic Simulation of Slow Processes in Semiconductors and Bio-materials by : Naveen Gupta
Download or read book Realistic Simulation of Slow Processes in Semiconductors and Bio-materials written by Naveen Gupta and published by . This book was released on 2007 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: In the past, the vast majority of studies in the field of materials science have been experimental in nature. With the recent developments in the field of computational materials science, which include faster computer speed, more reliable interatomic potentials and the increased ability of quantum mechanical calculations to handle moderately big systems, computational materials science has been increasingly sought as an aid for research in the field of materials science and allows looking at materials in ways not possible with experiments. Computational modeling of materials allows to design novel materials by virtually predicting their stability and properties, model the evolution of a materials system with time on different scales and evaluate and interpret experimental characterization data. In this work we will touch upon the latter two aspects for two different classes of materials. semiconductors and biomaterials, where the modeling challenge is the time scale. Although atomic-level detail is necessary to understand the formation of the final structures, the system evolution time is much longer than the typical atomic time scale which is given by the time period of the characteristic thermal vibrations and which dictates the maximum time that can be covered by atomic-level simulations. Thus, straightforward molecular dynamics simulation techniques cannot he applied. We will begin with a brief survey of different computational techniques that we use in our study. Next, we look at the problem of arsenic segregation in ion implanted silicon. Generally, arsenic segregation to the Si/SiO2 interface is attributed to binding of arsenic to point defects, which are also made responsible for the dopant deactivation. For even higher concentrations, ordering of the arsenic atoms and eventually precipitation of the SiAs phase can be expected. The plan of action for simulating the segregation process is to find from ab-initio calculations the equilibrium structures and energies of a Si-As system of a given composition and feed these data as input parameters into a continuum model, which is developed by our collaborators at the Fraunhofer Institute of Integrated Systems and Device Technology (IISB) in Erlangen, Germany. In our part of the work, we use ab-initio modeling to study the feasibility of arsenic layer formation and formation of the SiAs phrase in silicon. Starting from a purely substitutional arrangement of arsenic, we move on to arsenic layers and SiAs precipitates. We find that the energetically most favorable configurations are most stable in the neutral charge state. Charged state calculations suggest that at high enough concentrations of arsenic, atoms resulting in a non-silicon neighborhood make arsenic electrically inactive even without the explicit presence of point defects and hence result in dopant dose loss. Recent continuum modeling results from our collaboration based on our data confirm our results and seem to suggest that precipitation, which has not been considered in previous work, is indeed an important part of the deactivation process. Finally, we study the interaction of amino acids (which are the building blocks for proteins in the human body) with carbon nanotubes. DNA-wrapped carbon nanotubes have been recently suggested as a sensor material for application in living cells. In our study with small parts of proteins, we found that after sufficiently long time of molecular dynamics simulation, the protein coils around the in carbon nanotube. We find that the oxygen atoms in the amino acid chains bind to the carbon nanotube. Subsequently we applied Fourier filtering techniques to the molecular dynamics trajectories of these systems to separate the motion of the system corresponding to different time scales and be able to explain the wrapping-mechanisms step by step and to understand the role of the stiffness/floppiness of the different parts of the protein in this process. For that, we worked on optimzing the Fourier filtering technique by studying the effect of different cutoff frequencies on the filtered trajectory of atoms. We then give a qualitative idea about the rigidity of the amino acid chains and the groups present on it from the animation of the original and filtered trajectory for the system and discuss the wrapping process in detail.
