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As part of MS Thesis we developed electrostatic simulator for DG SOI devices by implementing the self consistent full band Schrodinger Poisson solver. We used the Empirical Pseudopotential method in conjunction with supercell approach to solve the Schrodinger Equation. EPM was chosen because it has few empirical parameters which give us good accuracy for experimental results. Also EPM is computationally less expensive as compared to the atomistic methods like DFT(Density functional theory) and NEGF (Non-equilibrium Green's function). In our workwe considered two crystallographic orientations of Si,namely [100] and [110].
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This research rst discusses a 2D planar MOSFET simulator and its numerical solver, pointing out its performance limit. By analyzing the algorithm complexity, Multigrid method is proposed to replace conventional Successive-Over-Relaxation method in a numerical solver. A variety of Multigrid methods (standard Multigrid, Algebraic Multigrid, Full Approximation Scheme, and Full Multigrid) are discussed and implemented. Their properties are examined through a set of numerical experiments. Finally, Algebraic Multigrid, Full Approximation Scheme and Full Multigrid are integrated into one advanced numerical solver based on the exact requirements of a semiconductor device simulator. A 2D MOSFET device is used to benchmark the performance, showing that the advanced Multigrid method has higher speed, accuracy and robustness.
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First, the electromechanical properties of 1,4-benzenedithiol molecular junctions are investigate. Counterintuitively, the conductance of this molecule is found to increase by more than an order of magnitude when stretched. This conductance increase is found to be reversible when the molecular junction is compressed. The current-voltage, conductance-voltage and inelastic electron tunneling spectroscopy characteristics are used to attribute the conductance increase to a strain-induced shift in the frontier molecular orbital relative to the electrode Fermi level, leading to resonant enhancement in the conductance.
Next, the effect of stretching-induced structural changes on charge transport in DNA molecules is studied. The conductance of single DNA molecules with lengths varying from 6 to 26 base pairs is measured and found to follow a hopping transport mechanism. The conductance of DNA molecules is highly sensitive to mechanical stretching, showing an abrupt decrease in conductance at surprisingly short stretching distances, with weak dependence on DNA length. This abrupt conductance decrease is attributed to force-induced breaking of hydrogen bonds in the base pairs at the end of the DNA sequence.
Finally, the effect of small mechanical modulation of the base separation on DNA conductance is investigated. The sensitivity of conductance to mechanical modulation is studied for molecules of different sequence and length. Sequences with purine-purine stacking are found to be more responsive to modulation than purine-pyrimidine sequences. This sensitivity is attributed to the perturbation of &pi-&pi stacking interactions and resulting effects on the activation energy and electronic coupling for the end base pairs.
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A 3-D technology computer aided design (TCAD) device simulation is done to compare the performance of FinFET and GAA nanowire structures with vertically stacked horizontal nanowires. Subthreshold slope, DIBL & saturation current are measured and compared between these devices. The FinFET’s device performance has been matched with the ASAP7 compact model with the impact of tensile and compressive strain on NMOS & PMOS respectively. Metal work function is adjusted for the desired current drive. The nanowires have shown better electrostatic performance over FinFETs with excellent improvement in DIBL and subthreshold slope. This proves that horizontal nanowires can be the potential candidate for 5 nm technology node. A GAA nanowire structure for 5 nm tech node is characterized with a gate length of 15 nm. The structure is scaled down from 7 nm node to 5 nm by using a scaling factor of 0.7.
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The coupled electro-thermal approach, initially developed for individual n-channel MOSFET (NMOS) devices, now allows multiple devices in tandem providing a platform for better comparison with heater-sensor experiments. The latest electro-thermal solver allows simulation of multiple NMOS and p-channel MOSFET (PMOS) devices, providing a platform for the study of complementary MOSFET (CMOS) circuit behavior. Modeling PMOS devices necessitates the inclusion of hole transport and hole-phonon interactions. The analysis of CMOS circuits uses the electro-thermal device simulation methodology alongside parametric iteration to ensure current continuity. Simulating a CMOS inverter and analyzing the extracted voltage transfer characteristics verifies the efficacy of this methodology. This work demonstrates the effectiveness of the dual-carrier electro-thermal solver in simulating thermal effects in CMOS circuits.
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It has been suggested that the extended intensity profiles surrounding Bragg reflections that arise when a series of finite crystals of varying size and shape are illuminated by the intense, coherent illumination of an x-ray free-electron laser may enable the crystal’s unit-cell electron density to be obtained ab initio via well-established iterative phasing algorithms. Such a technique could have a significant impact on the field of biological structure determination since it avoids the need for a priori information from similar known structures, multiple measurements near resonant atomic absorption energies, isomorphic derivative crystals, or atomic-resolution data. Here, we demonstrate this phasing technique on diffraction patterns recorded from artificial two-dimensional microcrystals using the seeded soft x-ray free-electron laser FERMI. We show that the technique is effective when the illuminating wavefront has nonuniform phase and amplitude, and when the diffraction intensities cannot be measured uniformly throughout reciprocal space because of a limited signal-to-noise ratio.
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This study explores the capabilities of the Coherent X-ray Imaging Instrument at the Linac Coherent Light Source to image small biological samples. The weak signal from small samples puts a significant demand on the experiment. Aerosolized Omono River virus particles of ∼40 nm in diameter were injected into the submicrometre X-ray focus at a reduced pressure. Diffraction patterns were recorded on two area detectors. The statistical nature of the measurements from many individual particles provided information about the intensity profile of the X-ray beam, phase variations in the wavefront and the size distribution of the injected particles. The results point to a wider than expected size distribution (from ∼35 to ∼300 nm in diameter). This is likely to be owing to nonvolatile contaminants from larger droplets during aerosolization and droplet evaporation. The results suggest that the concentration of nonvolatile contaminants and the ratio between the volumes of the initial droplet and the sample particles is critical in such studies. The maximum beam intensity in the focus was found to be 1.9 × 1012 photons per µm2 per pulse. The full-width of the focus at half-maximum was estimated to be 500 nm (assuming 20% beamline transmission), and this width is larger than expected. Under these conditions, the diffraction signal from a sample-sized particle remained above the average background to a resolution of 4.25 nm. The results suggest that reducing the size of the initial droplets during aerosolization is necessary to bring small particles into the scope of detailed structural studies with X-ray lasers.
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