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2013

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Articles 1 - 30 of 107

Full-Text Articles in Nanoscience and Nanotechnology

Biogenic Synthesis, Photocatalytic, And Photoelectrochemical Performance Of Ag–Zno Nanocomposite, S. A. Ansari, Mohammad Mansoob Khan Dr, M. O. Ansari, J. Lee, M. H. Cho Dec 2013

Biogenic Synthesis, Photocatalytic, And Photoelectrochemical Performance Of Ag–Zno Nanocomposite, S. A. Ansari, Mohammad Mansoob Khan Dr, M. O. Ansari, J. Lee, M. H. Cho

Dr. Mohammad Mansoob Khan

The development of coupled photoactive materials (metal/semiconductor) has resulted in significant advancements in heterogeneous visible light photocatalysis. This work reports the novel biogenic synthesis of visible light active Ag–ZnO nanocomposite for photocatalysis and photoelectrode using an electrochemically active biofilm (EAB). The results showed that the EAB functioned as a biogenic reducing tool for the reduction of Ag+, thereby eliminating the need for conventional reducing agents. The as-prepared Ag–ZnO nanocomposite was characterized by X-ray diffraction, transmission electron microscopy, diffuse reflectance spectroscopy, photoluminescence spectroscopy, and X-ray photoelectron spectroscopy. The photocatalytic experiments showed that the Ag–ZnO nanocomposite possessed excellent visible light photocatalytic activity …

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Vapor–Liquid–Solid Growth Of Serrated Gan Nanowires: Shape Selection Driven By Kinetic Frustration, Zheng Ma, Dillon Mcdowell, Eugen Panaitescu, Albert V. Davydov, Moneesh Upmanyu, Latika Menon Dec 2013

Vapor–Liquid–Solid Growth Of Serrated Gan Nanowires: Shape Selection Driven By Kinetic Frustration, Zheng Ma, Dillon Mcdowell, Eugen Panaitescu, Albert V. Davydov, Moneesh Upmanyu, Latika Menon

Moneesh Upmanyu

Compound semiconducting nanowires are promising building blocks for several nanoelectronic devices yet the inability to reliably control their growth morphology is a major challenge. Here, we report the Au-catalyzed vapor–liquid–solid (VLS) growth of GaN nanowires with controlled growth direction, surface polarity and surface roughness. We develop a theoretical model that relates the growth form to the kinetic frustration induced by variations in the V(N)/III(Ga) ratio across the growing nanowire front. The model predictions are validated by the trends in the as-grown morphologies induced by systematic variations in the catalyst particle size and processing conditions. The principles of shape selection highlighted …

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A Study Of Titania Nanotube Synthesis In Chloride-Ion-Containing Media, E. Panaitescu, C. Richter, L. Menon Dec 2013

A Study Of Titania Nanotube Synthesis In Chloride-Ion-Containing Media, E. Panaitescu, C. Richter, L. Menon

Eugen Panaitescu

We have completed a detailed experimental investigation into the recently discovered synthesis of titania nanotubes in chloride-ion-containing media. We show that the role of the chloride ions is catalytic and it has a strong effect in increasing the reactivity of the solution, while the nature of cations has no visible role. We have identified the critical parameters for optimal growth and fast production of nanotubes, and a basic growth mechanism for the tubes is proposed. This opens routes for significant improvements of the method toward uniformity and/or better overall yield, making it a viable alternative to the present established methods.

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Toward Tailored Functionality Of Titania Nanotube Arrays: Interpretation Of The Magnetic-Structural Correlations, Pegah M. Hosseinpour, Eugen Panaitescu, Don Heiman, Latika Menon, Laura H. Lewis Dec 2013

Toward Tailored Functionality Of Titania Nanotube Arrays: Interpretation Of The Magnetic-Structural Correlations, Pegah M. Hosseinpour, Eugen Panaitescu, Don Heiman, Latika Menon, Laura H. Lewis

Eugen Panaitescu

Ordered arrays of titania nanotubes (NTs) are considered as good candidates for photocatalytic applications including water splitting. Considering that the functionality of these nanostructures is influenced by their morphology, electronic and the crystallographic structure, fundamental understanding of these properties and their possible correlations can clarify the approaches toward enhanced photocatalytic efficiency. In this work, ordered arrays of titania NTs are synthesized electrochemically and are subjected to isochronal annealing treatments in various atmospheres (oxygen-rich, oxygen-deficient and reducing) to modify their morphology, crystal and electronic structure. Upon characterization of these NTs, direct correlations are found between the annealing atmosphere and the corresponding …

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Vapor–Liquid–Solid Growth Of Serrated Gan Nanowires: Shape Selection Driven By Kinetic Frustration, Zheng Ma, Dillon Mcdowell, Eugen Panaitescu, Albert V. Davydov, Moneesh Upmanyu, Latika Menon Dec 2013

Vapor–Liquid–Solid Growth Of Serrated Gan Nanowires: Shape Selection Driven By Kinetic Frustration, Zheng Ma, Dillon Mcdowell, Eugen Panaitescu, Albert V. Davydov, Moneesh Upmanyu, Latika Menon

Eugen Panaitescu

Compound semiconducting nanowires are promising building blocks for several nanoelectronic devices yet the inability to reliably control their growth morphology is a major challenge. Here, we report the Au-catalyzed vapor–liquid–solid (VLS) growth of GaN nanowires with controlled growth direction, surface polarity and surface roughness. We develop a theoretical model that relates the growth form to the kinetic frustration induced by variations in the V(N)/III(Ga) ratio across the growing nanowire front. The model predictions are validated by the trends in the as-grown morphologies induced by systematic variations in the catalyst particle size and processing conditions. The principles of shape selection highlighted …

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Toward Tailored Functionality Of Titania Nanotube Arrays: Interpretation Of The Magnetic-Structural Correlations, Pegah M. Hosseinpour, Eugen Panaitescu, Don Heiman, Latika Menon, Laura H. Lewis Dec 2013

Toward Tailored Functionality Of Titania Nanotube Arrays: Interpretation Of The Magnetic-Structural Correlations, Pegah M. Hosseinpour, Eugen Panaitescu, Don Heiman, Latika Menon, Laura H. Lewis

Donald Heiman

Ordered arrays of titania nanotubes (NTs) are considered as good candidates for photocatalytic applications including water splitting. Considering that the functionality of these nanostructures is influenced by their morphology, electronic and the crystallographic structure, fundamental understanding of these properties and their possible correlations can clarify the approaches toward enhanced photocatalytic efficiency. In this work, ordered arrays of titania NTs are synthesized electrochemically and are subjected to isochronal annealing treatments in various atmospheres (oxygen-rich, oxygen-deficient and reducing) to modify their morphology, crystal and electronic structure. Upon characterization of these NTs, direct correlations are found between the annealing atmosphere and the corresponding …

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Toward Tailored Functionality Of Titania Nanotube Arrays: Interpretation Of The Magnetic-Structural Correlations, Pegah M. Hosseinpour, Eugen Panaitescu, Don Heiman, Latika Menon, Laura H. Lewis Dec 2013

Toward Tailored Functionality Of Titania Nanotube Arrays: Interpretation Of The Magnetic-Structural Correlations, Pegah M. Hosseinpour, Eugen Panaitescu, Don Heiman, Latika Menon, Laura H. Lewis

Laura H. Lewis

Ordered arrays of titania nanotubes (NTs) are considered as good candidates for photocatalytic applications including water splitting. Considering that the functionality of these nanostructures is influenced by their morphology, electronic and the crystallographic structure, fundamental understanding of these properties and their possible correlations can clarify the approaches toward enhanced photocatalytic efficiency. In this work, ordered arrays of titania NTs are synthesized electrochemically and are subjected to isochronal annealing treatments in various atmospheres (oxygen-rich, oxygen-deficient and reducing) to modify their morphology, crystal and electronic structure. Upon characterization of these NTs, direct correlations are found between the annealing atmosphere and the corresponding …

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Toward Tailored Functionality Of Titania Nanotube Arrays: Interpretation Of The Magnetic-Structural Correlations, Pegah M. Hosseinpour, Eugen Panaitescu, Don Heiman, Latika Menon, Laura H. Lewis Dec 2013

Toward Tailored Functionality Of Titania Nanotube Arrays: Interpretation Of The Magnetic-Structural Correlations, Pegah M. Hosseinpour, Eugen Panaitescu, Don Heiman, Latika Menon, Laura H. Lewis

Latika Menon

Ordered arrays of titania nanotubes (NTs) are considered as good candidates for photocatalytic applications including water splitting. Considering that the functionality of these nanostructures is influenced by their morphology, electronic and the crystallographic structure, fundamental understanding of these properties and their possible correlations can clarify the approaches toward enhanced photocatalytic efficiency. In this work, ordered arrays of titania NTs are synthesized electrochemically and are subjected to isochronal annealing treatments in various atmospheres (oxygen-rich, oxygen-deficient and reducing) to modify their morphology, crystal and electronic structure. Upon characterization of these NTs, direct correlations are found between the annealing atmosphere and the corresponding …

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Vapor–Liquid–Solid Growth Of Serrated Gan Nanowires: Shape Selection Driven By Kinetic Frustration, Zheng Ma, Dillon Mcdowell, Eugen Panaitescu, Albert V. Davydov, Moneesh Upmanyu, Latika Menon Dec 2013

Vapor–Liquid–Solid Growth Of Serrated Gan Nanowires: Shape Selection Driven By Kinetic Frustration, Zheng Ma, Dillon Mcdowell, Eugen Panaitescu, Albert V. Davydov, Moneesh Upmanyu, Latika Menon

Latika Menon

Compound semiconducting nanowires are promising building blocks for several nanoelectronic devices yet the inability to reliably control their growth morphology is a major challenge. Here, we report the Au-catalyzed vapor–liquid–solid (VLS) growth of GaN nanowires with controlled growth direction, surface polarity and surface roughness. We develop a theoretical model that relates the growth form to the kinetic frustration induced by variations in the V(N)/III(Ga) ratio across the growing nanowire front. The model predictions are validated by the trends in the as-grown morphologies induced by systematic variations in the catalyst particle size and processing conditions. The principles of shape selection highlighted …

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Computational Nanoelectronics Research And Education At Nanohub.Org, Benjamin P. Haley, Gerhard Klimeck, Mathieu Luisier, Dragica Vasileska, Abhijeet Paul, Swaroop Shivarajapura, Diane L. Beaudoin Nov 2013

Computational Nanoelectronics Research And Education At Nanohub.Org, Benjamin P. Haley, Gerhard Klimeck, Mathieu Luisier, Dragica Vasileska, Abhijeet Paul, Swaroop Shivarajapura, Diane L. Beaudoin

Gerhard Klimeck

The simulation tools and resources available at nanoHUB.org offer significant opportunities for both research and education in computational nanoelectronics. Users can run simulations on existing powerful computational tools rather than developing yet another niche simulator. The worldwide visibility of nanoHUB provides tool authors with an unparalleled venue for publishing their tools. We have deployed a new quantum transport simulator, OMEN, a state-of-the-art research tool, as the engine driving two tools on nanoHUB. The educational resources of nanoHUB are one fo the most important aspects of the project, according to user surveys. new collections of tools into unified curricula have found …

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Structures And Energetics Of Si Nanotubes From Molecular Dynamics And Density Functional Theory, Amritanshu Palaria, Gerhard Klimeck, Alejandro Strachan Nov 2013

Structures And Energetics Of Si Nanotubes From Molecular Dynamics And Density Functional Theory, Amritanshu Palaria, Gerhard Klimeck, Alejandro Strachan

Gerhard Klimeck

We use molecular dynamics (MD) with a first principles-based force field (ReaxFF) and density functional theory (DFT) to predict the atomic structure, energetics and elastic propoerties of Si nanotubes. We find various low-energy and low-symmetry hollow structures with external diameters of about 1 nm. These are the most stable structures in this small-diameter regime reported so far and exhibit properties very different from the bulk. While the cohesive energies of the four most stable nanotubes reported here are similar (from 0.638 to 0.697 eV above bulk Si), they have disparate Young's moduli (from 72 to 123 GPa).

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Interface Trap Density Metrology From Sub-Threshold Transport In Highly Scaled Undoped Si N-Finfets, Abhijeet Paul, Giuseppe C. Tettamanz, Sunhee Lee, Saumitra R. Mehrotra, Nadine Collaert, Serge Biesemans, Sven Rogge, Gerhard Klimeck Nov 2013

Interface Trap Density Metrology From Sub-Threshold Transport In Highly Scaled Undoped Si N-Finfets, Abhijeet Paul, Giuseppe C. Tettamanz, Sunhee Lee, Saumitra R. Mehrotra, Nadine Collaert, Serge Biesemans, Sven Rogge, Gerhard Klimeck

Gerhard Klimeck

Channel conductance measurements can be used as a tool to study thermally activated electron transport in the sub-threshold region of state-of-art FinFETs. Together with theoretical Tight- Binding (TB) calculations, this technique can be used to understand the evolution of source-to- channel barrier height (Eb) and of active channel area (S) with gate bias (Vgs). The quantitative difference between experimental and theoretical values that we observe can be attributed to the interface traps present in these FinFETs. Therefore, based on the difference between measured and calculated values of (i) S and (ii) |∂Eb/∂Vgs| (channel to gate coupling), two new methods of …

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Enhanced Valence Force Field Model For The Lattice Properties Of Gallium Arsenide, Sebastian Steiger, Mehdi Salmani-Jelodar, Denis Areshkin, Abhijeet Paul, Tillmann Kubis, Michael Povolotskyi, Hong-Hyun Park, Gerhard Klimeck Nov 2013

Enhanced Valence Force Field Model For The Lattice Properties Of Gallium Arsenide, Sebastian Steiger, Mehdi Salmani-Jelodar, Denis Areshkin, Abhijeet Paul, Tillmann Kubis, Michael Povolotskyi, Hong-Hyun Park, Gerhard Klimeck

Gerhard Klimeck

An enhanced valence force field model for zinc-blende crystals is developed to provide a unified description of the isothermal static and dynamical lattice properties of gallium arsenide. The expression for the lattice energy includes a second-nearest-neighbor coplanar interaction term, the Coulomb interaction between partially charged ions, and anharmonicity corrections. General relations are derived between the microscopic force constants and the macroscopic elastic constants in zinc-blende crystals. Applying the model to gallium arsenide, parameter sets are presented that yield quantitative agreement with experimental results for the phonon dispersion, elastic constants, sound velocities, and Gru ̈neisen mode parameters.

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Rate Equations From The Keldysh Formalism Applied To The Phonon Peak In Resonant-Tunneling Diodes, Roger Lake, Gerhard Klimeck, Supriyo Datta Nov 2013

Rate Equations From The Keldysh Formalism Applied To The Phonon Peak In Resonant-Tunneling Diodes, Roger Lake, Gerhard Klimeck, Supriyo Datta

Gerhard Klimeck

Starting from the Keldysh formalism, general analytical expressions are derived for the current and the occupation of the well in the presence of inelastic scattering, both at the main peak and at the pho- non peak. These expressions are then evaluated from a continuous coordinate representation of a double-barrier potential profile and also from a tight-binding model of a weakly coupled central site. The resulting expressions are similar, and the analytical expressions derived from the continuous coordi- nate representation compare well with the results obtained from numerical simulations. The analytical expressions and the numerical results show that unlike the main …

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Atomistic Study Of Electronic Structure Of Pbse Nanowires, Abhijeet Paul, Gerhard Klimeck Nov 2013

Atomistic Study Of Electronic Structure Of Pbse Nanowires, Abhijeet Paul, Gerhard Klimeck

Gerhard Klimeck

Lead Selenide (PbSe) is an attractive ‘IV-VI’ semiconductor material to design optical sensors, lasers and thermoelectric devices. Improved fabrication of PbSe nanowires (NWs) enables the utilization of low dimensional quantum effects. The effect of cross-section size (W) and channel orientation on the bandstructure of PbSe NWs is studied using an 18 band sp3d5 tight-binding theory. The bandgap increases almost with the inverse of the W for all the orientations indicating a weak symmetry dependence. [111] and [110] NWs show higher ballistic conductance for the conduction and valence band compared to [100] NWs due to the significant splitting of the projected …

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Performance Analysis Of Statistical Samples Of Graphene Nanoribbon Tunneling Transistors With Line Edge Roughness, Mathieu Luisier, Gerhard Klimeck Nov 2013

Performance Analysis Of Statistical Samples Of Graphene Nanoribbon Tunneling Transistors With Line Edge Roughness, Mathieu Luisier, Gerhard Klimeck

Gerhard Klimeck

Using a three-dimensional, atomistic quantum transport simulator based on the tight-binding method, we investigate statistical samples of single-gate graphene nanoribbon (GNR) tunneling field-effect transistors (TFETs) with different line edge roughness probabilities. We find that as the nanoribbon edges become rougher, the device OFF-current drastically increases due to a reduction of the graphene band gap and an enhancement of source-to-drain tunneling leakage through the gate potential barrier. At the same time, the ON-current remains almost constant. This leads to a deterioration of the transistor subthreshold slopes and to unacceptably low ON/OFF current ratios limiting the switching performances of GNR TFETs.

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Spin-Valley Lifetimes In A Silicon Quantum Dot With Tunable Valley Splitting, C. H. Yang, A. Rossi, R. Ruskov, N. S. Lai, F. A. Mohiyaddin, S. Lee, C. Tahan, Gerhard Klimeck, A. Morello, A. S. Dzurak Nov 2013

Spin-Valley Lifetimes In A Silicon Quantum Dot With Tunable Valley Splitting, C. H. Yang, A. Rossi, R. Ruskov, N. S. Lai, F. A. Mohiyaddin, S. Lee, C. Tahan, Gerhard Klimeck, A. Morello, A. S. Dzurak

Gerhard Klimeck

Although silicon is a promising material for quantum computation, the degeneracy of the conduction band minima (valleys) must be lifted with a splitting sufficient to ensure the formation of well-defined and long-lived spin qubits. Here we demonstrate that valley separation can be accurately tuned via electrostatic gate control in a metal-oxide-semiconductor quantum dot, providing splittings spanning 0.3-0.8 meV. The splitting varies linearly with applied electric field, with a ratio in agreement with atomistic tight-binding predictions. We demonstrate single-shot spin read-out and measure the spin relaxation for different valley configurations and dot occupancies, finding one-electron lifetimes exceeding 2 s. Spin relaxation …

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Engineered Valley-Orbit Splittings In Quantum-Confined Nanostructures In Silicon, Rajib Rahman, J. Verdujin, Neerav Kharche, Gabriel Lansbergen, Purdue University Gerhard Klimeck, Lloyd Hollenberg, Sven Rogge Nov 2013

Engineered Valley-Orbit Splittings In Quantum-Confined Nanostructures In Silicon, Rajib Rahman, J. Verdujin, Neerav Kharche, Gabriel Lansbergen, Purdue University Gerhard Klimeck, Lloyd Hollenberg, Sven Rogge

Gerhard Klimeck

An important challenge in silicon quantum electronics in the few electron regime is the poten- tially small energy gap between the ground and excited orbital states in 3D quantum confined nanostructures due to the multiple valley degeneracies of the conduction band present in silicon. Understanding the “valley-orbit” (VO) gap is essential for silicon qubits, as a large VO gap prevents leakage of the qubit states into a higher dimensional Hilbert space. The VO gap varies considerably depending on quantum confinement, and can be engineered by external electric fields. In this work we investigate VO splitting experimentally and theoretically in a …

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Simulation Of Nanowire Tunneling Transistors: From The Wentzel-Kramers-Brillouin Approximation To Full-Band Phonon-Assisted Tunneling, Mathieu Luisier, Gerhard Klimeck Nov 2013

Simulation Of Nanowire Tunneling Transistors: From The Wentzel-Kramers-Brillouin Approximation To Full-Band Phonon-Assisted Tunneling, Mathieu Luisier, Gerhard Klimeck

Gerhard Klimeck

Nanowire band-to-band tunneling field-effect transistors 􏰀TFETs􏰁 are simulated using the Wentzel– Kramers–Brillouin 􏰀WKB􏰁 approximation and an atomistic, full-band quantum transport solver including direct and phonon-assisted tunneling 􏰀PAT􏰁. It is found that the WKB approximation properly works if one single imaginary path connecting the valence band 􏰀VB􏰁 and the conduction band 􏰀CB􏰁 dominates the tunneling process as in direct band gap semiconductors. However, PAT is essential in Si and Ge nanowire TFETs where multiple, tightly-coupled, imaginary paths exist between the VB and the CB. © 2010 American Institute of Physics. 􏰂doi:10.1063/1.3386521􏰃

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Role Of Surface Orientation On Atomic Layer Deposited Al2o3/Gaas Interface Structure And Fermi Level Pinning: A Density Functional Theory Study, Ganesh Hegde, Gerhard Klimeck, Alejandro Strachan Nov 2013

Role Of Surface Orientation On Atomic Layer Deposited Al2o3/Gaas Interface Structure And Fermi Level Pinning: A Density Functional Theory Study, Ganesh Hegde, Gerhard Klimeck, Alejandro Strachan

Gerhard Klimeck

We investigate the initial surface reaction pathways in the atomic layer deposition (ALD) of Al2O3 on GaAs (111)A and (111)B substrates using precursors trimethylaluminum (TMA) and water to ascertain the effect of surface orientation on device performance. We find that the condition of the respective substrates prior to deposition of TMA and water has a major impact on the surface reactions that follow and on the resulting interface structure. The simulations explain the atomistic mechanism of the interfacial self-cleaning effect in ALD that preferentially removes As oxides. The electronic structure of the resulting atomic configurations indicates states throughout the bandgap …

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Gate-Induced G-Factor Control And Dimensional Transition For Donors In Multivalley Semiconductors, Rajib Rahman, Seung H. Park, Timothy B. Boykin, Gerhard Klimeck, Sven Rogge, Lloyd Cl Hollenberg Nov 2013

Gate-Induced G-Factor Control And Dimensional Transition For Donors In Multivalley Semiconductors, Rajib Rahman, Seung H. Park, Timothy B. Boykin, Gerhard Klimeck, Sven Rogge, Lloyd Cl Hollenberg

Gerhard Klimeck

The dependence of the g factors of semiconductor donors on applied electric and magnetic fields is of immense importance in spin-based quantum computation and in semiconductor spintronics. The donor g-factor Stark shift is sensitive to the orientation of the electric and magnetic fields and is strongly influenced by the band-structure and spin-orbit interactions of the host. Using a multimillion atom tight-binding framework, the spin-orbit Stark parameters are computed for donors in multivalley semiconductors, silicon, and germanium. Comparison with limited experimental data shows good agreement for a donor in silicon. Results for gate-induced transition from three-dimensional to two-dimensional wave-function confinement show …

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Resonant Tunneling Through Quantum Dot Arrays, Guanlong Chen, Gerhard Klimeck, Supriyo Datta, Guanhua Chen, William A. Goddard Iii Nov 2013

Resonant Tunneling Through Quantum Dot Arrays, Guanlong Chen, Gerhard Klimeck, Supriyo Datta, Guanhua Chen, William A. Goddard Iii

Gerhard Klimeck

We apply the Hubbard Hamiltonian to describe quantum-dot arrays weakly coupled to two contacts. Exact diagonalization is used to calculate the eigenstates of the arrays containing up to six dots and the linear-response conductance is then calculated as a function of the Fermi energy. In the atomic limit the conductance peaks form two distinct groups separated by the intradot Coulomb repulsion, while in the band limit the peaks occur in pairs. The crossover is studied. A finite interdot repulsion is found to cause interesting rearrangements in the conductance spectrum.

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Design Space For Low Sensitivity To Size Variations In [110] Pmos Nanowire Devices: The Implications Of Anisotropy In The Quantization Mass, Neophytos Neophytou, Gerhard Klimeck Nov 2013

Design Space For Low Sensitivity To Size Variations In [110] Pmos Nanowire Devices: The Implications Of Anisotropy In The Quantization Mass, Neophytos Neophytou, Gerhard Klimeck

Gerhard Klimeck

A 20-band sp3d5s* spin-orbit-coupled, semiempirical, atomistic tight-binding model is used with a semiclassical, ballistic, field effect transistor (FET) model, to examine the ON-current variations to size variations of [110]-oriented PMOS nanowire devices. Infinitely long, uniform, rectangular nanowires of side dimensions from 3 to 12 nm are examined and significantly different behavior in width versus height variations are identified and explained. Design regions are identified, which show minor ON-current variations to significant width variations that might occur due to lack of line width control. Regions which show large ON-current variations to small height variations are also identified. The considerations of the …

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Influence Of Cross-Section Geometry And Wire Orientation On The Phonon Shifts In Ultra-Scaled Si Nanowires, Abhijeet Paul, Mathieu Luisier, Gerhard Klimeck Nov 2013

Influence Of Cross-Section Geometry And Wire Orientation On The Phonon Shifts In Ultra-Scaled Si Nanowires, Abhijeet Paul, Mathieu Luisier, Gerhard Klimeck

Gerhard Klimeck

Engineering of the cross-section shape and size of ultra-scaled Si nanowires (SiNWs) provides an attractive way for tuning their structural properties. The acoustic and optical phonon shifts of the free-standing circular, hexagonal, square and triangular SiNWs are calculated using a Modified Valence Force Field (MVFF) model. The acoustic phonon blue shift (acoustic hardening) and the optical phonon red shift (optical softening) show a strong dependence on the cross-section shape and size of the SiNWs. The triangular SiNWs have the least structural symmetry as revealed by the splitting of the degenerate flexural phonon modes and The show the minimum acoustic hardening …

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Electronic Structure Of Realistically Extended Atomistically Resolved Disordered Si:P Delta-Doped Layers, Sunhee Lee, Hoon Ryu, Lloyd Hollenberg, Michelle Simmons, Gerhard Klimeck Nov 2013

Electronic Structure Of Realistically Extended Atomistically Resolved Disordered Si:P Delta-Doped Layers, Sunhee Lee, Hoon Ryu, Lloyd Hollenberg, Michelle Simmons, Gerhard Klimeck

Gerhard Klimeck

The emergence of scanning tunneling microscope (STM) lithography and low temperature molecular beam epitaxy (MBE) opens the possibility of creating scalable donor based quantum computing architectures. In particular, atomically precise Si:P monolayer structures (delta-doped layers) serve as crucial contact regions and in-plane gates in single impurity devices. In this paper we study highly confined delta-doped layers to explain the disorder in the P dopant placements in realistically extended systems. The band structure is computed using the tight-binding formalism and charge-potential self-consistency. The exchange-correlation corrected impurity potential pulls down subbands below the silicon valley minima to create impurity bands. Our methodology …

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Performance Comparisons Of Tunneling Field-Effect Transistors Made Of Insb, Carbon, And Gasb-Inas Broken Gap Heterostructures, Mathieu Luisier, Gerhard Klimeck Nov 2013

Performance Comparisons Of Tunneling Field-Effect Transistors Made Of Insb, Carbon, And Gasb-Inas Broken Gap Heterostructures, Mathieu Luisier, Gerhard Klimeck

Gerhard Klimeck

Band-to-band tunneling transistors (TFETs) made of InSb, Carbon, and GaSb-InAs broken gap heterostructures are simulated using an atomistic and full-band quantum transport solver. The performances of two-dimensional single-gate and double-gate devices as well as three-dimensional gate-all-around structures are analyzed and compared to find the most promising TFET design. All transistor types are able to provide a region with a steep subthreshold slope, but despite their low band gap, InSb- and C-based (graphene nanoribbons and carbon nanotubes) devices do not offer high enough ON-currents, contrary to GaSb-InAs broken gap structures. However, the nanoribbon and nanotube TFETs can operate at much lower …

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Current Density And Continuity In Discretized Models, Timothy B. Boykin, Mathieu Luisier, Gerhard Klimeck Nov 2013

Current Density And Continuity In Discretized Models, Timothy B. Boykin, Mathieu Luisier, Gerhard Klimeck

Gerhard Klimeck

Discrete approaches have long been used in numerical modelling of physical systems in both research and teaching. Discrete versions of the Schr ¨ odinger equation employing either one or several basis functions per mesh point are often used by senior undergraduates and beginning graduate students in computational physics projects. In studying discrete models, students can encounter conceptual difficulties with the representation of the current and its divergence because different finite-difference expressions, all of which reduce to the current density in the continuous limit, measure different physical quantities. Understanding these different discrete currents is essential and requires a careful analysis of …

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The Composite Materials Manufacturaing Hub - Crowd Sourcing As The Norm, R. Byron Pipes, Gerhard Klimeck, Mark R. Pipes Nov 2013

The Composite Materials Manufacturaing Hub - Crowd Sourcing As The Norm, R. Byron Pipes, Gerhard Klimeck, Mark R. Pipes

Gerhard Klimeck

The Composites Manufacturing HUB puts compo- sites manufacturing simulations in the hands of those who need them to invent new and innovative ways to capture the extraordinary benefits of these high perfor- mance products at an acceptable manufactured cost. The HUB provides the user simple browser access to power- ful tools that simulate the actual steps and outcome con- ditions of a complex manufacturing process without the need to download and maintain software in the conven- tional manner. Learning use of the manufacturing simu- lation tools will also be accomplished on the HUB in or- der to allow for continuous …

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Feasibility, Accuracy, And Performance Of Contact Block Reduction Method For Multi-Band Simulations Of Ballistic Quantum Transport, Hoon Ryu, Hong-Hyun Park, Mincheol Shin, Dragica Vasileska, Gerhard Klimeck Nov 2013

Feasibility, Accuracy, And Performance Of Contact Block Reduction Method For Multi-Band Simulations Of Ballistic Quantum Transport, Hoon Ryu, Hong-Hyun Park, Mincheol Shin, Dragica Vasileska, Gerhard Klimeck

Gerhard Klimeck

Numerical utilities of the contact block reduction (CBR) method in evaluating the retarded Green’s function are discussed for 3D multi-band open systems that are represented by the atomic tight-binding (TB) and continuum k * p (KP) band model. It is shown that the methodology to approximate solutions of open systems, which has been already reported for the single-band effective mass model, cannot be directly used for atomic TB systems, since the use of a set of zinc blende crystal grids makes the inter-coupling matrix non-invertible. We derive and test an alternative with which the CBR method can be still practical …

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Atomistic Full-Band Simulations Of Si Nanowire Transistors: Effects Of Electron-Phonon Scattering, Mathieu Luisier, Gerhard Klimeck Nov 2013

Atomistic Full-Band Simulations Of Si Nanowire Transistors: Effects Of Electron-Phonon Scattering, Mathieu Luisier, Gerhard Klimeck

Gerhard Klimeck

An atomistic full-band quantum transport simulator has been developed to study three-dimensional Si nanowire field-effect transistors (FETs) in the presence of electron-phonon scattering. The Non-equilibrium Green's Function (NEGF) formalism is solved in a nearest-neighbor sp(3)d(5)s* tight-binding basis. The scattering self-energies are derived in the self-consistent Born approximation to inelastically couple the full electron and phonon energy spectra. The band dispersion and the eigenmodes of the confined phonons are calculated using a dynamical matrix that includes the bond and angle deformations of the nanowires. The optimization of the numerical algorithms and the parallelization of the NEGF scheme enable the investigation of …

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