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Birck and NCN Publications

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Articles 331 - 353 of 353

Full-Text Articles in Nanoscience and Nanotechnology

Spin-Orbit Splittings In Si/Sige Quantum Wells: From Ideal Si Membranes To Realistic Hterostructures, M. Prada, G. Klimeck, R. Joynt Jan 2009

Spin-Orbit Splittings In Si/Sige Quantum Wells: From Ideal Si Membranes To Realistic Hterostructures, M. Prada, G. Klimeck, R. Joynt

Birck and NCN Publications

We present a calculation of the wavevector-dependent subband level splitting from spin-orbit coupling in Si/SiGe quantum wells. We first use the effective-mass approach, where the splittings are parameterized by separating contributions from the Rashba and Dresselhaus terms. We then determine the inversion asymmetry parameters by fitting tight-binding numerical results obtained using the quantitative nanoelectronic modeling tool, NEMO-3D. We describe the relevant coefficients as a function of applied electric field and well width in our numerical simulations. Symmetry arguments can also predict the behavior, and an extensive analysis is also presented in this work. Using vast computational resources, we treat alloy …

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Nano-Switch For Study Of Gold Contact Behavior, Adam Fruehling, Shijun Xiao, Minghao Qi, Kaushik Roy, Dimitrios Peroulis Jan 2009

Nano-Switch For Study Of Gold Contact Behavior, Adam Fruehling, Shijun Xiao, Minghao Qi, Kaushik Roy, Dimitrios Peroulis

Birck and NCN Publications

In this paper we present the fabrication and characterization of a new NEMS DC switch as a vehicle to characterize Au-to-Au contacts at nano-scale. The switch consists of a 1050-nm long, 200-nm wide and 50-nm thick cantilever gold beam. The measured on-state resistance values range from 83 Omega to 640 Omega and the actuation voltages from 4 V to 22 V. All measurements are conducted at a current of 1 mu A and the obtained values are in good qualitative agreement with traditional elastic-plastic contact models. The calculated switching time is 55 ns. Characterization of contacts at nano-scale will be …

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Stabilizing Nanostructured Materials By Coherent Nanotwins And Their Grain Boundary Triple Junction Drag, C Saldana, T G. Murthy, M R. Shankar, E A. Stach, S Chandrasekar Jan 2009

Stabilizing Nanostructured Materials By Coherent Nanotwins And Their Grain Boundary Triple Junction Drag, C Saldana, T G. Murthy, M R. Shankar, E A. Stach, S Chandrasekar

Birck and NCN Publications

The role of nanotwin lamellae in enhancing thermal stability of nanostructured materials is examined. Nanostructured copper with varying densities of twins was generated by controlling the deformation strain rate during severe plastic deformation at cryogenic temperatures. While the nanostructured materials produced under cryogenic conditions are characteristically unstable even at room temperatures, their stability is markedly improved when a dense dispersion of nanotwins is introduced. Observations of the role of nanotwins in pinning grain and subgrain structures suggest an interfacial engineering approach to enhancing the stability of nanostructured alloys.

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Identification Of Multiple Oscillation States Of Carbon Nanotube Tipped Cantilevers Interacting With Surfaces In Dynamic Atomic Force Microscopy, Mark Strus, Arvind Raman Jan 2009

Identification Of Multiple Oscillation States Of Carbon Nanotube Tipped Cantilevers Interacting With Surfaces In Dynamic Atomic Force Microscopy, Mark Strus, Arvind Raman

Birck and NCN Publications

Carbon nanotubes (CNTs) have gained increased interest in dynamic atomic force microscopy (dAFM) as sharp, flexible, conducting, nonreactive tips for high-resolution imaging, oxidation lithography, and electrostatic force microscopy. By means of theory and experiments we lay out a map of several distinct tapping mode AFM oscillation states for CNT tipped AFM cantilevers: namely, noncontact attractive regime oscillation, intermittent contact with CNT slipping or pinning, or permanent contact with the CNT in point or line contact with the surface while the cantilever oscillates with large amplitude. Each state represents fundamentally different origins of CNT-surface interactions, CNT tip-substrate dissipation, and phase contrast …

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Orbital Start Effect And Quantum Confinement Transition Of Donors In Silicon, Rajib Rahman, G. P. Lansbergen, Seung H. Park, J. Verdujin, Gerhard Klimeck, S. Rogge, Lloyd C. L. Hollenberg Jan 2009

Orbital Start Effect And Quantum Confinement Transition Of Donors In Silicon, Rajib Rahman, G. P. Lansbergen, Seung H. Park, J. Verdujin, Gerhard Klimeck, S. Rogge, Lloyd C. L. Hollenberg

Birck and NCN Publications

Adiabatic shuttling of single impurity bound electrons to gate-induced surface states in semiconductors has attracted much attention in recent times, mostly in the context of solid-state quantum computer architecture. A recent transport spectroscopy experiment for the first time was able to probe the Stark shifted spectrum of a single donor in silicon buried close to a gate. Here, we present the full theoretical model involving large-scale quantum mechanical simulations that was used to compute the Stark shifted donor states in order to interpret the experimental data. Use of atomistic tight-binding technique on a domain of over a million atoms helped …

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Atomistic Full-Band Simulations Of Si Nanowire Transistors: Effects Of Electron-Phonon Scattering, Mathieu Luisier, Gerhard Klimeck Jan 2009

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

Birck and NCN Publications

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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Advancing Nanoelectronic Device Modeling Through Peta-Scale Computing And Deployment On Nanohub, Benjamin Haley, Sunhee Lee, Mathieu Luisier, Hoon Ryu, Faisal Saied, Steven Clark, Hansang Bae, Gerhard Klimeck Jan 2009

Advancing Nanoelectronic Device Modeling Through Peta-Scale Computing And Deployment On Nanohub, Benjamin Haley, Sunhee Lee, Mathieu Luisier, Hoon Ryu, Faisal Saied, Steven Clark, Hansang Bae, Gerhard Klimeck

Birck and NCN Publications

Recent improvements to existing HPC codes NEMO 3-D and OMEN, combined with access to peta-scale computing resources, have enabled realistic device engineering simulations that were previously infeasible. NEMO 3-D can now simulate 1 billion atom systems, and, using 3D spatial decomposition, scale to 32768 cores. Simulation time for the band structure of an experimental P doped Si quantum computing device fell from 40 minutes to I minute. OMEN can perform fully quantum mechanical transport calculations for real-word UTB FETs on 147,456 cores in roughly 5 minutes. Both of these tools power simulation engines on the nanoHUB, giving the community access …

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Nanoantenna Array-Induced Fluorescence Enhancement And Reduced Lifetimes, Reuben M. Bakker, V. P. Drachev, Zhengtong Liu, Hsiao-Kuan Yuan, Rasmus H. Pedersen, Alexandra Boltasseva, Jiji Chen, Joseph Irudayaraj, Alexander V. Kildishev, V. M. Shalaev Dec 2008

Nanoantenna Array-Induced Fluorescence Enhancement And Reduced Lifetimes, Reuben M. Bakker, V. P. Drachev, Zhengtong Liu, Hsiao-Kuan Yuan, Rasmus H. Pedersen, Alexandra Boltasseva, Jiji Chen, Joseph Irudayaraj, Alexander V. Kildishev, V. M. Shalaev

Birck and NCN Publications

Enhanced fluorescence is observed from dye molecules interacting with optical nanoantenna arrays. Elliptical gold dimers form individual nanoantennae with tunable plasmon resonances depending upon the geometry of the two particles and the size of the gap between them. A fluorescent dye, Rhodamine 800, is uniformly embedded in a dielectric host that coats the nanoantennae. The nanoantennae act to enhance the dye absorption. In turn, emission from the dye drives the plasmon resonance of the antennae; the nanoantennae act to enhance the fluorescence signal and change the angular distribution of emission. These effects depend upon the overlap of the plasmon resonance …

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Atomic-Layer-Deposited Al2o3/Gaas Metal-Oxide-Semiconductor Field-Effect Transistor On Si Substrate Using Aspect Ratio Trapping Technique, Y Q. Wu, M Xu, P. D. Ye, Z Cheng, J Li, J Park, J Hydrick, J Bai, M Carroll, J G. Fiorenza, A Lochtefeld Dec 2008

Atomic-Layer-Deposited Al2o3/Gaas Metal-Oxide-Semiconductor Field-Effect Transistor On Si Substrate Using Aspect Ratio Trapping Technique, Y Q. Wu, M Xu, P. D. Ye, Z Cheng, J Li, J Park, J Hydrick, J Bai, M Carroll, J G. Fiorenza, A Lochtefeld

Birck and NCN Publications

High quality GaAs epilayers grown by metal-organic chemical vapor deposition are demonstrated on a SiO2-patterned silicon substrate using aspect ratio trapping technique, whereby threading dislocations from lattice mismatch are largely reduced via trapping in SiO2 trenches during growth. A depletion-mode metal-oxide-semiconductor field-effect transistor (MOSFET) is demonstrated on a n-doped GaAs channel with atomic-layer deposited Al2O3 as the gate oxide. The 10 mu m gate length transistor has a maximum drain current of 88 mA/mm and a transconductance of 19 mS/mm. The surface mobility estimated from the accumulation drain current has a peak value of similar to 500 cm(2)/Vs, which is …

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Optical Hyperspace For Plasmons: Dyakonov States In Metamaterials, Zubin Jacob, Evgenii E. Narimanov Dec 2008

Optical Hyperspace For Plasmons: Dyakonov States In Metamaterials, Zubin Jacob, Evgenii E. Narimanov

Birck and NCN Publications

We show that the subdiffraction imaging behavior observed in the magnifying superlens experiment, [Smolyaninov , Science 317, 1699 (2007)] is due to the hyperbolic dispersion of Dyakonov plasmons supported by the device. These states which are a special case of Dyakonov surface waves [Dyakonov, Sov. Phys. JETP 67, 714 (1988)] exist at the interface of a metal and an anisotropic dielectric giving rise to plasmon beams on resonance. Furthermore, we describe how the unique properties of metamaterial Dyakonov plasmons can be tailored for plasmonic devices.

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Hydrodynamic Loading Of Microcantilevers Oscillating Near Rigid Walls, Ryan C. Tung, Jana Anirban, Arvind Raman Dec 2008

Hydrodynamic Loading Of Microcantilevers Oscillating Near Rigid Walls, Ryan C. Tung, Jana Anirban, Arvind Raman

Birck and NCN Publications

The vibrations of microcantilevers in atomic force microscopes (AFMs) or radio frequency (RF) switches are strongly influenced by the viscous hydrodynamics of the surrounding fluid in the vicinity of a rigid wall. While prior efforts to model this hydrodynamic loading have focused on squeeze film damping effects at high Knudsen and squeeze numbers, the regimes of low Knudsen and squeeze numbers are also very important for which squeeze film models need to be discarded in favor of unsteady Stokes hydrodynamics. We extend the work of Green and Sader [Phys Fluids 17, 073102 (2005); J. Appl. Phys. 98, 114913 (2005)] and …

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Solutions In Folded Geometries, And Associated Cloaking Due To Anomalous Resonance, Graeme W. Milton, Nicolae-Alexandru P. Nicorovici, Ross C. Mcphedran, Kirill Cherednichenko, Zubin Jacob Nov 2008

Solutions In Folded Geometries, And Associated Cloaking Due To Anomalous Resonance, Graeme W. Milton, Nicolae-Alexandru P. Nicorovici, Ross C. Mcphedran, Kirill Cherednichenko, Zubin Jacob

Birck and NCN Publications

Solutions for the fields in a coated cylinder where the core radius is bigger than the shell radius are seemingly unphysical, but can be given a physical meaning if one transforms to an equivalent problem by unfolding the geometry. In particular, the unfolded material can act as an impedance matched hyperlens, and as the loss in the lens goes to zero finite collections of polarizable line dipoles lying within a critical region surrounding the hyperlens are shown to be cloaked having vanishingly small dipole moments. This cloaking, which occurs both in the folded geometry and the equivalent unfolded one, is …

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Transformation Optics: Approaching Broadband Electromagnetic Cloaking, Alexander V. Kildishev, W Cai, U K. Chettiar, V. M. Shalaev Nov 2008

Transformation Optics: Approaching Broadband Electromagnetic Cloaking, Alexander V. Kildishev, W Cai, U K. Chettiar, V. M. Shalaev

Birck and NCN Publications

An approach to broadband cloaking of light waves is analysed for a simplified case of a scaling transformation for a general cylindrical coordinate system. The proposed approach requires metamaterials with specifically engineered dispersion. The restriction on the signs of gradients in the dispersion dependencies of the dielectric permittivity and the magnetic permeability for different operational wavelengths is revealed and is shown to cause difficulties unless additional gain-assisted compensation for losses or electromagnetically induced transparency is introduced in the cloaking system.

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Bright-Field Analysis Of Phi29 Dna Packaging Motor Using A Magnetomechanical System, Chun-Li Chang, Hui Zhang, Dan Shu, Peixuan Guo, Cagri A. Savran Oct 2008

Bright-Field Analysis Of Phi29 Dna Packaging Motor Using A Magnetomechanical System, Chun-Li Chang, Hui Zhang, Dan Shu, Peixuan Guo, Cagri A. Savran

Birck and NCN Publications

We report a simple and robust magnetomechanical system for direct visual observation of the DNA packaging behavior of the bacteriophage phi29 in real time. The system comprises a micron-sized magnetic bead attached to the free end of the viral DNA, a magnet and a bright-field microscope. We show that the phi29 DNA packaging activity can be observed and dynamically analyzed at the single molecular level in bright field with a relatively simple system. With this system we also visually demonstrate the phi29 motor transporting a cargo 10 000 times the viral size.

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Structures And Energetics Of Si Nanotubes From Molecular Dynamics And Density Functional Theory, Amritanshu Palaria, Gerhard Klimeck, Alejandro Strachan May 2008

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

Birck and NCN Publications

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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Nanopatterning Using Nsom Probes Integrated With High Transmission Nanoscale Bowtie Aperture, Nicholas Murphy-Dubay, Liang Wang, Edward C. Kinzel, Sreemanth Mv Uppuluri, Xianfan Xu Feb 2008

Nanopatterning Using Nsom Probes Integrated With High Transmission Nanoscale Bowtie Aperture, Nicholas Murphy-Dubay, Liang Wang, Edward C. Kinzel, Sreemanth Mv Uppuluri, Xianfan Xu

Birck and NCN Publications

Nanoscale ridge aperture antennas have been shown to have high transmission efficiency and confined nanoscale radiation in the near field region compared with regularly-shaped apertures. The radiation enhancement is attributed to the fundamental electric-magnetic field propagating in the TE10 mode concentrated in the gap between the ridges. This paper reports experimental demonstration of field enhancement using such ridge antenna apertures in a bowtie shape for the manufacture of nanometer size structures using an NSOM (near field scanning optical microscopy) probe integrated with nanoscale bowtie aperture. Consistent lines with width of 59 nm and as small as 24 nm have be …

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Simulation Of Phonon Transport Across A Non-Polar Nanowire Junction Using An Atomistic Green's Function Method, W Zhang, N Mingo, Timothy Fisher Nov 2007

Simulation Of Phonon Transport Across A Non-Polar Nanowire Junction Using An Atomistic Green's Function Method, W Zhang, N Mingo, Timothy Fisher

Birck and NCN Publications

Phonon transport across a non-polar nanowire situated between two semi-infinite contacts is simulated in this paper using the atomistic Green's function method. Abrupt geometric changes between the nanowire and bulk contacts are handled by self-energy matrices obtained from bare surface Green's functions. Transport properties such as phonon transmission functions and thermal conductances are calculated, and their dependencies on the interatomic potential, length, diameter, shape, and lattice orientation are investigated. The results reveal that the overall thermal conductance of the nanowire-bulk-contact structure increases with nanowire diameter while the normalized thermal conductance approaches an asymptotic value. Thermal conductance decreases significantly with increasing …

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Brillouin-Zone Unfolding Of Perfect Supercells Having Nonequivalent Primitive Cells Illustrated With A Si/Ge Tight-Binding Parameterization, Timothy B. Boykin, Neerav Kharche, Gerhard Klimeck Jul 2007

Brillouin-Zone Unfolding Of Perfect Supercells Having Nonequivalent Primitive Cells Illustrated With A Si/Ge Tight-Binding Parameterization, Timothy B. Boykin, Neerav Kharche, Gerhard Klimeck

Birck and NCN Publications

Numerical calculations of nanostructure electronic properties are often based on a nonprimitive rectangular unit cell, because the rectangular geometry allows for both highly efficient algorithms and ease of debugging while having no drawback in calculating quantum dot energy levels or the one-dimensional energy bands of nanowires. Since general nanostructure programs can also handle superlattices, it is natural to apply them to these structures as well, but here problems arise due to the fact that the rectangular unit cell is generally not the primitive cell of the superlattice, so that the resulting E(k) relations must be unfolded to obtain the primitive- …

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Resonant Tunneling Through Quantum Dot Arrays, Guanlong Chen, Gerhard Klimeck, Supriyo Datta, Guanhua Chen, William A. Goddard Iii Sep 1994

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

Birck and NCN Publications

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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Conductance Spectroscopy In Coupled Quantum Dots, Gerhard Klimeck, Guanlong Chen, Supriyo Datta Jul 1994

Conductance Spectroscopy In Coupled Quantum Dots, Gerhard Klimeck, Guanlong Chen, Supriyo Datta

Birck and NCN Publications

We investigate the linear-response conductance through a pair of coupled quantum dots. The conductance spectrum under ideal conditions is shown to consist of two sets of twin peaks whose locations and amplitudes are determined by the interdot coupling and the intradot charging. We will show that the qualitative features of the spectrum survive against experimental nonidealities such as (1) detuning of the individual dots, (2) interdot charging, (3) inelastic scattering, and (4) multiple lateral states. The effect of higher lateral states depends strongly on the nature of the interaction potential, screening lengths, and exchange terms, but the lowest set of …

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Rate Equations For The Phonon Peak In Resonant-Tunneling Structures, Roger Lake, Gerhard Klimeck, J. P. Anantram, Supriyo Datta Nov 1993

Rate Equations For The Phonon Peak In Resonant-Tunneling Structures, Roger Lake, Gerhard Klimeck, J. P. Anantram, Supriyo Datta

Birck and NCN Publications

The ratio of the phonon peak current to the main peak current in double-barrier resonant-tunneling structures is significantly enhanced by barrier asymmetry. Previously, using the Keldysh formalism, we derived analytical expressions, valid in the zero-temperature, high-bias regime, which explained this eftect. We now provide analytical expressions valid for finite temperature and bias obtained from (i) an intuitive derivation using a rate equation approach and (ii) a more general derivation using the Keldysh formalism. The results of the two difFerent approaches are shown to be essentially identical for the ex- perimental device parameters. The finite temperature expressions shed light on the …

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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 Mar 1993

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

Birck and NCN Publications

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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Laser Bandwidth-Induced Fluctuations In The Intensity Transmitted By A Fabry-Perot Interferometer, Gerhard Klimeck, Daniel Elliott, M. Hamilton Sep 1991

Laser Bandwidth-Induced Fluctuations In The Intensity Transmitted By A Fabry-Perot Interferometer, Gerhard Klimeck, Daniel Elliott, M. Hamilton

Birck and NCN Publications

We have measured the power spectrum of the intensity Auctuations of light transmitted by a Fabry- Perot interferometer when the input field is the real Gaussian field. The real Gaussian field is a field characterized by real, random (Gaussian) amplitude Auctuations. The bandwidth of the real Gaussian field was varied, taking on values less than that of the interferometer, as well as greater. Comparisons of the measured spectra with calculated spectra are quite satisfactory. Of special interest is a feature in the spectra centered at the laser-interferometer detuning frequency.

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