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Birck and NCN Publications

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Articles 121 - 150 of 353

Full-Text Articles in Nanoscience and Nanotechnology

Single-Molecule Tools Elucidate H2a.Z Nucleosome Composition, Jiji Chen, Andrew Miller, Ann L. Kirchmaier, Joseph M.K. Irudayaraj Jun 2012

Single-Molecule Tools Elucidate H2a.Z Nucleosome Composition, Jiji Chen, Andrew Miller, Ann L. Kirchmaier, Joseph M.K. Irudayaraj

Birck and NCN Publications

Although distinct epigenetic marks correlate with different chromatin states, how they are integrated within single nucleosomes to generate combinatorial signals remains largely unknown. We report the successful implementation of single molecule tools constituting fluorescence correlation spectroscopy (FCS), pulse interleave excitation-based Forster resonance energy transfer (PIE-FRET) and fluorescence lifetime imaging-based FRET (FLIM-FRET) to elucidate the composition of single nucleosomes containing histone variant H2A.Z (Htz1p in yeast) in vitro and in vivo. We demonstrate that yeast nucleosomes containing Htz1p are primarily composed of H4 K12ac and H3 K4me3 but not H3 K36me3 and that these patterns are conserved in mammalian cells. Quantification …

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Analysis Of Thermal Conductance Of Ballistic Point Contacts, Changwook Jeong, Mark S. Lundstrom Jun 2012

Analysis Of Thermal Conductance Of Ballistic Point Contacts, Changwook Jeong, Mark S. Lundstrom

Birck and NCN Publications

Substantial reduction of thermal conductance (K-ph) was recently reported for air gap heterostructures (AGHs) in which two bulk layers were connected by low-density nanopillars. We analyze K-ph using a full phonon dispersion and including important phonon scattering. We find a transition from ballistic at low temperatures to quasi-ballistic transport near room temperature and explain the slow roll-off in K-ph that occurs near room temperature. We show that the density of nanopillars deduced from the analysis depends strongly on the phonon dispersion assumed. Our model provides a good agreement with experiment that will be necessary to design AGHs for thermoelectric applications. …

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The Effects Of Diameter And Chirality On The Thermal Transport In Free-Standing And Supported Carbon-Nanotubes, Bo Qiu, Yan Wang, Xiulin Ruan, Qing Zhao Jun 2012

The Effects Of Diameter And Chirality On The Thermal Transport In Free-Standing And Supported Carbon-Nanotubes, Bo Qiu, Yan Wang, Xiulin Ruan, Qing Zhao

Birck and NCN Publications

We use molecular dynamics simulations to explore the lattice thermal transport in free-standing and supported single-wall carbon-nanotube (SWCNT) in comparison to that in graphene nanoribbon and graphene sheet. For free-standing SWCNT, the lattice thermal conductivity increases with diameter and approaches that of graphene, partly due to the curvature. Supported SWCNT thermal conductivity is reduced by 34%-41% compared to the free-standing case, which is less than that in supported graphene. Also, it shows an evident chirality dependence by varying about 10%, which we attribute to chirality-dependent interfacial phonon scattering. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4725194]

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On The Best Bandstructure For Thermoelectric Performance: A Landauer Perspective, Changwook Jeong, Raseong Kim, Mark S. Lundstrom Jun 2012

On The Best Bandstructure For Thermoelectric Performance: A Landauer Perspective, Changwook Jeong, Raseong Kim, Mark S. Lundstrom

Birck and NCN Publications

The question of what bandstructure produces the best thermoelectric device performance is revisited from a Landauer perspective. We find that a delta-function transport distribution function (TDF) results in operation at the Mahan-Sofo upper limit for the thermoelectric figure-of-merit, ZT. We show, however, the Mahan-Sofo upper limit itself depends on the bandwidth (BW) of the dispersion, and therefore, a finite BW dispersion produces a higher ZT when the lattice thermal conductivity is finite. Including a realistic model for scattering profoundly changes the results. Instead of a narrow band, we find that a broad BW is best. The prospects of increasing ZT …

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Parametric Noise Squeezing And Parametric Resonance Of Microcantilevers In Air And Liquid Environments, Gyan Prakash, Arvind Raman, Jeff F. Rhoads, Ronald G. Reifenberger Jun 2012

Parametric Noise Squeezing And Parametric Resonance Of Microcantilevers In Air And Liquid Environments, Gyan Prakash, Arvind Raman, Jeff F. Rhoads, Ronald G. Reifenberger

Birck and NCN Publications

In this work, parametric noise squeezing and parametric resonance are realized through the use of an electronic feedback circuit to excite a microcantilever with a signal proportional to the product of the microcantilever's displacement and a harmonic signal. The cantilever's displacement is monitored using an optical lever technique. By adjusting the gain of an amplifier in the feedback circuit, regimes of parametric noise squeezing/amplification and the principal and secondary parametric resonances of fundamental and higher order eigenmodes can be easily accessed. The exceptionally symmetric amplitude response of the microcantilever in the narrow frequency bandwidth is traced to a nonlinear parametric …

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Quantized Hall Effect And Shubnikov-De Haas Oscillations In Highly Doped Bi2se3: Evidence For Layered Transport Of Bulk Carriers, Helin Cao, Jifa Tian, Ireneusz Miotkowski, Tian Shen, Jiuning Hu, Shan Qiao, Yong P. Chen May 2012

Quantized Hall Effect And Shubnikov-De Haas Oscillations In Highly Doped Bi2se3: Evidence For Layered Transport Of Bulk Carriers, Helin Cao, Jifa Tian, Ireneusz Miotkowski, Tian Shen, Jiuning Hu, Shan Qiao, Yong P. Chen

Birck and NCN Publications

Bi2Se3 is an important semiconductor thermoelectric material and a prototype topological insulator. Here we report observation of Shubnikov-de Hass oscillations accompanied by quantized Hall resistances (R-xy) in highly doped n-type Bi2Se3 with bulk carrier concentrations of few 10(19) cm(-3). Measurements under tilted magnetic fields show that the magnetotransport is 2D-like, where only the c-axis component of the magnetic field controls the Landau level formation. The quantized step size in 1/R-xy is found to scale with the sample thickness, and average similar to e(2)/h per quintuple layer. We show that the observed magnetotransport features do not come from the sample surface, …

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Amorphous Ni/Al Nanoscale Laminates As High-Energy Intermolecular Reactive Composites, Karthik Guda Vishnu, Mathew Cherukara, Hojin Kim, Alejandro Strachan May 2012

Amorphous Ni/Al Nanoscale Laminates As High-Energy Intermolecular Reactive Composites, Karthik Guda Vishnu, Mathew Cherukara, Hojin Kim, Alejandro Strachan

Birck and NCN Publications

We use molecular dynamics simulations to explore the potential use of amorphous metals in intermolecular reactive composites. Our simulations show that amorphous Ni/Al nanolaminates lead to an increase in temperature of up to 260 K over their crystalline counterparts; this increase corresponds to over 20% of the heat of fusion and can be explained in terms of the amorphization energy. The reactions are diffusion controlled and crystallization is observed in laminates with relatively long periods where high temperatures are experienced for sufficiently long times prior to intermixing; the effect of this process on the energetics and time involved in the …

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Two-Temperature Nonequilibrium Molecular Dynamics Simulation Of Thermal Transport Across Metal-Nonmetal Interfaces, Yan Wang, Xiulin Ruan, Ajit K. Roy May 2012

Two-Temperature Nonequilibrium Molecular Dynamics Simulation Of Thermal Transport Across Metal-Nonmetal Interfaces, Yan Wang, Xiulin Ruan, Ajit K. Roy

Birck and NCN Publications

We have used a two-temperature nonequilibrium molecular dynamics method for predicting interfacial thermal resistance across metal-nonmetal interfaces. This method is an extension of the conventional nonequilibrium molecular dynamics for the dielectric-dielectric interface, where a temperature bias is imposed and the heat current is derived. We have included the electron degree of freedom for the interfacial thermal transport problem by treating the electron-phonon coupling with the two-temperature model. The method is demonstrated on two model systems, that is, silicon-copper interface and carbon-nanotube-copper interface. Temperature nonequilibrium between electrons and phonons in the metal side is quantitatively predicted, and a temperature drop across …

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Reduction Of Spectral Phonon Relaxation Times From Suspended To Supported Graphene, Bo Qiu, Xiulin Ruan May 2012

Reduction Of Spectral Phonon Relaxation Times From Suspended To Supported Graphene, Bo Qiu, Xiulin Ruan

Birck and NCN Publications

We have performed molecular dynamics simulations with phonon spectral analysis to predict the mode-wise phonon relaxation times (RT) of suspended and supported graphene at room temperature, and the findings are consistent with recent optical measurements. For acoustic phonons, RTs reduce from up to 50 ps to less than 5 ps when graphene is put on silicon dioxide substrate. Similarly, optical phonon RTs reduce by half when supported. Stronger interfacial bonding is found to result in more RT reduction. Our results provide a fundamental understanding at the spectral phonon property level for the observed thermal conductivity reduction in supported graphene. (C) …

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Properties Of Metal-Graphene Contacts, Joachim Knoch, Zhihong Chen, Joerg Appenzeller May 2012

Properties Of Metal-Graphene Contacts, Joachim Knoch, Zhihong Chen, Joerg Appenzeller

Birck and NCN Publications

We present a study on the metal-graphene contact properties. Utilizing a dual-gate field-effect transistor device, an energetic separation between the Fermi level and the Dirac point in the contact areas can be adjusted deliberately by applying an appropriate front-gate voltage that acts only on the channel. This front-gate voltage is compensated by an opposite large-area back-gate voltage, thereby mimicking the metal induced doping effect. A back-gate voltage sweep enables identifying two distinct resistance peaks-a result of the combined impact of the graphene cones in the contact and in the channel region. Comparing our experimental data with simulations allows extracting the …

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Electric Field Tuning Of Spin Splitting In A Quantum Dot Coupled To A Semimagnetic Quantum Dot, Yuli Lyanda-Geller, T.L. Reinecke, G. Bacher May 2012

Electric Field Tuning Of Spin Splitting In A Quantum Dot Coupled To A Semimagnetic Quantum Dot, Yuli Lyanda-Geller, T.L. Reinecke, G. Bacher

Birck and NCN Publications

We develop an approach for tuning the spin splitting and g-factor of a quantum dot by coupling it to semi-magnetic quantum dot and tuning the electric field. We show that spin splittings and g-factors of the states of a non-magnetic quantum dot coupled to semi-magnetic quantum dot can be enhanced orders of magnitude. Evaluations are made for coupled CdTe/CdMnTe quantum dots. These effects are caused by electric field control of repulsion of spin sublevels in the non-magnetic dot due to tunnel coupling of quantum dots. Electric field control of spin splittings in quantum dots is of potential interest in connection …

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Thermal Conductivity Of Bulk And Thin-Film Silicon: A Landauer Approach, Changwook Jeong, Supriyo Datta, Mark S. Lundstrom May 2012

Thermal Conductivity Of Bulk And Thin-Film Silicon: A Landauer Approach, Changwook Jeong, Supriyo Datta, Mark S. Lundstrom

Birck and NCN Publications

The question of what fraction of the total heat flow is transported by phonons with different mean-free-paths is addressed using a Landauer approach with a full dispersion description of phonons to evaluate the thermal conductivities of bulk and thin film silicon. For bulk Si, the results reproduce those of a recent molecular dynamic treatment showing that about 50% of the heat conduction is carried by phonons with a mean-free-path greater than about 1 mu m. For the in-plane thermal conductivity of thin Si films, we find that about 50% of the heat is carried by phonons with mean-free-paths shorter than …

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Spectroscopy Of A Deterministic Single-Donor Device In Silicon, M. Fuechsle, J. A. Miwa, S. Mahapatra, H. Ryu, S. Lee, O. Warschkow, L. C. L. Hollenberg, G. Klimeck, M. Y. Simmons May 2012

Spectroscopy Of A Deterministic Single-Donor Device In Silicon, M. Fuechsle, J. A. Miwa, S. Mahapatra, H. Ryu, S. Lee, O. Warschkow, L. C. L. Hollenberg, G. Klimeck, M. Y. Simmons

Birck and NCN Publications

We present a single electron transistor (SET) based on an individual phosphorus dopant atom in an epitaxial silicon environment. Using scanning tunneling microscope (STM) hydrogen lithography, the single impurity is deterministically placed with a spatial accuracy of ±1 lattice site within a donor-based transport device. Low temperature transport measurements confirm the presence of the single donor and show that the donor charge state can be precisely controlled via gate voltages. We observe a charging energy that is remarkably similar to the value expected for isolated P donors in bulk silicon, which is in sharp contrast to previous experiments on single-dopant …

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Broadband Purcell Effect: Radiative Decay Engineering With Metamaterials, Zubin Jacob, Igor I. Smolyaninov, Evgenii E. Narimanov Apr 2012

Broadband Purcell Effect: Radiative Decay Engineering With Metamaterials, Zubin Jacob, Igor I. Smolyaninov, Evgenii E. Narimanov

Birck and NCN Publications

We show that metamaterials with hyperbolic dispersion support a large number of electromagnetic states that can couple to quantum emitters leading to a broadband Purcell effect. The proposed approach of radiative decay engineering, useful for applications such as single photon sources, fluorescence imaging, biosensing, and single molecule detection, also opens up the possibility of using hyperbolic metamaterials to probe the spontaneous emission properties of atoms and artificial atoms such as quantum dots. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4710548]

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Drive-Amplitude-Modulation Atomic Force Microscopy: From Vacuum To Liquids, Miriam Jaafar, David Martinez-Martin, Mariano Cuenca, John Melcher, Arvind Raman, Julio Gomez-Herrero Apr 2012

Drive-Amplitude-Modulation Atomic Force Microscopy: From Vacuum To Liquids, Miriam Jaafar, David Martinez-Martin, Mariano Cuenca, John Melcher, Arvind Raman, Julio Gomez-Herrero

Birck and NCN Publications

We introduce drive-amplitude-modulation atomic force microscopy as a dynamic mode with outstanding performance in all environments from vacuum to liquids. As with frequency modulation, the new mode follows a feedback scheme with two nested loops: The first keeps the cantilever oscillation amplitude constant by regulating the driving force, and the second uses the driving force as the feedback variable for topography. Additionally, a phase-locked loop can be used as a parallel feedback allowing separation of the conservative and nonconservative interactions. We describe the basis of this mode and present some examples of its performance in three different environments. Drive-amplutide modulation …

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Control Of Absorption With Hyperbolic Metamaterials, T.U. Tumkur, Lei Gu, J.K. Kitur, Evgenii E. Narimanov, M.A. Noginov Apr 2012

Control Of Absorption With Hyperbolic Metamaterials, T.U. Tumkur, Lei Gu, J.K. Kitur, Evgenii E. Narimanov, M.A. Noginov

Birck and NCN Publications

We show that absorption of thin dye-doped polymeric films can be tuned and enhanced ( nearly threefold) by metallic and lamellar metal-dielectric hyperbolic metamaterial substrates. The effect can be controlled by a combination of the substrate's geometry and composition. As the enhancement of absorption is sustained over large range of incidence angles, the demonstrated phenomenon can lead to a variety of important applications, including solar cell technology. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4703931]

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Tunable Thermal Rectification In Graphene Nanoribbons Through Defect Engineering: A Molecular Dynamics Study, Yan Wang, Siyu Chen, Xiulin Ruan Apr 2012

Tunable Thermal Rectification In Graphene Nanoribbons Through Defect Engineering: A Molecular Dynamics Study, Yan Wang, Siyu Chen, Xiulin Ruan

Birck and NCN Publications

Using non-equilibrium molecular dynamics, we show that asymmetrically defected graphene nanoribbons (GNR) are promising thermal rectifiers. The optimum conditions for thermal rectification (TR) include low temperature, high temperature bias, similar to 1% concentration of single-vacancy or substitutional silicon defects, and a moderate partition of the pristine and defected regions. TR ratio of similar to 80% is found in a 14-nm long and 4-nm wide GNR at a temperature of 200 K and bias of 90 K, where heat conduction is in the ballistic regime since the bulk effective phonon mean-free-path is around 775 nm. As the GNR length increases towards …

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Non-Equilibrium Green's Function Calculation For Gan-Based Terahertz-Quantum Cascade Laser Structures, H. Yasuda, T. Kubis, I. Hosako, K. Hirakawa Apr 2012

Non-Equilibrium Green's Function Calculation For Gan-Based Terahertz-Quantum Cascade Laser Structures, H. Yasuda, T. Kubis, I. Hosako, K. Hirakawa

Birck and NCN Publications

We theoretically investigated GaN-based resonant phonon terahertz-quantum cascade laser (QCL) structures for possible high-temperature operation by using the non-equilibrium Green's function method. It was found that the GaN-based THz-QCL structures do not necessarily have a gain sufficient for lasing, even though the thermal backfilling and the thermally activated phonon scattering are effectively suppressed. The main reason for this is the broadening of the subband levels caused by a very strong interaction between electrons and longitudinal optical (LO) phonons in GaN. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4704389]

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Tuning Entanglement And Ergodicity In Two-Dimensional Spin Systems Using Impurities And Anisotropy, Gehad Sadiek, Qing Xu, Sabre Kais Apr 2012

Tuning Entanglement And Ergodicity In Two-Dimensional Spin Systems Using Impurities And Anisotropy, Gehad Sadiek, Qing Xu, Sabre Kais

Birck and NCN Publications

We consider the entanglement in a two-dimensional XY model in an external magnetic field h. The model consists of a set of seven localized spin-1/2 particles in a two-dimensional triangular lattice coupled through nearest-neighbor exchange interaction J. We examine the effect of single and double impurities in the system as well as the degree of anisotropy on the nearest-neighbor entanglement and ergodicity of the system. We have found that the entanglement of the system at the different degrees of anisotropy mimics that of the one-dimensional spin systems at the extremely small and large values of the parameter lambda = h/J. …

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Room Temperature Deposition Of Alumina-Doped Zinc Oxide On Flexible Substrates By Direct Pulsed Laser Recrystallization, Martin Y. Zhang, Qiong Nian, Gary J. Cheng Apr 2012

Room Temperature Deposition Of Alumina-Doped Zinc Oxide On Flexible Substrates By Direct Pulsed Laser Recrystallization, Martin Y. Zhang, Qiong Nian, Gary J. Cheng

Birck and NCN Publications

In this study, a method combining room temperature pulsed laser deposition (PLD) and direct pulsed laser recrystallization (DPLR) is introduced to deposit transparent conductive oxide (TCO) layer on low melting point flexible substrates. Alumina-doped zinc oxide (AZO), as one of the most promising TCO candidates, has now been widely used in solar cells. However, to achieve optimal, electrical, and optical properties of AZO on low melting point, flexible substrate is challenging. DPLR technique is a scalable, economic, and fast process to remove crystal defects and generate recrystallization at room temperature. It features selective processing by only heating up the TCO …

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The Integration Of High-K Dielectric On Two-Dimensional Crystals By Atomic Layer Deposition, Han Liu, Kun Xu, Xujie Zhang, Peide Ye Apr 2012

The Integration Of High-K Dielectric On Two-Dimensional Crystals By Atomic Layer Deposition, Han Liu, Kun Xu, Xujie Zhang, Peide Ye

Birck and NCN Publications

We investigate the integration of Al2O3 high-k dielectric on two-dimensional (2D) crystals of boron nitride (BN) and molybdenum disulfide (MoS2) by atomic layer deposition (ALD). We demonstrate the feasibility of direct ALD growth with trimethylaluminum and water as precursors on both 2D crystals. Through theoretical and experimental studies, we found that the initial ALD cycles play the critical role, during which physical adsorption dominates precursor adsorption at the crystal surface. We model the initial ALD growth stages at the 2D surface by analyzing Lennard-Jones potentials, which could guide future optimization of the ALD process on 2D crystals. (C) 2012 American …

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Exploration Of The Limits To Mobility In Two-Dimensional Hole Systems In Gaas/Algaas Quantum Wells, J.D. Watson, S. Mondal, G. Gardner, Gabor A. Csathy, Michael J. Manfra Apr 2012

Exploration Of The Limits To Mobility In Two-Dimensional Hole Systems In Gaas/Algaas Quantum Wells, J.D. Watson, S. Mondal, G. Gardner, Gabor A. Csathy, Michael J. Manfra

Birck and NCN Publications

We report on the growth and electrical characterization of a series of two-dimensional hole systems (2DHSs) used to study the density dependence of low temperature mobility in 20-nm GaAs/AlGaAs quantum wells. The hole density was controlled by changing the Al mole fraction and the setback of the delta-doping layer. We varied the density over a range from 1.8 x 10(10) cm(-2) to 1.9 x 10(11) cm(-2) finding a nonmonotonic dependence of mobility on density at T = 0.3 K. Surprisingly, a peak mobility of 2.3 x 10(6) cm(2)/Vs was measured at a density of 6.5 x 10(10) cm(-2), with further …

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Interface Barriers At The Interfaces Of Polar Gaas(111) Faces With Al2o3, H.Y. Chou, E. O'Connor, P.K. Hurley, V.V. Afanas'ev, M. Houssa, A. Stesmans, Peide Ye, S.B. Newcomb Apr 2012

Interface Barriers At The Interfaces Of Polar Gaas(111) Faces With Al2o3, H.Y. Chou, E. O'Connor, P.K. Hurley, V.V. Afanas'ev, M. Houssa, A. Stesmans, Peide Ye, S.B. Newcomb

Birck and NCN Publications

Internal photoemission measurements of barriers for electrons at interfaces between GaAs(111) and atomic-layer deposited Al2O3 indicate that changing the GaAs polar crystal face orientation from the Ga-terminated (111)A to the As-terminated (111)B has no effect on the barrier height and remains the same as at the non-polar GaAs(100)/Al2O3 interface. Moreover, the presence of native oxide on GaAs(111) or passivation of this surface with sulphur also have no measurable influence on the GaAs(111)/Al2O3 barrier. These results suggest that the orientation and composition-sensitive surface dipoles conventionally observed at GaAs surfaces are effectively compensated at GaAs/oxide interfaces. (C) 2012 American Institute of Physics. …

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Magnetoplasmon Resonance In A Two-Dimensional Electron System Driven Into A Zero-Resistance State, A. T. Hatke, M. A. Zudov, J. D. Watson, Michael J. Manfra Mar 2012

Magnetoplasmon Resonance In A Two-Dimensional Electron System Driven Into A Zero-Resistance State, A. T. Hatke, M. A. Zudov, J. D. Watson, Michael J. Manfra

Birck and NCN Publications

We report on a very strong, and a rather sharp, photoresistance peak originating from a dimensional magnetoplasmon resonance (MPR) in a high-mobility GaAs/AlGaAs quantum well driven by microwave radiation into a zero-resistance state (ZRS). The analysis of the MPR signal reveals a negative background, providing experimental evidence for the concept of absolute negative resistance associated with the ZRS. When the system is further subject to a dc field, the maxima of microwave-induced resistance oscillations decay away and the system reveals a state with close-to-zero differential resistance. The MPR peak, on the other hand, remains essentially unchanged, indicating robust Ohmic behavior …

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Design Of Three-Well Indirect Pumping Terahertz Quantum Cascade Lasers For High Optical Gain Based On Nonequilibrium Green's Function Analysis, Tao Liu, Tillmann Kubis, Qi Jie Wang, Gerhard Klimeck Mar 2012

Design Of Three-Well Indirect Pumping Terahertz Quantum Cascade Lasers For High Optical Gain Based On Nonequilibrium Green's Function Analysis, Tao Liu, Tillmann Kubis, Qi Jie Wang, Gerhard Klimeck

Birck and NCN Publications

The nonequilibrium Green's function approach is applied to the design of three-well indirect pumping terahertz (THz) quantum cascade lasers (QCLs) based on a resonant phonon depopulation scheme. The effects of the anticrossing of the injector states and the dipole matrix element of the laser levels on the optical gain of THz QCLs are studied. The results show that a design that results in a more pronounced anticrossing of the injector states will achieve a higher optical gain in the indirect pumping scheme compared to the traditional resonant-tunneling injection scheme. This offers in general a more efficient coherent resonant-tunneling transport of …

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Enhanced Optical Nonlinearity In Beta-Agvo3 Nanobelts On Decoration With Ag Nanoparticles, Manas R. Parida, C. Vijayan, Chandra Sekhar Rout, C.S. Suchand Sandeep, Reji Philip Mar 2012

Enhanced Optical Nonlinearity In Beta-Agvo3 Nanobelts On Decoration With Ag Nanoparticles, Manas R. Parida, C. Vijayan, Chandra Sekhar Rout, C.S. Suchand Sandeep, Reji Philip

Birck and NCN Publications

This paper reports on the optical nonlinearity of beta-AgVO3 nanobelts and the modification in the physical mechanisms of nonlinear response on decorating with silver nanoparticles. The nanobelts are synthesized by a hydrothermal technique and characterized using SEM, TEM, and XRD etc. The nanobelts are found to exhibit large nonlinear optical absorption as revealed by open Z-scan measurements using 5 ns laser pulses at 532 nm. Nonlinearity appears to be arising from a combination of mechanisms of two photon absorption and saturable absorption (SA). Decoration with Ag nanoparticles is found to enhance the saturable absorption and alter the coefficient of nonlinear …

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Theory Of Charging And Charge Transport In “Intermediate” Thickness Dielectrics And Its Implications For Characterization And Reliability, Sambit Palit, Muhammad A. Alam Mar 2012

Theory Of Charging And Charge Transport In “Intermediate” Thickness Dielectrics And Its Implications For Characterization And Reliability, Sambit Palit, Muhammad A. Alam

Birck and NCN Publications

Thin film dielectrics have broad applications, and the performance degradation due to charge trapping in these thin films is an important and pervasive reliability concern. It has been presumed since the 1960s that current transport in intermediate-thickness (IT) oxides (∼10–100 nm) can be described by Frenkel-Poole (FP) conduction (originally developed for ∼mm-thick films) and algorithms based on the FP theory can be used to extract defect energy levels and charging-limited lifetime. In this paper, we review the published results to show that the presumption of FP-dominated current in IT oxides is incorrect, and therefore, the methods to extract trap-depths to …

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Dynamics Of Surface-Coupled Microcantilevers In Force Modulation Atomic Force Microscopy - Magnetic Vs. Dither Piezo Excitation, Xin Xu, Marisol Koslowski, Arvind Raman Mar 2012

Dynamics Of Surface-Coupled Microcantilevers In Force Modulation Atomic Force Microscopy - Magnetic Vs. Dither Piezo Excitation, Xin Xu, Marisol Koslowski, Arvind Raman

Birck and NCN Publications

Force modulation atomic force microscopy is widely used for mapping the nanoscale mechanical properties of heterogeneous or composite materials using low frequency excitation of a microcantilever scanning the surface. Here we show that the excitation mode - magnetic or dither piezo, has a major influence on the surface-coupled microcantilever dynamics. Not only is the observed material property contrast inverted between these excitation modes but also the frequency response of the surface-coupled cantilever in the magnetic mode is near-ideal with a clear resonance peak and little phase distortion thus enabling quantitative mapping of the local mechanical properties. (C) 2012 American Institute …

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Collective Nature Of The Reentrant Integer Quantum Hall States In The Second Landau Level, N. Deng, A. Kumar, Michael J. Manfra, L. N. Pfeiffer, K. W. West, Gabor A. Csathy Feb 2012

Collective Nature Of The Reentrant Integer Quantum Hall States In The Second Landau Level, N. Deng, A. Kumar, Michael J. Manfra, L. N. Pfeiffer, K. W. West, Gabor A. Csathy

Birck and NCN Publications

We report an unexpected sharp peak in the temperature dependence of the magnetoresistance of the reentrant integer quantum Hall states in the second Landau level. This peak defines the onset temperature of these states. We find that in different spin branches the onset temperatures of the reentrant states scale with the Coulomb energy. This scaling provides direct evidence that Coulomb interactions play an important role in the formation of these reentrant states evincing their collective nature.

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Direct Measurements And Numerical Simulations Of Gas Charging In Microelectromechanical System Capacitive Switches, A. Venkattraman, A. Garg, Dimitrios Peroulis, Alina A. Alexeenko Feb 2012

Direct Measurements And Numerical Simulations Of Gas Charging In Microelectromechanical System Capacitive Switches, A. Venkattraman, A. Garg, Dimitrios Peroulis, Alina A. Alexeenko

Birck and NCN Publications

Gas breakdown in microelectromechanical system capacitive switches is demonstrated using high resolution current measurements and by particle-in-cell/Monte Carlo collision (PIC/MCC) simulations. Measurements show an electric current through a 3 mu m air gap increasing exponentially with voltage, starting at 60 V. PIC/MCC simulations with Fowler-Nordheim [Proc. R. Soc. London, Ser. A 119, 173 (1928)] field emission reveal self-sustained discharges with significant ion enhancement and a positive space charge. The effective ion-enhanced field emission coefficient increases with voltage up to about 0.3 with an electron avalanche occurring at 159 V. The measurements and simulations demonstrate a charging mechanism for microswitches consistent …

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