Statistical Properties of Interacting Bose Gases in Quasi-2D Harmonic Traps

The analytical probability distribution of the quasi-2D (and purely 2D) ideal and interacting Bose gas are investigated by using a canonical ensemble approach. Using the analytical probability distribution of the condensate, the statistical properties such as the mean occupation number and particle number fluctuations of the condensate are calculated. Researches show that there is a continuous crossover of the statistical properties from a quasi-2D to a purely 2D ideal or interacting gases. Different from the case of a 3D Bose gas, the interaction between atoms changes in a deep way the nature of the particle number fluctuations.Comment: RevTex, 10pages, 4 figures, E-mail: [email protected]

Control of threshold voltage in E-mode and D-mode GaN-on-Si metal-insulator-semiconductor heterostructure field effect transistors by in-situ fluorine doping of atomic layer deposition Al2O3 gate dielectrics

We report the modification and control of threshold voltage in enhancement and depletion mode AlGaN/GaN metal-insulator-semiconductor heterostructure field effect transistors through the use of in-situ fluorine doping of atomic layer deposition Al2O3. Uniform distribution of F ions throughout the oxide thickness are achievable, with a doping level of up to 5.5 × 1019 cm−3 as quantified by secondary ion mass spectrometry. This fluorine doping level reduces capacitive hysteretic effects when exploited in GaN metal-oxide-semiconductor capacitors. The fluorine doping and forming gas anneal also induces an average positive threshold voltage shift of between 0.75 and 1.36 V in both enhancement mode and depletion mode GaN-based transistors compared with the undoped gate oxide via a reduction of positive fixed charge in the gate oxide from +4.67 × 1012 cm−2 to −6.60 × 1012 cm−2. The application of this process in GaN based power transistors advances the realisation of normally off, high power, high speed devices

1H NMR of Deep Eutectic Solvents

Deep Eutectic Solvents (DESs) form between a variety of quaternary ammonium or phosphonium salts and hydrogen-bond donors. Over the past decade, DESs have been studied as green solvents with potential applications in industrial processes, chemical extractions, and pharmaceuticals. The recent suggestion that many plants produce natural deep eutectic solvents (NADES) from primary metabolites led to investigation of the potential uses of DESs in biophysics research. This study examined the 1H NMR spectra of the choline chloride:urea 1:2, and choline chloride:ethylene glycol 1:3 molar ratio DES. Spectra of the choline chloride:urea 1:2 with various solutes were acquired to see what effect these solutes had on the DESs NMR spectrum. For both DESs tested, the NMR spectra were a superposition of the spectra of the components. DES-solute spectra showed that interaction between components persisted, indicating the solvent properties of the DESs were not lost upon addition of solutes

Nano-cathodoluminescence reveals the effect of electron damage on the optical properties of nitride optoelectronics and the damage threshold

Nano-cathodoluminescence (Nano-CL) reveals optical emission from individual InGaN quantum wells for applications in optoelectronic devices. We show the luminescent intensity decays over time with exposure to the electron beam for energies between 80 and 200 keV. Measurements of the CL intensity over time show an exponential decline in intensity, which we propose is due to the formation of nitrogen Frenkel defects. The measured CL damage decreases with reductions in the electron accelerating voltage and we suggest that the electron induced structural damage may be suppressed below the proposed damage threshold. The electron beam induced damage leads to a non-radiative region that extends over the measured minority carrier diffusion length. Nano-CL may thus serve as a powerful technique to study III-nitride optoelectronics.This work was carried out with the support of the United Kingdom Engineering and Physical Sciences Research Council under Grant Nos. EP/NO17927/1 and EP/J003603/1. R. Oliver acknowledges funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013) ERC grant agreement number 279361 (MACONS) and the from the Royal Academy of Engineers/Leverhulme Trust senior research fellowship

Impact of buffer charge on the reliability of carbon doped AlGaN/GaN-on-Si HEMTs

Charge trapping and transport in the carbon doped GaN buffer of an AlGaN/GaN-on-Si HEMT have been investigated. Back-gating and dynamic RON experiments show how the onset of leakage in the strain relief layer at a lower field than that through the upper part of the structure can result in serious long-term trapping leading to current collapse under standard device operating conditions. Controlling current-collapse requires control of not only the layer structures and its doping, but also the precise balance of leakage in each layer

Quantum Revivals in Periodically Driven Systems close to nonlinear resonance

We calculate the quantum revival time for a wave-packet initially well localized in a one-dimensional potential in the presence of an external periodic modulating field. The dependence of the revival time on various parameters of the driven system is shown analytically. As an example of application of our approach, we compare the analytically obtained values of the revival time for various modulation strengths with the numerically computed ones in the case of a driven gravitational cavity. We show that they are in very good agreement.Comment: 14 pages, 1 figur

Interference of Bose-Einstein condensates in momentum space

We suggest an experiment to investigate the linear superposition of two spatially separated Bose-Einstein condensates. Due to the coherent combination of the two wave functions, the dynamic structure factor, measurable through inelastic photon scattering at high momentum transfer $q$, is predicted to exhibit interference fringes with frequency period $\Delta\nu = q/md$ where $d$ is the distance between the condensates. We show that the coherent configuration corresponds to an eigenstate of the physical observable measured in the experiment and that the relative phase of the condensates is hence created through the measurement process.Comment: 4 pages and 2 eps figure

Heterogeneous integration of gallium nitride light-emitting diodes on diamond and silica by transfer printing

We report the transfer printing of blue-emitting micron-scale light-emitting diodes (micro-LEDs) onto fused silica and diamond substrates without the use of intermediary adhesion layers. A consistent Van der Waals bond was achieved via liquid capillary action, despite curvature of the LED membranes following release from their native silicon growth substrates. The excellence of diamond as a heat-spreader allowed the printed membrane LEDs to achieve optical power output density of 10 W/cm2 when operated at a current density of 254 A/cm2. This high-currentdensity operation enabled optical data transmission from the LEDs at 400 Mbit/s

A quantum mechanical description of the experiment on the observation of gravitationally bound states

Quantum states in the Earth's gravitational field were observed, when ultra-cold neutrons fall under gravity. The experimental results can be described by the quantum mechanical scattering model as it is presented here. We also discuss other geometries of the experimental setup which correspond to the absence or the reversion of gravity. Since our quantum mechanical model describes, particularly, the experimentally realized situation of reversed gravity quantitatively, we can practically rule out alternative explanations of the quantum states in terms of pure confinement effects.Comment: LaTeX, 10 pages, 4 figures, v2: references adde