Imaging Electron Wave Functions Inside Open Quantum Rings

Combining Scanning Gate Microscopy (SGM) experiments and simulations, we demonstrate low temperature imaging of electron probability density $|\Psi|^{2}(x,y)$ in embedded mesoscopic quantum rings (QRs). The tip-induced conductance modulations share the same temperature dependence as the Aharonov-Bohm effect, indicating that they originate from electron wavefunction interferences. Simulations of both $|\Psi|^{2}(x,y)$ and SGM conductance maps reproduce the main experimental observations and link fringes in SGM images to $|\Psi|^{2}(x,y)$.Comment: new titl

Long dephasing time and high temperature ballistic transport in an InGaAs open quantum dot

We report on measurements of the magnetoconductance of an open circular InGaAs quantum dot between 1.3K and 204K. We observe two types of magnetoconductance fluctuations: universal conductance fluctuations (UCFs), and 'focusing' fluctuations related to ballistic trajectories between openings. The electron phase coherence time extracted from UCFs amplitude is larger than in GaAs/AlGaAs quantum dots and follows a similar temperature dependence (between T^-1 and T^-2). Below 150K, the characteristic length associated with 'focusing' fluctuations shows a slightly different temperature dependence from that of the conductivity.Comment: 6 pages, 4 figures, proceedings of ICSNN2002, to appear in Physica

Imaging and controlling electron transport inside a quantum ring

Traditionally, the understanding of quantum transport, coherent and ballistic1, relies on the measurement of macroscopic properties such as the conductance. While powerful when coupled to statistical theories, this approach cannot provide a detailed image of "how electrons behave down there". Ideally, understanding transport at the nanoscale would require tracking each electron inside the nano-device. Significant progress towards this goal was obtained by combining Scanning Probe Microscopy (SPM) with transport measurements2-7. Some studies even showed signatures of quantum transport in the surrounding of nanostructures4-6. Here, SPM is used to probe electron propagation inside an open quantum ring exhibiting the archetype of electron wave interference phenomena: the Aharonov-Bohm effect8. Conductance maps recorded while scanning the biased tip of a cryogenic atomic force microscope above the quantum ring show that the propagation of electrons, both coherent and ballistic, can be investigated in situ, and even be controlled by tuning the tip potential.Comment: 11 text pages + 3 figure

The impact of an exercise physiologist coordinated resistance exercise program on the physical function of people receiving hemodialysis: a stepped wedge randomised control study

Background:Exercise during hemodialysis treatments improves physical function, markers of cardiovascular disease and quality of life. However, exercise programs are not a part of standard therapy in the vast majority of hemodialysis clinics internationally. Hemodialysis unit-based accredited exercise physiologists may contribute to an increased intradialytic exercise uptake and improved physical function.Methods and design: This is a stepped wedge cluster randomised controlled trial design. A total of 180 participants will be recruited from 15 community satellite hemodialysis clinics in a large metropolitan Australian city. Each clinic will represent a cluster unit. The stepped wedge design will consist of three groups each containing five randomly allocated cluster units, allocated to either 12, 24 or 36 weeks of the intervention. The intervention will consist of an accredited exercise physiologist-coordinated program consisting of six lower body resistance exercises using resistance elastic bands and tubing. The resistance exercises will include leg abduction, plantar flexion, dorsi flexion, straight-leg/bent-knee raise, knee extension and knee flexion. The resistance training will incorporate the principle of progressive overload and completed in a seated position during the first hour of hemodialysis treatment. The primary outcome measure is objective physical function measured by the 30-second sit to stand test. Secondary outcome measures include the 8-foot timed-up-and-go test, the four square step test, quality of life, cost-utility analysis, uptake and involvement in community activity, self-reported falls, fall\u27s confidence, medication use, blood pressure and morbidity (hospital admissions). Discussion: The results of this study are expected to determine the efficacy of an accredited exercise physiologist supervised resistance training on the physical function of people receiving hemodialysis and the cost-utility of exercise physiologists in hemodialysis centres. This may contribute to intradialytic exercise as standard therapy using an exercise physiologist workforce model.</div

Low frequency noise conversion in fets under nonlinear operation

Based upon the active line concept, the conversion mechanisms of microscopic low frequency noise (e.g. generation-recombination noise) located in the channel of a Field Effect Transistor (FET) which is driven by a large RF signal is demonstrated. The first consequence is that the based band (low frequency) input gate noise voltage spectral density is dependent on the magnitude of the input RF power applied to the FET. Moreover, the microscopic generation-recombination noise sources located in the channel are responsible of up-converted input gate noise voltage spectral density around the RF frequency

0.12 µm GATE LENGTH In0.52Al0.48As/In0.53Ga0.47As HEMTs on transferred substrate

New In0.52Al0.48As/In0.53Ga0.47As transferred-substrate high electron mobility transistors (TS-HEMTs) have been successfully fabricated on 2 inch Silicon substrate with 0.12 µm T-shaped gate length. These new TS-HEMTs exhibit typical drain currents of 450 mA/mm and extrinsic transconductance up to 770 mS/mm. An extrinsic current cutoff frequency fT of 185 GHz is obtained. That result is the first reported for In0.52Al0.48As/In0.53Ga0.47As TS-HEMTs on Silicon substrate

Hemt structures and technology on GAAS and inp for power amplification in millimetre wave range

The paper introduces a simple and efficient approach for the modelling of low-frequency dispersive phenomena in FETs. It is based on the definition of a virtual, non-dispersive associated device controlled by equivalent port voltages and it is suitable for modelling based on standard nonlinear dynamic approaches, such as lumped-element equivalent circuits. The proposed approach is justified on the basis of a physically-consistent, charge-controlled description of the device, but the results are general and provide a valuable tool for taking into account dispersive effects in FETs by means of an intuitive circuit solution, in the framework of any existing nonlinear dynamic model of the associated non-dispersive device. The new equivalent-voltage description, identified on the basis of conventional measurements carried out under static and small-signal dynamic operating conditions, allows for the accurate prediction of dispersive effects above the frequency cut-off, but the formulation is still compatible, without for al modification, for the modelling of the device behaviour under signal excitations having spectral components in the dispersive low-frequency range. Preliminary results are presented which conferm the validity of the proposed approach

A new gate process for the realization of lattice - matched HEMT on InP for high yield MMICs

A new gate process for the realization of ultra short gate HEMT on InP is presented. In this technology, the top of the gate is deposited on a Si3N4 layer. This gate process leads to small footprints, mechanically strong devices and good yield. Using this gate technology, HEMT with high Ft were realized and characterized. The influence of the Si3N4 removing was also investigated