Fabrication and Characterization of Electrostatic Quantum Dots in a Si/SiGe 2D Electron Gas, Including an Integrated Read-out Channel

A new fabrication technique is used to produce quantum dots with read-out channels in silicon/silicon-germanium two-dimensional electron gases. The technique utilizes Schottky gates, placed on the sides of a shallow etched quantum dot, to control the electronic transport process. An adjacent quantum point contact gate is integrated to the side gates to define a read-out channel and thus allow for noninvasive detection of the electronic occupation of the quantum dot. Reproducible and stable Coulomb oscillations and the corresponding jumps in the read-out channel resistance are observed at low temperatures. The fabricated dot combined with the read-out channel represent a step towards the spin-based quantum bit in Si/SiGe heterostructures.Comment: 3 pages, 4 fig

Sputtered Gold as an Effective Schottky Gate for Strained Si/SiGe Nanostructures

Metallization of Schottky surface gates by sputtering Au on strained Si/SiGe heterojunctions enables the depletion of the two dimensional electron gas (2DEG) at a relatively small voltage while maintaining an extremely low level of leakage current. A fabrication process has been developed to enable the formation of sub-micron Au electrodes sputtered onto Si/SiGe without the need of a wetting layer.Comment: 3 pages, 3 figure

Searching for Hyperbolicity

This is an expository paper, based on by a talk given at the AWM Research Symposium 2017. It is intended as a gentle introduction to geometric group theory with a focus on the notion of hyperbolicity, a theme that has inspired the field from its inception to current-day research

Difficulty of distinguishing product states locally

Non-locality without entanglement is a rather counter-intuitive phenomenon in which information may be encoded entirely in product (unentangled) states of composite quantum systems in such a way that local measurement of the subsystems is not enough for optimal decoding. For simple examples of pure product states, the gap in performance is known to be rather small when arbitrary local strategies are allowed. Here we restrict to local strategies readily achievable with current technology; those requiring neither a quantum memory nor joint operations. We show that, even for measurements on pure product states there can be a large gap between such strategies and theoretically optimal performance. Thus even in the absence of entanglement physically realizable local strategies can be far from optimal for extracting quantum information.Comment: 5 pages, 1 figur

A Comparison of Rainfall Estimation Techniques

This study compares two techniques that have been developed for rainfall and streamflow estimation with the aim of identifying strengths and weaknesses of each. The first technique utilises thin plate smoothing splines to develop rainfall surfaces for the catchment, which are then, in conjunction with daily point-wise rainfall data used to determine areal catchment estimates. The second technique develops a regression-based model relating elevation to total annual rainfall in order to scale rainfall for daily mean catchment rainfall estimates. Both approaches are compared in common catchments in the upper Murrumbidgee catchment. The comparison includes using the data from each of the approaches as input to a rainfall-runoff model and by comparison of the quality of modelled results to observed streamflow. The strengths, weaknesses and use for catchment managers in decision making are identified. The study results revealed that where rain station spatial density and data quality are high, both regression and the spline method perform equally as well in estimating long term rainfall trends. In conclusion, catchment managers could apply the simple regression technique over the sophisticated spline method to achieve the comparable results. This is particularly useful where an efficient yet simple method is required for assessing streamflow within similar catchments

Design of water quality monitoring programs and automatic sampling techniques

An important means of characterising the health of streams is through the measurement of the sediment and nutrient fluxes that they transport. Cost effective and targeted water quality monitoring programs are required to properly quantify both the total loads and temporal distribution of these fluxes at catchment scales. Careful analysis of data from such programs ensures ameliorative efforts to reduce the biological, chemical and physical impacts of high loads are targeted to have the best effect. This paper reports on the development of a monitoring program in tributaries of the upper Murrumbidgee River. The aim of the program is to provide data for the modelling of both nutrient and sediment loads transported from upland catchments. The objective of the modelling is to spatially identify sediment transport and storage dynamics together with source strength variations in upland catchments. A brief review of design considerations for water quality programs is made with reference to the Murrumbidgee case study. The tools, techniques and sites of an alternative monitoring program in tributaries of the upper Murrumbidgee River are detailed. Included in the paper are modifications to the design of Graczyk et al. (2000) for an inexpensive, rising-stage water quality sampler, suitable for Australian conditions and currently in use. The research demonstrates that water quality data can be collected simply and cost effectively if programs are appropriately designed

Silicon-Germanium Films Grown on Sapphire for Ka-Band Communications Applications

NASA's vision in the space communications area is to develop a broadband data network in which there is a high degree of interconnectivity among the various satellite systems, ground stations, and wired systems. To accomplish this goal, we will need complex electronic circuits integrating analog and digital data handling at the Ka-band (26 to 40 GHz). The purpose of this project is to show the feasibility of a new technology for Ka-band communications applications, namely silicon germanium (SiGe) on sapphire. This new technology will have several advantages in comparison to the existing silicon-substrate- based circuits. The main advantages are extremely low parasitic reactances that enable much higher quality active and passive components, better device isolation, higher radiation tolerance, and the integration of digital and analog circuitry on a single chip

Filling minimality of Finslerian 2-discs

We prove that every Riemannian metric on the 2-disc such that all its geodesics are minimal, is a minimal filling of its boundary (within the class of fillings homeomorphic to the disc). This improves an earlier result of the author by removing the assumption that the boundary is convex. More generally, we prove this result for Finsler metrics with area defined as the two-dimensional Holmes-Thompson volume. This implies a generalization of Pu's isosystolic inequality to Finsler metrics, both for Holmes-Thompson and Busemann definitions of Finsler area.Comment: 16 pages, v2: improved introduction and formattin

High Mobility SiGe/Si n-Type Structures and Field Effect Transistors on Sapphire Substrates

SiGe/Si n-type modulation doped field effect transistors (MODFETs) fabricated on sapphire substrates have been characterized at microwave frequencies for the first time. The highest measured room temperature electron mobility is 1380 sq cm/V-sec at a carrier density of 1.8 x 10(exp 12)/sq cm for a MODFET structure, and 900 sq cm/V-sec at a carrier density of 1.3 x 10/sq cm for a phosphorus ion implanted sample. A two finger, 2 x 200 micron gate n-MODFET has a peak transconductance of 37 mS/mm at a drain to source voltage of 2.5 V and a transducer gain of 6.4 dB at 1 GHz