Xu, Shuyan

Information technology is a critical element in teaching and learning and is central to our mission of preparing students for the 21St century. This work explores the use and benefit of computer aided techniques in undergraduate physics teaching. It is demonstrated that the computer aided teaching techniques indeed promote students' deep learning and critical thinking skills, especially for undergraduate theoretical and experimental physics courses. The results show that such a non-conventional approach provides a great opportunity to effectively motivate students in understanding some abstractive physical concepts and principles.

Surface texturing is a method widely adopted by industries to reduce the reflective losses in photovoltaic (PV) cells. In this work, a multi-chambered Integrated Plasma Photovoltaic Nanofabrication Cluster facility was used to produce nanocone surface textured polycrystalline (PX) PV cells. An inductively coupled plasma (ICP) discharge of O2 and SF6 was used to remove damage on PX p-type silicon wafers. Following that, a mixture of H2 and Ar plasma was used to texture an anti-reflecting array of silicon nanocones on the surface, while simultaneously forming a p-n junction. A plasma enhanced chemical vapour deposition (PECVD) process was utilized using SiH4, CO2, N2 and H2 precursors for front and back surface passivation for growth of SiNx:H and SiOxH thin films. Aluminium electrodes were sputtered on using an RF magnetron sputtering facility to provide the contacts for the PV cell. Scanning electron microscopy of textured sample surfaces revealed uniform, well defined, high aspect ratio nanocones. The absorption spectra of the resulting surface show dramatic reductions in the reflectance of the wafers, and external quantum efficiency measurements show improved spectral response for the 300 nm – 1100 nm region. The resulting cells showed promising photovoltaic responses, with short circuit-currents of 36 mA/cm2, open circuit voltages of 560 mV, fill factors reaching 80% and conversion efficiencies of up to 14.8%. The feedstock gases utilized in this entire process were mostly environmentally friendly, and the single plasma based processing cluster eliminated the need for excessive waste generated from chemicals that would be otherwise found in commercial production lines. This work shows exciting potential in the pursuit of fabricating low cost, environmentally friendly and highly efficient PV modules to address the problems posed by the global energy crisis.

The age of space electric propulsion arrived and found the space exploration endeavors at a paradigm shift in the context of new space. Mega-constellations of small satellites on low-Earth orbit (LEO) are proposed by many emerging commercial actors. Naturally, the boom in the small satellite market drives the necessity of propulsion systems that are both power and fuel efficient and accommodate small form-factors. Most of the existing electric propulsion technologies have reached the maturity level and can be the prime choices to enable mission versatility for small satellite platforms in Earth orbit and beyond. At the Plasma Sources and Applications Centre/Space Propulsion Centre (PSAC/SPC) Singapore, a continuous effort was dedicated to the development of low-power electric propulsion systems that can meet the small satellites market requirements. This review presents the recent progress in the field of electric propulsion at PSAC/SPC Singapore, from Hall thrusters and thermionic cathodes research to more ambitious devices such as the rotamak-like plasma thruster. On top of that, a review of the existing vacuum facilities and plasma diagnostics used for electric propulsion testing and characterization is included in the present research.

This focused review aims to reveal and illustrate some unique features of processes triggered by high-density energy applied to liquids and gas-liquid interfaces and to highlight a wide spectrum of their technological applications capable of producing various advantageous effects, ranging from nanosynthesis to biological and medical applications. Plasma, electric discharges, laser, and ultrasound power effects were selected as representative examples of high-density energy and liquid interactions, yet the available possibilities are not limited by these quite different types of power and thus the reader could extrapolate the outlined features and effects to other kinds of powerful impacts. The basic physical mechanisms are briefly reviewed with the aim to familiarize the readers with the potential capabilities of high-density energy processes in liquids. These will be of direct interest to researchers tasked with the development, optimization, and characterization of processes and highly reactive environments for highly controlled transformation of matter in abiotic and biological systems. It could also be highly useful for under- and post-graduate students specializing in the related fields and general physical audience involved in various plasma, materials, energy conversion, and other concurrent research activities.

Inhospitable, inaccessible, and extremely remote alike the famed pole of inaccessibility, aka Point Nemo, the isolated locations in deserts, at sea, or in outer space are difficult for humans to settle, let alone to thrive in. Yet, they present a unique set of opportunities for science, economy, and geopolitics that are difficult to ignore. One of the critical challenges for settlers is the stable supply of energy both to sustain a reasonable quality of life, as well as to take advantage of the local opportunities presented by the remote environment, e.g., abundance of a particular resource. The possible solutions to this challenge are heavily constrained by the difficulty and prohibitive cost of transportation to and from such a habitat (e.g., a lunar or Martian base). In this essay, the advantages and possible challenges of integrating Fischer–Tropsch, artificial photosynthesis, and plasma catalysis into a robust, scalable, and efficient self-contained system for energy harvesting, storage, and utilization are explored.

Structural stability, electronic, and optical properties of InN under high pressure are studied using the first-principles calculations. The lattice constants and electronic band structure are found consistent with the available experimental and theoretical values. The pressure of the wurtzite-to-rocksalt structural transition is 13.4 GPa, which is in an excellent agreement with the most recent experimental values. The optical characteristics reproduce the experimental data thus justifying the feasibility of our theoretical predictions of the optical properties of InN at high pressures.

Heated thermionic cathodes based on LaB6 emitters are known to consume a relatively large amount of power during the heating part of the ignition phase. Miniaturized electric propulsion systems, and in particular low-power Hall thrusters, rely on the operation of self-sustained cathodes at low-current emission, typically below 1 A. At PSAC/SPC, an open-end knife-edge LaB6 emitter hollow cathode was developed and tested, denoted herein as the PSAC-KE cathode. Here, a detailed description of the new model's design and comparison to the older version, the PSAC cathode, is included. Electrostatic simulations suggested that the open-end emitter geometry allowed for an enhanced electric field within the emitter region during cathode startup and steady-state operation as compared to the orificed emitter PSAC cathode. The PSAC-KE cathode's thermal management was improved based on iterative thermal simulations driven by different cathode geometries and various combinations of materials. The new cathode was tested with xenon in diode mode with an external anode and triode mode with the external anode and the keeper electrode. Furthermore, results from the coupling tests with a low-power Hall thruster are presented. Cathode performance was monitored over a range of anode current from 0.1 to 1 A, mass flow rates from 0.057 to 0.3 mg s−1 and keeper current of 0.05, 0.1, and 0.15 A. The cathode's thermal design was assessed with thermocouple measurements and compared with thermal simulations and results obtained for the PSAC cathode. The preliminary tests showed that the PSAC-KE cathode achieved ignition at low heating power below 35 W, self-sustained operation at 1 A when in standalone mode, and <1 A when against a low-power Hall thruster.

The development of plasma-based propulsion thrusters for spacecraft has seen a rapid growth over the past few decades, with the number of spacecraft including small satellites and Cubesats increasing exponentially. Although traditional chemical propulsion is still widely employed in space flights, it cannot meet the more challenging requirements for deep space travel due to low specific impulse. Electric propulsion thrusters have already helped humans travel further from Earth and have the potential to be developed for interstellar flights due to their advantages such as high velocity increments, long operational lifetimes, high impulse-to-weight ratios and high impulse-to-power ratios. The electrodynamic thrusters have significant potential for applications in the remote regions of space, and several types of electrodynamic plasma thrusters are currently under investigation. In this paper we present conceptual experiments to study a miniaturized Rotamak-type device initially proposed for the controlled thermonuclear fusion, with a view to assess its potential for the application as a small space thruster. An outline of the physical characteristics of the experiments that has been carried out, and measurements were done to try to elucidate the important mechanisms at work in the Rotamak, which will help design next-generation thruster capabilities. A discussion is also presented about the Rotamak systems and the opportunities they present for space applications.

Silicon based photovoltaic cells still remain a mainstay in the industries due to its relatively low cost for manufacturing and implementation. A good knowledge base of the material has also been built up over the years and there is no doubt that silicon based photovoltaic cells would continue to lay the basis for renewable energy for many years to come. However, it is widely known that conventional silicon photovoltaic cells have relatively lower power conversion efficiencies as compared to its next generation counterparts. This is partly due to the high optical losses on surfaces, resulting in poor harvesting of energy from incident light. In this work, an ICP process was developed to fabricate ultra-low reflective silicon surfaces for photovoltaic applications. An Ar + H2 feedstock was used to texture nanocones on the surface of silicon wafers, reducing the reflective losses and forming a high quality pn junction simultaneously. Reflectivity of the samples were characterised with a Zolix SCS10-X150-DSSC UV-Vis spectrometer with an attached integrating sphere, while the photovoltaic properties were measured with a PV characterization suite from Sinton instruments. The low reflectivity with promising electronic properties of the processed materials shows propitious potential for applications in the field of photovoltaics.