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.

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.

Plasma instabilities in the plume of hollow cathodes have been extensively researched in particular for high-current operation. The rise of plume mode ionization-like instability leads to a degradation of cathode’s performance along with the emergence of highly energetic ions that can produce sputtering of various cathode’s surfaces. Numerical simulations using 2D fluid or hybrid codes brought forward an interesting correlation between the evolution of ion acoustic turbulence (IAT) and emergence of plume mode oscillations. Such numerical findings were proven to be true by experimental measurements of wave dispersion and plume mode-IAT correlation in the plume of cathodes emitting currents >10 A. This study brings forward evidence of the correlation between plume mode oscillations and IAT in the plume of low-current cathodes operating with Kr at sub-ampere current levels. It is shown that at <1 A the plume mode instability is highly correlated with the IAT and the anomalous electron collision drives the electron transport in the cathode plume. The fluctuations in IAT wave energy lead to large temperature oscillations which then drive fluctuations in the density via ionization.

The Hall Micro Thrusters (HMTs) use cold gas or accelerated plasma dual mode to provide ultra-precise spacecraft altitude control. They were operated in space for the first time as part of the demonstration payloads on Chinese Academy of Science’s (CASs) Taiji-1 spacecraft since September 2019. Hall Micro Thruster Assemblies (HMTAs) were the actuators in drag-free control, and will compensate the nonconservative force for gravity wave observatories. The HMTAs meet the requirements of operating at 5-100 μ N of thrust with 0.7 μ N resolution and ≤0.6 μ N/Hz^1/2 (0.01-1 Hz) noise to deliver the nanometer-level precision control as fast as 30 ms measured by Gravitational Reference Sensor (GRS). A transfer function model in z-domain was fit and used to filter HMTs cathode voltage to predict GRSs thrust noise response. Simulations of a single or dual-frequency disturbance and the corresponding compensation demonstrated that HMTAs could deliver the required thrust profile expected. The capability to meet the requirements of thruster noise in drag-free control is critical for future missions because the acceleration noise on test mass directly relates to the gravity wave signa l. Preliminary in-orbit verification of Taiji-1 has showed HMTAs’ great potential in future, and the data in the experiments are presented in this paper.

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.

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.

Thermionic cathodes are essential for the operation of various electrostatic propulsion devices. They strongly influence the performance and lifetime of the propulsion system. In this study, a 1 A-class LaB6 laboratory model hollow cathode has been tested with krypton in diode and triode configurations in order to assess for the cathode discharge mode transition behavior. Measurements have been performed over a range of krypton mass flow rates (0.1, 0.15 and 0.21 mg/s, or 1.6, 2.4 and 3.4 sccm), keeper (0.1, 0.15, 0.2 A) and anode currents (0.1 to 1 A) at a fixed cathode-to- anode distance. Seven criteria were used to distinguish between the spot and plume mode operations. The results show that the mode transition in low-current cathodes may be a non-linear phenomenon and only some of the existing mode transition criteria can be used to accurately predict the spot/plume discharge regions at low emission currents.

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.

Plasma processing of materials in low frequency inductively coupled plasma (LF-ICP) reactors has limitations involving the presence of contaminant species found in the discharge. It has been shown in previous work through optical emission spectroscopy that a main source of contaminants were oxygen related species which were not part of the feedstock recipe. In this work, amorphous silicon thin films were grown on silicon substrates with a LF-ICP reactor. The dielectric top lid plays an important role in the reduction of oxygen species detected in the thin films. It was postulated that the source of the contaminants came from sputtering of the lids. The replacement of the conventional quartz (SiO2) lid with that of alumina (Al2O3) reduced the oxygen species present in the resulting discharge, which is often a source of contamination in the resulting thin films, impinging the passivation grade of the resulting films. The modified reactor configuration also resulted in increased hydrogenation and deposition rate of the thin films. The results show that alumina lids serve as a promising alternative in replacing the conventional quartz lids in LF-ICP reactors for materials processing, resulting in efficient power transfer to the plasma and films which are rid of contaminant species.