Piezoelectric rotator for studying quantum effects in semiconductor nanostructures at high magnetic fields and low temperatures

We report the design and development of a piezoelectric sample rotation system, and its integration into an Oxford Instruments Kelvinox 100 dilution refrigerator, for orientation-dependent studies of quantum transport in semiconductor nanodevices at millikelvin temperatures in magnetic fields up to 10T. Our apparatus allows for continuous in situ rotation of a device through >100deg in two possible configurations. The first enables rotation of the field within the plane of the device, and the second allows the field to be rotated from in-plane to perpendicular to the device plane. An integrated angle sensor coupled with a closed-loop feedback system allows the device orientation to be known to within +/-0.03deg whilst maintaining the sample temperature below 100mK.Comment: 8 pages, 5 figure

Correlated enhancement of Hc2 and Jc in carbon nanotube-doped MgB2

The use of MgB2 in superconducting applications still awaits for the development of a MgB2-based material where both current-carrying performance and critical magnetic field are optimized simultaneously. We achieved this by doping MgB2 with double-wall carbon nanotubes (DWCNT) as a source of carbon in polycrystalline samples. The optimum nominal DWCNT content for increasing the critical current density, Jc is in the range 2.5-10%at depending on field and temperature. Record values of the upper critical field, Hc2(4K) = 41.9 T (with extrapolated Hc2(0) ~ 44.4 T) are reached in a bulk sample with 10%at DWCNT content. The measured Hc2 vs T in all samples are successfully described using a theoretical model for a two-gap superconductor in the dirty limit first proposed by Gurevich et al.Comment: 12 pages, 3 figure

Low disordered, stable, and shallow germanium quantum wells: a playground for spin and hybrid quantum technology

Buried-channel semiconductor heterostructures are an archetype material platform to fabricate gated semiconductor quantum devices. Sharp confinement potential is obtained by positioning the channel near the surface, however nearby surface states degrade the electrical properties of the starting material. In this paper we demonstrate a two-dimensional hole gas of high mobility ($5\times 10^{5}$ cm$^2$/Vs) in a very shallow strained germanium channel, which is located only 22 nm below the surface. This high mobility leads to mean free paths $\approx6 \mu m$, setting new benchmarks for holes in shallow FET devices. Carriers are confined in an undoped Ge/SiGe heterostructure with reduced background contamination, sharp interfaces, and high uniformity. The top-gate of a dopant-less field effect transistor controls the carrier density in the channel. The high mobility, along with a percolation density of $1.2\times 10^{11}\text{ cm}^{-2}$, light effective mass (0.09 m$_e$), and high g-factor (up to $7$) highlight the potential of undoped Ge/SiGe as a low-disorder material platform for hybrid quantum technologies

Towards Sustainable Municipal Solid Waste Management in Malaysia

This work is part of the SYNERGORS project (“A Systems Approach to Synergistic Utilisation of Secondary Organic Streams”) funded by the UKRI Natural Environment Research Council (NE/R012938/1) through the UKRI/NERC Industrial Innovation Fellowship Programme (2018-2021). This project was led by Dr Kok Siew Ng at University of Oxford. Website: https://eng.ox.ac.uk/synergorsProject summary report: https://eng.ox.ac.uk/media/10670/synergors-final-report.pdfEXECUTIVE SUMMARY: The increasing amount of municipal solid waste (MSW) generation and the lack of strategic improvements on solid waste management in Malaysia require urgently the attention of the government and the public.It has been estimated that 1.17 kg/capita/day of MSW is generated in Malaysia, 65% of which is household solid waste that has doubled over the past 20 years due to population growth and urbanisation. Without a sufficient waste treatment and recycling infrastructure in place, most of the MSW is destined to continue to be landfilled. Not only it can cause pollution and health hazards, MSW is also one of the major sources of global methane emissions accounting for 11%. As methane is the second largest contributor of global greenhouse gas emissions after carbon dioxide, it is critical that Malaysia develops systemic sound solid waste management as part of its climate actions guided by the Paris agreement. Also, by treating waste as resource, the recent shift in the government strategy to move towards the circular economy should be aligned with SDG 12 targets (Responsible Consumption and Production). Although the quantity of recyclable waste collected tripled between 2018 and 2021, the officially reported recycling rate of 31.5% in 2021 remains questionable as the recycling infrastructure in Malaysia is not yet well established. This points to the significant efforts Malaysia needs to make to move towards a sustainable waste management regime, and to achieve its ambition for reaching a recycling target of 40% by 2025. Malaysia started implementing a plan for moving towards sustainable waste management in the early 1990s. However, the recycling programmes were not well received by the public at that time, and it was only in 2001, that policy goals for sustainable waste management have been included in the regulatory landscape through the 8th Malaysia Plan (2001-2005). In 2005, the National Strategic Plan for Solid Waste Management was developed to guide solid waste policy planning and resource allocation. Two years after, the Solid Waste and Public Cleansing Management Act 2007 (Act 672) was created that came into enforcement in September 2011 in six out of the thirteen states (Perlis, Kedah, Pahang, Negeri Sembilan, Melaka, Johor) and two out of the three federal territories (i.e. Kuala Lumpur and Putrajaya). This partial adoption of the Act has created inconsistency in waste management and planning as well as incomplete waste data gathering. This,has led to ineffective waste management practices, that, in turn, resulted in long-term environmental, economic and social consequences. Even though sustainable waste management goals continue to be included in the recent 12th Malaysia Plan (2021-2025), the lack of public awareness on the importance of source separation of waste and recycling prevents progress in this field. The infrastructure for waste collection and treatment is also insufficient to serve the needs. All these factors have created significant barriers for Malaysia to realise sustainable waste management.UK Natural Environment Research Council (NE/R012938/1

Art, Artifact, Archive: African American Experiences in the Nineteenth Century

Angelo Scarlato’s extraordinary and vast collection of art and artifacts related to the Civil War, and specifically to the Battle of Gettysburg, the United States Colored Troops, slavery and the African American struggle for emancipation, citizenship and freedom has proved to be an extraordinary resource for Gettysburg College students. The 2012-14 exhibition in Musselman Library’s Special Collections, curated by Lauren Roedner ’13, entitled Slaves, Soldiers, Citizens: African American Artifacts of the Civil War Era and its corresponding catalogue provided a powerful and comprehensive historical narrative of the period. This fall, students in my course at Gettysburg College “Art and Public Policy”—Diane Brennan, Maura Conley, Abigail Conner, Nicole Conte, Victoria Perez-Zetune, Savannah Rose, Kaylyn Sawyer, Caroline Wood and Zoe Yeoh—selected additional objects of material and print culture from Angelo’s private collection and drew from Lauren’s expertise for the exhibition Art, Artifact, Archive: African American Experiences in the Nineteenth Century to investigate public representations of a newly freed population as well as their more personal perspectives. [excerpt]https://cupola.gettysburg.edu/artcatalogs/1015/thumbnail.jp

Enhancement of Transition Temperature in FexSe0.5Te0.5 Film via Iron Vacancies

The effects of iron deficiency in FexSe0.5Te0.5 thin films (0.8<x<1) on superconductivity and electronic properties have been studied. A significant enhancement of the superconducting transition temperature (TC) up to 21K was observed in the most Fe deficient film (x=0.8). Based on the observed and simulated structural variation results, there is a high possibility that Fe vacancies can be formed in the FexSe0.5Te0.5 films. The enhancement of TC shows a strong relationship with the lattice strain effect induced by Fe vacancies. Importantly, the presence of Fe vacancies alters the charge carrier population by introducing electron charge carriers, with the Fe deficient film showing more metallic behavior than the defect-free film. Our study provides a means to enhance the superconductivity and tune the charge carriers via Fe vacancy, with no reliance on chemical doping.Comment: 15 pages, 4 figure