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Physical computing is becoming mainstream. More people than ever---from artists, makers and entrepreneurs to educators and students---are connecting microcontrollers with sensors and actuators to create new interactive devices. However, physical computing still presents many challenges and demands many skills, spanning electronics, low-level protocols, and software---road blocks that reduce participation. While USB has made connecting peripherals to a personal computing device (PC) trivial, USB components are expensive and require a PC to operate. This makes USB impractical for many physical computing scenarios where cost, size and low power operation are often important.

We present transport measurements of bilayer graphene with 1.38{\deg} interlayer twist and apparent additional alignment to its hexagonal boron nitride cladding. As with other devices with twist angles substantially larger than the magic angle of 1.1{\deg}, we do not observe correlated insulating states or band reorganization. However, we do observe several highly unusual behaviors in magnetotransport. For a large range of densities around half filling of the moir\'e bands, magnetoresistance is large and quadratic. Over these same densities, the magnetoresistance minima corresponding to gaps between Landau levels split and bend as a function of density and field. We reproduce the same splitting and bending behavior in a simple tight-binding model of Hofstadter's butterfly on a square lattice with anisotropic hopping terms. These features appear to be a generic class of experimental manifestations of Hofstadter's butterfly and may provide insight into the emergent states of twisted bilayer graphene., Comment: 8 pages, 4 figures; updated supplemental material; added additional device measurements and updated toy model

Auger recombination in semiconductors is a many-body phenomenon in which recombination of electrons and holes is accompanied by excitation of other charge carriers. Being nonradiative, it is detrimental to light emission. The excess energy of the excited carriers is normally rapidly converted to heat, making Auger processes difficult to probe directly. Here, we employ a technique in which the Auger-excited carriers are detected by their ability to tunnel out of the semiconductor through a thin barrier, generating a current. We employ vertical van der Waals (vdW) heterostructures with monolayer WSe2 as the semiconductor and the wide band gap hexagonal boron nitride (hBN) as the tunnel barrier to preferentially transmit high-energy Auger-excited carriers to a graphite electrode. The unambiguous signatures of Auger processes are a rise in the photocurrent when excitons are created by resonant excitation, and negative differential photoconductance resulting from the shifts of the exciton resonances with voltage. We detect holes Auger-excited by both neutral and charged excitons, and find that the Auger scattering is surprisingly strong under weak excitation. The selective extraction of Auger carriers at low, controlled carrier densities that is enabled by vdW heterostructures illustrates an important addition to the techniques available for probing relaxation processes in 2D materials.

The micro:bit is a small programmable and embeddable computer designed, developed, and deployed by the BBC and 29 project partners to approximately 800,000 UK Year 7 (11/12 year old) school children in 2015-2016. The micro:bit has been described by the BBC as "its most ambitious education initiative in 30 years, with an ambition to inspire digital creativity and develop a new generation of tech pioneers". This article describes the design of the BBC micro:bit, the realization of its goals through examples of the diverse projects crested with the micro:bit, reviews the project's history as it transitioned from a UK-centric to a worldwide project, and concludes with lessons learned and project outcomes.

As IoT becomes increasingly pervasive, children are more regularly encountering IoT. The recent GDPR legislation in Europe goes some way toward protecting children as they make use of these IoT and other technologies, but there remain significant challenges in ensuring that the IoT that pervades children's world is socially responsible. This paper explores some of the reasons why the ethical implications of IoT for children is difficult to contain, and suggests several ways that design might make progress toward socially responsible IoT.

We present the design and implementation of a measurement system that enables parallel drive and detection of small currents and voltages at numerous electrical contacts to a multi-terminal electrical device. This system, which we term a feedback lock-in, combines digital control-loop feedback with software-defined lock-in measurements to dynamically source currents and measure small, pre-amplified potentials. The effective input impedance of each current/voltage probe can be set via software, permitting any given contact to behave as an open-circuit voltage lead or as a virtually grounded current source/sink. This enables programmatic switching of measurement configurations and permits measurement of currents at multiple drain contacts without the use of current preamplifiers. Our 32-channel implementation relies on commercially available digital input/output boards, home-built voltage preamplifiers, and custom open-source software. With our feedback lock-in, we demonstrate differential measurement sensitivity comparable to a widely used commercially available lock-in amplifier and perform efficient multi-terminal electrical transport measurements on twisted bilayer graphene and SrTiO3quantum point contacts. The feedback lock-in also enables a new style of measurement using multiple current probes, which we demonstrate on a ballistic graphene device.

Historically, embedded systems development has been a specialist skill, requiring knowledge of low-level programming languages, complex compilation toolchains, and specialist hardware, firmware, device drivers and applications. However, it has now become commonplace for a broader range of non-specialists to engage in the making (design and development) of embedded systems - including educators to motivate and excite their students in the classroom. This diversity brings its own set of unique requirements, and the complexities of existing embedded systems development platforms introduce insurmountable barriers to entry. In this paper we present the motivation, requirements, implementation, and evaluation of a new programming platform that enables novice users to create effective and efficient software for embedded systems. The platform has two major components: (1) Microsoft MakeCode ( www.makecode.com ), a web app that encapsulates an accessible IDE for microcontrollers; and (2) CODAL, an efficient component-oriented C++ runtime for microcontrollers. We show how MakeCode and CODAL combine to provide an accessible, cross-platform, installation-free, high level programming experience for embedded devices without sacrificing performance and efficiency.

Technology has become increasingly pervasive in the creative and experimental environment of the avant-garde fashion runway, particularly in relation to its garments. However, several disciplines are often necessary when exploring technologies for the construction of expressive garments (e.g. garments that respond to their environment), creating a barrier for fashion designers that has limited their ability to leverage new technologies. To help overcome this barrier, we designed and deployed Brookdale, a prototyping system for wearable technology consisting of new plug-and-play hardware that can be programmed using drag-and-drop software. Brookdale was created using a 24-week participatory design process with 17 novice fashion-tech designers. At the end of the 24 week process, designers showcased their Brookdale-enhanced garment collections at an avant-garde fashion-tech runway show in New York City. We report on the experiences, outcomes, and lessons learned throughout this process, and describe results from interviews with the fashion-tech designers 16 weeks after the fashion show, demonstrating the lasting positive impact of Brookdale.

We have previously reported ferromagnetism evinced by a large hysteretic anomalous Hall effect in twisted bilayer graphene (tBLG). Subsequent measurements of a quantized Hall resistance and small longitudinal resistance confirmed that this magnetic state is a Chern insulator. Here we report that, when tilting the sample in an external magnetic field, the ferromagnetism is highly anisotropic. Because spin-orbit coupling is negligible in graphene such anisotropy is unlikely to come from spin, but rather favors theories in which the ferromagnetism is orbital. We know of no other case in which ferromagnetism has a purely orbital origin. For an applied in-plane field larger than $5\ \mathrm{T}$, the out-of-plane magnetization is destroyed, suggesting a transition to a new phase., Comment: 30 pages, 10 figures

Policymakers and educators around the globe acknowledge the importance of computer science (CS) education. But traditional CS teaching tools and methodologies do not necessarily address the needs of a diverse, global student population or the latest developments in modern programming and data science. Physical computing – combining software and hardware to build interactive physical systems that sense and respond to the real world – has been shown to result in broad engagement across a spectrum of users. In this paper we review prior research into physical computing in the classroom and combine this with our own experiences. We summarise the reported benefits and show how recent trends in the design and implementation of physical computing devices and systems are resulting in growing adoption. By way of example, we provide a detailed description of a recently developed physical computing system, the BBC micro:bit.

In this paper we report on research exploring the privacy, security and safety implications of children being able to program Internet of Things devices. We present our methodology for understanding the contexts in which children may wish to use programmable IoT, identifying risks that emerge in such contexts, and creating a set of questions that might guide design of such technologies so that they are safe for child users. We evaluate the success of the methodology, discuss the limitations of the approach, and describe future work.

The growing maker movement has created a number of hardware and construction toolkits that lower the barriers of entry into programming for youth and others, using a variety of approaches, such as gaming or robotics. For constructionist-like kits that use gaming, many are focused on designing and programming games that are single player, and few explore using physical and craft-like approaches that move beyond the screen and single player experiences. Moving beyond the screen to incorporate physical sensors into the creation of gaming experiences provides new opportunities for learning about concepts in a variety of areas in computer science and making. In this early work, we elucidate our design goals and prototype for a mini-arcade system that builds upon principles in constructionist gaming - making games to learn programming - as well as physical computing.