Doping, as a primary technique to modify semiconductor transport, has achieved tremendous success in the past decades. For example, boron and phosphorus doping of Si modulates the dominant carrier type between p-type and n-type, serving as the backbone for the modern microelectronic technologies. Doped III-V semiconducting systems exhibit phenomenal optoelectronic properties. Magnesium doped gallium nitride plays an important role to build efficient blue light-emitting diode (LED), which won Nobel Prize in physics in 2014. The rise of two-dimensional (2D) materials sheds light on their potential in next generation electronic, optoelectronic, and quantum applications. These properties can further be controlled via doping of 2D materials, however, many challenges still remain in this field. Here, we present a rapid review on the recent achievements and challenges in the metastable and substitutional doping of 2D materials, followed by providing an outlook on integrating 2D materials into more advanced electronic architectures.

Semiconductor nanowires (NWs) have widely been studied as an ideal platform for developing electronic, photovoltaic, photonic devices and biological probes in the nanoscale. The ability to synthesize high-quality NWs of various materials with a precise control in shape, doping and crystal structure is the key to the growth of NW-based technologies. In the past decade, there has been growing interest in controllably creating NW heterojunctions and periodically-modulated superlattices (SLs) because it is expected to bring new functionalities that are not present in uniform NWs. In particular, the interaction of NW SLs with light has been one of the central interests because the diameter and modulation length scale are on the same order as the wavelength of light in the optical regime. Also, degenerately-doped semiconductor NWs exhibit localized surface plasmon resonances (LSPRs), which comprises unexpected long-range interactions when the plasmon resonators are regularly placed in NW SLs. In this review, I will summarize the recent progress in photonics research of NW SLs. The topics discussed include preparation and types of NW SLs, light-trapping and light-emission properties, and plasmonic optical- and thermal-transport properties.

Solar water splitting can potentially play a significant role in the future, sustainable and carbon-neutral energy infrastructure - by generating hydrogen as a green fuel from renewable sources and liquid-fuels via carbon-dioxide reduction. Hydrogen has higher gravimetric energy-yield compared to most of the conventional fossil fuels, is storable and transportable on demand. With the prospective green hydrogen economy in mind, considerable efforts have been made in the quest for a stable and efficient photocatalyst/photoelectrode which can eventually lead towards the realization of large-scale hydrogen production system. This snapshot review provides a summary of the basic principles and challenges associated with unassisted overall water splitting, and highlights the recent technological advancements made on the device and system designs on lab-scale - to improve different performance metrics, i.e., efficiency, stability, scalability and large-scale prototypes with demonstrated potentials for future developments.

In recent decades, increasing research interest has shifted from traditional rigid skeleton robotics to flexible, shape-programmable, environmentally adaptive and stimuli-responsive “soft robotics”. Within this discipline, soft-robots capable of untethered and/or remote-controlled operation are of particular interest given their utility for actuation in complex situations with larger range of mobility and higher degrees of freedom. The use of new materials and the development of advanced fabrication techniques enable better performance and expand the utility of such soft actuators, moving them towards real-world applications. This review outlines some recent advances in untethered soft robotics and actuators to illustrate the promise of these applications at the interface of material science and device engineering.

There is widespread research and popular interest in developing micro-invasive neural interfacing modalities. An increasing variety of probes have been developed and reported in the literature. Newer, smaller probes show significant benefit over larger ones in reducing tissue damage and scarring. A different set of obstacles arise, however, as probes become smaller. These include reliable insertion and robustness. This review articulates the impact of various design parameters (material, geometry, size) on probe insertion mechanisms, chronic viability, and glial scarring. We highlight various emerging technologies utilizing novel form factors including micron-scale interfaces and bio-inspired designs for probe insertion and steering.

An emerging family of materials—metal halide perovskites (MHPs)—have made incredible achievements in optoelectronics in the past decade. Owing to its potential role in optoelectronic properties, the ferroic state of MHPs has been investigated by lots of researchers. Here, we review the literature regarding investigations into possible ferroic behaviors in MHPs. We summarize the recent discoveries of ferroic twin domains in MHPs. We examine the ferroelasticity and the ferroelectricity of these twin domains. Several properties relevant to the twin domains are critically analyzed, including crystallographic structure, mechanical variation, chemical variation, etc. Finally, we discussed the effects of these domains on materials’ optoelectronic properties and their potential roles in photovoltaic action.

High resolution (< 1 µm) computed tomography is an attractive tool in materials research due to its ability to non-destructively visualize the three-dimensional internal microstructures of the material. Recently, this technique has been further empowered by adding a fourth (temporal) dimension to study the time-lapse material response under load. Such studies are referred to as four-dimensional or in situ testing. In this snapshot review, we highlight three representative examples of in situ testing using synchrotron radiation computed tomography (SRCT) for composites failure analysis, measurement of local corrosion rate in alloys, and visualization and quantification of electrochemical reactions in lithium-ion batteries, as well as forward-looking integration of machine learning with in situ CT. Lastly, the future opportunities and challenges of in situ SRCT testing are discussed.

The energy density of electrodeposition reactions makes them attractive for energy storage. Although its scientific inquiries nearly date back to the inception of electrochemistry, its behavior at microscopic dimensions (relevant to battery application) is mysteriously uncontrollable. We examine experimental reports of singular spatiotemporal evolutions with a hope to identify universality in deposition patterns. We conclude that a macroscopic mass transport instability cannot account for various growth morphologies and alludes to poorly understood materials interplay at smaller scales. We summarize representative characteristics of electrodeposition to encourage mechanistic investigations.