To fully exploit the potential of semiconducting nanowires for devices, high quality electrical contacts are of paramount importance. This work presents a detailed in situ transmission electron microscopy (TEM) study of a very promising type of NW contact where aluminum metal enters the germanium semiconducting nanowire to form an extremely abrupt and clean axial metal–semiconductor interface. We study this solid-state reaction between the aluminum contact and germanium nanowire in situ in the TEM using two different local heating methods. Following the reaction interface of the intrusion of Al in the Ge nanowire shows that at temperatures between 250 and 330 °C the position of the interface as a function of time is well fitted by a square root function, indicating that the reaction rate is limited by a diffusion process. Combining both chemical analysis and electron diffraction we find that the Ge of the nanowire core is completely exchanged by the entering Al atoms that form a monocrystalline nanowire with the usual face-centered cubic structure of Al, where the nanowire dimensions are inherited from the initial Ge nanowire. Model-based chemical mapping by energy dispersive X-ray spectroscopy (EDX) characterization reveals the three-dimensional chemical cross-section of the transformed nanowire with an Al core, surrounded by a thin pure Ge (∼2 nm), Al2O3 (∼3 nm), and Ge containing Al2O3 (∼1 nm) layer, respectively. The presence of Ge containing shells around the Al core indicates that Ge diffuses back into the metal reservoir by surface diffusion, which was confirmed by the detection of Ge atoms in the Al metal line by EDX analysis. Fitting a diffusion equation to the kinetic data allows the extraction of the diffusion coefficient at two different temperatures, which shows a good agreement with diffusion coefficients from literature for self-diffusion of Al.

First results on the experimental realisation of a 2 × 2 programmable phase plate for electrons are presented. The design consists of an array of electrostatic elements that influence the phase of electron waves passing through 4 separately controllable aperture holes. This functionality is demonstrated in a conventional transmission electron microscope operating at 300 kV and results are in very close agreement with theoretical predictions. The dynamic creation of a set of electron probes with different phase symmetry is demonstrated, thereby bringing adaptive optics in TEM one step closer to reality. The limitations of the current design and how to overcome these in the future are discussed. Simulations show how further evolved versions of the current proof of concept might open new and exciting application prospects for beam shaping and aberration correction.

BackgroundIn Cambodia, HIV prevalence is high while HIV testing rates remain low among transgender women (TG women), men who have sex with men (MSM), and female entertainment workers (FEW). Introducing self-testing for HIV to these key populations (KPs) could potentially overcome the under-diagnosis of HIV and significantly increase testing rates and receipt of the results, and thus could decrease transmission. Therefore, this study aimed to determine the acceptability of HIV self-testing (HIVST) among these three categories of KPs.MethodsThis study was conducted through focus group discussions (FGDs) with TG women, MSM, and FEW in Phnom Penh city, Kampong Cham, Battambang, and Siem Reap provinces of Cambodia. Convenience sampling was used to recruit the participants. Two FGDs (six participants in each FGD) were conducted in each target group in each study site, totaling 24 FGDs (144 participants). Thematic analysis was performed to identify common or divergent patterns across the target groups.ResultsAlmost all participants among the three groups (TG women, MSM, and FEW) had not heard about HIVST, but all of them expressed willingness to try it. They perceived HIVST as confidential, convenient, time-saving, and high-tech. Barriers to obtaining HIVST included cost, access, administration technique, embarrassment, and fear of pain. The majority preferred counseling before and after testing.ConclusionsParticipants showed high willingness to use and acceptability of HIVST due to its confidentiality/privacy and convenience even if it is not linked to a confirmatory test or care and treatment. Notwithstanding, to increase HIVST, the target groups would need affordable self-test kits, education about how to perform HIVST and read results, assurance about accuracy and reliability of HIVST, and provision of post-test counseling and facilitation of linkage to care and treatment.

Nanowire photodetectors are investigated because of their compatibility with flexible electronics, or for the implementation of on-chip optical interconnects. Such devices are characterized by ultrahigh photocurrent gain, but their photoresponse scales sublinearly with the optical power. Here, we present a study of single-nanowire photodetectors displaying a linear response to ultraviolet illumination. Their structure consists of a GaN nanowire incorporating an AlN/GaN/AlN heterostructure, which generates an internal electric field. The activity of the heterostructure is confirmed by the rectifying behavior of the current-voltage characteristics in the dark, as well as by the asymmetry of the photoresponse in magnitude and linearity. Under reverse bias (negative bias on the GaN cap segment), the detectors behave linearly with the impinging optical power when the nanowire diameter is below a certain threshold (≈80 nm), which corresponds to the total depletion of the nanowire stem due to the Fermi level pinning at the sidewalls. In the case of nanowires that are only partially depleted, their nonlinearity is explained by a nonlinear variation of the diameter of their central conducting channel under illumination.

The electrical and optical properties of low dimensional nanostructures depend critically on size and geometry and may differ distinctly from those of their bulk counterparts. In particular, ultra-thin semiconducting layers as well as nanowires have already proven the feasibility to realize and study quantum size effects enabling novel ultra-scaled devices. Further, plasmonic metal nanostructures attracted recently a lot of attention because of appealing near-field mediated enhancement effects. Thus, combining metal and semiconducting constituents in quasi 1D heterostructures will pave the way for ultra-scaled systems and high-performance devices with exceptional electrical, optical and plasmonic functionality.This paper reports on the sophisticated fabrication and structural properties of axial and radial, Al-Ge and Al-Si nanowire heterostructures, synthesized by a thermally induced exchange reaction of single-crystalline Ge-Si core-shell nanowires and Al pads. This enables a selfaligned metallic contact formation to Ge segments beyond lithographic limitations as well as ultra-thin semiconducting layers wrapped around monocrystalline Al core nanowires. High-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy and µ-Raman measurements proved the composition and perfect crystallinity of these metal-semiconductor nanowire heterostructures. This exemplary selective replacement of Ge by Al represents a general approach for the elaboration of radial and axial metal-semiconductor heterostructures in various Ge-semiconductor heterostructures.

The functional diversification and adaptability of the elementary switching units of computational circuits are disruptive approaches for advancing electronics beyond the static capabilities of conventional complementary metal-oxide-semiconductor-based architectures. Thereto, in this work the onedimensional nature of monocrystalline and monolithic Al−Gebased nanowire heterostructures is exploited to deliver charge carrier polarity control and furthermore to enable distinct programmable negative differential resistance at runtime. The fusion of electron and hole conduction together with negative differential resistance in a universal adaptive transistor may enable energy-efficient reconfigurable circuits with multivalued operability that are inherent components of emerging artificial intelligence electronics.

Semiconductor-superconductor hybrid systems have outstanding potential for emerging high performance nanoelectronics and quantum devices. However, critical to their successful application is the fabrication of high quality and reproducible semiconductor-superconductor interfaces. Here, we realize and measure axial Al-Ge-Al nanowire heterostructures with atomically precise interfaces, enwrapped by an ultra-thin epitaxial Si layer further denoted as Al-Ge/Si-Al nanowire heterostructures. The heterostructures were synthesized by a thermally induced exchange reaction of single-crystalline Ge/Si core/shell nanowires and lithographically defined Al contact pads. Applying this heterostructure formation scheme enables self-aligned quasi one-dimensional crystalline Al leads contacting ultra-scaled Ge/Si segments with contact transparencies greater than 98%. Integration into back-gated field-effect devices and continuous scaling beyond lithographic limitations allows us to exploit the full potential of the highly transparent contacts to the 1D hole gas at the Ge-Si interface. This leads to the observation of ballistic transport as well as quantum confinement effects up to temperatures of 150 K. Low temperature measurements reveal proximity-induced superconductivity in the Ge/Si core/shell nanowires. The realization of a Josephson field-effect transistor allows us to study the subharmonic energy-gap structure caused by multiple Andreev reflections. Most importantly, the absence of a quantum dot regime indicates a hard superconducting gap originating from the highly transparent contacts to the 1D hole-gas,

Among the many possible phase‐change materials that can be used in digital memories, Ge‐rich GeSbTe (GGST) alloys are of special interest due to their much higher thermal stability, i.e., the higher crystallization temperature, they offer. However, in contrast to congruent materials which may transit from the amorphous to the crystalline state while keeping the same homogeneous chemical composition, GGST crystallization is obtained through the successive formation of the Ge and GST‐225 phases. For this reason, they show distinct properties and characteristics from those found in the canonical GST‐225 and GeTe alloys. Herein, some of these characteristics, their crystallization kinetics, the effect of N doping and oxidation, and their electrical properties are reviewed and highlighted.