Tunable coupling between InSb nanowires and superconductors

The quest for topological states in hybrid nanowire devices has ignited substantial research in perfecting the nanowire-superconductor interface. Recent proposals, however, suggest that these immaculate interfaces can lead to an overly strong superconducting-semiconducting coupling that "metalizes"the nanowire (i.e., dominates its intrinsic properties which are essential for hosting topological particles). One way to reduce this coupling is to add an insulating shell between the nanowire and the superconductor. Here, we explore cadmium telluride (CdTe) shells as a tunnel barrier at the interface between indium antimonide (InSb) nanowires and a superconductor. We demonstrate the growth of epitaxial, defect-free CdTe on InSb and high-quality superconductor deposition at cryogenic temperatures, enabled by the near perfect lattice match of CdTe and InSb and their comparable thermal-expansion coefficients. Using growth and etching, we control the thickness of CdTe shells down to a few monolayers. This level of control indicates the potential of these shells to serve as a knob that modulates the coupling between a nanowire and a superconductor, possibly introducing a new generation of nanowire hybrids suitable for topological Majorana devices.</p

Asymmetric magnetic bubble expansion under in-plane field in Pt/Co/Pt: effect of interface engineering

We analyse the impact of growth conditions on asymmetric magnetic bubble expansion under in-plane field in ultrathin Pt / Co / Pt films. Specifically, using sputter deposition we vary the Ar pressure during the growth of the top Pt layer. This induces a large change in the interfacial structure as evidenced by a factor three change in the effective perpendicular magnetic anisotropy. Strikingly, a discrepancy between the current theory for domain-wall propagation based on a simple domain-wall energy density and our experimental results is found. This calls for further theoretical development of domain-wall creep under in-plane fields and varying structural asymmetry.Comment: 16 pages, 3 figure

Study of surface damage in silicon by irradiation with focused rubidium ions using a cold-atom ion source

Cold-atom ion sources have been developed and commercialized as alternative sources for focused ion beams (FIBs). So far, applications and related research have not been widely reported. In this paper, a prototype rubidium FIB is used to study the irradiation damage of 8.5 keV beam energy Rb + ions on silicon to examine the suitability of rubidium for nanomachining applications. Transmission electron microscopy combined with energy dispersive x-ray spectroscopy is applied to silicon samples irradiated by different doses of rubidium ions. The experimental results show a duplex damage layer consisting of an outer layer of oxidation without Rb and an inner layer containing Rb mostly at the interface to the underlying Si substrate. The steady-state damage layer is measured to be 23.2(±0.3)  nm thick with a rubidium staining level of 7(±1) atomic percentage

Strain engineering in Ge/GeSn core/shell nanowires

Strain engineering in Sn-rich group IV semiconductors is a key enabling factor to exploit the direct band gap at mid-infrared wavelengths. Here, we investigate the effect of strain on the growth of GeSn alloys in a Ge/GeSn core/shell nanowire geometry. Incorporation of Sn content in the 10-20 at.% range is achieved with Ge core diameters ranging from 50nm to 100nm. While the smaller cores lead to the formation of a regular and homogeneous GeSn shell, larger cores lead to the formation of multi-faceted sidewalls and broadened segregation domains, inducing the nucleation of defects. This behavior is rationalized in terms of the different residual strain, as obtained by realistic finite element method simulations. The extended analysis of the strain relaxation as a function of core and shell sizes, in comparison with the conventional planar geometry, provides a deeper understanding of the role of strain in the epitaxy of metastable GeSn semiconductors

Control by atomic layer deposition over the chemical composition of nickel cobalt oxide for the oxygen evolution reaction

Anion exchange membrane water electrolysis (AEMWE) is a promising technology for renewable electricity-driven water splitting toward hydrogen production. However, application of AEMWE at industrial scale requires the development of oxygen evolution reaction (OER) electrocatalysts showing long-term stability under mild alkaline conditions. Among these, nickel cobalt oxide thin films are considered promising candidates. The ideal chemical composition of these oxides remains debatable, with recent literature indicating that rock-salt NiCoO2 may exhibit similar OER activity as the traditional spinel NiCo2O4. In this work, we present the development of a plasma-enhanced atomic layer deposition (ALD) process of nickel cobalt oxide thin films (∼20 nm) with focus on the role of their chemical composition and crystal structure on the OER activity. The film composition is tuned using a supercycle approach built upon CoOx cycles with CoCp2 as a precursor and O2 plasma as a co-reactant and NiOx cycles with Ni(MeCp)2 as a precursor and O2 plasma as a co-reactant. The films exhibit a change in the crystallographic phase from the rock-salt to spinel structure for increasing cobalt at. %. This change is accompanied by an increase in the Ni3+-to-Ni2+ ratio. Interestingly, an increase in electrical conductivity is observed for mixed oxides, with an optimum of (2.4 ± 0.2) × 102 S/cm at 64 at. % Co, outperforming both NiO and Co3O4 by several orders of magnitude. An optimal electrocatalytic performance is observed for 80 at. % Co films. Cyclic voltammetry measurements simultaneously show a strong dependence of the OER-catalytic performance on the electrical conductivity. The present study highlights the merit of ALD in controlling the nickel cobalt oxide chemical composition and crystal structure to gain insight into its electrocatalytic performance. Moreover, these results suggest that it is important to disentangle conductivity effects from the electrocatalytic activity in future work

Interface formation of two- and three-dimensionally bonded materials in the case of GeTe-Sb2Te3 superlattices

GeTe–Sb2Te3 superlattices are nanostructured phase-change materials which are under intense investigation for non-volatile memory applications. They show superior properties compared to their bulk counterparts and significant efforts exist to explain the atomistic nature of their functionality. The present work sheds new light on the interface formation between GeTe and Sb2Te3, contradicting previously proposed models in the literature. For this purpose [GeTe(1 nm)–Sb2Te3(3 nm)]15 superlattices were grown on passivated Si(111) at 230 °C using molecular beam epitaxy and they have been characterized particularly with cross-sectional HAADF scanning transmission electron microscopy. Contrary to the previously proposed models, it is found that the ground state of the film actually consists of van der Waals bonded layers (i.e. a van der Waals heterostructure) of Sb2Te3 and rhombohedral GeSbTe. Moreover, it is shown by annealing the film at 400 °C, which reconfigures the superlattice into bulk rhombohedral GeSbTe, that this van der Waals layer is thermodynamically favored. These results are explained in terms of the bonding dimensionality of GeTe and Sb2Te3 and the strong tendency of these materials to intermix. The findings debate the previously proposed switching mechanisms of superlattice phase-change materials and give new insights in their possible memory application

Prospective multicentre observational cohort to assess quality of life, functional outcomes and cost-effectiveness following minimally invasive surgical techniques for rectal cancer in 'dedicated centres' in the Netherlands (VANTAGE trial):A protocol

Introduction: Total mesorectal excision is the standard of care for rectal cancer, which can be performed using open, laparoscopic, robot-assisted and transanal technique. Large prospective (randomised controlled) trials comparing these techniques are lacking, do not take into account the learning curve and have short-term or long-term oncological results as their primary endpoint, without addressing quality of life, functional outcomes and cost-effectiveness. Comparative data with regard to these outcomes are necessary to identify the optimal minimally invasive technique and provide guidelines for clinical application. Methods and analysis: This trial will be a prospective observational multicentre cohort trial, aiming to compare laparoscopic, robot-assisted and transanal total mesorectal excision in adult patients with rectal cancer performed by experienced surgeons in dedicated centres. Data collection will be performed in collaboration with the prospective Dutch ColoRectal Audit and the Prospective Dutch ColoRectal Cancer Cohort. Quality of life at 1 year postoperatively will be the primary outcome. Functional outcomes, cost-effectiveness, short-term outcomes and long-term oncological outcomes will be the secondary outcomes. In total, 1200 patients will be enrolled over a period of 2 years in 26 dedicated centres in the Netherlands. The study is registered at https://www.trialregister.nl/9734 (NL9734). Ethics and dissemination: Data will be collected through collaborating parties, who already obtained approval by their medical ethical committee. Participants will be included in the trial after having signed informed consent. Results of this study will be disseminated to participating centres, patient organisations, (inter)national society meetings and peer-reviewed journals

Toolbox of Advanced Atomic Layer Deposition Processes for Tailoring Large-Area MoS2 Thin Films at 150 °C

Two-dimensional MoS2 is a promising material for applications, including electronics and electrocatalysis. However, scalable methods capable of depositing MoS2 at low temperatures are scarce. Herein, we present a toolbox of advanced plasma-enhanced atomic layer deposition (ALD) processes, producing wafer-scale polycrystalline MoS2 films of accurately controlled thickness. Our ALD processes are based on two individually controlled plasma exposures, one optimized for deposition and the other for modification. In this way, film properties can be tailored toward different applications at a very low deposition temperature of 150 °C. For the modification step, either H2 or Ar plasma can be used to combat excess sulfur incorporation and crystallize the films. Using H2 plasma, a higher degree of crystallinity compared with other reported low-temperature processes is achieved. Applying H2 plasma steps periodically instead of every ALD cycle allows for control of the morphology and enables deposition of smooth, polycrystalline MoS2 films. Using an Ar plasma instead, more disordered MoS2 films are deposited, which show promise for the electrochemical hydrogen evolution reaction. For electronics, our processes enable control of the carrier density from 6 × 1016 to 2 × 1021 cm–3 with Hall mobilities up to 0.3 cm2 V–1 s–1. The process toolbox forms a basis for rational design of low-temperature transition metal dichalcogenide deposition processes compatible with a range of substrates and applications