18 research outputs found
Shadow epitaxy for in-situ growth of generic semiconductor/superconductor devices
Uniform, defect-free crystal interfaces and surfaces are crucial ingredients
for realizing high-performance nanoscale devices. A pertinent example is that
advances in gate-tunable and topological superconductivity using
semiconductor/superconductor electronic devices are currently built on the hard
proximity-induced superconducting gap obtained from epitaxial indium
arsenide/aluminium heterostructures. Fabrication of devices requires selective
etch processes; these exist only for InAs/Al hybrids, precluding the use of
other, potentially superior material combinations. We present a crystal growth
platform -- based on three-dimensional structuring of growth substrates --
which enables synthesis of semiconductor nanowire hybrids with in-situ
patterned superconductor shells. This platform eliminates the need for etching,
thereby enabling full freedom in choice of hybrid constituents. We realise and
characterise all the most frequently used architectures in superconducting
hybrid devices, finding increased yield and electrostatic stability compared to
etched devices, along with evidence of ballistic superconductivity. In addition
to aluminium, we present hybrid devices based on tantalum, niobium and
vanadium.
This is the submitted version of the manuscript. The accepted, peer reviewed
version is available from Advanced Materials:
http://doi.org/10.1002/adma.201908411
Previous title: Shadow lithography for in-situ growth of generic
semiconductor/superconductor device
Glymphatic-assisted perivascular brain delivery of intrathecal small gold nanoparticles
Nanoparticles are ultrafine particulate matter having considerable potential for treatment of central nervous system (CNS) disorders. Despite their tiny size, the blood-brain barrier (BBB) restricts their access to the CNS. Their direct cerebrospinal fluid (CSF) administration bypasses the BBB endothelium, but still fails to give adequate brain uptake. We present a novel approach for efficient CNS delivery of 111In-radiolabelled gold nanoparticles (AuNPs; 10-15 nm) via intra-cisterna magna administration, with tracking by SPECT imaging. To accelerate CSF brain influx, we administered AuNPs intracisternally in conjunction with systemic hypertonic saline, which dramatically increased the parenchymal AuNP uptake, especially in deep brain regions. AuNPs entered the CNS along periarterial spaces as visualized by MRI of gadolinium-labelled AuNPs and were cleared from brain within 24 h and excreted through the kidneys. Thus, the glymphatic-assisted perivascular network augment by systemic hypertonic saline is a pathway for highly efficient brain-wide distribution of small AuNPs.Peer reviewe
Molecular beam epitaxy of CuMnAs
We present a detailed study of the growth of the tetragonal polymorph of
antiferromagnetic CuMnAs by the molecular beam epitaxy technique. We explore
the parameter space of growth conditions and their effect on the
microstructural and transport properties of the material. We identify its
typical structural defects and compare the properties of epitaxial CuMnAs
layers grown on GaP, GaAs and Si substrates. Finally, we investigate the
correlation between the crystalline quality of CuMnAs and its performance in
terms of electrically induced resistance switching.Comment: 10 pages, 8 figures and supplementary materia
Strong Metal Support Interaction of Pt and Ru Nanoparticles Deposited on HOPG Probed by the H-D Exchange Reaction
Superconductivity and Parity Preservation in As-Grown in Islands on InAs Nanowires
We report in-situ synthesis of crystalline indium islands on InAs nanowires
grown by molecular beam epitaxy. Structural analysis by transmission electron
microscopy showed that In crystals grew in a tetragonal body-centred crystal
structure within two families of orientations relative to wurtzite InAs. The
crystalline islands had lengths < 500 nm and low-energy surfaces, suggesting
that growth was driven mainly by surface energy minimization. Electrical
transport through In/InAs devices exhibited Cooper pair charging, evidencing
charge parity preservation and a pristine In/InAs interface, with an induced
superconducting gap ~ 0.45 meV. Cooper pair charging persisted to temperatures
> 1.2 K and magnetic fields ~ 0.7 T, demonstrating that In/InAs hybrids belong
to an expanding class of semiconductor/superconductor hybrids operating over a
wider parameter space than state-of-the-art Al-based hybrids. Engineering
crystal morphology while isolating single islands using shadow epitaxy provides
an interesting alternative to previous semiconductor/superconductor hybrid
morphologies and device geometries.Comment: Published in Nano Letters:
https://pubs.acs.org/doi/10.1021/acs.nanolett.1c0248
Three-fold Symmetric Doping Mechanism in GaAs Nanowires
A new dopant incorporation mechanism in Ga-assisted GaAs nanowires
grown by molecular beam epitaxy is reported. Off-axis electron holography
revealed that p-type Be dopants introduced in situ during molecular
beam epitaxy growth of the nanowires were distributed inhomogeneously
in the nanowire cross-section, perpendicular to the growth direction.
The active dopants showed a remarkable azimuthal distribution along
the (111)B flat top of the nanowires, which is attributed to preferred
incorporation along 3-fold symmetric truncated facets under the Ga
droplet. A diffusion model is presented to explain the unique radial
and azimuthal variation of the active dopants in the GaAs nanowires