Bending and precipitate formation mechanisms in epitaxial Ge-core/GeSn-shell nanowires.

Core-shell Ge/GeSn nanowires provide a route to dislocation-free single crystal germanium-tin alloys with desirable light emission properties because the Ge core acts as an elastically compliant substrate during misfitting GeSn shell growth. However, the uniformity of tin incorporation during reduced pressure chemical vapor deposition may be limited by the kinetics of mass transfer to the shell during GeSn growth. The balance between Sn precursor flux and available surfaces for GeSn nucleation and growth determines whether defects are formed and their type. On the one hand, when the Sn precursor delivery is insufficient, local variations in Sn arrival rate at the nanowire surfaces during GeSn growth produce asymmetries in shell growth that induce wire bending. This inhomogeneous elastic dilatation due to the varying composition occurs via deposition of Sn-poor regions on some of the {112} sidewall facets of the nanowires. On the other hand, when the available nanowire surface area is insufficient to accommodate the arriving Sn precursor flux, Sn-rich precipitate formation results. Between these two extremes, there exists a regime of growth conditions and nanowire densities that permits defect-free GeSn shell growth.

Electrical tuning of phase-change antennas and metasurfaces.

The success of semiconductor electronics is built on the creation of compact, low-power switching elements that offer routing, logic and memory functions. The availability of nanoscale optical switches could have a similarly transformative impact on the development of dynamic and programmable metasurfaces, optical neural networks and quantum information processing. Phase-change materials are uniquely suited to enable their creation as they offer high-speed electrical switching between amorphous and crystalline states with notably different optical properties. Their high refractive index has already been harnessed to fashion them into compact optical antennas. Here, we take the next important step, by showing electrically-switchable phase-change antennas and metasurfaces that offer strong, reversible, non-volatile, multi-phase switching and spectral tuning of light scattering in the visible and near-infrared spectral ranges. Their successful implementation relies on a careful joint thermal and optical optimization of the antenna elements that comprise a silver strip that simultaneously serves as a plasmonic resonator and a miniature heating stage. Our metasurface affords electrical modulation of the reflectance by more than fourfold at 755 nm.

Revealing multiple classes of stable quantum emitters in hexagonal boron nitride with correlated optical and electron microscopy.

Defects in hexagonal boron nitride (hBN) exhibit high-brightness, room-temperature quantum emission, but their large spectral variability and unknown local structure challenge their technological utility. Here, we directly correlate hBN quantum emission with local strain using a combination of photoluminescence (PL), cathodoluminescence (CL) and nanobeam electron diffraction. Across 40 emitters, we observe zero phonon lines (ZPLs) in PL and CL ranging from 540 to 720 nm. CL mapping reveals that multiple defects and distinct defect species located within an optically diffraction-limited region can each contribute to the observed PL spectra. Local strain maps indicate that strain is not required to activate the emitters and is not solely responsible for the observed ZPL spectral range. Instead, at least four distinct defect classes are responsible for the observed emission range, and all four classes are stable upon both optical and electron illumination. Our results provide a foundation for future atomic-scale optical characterization of colour centres.

Living well with dementia groups: changes in participant and therapist verbal behaviour.

OBJECTIVES: This paper reports two related analyses of verbal material from seven Living Well with Dementia groups: the first examines changes in the verbal behaviours of participants across the course of the sessions in all seven groups; while the second contrasts therapist behaviour in two groups. METHODS: In the first analysis, recordings of three sessions from each group were transcribed and participant descriptions of dementia were analysed using the Markers of Assimilation of Problematic Experiences of Dementia (MAPED) rating procedure. In the second analysis, therapist behaviour in weeks 2 and 8 from two groups (F and G) was analysed using the Hill Counsellor Verbal response rating scale. Inter-rater reliabilities for the two sets of ratings were 'good' and 'very good', respectively. RESULTS: For the MAPED ratings, a five by four contingency table was analysed using chi-squared, which indicated a highly significant change in assimilation. There were significant higher levels of level 1 and 2 markers in the first two sessions and level 4 for sessions 5 and 6. Facilitators used significantly more direct guidance and information giving behaviour in the second session at Location F compared to Location G. CONCLUSIONS: The results suggest that important changes occurred in the way that dementia was described across the seven LivDem groups: this includes both reductions in the avoidance of direct references to dementia after the first two sessions, as well as an increase in 'insight' statements. Directive facilitator behaviour may be associated with poorer outcomes.

Two-dimensional limit of crystalline order in perovskite membrane films.

Long-range order and phase transitions in two-dimensional (2D) systems-such as magnetism, superconductivity, and crystallinity-have been important research topics for decades. The issue of 2D crystalline order has reemerged recently, with the development of exfoliated atomic crystals. Understanding the dimensional limit of crystalline phases, with different types of bonding and synthetic techniques, is at the foundation of low-dimensional materials design. We study ultrathin membranes of SrTiO3, an archetypal perovskite oxide with isotropic (3D) bonding. Atomically controlled membranes are released after synthesis by dissolving an underlying epitaxial layer. Although all unreleased films are initially single-crystalline, the SrTiO3 membrane lattice collapses below a critical thickness (5 unit cells). This crossover from algebraic to exponential decay of the crystalline coherence length is analogous to the 2D topological Berezinskii-Kosterlitz-Thouless (BKT) transition. The transition is likely driven by chemical bond breaking at the 2D layer-3D bulk interface, defining an effective dimensional phase boundary for coherent crystalline lattices.

Markers of assimilation of problematic experiences in dementia within the LivDem project.

This study aimed to determine whether the Markers of Assimilation of Problematic Experiences in Dementia scale (MAPED) can be used to identify whether the way in which participants talk about dementia changed during the group. All eight sessions of a LivDem group, which were attended by participants were recorded and transcribed. An initial analysis identified 160 extracts, which were then rated using the MAPED system. Inter-rater reliability was 61% and following a resolution meeting, 35 extracts were discarded, leaving 125 extracts with an agreed marker code. All of the participants were identified as producing a speech marker relating to dementia, and these varied between 0 (warding off) to 6 (problem solution). Examples of these markers are provided. The proportion of emergence markers (indicating the initial stages of assimilation) compared to later markers changed significantly between the first four sessions and the final sessions. This difference was still significant even when the markers produced by the most verbal participant, Graham, were excluded. The use of process measures within psychotherapy complements more conventional outcome measures and has both theoretical and clinical implications.

Core-Shell Germanium/Germanium-Tin Nanowires Exhibiting Room-Temperature Direct- and Indirect-Gap Photoluminescence.

Germanium-tin alloy nanowires hold promise as silicon-compatible optoelectronic elements with the potential to achieve a direct band gap transition required for efficient light emission. In contrast to Ge1-xSnx epitaxial thin films, free-standing nanowires deposited on misfitting germanium or silicon substrates can avoid compressive, elastic strains that inhibit formation of a direct gap. We demonstrate strong room temperature photoluminescence, consistent with band edge emission from both Ge core nanowires, elastically strained in tension, and the almost unstrained Ge1-xSnx shells grown around them. Low-temperature chemical vapor deposition of these core-shell structures was achieved using standard precursors, resulting in Sn incorporation that significantly exceeds the bulk solubility limit in germanium.

Parallel preparation of plan-view transmission electron microscopy specimens by vapor-phase etching with integrated etch stops.

Specimen preparation remains a practical challenge in transmission electron microscopy and frequently limits the quality of structural and chemical characterization data obtained. Prevailing methods for thinning of specimens to electron transparency are serial in nature, time consuming, and prone to producing artifacts and specimen failure. This work presents an alternative method for the preparation of plan-view specimens using isotropic vapor-phase etching with integrated etch stops. An ultrathin amorphous etch-stop layer simultaneously serves as an electron transparent support membrane whose thickness is defined by a controlled growth process such as atomic layer deposition with sub-nanometer precision. This approach eliminates the need for mechanical polishing or ion milling to achieve electron transparency, and reduces the occurrence of preparation induced artifacts. Furthermore, multiple specimens from a plurality of samples can be thinned in parallel due to high selectivity of the vapor-phase etching process. These features enable dramatic reductions in preparation time and cost without sacrificing specimen quality and provide advantages over wet etching techniques. Finally, we demonstrate a platform for high-throughput transmission electron microscopy of plan-view specimens by combining the parallel preparation capabilities of vapor-phase etching with wafer-scale micro- and nanofabrication.

Spontaneous, Defect-Free Kinking via Capillary Instability during Vapor-Liquid-Solid Nanowire Growth.

Kinking, a common anomaly in nanowire (NW) vapor-liquid-solid (VLS) growth, represents a sudden change of the wire's axial growth orientation. This study focuses on defect-free kinking during germanium NW VLS growth, after nucleation on a Ge (111) single crystal substrate, using Au-Ge catalyst liquid droplets of defined size. Statistical analysis of the fraction of kinked NWs reveals the dependence of kinking probability on the wire diameter and the growth temperature. The morphologies of kinked Ge NWs studied by electron microscopy show two distinct, defect-free, kinking modes, whose underlying mechanisms are explained with the help of 3D multiphase field simulations. Type I kinking, in which the growth axis changes from vertical [111] to ⟨110⟩, was observed in Ge NWs with a nominal diameter of ∼ 20 nm. This size coincides with a critical diameter at which a spontaneous transition from ⟨111⟩ to ⟨110⟩ growth occurs in the phase field simulations. Larger diameter NWs only exhibit Type II kinking, in which the growth axis changes from vertical [111] directly to an inclined ⟨111⟩ axis during the initial stages of wire growth. This is caused by an error in sidewall facet development, which produces a shrinkage in the area of the (111) growth facet with increasing NW length, causing an instability of the Au-Ge liquid droplet at the tip of the NW.

A pilot randomised controlled trial to compare changes in quality of life for participants with early diagnosis dementia who attend a 'Living Well with Dementia' group compared to waiting-list control.

OBJECTIVES: The aim of this paper is to report a pilot study in which participants who had recently received a diagnosis of dementia were randomised to either a 10-week group intervention or a waiting-list control. METHOD: Memory clinic staff with limited previous experience of group therapy were trained to lead a 10-week group therapy intervention called 'Living Well with Dementia'. Fifty-eight participants, all of whom had received a diagnosis of Alzheimer's disease, vascular or Lewy body dementia within the previous 18 months, were randomised to receive either the intervention or treatment as usual (waiting-list control). Data collection occurred at baseline, within two weeks after the intervention finished and at 10-week follow-up. RESULTS: The study met its recruitment targets, with a relatively low attrition rate for the intervention arm. The acceptability of the intervention and research methods was examined qualitatively and will be reported on elsewhere. For the primary outcome, measure of quality of life in Alzheimer's disease (QoL-AD), and secondary outcome, self-esteem, there was some evidence of improvement in the intervention group compared to the control group. There was, also, evidence of a reduction in cognitive functioning in the treatment group compared to the control. Such reported differences should be treated with caution because they are obtained from a pilot and not a definitive study. CONCLUSION: This pilot study succeeded in collecting data to inform a future definitive cost effectiveness clinical trial of Living Well with Dementia group therapy.

Ultrafast electronic and structural response of monolayer MoS2 under intense photoexcitation conditions.

We report on the dynamical response of single layer transition metal dichalcogenide MoS2 to intense above-bandgap photoexcitation using the nonlinear-optical second order susceptibility as a direct probe of the electronic and structural dynamics. Excitation conditions corresponding to the order of one electron-hole pair per unit cell generate unexpected increases in the second harmonic from monolayer films, occurring on few picosecond time-scales. These large amplitude changes recover on tens of picosecond time-scales and are reversible at megahertz repetition rates with no photoinduced change in lattice symmetry observed despite the extreme excitation conditions.

The usefulness of the cell transfer technique for immunocytochemistry of fine-needle aspirates.

BACKGROUND: The use of immunocytochemistry as an important ancillary technique for the workup of fine-needle aspiration (FNA) specimens is an important component in the daily practice of cytopathology. Although cell block preparations are commonly used, immunocytochemistry cannot be completed if the cell blocks are hypocellular. As an alternative approach when conventional cell blocks fail, immunocytochemistry can be performed on cell-transferred direct smears. Multiple immunostains can be applied to a single direct smear using the cell transfer technique (CTT). METHODS: A retrospective review of all FNA cases performed at the study institution over a 3-year period was conducted. All cases in which CTT was used for immunocytochemistry were identified. The contribution of CTT to the final diagnosis in these cases was assessed. RESULTS: CTT was used in 152 of the 11,259 FNAs performed. A total of 431 immunocytochemistry stains, including 46 different antibodies, were performed using CTT. In 118 of 150 cases, the immunocytochemistry results contributed significantly to the final diagnosis. It provided no added value in the remaining 32 cases and failed in 2 cases. CONCLUSIONS: CTT is a very useful tool for the workup and diagnosis of FNA specimens when conventional cell blocks lack adequate cellularity. Although CTT was used in only 1.4% of FNA cases in the current study, it contributed to the final diagnosis in 79% of the cases in which it was used. For these patients, CTT reduced the need for repeat FNAs, thereby reducing potential patient morbidity and health care costs.

Thermal stability and surface passivation of Ge nanowires coated by epitaxial SiGe shells.

Epitaxial growth of a highly strained, coherent SiGe alloy shell around a Ge nanowire core is investigated as a method to achieve surface passivation and carrier confinement, important in realizing nanowire devices. The high photoluminescence intensity observed from the core-shell nanowires with spectral features similar to that of bulk Ge indicates effective surface passivation. Thermal stability of these core-shell heterostructures has been systematically investigated, with a method demonstrated to avoid misfit strain relaxation during postgrowth annealing.

Hexagonal close-packed structure of au nanocatalysts solidified after ge nanowire vapor-liquid-solid growth.

We report that approximately 10% of the Au catalysts that crystallize at the tips of Ge nanowires following growth have the close-packed hexagonal crystal structure rather than the equilibrium face-centered-cubic structure. Transmission electron microscopy results using aberration-corrected imaging, and diffraction and compositional analyses, confirm the hexagonal phase in these 40-50 nm particles. Reports of hexagonal close packing in Au, even in nanoparticle form, are rare, and the observations suggest metastable pathways for the crystallization process. These results bring new considerations to the stabilization of the liquid eutectic alloy at low temperatures that allows for vapor-liquid-solid growth of high quality, epitaxial Ge nanowires below the eutectic temperature.

Facile synthesis, silanization, and biodistribution of biocompatible quantum dots.

A facile strategy for the synthesis of silica-coated quantum dots (QDs) for in vivo imaging is reported. All the QD synthesis and silanization steps are conducted in water and methanol under mild conditions without involving any organometallic precursors or high-temperature, oxygen-free environments. The as-prepared silica-coated QDs possess high quantum yields and are extremely stable in mouse serum. In addition, the silanization method developed here produces nanoparticles with small sizes that are difficult to achieve via conventional silanization methods. The silica coating helps to prevent the exposure of the QD surface to the biological milieu and therefore increases the biocompatibility of QDs for in vivo applications. Interestingly, the silica-coated QDs exhibit a different biodistribution pattern from that of commercially available Invitrogen QD605 (carboxylate) with a similar size and emission wavelength. The Invitrogen QD605 exhibits predominant liver (57.2% injected dose (ID) g(-1)) and spleen (46.1% ID g(-1)) uptakes 30 min after intravenous injection, whereas the silica-coated QDs exhibit much lower liver (16.2% ID g(-1)) and spleen (3.67% ID g(-1)) uptakes but higher kidney uptake (8.82% ID g(-1)), blood retention (15.0% ID g(-1)), and partial renal clearance. Overall, this straightforward synthetic strategy paves the way for routine and customized synthesis of silica-coated QDs for biological use.

Near-infrared light emitting luciferase via biomineralization.

A new strategy based on biomineralization is presented to rationally tune the emission wavelength of luciferase. In this study luciferase (Luc8) was used as a template to direct the synthesis of near-infrared (NIR) light emitting PbS quantum dots (QDs) at ambient conditions to form a Luc8-PbS nanocomplex. The as-synthesized PbS QDs exhibited photoluminescence in the range of 800-1050 nm, and the Luc8 enzyme remained active within the Luc8-PbS complex. Upon the addition of the substrate coelenterazine, the energy produced by Luc8 was nonradiatively transferred to PbS QDs via bioluminescence resonance energy transfer (BRET) and enabled the complex to emit NIR light. This is the first study to form dual functional bioinorganic hybrid nanostructures via active enzyme-templated synthesis of inorganic nanomaterials.

A 61-year-old woman with osteomalacia and a thoracic spine lesion.

Phosphaturic mesenchymal tumor, mixed connective tissue variant (PMT-MCT) is a rare, largely benign, mesenchymal neoplasm almost invariably associated with oncogenic osteomalacia. It is generally found in the soft tissue and bone of the extremities. We report a case of a 61-year-old female with long-standing osteomalacia who was found to have PMT-MCT of the thoracic spine. There have been very few previously reported cases of PMT involving the spinal vertebrae and neuropathologists should be aware of this lesion. Recognition of PMT-MCT is critical for optimal patient care since complete surgical resection without additional therapy is curative.

Gold-catalyzed vapor-liquid-solid germanium-nanowire nucleation on porous silicon.

Nanoporous Si(111) substrates are used to study the effects of Au catalyst coarsening on the nucleation of vapor-liquid-solid-synthesized epitaxial Ge nanowires (NWs) at temperatures less than 400 degrees C. Porous Si substrates, with greater effective interparticle separations for Au surface diffusion than nonporous Si, inhibit catalyst coarsening and agglomeration prior to NW nucleation. This greatly reduces the variation in wire diameter and length and increases the yield compared to nucleation on identically prepared nonporous Si substrates.

Inhibiting strain-induced surface roughening: dislocation-free Ge/Si and Ge/SiGe core-shell nanowires.

Elastic strain is a critical factor in engineering the electronic behavior of core-shell semiconductor nanowires and provides the driving force for undesirable surface roughening and defect formation. We demonstrate two independent strategies, chlorine surface passivation and growth of nanowires with low-energy sidewall facets, to avoid strain-induced surface roughening that promotes dislocation nucleation in group IV core-shell nanowires. Metastably strained, dislocation-free, core-shell nanowires are obtained, and axial strains are measured and compared to elasticity model predictions.