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The extension of X-ray photoelectron spectroscopy (XPS) to measure layers and interfaces below the uppermost surface requires higher X-ray energies and electron energy analysers capable of measuring higher electron kinetic energies. This has been enabled at synchrotron radiation facilities and by using lab-based instruments which are now available with sufficient sensitivity for measurements to be performed on reasonable timescales. Here, we detail measurements on buried interfaces using a Ga Kα (9.25 keV) metal jet X-ray source and an EW4000 energy analyser (ScientaOmicron GmbH) in the Henry Royce Institute at the University of Manchester. Development of the technique has required the calculation of relative sensitivity factors (RSFs) to enable quantification analogous to Al Kα XPS, and here we provide further substantiation of the Ga Kα RSF library. Examples of buried interfaces include layers of memory and energy materials below top electrode layers, semiconductor heterostructures, ions implanted in graphite, oxide layers at metallic surfaces, and core-shell nanoparticles. The use of an angle-resolved mode enables depth profiling from the surface into the bulk, and is complemented with surface-sensitive XPS. Inelastic background modelling allows the extraction of information about buried layers at depths up to 20 times the photoelectron inelastic mean free path.

The structural, chemical and electrical properties of Ni/Au contacts to the atomic layer deposited α-Ga2O3 were investigated. Ni forms a Schottky contact with α-Ga2O3, irrespectively of the post-annealing temperature. No sign of metal oxidation was observed at the metal-semiconductor interface (unlike what is observed for other metals like Ti), and instead, the metallurgical processes of the Ni–Au bilayer dominate the electrical properties. It is found that 400 °C–450 °C is the optimal annealing temperature, which allows for metal diffusion to heal gaps at the metal/semiconductor interface, but is not sufficient for Ni and Au to significantly interdiffuse and form an alloy with compositional inhomogeneities.

LEDs based on hexagonal InGaN/GaN quantum wells are dominant technology for many lighting applications. However, their luminous efficacy for green and amber emission and at high drive currents remains limited. Growing quantum wells instead in the cubic phase is a promising alternative because, compared to hexagonal GaN, it benefits from a reduced bandgap and is free of the strong polarization fields that can reduce the radiative recombination rate. Initial attempts to grow cubic GaN in the 1990s employed molecular beam epitaxy, but now, metal-organic chemical vapor deposition can also be used. Nonetheless, high phase purity requires careful attention to growth conditions and the quantification of any unwanted hexagonal phase. In contrast to hexagonal GaN, in which threading dislocations are key, at its current state of maturity, the most important extended structural defects in cubic GaN are stacking faults. These modify the optical properties of cubic GaN films and propagate into active layers. In quantum wells and electron blocking layers, segregation of alloying elements at stacking faults has been observed, leading to the formation of quantum wires and polarized emission. This observation forms part of a developing understanding of the optical properties of cubic InGaN quantum wells, which also offer shorter recombination lifetimes than their polar hexagonal counterparts. There is also growing expertise in p-doping, including dopant activation by annealing. Overall, cubic GaN has rapidly transitioned from an academic curiosity to a real prospect for application in devices, with the potential to offer specific performance advantages compared to polar hexagonal material.

The suitability of Al x Ga1−x N nucleation layers (NLs) with varying Al fraction x for the metal organic vapour phase epitaxy of zincblende GaN on (001) 3C-SiC was investigated, using x-ray photoelectron spectroscopy, atomic force microscopy, and x-ray diffraction. The as-grown NLs exhibited elongated island structures on their surface, which reduce laterally into smaller, more equiaxed islands with increasing AlN composition. During high-temperature annealing in a mixture of NH3 and H2 the nucleation islands with low Al fraction ripened and increased in size, whereas this effect was less pronounced in samples with higher Al fraction. The compressive biaxial in-plane strain of the NLs increases with increasing AlN composition up to x = 0.29. GaN epilayers grown over NLs that have low Al fraction have high cubic zincblende phase purity and are slightly compressively strained relative to 3C-SiC. However, those samples with a measured Al fraction in the NL higher than 0.29 were predominantly of the hexagonal wurtzite phase, due to formation of wurtzite inclusions on various {111} facets of zb-GaN, thus indicating the optimal Al composition for phase-pure zb-GaN epilayer growth.

Zincblende GaN has the potential to bridge the “green gap” due to the absence of internal electric fields with respect to wurtzite GaN. However, at present, the quality of zincblende GaN light emitting diodes (LEDs) is not yet sufficient for useful efficient green devices. One of the major challenges is the poor spectral purity of the emitted light. A multimicroscopy approach, combining scanning electron microscopy-cathodoluminescence (SEM-CL), scanning transmission electron microscopy (STEM), and scanning electron diffraction (SED), is applied on a single feature to enable cross correlation between techniques and to investigate the possible causes for the broad optical emission of a zincblende GaN LED structure. This investigation demonstrates that SEM-CL on a site-specific TEM cross section prepared by focused ion beam (FIB) microscope can provide access to nanoscale light emission variations that can be directly related to structural differences seen in STEM. We demonstrate that the general large quantum well (QW) emission peak width relates to quantum well thickness and In content fluctuations. Multiple low-energy QW emission peaks are found to be linked with stacking fault bunches that intersect the QWs. Splitting of the QW emission peak is also found to be caused by the formation of wurtzite-phase inclusions associated with twins formed within the zincblende matrix. Our characterization also illustrates the quantum well structure within such wurtzite inclusions and their impact on the optical emission.

Porous nitride semiconductors are a fast-developing area of study, which open up a wide range of new properties and applications, including strain free optical reflectors, chemical sensors and as a pathway to device lift-off. This article reviews the current progress in porous nitrides formed through electrochemical and photoelectrochemical methods. Using a simple electrochemical cell, pores are formed by injecting holes into the surface layer in order to oxidise the material into a soluble form and releasing nitrogen gas. The process is controlled principally by the electric field that drives the injection of holes and hence the applied potential and doping density are the key parameters for controlling pore morphology, along with how and whether illumination is used. We describe the mechanisms responsible for this process in detail and outline the trends for changing pore size and pore shape. For example, larger applied potential creates a larger electric field and hence larger pores. These methods have been used to produce a wide variety of different structures. We present a layered porous structure created by the modulation of the applied potential. Alternatively, layered structures can be produced by growing alternate doped and non-intentionally doped layers. Electrochemical etching can then create pores only in the doped layers, as they are conductive. This process can be performed by etching laterally through access trenches that expose the doped material or through the etching of dislocations to create nanopipes that allow subsurface porosity to form. This process requires no prior processing steps. We combine this method with patterning of surface protective layers to influence where the resulting pores grow. Based on these various fabrication processes, significant progress has been made towards applications of porous GaN across optoelectronics, sensing and for improving material quality.

Halide double perovskites have gained significant attention, owing to their composition of low‐toxicity elements, stability in air, and recent demonstrations of long charge‐carrier lifetimes that can exceed 1 µs. In particular, Cs2AgBiBr6 is the subject of many investigations in photovoltaic devices. However, the efficiencies of solar cells based on this double perovskite are still far from the theoretical efficiency limit of the material. Here, the role of grain size on the optoelectronic properties of Cs2AgBiBr6 thin films is investigated. It is shown through cathodoluminescence measurements that grain boundaries are the dominant nonradiative recombination sites. It also demonstrates through field‐effect transistor and temperature‐dependent transient current measurements that grain boundaries act as the main channels for ion transport. Interestingly, a positive correlation between carrier mobility and temperature is found, which resembles the hopping mechanism often seen in organic semiconductors. These findings explain the discrepancy between the long diffusion lengths >1 µm found in Cs2AgBiBr6 single crystals versus the limited performance achieved in their thin film counterparts. This work shows that mitigating the impact of grain boundaries will be critical for these double perovskite thin films to reach the performance achievable based on their intrinsic single‐crystal properties.

Single-photon emitters with high degrees of purity are required for photonic-based quantum technologies. InGaN/GaN quantum dots are promising candidates for the development of single-photon emitters but have typically exhibited emission with insufficient purity. Here, pulsed single-photon emission with high purity is measured from an InGaN quantum dot. A raw g(2)(0) value of 0.043 ± 0.009 with no corrections whatsoever is achieved under quasi-resonant pulsed excitation. Such a low value is, in principle, sufficient for use in quantum key distribution systems.

Core-shell nanorod based light-emitting diodes (LEDs) with their exposed non-polar surfaces have the potential to overcome the limitations of planar LEDs by circumventing the quantum confined stark effect. In this experiment, InGaN/GaN core-shell nanorods were fabricated by a combination of top-down etching and bottom-up regrowth using metal-organic vapour phase epitaxy. When viewing the nanorods along their long axis, monochromatic cathodoluminescence maps taken at the GaN near-band-edge emission energy (3.39 eV) reveal a ring-like region of lower emission intensity. The diameter of this ring is found to be 530 (±20)nm corresponding to the ∼510 nm diameter nickel etch masks used to produce the initial GaN nanopillars. Thus, the dark ring corresponds to the regrowth interface. To understand the origin of the ring, scanning transmission electron microscopy (STEM) and cathodoluminescence (CL) hyperspectral mapping at 10K were performed. STEM imaging reveals the absence of extended defects in the nanorods and indeed near the regrowth interface. Monochromatic CL maps recorded at 10K show that the ring remains dark for monochromatic maps taken at the GaN near-band-edge emission energy (3.47 eV) but is bright when considering the donor-acceptor pair emission energy (3.27 eV). This peculiar anticorrelation indicates that the dark ring originates from an agglomeration of point defects associated with donor-acceptor pair emission. The point defects are incorporated and buried at the GaN regrowth interface from the chemical and/or physical damage induced by etching and lower the radiative recombination rate; limiting the radiative efficiency close to the regrowth interface.

© 2019 Author(s). Halide perovskites hold exceptional promise as cheap, low temperature solution-processed optoelectronic materials. Yet they are hindered by poor structural and chemical stability, rapidly degrading when exposed to moisture or air. We demonstrate a solution-phase method for infiltrating methylammonium lead bromide perovskite (CH 3 NH 3 PbBr 3 , or MAPbBr 3 ) into nanoporous GaN which preserved the green photoluminescence of the perovskite after up to 1 year of storage under ambient conditions. Besides a protective effect, confinement within the porous GaN matrix also resulted in a blueshift of the perovskite emission with decreasing pore size, suggesting an additional templating effect of the pores on the size of the perovskite crystals within. We anticipate that our method may be generalised to related perovskite materials, offering a route to producing composites of interest for use in optoelectronic devices for various applications.

The influence of growth temperature and V/III-ratio on the surface morphology of (001) cubic zincblende GaN epilayers during metal organic vapour phase epitaxy growth has been investigated using atomic force microscopy and transmission electron microscopy. The zincblende phase purity as determined by X-ray diffraction was found to be above 98% for most GaN epilayers studied. As the growth temperature was increased from 850 °C to 910 °C and as the V/III-ratio was separately increased from 38 to 300, surface features were found to be elongated in the [1-10] direction, and the ratio of the length to width of such surface features was found to increase. Faceting was observed at V/III-ratios below 38 and above 300, which in the latter case was accompanied by a reduction of the zincblende phase purity. An explanation for these morphological trends is proposed based on effects such as the reduced symmetry of the top monolayer of the (001)-oriented zincblende GaN lattice, diffusion of Ga and N adatoms on such a surface, and the relative energies of the crystal facets.

Low temperature atomic layer deposition was used to deposit α-Ga2O3 films, which were subsequently annealed at various temperatures and atmospheres. The α-Ga2O3 phase is stable up to 400 oC, which is also the temperature that yields the most intense and sharpest reflection by X-ray diffraction. Upon annealing at 450 oC and above, the material gradually turns into the more thermodynamically stable ε or β phase. The suitability of the materials for solar-blind photodetector applications has been demonstrated with the best responsivity achieved being 1.2 A/W under 240 nm illumination and 10 V bias, for the sample annealed at 400 oC in argon. It is worth noting however that the device performance strongly depends on the annealing conditions, with the device annealed in forming gas behaving poorly. Given that the tested devices have similar microstructure, the discrepancies in device performance are attributed to hydrogen impurities.

Airway hyperresponsiveness (AHR) is a critical feature of wheezing and asthma in children, but the initiating immune mechanisms remain unconfirmed. We demonstrate that both recombinant interleukin-33 (rIL-33) and allergen [house dust mite (HDM) or Alternaria alternata] exposure from day 3 of life resulted in significantly increased pulmonary IL-13+CD4+ T cells, which were indispensable for the development of AHR. In contrast, adult mice had a predominance of pulmonary LinnegCD45+CD90+IL-13+ type 2 innate lymphoid cells (ILC2s) after administration of rIL-33. HDM exposure of neonatal IL-33 knockout (KO) mice still resulted in AHR. However, neonatal CD4creIL-13 KO mice (lacking IL-13+CD4+ T cells) exposed to allergen from day 3 of life were protected from AHR despite persistent pulmonary eosinophilia, elevated IL-33 levels, and IL-13+ ILCs. Moreover, neonatal mice were protected from AHR when inhaled Acinetobacter lwoffii (an environmental bacterial isolate found in cattle farms, which is known to protect from childhood asthma) was administered concurrent with HDM. A. lwoffii blocked the expansion of pulmonary IL-13+CD4+ T cells, whereas IL-13+ ILCs and IL-33 remained elevated. Administration of A. lwoffii mirrored the findings from the CD4creIL-13 KO mice, providing a translational approach for disease protection in early life. These data demonstrate that IL-13+CD4+ T cells, rather than IL-13+ ILCs or IL-33, are critical for inception of allergic AHR in early life.

In this work, comparative x-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) measurements allow a comprehensive characterization of Al$_{1-x}$In$_x$N thin films grown on GaN. Within the limits of experimental accuracy, and in the compositional range 0.08 < $x$ < 0.28, the lattice parameters of the alloys generally obey Vegard's rule, varying linearly with the InN fraction. Results are also consistent with the small deviation from linear behaviour suggested by Darakchieva $\textit{et al}$ (2008 Appl. Phys. Lett. 93 261908). However, unintentional incorporation of Ga, revealed by atom probe tomography (APT) at levels below the detection limit for RBS, may also affect the lattice parameters. Furthermore, in certain samples the compositions determined by XRD and RBS differ significantly. This fact, which was interpreted in earlier publications as an indication of a deviation from Vegard's rule, may rather be ascribed to the influence of defects or impurities on the lattice parameters of the alloy. The wide-ranging set of Al$_{1-x}$In$_x$N films studied allowed furthermore a detailed investigation of the composition leading to lattice-matching of Al$_{1-x}$In$_x$N/GaN bilayers.

Solid-state single photon sources with polarisation control operating beyond the Peltier cooling barrier of 200 K are desirable for a variety of applications in quantum technology. Using a non-polar InGaN system, we report the successful realisation of single photon emission with a g(2)(0) of 0.21, a high polarisation degree of 0.80, a fixed polarisation axis determined by the underlying crystallography, and a GHz repetition rate with a radiative lifetime of 357 ps at 220 K in semiconductor quantum dots. The temperature insensitivity of these properties, together with the simple planar epitaxial growth method and absence of complex device geometries, demonstrates that fast single photon emission with polarisation control can be achieved in solid-state quantum dots above the Peltier temperature threshold, making this system a potential candidate for future on-chip applications in integrated systems.

In this work, comparative x-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) measurements allow a comprehensive characterization of Al1-xInxN thin films grown on GaN. Within the limits of experimental accuracy, and in the compositional range 0.08 < x < 0.28, the lattice parameters of the alloys generally obey Vegard's rule, varying linearly with the InN fraction. Results are also consistent with the small deviation from linear behaviour suggested by Darakchieva et al (2008 Appl. Phys. Lett. 93 261908). However, unintentional incorporation of Ga, revealed by atom probe tomography (APT) at levels below the detection limit for RBS, may also affect the lattice parameters. Furthermore, in certain samples the compositions determined by XRD and RBS differ significantly. This fact, which was interpreted in earlier publications as an indication of a deviation from Vegard's rule, may rather be ascribed to the influence of defects or impurities on the lattice parameters of the alloy. The wide-ranging set of Al1-xInxN films studied allowed furthermore a detailed investigation of the composition leading to lattice-matching of Al1-xInxN/GaN bilayers.

The digital image correlation (DIC) of speckle patterns obtained by vapour-assisted gold remodelling at 200 – 350 °C has already been used to map plastic strains with submicron resolution. However, it has not so far proved possible to use such patterns for testing at high temperatures. Here we demonstrate how a gold speckle pattern can be made that is stable at 700 °C, to study deformation in a commercial TiAl alloy (Ti-45Al-2Nb- 2Mn(at%)-0.8 vol% TiB$_2$). The pattern is made up of a uniformly sized random array of Au islands as small as 15 nm in diameter, depending on reconstruction parameters, with a sufficiently small spacing to be suitable for nano-scale, nDIC, strain mapping at a subset size of 60 × 60 nm$^2$ . It can be used at temperatures up to 700 °C for many hours, for high cycle fatigue testing for instance. There is good particle attachment to the substrate. It can withstand ultra-sound cleaning, is thermally stable and has a high atomic number contrast for topography-free backscatter electron imaging.

The efficiency of light emitting diodes (LEDs) remains a topic of great contemporary interest due to their potential to reduce the amount of energy consumed in lighting. The current consensus is that electrons and holes distribute themselves through the emissive region by a drift-diffusion process which results in a highly non-uniform distribution of the light emission and can reduce efficiency. In this paper, the measured variations in the external quantum efficiency of a range of InGaN/GaN LEDs with different numbers of quantum wells (QWs) are shown to compare closely with the predictions of a revised ABC model, in which it is assumed that the electrically injected electrons and holes are uniformly distributed through the multi-quantum well (MQW) region, or nearly so, and hence carrier recombination occurs equally in all the quantum wells. The implications of the reported results are that drift-diffusion plays a far lesser role in cross-well carrier transport than previously thought; that the dominant cause of efficiency droop is intrinsic to the quantum wells and that reductions in the density of non-radiative recombination centers in the MQW would enable the use of more QWs and thereby reduce Auger losses by spreading carriers more evenly across a wider emissive region.

A non-polar m-plane structure consisting of five InGaN/GaN quantum wells (QWs) was grown on ammonothermal bulk GaN by metal-organic vapor phase epitaxy. Surface step bunches propagating through the QW stack were found to accommodate the 2° substrate miscut towards the -c direction. Both large steps with heights of a few tens of nanometres and small steps between one and a few atomic layers in height are observed, the former of which exhibit cathodoluminescence at longer wavelengths than the adjacent m-plane terraces. This is attributed to the formation of semi-polar facets at the steps on which the QWs are shown to be thicker and have higher Indium contents than those in the adjacent m-plane regions. Discrete basal-plane stacking faults (BSFs) were occasionally initiated from the QWs on the main m-plane terraces, but groups of BSFs were frequently observed to initiate from those on the large steps, probably related to the increased strain associated with the locally higher indium content and thickness.

We present a combined theoretical and experimental analysis of the optical properties of $\textit{m}$-plane InGaN/GaN quantum wells. The sample was studied by photoluminescence and photoluminescence excitation spectroscopy at low temperature. The spectra show a large Stokes shift between the lowest exciton peak in the excitation spectra and the peak of the photoluminescence spectrum. This behavior is indicative of strong carrier localization effects. These experimental results are complemented by tight-binding calculations, accounting for random alloy fluctuations and Coulomb effects. The theoretical data explain the main features of the experimental spectra. Moreover, by comparison with calculations based on a virtual crystal approximation, the importance of carrier localization effects due to random alloy fluctuations is explicitly shown.

We report on a comparative study of the low temperature emission and polarisation properties of InGaN/GaN quantum wells grown on nonpolar (11$\bar 2$0) $\textit{a}$-plane and (10$\bar 1$0) m-plane free-standing bulk GaN substrates where the In content varied from 0.14 to 0.28 in the m-plane series and 0.08 to 0.21 for the a-plane series. The low temperature photoluminescence spectra from both sets of samples are broad with full width at half maximum height increasing from 81 to 330 meV as the In fraction increases. Photoluminescence excitation spectroscopy indicates that the recombination mainly involves strongly localised carriers. At 10 K the degree of linear polarisation of the $\textit{a}$-plane samples is much smaller than of the $\textit{m}$-plane counterparts and also varies across the spectrum. From polarisation-resolved photoluminescence excitation spectroscopy we measured the energy splitting between the lowest valence sub-bands to lie in the range of 23–54 meV for the $\textit{a}$- and $\textit{m}$-plane samples in which we could observe distinct exciton features. Thus the thermal occupation of a higher valence sub-band cannot be responsible for the reduction of the degree of linear polarisation at 10 K. Time-resolved spectroscopy indicates that in $\textit{a}$-plane samples there is an extra emission component which is at least partly responsible for the reduction in the degree of linear polarisation., This work was supported by UK Engineering and Physical Sciences Research Council [grant numbers EP\J001627\1, EP\J003603\1]; and Science Foundation Ireland [grant number 13/SIRG/2210].

We present measurements of microphotoluminescence decay dynamics for single InGaN quantum dots. The recombination is shown to be characterized by a single exponential decay, in contrast to the non-exponential recombination dynamics seen in the two-dimensional wetting layer. The lifetimes of single dots in the temperature range 4 K to 60 K decrease with increasing temperature. Microphotoluminescence measurements of exciton complexes in single MOVPE-grown InGaN quantum dots are also reported. We find the exciton-biexciton and exciton-charged exciton splitting energies to be 25 meV and 10 meV to the higher-energy side of the exciton ground state, respectively. Assignments of the ground state exciton, biexciton and charged exciton are supported by theoretical calculations. These measurements have been extended to investigate the time-resolved dynamics of biexciton transitions in the quantum dots. The measurements yield a radiative recombination lifetime of 1.0 ns for the exciton and 1.4 ns for the biexciton. The data can be fitted to a coupled differential equation rate equation model, confirming that the exciton state is refilled as biexcitons undergo radiative decay.

No Abstract.

InₓGa₁₋ₓN structures epitaxially grown on a-plane or m-plane GaN exhibit in-plane optical polarization. Linear elasticity theory treats the two planes equivalently and is hence unable to explain the experimentally observed higher degree of linear polarization for m-plane than a-plane InₓGa₁₋ₓN. Using density functional theory, we study the response of InₓGa₁₋ₓN random alloys to finite biaxial strains on both non-polar planes. The calculated m-plane InₓGa₁₋ₓN valence band splitting is larger than that of a-plane, due to a greater degree of structural relaxation in a-plane InₓGa₁₋ₓN. We provide a parameterization of the valence band splitting of InₓGa₁₋ₓN strained to a-plane and m-plane GaN for In compositions between 0 and 0.5, which agrees with experimental measurements and qualitatively explains the experimentally observed difference between a-plane and m-plane polarization.

Non-polar a-plane gallium nitride (GaN) lms have been grown on r-plane (1102) sapphire by metal organic vapour phase epitaxy (MOVPE). A total of ve in-situ defect reduction techniques for a-plane GaN are compared, including two variants with a low temperature GaN nucleation layer (LTNL) and three variants without LTNL, in which the high- temperature growth of GaN is performed directly on the sapphire using various crystallite sizes. The material quality is investigated by photoluminescence (PL), x-ray di raction, cathodoluminescence, atomic force and optical microscopy. It is found that all layers are anisotropically strained with threading dislocation densities over 109 cm􀀀2. The PL spectrum is typically dominated by emission from basal plane stacking faults. Overall, growth techniques without LTNL do not yield any particular improvement and even result in the creation of new defects, ie. inversion domains, which are seldom observed if a low temperature GaN nucleation layer is used. The best growth method uses a LTNL combined with a single silicon nitride interlayer.

Because hypoperfusion of brain tissue precedes atrophy in dementia, the detection of dementia may be advanced by the use of perfusion information. Such information can be obtained noninvasively with arterial spin labeling (ASL), a relatively new MR technique quantifying cerebral blood flow (CBF). Using ASL and structural MRI, we evaluated diagnostic classification in 32 prospectively included presenile early stage dementia patients and 32 healthy controls. Patients were suspected of Alzheimer's disease (AD) or frontotemporal dementia. Classification was based on CBF as perfusion marker, gray matter (GM) volume as atrophy marker, and their combination. These markers were each examined using six feature extraction methods: a voxel-wise method and a region of interest (ROI)-wise approach using five ROI-sets in the GM. These ROI-sets ranged in number from 72 brain regions to a single ROI for the entire supratentorial brain. Classification was performed with a linear support vector machine classifier. For validation of the classification method on the basis of GM features, a reference dataset from the AD Neuroimaging Initiative database was used consisting of AD patients and healthy controls. In our early stage dementia population, the voxelwise feature-extraction approach achieved more accurate results (area under the curve (AUC) range = 86-91%) than all other approaches (AUC = 57-84%). Used in isolation, CBF quantified with ASL was a good diagnostic marker for dementia. However, our findings indicated only little added diagnostic value when combining ASL with the structural MRI data (AUC = 91%), which did not significantly improve over accuracy of structural MRI atrophy marker by itself. (C) 2014 Wiley Periodicals, Inc.

Background The underlying mechanisms of idiopathic pulmonary fibrosis (IPF) are unknown. This progressive disease has high mortality rates and current models for prediction of mortality have limited value in identifying which patients will progress. We previously showed that the glycoprotein fibulin-1 is involved in enhanced proliferation and wound repair by mesenchymal cells, thus may contribute to lung fibrosis in IPF. Methods Serum, lung tissue and lung function values were obtained from four independent locations (Sydney and Perth, Australia, San Francisco, USA and Modena, Italy). Patients with IPF were followed for a minimum of one year and progression was defined as a significant decline in lung function or death. Primary parenchymal lung fibroblasts of 15 patients with and without IPF were cultured under non-stimulatory conditions. Fibulin-1 levels in serum and secreted or deposited by fibroblasts were measured by western blot and in lung tissue by immunohistochemistry. Results Serum fibulin-1 levels were increased in patients with IPF compared to subjects without lung disease (p=0.006). Furthermore, tissue fibulin-1 levels were increased in patients with IPF (p=0.02) and correlated negatively with lung function (r=-0.9, p

Control of leakage currents in the buffer layers of GaN based transistors on Si substrates is vital for the demonstration of high performance devices. Here, we show that the growth conditions during the metal organic chemical vapour deposition growth of the graded AlGaN strain relief layers (SRLs) can significantly influence the vertical leakage. Using scanning capacitance microscopy, secondary ion mass spectrometry, and transmission electron microscopy, we investigate the origins of leakage paths and show that they result from the preferential incorporation of oxygen impurities on the side wall facets of the inverted hexagonal pyramidal pits which can occur during the growth of the graded AlGaN SRL. We also show that when 2D growth of the AlGaN SRL is maintained a significant increase in the breakdown voltage can be achieved even in much thinner buffer layer structures. These results demonstrate the importance of controlling the morphology of the high electron mobility transistor buffer layer as even at a very low density the leakage paths identified would provide leakage paths in large area devices.

The use of pulsed mode scanning electron microscopy cathodoluminescence (CL) for both hyperspectral mapping and time-resolved measurements is found to be useful for the study of hybrid perovskite films, a class of ionic semiconductors that have been shown to be beam sensitive. A range of acquisition parameters is analysed, including beam current and beam mode (either continuous or pulsed operation), and their effect on the CL emission is discussed. Under optimized acquisition conditions, using a pulsed electron beam, the heterogeneity of the emission properties of hybrid perovskite films can be resolved via the acquisition of CL hyperspectral maps. These optimized parameters also enable the acquisition of time-resolved CL of polycrystalline films, showing significantly shorter lived charge carriers dynamics compared to the photoluminescence analogue, hinting at additional electron beam-specimen interactions to be further investigated. This work represents a promising step to investigate hybrid perovskite semiconductors at the nanoscale with CL.

Nano-cathodoluminescence (Nano-CL) reveals optical emission from individual InGaN quantum wells for applications in optoelectronic devices. We show the luminescent intensity decays over time with exposure to the electron beam for energies between 80 and 200 keV. Measurements of the CL intensity over time show an exponential decline in intensity, which we propose is due to the formation of nitrogen Frenkel defects. The measured CL damage decreases with reductions in the electron accelerating voltage and we suggest that the electron induced structural damage may be suppressed below the proposed damage threshold. The electron beam induced damage leads to a non-radiative region that extends over the measured minority carrier diffusion length. Nano-CL may thus serve as a powerful technique to study III-nitride optoelectronics.

Nitride microcavities offer an exceptional platform for the investigation of light-matter interactions as well as the development of devices such as high efficiency light emitting diodes (LEDs) and low-threshold nanolasers. Microdisk geometries in particular are attractive for low-threshold lasing applications due to their ability to support high finesse whispering gallery modes (WGMs) and small modal volumes. In this article we review the effect of defects on the properties of nitride microdisk cavities fabricated using photoelectrochemical (PEC) etching of an InGaN sacrificial superlattice (SSL). Threading dislocations originating from either the original GaN pseudosubstrate are shown to hinder the undercutting of microdisk cavities during the photoelectric chemical (PEC) etching process resulting in whiskers of unetched material on the underside of microdisks. The unetched whiskers provide a pathway for light to escape, reducing microdisk Q-factor if located in the region occupied by the WGMs. Additionally, dislocations can affect the spectral stability of quantum dot emitters, thus hindering their effective integration in microdisk cavities. Though dislocations are clearly undesirable, the limiting factor on nitride microdisk Q-factor is expected to be internal absorption, indicating that the further optimisation of nitride microdisk cavities must incorporate both the elimination of dislocations and careful tailoring of the active region emission wavelength and background doping levels.