Investigation of electron energy states in InGaN/GaN multiple quantum wells

Blue light emitting diodes (LED) consisting of InGaN/GaN multiple quantum wells (MQWs) have been grown by metal organic chemical vapor deposition (MOCVD) on sapphire. The width of the quantum wells (InGaN) was maintained in the range of 3–5 nm with a barrier of 10–15 nm of GaN. Various diagnostic techniques were employed for the characterization of the InGaN/GaN heterostructure. Carrier concentration depth profile from C–V measurements demonstrated the presence of MQWs. The higher value of built-in voltage (15 V) determined from C⁻²–V plot also supported the presence of MQWs as assumed to alter the space-charge region width and hence the intercept voltage. Arrhenius plots due to DLTS spectra from the device revealed at least four energy states (eV) 0.1, 0.12, 0.15 and 0.17, respectively in the quantum wells, with respect to the barrier. Further the photoluminescence spectrum showed an InGaN-based broad band centered at 2.9 eV and the GaN peak at 3.4 eV. A comparison of the PL spectrum with the literature helped to estimate the indium content in the QW (InGaN) and its width to be ∼13% and ∼3 nm, respectively. The results were consistent with the DLTS findings.     

MOCVD growth of GaN on Si(1 1 1) substrates using an ALD-grown Al2O3 interlayer

GaN thin films have been grown on Si(1 1 1) substrates using an atomic layer deposition (ALD)-grown Al₂O₃ interlayer. This thin Al₂O₃ layer reduces strain in the subsequent GaN layer, leading to lower defect densities and improved material quality compared to GaN thin films grown by the same process on bare Si. XRD ω-scans showed a full width at half maximum (FWHM) of 549 arcsec for GaN grown on bare Si and a FWHM as low as 378 arcsec for GaN grown on Si using the ALD-grown Al₂O₃ interlayer. Raman spectroscopy was used to study the strain in these films in more detail, with the shift of the E₂(high) mode showing a clear dependence of strain on Al₂O₃ interlayer thickness. This dependence of strain on Al₂O₃ thickness was also observed via the redshift of the near bandedge emission in room temperature photoluminescence (RT-PL) spectroscopy. The reduction in strain results in a significant reduction in both crack density and screw dislocation density compared to similar films grown on bare Si. Screw dislocation density of the films grown on Al₂O₃/Si substrates approaches that of typical GaN layers on sapphire. This work shows great promise for the use of oxide interlayers for growth of GaN-based LEDs on Si.     

Reliability of Clinician-Based (GRBAS and CAPE-V) and Patient-Based (V-RQOL and IPVI) Documentation of Voice Disorders

This study examined the reliability of two methods for documenting voice quality by clinicians and compared the methods for documenting patients' perceptions of voice quality. It involved a prospective reliability study and a retrospective chart review. Reliability of two clinician-based voice assessment protocols-Grade, Roughness, Breathiness, Asthenia, Strain (GRBAS) and Consensus Auditory Perceptual Evaluation-Voice (CAPE-V)-was evaluated. These two protocols were then compared after use in voice assessments of 42 males and 61 females performed by a certified speech-language pathologist specializing in the assessment of voice disorders. In addition, two patient-based scales (Voice Related Quality of Life, or V-RQOL, and Iowa Patient's Voice Index, or IPVI) obtained from the same patients were compared with each other and with the clinician-based scales. Reliability of clinicians' ratings of overall severity of dysphonia using GRBAS and CAPE-V scales was very good (r>0.80). Agreement between V-RQOL Total scores and IPVI ratings of the patient's perceptions of impact of dysphonia was less strong (Spearman's r=-0.76). There was relatively weak agreement between patient-based and clinician-based scales. Clinician's perceptions of dysphonia appeared to be reliable and unaffected by rating tool, as indicated by the high level of agreement between the two rating systems when they were used together. The CAPE-V system appeared to be more sensitive to small differences within and among patients than the GRBAS system. The V-RQOL and IPVI approaches to documenting patient's perceptions of dysphonia agreed less well possibly due to differences in patient dependence on voice and on interpretation of the rating tool items. The differences between clinician-based and patient-based data support the conclusion that clinicians and patients experience and consider dysphonia very differently.     

Analysis of sialyl oligosaccharides by high-performance liquid chromatography-electrospray ionisation-mass spectrometry with differentiation of alpha2-3 and alpha2-6 sialyl linkages

A method for analysing sialyl oligosaccharides from bovine colostrum using high-performance liquid chromatography-electrospray ionisation-mass spectrometry (HPLC-ESI-MS) is described. Under positive ionisation mode, mass spectra of alpha2-3 and alpha2-6 linkages were different, and the former produced a prominent B2 (or B3 in disialyl lactose) mass fragment. This fragment was absent from mass spectra with alpha2-6 linkages. Two sialyl oligosaccharides, which have not been reported previously, were tentatively identified. One comprises a N-acetyl neuraminic acid (Neu5Ac), two hexoses (Hex), and one N-acetyl hexosamine (HexNAc) residue ((Neu5Ac)1 (Hex)2 (HexNAc)1), and the other comprises one Neu5Ac and one Hex residue ((Neu5Ac)1(Hex)1).     

ALDH2 Mediates 5-Nitrofuran Activity in Multiple Species

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Highlights? Zebrafish provide a viable assay for the biological toxicity of 5-nitrofurans ? ALDH2 inhibitors prevent 5-nitrofuran toxicity in zebrafish and yeast ? Genetic dependence on ALDH2 for 5-nitrofuran toxicity in zebrafish and yeast systems ? 5-Nitrofurans bind to and are substrates of human ALDH2     

An equation describing aqueous and non-aqueous foam collapse

The collapse profiles of foams formed from model aqueous and non-aqueous foaming solutions have been recorded using a novel device, the Optical Transmission Foam Meter. An equation comprising two exponential terms has been used to describe the profiles and an attempt has been made to relate the equation parameters to some of the physical properties of the gas and liquid phases.     

Experiments with longitudinally polarized electrons in a storage ring using a siberian snake

We report on first measurements with polarized electrons stored in a medium-energy ring and with a polarized internal target. Polarized electrons were injected at 442 MeV (653 MeV), and a partial (full) Siberian snake was employed to preserve the polarization. Longitudinal polarization at the interaction point and polarization lifetime of the stored electrons were determined with laser backscattering. Spin observables were measured for electrodisintegration of polarized 3He, with simultaneous detection of scattered electrons, protons, neutrons, deuterons, and 3He nuclei, over a large phase space.     

Nuclear magnetic resonance relaxometry as a spectroscopic probe of the coordination sphere of a paramagnetic metal bound to a humic acid mixture

Protons on water molecules are strongly affected by paramagnetic ions. Since the acid-base properties of water facilitate rapid proton exchange, a single proton nuclear magnetic resonance (NMR) signal is seen in aqueous solutions of paramagnetic ions. Proton relaxation times are significantly affected by paramagnetic species and the readily detectable single signal serves as a powerful amplifier of the information contained concerning the protons in the paramagnetic environment. Where water molecules coordinated to free paramagnetic ions and to metal complexes of ligands that form non-labile (on the NMR time scale) complexes, the effects on water in the two environments can be distinguished. This can provide information on the nature of the ligand binding sites. The example of Cu²⁺ bound to the Laurentian humic acid mixture reported here using convenient low field NMR relaxometers shows that the information can enrich our understanding of complexation and speciation in the presence of complex mixture ligands characteristic of natural water systems. In this case, the data underline the role of aggregation and conformation in defining the complexation sites.