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Semi-polar group III nitrides and their alloys (AlGaN, InGaN) show great promise for future opto-electronic devices. For these orientations, specific X-ray diffraction (XRD) methods have been developed to measure the alloy content. The XRD methods proposed in the literature all use approximations at different levels. Here, we introduce a novel exact model, against which we compare each simplifying assumption previously used. The relevant approximations are then assembled to produce an accurate linearized model, which shares the same mathematical form as that of the standard polar or non-polar nitride analysis. This linearized model can be further simplified to provide an analytic expression for correction of the alloy content when a tilt (partial relaxation) is found between the alloy epilayer and the semi-polar GaN template. For a given model-alloy content and tilt angle- we can compute the expected XRD data. Vice-versa, the alloy content can be obtained from the experimental measurements-tilt angle and difference in d-spacing. This work focuses on the typical semi-polar planes studied in the literature: inclined a-planes ([formula]), e.g., ([formula]), and inclined m-planes ([formula]), e.g., ([formula]) or ([formula]). [ABSTRACT FROM AUTHOR]

Objective: Maternal obesity is associated with obesity and metabolic disorders in offspring. However, there remains a paucity of data on strategies to reverse the effects of maternal obesity on maternal and offspring health. With maternal undernutrition, taurine supplementation improves outcomes in offspring mediated in part via improved glucose–insulin homeostasis. The efficacy of taurine supplementation in the setting of maternal obesity on health and well-being of offspring is unknown. We examined the effects of taurine supplementation on outcomes related to growth and metabolism in offspring in a rat model of maternal obesity. Design: Wistar rats were randomised to: 1) control diet during pregnancy and lactation (CON); 2) CON with 1.5% taurine in drinking water (CT); 3) maternal obesogenic diet (MO); or 4) MO with taurine (MOT). Offspring were weaned onto the control diet for the remainder of the study. Results: At day 150, offspring body weights and adipose tissue weights were increased in MO groups compared to CON. Adipose tissue weights were reduced in MOT versus MO males but not females. Plasma fasting leptin and insulin were increased in MO offspring groups but were not altered by maternal taurine supplementation. Plasma homocysteine concentrations were reduced in all maternal taurine-supplemented offspring groups. There were significant interactions across maternal diet, taurine supplementation and sex for response to an oral glucose tolerance test , a high-fat dietary preference test and pubertal onset in offspring. Conclusions: These results demonstrate that maternal taurine supplementation can partially ameliorate adverse developmental programming effects in offspring in a sex-specific manner. [ABSTRACT FROM AUTHOR]

Glucose intolerance during pregnancy – a major driver of gestational diabetes mellitus (GDM) – has significant short- and long-term health consequences for both the mother and child. As GDM prevalence continues to escalate, there is growing need for preventative strategies. There is limited but suggestive evidence that myo-inositol (MI) and probiotics (PB) could improve glucose tolerance during pregnancy. The present study tested the hypothesis that MI and/or PB supplementation would reduce the risk of glucose intolerance during pregnancy. Female C57BL/6 mice were randomised to receive either no treatment, MI, PB (Lactobacillus rhamnosus and Bifidobacterium lactis) or both (MIPB) for 5 weeks. They were then provided with a high-fat diet for 1 week before mating commenced and throughout mating/gestation, while remaining on their respective treatments. An oral glucose tolerance test occurred at gestational day (GD) 16·5 and tissue collection at GD 18·5. Neither MI nor PB, separately or combined, improved glucose tolerance. However, MI and PB both independently increased adipose tissue expression of Ir , Irs1 , Akt2 and Pck1 , and PB also increased Pparγ. MI was associated with reduced gestational weight gain, whilst PB was associated with increased maternal fasting glucose, total cholesterol and pancreas weight. These results suggest that MI and PB may improve insulin intracellular signalling in adipose tissue but this did not translate to meaningful differences in glucose tolerance. The absence of fasting hyperglycaemia or insulin resistance suggests this is a very mild model of GDM, which may have affected our ability to assess the impact of these nutrients. [ABSTRACT FROM AUTHOR]

There is increasing interest in III-nitride films and multiple quantum well structures grown in non-polar or semi-polar orientations for application in light-emitting devices. We describe a method to obtain the compositions and the thicknesses of layers within III-nitride quantum well or superlattice structures grown in non-polar or semi-polar orientations, based on X-ray scattering. For each new crystallographic orientation considered, new axes were obtained and both the lengths and angles of these new axes calculated relative to the original conventional reference axes. These angles provide the coefficients of the matrix to transform the elastic constants published in the conventional setting (as used for polar c-plane oriented III-nitrides) into the appropriate new values. The new characteristic lengths and new elastic constants are then put into the general equation that relates the composition of a fully strained layer to the experimentally measured out-of-plane alloy d-spacing. Thus we have (a) determined the alloy composition from the difference between the experimentally measured alloy d-spacing and that of the substrate and (b) calculated the strained d-spacing for a given alloy composition for input to simple kinematical simulation software. In addition for quantum well structures the thickness ratio of well-to-barrier must be determined. Here we use the minima in the low angle reflectivity data. The repeat thickness and thus the thicknesses of the well and barrier layers, can be obtained from either the low or the high-angle data. We then cross-check by comparing the experimental and the simulated high-angle diffraction data. This method has been applied successfully to heteroepitaxial non-polar and semi-polar GaN/AlGaN and InGaN/GaN multiple quantum well structures and may also be used to find the composition of epilayers. The method works even in the presence of tilt between the superlattice and the GaN 'template', although in this case additional high-angle diffraction data at different settings must be collected. [ABSTRACT FROM AUTHOR]

The full width at half maximum (FWHM) of x-ray rocking curves is often used as a measure of the crystalline quality of thin films. In this paper, the effects of wafer curvature on the x-ray rocking curves (ω-scans) obtained from a 2 in. 0001-oriented sapphire wafer and an epitaxial 0001-oriented GaN film grown on such a wafer are discussed. Beam height reduction can limit curvature-related effects for symmetric and asymmetric reflections; these effects are generally significant for low dislocation density GaN films. Due to the shape of the area illuminated by the x-ray beam in the skew symmetric geometry, beam width reduction is instead appropriate, but this still gives an underestimate of ω-FWHM values obtained with an open detector and an overestimate of ω-FWHM values obtained with an analyzer. Therefore, skew symmetric ω-FWHM values from curved samples are often unreliable. Additionally, Williamson–Hall analysis using ω-scans is rendered unreliable in the presence of significant curvature. Variations in ω-FWHM values for different experimental configurations are attributed to nonspherical wafer curvature, changes in illuminated area for each reflection, and changes in sampled volume at each step in the ω-scan. Although this paper focuses on GaN films, the results are applicable to a wide range of other materials exhibiting wafer curvature. [ABSTRACT FROM AUTHOR]

We have determined the indium content and the layer thicknesses in an InGaN epilayer and InGaN/ GaN quantum well structures by high-resolution x-ray diffraction (XRD) using the (002) reflection. The thickness of the total repeat (an InGaN well plus a GaN barrier) in the superlattice is easily determined from the spacing between the satellite peaks in an omega/2theta scan. Measurement of the individual thickness of InGaN and GaN layers and the indium content is less straightforward, since for multilayer structures the peak positions are influenced by both the indium content and the thickness ratio of the GaN to the InGaN layer. Thus, several different models may give reasonable fits to data collected over a limited range (about 1° omega/2theta either side of the (002)) showing only lower-order (-3 to +3) satellite peaks. Whenever possible, we have collected data over a wide range (about 4° omega/2theta) and determined the thickness ratio by examination of the relative intensities of weak higher-order satellite peaks (-7 to +5). An alternative but less sensitive method is to use relative intensities from x-ray reflectivity measurements to give the thickness ratio. Once the thickness of both the InGaN and GaN layers has been established, the InGaN composition can be determined from the peak positions. If the quality of the samples is poor, because of inhomogeneities or wide diffuse interfaces, there are insufficient data to characterize the structures. There is good agreement between the composition of the epilayer as determined by XRD and secondary ion mass spectroscopy and good agreement between x-ray and electron microscopy results for the quantum well structures. We find no variation from Vegard's rule for In contents less than 0.20. This article shows that structural parameters of high-quality InGaN/GaN superlattices with 10 and 5 repeats can be determined reliably by x-ray techniques: The InGaN and GaN thicknesses to ±1 Å and the In... [ABSTRACT FROM AUTHOR]