Influence of Ga/N ratio on morphology, vacancies, and electrical transport in GaN grown by molecular beam epitaxy at high temperature

The effect of Ga/N flux ratio on surface morphology, incorporation of point defects and electrical transport properties of GaN films grown by plasma-assisted molecular beam epitaxy in a recently developed high-temperature growth regime was investigated. The homoepitaxial (0001) GaN films grown at ∼780–790 °C showed smoothest morphologies near the cross-over between N-rich and Ga-rich growth(0.75<Ga/N<1.1) contrasting previous observations for low-temperature growth. The higher-quality growth near Ga/N∼1 resulted from lower thermal decomposition rates and was corroborated by slightly lower Ga vacancy concentrations [VGa], lower unintentional oxygen incorporation, and improved electron mobilities. The consistently low [VGa], i.e., ∼10exp16 cm−3 for all films attribute further to the significant benefits of the high-temperature growth regime.Peer reviewe

On the interplay of point defects and Cd in non-polar ZnCdO films

Non-polar ZnCdO films, grown over m- and r-sapphire with a Cd concentration ranging between 0.8% and 5%, have been studied by means of slow positron annihilation spectroscopy (PAS) combined with chemical depth profiling by secondary ion mass spectroscopy and Rutherford back-scattering. Vacancy clusters and Zn vacancies with concentrations up to 10exp17 cm−3 and 10exp18 cm−3, respectively, have been measured inside the films. Secondary ion mass spectroscopy results show that most Cd stays inside the ZnCdO film but the diffused atoms can penetrate up to 1.3 μm inside the ZnO buffer. PAS results give an insight to the structure of the meta-stable ZnCdO above the thermodynamical solubility limit of 2%. A correlation between the concentration of vacancy clusters and Cd has been measured. The concentration of Zn vacancies is one order of magnitude larger than in as-grown non-polar ZnO films and the vacancy cluster are, at least partly, created by the aggregation of smaller Zn vacancy related defects. The Zn vacancy related defects and the vacancy clusters accumulate around the Cd atoms as a way to release the strain induced by the substitutional CdZn in the ZnO crystal.Peer reviewe

Statistical Physics of Fracture Surfaces Morphology

Experiments on fracture surface morphologies offer increasing amounts of data that can be analyzed using methods of statistical physics. One finds scaling exponents associated with correlation and structure functions, indicating a rich phenomenology of anomalous scaling. We argue that traditional models of fracture fail to reproduce this rich phenomenology and new ideas and concepts are called for. We present some recent models that introduce the effects of deviations from homogeneous linear elasticity theory on the morphology of fracture surfaces, succeeding to reproduce the multiscaling phenomenology at least in 1+1 dimensions. For surfaces in 2+1 dimensions we introduce novel methods of analysis based on projecting the data on the irreducible representations of the SO(2) symmetry group. It appears that this approach organizes effectively the rich scaling properties. We end up with the proposition of new experiments in which the rotational symmetry is not broken, such that the scaling properties should be particularly simple.Comment: A review paper submitted to J. Stat. Phy

Damage growth in random fuse networks

The correlations among elements that break in random fuse network fracture are studied, with disorder strong enough to allow for volume damage before final failure. The growth of microfractures is found to be uncorrelated above a lengthscale, that increases as the final breakdown approaches. Since the fuse network strength decreases with sample size, asymptotically the process resembles more and more mean-field-like (“democratic fiber bundle”) fracture. This is found from the microscopic dynamics of avalanches or microfractures, from a study of damage localization via entropy, and from the final damage profile. In particular, the last one is statistically constant, except exactly at the final crack zone, in spite of the fact that the fracture surfaces are self-affine. This also implies that the correlations in damage are not extensive

Fast track surgery versus conventional recovery strategies for colorectal surgery

BACKGROUND: In recent years the Enhanced Recovery after Surgery (ERAS) postoperative pathway in (ileo-)colorectal surgery, aiming at improving perioperative care and decreasing postoperative complications, has become more common. OBJECTIVES: We investigated the effectiveness and safety of the ERAS multimodal strategy, compared to conventional care after (ileo-)colorectal surgery. The primary research question was whether ERAS protocols lead to less morbidity and secondary whether length of stay was reduced. SEARCH STRATEGY: To answer the research question we entered search strings containing keywords like "fast track", "colorectal and surgery" and "enhanced recovery" into major databases. We also hand searched references in identified reviews concerning ERAS. SELECTION CRITERIA: We included published randomised clinical trials, in any language, comparing ERAS to conventional treatment in patients with (ileo-) colorectal disease requiring a resection. RCT's including at least 7 ERAS items in the ERAS group and no more than 2 in the conventional arm were included. DATA COLLECTION AND ANALYSIS: Data of included trials were independently extracted by the reviewers. Analyses were performed using "REVMAN 5.0.22". Data were pooled and rate differences as well as weighted mean differences with their 95% confidence intervals were calculated using either fixed or random effects models, depending on heterogeneity (I(2)). MAIN RESULTS: 4 RCTs were included and analysed. Methodological quality of included studies was considered low, when scored according to GRADE methodology. Total numbers of inclusion were limited. The trials included in primary analysis reported 237 patients, (119 ERAS vs 118 conventional). Baseline characteristics were comparable. The primary outcome measure, complications, showed a significant risk reduction for all complications (RR 0.50; 95% CI 0.35 to 0.72). This difference was not due to reduction in major complications. Length of hospital stay was significantly reduced in the ERAS group (MD -2.94 days; 95% CI -3.69 to -2.19), and readmission rates were equal in both groups. Other outcome parameters were unsuitable for meta-analysis, but seemed to favour ERAS. AUTHORS' CONCLUSIONS: The quantity and especially quality of data are low. Analysis shows a reduction in overall complications, but major complications were not reduced. Length of stay was reduced significantly. We state that ERAS seems safe, but the quality of trials and lack of sufficient other outcome parameters do not justify implementation of ERAS as the standard of care. Within ERAS protocols included, no answer regarding the role for minimally invasive surgery (i.e. laparoscopy) was found. Furthermore, protocol compliance within ERAS programs has not been investigated, while this seems a known problem in the field. Therefore, more specific and large RCT's are needed

On the interplay of point defects and Cd in non-polar ZnCdO films

Non-polar ZnCdO films, grown over m- and r-sapphire with a Cd concentration ranging between 0.8% and 5%, have been studied by means of slow positron annihilation spectroscopy (PAS) combined with chemical depth profiling by secondary ion mass spectroscopy and Rutherford back-scattering. Vacancy clusters and Zn vacancies with concentrations up to 1017 cm−3 and 1018 cm−3, respectively, have been measured inside the films. Secondary ion mass spectroscopy results show that most Cd stays inside the ZnCdO film but the diffused atoms can penetrate up to 1.3 μm inside the ZnO buffer. PAS results give an insight to the structure of the meta-stable ZnCdO above the thermodynamical solubility limit of 2%. A correlation between the concentration of vacancy clusters and Cd has been measured. The concentration of Zn vacancies is one order of magnitude larger than in as-grown non-polar ZnO films and the vacancy cluster are, at least partly, created by the aggregation of smaller Zn vacancy related defects. The Zn vacancy related defects and the vacancy clusters accumulate around the Cd atoms as a way to release the strain induced by the substitutional CdZn in the ZnO crystal. This research was originally published in the Journal of Applied Physics. © AIP Publishin