Metrology of crystal defects through intensity variations in secondary electrons from the diffraction of primary electrons in a scanning electron microscope.

Understanding defects and their roles in plastic deformation and device reliability is important for the development of a wide range of novel materials for the next generation of electronic and optoelectronic devices. We introduce the use of gaseous secondary electron detectors in a variable pressure scanning electron microscope for non-destructive imaging of extended defects using electron channelling contrast imaging. We demonstrate that all scattered electrons, including the secondary electrons, can provide diffraction contrast as long as the sample is positioned appropriately with respect to the incident electron beam. Extracting diffraction information through monitoring the modulation of the intensity of secondary electrons as a result of diffraction of the incident electron beam, opens up the possibility of performing low energy electron channelling contrast imaging to characterise low atomic weight and ultra-thin film materials. Our methodology can be adopted for large area, nanoscale structural characterisation of a wide range of crystalline materials including metals and semiconductors, and we illustrate this using the examples of aluminium nitride and gallium nitride. The capability of performing electron channelling contrast imaging, using the variable pressure mode, extends the application of this technique to insulators, which usually require conducting coatings on the sample surface for traditional scanning electron microscope based microstructural characterisation.

Determining GaN Nanowire Polarity and its Influence on Light Emission in the Scanning Electron Microscope.

The crystal polarity of noncentrosymmetric wurtzite GaN nanowires is determined nondestructively in the scanning electron microscope using electron backscatter diffraction (EBSD). The impact of the nanowire polarity on light emission is then investigated using cathodoluminescence (CL) spectroscopy. EBSD can determine polarity of noncentrosymmetric crystals by interrogating differences in the intensity distribution of bands of the EBSD pattern associated with semipolar planes. Experimental EBSD patterns from an array of GaN nanowires are compared with theoretical patterns produced using dynamical electron simulations to reveal whether they are Ga- or N-polar or, as in several cases, of mixed polarity. CL spectroscopy demonstrates the effect of the polarity on light emission, with spectra obtained from nanowires of known polarity revealing a small but measurable shift (≈28 meV) in the GaN near band edge emission energy between those with Ga and N polarity. We attributed this energy shift to a difference in impurity incorporation in nanowires of different crystal polarity. This approach can be employed to nondestructively identify polarity in a wide range of noncentrosymmetric nanoscale material systems and provide direct comparison with their luminescence.

Hysteretic photochromic switching of Eu-Mg defects in GaN links the shallow transient and deep ground states of the Mg acceptor.

Although p-type activation of GaN by Mg underpins a mature commercial technology, the nature of the Mg acceptor in GaN is still controversial. Here, we use implanted Eu as a 'spectator ion' to probe the lattice location of Mg in doubly doped GaN(Mg):Eu. Photoluminescence spectroscopy of this material exemplifies hysteretic photochromic switching (HPS) between two configurations, Eu0 and Eu1(Mg), of the same Eu-Mg defect, with a hyperbolic time dependence on 'switchdown' from Eu0 to Eu1(Mg). The sample temperature and the incident light intensity at 355 nm tune the characteristic switching time over several orders of magnitude, from less than a second at 12.5 K, ~100 mW/cm2 to (an estimated) several hours at 50 K, 1 mW/cm2. Linking the distinct Eu-Mg defect configurations with the shallow transient and deep ground states of the Mg acceptor in the Lany-Zunger model, we determine the energy barrier between the states to be 27.7(4) meV, in good agreement with the predictions of theory. The experimental results further suggest that at low temperatures holes in deep ground states are localized on N atoms axially bonded to Mg acceptors.

Correction: Site controlled red-yellow-green light emitting InGaN quantum discs on nano-tipped GaN rods.

Correction for 'Site controlled red-yellow-green light emitting InGaN quantum discs on nano-tipped GaN rods' by M. Conroy et al., Nanoscale, 2016, 8, 11019-11026.

Site controlled red-yellow-green light emitting InGaN quantum discs on nano-tipped GaN rods.

We report a method of growing site controlled InGaN multiple quantum discs (QDs) at uniform wafer scale on coalescence free ultra-high density (>80%) nanorod templates by metal organic chemical vapour deposition (MOCVD). The dislocation and coalescence free nature of the GaN space filling nanorod arrays eliminates the well-known emission problems seen in InGaN based visible light sources that these types of crystallographic defects cause. Correlative scanning transmission electron microscopy (STEM), energy-dispersive X-ray (EDX) mapping and cathodoluminescence (CL) hyperspectral imaging illustrates the controlled site selection of the red, yellow and green (RYG) emission at these nano tips. This article reveals that the nanorod tips' broad emission in the RYG visible range is in fact achieved by manipulating the InGaN QD's confinement dimensions, rather than significantly increasing the In%. This article details the easily controlled method of manipulating the QDs dimensions producing high crystal quality InGaN without complicated growth conditions needed for strain relaxation and alloy compositional changes seen for bulk planar GaN templates.

Photoluminescence studies of a perceived white light emission from a monolithic InGaN/GaN quantum well structure.

In this work we demonstrate by photoluminescence studies white light emission from a monolithic InGaN/GaN single quantum well structure grown by metal organic chemical vapour deposition. As-grown and thermally annealed samples at high temperature (1000 °C, 1100 °C and 1200 °C) and high pressure (1.1 GPa) were analysed by spectroscopic techniques, and the annealing effect on the photoluminescence is deeply explored. Under laser excitation of 3.8 eV at room temperature, the as-grown structure exhibits two main emission bands: a yellow band peaked at 2.14 eV and a blue band peaked at 2.8 eV resulting in white light perception. Interestingly, the stability of the white light is preserved after annealing at the lowest temperature (1000 °C), but suppressed for higher temperatures due to a deterioration of the blue quantum well emission. Moreover, the control of the yellow/blue bands intensity ratio, responsible for the white colour coordinate temperatures, could be achieved after annealing at 1000 °C. The room temperature white emission is studied as a function of incident power density, and the correlated colour temperature values are found to be in the warm white range: 3260-4000 K.

Rapid nondestructive analysis of threading dislocations in wurtzite materials using the scanning electron microscope.

We describe the use of electron channeling contrast imaging in the scanning electron microscope to rapidly and reliably image and identify threading dislocations (TDs) in materials with the wurtzite crystal structure. In electron channeling contrast imaging, vertical TDs are revealed as spots with black-white contrast. We have developed a simple geometric procedure which exploits the differences observed in the direction of this black-white contrast for screw, edge, and mixed dislocations for two electron channeling contrast images acquired from two symmetrically equivalent crystal planes whose g vectors are at 120° to each other. Our approach allows unambiguous identification of all TDs without the need to compare results with dynamical simulations of channeling contrast.

Are periods of low atmospheric pressure associated with an increased risk of abdominal aortic aneurysm rupture?

INTRODUCTION: Seasonal variation in rates of abdominal aortic aneurysm (AAA) rupture has previously been described. However, only two studies, to date, have suggested that periods of low atmospheric pressure may account for this observation and both returned apparently contradictory findings. The objective of this study was to demonstrate whether periods of low atmospheric pressure are indeed associated with an increased likelihood of AAA rupture presentation. PATIENTS AND METHODS: A total of 182 cases of ruptured AAA were identified retrospectively from two centres over a 6-year period from January 2000 to December 2005. Local meteorological data for the corresponding period was obtained from the UK Meteorological Office which was recorded daily at a local weather station. Statistical analysis using Student's t-test, ANOVA (Kruskal-Wallis), linear regression and multiple logistic regression was conducted to identify significant relationships from the data. RESULTS: Days of rupture presentation were associated with a significantly lower daily mean atmospheric pressure when compared with days when no rupture occurred (P = 0.025). Multiple logistic regression demonstrated a significant association between low daily atmospheric pressure and rupture incidence (P = 0.033) which appeared to be independent of temperature. A significant seasonal trough in atmospheric pressure was observed in October and November (Kruskal-Wallis, P < 0.001); however, there was no corresponding autumnal peak in rupture incidence (P = 0.232). CONCLUSIONS: The findings of this study appear to confirm the assertion that low atmospheric pressure is associated with an increased risk of AAA rupture on a day-to-day basis; however, no evidence was identified to support a change in policy regarding prioritising elective surgery based on seasonal risk.

Second-hand smoke levels in UK pubs and bars: do the English Public Health White Paper proposals go far enough?

BACKGROUND: The English Public Health White Paper proposes introducing smoke-free workplaces except in pubs and bars that do not prepare and serve food. The bar area will be non-smoking in exempted pubs. OBJECTIVE: To explore the likely impact of these proposals in UK pubs and bars. METHODS: A total of 59 pubs and bars within Greater Manchester in 2001 were chosen. Thirteen were mechanically ventilated, 12 were naturally ventilated and 34 had extractor fans; 23 provided non-smoking areas. We measured time-weighted average concentrations of respirable suspended particles (RSP), solanesol tobacco-specific particles and vapour-phase nicotine (VPN) over a 4-h sampling period on a Tuesday or Saturday night. RESULTS: Second-hand smoke (SHS) levels in smoking areas were high (mean RSP 114.5 microg/m3, VPN 88.2 microg/m3, solanesol 101.7 microg/m3). There were only small (5-13 per cent) reductions in bar areas. Mean levels were lower in non-smoking areas: by 33 per cent for RSPs, 52 per cent for solanesol particles and 69 per cent for VPN. Compared with other settings (homes and other workplaces) with unrestricted smoking, mean SHS levels were high throughout all areas of the pubs regardless of ventilation strategy. CONCLUSION: Partial measures, like those in the English Public Health White Paper, will leave bar staff in exempted pubs unprotected from the occupational hazard of SHS.

Emergency repair of groin herniae: outcome and implications for elective surgery waiting times.

Patients with groin herniae do not always seek medical advice and, when listed for surgery, often wait many months for elective repair. We audited our emergency admissions for complicated groin herniae to establish whether a change in policy for elective surgery could lower their incidence. We performed a retrospective review of all admissions for complicated groin herniae from 1 January 2000 to 31 December 2001. Besides outcome, we recorded patients' awareness of their diagnosis before admission and whether they had been listed for elective surgery. We identified 19 patients (16 men and three women) with an inguinal and 19 (four men and 15 women) with a femoral hernia. Sixteen (42%) knew of their hernia before admission (11 inguinal and five femoral), but only three had been awaiting surgical repair for 1, 7 and 26 weeks, respectively. The median (interquartile range) age was 70 (54-84) years in inguinal and 79 (64-88) years in femoral herniae. Surgery was performed in all but an 84-year-old man who died pre-operatively. Two patients with inguinal and 11 with femoral herniae required a laparotomy (p = 0.006). Bowel resection was necessary in one patient with an inguinal and 12 with femoral herniae (p = 0.001). Complications occurred in 12 cases (31%). Four patients, all with femoral herniae, died post-operatively, for an overall mortality of 13% (5/38). Morbidity and mortality for complicated groin hernia, particularly femoral, remain high. As most patients were elderly and unaware of their diagnosis, reducing waiting times for elective repair is unlikely to influence the incidence of complicated herniae.

Cross-sectional survey of beta-blockers use in primary and secondary care for patients with arterial disease.

Beta-blockers reduce mortality in ischaemic heart disease and, when given perioperatively, in vascular surgery. We investigated the use of and attitudes towards beta-blockers by British vascular surgeons and primary care physicians (GPs). We performed a cross-sectional postal survey by questionnaire sent to 367 GPs and 397 members of the Vascular Surgical Society. Specific questions related to beta-blockers use and indications. Two hundred and thirty-four GPs, 95 full-time vascular surgeons (VS) and 137 general surgeons (GS) with a vascular interest responded. Thirty-eight percent of VS and 16% of GS often or always used perioperative beta-blockade (p<0.001). Common indications were ischaemic heart disease (39.2%), hypertension (30.6%), arrhythmia (16.3%) and myocardial protection (6.9%). Sixty-eight percent of VS and 42% of GS would prescribe beta-blockers to patients with occlusive arterial disease (p < 0.001). Common indications were ischaemic heart disease (39.6%), hypertension (29.2%) and arrhythmia (13.3%). Of those who would not prescribe beta-blockers in occlusive arterial disease, 65% felt that beta-blockers were contraindicated in this condition. GPs widely regarded occlusive arterial disease as a contraindication to beta-blockade. Beta-blockers are underused by GPs and GS especially, perhaps because of a perceived risk of side effects in patients with occlusive arterial disease. Further evidence is needed on the effect of beta-blockade on quality of life of patients with arterial disease.

Management of gallstone disease in the elderly.

AIM: To determine the outcome of management of symptomatic gallstone disease (GSD) in patients aged 80 years or more. PATIENTS AND METHODS: A retrospective review of the outcome of 79 patients admitted to 2 district general hospitals with symptomatic GSD over a 1-year period was undertaken. Patients were grouped according to method of management: non-operative, ERCP, and cholecystectomy. POSSUM scores for the ERCP and cholecystectomy groups were calculated and observed, and predicted outcome compared. RESULTS: Obstructive jaundice and biliary colic were the most common presenting symptoms. Each patient had been admitted at least once before the study period (median, 2; range, 1-3). Outcomes are detailed in Table 1. Non-operative management failed in 18 of 23 patients, with 17.4% mortality. ERCP was successful in 40 of 47 patients with 3 complications (0.24 of predicted) and no mortality. In all, 11 laparoscopic and 12 open cholecystectomies were performed with 6 complications and 1 mortality (0.95 and 0.83 of predicted, respectively): 4 complications and the only death occurring after emergency cholecystectomy. Table 1 Outcomes Management Number Mortality Morbidity Outcome Non-operative 23 4 9 5 OK, 13 re-admitted, 4 still symptomatic ERCP 47 0 3 1 PTC, 6 operated Operative 23 1 6 CONCLUSIONS: This study suggests that recurrent GSD in elderly patients managed non-operatively may have fatal outcome. Elective cholecystectomy has acceptable morbidity and mortality in this age group and there is often ample opportunity to avoid emergency surgery, but a prospective randomised study is required to improve clinical algorithms.

Maternal hypothyroidism in the rat influences placental and liver glycogen stores: fetal growth retardation near term is unrelated to maternal and placental glucose metabolic compromise.

Maternal hypothyroidism impairs fetal growth in the rat, but the mechanisms by which this occurs are unknown. Since the fetus derives its glucose supply from the mother, and maternal thyroidectomy may disturb maternal and placental glucose metabolism, we postulated that maternal and/or placental glucose metabolic compromise may contribute to fetal growth retardation in hypothyroid dams. Feto-placental growth, tissue glycogen stores and glucose levels in sera and amniotic fluid were determined in rat dams partially thyroidectomized (TX) before pregnancy and in euthyroid controls. Fetal body weight at 16, 19 and 21 days gestation (d.g.) was related to pre-mating maternal serum total thyroxine (TT(4)) levels; permanent fetal growth retardation occurred in severely (TX(s); pre-mating maternal serum TT(4)

Prospective randomized double-blind placebo-controlled trial of glyceryl trinitrate in endoscopic retrograde cholangiopancreatography-induced pancreatitis.

BACKGROUND: One possible aetiology of pancreatitis following endoscopic retrograde cholangio pancreatography (ERCP) is cannulation-induced spasm of the sphincter of Oddi and consequent pancreatic duct obstruction. Sublingual glyceryl trinitrate (GTN) has been shown to produce periampullary sphincter relaxation. The aim of this study was to determine whether prophylactic long-acting GTN could reduce the incidence of ERCP-induced pancreatitis. METHODS: In a randomized double-blind study, prophylactic treatment with GTN (2 mg given sublingually 5 min before endoscopy) was compared with placebo in 186 patients who presented for elective ERCP. The primary endpoint was the occurrence of pancreatitis within 24 h, defined as a serum amylase concentration greater than 1000 units/ml in association with a visual analogue pain score of more than 5. RESULTS: The incidence of pancreatitis was lower in the GTN group compared with placebo (seven of 90 versus 17 of 96; P < 0.05). Mean serum amylase values were similar in the two groups. The protective effect of GTN appears to be highest in the diagnostic ERCP group (one of 54 versus ten of 66; P = 0.012) and in the group in which cholangiography alone was performed (one of 54 versus eight of 57; P = 0.032). CONCLUSION: Prophylactic treatment with GTN reduces the incidence of pancreatitis following ERCP but does not seem to reduce the extent of hyperamylasaemia or the severity of pancreatitis.

Outcome for children born after in utero laser ablation therapy for severe twin-to-twin transfusion syndrome.

OBJECTIVE: To examine the postnatal development of a group of children born after in utero laser ablation therapy for severe twin-to-twin transfusion syndrome. DESIGN: Retrospective cohort outcome study involving assessment of neurodevelopment and physical well being. SETTING: Harris Birthright Centre, King's College Hospital, London. PARTICIPANTS: Twins and singleton survivors treated via laser ablation therapy for twin-to-twin transfusion syndrome over a four-year period. METHODS: Of 54 families contacted to participate in the study, who had been treated for twin-to-twin transfusion syndrome during a four-year period, 24 families attended for paediatric assessment; 12 pairs of twins and 12 singleton survivors were assessed for perinatal, neurological and neurodevelopmental outcome using the Griffiths scales of mental development. A further 20 families were assessed via a proforma after contact with their general practitioner. A comparison of these groups showed no significant differences in sociodemographic factors or severity of disease between responders (44 families, 81.5%) and non-responders (10 families). RESULTS: The group of children assessed by a paediatrician had low birthweight (1619g donor, 1814g recipient, 1877g singleton) and had been born preterm (33 weeks twins, 31.2 weeks singleton) with attendant increased resuscitation, neonatal unit admission (mean 40 days) and instrumental delivery. Mean Griffiths scores were within the normal range of ability (91.2 donor vs 97.7 recipient and 101.6 singletons) with the only significant difference being in the locomotor subscale where donor (82.6) and recipient (85.3) were less than singletons: -99.1 (P < 0.05). There was no cerebral palsy in the singleton survivors, but there were five cases in the twin group. All except one affected child (with quadriplegia) had mean Griffiths scores in the normal range. In the GP proforma group there was one case, in a twin, of cerebral palsy. CONCLUSION: The overall cerebral palsy rate was 9%: 0% in the singleton survivors group and 13.3% in the twin survivors group. This pilot data highlights the need for careful long term follow up of children affected by twin-to-twin transfusion syndrome.

Exercise training for claudicants: changes in blood flow, cardiorespiratory status, metabolic functions, blood rheology and lipid profile.

OBJECTIVE: Exercise training improves the walking distance of claudicants. The aim of this study was to investigate factors associated with the improvement in the maximum walking distance (MWD) in respect to cardiovascular, respiratory and metabolic adaptations. METHODS: Forty claudicants were studied. Common femoral artery blood flow (BF), heart rate (HR), oxygen consumption (VO(2)), respiratory exchange ratio (RER), lactate levels, blood rheology and lipid profiles were measured. Tests were repeated after 3 months of exercise training. RESULTS: Fifteen patients did not complete the exercise program. For patients who did complete the program, MWD improved by 82%. A significant reduction in HR and VO(2)during exercise was demonstrated. No significant changes occurred in BF or RER. Although MWD increased significantly, there was no increase in recovery VO(2)(oxygen debt). A significant reduction in post-exercise lactate levels occurred. Blood rheology was unchanged, but an improvement in HDL levels was noted. CONCLUSIONS: Many claudicants could not complete an exercise program, mainly due to osteoarthritis. Exercise training improved exercise tolerance significantly without any increase in BF. The HR and oxygen cost of similar exercise was reduced. An improved MWD did not correlate with a higher oxygen debt or lactate load. Favourable changes in lipid profiles occurred.

Exercise training and peripheral vascular disease.

BACKGROUND: Conservative management is advocated as a treatment of choice for patients with intermittent claudication. This is a review of the mechanisms behind the improvement following an exercise rehabilitation programme. METHODS: All Medline articles from the National Library of Medicine, USA containing the text words 'claudication' or 'peripheral vascular disease' and 'exercise' were reviewed. Cross-referencing from relevant articles was carried out. RESULTS AND CONCLUSION: The poor physical status of a patient with intermittent claudication is not solely due to a reduction in blood flow to the lower limbs; associated factors, such as metabolic inefficiency, poor cardiorespiratory reserve and exercise-induced inflammation contribute. An exercise programme frequently improves both the physical aspect and quality of life, and the success of such exercise is multifactorial. An increase in the blood flow to the lower extremity is uncommon. Other factors, such as a redistribution of blood flow, changes in oxidative capacity of the skeletal muscles and greater utilization of oxygen, occur and the associated metabolic dysfunction of the skeletal muscles is rectified. Following exercise training, blood rheology improves and exercise-induced inflammation is ameliorated; cardiorespiratory status also benefits and the oxygen cost of exercise decreases.

Maternal hypothyroxinemia influences glucose transporter expression in fetal brain and placenta.

The influence of maternal hypothyroxinemia on the expression of the glucose transporters, GLUT1 and GLUT3, in rat fetal brain and placenta was investigated. Fetal growth was retarded in hypothyroxinemic pregnancies, but only before the onset of fetal thyroid hormone synthesis. Placental weights were normal, but placental total protein concentration was reduced at 19 days gestation (dg). Immunoblotting revealed a decreased abundance of GLUT1 in placental microsomes at 16 dg, whereas GLUT3 was increased. Fetal serum glucose levels were reduced at 16 dg. In fetal brain, the concentration of microsomal protein was deficient at 16 dg and the abundance of parenchymal forms of GLUT1 was further depressed, whereas GLUT3 was unaffected. Northern hybridization analysis demonstrated normal GLUT1 mRNA levels in placenta and fetal brain. In conclusion, maternal hypothyroxinemia results in fetal growth retardation and impaired brain development before the onset of fetal thyroid function. Glucose uptake in fetal brain parenchyma may be compromised directly, due to deficient GLUT1 expression in this tissue, and indirectly, as a result of reduced placental GLUT1 expression. Though corrected by the onset of fetal thyroid hormone synthesis, these deficits are present during the critical period of neuroblast proliferation and may contribute to long term changes in brain development and function seen in this model and in the progeny of hypothyroxinemic women.

SHORT COMMUNICATION maternal thyroid dysfunction and c- fos and c- jun expression in rat placenta.

Maternal thyroid dysfunction is associated with perturbed fetal brain development and neurological deficits in adulthood in rat and human. To investigate whether these effects occur secondary to placental dysfunction, c- fos and c- jun expression in placenta from normal (euthyroid) and moderately hypothyroid rat dams were investigated by Northern hybridization analysis. In normal placenta, c- fos expression increased by 74 per cent between 16 and 21 days of gestation (dg) whereas c- jun expression declined by 46 per cent. Moderate maternal hypothyroidism depressed placental c- fos expression by 32 per cent at 19 dg, but elevated c- fos and c- jun expression by 139 and 86 per cent, respectively, at 21 dg. Maternal hypothyroidism may therefore induce c- fos/c- jun -related placental dysfunction, but only relatively late in gestation when fetal thyroid function is already established.