Quantitative analysis of carbon impurity concentrations in GaN epilayers by cathodoluminescence.

In this work, a technique for quantifying carbon doping concentrations in GaN:C/AlGaN buffer structures using cathodoluminescence (CL) is presented. The method stems from the knowledge that the blue and yellow luminescence intensity in CL spectra of GaN varies with the carbon doping concentration. By calculating the blue and yellow luminescence peak intensities normalised to the peak GaN near-band-edge intensity for GaN layers of known carbon concentrations, calibration curves that show the change in normalised blue and yellow luminescence intensity with carbon concentration in the 1016 - 1019 cm-3 range were derived at both room temperature and 10 K. The utility of such calibration curves was then examined by testing against an unknown sample containing multiple carbon-doped GaN layers. The results obtained from CL using the normalised blue luminescence calibration curves are in close agreement with those from secondary-ion mass spectroscopy (SIMS). However,the method fails when applying calibration curves obtained from the normalised yellow luminescence likely due to the influence of native VGa defects acting in this luminescence region. Although this work shows that indeed CL can be used as a quantitative tool to measure carbon doping concentrations in GaN:C, it is noted that the intrinsic broadening effects innate to CL can make it difficult to differentiate between the intensity variations in thin ( < 500 nm) multilayered GaN:C structures such as the ones studied in this work.

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.

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.

The mortality experience of Dow Chemical Louisiana Division employees, 1956-1986.

A major objective of the epidemiology department of the Dow Chemical Company is to report at periodic intervals the cause-specific mortality experience of its employees. This study analyzed the cause-specific mortality experience of 4,229 male and female employees of the Louisiana Division who were employed for at least 1 year from 1956 through 1986. Regardless of the comparison population used to calculate expected numbers (United States, Louisiana, or the surrounding five parish area), fewer deaths were observed for all causes combined as well as for all malignant neoplasms, diseases of the circulatory system, and external causes of death.

The positive known association design: a quality assurance method for occupational health surveillance data.

Quality control must be an integral component of an occupational health surveillance program. The positive known association design offers the occupational health physician a method to test, on a population basis (ie, high periodic medical surveillance examination participation rates by the employees), the quality of periodic medical surveillance data. Several well-established biological associations were evaluated and observed in this study, including a dramatic relation between white blood cell counts and smoking. We highly recommend that the positive known association design be incorporated in the quality assurance procedures of occupational health surveillance programs.

Monochloroacetic acid exposure: a case report.

Monochloroacetic acid exposure causes significant burns but can also be lethal following exposures of less than ten percent of body surface area. There have been two known survivors of significant monochloroacetic acid exposure. This is a case report of one of those survivors. The mechanism of toxicity is unknown, and attempts to relate monochloroacetic acid toxicity is to that of monofluoroacetic acid have yielded inconsistent results. The best mode of therapy is unclear, and no antidote has been proven effective, although ethanol and glycerol monoacetate have been suggested. The details of this case may be helpful to those faced with similar situations and to those investigating the toxicology of monochloroacetic acid.

[Rocky Mountain spotted fever]. / Rocky-Mountain-Fleckfieber.

After returning from a holiday in the USA a 24-year-old man fell ill with diarrhoea, high fever and marked rash including the palms of the hands and soles of the feet. When a history of a tick bite in the USA was elicited, a rickettsial infection was suspected. Treatment with doxycycline, 100 mg twice daily, was instituted finally and the fever slowly resolved. The patient became completely well again within four weeks. Serological tests confirmed the diagnosis of Rocky Mountain spotted fever.

The effect of long-term ethanol treatment on a metal binding protein fraction in liver and kidneys of mice.

In mice 4-12 weeks ingestion of ethanol decreased the concentration of a metallothionein-like protein fraction in the liver but not in the kidneys. The zinc and copper concentration also tended to decrease in the liver and remained unaffected in the kidneys.