Chemical and electrical characteristics of annealed Ni/Au and Ni/Ir/Au contacts on AlGaN

The evolution of Ni/Au and Ni/Ir/Au metal contacts deposited on AlGaN was investigated at different annealing temperatures. The samples were studied with electrical and chemical composition techniques. I-V characteristics of the Schottky diodes were optimum after 500 and 600 ºC annealing for Ni/Au and Ni/Ir/Au based diodes, respectively. The depth profiles of the contacts were measured by x-ray photoelectron spectroscopy and time of flight secondary ion mass spectroscopy. These chemical composition techniques were used to examine the evolution of the metal contacts in order to verify the influence the metals have on the electrical properties of the diodes. The insertion of Ir as a diffusion barrier between Ni and Au effected the electrical properties, improving the stability of the contacts at high temperatures. Gold diffuses into the AlGaN film, degrading the electrical properties of the Ni/Au diode. At 500 ºC, the insertion of Ir, however, prevented the in-diffusion of Au into the AlGaN substrate.The National Research Foundation of South Africa (Grant specific unique reference number (UID) 87352).http://www.journals.elsevier.com/physica-b-condensed-matterhb2017Physic

Ionic diffusion in iPP: DC electrical conductivity

This study provides a new insight into the relationships between absorption and adsorption processes that occur during the treatment of iPP in aqueous solutions of metal-chloride salts, as well as the impact of these processes on the electrical conductivity of this nonpolar polymer. The polypropylene films (0.5 mm) were exposed to three-day treatments in aqueous solutions of chlorine salts of some alkali and transition metals at temperatures of 22 C and 80 C. The treatments induced an increase in the electrical conductivity of iPP, up to 800%. DC conductivity is not directly proportional to the concentrations of metals in the treated films due to the complex relationships between diffusion and adsorption processes. The experiment was set up to simulate the real-world conditions and the study provides practical knowledge on the stability of the electrical conductivity of iPP under exposure to aqueous solutions. The influence of electric aging on the electrical conductivity of the treated films was also examined.This work was supported in part by the Ministry of Education, Science and Technological Development of the Republic of Serbia, by the Ministry of Scientific and Technological Development, Higher Education and Information Society of the Republic of Srpska (project: 19.032/961-112/19) and by the National Research Foundation, South Africa.Scopu

The ASOS Surgical Risk Calculator: development and validation of a tool for identifying African surgical patients at risk of severe postoperative complications

Background: The African Surgical Outcomes Study (ASOS) showed that surgical patients in Africa have a mortality twice the global average. Existing risk assessment tools are not valid for use in this population because the pattern of risk for poor outcomes differs from high-income countries. The objective of this study was to derive and validate a simple, preoperative risk stratification tool to identify African surgical patients at risk for in-hospital postoperative mortality and severe complications. Methods: ASOS was a 7-day prospective cohort study of adult patients undergoing surgery in Africa. The ASOS Surgical Risk Calculator was constructed with a multivariable logistic regression model for the outcome of in-hospital mortality and severe postoperative complications. The following preoperative risk factors were entered into the model; age, sex, smoking status, ASA physical status, preoperative chronic comorbid conditions, indication for surgery, urgency, severity, and type of surgery. Results: The model was derived from 8799 patients from 168 African hospitals. The composite outcome of severe postoperative complications and death occurred in 423/8799 (4.8%) patients. The ASOS Surgical Risk Calculator includes the following risk factors: age, ASA physical status, indication for surgery, urgency, severity, and type of surgery. The model showed good discrimination with an area under the receiver operating characteristic curve of 0.805 and good calibration with c-statistic corrected for optimism of 0.784. Conclusions: This simple preoperative risk calculator could be used to identify high-risk surgical patients in African hospitals and facilitate increased postoperative surveillance. © 2018 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.Medical Research Council of South Africa gran