Electroslag remelting for low oxygen metal manufacturing

International audienc

Thermometry of AlGaN/GaN 2D Channels at High Electric Fields Using Electrical and Optical Methods

Abstract The active channels in AlGaN/GaN‐based heterostructures are studied under different applied electrical fields to identify the Joule heating factors affecting the temperature values in the channels. The temperature in active channels of two different lengths (30 and 180 µm) is characterized using optical methods, and electrical methods are used as a reference. The technique of optical thermometry is based on the data of micro‐photoluminescence and micro‐Raman experiments. The electrical method is based on the measurements of current–voltage characteristics for comparison. It is shown that photoluminescence‐ and electrical‐based temperature values demonstrate similar behavior and good correlation. The Raman‐based method, exploiting the temperature dependence of the frequency position of E2high vibrational band in GaN, shows a significant deviation compared with electrical‐ and luminescence‐based methods. This deviation is shown to be related to the residual mechanical strain in the layered structure and the formation of hot phonons. The influence of hot phonons and mechanical strain effects increases at high electrical load (>5 kV cm−1) and at high temperatures (>400 °C), respectively

Optical Characterization of SERS Substrates Based on Porous Au Films Prepared by Pulsed Laser Deposition

The SERS (surface enhanced Raman spectroscopy) substrates based on nanocomposite porous films with gold nanoparticles (Au NPs) arrays were formed using the method of the pulsed laser deposition from the back low-energy flux of erosion torch particles on the glass substrate fixed at the target plain. The dependencies of porosity, and morphology of the surface of the film regions located near and far from the torch axis on the laser ablation regime, laser pulses energy density, their number, and argon pressure in the vacuum chamber, were ascertained. The Au NPs arrays with the controllable extinction spectra caused by the local surface plasmon resonance were prepared. The possibility of the formation of SERS substrates for the detection of the Rhodamine 6G molecules with the concentration 10−10 Mol/L with the enhancement factor 4·107 was shown