Ge quantum dots on silicon for terahertz detection
Terahertz has attracted attention from both millimeter and infrared technologies. Currently, solutions consist of expensive sensor systems limiting the amount of applications. To obtain a low cost solution, one approach is to use thermistor material based on Ge on Si quantum dots on microbolometers. It has been demonstrated that SiGe monocrystalline materials have superior properties to amorphous silicon or VOx regarding the temperature coefficient of resistivity and 1/f noise. Unfortunately, the calculated critical thickness for strained SiGe material show unreasonable layer thickness for high Ge amounts. To avoid this, Ge dots instead of SiGe layers are preferred. This article focuses on optimizing the thermistor properties of Ge-dots. All samples were grown on Si (100) substrates in a temperature range of 500-650 C at 20 torr by RPCVD. They were characterized (XRD, HRSEM and AFM etc.) determining the diameter, thickness, density and uniformity. Fourier transform photoluminescence was performed to find the spatially direct (EA) and indirect (EB) bandgap transitions.
Group IV Materials for Low Cost and High Performance Bolometers
Infrared (IR) imaging has absorbed a large attention during the last two decades due to its application in both civil and military applications (Per Ericsson et al., 2010; Lapadatu et al., 2010; Sood et al., 2010). Thermal detector is presently revolutionizing the IR technology field and it is expected to expand the market for cameras. These detectors are micro-bolometers and are manufactured through micro-maching of a thermistor material. Since these detectors demand no cryogenic cooling, they provide the opportunity for producing compact, light-weight, and potentially low-cost cameras. The preferred functioning wavelength regions for these detectors are usually 8–12 ┤m due to the high transparency of the atmosphere in these regions.
Fieldwork in geography teaching: A critical review of the literature and approaches
Abstract Virtually all lecturers in geography recognise the importance of fieldwork as a vital mode of teaching in the subject. This paper draws on material produced as part of a HEFCE review of teaching and learning in the field and assesses the implications of recent changes in higher education for field studies in geography. The literature on the development of, and recent changes in, fieldwork practice is reviewed and assumptions about appropriate forms of teaching and assessment are challenged. The need for carefully integrated preparation of project‐orientated fieldwork is stressed and the importance of debriefing and feedback after field visits is emphasised. Various suggestions for guidelines on good practice are presented. Finally, a range of future issues and problems in fieldwork is identified and discussed.