Prof Michael Johnston

Abstract:

Quantitative measurement based on THz absorption spectrum is of great importance in THz applications. Several researchers have worked on it and gained some achievements, but most of them explored pure component or no more than 2-component s samples. In this paper, a mixture sample consisting of Glutamine, Histidine and Threonine is investigated in the frequency range from 0.3 to 2.6 THz. The quantitative measurement principle is the Lambert-Beer's Law which have been accepted in infrared and visible spectra. Our experiments show the validation of the law in THz region. A Least-Mean-Square algorithm is adopted and measurement errors of Glutamine, Histidine and Threonine are 17.60%, 4.44% and 2.59%.© 2012 SPIE.

Abstract:

Graphene is a single layer of covalently bonded carbon atoms, which was discovered only 8 years ago and yet has already attracted intense research and commercial interest. Initial research focused on its remarkable electronic properties, such as the observation of massless Dirac fermions and the half-integer quantum Hall effect. Now graphene is finding application in touch-screen displays, as channels in high-frequency transistors and in graphene-based integrated circuits. The potential for using the unique properties of graphene in terahertz-frequency electronics is particularly exciting; however, initial experiments probing the terahertz-frequency response of graphene are only just emerging. Here we show that the photoconductivity of graphene at terahertz frequencies is dramatically altered by the adsorption of atmospheric gases, such as nitrogen and oxygen. Furthermore, we observe the signature of terahertz stimulated emission from gas-adsorbed graphene. Our findings highlight the importance of environmental conditions on the design and fabrication of high-speed, graphene-based devices.

Abstract:

We review various III-V compound semiconductor nanowires grown by metalorganic chemical vapor deposition. Transmission and scanning electron microscopy, micro-photoluminescence and micro-Raman spectroscopy have been used to understand the crystal structure, light emission and band structure. © 2011 AOS.