Korea Advanced Institute of Science and Technology

Si Kyung Choi

Sung Yoon Chung

Suk Joong Kang

Byung Sung Kang

Dong Gu Choi

Suk Pil Kim

Sung Ryul Kim

Disclosed is a method for preparing heteroepitaxial thin films which are free of island structures which have a bad influence on the photoelectric properties and interfacial reactivity of the thin films. These heteroepitaxial thin films are deposited on grooved or curved surfaces of substrates. The use of grooved substrates relieves the coherent elastic strain from the thin films, thereby inhibiting the surface roughening and the island structure formation in the heteroepitaxial thin films. The method can be applied to all of the thin films that show island structures, including GaAs/Si and SiGe/Si typically used in semiconductor devices and various electronic parts, enabling the thin films to be flatly deposited at a significant thickness on various substrates without additionally processing.

Method for preparing heteroepitaxial thin film

Disclosed is a method for testing the photoinduced domain switching of ferroelectric ceramics using AE. A ferroelectric ceramic specimen,was tested for the AE signal and photovoltaic current upon application of light. Light emanating from a xenon lamp,is focused into a specimen,through a waveguide,and a lens,. Raw AE signals are detected through an AE sensor,. The output signals from the AE sensor,are forwarded to a bandpass filter,which filtered the signals. Then, the AE signals are amplified by 40 dB by a pre-amplifier,and further by 30 dB by an AET 5500 system,which is connected to a computer,for analyzing the signals. The AE events which show a peak amplitude greater than or as great as a predetermined threshold voltage are counted with respect to an irradiation period of time, followed by calculating an occurrence rate of the AE event counts. From these data, the activity of the photoinduced domain switching can be qualitatively evaluated. The energy of the AE signals is calculated from the formula: AE Energy(dB)&equals;Peak Amplitude(dB)&plus;10 log Duration Time(&mgr;s), so as to recognize the distributions of the energy. By investigating the types of domain switching which exist in the energy distributions, to which types of domain switching the AE signals are attributed can be determined.

Method for testing photoinduced domain switching of ferroelectric ceramics using acoustic emission

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Taejeon, South Korea

Si Kyung Choi