Contact free potential mapping by vibrating capacitor
The contact free vibrating capacitor method is a valuable tool for investigating the surface potentials of solid surfaces. The purpose of the present article is to summarize the theory and capabilities of the vibrating capacitor method, especially scanning vibrating capacitor pictures in the electronics. After a brief review some results will be discussed, such as a contact potential map taken from a printed circuit board, a surface potential map from a biased ceramic thick film circuit and some results from silicon solid state devices and solar cells. Potential maps contain a lot of information concerning the surface conditions, included the inhomogeneities of the technology, bias and other additional excitation. These potential maps may help in the development, quality control and defect analysis
Vibrating capacitor method in the development of semiconductor gas sensors
Abstract Adsorption usually results in work function shifts on catalytically active surfaces such as semiconductor gas sensors. The purpose of the present article is to summarise the capabilities of the vibrating capacitor from the simplest adsorption-induced work function tests to the scanning, vibrating, capacitor-yielded olfactory pictures and other chemical pictures. After a brief history and review of theoretical bases, the latest results will be discussed in detail. Olfactory pictures from semiconductor surfaces give a new chance to improve the selectivity of gas analysis. Chemical pictures from thin SnO 2 layers produced by atomic layer epitaxy reveal the inhomogeneities of the technology. CPD maps taken from Pd nanolayer (activator)-covered surfaces help to find the best layer-depositing parameters for the activation process of the thin semiconductor gas sensor films.
High-frequency hearing thresholds: effects of age, occupational ultrasound and noise exposure
AbstractPurpose
It has been suggested that high-frequency audiometry (HFA) could represent a useful preventive measure in exposed workers. The aim was to investigate the effects of age, ultrasound and noise on high-frequency hearing thresholds.MethodsWe tested 24 industrial ultrasound-exposed subjects, 113 industrial noise-exposed subjects and 148 non-exposed subjects. Each subject was tested with both conventional-frequency (0.125–8 kHz) and high-frequency (9–18 kHz) audiometry.ResultsThe hearing threshold at high frequency deteriorated as a function of age, especially in subjects more than 30 years old. The ultrasound-exposed subjects had significantly higher hearing thresholds than the non-exposed ones at the high frequencies, being greatest from 10 to 14 kHz. This hearing loss was already significantly evident in subjects with exposure <5 years and increased with years of exposure and advancing age. The noise exposure group had significantly higher hearing thresholds than the non-exposed group at the conventional frequencies 4 and 6 kHz and at the high frequency of 14 kHz. After stratification for age, there was a significant difference between the two groups at 9–10 and 14–15 kHz only for those under 30 years of age.ConclusionMultivariate analysis indicated that age was the primary predictor, and noise and ultrasound exposure the secondary predictors of hearing thresholds in the high-frequency range. The results suggest that HFA could be useful in the early diagnosis of noise-induced hearing loss in younger groups of workers (under 30 years of age).
