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An important property of thin film silicon and related materials is the microstructure which may involve the presence of interconnected and isolated voids. We report on effusion measurements of implanted helium (He) to detect such voids. Several series of hydrogenated and unhydrogenated amorphous silicon films prepared by the methods of plasma deposition, hot wire deposition and vacuum evaporation were investigated. The results show common features like a He effusion peak at low temperatures attributed to He out-diffusion through a compact material or through interconnected voids, and a He effusion peak at high temperatures attributed to He trapped in isolated voids. While undoped plasma-grown device-grade hydrogenated amorphous silicon (a-Si:H) films show a rather low concentration of such isolated voids, its concentration can be rather high in doped a-Si:H, in unhydrogenated evaporated material and others.

Laser heating and annealing of hydrogenated amorphous silicon (a-Si:H) films is of interest for improved material properties. Due to the variety of possible laser treatments with regard to wavelength, pulse duration, scan time etc., the definition of laser impact on the material is a challenge which we try to approach by comparing properties of laser and oven treated materials. Here we report on the effect of oven heat treatment (up to T A = 575°C) on microstructure and hydrogen content of hydrogenated amorphous silicon films, as detected by measurements of infrared absorption and of effusion of hydrogen as well as of implanted helium. The latter technique has been found to measure isolated voids (cavities) of the size of silicon divacancies and larger. Undoped as well as phosphorus and boron doped plasma-deposited aSi:H films of various hydrogen content (< 15 at.%) were investigated, including undoped device grade a-Si:H. The results show little indication for void-related microstructure in the asdeposited and annealed state for material with a concentration of silicon bonded hydrogen below 5 at. %. At higher hydrogen concentration, evidence is found that hydrogen out-diffusion due to annealing causes isolated voids in concentrations up to about 10 20 cm -3 . A possible mechanism for the annealing induced (micro-)void generation is discussed.

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Wasseranalysensysteme werden dort eingesetzt, wo mehrere Meßgrößen in der gleichen Wasserprobe erfaßt werden sollen. Man unterscheidet dabei das Eintauchverfahren, bei welchem die Meßfühler unmittelbar in das Gewässer oder die Kanalisation eingetaucht werden, und das Durchflußverfahren, bei welchem aus dem Gewässer oder der Kanalisation mit Hilfe einer Förderpumpe eine Probe entnommen und dem Gebersystem im Durchlauf zugeführt wird. Der kontinuierliche Betrieb derartiger Wasseranalysensysteme wird durch die mehr oder weniger starke Verschmutzung der Wasserproben gefährdet und erfordert besondere Maßnahmen, um die Funktionssicherheit und Meßgenauigkeit über längere Zeiträume aufrecht zu erhalten. Durch eine automatische Eichkontrolle kann die Funktion und die Meßgenauigkeit des Systems kontrolliert werden. Gegebenenfalls werden Steuergeräte und Grenzwertmelder sowie in bestimmten Fällen auch Einrichtungen zur Datenfernübertragung und zur Rechneradaption vorgesehen.