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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Laser scanning system for microscopic and macroscopic investigations of chemical semiconductor sensors

Author: LINKE, Sebastian

Year: 2012

Supervisor(s): Steffi Krause

The aim of this thesis was to develop laterally resolved measurement systems for analysing Metal Insulator Semiconductor (MIS)-based potentiometric chemical sensors. Therefore, the Light-Addressable Potentiometric Sensors (LAPS) principle was used to provide chemical images. Two main system variants were under investigation. The first was a high-resolution so called LAPS-Microscope suitable for life science applications such as the investigation of pH changes of living cells. The second was developed for the analysis of the gas response of alloys on large scale semiconductor samples (25x25 mm2). Therefore, the system was called a LAPS-Macroscope. The LAPS-Microscope resolution depends on the optical focus and semiconductor properties. To reduce the semiconductor dependent resolution, 18 different types of samples were prepared varying the boron and carbon doping in thin silicon films. To analyse the LAPS resolution, different techniques were developed. A resolution improvement down to 3 ?m compared to bulk silicon was achieved. A sputter target configuration was developed to produce ternary alloys on semiconductor samples with a continuous gradient in metal concentration. Different analysis methods such as EDX and AES were used to characterise the thin alloy films. Using the LAPS-Macroscope, the gas sensitivity of more than 106 different alloy compositions at a single sample can be investigated. As a result, metal concentration differences down to 0.03% can be distinguished. Typically, the sensor response of 625 different alloy compositions to changes in the hydrogen concentration was investigated within 16 min. The ternary alloy system PdxNiyCo1-x-y was analysed with the LAPS-Macroscope showing that nickel in the range up to 24 atom% reduces the hydrogen sensitivity. There was no significant influence of cobalt in the concentration range tested. Further, poisoning experiments with H2S showed improved behaviour of palladium alloys with nickel in the range of ~5-10 atom%. It was shown that an effective high-throughput method for the characterisation of ternary alloys was established, which is called a Continuous Gradient High Throughput Screening Macroscope CG-HTSM.