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Absfracf-The recently developed large-area field-emission photocathode is described. It consists of a finely spaced array of point emitters fabricated by etching of p-type silicon or other semiconductor. Uniform emission over areas of 6-7 cm2 have been obtained. For Si, the spectral response extends from 0.4 to 1.1 pm. Quantum yields of 25 percent at 0.86 pm have been measured, which is about five times the value reported for the extended S-20 photocathode and comparable to the best 111-V photoemitters. Calculations indicate that quantum yields of up to 40 percent at 0.86 rm and 28 percent at 0.9 pm are attainable with the present photocathode structures. For low dark current densities, photocathode cooling to temperatures approaching 77 IC must be employed at present. The dark current is shown to be dominated by surface-generated electrons in the space-charge region of the emitters. Effects of phosphorus gettering and annealing treatments on dark current are discussed, and the spatial frequency response of the device is determined. The results of a computer study show that the field intensification factor of p-semiconductor field emitters behaves quite differently from that of metallic emitters.

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Micromachining is a technology that miniaturizes mechanical sensors and actuators through the use of tools and materials commonly used in the integrated circuit industry. The physics of the devices formed in this way are sometimes similar and sometimes different to achieve the same functionality of current macroscopic devices, but in sizes that are hundreds or thousands of times smaller. This article will discuss a few chemical detectors being developed as examples of the application of microelectromechanical systems ͑MEMS͒ for nonoptical laboratory instruments. In this article, we will report on the development and demonstration of two approaches ͑quadrupole and magnetic Lorentz͒ to fabricate a mass filter as part of a mass spectrometer. This article is not meant as a review of the field of MEMS chemical sensors, but rather a tutorial on how miniaturization is achievable through the use of MEMS fabrication techniques for mass spectrometers.

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