Hall-effect measurements are routinely used to determine the doping concentrations in semiconductor material. We show that for Si : In such measurements give erroneously high results. The Hall concentrations, determined by curve fitting, are typically twice those determined from C-V and junction-breakdown measurements, which measure the doping concentrations directly. We consider the latter data more reliable.
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.
The critical parameters in the single-target magnetron sputtering of YBa2Cu3O7 have been identified and sufficiently optimized to allow the reproducible deposition of films with Tc’s of ≳90 K and Jc’s of ≫ 106 A/cm2 at 77 K. It was found that during film growth the bombardment of the YBa2Cu3O7 by energetic particles must be minimized and also a stronger oxidizing agent than molecular oxygen must be present to obtain films with these properties. Otherwise, films are deposited that, by x-ray diffraction and energy dispersive x-ray spectroscopy analyses, are indistinguishable from the highest-Tc 1:2:3 stoichiometric material but which have critical temperatures of ≪90 K. Films need not have 1:2:3 overall stoichiometry to have optimum superconducting properties. In such cases the excess elements are present as second-phase particles.
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