Advances in electronics and electron physics 

About: Advances in electronics and electron physics is an academic journal. The journal publishes majorly in the area(s): Image intensifier & Photocathode. It has an ISSN identifier of 0065-2539. Over the lifetime, 959 publications have been published receiving 13577 citations.

Signal and Noise Properties of Gallium Arsenide Microwave Field-Effect-Transistors

Abstract: Publisher Summary This chapter examines the signal and noise properties of gallium arsenide (GaAs) microwave field-effect transistors (FET) High frequency gallium arsenide field-effect transistors (GaAs FETs) have demonstrated remarkably low noise figures and high power gains at microwave frequencies A practical microwave GaAs FET is usually fabricated by deposition or diffusion of source, gate, and drain contacts on the surface of an appropriately doped thin epitaxial n-type layer This layer, in turn, is grown on a semi-insulating wafer by either a vapor or liquid epitaxial technique The apparent minor role played by the negative resistance region in practical short-gate FETs suggests that radiofrequency instabilities due to this region, if they exist, occur at frequencies far above the normal frequency regime of microwave FETs The small-signal equivalent circuit of the FET, valid up to moderately high frequencies is elaborated It is found that noise in a microwave GaAs FET is produced both by sources intrinsic to the device and by thermal sources associated with the parasitic resistances

Electron Probe Microanalysis

Abstract: Publisher Summary This chapter describes various aspects of electron probe microanalysis. The principal elements of a conventional electron probe microanalyzer are four in number. An electron optics system, consisting of an electron gun followed by reducing lenses, whose role is to produce at the level of the sample an electron probe with a diameter approximately between the limits of 0.1 and 2 μ. The probe is obtained by forming, by means of electron lenses, a much reduced image of the crossover produced by an electron gun. The gun is of the conventional hot cathode triode type. When the maximum Gaussian diameter compatible with complete occultation is obtained, a measurement is made by means of a Faraday cylinder, of the current carried by the beam. This can then be compared with the theoretical value deduced from the emissivity of the filament and from the spherical aberration of the probe-forming lens. The physical basis of the emission-concentration relation is also elaborated.

Foundations of Environmental Scanning Electron Microscopy

Abstract: Publisher Summary The purposes of this chapter are (1) to present new theoretical derivations and computations, (2) to explain and review experimental findings, (3) to survey existing literature and collect data and information relevant to environmental scanning electron microscope or microscopy (ESEM), and (4) to create the foundations for further use and development of ESEM. The chapter emphasizes on the understanding and development of the theory of the ESEM. Doing this requires not only knowledge within the electron microscopy field in its present form, but also from other disciplines such as fluid mechanics, ionization of gases and plasma physics. The electron beam penetration of gases and the overall performance of the instrument have been analyzed in the chapter. Mathematical derivations for the stationary gas in the specimen chamber and the gas flowing through apertures, tubes and pumps have been given in the chapter. Theoretical calculations can be made for some cases, while for others the predictions may be poor and the employment of experimental methods more practical. The chapter outlines the general reactions in the broadest terms and some of these are analyzed. The study of the electron physics of the beam-gas system in relation to the most elementary and immediate needs of ESEM has been mentioned.

Energy-filtering transmission electron microscopy

Abstract: Publisher Summary In energy-filtering transmission electron microscopy (EFTEM), the zero-loss electrons or electrons passing an energy-loss window of the electron energy-loss spectroscopy (EELS) are used for image formation. This can be achieved by using the scanning mode in a dedicated scanning transmission electron microscope (STEM) or in a TEM with a spectrometer behind the camera chamber or by using an imaging filter lens in the column of a TEM. The conventional TEM and STEM modes can be combined in this way with the mode of electron spectroscopic imaging (ESI) and electron spectroscopic diffraction (ESD), and different modes can be used to record an EELS spectrum. An EFTEM can therefore make full use of elastic and inelastic electron-specimen interactions. This chapter provides an overview of the physical background and the possibilities of EFTEM. The relevant physics of elastic and inelastic scattering is also discussed followed by the instrumentation of EFTEM. The theoretical approaches for understanding the contrast and examples of application are presented for ESI and for ESD.

The Biological Effects of Microwaves and Related Questions

Abstract: Publisher Summary This chapter discusses the biological effects of microwaves. It is emphasized that an appropriate discussion of the experimental results with regard to nonthermal effects must frequently consider thermal effects as well. The amount of energy transfer from the radiation to the material varies slowly with frequency and is largely governed by the dielectric loss. Within reasonable limits, this loss is proportional to the intensity of the radiation. Nonthermal effects, on the other hand, occur in certain frequency regions only, and usually exhibit saturation at rather low intensity. As a consequence, nonthermal effects might be drowned by the thermal ones. This is in particular to be expected when the sign of the considered effect in the nonthermal region is opposite to that of the thermal effect. As an example, consider the reduction of the rate of growth of certain bacteria arising from irradiation at 73.6 Hz as discussed. Temperature increase, on the other hand, increases the rate of growth, thus canceling the nonthermal effect at sufficiently high intensity.