L. Marton

An Electron Interferometer

An interferometer of the amplitude‐splitting type has been constructed which operates with electron beams and produces a system of fringes in the viewing instrument. The appearance of the fringes may be varied at will by introducing changes in one of the (electron) optical paths. The instrument utilizes crystalline diffraction for beam splitting and recombining.

Improved Electron Filter Lens

A filter lens of improved characteristics obtained by use of an intermediate image is described. The design has the advantage of longer focus and increased aperture while maintaining an energy resolution, at 5‐kev primary energy, of less than thermal spread of the initial beam.

Electron Absorption Spectrometer Using an Improved Velocity Analyzer

An electron absorption spectrometer with an improved velocity analyzer using the principle of individually designed stages for deceleration, dispersion, and reacceleration is described. The instrument is usable over an energy range of 1 to 50 kev and can obtain angular distribution data over a range of ±0.1 radian. The angular resolution is better than 10−3 radian. The demonstrated energy resolution at 20 kev is 0.6 ev. This resolution appears to be limited by the primary beam energy spread which is characteristic of a beam produced by a telefocus gun with a tungsten cathode.

Widths of Transmission Kikuchi Lines in Silicon and Diamond

Detailed transmission Kikuchi patterns for silicon and diamond at 80 keV have been measured with high angular resolution (∼10−4 rad). Linewidths of all simple Bragg reflections are consistent with an elastic‐scattering model, which uses scattering amplitudes calculated by Ibers in a first Born approximation. Various interferences between strong Bragg reflections are observed.

Cryostat for Electron Bombardment and Electron Diffraction Work

A cryostat was constructed for the production of free radicals by electron bombardment of condensed gases at liquid helium and liquid hydrogen temperature. Provisions were made for simultaneous investigations of the bombardment products by electron diffraction and optical spectroscopy.

Automatic Instrument for Electron Scattering Measurements

An instrument capable of automatically recording the distribution in energy and angle of electrons scattered from solids is described. The energy range of the primary electrons is 10 to 50 kev. On a two‐second cycle the instrument obtains and records an energy loss spectrum at a fixed angle, advances in angle, and repeats. The instrument will distinguish energy peaks less than 20 volts apart at 20 kev and angular details less than 10−3 radian apart.

Widths of Kikuchi Lines in Germanium

Transmission Kikuchi patterns at 80 keV from wedges of germanium have been measured with high angular resolution. Linewidths are compared with the Fourier potential calculated from a simple coherent‐elastic‐amplitude model. Germanium shows a higher experimental curve of scattering amplitude per unit cell volume than silicon, as may be expected from its greater atomic scattering potential. Suppressed contrast is found for the (111) reflection; this is interpreted as an overlap between the halves of the line‐pair or band.

Characteristic energy losses of electrons

It has been recognized for more than 20 years (1) that one of the most important factors in the formation of electron microscope images is electron scattering. A number of papers have appeared (2) based on accepted theories of elastic and inelastic scattering. In order to obtain numerical results, approximations were made and in some cases the results were in fair agreement with experiments (3). We now believe that this agreement was only fair, due to the fact that the theoretical treatments were essentially based on statistical considerations where an average energy loss was used for the inelastic part of the scattering. During the last few years, quite an effort has been made, both experimental and theoretical, toward a better exploration of the inelastic process.As a result, we are now in a much better position to say something more definite about the factors contributing to the inelastic part of the electron scattering process and its role in image formation in electron microscopy.

Apparatus for Electron Optical Study of Low-density Gas Flow*

An apparatus has been developed and built at the National Bureau of Standards to study low-density (~4014particles/cm3or 40-4 mm Hg) gas flow.1, 2This is an electron—optical schlieren technique which depends on the scattering of electrons in collision with individual gas molecules or atoms to form a dark field image of the gas. The apparatus consists of a bakeable stainless steel low-pressure chamber and other chambers containing brass and glass electron optical components which are not baked. The low-pressure chamber (~10-8 mm Hg) is connected to three other chambers (~10-6 mm Hg) through two small apertures and a slit. Metal gaskets are used on the bakeable chamber. The system is pumped by four oil diffusion pumps each with a liquid nitrogen trap. A small liquid helium trap (~1 1.) will be used to decrease the residual pressure from 10-7 mm Hg to 10-8 mm Hg or better.

Limiting Resolution of Electron Spectrometers

The performance of electron spectrometers is compared by plotting the energy or the momentum resolution vs. the transmission of the instrument. Empirical relationships are derived for the grouping of the performances of randomly chosen instruments. (W.D.M.)