Tungsten filament electron

The usual source of electrons is a tungsten filament electron gun held at a negative potential (typically 10-30 kV), and magnetic lenses focus the beam into a fine probe incident on the surface of the specimen. A probe diameter of 0.2-1 pm is typical, with a current of 1-100 nA. 

Source Optical tungsten filament Electron tungsten filament Field emission source ... 

Cesium was first produced ia the metallic state by electrolysis of a molten mixture of cesium and barium cyanides (2). Subsequentiy the more common thermochemical—reduction techniques were developed (3,4). There were essentially no iadustrial uses for cesium until 1926, when it was used for a few years as a getter and as an effective agent ia reduciag the electron work function on coated tungsten filaments ia radio tubes. Development of photoelectric cells a few years later resulted ia a small but steady consumption of cesium and other appHcations for cesium ia photosensing elements followed. 

There are three major types of electron sources thermionic tungsten, LaBg, and hot and cold field emission. In the first case, a tungsten filament is heated to allow... 

A simple spectrometer that we have used successfully is shown in Figure 2. Electrons from an electron microscope hairpin tungsten filament are focused with an Einzel lens onto the monochromator entrance slit, pass through the monochromator and exit slit, and are focused on the sample s surface by additional electrostatic... 

HREELS experiments [66] were performed in a UHV chamber. The chamber was pre-evacuated by polyphenylether-oil diffusion pump the base pressure reached 2 x 10 Torr. The HREELS spectrometer consisted of a double-pass electrostatic cylindrical-deflector-type monochromator and the same type of analyzer. The energy resolution of the spectrometer is 4-6 meV (32-48 cm ). A sample was transferred from the ICP growth chamber to the HREELS chamber in the atmosphere. It was clipped by a small tantalum plate, which was suspended by tantalum wires. The sample was radia-tively heated in vacuum by a tungsten filament placed at the rear. The sample temperature was measured by an infrared (A = 2.0 yum) optical pyrometer. All HREELS measurements were taken at room temperature. The electron incident and detection angles were each 72° to the surface normal. The primary electron energy was 15 eV. 

Primary X-rays are produced by the bombardment of a suitable target with a stream of accelerated electrons. A typical X-ray generator uses an evacuated tube into which the target (e.g. tungsten) projects as a cooled anode together with a tungsten filament cathode. At a potential of 20-50 keV electrons are emitted from the cathode and bombard the... 

The most common conventional gas source is an electron impact (El) source. This consists of a metal chamber with a volume of a few cm3, through which the sample flows in the form of a gas. Electrons produced by thermionic emission from a heated tungsten filament are passed through this gas, and accelerated by a relatively low voltage ( 100eV), causing ionization within the sample gas. A plate inside the chamber carries a low positive potential (the repeller ) which ejects the positive ions into a region which contains a series of plates (called lenses) and slits, which serve to focus, collimate, and accelerate the ion beam into the next part of the system... 

General Description of Method.— The gas is ionized by impact electrons emitted by a hot tungsten filament, and, by means of an electric field the positive ions formed are drawn through a narrow slit into a magnetic field, where they are resolved into constituents of different ratios of charge to mass by a method very similar to that employed by Dempster in his positive ray analysis. The ionization potential necessary to produce each ion is determined by gradually reducing the potential applied to the impact electrons until no trace of the particular ion can be detected. 

In the fall of 1934, Dr. Grosse reduced this pure oxide by two methods and obtained from it the metal protactinium, which is even rarer than radium, but much more permanent in air. In die first method, he bombarded the oxide on a copper target, in a high vacuum, with a stream of electrons. After a few hours, he obtained a shiny, partly sintered, metallic mass, stable in air. In his second method, he converted the oxide to the iodide (or chloride or bromide) and cracked it in a high vacuum on an electrically heated tungsten filament, according to the reaction ... 

An electrically heated filament, usually tungsten, emits electrons, which are accelerated by a high potential difference (20-50 kV) and allowed to strike a metal target or anode which is water cooled (Figure 2.1 (a)). The anode emits a continuous spectrum of white X-radiation but superimposed on this are sharp, intense X-ray... 

Electron microscopy is widely used in the characterization of solids to study structure, morphology, and crystallite size, to examine defects and to determine the distribution of elements. An electron microscope is similar in principle to an optical microscope. The electron beam is produced by heating a tungsten filament, and focused by magnetic fields in a high vacuum (the vacuum prevents interaction of the beam with any extraneous particles in the atmosphere). The very short wavelength of the electrons allows resolution down to 0.1 nm. 

Linear cathode accelerators employ a cylindrical vacuum chamber in which a longitudinal heated tungsten filament cathode is raised to the negative accelerating potential. The electrons emitted from the cathode are accelerated to the exit... 

Multi-Filament Linear Cathode Electron Accelerators In this design, multiple emitter assembly with heated tungsten filaments placed in parallel to a product s direction. The beam current is controlled by molybdenum grids held at a common potential. A planar screen grid is placed below the control grids. In... 

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