A type of electron microscope in which a high negative voltage is applied to a metal tip placed in an evacuated vessel some distance from a glass screen with a fluorescent coating. The tip produces electrons by field emission. The emitted electrons form an enlarged pattern on the fluorescent screen, related to the individual exposed planes of atoms. As the resolution of the instrument is limited by the vibrations of the metal atoms, it is helpful to cool the tip in liquid helium. Although the individual atoms forming the point are not displayed, individual adsorbed atoms of other substances can be, and their activity is observable.
Field-emission microscope.
A type of electron microscope in which a high negative voltage is applied to a metal tip placed in an evacuated vessel some distance from a glass screen with a fluorescent coating. The tip produces electrons by field emission, i.e. the emission of electrons from an unheated sharp metal part as a result of a high electric field. The emitted electrons form an enlarged pattern on the fluorescent screen, related to the individual exposed planes of atoms. As the resolution of the instrument is limited by the vibrations of the metal atoms, it is helpful to cool the tip in liquid helium. Although the individual atoms forming the point are not displayed, individual adsorbed atoms of other substances can be, and their activity is observable.
Field-emission microscope
An instrument for studying the surface of a solid, usually a metal, by causing it to undergo field emission. A simple microscope is shown in the diagram. A high voltage is applied in a vacuum between the single crystal solid tip and the curved fluorescent screen. The electrons emitted from the tip form an image on the screen; the different intensities of the image represent areas on the tip that have different work functions. Vibrations of the metal atoms limit the resolution and the tip is usually held at liquid helium or hydrogen temperature. The structure of alloys, the behaviour of impurities in metals, and the effect of adsorption at the metal point can be studied.
Field-emission microscope
A type of electron microscope in which a high negative voltage is applied to a metal tip placed in an evacuated vessel some distance from a glass screen with a fluorescent coating. The tip produces electrons by field emission, i.e. the emission of electrons from an unheated sharp metal part as a result of a high electric field. The emitted electrons form an enlarged pattern on the fluorescent screen, related to the individual exposed planes of atoms. As the resolution of the instrument is limited by the vibrations of the metal atoms, it is helpful to cool the tip in liquid helium. Although the individual atoms forming the point are not displayed, individual adsorbed atoms of other substances can be, and their activity is observable.
- Alt key
- Altman, Scott Douglas (1959– )
- Altman, Sidney
- alto-
- altocumulus
- Altonian
- altostratus
- altricial species
- altruism
- alt text
- ALU
- Alu element
- alum
- alumina
- alumina(symbol: A12O3)
- aluminate
- aluminium
- aluminium acetate
- aluminium antimonide(symbol: AlSb)
- aluminium chloride
- aluminium ethanoate
- aluminium hydroxide
- aluminium oxide
- aluminium PCB
- aluminium potassium sulphate