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    1-4 Atomic Surface Structure of the Common Transition Metals and the Effect of Adhesion as Seen by Field Ion Microscopy

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    The field ion microscope has so far mostly been used for the direct observation of atomic details on the surface of refractory metals. The application of the instrument to the common transition metals like iron, cobalt and nickel was difficult because of the high rate of field evaporation and the field induced disordered structure of the surface layers of these metals in a field of about 440 MV/cm which is necessary for a high resolution helium ion image. In order to obtain a stable and undisturbed surface, it is necessary to find an imaging gas which fulfills the following conditions: the imaging field is lower than the evaporation field of the specimen metals and the field stress on the metal surface at the evaporation field does not exceed the yield stress of the metals. Hydrogen as an imaging gas gives a stable image of the common transition metals and the field induced chemical reaction of hydrogen with the metals decreases the evaporation field considerably. However, the resolution of the pure hydrogen ion image even at 21°K is only 4A and the rearrangement of surface atoms due to the chemical reaction is severe and strongly temperature dependent. A satisfactory image quality is obtained with helium containing a very small addition of hydrogen which reduces the evaporation field so that the metal does not yield mechanically at this lower field stress. Loosely bound hydrogen molecules at the surface act as intermediate collision partners between incoming helium atoms and the heavy surface metal atoms, thereby increasing the helium accommodation and lowering the imaging field. Field ion micrographs of iron, cobalt, nickel and carbon steel now show detailed and undisturbed surface structures.

    Author Information:

    Müller, Erwin W.
    The Pennsylvania State University,

    Nishikawa, O.
    The Pennsylvania State University,

    Committee/Subcommittee: C24.30

    DOI: 10.1520/STP45156S