Molecular-Beam Sources for Vapor Deposition on field Emitter Substrates

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Abstract
Molecular beam vapor sources suitable for use in high vacuum (10−10 Torr or less) and for deposition of a known flux of vapor in the field electron emission microscope (FEM) are described. The field emitter itself is used as a substrate. Because of the sensitivity of the FEM to contaminants, a vapor source design must be used that will permit (1) establishment and maintenance of a clean FEM pattern during deposition, (2) minimization of metallic mass in the system, (3) reproducible achievement of the required vacuum, (4) flexibility in operation of sources as regards outgassing, loading, and controlling flux, and (5) quantitative determination of the impinging flux. The construction, calibration, and use of four vapor sources are discussed. The methods used to outgas these sources and to load them with an evaporant under high vacuum are given. Movement within the vacuum system to effect loading or transfer operations of the evaporant or source is accomplished by using externally actuated rod magnets. Nucleation of silver on tungsten is given as an example to illustrate the difference in FEM patterns obtained in deposition of silver from vapor with a ``clean'' source and a ``dirty'' source.