Surface reactions of boron with clean tungsten substrates

"A model developed to predict adsorbate-induced work-function changes for thermionic emitters is shown here to apply to a more general class of electron emission phenomena and a much broader range of adsorbates. This model predicts that chemically, vapor-deposited boron will increase the work function of a clean tungsten substrate at coverages between 0 and 1 monolayer. This is the first time that a single model has been shown to predict both positive and negative work function changes for different adsorbates. The reactions of chemically, vapor-deposited (CVD) boron with clean tungsten substrates were studied using field emission microscopy (FEM) and low energy electron diffraction (LEED). The studies by FEM indicate that boron nucleates in the vicinals of and grows across the central tungsten (110) plane. The single-spot, electron emission pattern thus formed is the result of a cap-shaped nucleus of boron which raises the local field strength in the (110) region by decreasing the local radius of curvature. The reversal of the emission characteristic of the clean tungsten (110) plane is not the result of submonolayer adsorption and therefore produces intense, confined electron emission which is independent of adsorption induced work function changes predicted by the general model. The FEM observations on and around the (100) planes are shown to correlate well with the general model showing a decreased emission (increased work function) with boron adsorption. The LEED study indicates that the CVD boron atoms on a clean tungsten (100) surface occupy epitaxial sites at coverages between 0 and 1 monolayer. These are the same sites that the next layer of tungsten atoms would occupy and represent the simplest potential minima available on the surface"--Abstract, pages iii-iv.

Name thesis:degree_name

Ph. D. in Ceramic Engineering

Grantor

University of Missouri--Rolla

Year dc:date.available

2016

Author dc:creator

• Flaim, Thomas A.

• Ceramic Materials

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/1855

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-2857