Date

August 1987

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Applied Physics

Institution

Oregon Graduate Center

Abstract

The first aim of the research was the production of single crystal samples of ZrC using an arc heated floating zone technique. The second was a work function study of single crystal planes of ZrC using thermionic emission techniques, supplemented with field emission data. A semi-empirical work function theory is developed to predict the clean surface work functions of ZrC, as a function of crystallographic orientation. The theory predicts work function variations with stoichiometry for ZrC and other transition metal carbides. A detailed description is given of the apparatus and the procedures used for the production of single crystal samples of ZrC. The initial material was sintered ZrC having an average C/Zr ratio of 0.98. The final products were centerless ground single crystal samples with stoichiometries between 0.84 and 0.96. To obtain accurate thermionic data the spectral emissivity of crystalline ZrC [subscript 0.91] was measured with resulting data yielding € (0.65 µm) in the temperature range 1200 < T < 2400 K. There were no effects due to crystallographic direction noted. Thermionic work function measurements are reported for five ZrC [subscript 0.896] crystal samples. Data were taken for temperatures in the range 1800 to 2500 K and analyzed using Schottky plots and Richardson's equation with the pre-exponential constant equal to 120 A-cm[superscript -2]K[superscript -2]. Results obtained from (100) and (210) crystal planes are graphed to show the temperature dependence of the effective thermionic work function. Relative work functions are presented using direct observation of thermionic emission patterns from a hemispherical ZrC single crystal. The relative effect of oxygen on single plane thermionic work functions is also depicted. The thermionic work function data are compared with absolute, room temperature work function measurements made using the field emission retarding potential method. These data are correlated with Auger electron spectroscopic data taken to show temperatures needed for thermal desorption of adsorbates and stoichiometric changes as a function of temperature. Finally, a cursory examination of the field emission properties of ZrC is made. Cathode etching and mounting procedures are examined and an emission pattern produced from a clean ZrC surface. The relative work function ordering of the crystal planes agrees with the thermionic data and the work function model's predictions.

Identifier

doi:10.6083/M4FX77CN

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