November 1980

Document Type


Degree Name



Dept. of Applied Physics


Oregon Graduate Center


Nonlinear photoemission mechanisms have been investigated for GaAs and LiNbO[subscript 3] and their nonlinear photoelectric yield characteristics have been obtained. These yields were achieved using several different sample preparation techniques. GaAs was used as a bare, polished crystal with or without a thin layer of cesium applied to the surface. The LiNbO[subscript 3] samples investigated were polished crystals coated with a thin tungsten layer alone, or with an additional thin layer of cesium. The coatings used were measured to have thicknesses very much less than visible light wavelengths; guided waves propagating in LiNbO[subscript 3] or GaAs substrate were able to penetrate the coating layer. The current densities required for high resolution imaging can be produced by the nonlinear emission in these materials with optical intensities below the damage threshold. Simple, low-resolution electron optics have been used to form images of waves propagating in samples of GaAs and LiNbO[subscript 3]. An ultraviolet illuminator suitable for linear photoemission microscopy has been developed and used to obtain high resolution electron micrographs at wavelengths of 266 and 213 nm. This ultra-violet source is useful for obtaining an image of the sample to be studied using nonlinear emission and also provides illumination for operator adjustment of the electron optics. The aberrations introduced into photoelectron emission imaging by the use of high current density electron beams have been considered. A variety of physical processes occurring in the anode-cathode space in the photoelectron microscope have been analyzed and the parametric dependence of the image aberrations has been found. These results indicate that aberrations will introduce image blur of less than ~500 Å for current densities as high as 1 A[ampere]/cm2 in narrow beams. Nonlinear photocurrent densities much less than 1 A[ampere]/cm2 are needed for submicron imaging, and these space charge dependent aberrations should not be limiting factors in obtaining image resolutions down to 500 Å.





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