The study of disordered phases on solid surfaces by diffuse low-energy electron diffraction

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The system of measuring the intensity distribution diffuse LEED images was developed. LEED images on the fluorescent screen of four-grid type LEED apparatus were taken with a CCD camera, digitized and stored with an A/D converter and a 16-bit buffer memory. Noises from the CCD camera were highly suppressed by cooling CCD devise with water. Consequently, the intensities of very weak incoherently-scattered beams were able to be measured correctly as well as those of normal coherent beams. Intensity vs. voltage (I-V) curves were evaluated using a specific software from memorized intensity data.The diffuse LEED images from disordered Cu (100) pseudo-c (2*2)-O phase were measured with this system. The coverage of oxygen on the Cu (100) surface was estimated to be about 0.1 monolayrs. Oxygen was adsorbed on the surface at low temperature (110K), followed by the post annealing of the surface at 300K.The measurement was also performed at 110K.Noise due to lattice vibrations of surface atoms were eliminated by the subtraction of a LEED image of clean surface from that of the disordered surface. The intensity of a fixed on the LEED image was measured by an integration of intensities within a square electric window. Using a trial-and-error approach, it was shown that the side of the electric window must be smaller than 1/3 of the basic reciprocal lattice vector of clean surface. After the procedure, I-V curves with a high degree of accuracy were successfully obtained from the disordered Cu (100) pseudo-c (2*2) -O phase.