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

研制了LEED漫反射图像光强分布测量系统。四栅式LEED装置荧光屏上的LEED图像用CCD摄像机拍摄，数字化后用A/D转换器和16位缓冲存储器存储。通过用水冷却CCD器件，可以有效地抑制来自摄像机的噪声。因此，能够正确测量极弱非相干散射光束的强度，以及正常相干光束的强度。利用特定的软件从存储的强度数据中计算出强度-电压(I-V)曲线，并利用该系统测量了无序的Cu(100)准c(2*2)-O相的LEED漫反射图像。氧在铜(100)表面的覆盖率约为0.1个单分子层。氧在低温(110K)下被吸附在表面上，然后在300K下进行后退火，在110K下也进行了测量，通过从无序表面减去清洁表面的LEED图像来消除由于表面原子晶格振动而引起的噪声。固定在LEED图像上的强度通过正方形电子窗口内的强度积分来测量。用试错法证明，电窗口的边数必须小于清洁表面基本倒易晶格矢量的1/3。经过这一过程，成功地从无序的Cu(100)伪c(2*2)-O相获得了高精度的I-V曲线。

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.