SUBPIXEL DETECTION IN VIDEO RHEED IMAGE-ANALYSIS

A CCD camera and computer data acquisition system is used for surface investigation by means of the reflection high energy electron diffract ion (RHEED) method. Accuracy of these measurements, especially of latt ice parameter determination, is limited by camera spatial distortion, high noise, and diffraction-spot broadening. In order to resolve this problem a detection method of a virtual camera subpixel detector is pr oposed. The conversion function between a real camera and a perfect vi rtual pinhole model camera is established using a method of reference calibrate grid. The RHEED intensity diffraction patterns are approxima ted by analytical functions which fit the simple diffraction intensity profiles well. Then the centres of the diffraction lines and points a re calculated with high (subpixel) precision. The accuracy of the meth od is demonstrated by analysis of RHEED diffraction patterns obtained from a Pd(111) surface. It is shown that the error of determination of the diffraction spot position is lower than 0.4%. The use of the meth od is shown for the example of Pd epitaxial film growth on a NaCl subs trate where increased vertical lattice parameters are found.