The Fourier transform of measured diffraction intensities, the so-called Patterson function (PF), is a useful tool for surface structure determination. Despite significant progress in direct low-energy electron diffraction (LEED) methods [1], reflection high-energy electron diffraction (RHEED) has attracted less attention. Due to the experimental setup crystal truncation rod (CTR) measurements seem not as straightforward in the case of RHEED as compared to LEED intensity-voltage (I-V) curve measurements. However, it has been shown recently that RHEED intensities of a significant volume of k-space can be measured by the azimuthal scan technique [2-4].
In our work, the PF has been calculated from RHEED CTRs that were measured from azimuthal scans of the sample. The azimuthal scan RHEED patterns were measured from the Ge(001)-(1x2)/GaAs(001) surface reconstruction prepared by molecular beam epitaxy (MBE). Line scans through the whole azimuthal range of 20 keV RHEED patterns have been measured with a periodic step along the CTR. As a result, we are able to access and measure higher order (nH, nK, nL) diffraction spots with n up to 5 that correspond to a volume in reciprocal space of 20 x 20 x 6.25 Å-3. The measured curves have been compared with data measured by x-ray diffraction in situ from the same surface. The differences between the data sets allow an assessment of the multiple scattering of the RHEED electrons and the resulting Kikuchi line effects on the CTRs.
References:
1. H. Wu and S. Y. Tong, Phys. Rev. Lett. 87 (2001) 036101
2. O. Romanyuk, K. Kataoka, F. Matsui, K. Hattori and H. Daimon, Czech. J. Phys. 56 (2006) 267
3. W. Braun, D.K. Satapathy, K.H. Ploog, Surf. Sci. 600 (2006) 3950
4. T. Abukawa, T. Yamazaki, K. Yajima and K. Yoshimura, Phys. Rev. Lett. 97 (2006) 245502 |