X - ray standing wave imaging of the 13 monolayer Sn Õ Ge „ 111 ... surface

X-ray standing waves ~XSW! are used to measure the structure of the ()3))R30° to (333) lowtemperature phase transition for the 1 3 monolayer Sn/Ge~111! surface. A three-dimensional direct-space imaging approach, based on the summation of several hkl XSW-measured Fourier coefficients, is demonstrated. At room temperature, the Sn atoms are found to occupy the T4-adsorption sites with one-third of the Sn atoms 0.45 Å higher than the remaining two-thirds. The (333) phase has no significant change in the XSWmeasured structural parameters. This is consistent with an order-disorder-type phase transition.