Design and Performance of Undulator Beamline (BL7U) for in-situ Observation of Synchrotron Radiation Stimulated Etching by STM

An undulator beamline (BL7U) equipped with an ultra-high vacuum STM system is constructed at the UVSOR facility to investigate excitation energy dependence in synchrotron radiation (SR) stimulated etching. The SR beam is focused using two cylindrical mirrors on the sample surface just under the STM tip. The sample is cleaned by direct current heating and transferred to the sample holder for the STM measurements. The photon flux density is calculated to be 1019 photons (cm2 sec 100mA)-1 within the spot of 0.67 mm (H) X 0.17 mm (V) on the sample surface at the first harmonic tuned to 100 eV. The hydrogen adsorbed Si (111) surfaces were investigated using the STM apparatus before the undulator irradiation experiments were performed.