(a) A photograph of the cantilever for applying force in the opposite direction to gravity. (b) The geometry of the sample and X-rays. (c) A schematic diagram of the measuring system after the Si(111) double-crystal monochromator in Fig. 2(c). An Si(220) perfect crystal is inserted between the double-crystal monochromator and Slit 1 in Fig. 2(c). Slit 1 is rotated 34° anticlockwise and Slit 2 34° clockwise from the positions in Fig. 2(c). The vertical widths of Slit 1 and Slit 2 are both 40 µm.