Coherent scattering from silicon monocrystal surface

Using coherent X-ray scattering, we evidenced atomic step roughness at the (111) vicinal surface of a silicon monocrystal of 0.05° miscut. Close to the 1 2 1 2 1 2 anti-Bragg position of the reciprocal space which is particularly sensitive to the (111) surface, the truncation rod exhibits a contrasted speckle pattern that merges into a single peak closer to the 111 Bragg peak of the bulk. The elongated shape of the speckles along the (111) direction confirms the monoatomic step sensitivity of the technique. This experiment opens the way towards studies of step dynamics on crystalline surfaces.