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We have observed simple oscillations in three-dimensional (3D) patterns of electron thermal diffuse scattering (separated from electron-electron energy loss) measured on a Si(001) surface. We interpret these oscillations as coherent interference within a small cluster of atoms in which vibrational correlation within the nearest neighbors (NN) is dominant. A 3D Patterson function analysis of the oscillation reveals the atomic structure of the Si(001) surface consisting of NN pairs including dimers. This finding provides a promising new clue to determine the structures of bulk and the surface of solids.

X-ray photoelectron diffraction patterns of K $2p$ core levels have been measured for the Si(001) 2 \ifmmode\times\else\texttimes\fi{} 1-K surface. From a kinematical analysis of the diffraction patterns, it is concluded that a sawtooth-type arrangement of the potassium double array is present over the substrate. This is in disagreement with an existing assumption of the one dimensionality of the alkalimetal-Si(001) systems.