Photoelectron diffraction study of Si(001) 2 × 1-K surface: Existence of a potassium double layer

X-ray photoelectron diffraction patterns of K $2p$ core levels have been measured for the Si(001) 2 × 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.