Molecular impurities at the NaCl(100) surface observed by scanning force microscopy

We have studied cleavage faces of NaCl crystals containing (OCN)(-) molecul es with a scanning force microscope in ultra-high vacuum. The dopant conten t in the crystals was determined using infrared spectroscopy. The molecular impurities appear as nm-sized elevations in the scanning force micrographs . Their position at cleavage steps is discussed in terms of both diffusion and step formation during cleavage. Although the atomic periodicity of the NaCl lattice is imaged, high-resolution investigations of impurities are li mited by a convolution between the tip apex and the elongated molecules sti cking out of the surface.