Two kinds of semiconductor nanometer particles, prepared by Langmuir-Blodgett techniques and the colloid method, were studied on highly oriented pyrolytic graphite using a scanning tunneling microscope operating in air. For PbS nanometer particles, striped structures of about 20-30 nm width were found. Further studies demonstrated that the striped structures are caused by tip-sample interactions and preparation processes. Tip-sample interactions can cause lateral motion and vertical transfer of the nanometer particles which are weakly adsorbed on graphite surface. But the preparation method and the properties of the nanometer materials are the decisive reasons for the ultimate structure formation.