Imaging and manipulation properties of nanoparticles in scanning tunneling microscopy

Nanometer-sized particles manufactured by two different techniques and deposited on wet chemically treated Si(111) substrates are explored at room temperature with a scanning tunneling microscope (STM) in the light of their stability upon repeated imaging and the feasibility to manipulate them with the probing tip. The two preparation techniques include field-induced transfer of Au from the STM tip stimulated by voltage pulsing and a wet chemical method. In the latter case, a colloidal solution of specified admixtures is prepared delivering CdS particles with a diameter of approximately 5 nm. In STM images, they protrude as 50-nm-high isolated hillocks or as one particle-high islands containing a varying number of individual constituents. The STM imaging process does not cause any changes in the structure of the islands or in the position of single particles. Upon traversing the tip through particle islands, several constituents can be removed. Depending on the deposition conditions in the field-induced transfer mode, the created Au deposits either adhere strongly to the substrate or they are displaced by the STM tip while imaging.