Physical mechanism of hydrogen deposition from a scanning tunneling microscopy tip

We report on the first successful deposition of individual hydrogen atoms from a tungsten tip of a scanning tunneling microscope onto a monohydride Si(100)-2x1:H surface. Hydrogen atoms adsorbed on the tungsten tip are first diffused to the tip apex from the surroundings of the tip by the application of +3.5 V bias to the sample for approximate to 300 ms, and subsequently deposited onto the surface by the application of -8.5 V 300 ms pulses to the sample. The physical mechanisms involved are hydrogen diffusion on the tip via field-gradient-induced diffusion and hydrogen deposition due to electronic excitation.