Atom mounds were formed by appling 4V,300ns voltage pulses on Au tip in scanning tunneling microscope (STM) in atomsphere.Each mound measures about 30 nm in diameter and 1\|2 nm in height.With the aid of this,we succeed in writing nanometer scale characters.There exists a narrow threshold field and we refer it a field evaporation process.Both positive and negative ions could be field evaporated.The re\|examination of charge\|exchange model for the field evaporation in STM and ...