nanometer-scale features are being produced in air on metallic surfaces using a scanning tunneling microscope developed for microscopy, spectroscopy, and fabrication. the instrument has sufficient stability, computer control, and in-process measurement capability to record important processing signals while creating nanoscale patterns. nanoscale features have been produced with various tip and sample material combinations. the surface can be quantitatively characterized using both tunneling spectroscopy and imaging before and after pulsing the tip-sample voltage. the before-and-after images show that the form of the created features ranges from craters to mounds when the voltage exceeds a threshold value. the tip-sample current waveform recorded during a surface modification also indicates the nature of the created feature measurements of the variation of threshold tip-sample voltage with tip-sample spacing shows that a threshold electric field of the order of v/a is characteristic of the process. computations of the electrostatic field between tip and sample yield values sufficient to remove atoms by high-field processes