Determination of nanosecond high‐voltage pulse shapes at the surface of needle emitters

A method is described for determining, i n s i t u, the shapes of nanosecond, positive high‐voltage desorption pulses at the surface of a field‐ion specimen, without the use of waveform‐distorting probes or voltage dividers. In practice, a negative pulse known to be identical in shape to the positive desorption pulse is used to initiate field electron emission from the specimen surface. The resulting time‐varying field emission current is recorded by a detector, and the Fowler–Nordheim equation is iterated to obtain the actual time‐varying specimen potential. The pulse shape obtained can be used to predict accurately the arrival time of unknown surface species in time‐of‐flight atom‐probe instruments, or to monitor the effect of changes in the pulse transmission line to the specimen. When applied to pulsed e‐beam devices and flash x‐ray machines, time‐varying potentials at field‐emission cathodes can be determined with nanosecond resolution.