  These comments aim to correct some apparent weaknesses in the theory of field
electron emission given in a recent paper about nanoscale vacuum channel
transistors, and to improve the presentation of this theory. In particular, it
is argued that a "simplified" formula stated in the paper should not be used,
because this formula is known to under-predict emission current densities by a
large factor (typically around 300 for an emitting surface with local work
function 4.5 eV). Thus, the "simplified" formula may significantly
under-predict the practical performance of a nanoscale vacuum channel
transistor.
