Marc Steinmetz Photography | The seven SI base units

ELECTRON TUNNEL
Production of SET chips with an elec-
tron beam lithography system at the
PTB’s clean room centre. En route
towards a redifinition of the ampere
by tying it to the charge of an elec-
tron, PTB scientists are engaged in
elaboration of SET chips – single-
electron tunneling – which transport
and count electrons. The screen
shows the submicrometer layout of
a single electron pump.

[A] ‘The AMPERE is that con-
stant current which, if maintained
in two straight parallel conductors of
infinite length, of negligible circular
cross-section, and placed 1 metre
apart in vacuum, would produce
between these conductors a force
equal to 2·10^–7 newton per meter
of length.’