  The generation of low-emittance electron beams has received significant
interest in recent years. Driven by the requirements of X-ray free electron
lasers, the emittance of photocathode injectors has been reduced significantly,
with a corresponding increase in beam brightness. At the same time, this has
put increasingly stringent requirements on the instrumentation to measure the
beam size. These requirements are even more stringent for novel accelerator
developments, such as laser-driven accelerators based on dielectric structures
or on a plasma, or for linear colliders at the energy frontier. We present here
the generation and measurement of a sub-micrometer electron beam, at a particle
energy of 330 MeV, and a bunch charge below 1 pC. An electron beam optics with
a beta-function of a few millimeters in the vertical plane had been set up. The
beam was characterized through a wire scanner that employs a 1 um wide metallic
structure fabricated using the electron beam lithography on a silicon nitride
membrane. The smallest (rms) beam size presented here is less than 500 nm.
