Apparatus for determining the density of unoccupied electronic states of a material

An apparatus for determining the density of the unoccupied electron states of a material located above the Fermi level and for carrying out the analysis by ultraviolet fluorescence of a material excited by electrons comprising a vacuum enclosure which can contain a sample of a material;

• means for creating an electron beam of energy E.sub.i for interacting with the sample, said beam having an adequate intensity to ensure that the interaction of said beam with the sample can easily be detected, the electrons then acquiring energy levels E.sub.f below E.sub.i, the passage between the two energy levels accompanying an emission of photons, whose energy hv.sub.if is such that hv.sub.if =E.sub.i -E.sub.f ;
• means for performing a scan in energy E.sub.i ;
• and means for measuring the radiation coming from the sample;
• wherein the measuring means are placed under a vacuum and comprise a second enclosure provided with two tubes, which are inclined relative to one another, a first tube entering the vacuum enclosure, provided with a regulatable width entrance slit located in the vacuum enclosure, and a second tube provided with a regulatable exit slit;
• a diffraction grating having etching marks, said grating able to rotate about an axis parallel to said etching marks, thus enabling the selection of one of the wavelengths of the emitted photons, said grating being located in the second enclosure;
• means for rotating the said grating, its rotation angle being linked with the selection of the wavelength;
• and means for detecting photons of the same wavelength selected by the grating, said means facing the exit slit.