NORMAL INCIDENCE GRATING SPECTROMETER FOR INVERSE-PHOTOEMISSION

An ultraviolet k-resolved inverse photoemission spectrometer (KRIPES) is constructed for studies of the unoccupied electronic states of solids and surfaces. The spectrometer is based on the spherical grating in the off-Rowland geometry The sample is bombarded by low-energy electrons from the electron source with the minimum energy distribution width of 0.25 eV. The UV photons emitted from the sample are dispersed by the grating onto the position-sensitive defector. The spectra can be measured in the photon energy range from 10 eV to 40 eV with parallel detection of the wavelength region 560 Angstrom and with an optical resolution of about 8 Angstrom. The overall resolution of the spectrometer is determined to be from 0.26 eV at 10.0 eV to 0.6 eV at 30 eV by measuring the Fermi edge of the polycrystalline gold sample. The typical collection time per spectrum is about an hour with total amount of 3000 c/ch at the Fermi edge of gold when the beam current and energy are 25 mu A and 23 eV, respectively. The resolution of the optical system is obtained from the emission line of a uncleaned tantalum sample at the photon energy of 14.8 eV. In the k-resolved measurement of Cu(110) surface the spectra show the typical band dispersion.