I n conjunction with ongoing measurements on electrical properties [l to 31 and band structure calculations [4] for NbO, the X-ray photoelectron spectra (XPS) of this compound have been measwed. No prior work of this type seems to have been reported for this material.Single crystals of high perfection and purity were grown as described elsewhere [5]. The experimental procedures and requisite precautions for the XPS mearurements have been discussed in publications pertaining to SrTiO, [6] and V20, [7]. The purity of the oxide and, more particularly, the absence of any other oxide of NbO, was checked by examining the 0-1s and Nb3d peaks. It was found that although immediately after surface cleaning by argon ion bombardment, the oxygen peak was narrow and reasonably symmetric, it became asymmetric and broad after several hours of run required for mapping the conduction band. However, this problem was minimized to a considerable extent, when the sample inlet tube of the machine was enclosed in a dry box maintained in an atmosphere of dry nitrogen. The sample was subjected to Ar ion bombardment to etch the surface.The instrument calibration was done by measuring the binding energy of 4fvl2 level of gold from a thin layer evaporated on to the sample and setting this value equal to 83.8 eV. All the measured levels were thus referenced to the Fermi level of gold and hence, indirectly, to that of NbO.

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