Apparatus and techniques are described for cleaving large (1 cm3) crystals of CdS and for making photoemission quantum yield and energy distribution measurements in the vacuum ultraviolet (hv≤ 11.8 eV; &lgr; ≥ 1050 Å) and at longer wavelengths. It is found that CdS cleaves only in the (101¯0) and (12¯10) planes. The cleaving and measurements are done at pressures of 10−9Torr or less, in a metal system provided with a VacIon and a titanium sublimation pump. For measurements in the vacuum ultraviolet, the sample chamber is provided with a LiF window and a special face plate which can be attached directly to the output housing of a vacuum monochromator. Measurements have been made forhv≤ 21.2 eV by mounting the cleaving chamber directly on the output housing of the vacuum monochromator, with no window between the sample and the vacuum monochromator. In this case the cleaving and measurements are carried out at the much higher pressure (10−4Torr or greater) of the vacuum monochromator.