DIRECT OBSERVATION OF LaB//6(001) SURFACE AT HIGH TEMPERATURES BY X-RAY AND ULTRAVIOLET PHOTOELECTRON SPECTROSCOPY, LOW-ENERGY ELECTRON DIFFRACTION, AUGER ELECTRON SPECTROSCOPY, AND WORK-FUNCTION MEASUREMENTS.

The properties of the LaB//6(001) surface which is in equilibrium with oxygen (ultrahigh vacuum - 10** minus **6 Torr) at high temperatures (room temperature about 1500 degree C) have been studied by XPS, UPS, LEED, AES, work-function measurements, and so on. In the case of the clean surface (experiments under ultrahigh vacuum), the chemical composition of the surface does not change up to about 1500 degree C. Under an oxygen atmosphere, the surface is covered by an oxide and has a high work function below a critical temperature T//c which depends on the oxygen pressure P//O//2. Above T//c, the surface oxide, which is rich in lanthanum content, evaporates, and the chemical composition and work function of the surface become identical to those of the clean surface under ultrahigh vacuum.