Changes in the Chemical State and Composition of the Clean Surface of K2CrO4 and K2Cr2O7 due to Air Exposure and Argon Ion Bombardment

Abstract

X-ray photoelectron spectra have been used for characterizing changes in the chemical state and composition of the clean surface of single K2CrO4 (potassium chromate) and K2Cr2O7 (potassium dichromate) crystals with Cr(VI) due to air exposure and argon ion bombardment. Their clean surface was prepared by cleaving these crystals in UHV, and XPS spectra from the surface were successfully obtained only by optimizing conditions of the neutralizer because of non-conductivity. The chemical state of constituent elements in the surface of K2CrO4 and K2Cr2O7 was not significantly affected by air exposure, although the surface concentration was changed. On the other hand, argon ion bombardment considerably induced reduction of chromium ions, Cr(VI) to Cr(III), in K2CrO4 and K2Cr2O7, while the chemical state of potassium and oxygen is almost unchanged by the bombardment. It was also found that the preferential sputtering of potassium in K2CrO4 and K2Cr2O7 takes place during the argon ion bombardment, and the degree of the preferential sputtering in K2Cr2O7 is about twice as high as that in K2CrO4. From the correlation between the variation in the chemical state of chromium and the preferential sputtering of potassium, the reduction behavior of chromium ions by the ion bombardment is considered mainly attributed to the preferential sputtering of potassium from the surface of K2CrO4 and K2Cr2O7 crystals. © 1997 by John Wiley & Sons, Ltd.