Hyperchanneling of low energy ions on the platinum(111) and gold(110) surfaces and ion scattering spectrometry of ferroelectric lithium tantalate.

摘要

The thesis mainly includes two parts: (1) The Scattering And Recoiling Imaging Code (SARIC) was employed to perform classical ion trajectory simulations of the hyperchanneling phenomena of low energy ions on the surface channels of Pt(111) and Au(110) surfaces. The results confirm and clarify the concept of hyperchanneling. In addition, it was found that the mass of the ions and the shape of surface channels had a profound effect on the hyperchanneling conditions. As hyperchanneled ions suffered very little energy loss and energy spread, hyperchanneling phenomenon is predicted to be useful for generating a pulsed neutral beam, which can act as a probe of insulating materials. Because of the sensitivity of hyperchanneling to the thermal vibration amplitudes, hyperchanneling is considered to be capable of determining the surface Debye temperature of a solid. (2) Ferroelectrics possess interesting surface voltage properties and charge emission characteristics, as a result of spontaneous polarization changes responding to an external physical attribute (e.g., electric field, temperature or pressure). We have found that time-of-flight scattering and recoiling spectrometry (TOF-SARS) is not only applicable of determining surface composition of a ferroelectric but also measuring surface voltage and charge emission induced by spontaneous polarization changes. The concept and feasibility of this methodology are illustrated by the data collected from a LiTaO₃ (0001) crystal with 4keV Ne + beam in a standard TOF-SARS instrument. The applicability to surface studies of ferroelectrics, particularly the ion-induced electron emission and negative ion emission, is demonstrated.