A new method for the investigation of SAW (surface acoustic wave) fields is presented using a modified version of a scanning tunneling microscope. By adding a high frequency sinusoidal signal to the dc tip voltage the tunneling current contains a component at the difference of the frequencies of this signal and the SAW. There is a remarkable variation of phase for areas much smaller than the SAW wavelength, due to different contributions of the normal and horizontal components of the SAW.
Abstract. Amplitude and phase of high frequency surface acoustic wave (SAW) fields are investigated by a novel scanning tunnehg microscopy technique. The gap voltage is modulated at a slightly detuned high frequency. Due to the nonlinearity of the tunneling process a frequency mixing appears. For scanned areas with dimensions much smaller than the wavelength of the SAW a remarkable local variation of amplitude and phase of the tunneling current at the difference frequency is observed. Depending on the local morphology different components of the particle displacement vector are detected. Model calculations of amplitude and phase images are presented for a real topography.
The influence of surface contaminations on the ignition and maintenance of vacuum discharges is discussed qualitatively. Surface analysis of the electrodes and gas analysis during the discharges demonstrate that fresh electrodes contain always impurities within the upper surface layers, which affect the behaviour of vacuum arcs and vacuum breakdowns. The most effective way for cleaning the surfaces are the dischnrges themselves, if they burn in UHV. During that cleaning the following variations have been found: Arc cnthodes spots change from rapid moving ones with small erosion (type 1) to slow ones with strong erosion (type 2). The ignition of nanosecond discharges needs higher field strength and field emission current density. Polishing effects by short discharges (< 5 n s ) become more pronounced. Erosion craters in nanosecond discharges increase.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.