Development of an energy-domain 57Fe-Mössbauer spectrometer using synchrotron radiation and its application to ultrahigh-pressure studies with a diamond anvil cell.

An energy-domain (57)Fe-Mössbauer spectrometer using synchrotron radiation (SR) with a diamond anvil cell (DAC) has been developed for ultrahigh-pressure measurements. The main optical system consists of a single-line pure nuclear Bragg reflection from an oscillating (57)FeBO(3) single crystal near the Néel temperature and an X-ray focusing device. The developed spectrometer can filter the Doppler-shifted single-line (57)Fe-Mössbauer radiation with a narrow bandwidth of neV order from a broadband SR source. The focused incident X-rays make it easy to measure a small specimen in the DAC. The present paper introduces the design and performance of the SR (57)Fe-Mössbauer spectrometer and its demonstrative applications including the newly discovered result of a pressure-induced magnetic phase transition of polycrystalline (57)Fe(3)BO(6) and an unknown high-pressure phase of Gd(57)Fe(2) alloy placed in a DAC under high pressures up to 302 GPa. The achievement of Mössbauer spectroscopy in the multimegabar range is of particular interest to researchers studying the nature of the Earth's core.

Observation of HOPG by STM and contact AFM in various gas atmospheres under pressures up to 1.1 MPa.

Apparatus comprising a scanning tunneling microscopy (STM) and an atomic force microscopy (AFM) has been developed for use under supra-atmospheres. Observations of highly oriented pyrolytic graphite (HOPG) were carried out by STM and contact AFM operating in air and various gas atmospheres (hydrogen, helium, neon and argon) under pressures up to 1.1 MPa. Atomic resolution images of the HOPG were obtained by STM in all the gas atmospheres studied. However, it was found that the presence of water vapor gave rise to a noise current at increased pressures. Using contact AFM, the atomic resolution in an argon atmosphere decreased with increasing pressure, while atomic images were obtained under the other gas atmospheres at 1.1 MPa.

Investigation of influence of gas atmosphere and pressure upon non-contact atomic force microscopy.

Resonance measurements and atomic force microscopy (AFM) observations were carried out by the non-contact AFM operating in various gas atmospheres (hydrogen, helium, nitrogen and argon) over the range of pressures from 0.1 to 1.1 MPa. In each atmosphere, the resonance frequency of the AFM cantilever depended on the pressure of gases studied. The plots of the relative resonance frequency at a constant pressure vs. the gas density gave a straight line. It was found that the characteristic of the resonance frequency for the AFM cantilever were dependent on the density of the gas species. The resolution of the AFM was hardly influenced by the gas atmosphere under the present experimental conditions.