Feasibility Study of Thin Film Surface Analysis Using Synchrotron Low-Angle Incidence Conversion Electron M?ssbauer Spectroscopy

A feasibility study was conducted on thin film surface analysis using conversion electron M & ouml;ssbauer spectroscopy(CEMS) measured at incident angles more than the critical angle and less than several degrees, utilizing a synchrotron M & ouml;ssbauer source. To identify the minimum incident angle yielding a CEMS spectrum with experimentally negligible nuclear specular reflection effects,gamma-ray reflection and CEMS of a57Fe [90%] enriched thinfilm were studied by grazing-incidence synchrotron M & ouml;ssbauer spectroscopy, varying the incident angle in the range of 0.3 to 3 degrees. Since the incident angles were larger than the critical angle (theta c similar to 0.22 degrees) of the iron film for 14.4 keV X-rays, the photons passing through the nuclear resonant channel, rather than the electronic non-resonant channel, predominantly contributed to the specular reflection. Consequently, at theta in= 0.3 degrees, strong scattering peaks appeared at nuclear resonance energies, and then CEMS showed an anomalous spectral profile. At theta in>theta c, the nuclear specular reflection gradually decreased withincreasing theta in, whereas nuclear resonance peaks were persistently observed up to theta in= 1.5 degrees. Finally, the reflection signals were nearly extinguished at around theta in= 3 degrees, and the CEMS showed an experimentally normal spectral profile in usual use. Low-angle incidence CEMS with negligible nuclear specular reflection is advantageous for surface analysis of thin films because the penetration depth of gamma-rays is still shorter than the conversion electron escape depth. Furthermore, a surface analysis of an annealed57Fe-richfilm was conducted using low-angle incidence CEMS with circularly polarized synchrotron M & ouml;ssbauer source. The present paper also describes the theoretical background and additional benefits in instrument development.