Nanoplasmonics and surface enhanced spectroscopy

Thermal expansion of the FeNi51 alloy surface
Yanchuk V.V.1, Voloshko S.М. 1, Vasylyev M.A.2, Shyvanyuk V.N.2, Kolesnik V.N.2
1 National Technical University of Ukraine "KPI name Igor Sikorsky,
Prospekt Pobedy, 37, Kyiv-03056, Ukraine 
E-mail: yan4uk.v@gmail.com
2 G.V. Kurdyumov Institute for Metal Physics, N.A.S. of Ukraine 
36 Academician Vernadsky Boulevard, Kyiv-03142, Ukraine

It is known that the effects of anharmonicity in the volume of the crystal and on its surface differ significantly. In particular, the thermal expansion of near-surface has its own characteristics due to the differences in interatomic interactions on the surface and in the volume [1,2].
For the first time low-energy plasmons reflection spectroscopy was used to determine the coefficient of thermal expansion (CTE) of the polycrystalline FeNi51 alloy surface. The experiment was carried out under ultrahigh vacuum conditions. A detailed analysis of the plasmons energy loss spectra of primary electrons in the 50‑600 eV range for surface layers was performed. 
The method for determining the CTE is based on measuring of the temperature dependence of the surface and the bulk plasmons’ energy shifts in the temperature range from room temperature to 300 oC. Taking into account the energy shifts when the alloy sample is heated, for the surface and bulk plasmons the following CTE values are obtained: =7,54х10-5 К-1 and =4,24х10-5 К-1, respectively. Such results can be explained by the features of the metal-vacuum interface’s structure, physical and chemical state of the metal surface [3,4].

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