Physico-Chemical nanomaterials science 
Nanoelastics of Ge1-xSnx films driven by composition and structural relaxation 
Malyuta S.V.1,2, Lytvyn P.M.1, Kuchuk A.V.1, Kondratenko S.V.3, Mazur Yu.I.4
1 V.E. Lashkaryov Institute of Semiconductor Physics NASU, 41 Nauky pr., 03028 Kyiv, Ukraine 
E-mail: serhiy.malyuta@gmail.com
2 National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, 37 Peremohy, av. 03056 Kyiv, Ukraine
3 Taras Shevchenko National University of Kyiv, 64 Volodymyrs'ka St., 01601, Kyiv, Ukraine
4 Institute of Nano Science and Engineering, University of Arkansas, Fayetteville, AR, 72701, USA

Recently, there has been increased interest in Ge1-xSnx compounds as the material for mid-range infrared optoelectronics. There is a fundamental possibility to control the bandgap ranging from semiconductor to semimetal. The transition from the indirect to direct-band gap configuration is relatively easy to implement, increasing the tin content over 6.5 at. % in these alloys. Within the last few years, significant progress has been made in the development of GeSn-based lasers, photodetectors, emitting diodes, and transistors. Nevertheless, the Ge1-xSnx structural stability is a case to solve. A large number of dislocations of various types, surface segregation of tin atoms, and phase separation of metastable GeSn layers decrease a conductivity channel and increase the density of non-radiative recombination centers. 
Nanomechanical properties, in particular elastic characteristics, of GeSn thin films are extremely important in the problem of deformation engineering of their band structure. Nonmonotonic dependences of Young's modulus value for the   Ge1-xSnx/Ge/Si nanostructures with variations in their composition and thickness are revealed by the “atomic force” indentation. It is shown that for Ge1-xSnx films of subcritical thicknesses and small x (1÷5%) the changes in Young's modulus are caused by the change in the composition. With the onset of plastic relaxation for the mean values ​​of x (5÷8%), the increase of Young's modulus correlates with the amount of dislocation hardening effect. The phase separation processes and the segregation of tin on the surface at the supercritical thicknesses and high Sn content (~ 12%) lead to Young's modulus decreasing with increasing Ge1-xSnx film thickness.