Direct strain and elastic energy evaluation in rolled-up semiconductor tubes by x-ray micro-diffraction

We depict the use of x-ray diffraction as a tool to directly probe the strain status in rolled-up semiconductor tubes. By employing continuum elasticity theory and a simple model we are able to simulate quantitatively the strain relaxation in perfect crystalline III-V semiconductor bi- and multilayers as well as in rolled-up layers with dislocations. The reduction in the local elastic energy is evaluated for each case. Limitations of the technique and theoretical model are discussed in detail.Comment: 32 pages (single column), 9 figures, 39 reference

Surface composition of BaTiO3/SrTiO3(001) films grown by atomic oxygen plasma assisted molecular beam epitaxy

We have investigated the growth of BaTiO3 thin films deposited on pure and 1% Nb-doped SrTiO3(001) single crystals using atomic oxygen assisted molecular beam epitaxy (AO-MBE) and dedicated Ba and Ti Knudsen cells. Thicknesses up to 30 nm were investigated for various layer compositions. We demonstrate 2D growth and epitaxial single crystalline BaTiO3 layers up to 10 nm before additional 3D features appear; lattice parameter relaxation occurs during the first few nanometers and is completed at {\guillemotright}10 nm. The presence of a Ba oxide rich top layer that probably favors 2D growth is evidenced for well crystallized layers. We show that the Ba oxide rich top layer can be removed by chemical etching. The present work stresses the importance of stoichiometry and surface composition of BaTiO3 layers, especially in view of their integration in devices.Comment: In press in J. Appl. Phy

An investigation by EXAFS of local atomic structure in an Mg-Nd alloy after processing by high-pressure torsion and ageing.

The local atomic structure of an Mg-1.44Nd (wt.%) alloy was investigated after solution annealing, high-pressure torsion (HPT) processing up to 1 and 10 turns and ageing at 250 °C for 5 h using X-ray absorption fine structure (XAFS) measurements at the Nd LIII-edge. The results show that HPT processing has no effect on the atomic structure around Nd atoms compared to the unprocessed state, whereas ageing at 250 °C for 5 h induces a significant modification in the coordination number and interatomic distances around the Nd atoms. These variations are analyzed based on the correlations between precipitation, defects and atomic mobility of the chemical species

Local structure of a rolled-up single crystal: An X-ray microdiffraction study of individual semiconductor nanotubes

Crystals with cylindrical symmetry, not existing in nature, are mimicked by the roll-up of single-crystalline and highly strained semiconductor bilayers. Exploiting this, the local structure of such individual rolled-up nanotubes is locally probed and quantified nondestructively by x-ray microbeam diffraction. A comparison to simulations, based on the minimization of the elastic energy, allows us to determine layer thicknesses and lattice parameter distributions within the strongly curved bilayers

In situ X-ray diffraction observation of two-step fullerene coalescence in carbon peapods

We report an in situ X-ray diffraction study of the high-temperature coalescence of C60 and C70 peapods. The monitoring of the structural evolution with time at two successive temperatures (1000 °C and 1200 °C) allows highlighting the occurrence of a two-step process for both peapods samples. The first step of the process, slower for C70 peapods than for C60 ones, is attributed to the transformation of individual molecules into corrugated tubules recalling the fullerenes one-dimensional periodicity. Even after long annealing time at 1000 °C this transformation is found to stagnate, until the temperature is set higher than 1050 °C, where the corrugated tubules evolve into well-formed inner nanotubes