Variation in hyperfine field with atomic order in FeCo and FeNi3

The variation in hyperfine field with long range order parameter is estimated both in FeCo and FeNi₃ with the help of an emperical relation connecting field and magnetic moments. The agreement is good with the available experimental values.     

Two-dimensional electron-hole liquid in single Si quantum wells with large electronic and dielectric confinement

We report a luminescence study of the electronic properties of the 2D electron-hole liquid in crystalline Si quantum wells with SiO2 dielectric barriers. The Fermi-Dirac condensation of e-h pairs into a metallic liquid is strongly enhanced by spatial localization. We present experimental evidence for the formation of liquid nanodroplets, with size increasing with e-h pair density. The quantum confined regime is observed for well width below 15 nm. The data are analyzed in a confinement model that takes account of the band-gap renormalization by 2D many-body effects and the increase of the Coulomb interactions due to the dielectric mismatch between the Si well and the SiO2 barriers.     

Controlled surface nanopatterning with buried dislocation arrays

Self-assembled configurations of nanostructures are expected to play an increasing role in devices design, as an alternative to conventional microelectronics. The key limitation is the lack of control on localisation, density and size uniformity of the structures. Here we show how to create a template to overcome these problems. A periodic nanometre scale patterning can be induced at a silicon surface by buried dislocation networks obtained by twist wafer bonding, using stress selective etching of the surface. These templates are morphologically characterised by scanning tunnelling microscopy and grazing incidence X-ray diffraction. Stress fields and elastic energy densities are calculated for the non-etched solid, and the selective etching mechanisms are discussed. Germanium growth experiments on such a Si patterned surface give a demonstration of the ordering efficiency. This study provides a general method to create a template, which organises nanostructures with controlled periodicity over the full size of a Si wafer.     

Structure and stability of Fe−Mg amorphous alloys prepared by coevaporation

The structure, stability and magnetic properties at 77K of Fe₆₀Mg₄₀ amorphous thin films prepared by coevaporation are investigated using mainly Mössbauer effect working in scattering geometry and transmission electron microscopy. The temperature range of the amorphous to crystal transition is determined; moreover a superparamagnetic-like behaviour of the films is pointed out at 77K.

     

(001) silicon surfacial grain boundaries obtained by direct wafer bonding process: accurate control of the structure before bonding

Ultra-thin (001) silicon films bonded onto (001) silicon wafers, which form ‘surfacial grain boundaries’, are analysed by transmission electron microscopy and X-ray diffraction. The aim of this study is to find a way of controlling precisely, before direct wafer bonding, the structure of the Si/Si (001) interface. Two kinds of dislocation networks are found at the bonded interface. A square array of screw dislocations accommodates the twist between the two crystals, whereas a linear network of mixed dislocations accommodates the tilt resulting from the residual vicinality of the initial surfaces. A theoretical study shows that knowing and choosing before bonding the characteristics of these interfacial dislocations depend on the control of the ‘twist’ angle during the hydrophobic molecular bonding process. Recently, a new bonding method allows us to obtain an accuracy of ±?0.005° for the ‘twist’ angle from patterned grooves without any crystallographic measurement. The precision of this technique is compared with three different measurement of the disorientation between the two grains taken after bonding. The first one is deduced from the periodicity of the dislocation networks located at the interface. The second one is calculated from large angle convergent beam electron diffraction patterns. The last one is obtained by synchrotron X-ray diffraction. The possibility of choosing precisely the characteristics of the Si (001) ‘surfacial grain boundaries’ before direct wafer bonding process is then discussed in light of an experimental study.     

Ion-implantation induced phase transitions: Order-disorder and amorphous-crystal transformations (CEMS studies)

The implantation induced disordering of intermetallic compounds is studied using the CEMS technique. The results mainly concern a magnetic transition in Fe−Al 40%at. and the crystallization process in⁵⁷Fe implanted Ni−Ti 50%at.