J. P. Riviere

A new technique for fullerene onion formation

We present an original technique for growing large fullerene onions: carbon-ion implantation at high temperature into copper substrates. Used for carbon film growth (diamond or turbostratic carbon), this method is based on the immiscibility of carbon into copper and can produce an important density of giant carbon onions with size up to some micrometres which is the largest size observed up to now. We characterize these giant fullerenes by TEM, HRTEM and for the first time with AFM. On the basis of both experimental and numerical results we propose a mechanism of formation of the carbon onions during the implantation process.

Stacking fault energy in sapphire (α-Al203)

Abstract Stacking faults associated with climb-dissociated basal and prism plane dislocations in sapphire (α-Al2O3) after plastic deformation at elevated temperatures have been studied. In both cases, the fault vector is 1 3 〈1010〉 and it is only the cation sublattice which is faulted. The fault energy on and planes are similar, between 0.1 and 0.25 J/m2. Analysis of the geometry of the 1 3 〈1010〉 fault show that one vacancy and two distinct interstitial faults are possible in this structure; one of the interstitial faults is thought to have the lowest energy.

Material flow under an indentor in indium phosphide

Single crystals of indium phosphide, oriented in the 〈001〉 direction and at the temperature of 400 °C, have been deformed by a Vickers indentor. The generation and the development of the dislocations was deduced from the topographical observations of the deformed samples. The dislocation distribution under the indented surface was explained taking into account the dislocation interactions. Finally, both aspects have allowed a greater understanding of material flow under the indentor to be presented.

Indentation-induced deformations of GaAs(011) at a high temperature

Indentation tests were performed at a high temperature on GaAs(011). This orientation allowed the activation of normal and inclined slip systems. Samples with two different thicknesses were prepared and a large range of loads was used. Observations on decreasing scales were carried out using different microscopies and more particularly transmission electron microscopy on thin foils prepared by the focused-ion-beam technique. The back side of the thinnest samples could be deformed using the highest loads. The deformation was observed to be anisotropic on the back side as well as at the indented surface. On one side of the indentation, an anisotropic climb of matter was revealed and associated with microtwinning development. Convergent-beam electron diffraction as well as chemical etching allowed us to determine rigorously the polarity of the samples and the character of dislocations ( for g) generated by the indenter. The dislocations extending deeper into the samples were determined to be fdislocations. This result was discussed in view of the difference between the core reconstructions and mobilities of fand gdislocations.

Indentation punching through thin (011) InP

Thin (011) InP samples have been deformed by a Vickers indenter at 400°C under loads ranged between 0.4 N and 2.35 N. Profilometry, optical microscopy as well as scanning electron microscopy in the cathodoluminescent mode were used to get a better understanding of the plastic flow through thin samples. For the thinnest samples and highest loads, punching through the sample was detected at the opposite face. In this case, no pile up around the indent site was detected. A model describing the material flow through the samples is proposed.

Fullerene onion formation by carbon-ion implantation into copper

We have performed high-dose carbon-ion implantations into copper substrates at high temperature with the objective of producing single crystalline diamond thin films. An important density of giant carbon onions has been identified in a turbostratic graphite layer formed on the copper surface. We have characterized these giant fullerenes (up to 1 μm in diameter) by transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and electron energy loss spectroscopy (EELS), and we propose two possible mechanisms of formation of the carbon onions during the implantation process.

Material Flow at the Surface of Indented Indium Phosphide

Single crystals of indium phosphide oriented in the (001) direction have been deformed by microhardness indentation. The surface topography was observed by interferential optical microscopy and scanning electron microscopy in the secondary electron mode. The dislocation distribution and their nature at the surface were investigated by scanning electron microscopy in the cathodoluminescent mode and transmission electron microscopy. Both observations have led us to a better understanding of the material flow at the surface sample when it is indented.

Vickers indentation of thin GaAs (001) samples

Thin GaAs (001) samples have been deformed using a Vickers indenter at temperatures around 350°C under loads ranging between 0.4 and 2.35 N. Optical microscopy, optical interferometry and transmission electron microscopy were used to obtain a better understanding of the plastic flow through the specimens. Anisotropic plastic flow through the thin foils could be detected at the face opposite to the indented face under large loads. In this case pile-up at the indented surface progressively vanished. An α-dislocation-based model describing the material flow through the samples is proposed.

Characterization and growth of carbon phases synthesized by high temperature carbon ion implantation into copper

Abstract In the early 1990s, a new process using high dose carbon-ion implantation into hot copper substrates was proposed to synthesize heteroepitaxial diamond thin films onto copper. In order to determine the parameter that controls diamond formation, we have performed the same kind of experiments, varying systematically implantation parameters. Whatever the experimental conditions are, we have characterized a uniform (0001)-oriented graphite layer and carbon onions onto the implanted copper substrate but never diamond. We propose a growth mechanism for the different carbon phases based on copper preferential sputtering, carbon diffusion and discharge phenomena.

Transmission electron microscope observations of dislocations in heteroepitaxial layers of CdTe-(CdHg)Te on GaAs

Abstract Growth of (CdHg)Te on GaAs has been performed by metal-organic vapor phase epitaxy (MOVPE) with ZnTe as a buffer. The various steps of the deposition have been studied by transmission electron microscopy with a special emphasis on dislocation generation. The high density of dislocations is a consequence of the large misfit between the substrate and the II–VI semiconductors. The intercalation of strained layers is not under control in order to decrease the number of dislocations in the upper part of the system.