J. Beauvillain

Cross‐sectional high‐resolution electron microscopy investigation of argon‐ion implantation‐induced amorphization of silicon

Cross‐sectional high‐resolution transmission electron microscopy and related diffraction techniques are applied to the characterization of argon implantation‐induced amorphization of silicon at room temperature. Damage calculations have been performed to provide a theoretical support for the cross‐sectional transmission electron microscopy observations. It is shown that the amorphous‐crystalline interfacial roughness is strongly dependent on ion dose and hence on its depth location. The a‐c transition region was found to have sharply defined boundaries and sometimes exhibits defects such as dislocations and stacking‐fault nuclei. Combining the experimental measurement of the extension of the a layer for increasing dose, with concepts arising from the ‘‘critical damage energy density’’ model leads to a value of about 10 eV/atom for the c→a transformation. It is suggested that temperature effects are responsible for the observation that higher damage energy densities are apparently needed to produce a first...

Comparative study of micro- and ultrafiltration membranes using STM, AFM and SEM techniques

Abstract In this work, Nuclepore ultrafiltration membranes are studied by various techniques (STM, AFM and SEM), in order to determine the method best suited for the study considered. AFM allows direct measurement of pore density and turns out to be highly reliable. However, in terms of surface corrugation, this technique remains limited at high magnifications. Despite the conductor film deposition needed for achieving a tunnel effect, STM yields the best resolution for defining surface corrugation. With respect to the study of ultrafiltration membranes, the resolution obtained from STM or AFM is much better than that of SEM whose electron beam also damages the polymer surface. These results are confirmed by the STM study of organic sulphonated polysulphone membranes.

Metal/n-CdTe interfaces: A study of electrical contacts by deep level transient spectroscopy and ballistic electron emission microscopy

This paper summarises the characteristics of chemically etched CdTe surfaces obtained by photoluminescence studies and the results of extensive transport measurements involving metal contacts fabricated on them. Fermi level pinning at five discrete levels; 0.40 +/- 0.02, 0.65 +/- 0.02, 0.73 +/- 0.02, 0.96 +/- 0.04 and 1.18 +/- 0.02 eV has been observed. Deep level transient spectroscopy (DLTS) and ballistic electron emission microscopy (BEEM) experiments have been performed on contacts made under the same conditions to compare and confirm these results. DLTS reveal similar values for electron traps in the band gap confirming a relationship between Fermi level pinning and bulk defect levels. BEEM experiments performed on contacts showing I-V barrier heights of 0.96 eV reveal significant planar non-uniformity but confirm 0.96 eV as the controlling barrier height or charge transport across the junction

A spatial damage energy distribution calculation for ion-implanted materials

Abstract A simple method allowing easy calculation of the spatial damage energy distributions for ion-implanted materials is presented. The direct procedure takes account of the variation with depth of the lateral spreading of implanted ions, as well as the effects of energy transport by the recoiling target atoms. The subsequent computer program LUPIN-3D provides three-dimensional damage distributions and allows the construction of damage energy mappings. Various substrates of technological interest are investigated and several fields of application of the calculation are envisaged. The density of cascades can therefore be determined and heterogeneous amorphization models can be implemented.

Schottky barrier formation at metal/n-ZnSe interfaces and characterization of Au/n-ZnSe by ballistic electron emission microscopy

Current transport and ballistic electron emission microscopy (BEEM) studies have been carried out on metal contacts fabricated on chemically etched n-ZnSe epitaxial layers grown by molecular beam epitaxy. The contact materials Ag, Sb, Au, Ge/Au, Sn, Ni, and Pd form one or more barrier heights out of the following seven discrete values: 0.90, 1.20, 1.32, 1.50, 1.67, 1.80, and 2.10±0.04 eV observed to date. BEEM work carried out on Au/n-ZnSe systems has identified four levels 1.32 [Morgan et al., J. Appl. Phys. 79, 1532 (1996)], 1.50, 1.67 [Coratger et al., Phys. Rev. B 15, 2357 (1995)] and 1.80 eV to date, confirming Fermi-level pinning at different positions. Schottky barrier formation at metal/n-ZnSe systems cannot be explained by the simple Schottky model. The strong Fermi-level pinning observed could be due to bulk and/or surface defects of the ZnSe material.

Comparison between “intermediate”- and “heavy”-ion-bombardment-induced silicon amorphization at room temperature☆

Abstract Cross-sectional electron microscopy and related diffraction techniques have been applied to the characterization of argon- and xenon-bombardment-induced amorphization of silicon at room temperature. “Damage” calculations have been performed to provide a theoretical support to the observations. Combining the experimental measurement of the extension of the amorphous layer for increasing doses with concepts arising from the “critical damage energy density” model leads to E dc values of about 4 eV atom −1 and 10 eV atom −1 for xenon and argon respectively, for the crystalline-to-amorphous transformation to occur. It is then suggested that “heavy” ions in contrast with “light” or “intermediate” ions are as efficient at room temperature for producing an amorphous layer as at low temperatures.

Kinetics of silicon amorphization by N+ implantation: Dose rate and substrate temperature effects

Abstract We have observed by cross-sectional electron microscopy the kinetics of silicon amorphization by nitrogen implantation as functions of the dose rate and substrate temperature for 40 keV and 20 keV beam energies. It is shown that amorphization occurs through the accumulation of point defects or complexes. The progression of the c-a interface for increasing dose can be accurately described by the critical damage energy density model (CDED) assuming a CDED value of 30 eV atom −1 for a 40 keV implantation at room temperature using a beam current density of 1.6 μA cm −2 . When increasing the dose rate, the efficiency of the amorphization process is improved, suggesting that the generation rate of point defects is a crucial parameter in the case of light ion-induced amorphization. It is finally shown that higher dose rates and low substrate temperature are to be used to promote the complete amorphization of the substrate by light ion implantation.

3D simulations of ion implantation processes

Abstract We present a simple theoretical approach and a few calculations that shed light on the slowing down process of the ion itself and of the motion of recoil atoms. The subsequent computer code LUPIN-3D provides three-dimensional concentration and damage energy mappings due to a single ion impact. Hence, the effect of implantation through an opening in a mask can be described. Two systems, P/Si, 100 keV and Si/GaAs, 100 keV are taken as examples for this work and we show that the geometry of the dopant profile and of the amorphous layer created beneath the opening by the bombardment can be predicted.

Scanning tunneling microscopy of a liquid crystalline phase of poly((dA-dT) · (dA-dT)) induced by a histone H1 peptide

In this report, we present the first observations of uncoated poly((dA-dT).(dA-dT)) molecules organized in a liquid crystalline phase induced by the binding of a histone H1 peptide. The effect of the peptide on the polymer condensation is clearly illustrated on the large-scale STM images which reveal a well defined spacing between parallel DNA helices. High resolution images of rare isolated molecules of poly((dA-dT).(dA-dT)) exhibit two sets of helical pitch values, 6 and 7.5 nm. While the lower value can be correlated with the pitch of poly((dA-dT).(dA-dT)), the larger one may arise from peptide binding in the polymer minor groove.

Two‐dimensional damage distribution induced by ion implantation in Si under arbitrarily shaped mask edges: Simulations and cross‐sectional transmission electron microscopy observations

A method is presented to calculate two‐dimensional defect distributions induced by ion implantation through openings in a masking layer. It is shown that a realistic description of this model requires depth‐dependent lateral standard deviations to describe the dopant and the damage point response functions. Further refinements of the theory include arbitrary shapes for the mask edges and different materials in the masking layer and in the substrate. Cross‐sectional electron microscopy observations have been carried out to visualize the two‐dimensional extension of amorphous layers created by As implantation in silicon for different mask edge angles. It is shown that the theory fits well the cross‐sectional transmission electron microscopy observations. More generally, this study shows that for abrupt mask edges, the lateral extension of the two‐dimensional defect profile beneath the mask edge is directly governed by scattering of the ions and of the subsequent recoil atoms and, as a direct consequence, by...