Ph. Goudeau

Characterization of photoluminescent porous Si by small‐angle scattering of x rays

A microstructural study of high‐porosity porous silicon layers formed on lightly P‐doped wafers has been performed by x‐ray small‐angle scattering (SAXS) using the powerful and parallel beam of the synchrotron radiation. When the porosity of the sample is increased from 55% to 85% there is a continuous modification in the shape of the scattering profiles. The silicon skeleton mass fractal dimension decreases continuously. For porosity around 85%, the value for which the sample starts to display a strong photoluminescence at room temperature, there is a large increase in the pore size. The scattering profiles are characteristic of an isotropic three‐dimensional structure.

Effect of the hydrogen on the intrinsic stress in hydrogenated amorphous carbon films deposited from an electron cyclotron resonance plasma

The intrinsic stresses have been investigated in detail in particular diamondlike carbon films prepared by chemical vapor deposition assisted by electron cyclotron resonance plasma, as a function of the substrate bias and sample thickness in relation with the H content and bonding. Combined infrared absorption, elastic recoil detection analysis, and residual stress measurements are used to fully characterize the films in their as deposited state. The results indicate clearly that both the low and high biased samples exhibit compressive stresses. The stresses are found to be higher in the high biased films and are affected not only by the [H]/[C] ratio but also by the C–H and C–C volumetric distortions.

Determination of the residual stress tensor in Cu/W multilayers by x‐ray diffraction

A direct determination of the residual stress tensor in Cu/W multilayers has been performed by x‐ray diffraction using the ‘‘sin2 ψ’’ method. In tungsten sublayers, we found a compressive and isotropic stress in the plane parallel to the multilayer surface of a very high value equal to −6.4 GPa. Furthermore, using stress‐strain relations, the tungsten lattice structure resulting from strains is calculated: the strained W bcc structure is found to be similar to a monoclinic‐like structure leading to important modifications of the diffraction pattern.

X‐ray small‐angle scattering analysis of porous silicon layers

A small‐angle x‐ray scattering study of porous layers prepared on lightly doped and heavily doped silicon wafers reveals strong differences according to the dopant type. The p‐type silicon layers show a roughness between matter and voids below a space‐correlation length of about 10 nm and a fractal dimension of aggregates for a length scale higher than 25 nm. The lightly doped n‐type is different: the scattering curve obeys the Porod law according to the rod‐like structure of the pores. However, the structure of the heavily doped p+ sample is more complicated and not yet well understood.A small‐angle x‐ray scattering study of porous layers prepared on lightly doped and heavily doped silicon wafers reveals strong differences according to the dopant type. The p‐type silicon layers show a roughness between matter and voids below a space‐correlation length of about 10 nm and a fractal dimension of aggregates for a length scale higher than 25 nm. The lightly doped n‐type is different: the scattering curve obeys the Porod law according to the rod‐like structure of the pores. However, the structure of the heavily doped p+ sample is more complicated and not yet well understood.

Determination of elastic constants of a fiber-textured gold film by combining synchrotron x-ray diffraction and in situ tensile testing

The elastic behavior of gold thin films deposited onto Kapton substrate has been studied using in situ tensile tester in a four-circle goniometer on a synchrotron beam line (LURE facility, France). The mechanical description of the substrate-thin film composite structure has been developed to determine the stress tensor in the film while the strong {111} fiber texture was taken into account using the crystallite group method (CGM). CGM strain analysis allowed us to forecast the nonlinear relationship between strain and sin2Ψ obtained for the thin films due to the strong anisotropy of gold. A least-square method was used to fit the overall experimental data with good accuracy and allows determining all single-crystal elastic constants.

Small‐angle x‐ray scattering study of anodically oxidized porous silicon layers

Small‐angle x‐ray scattering was used to investigate the microstructural change induced by electrochemical oxidation of porous silicon (PS) layers. It is shown that when the oxidation level increases, the size of the crystalline Si domains, which constitute the PS layer, decreases. This size reduction is correlated to the blue‐shift observed in the photoluminescence spectra when the oxidation level is increased. Moreover, we found that a ‘‘fuzzy’’ surface appears between pores (voids) and matter when the samples are electrochemically oxidized. This interface is found very sharp for the as‐prepared and nonoxidized PS layers.

Tungsten phase transformation induced by low-fluence Ar irradiation in CuW multilayers

Abstract Changes occurring in equiatomic CuW superlattices, prepared by direct sputtering, after low-fluence 300 keV Ar2+ ion irradiation were investigated by X-ray diffraction. The profiles were measured in θ–2θ geometry. A shift of satellite superlattice peaks to higher 2θ angles was observed for ion doses up to 2 × 1014ions/cm2. There were no further changes in peak position for higher doses. This effect cannot be interpreted as being caused by an ion mixing process in the copper-tungsten interface regions nor by stress relaxation effects. X-ray diffraction measurements performed on a pure tungsten layer, 1000 A thick and prepared in the same conditions as the superlattices, revealed the presence of the β-W phase. After 300 keV Ar2+ ion irradiation with low dose (2 × 1014ions/cm2), the 110 peak of the α-W structure appeared whereas the 210 peak of the β-W phase disappeared in the X-ray diffraction profile. Thus, during the first stages of irradiation, the transformation from β to α phase occurred in tungsten sublayers.

Modification of Cu—W superlattices by ion irradiation

Abstract The structure of low temperature ion irradiated Cu-W superlattices is investigated by small and large angle X-ray diffraction. During the initial stages of irradiation a large shift of the superlattice peaks to higher 2.Theta; angles is observed. This shift indicates the decrease of the superlattice period (0.9–1.4%). This effect is attributed to a stress relaxation process during ion irradiation. For higher ion doses, the formation of Cu-rich and W-rich solid solutions in thin layers in all interfacial regions is evidenced. The study shows that limited miscibility in this thermodynamically “immiscible” system is possible.

Residual stress determination by X-ray diffraction in tungsten thin films

Abstract In this study, the complete residual stress tensor has been determined by X-ray diffraction, using the sin 2 ψ method, in 1000 and 2500 A tungsten thin films deposited by ion beam sputtering on a silicon monocrystal. In the first case, we found very high tension stresses (about 1.5 GPa) for the as-prepared state and important compressive stresses (about – 1.3 GPa) after an implantation with a dose of 10 16 Xe 2+ ions/cm 2 at 320 keV. In the second case, the film was almost detached from its substrate and the stresses were compressive (about – 0.9 GPa). In all cases, the free-stress lattice parameter was different from the bulk one, indicating significant differences between the microstructure of these thin tungsten films and the one of the bulk. The size of the coherent domains of diffraction was also determined and was found to largely vary from one case to the other.

Interface of the CuW multilayers

Abstract The interface of the CuW system is investigated using small and large-angle X-ray diffraction (SAXRD, LAXRD) and high resolution transmission electron microscopy (HRTEM). Analysis of the spectra is performed using the ‘statistical’ model of the superlattice structure. The CuW superlattices reveal sharp interface with a rms roughness less than 2 ML (monolayers). Cross-sections of the CuW multilayers are analysed by HRTEM in a JEM 3010. Micrographs show a misorientation between copper and tungsten monolayers of about 5°. In other micrographs continuity of plans crossing the CuW interface with the same misorientation is found.