J. Dixmier

Bimodal crystal size distribution in annealed r.f. magnetron silicon films: a memory effect of the local order inhomogeneities in the initial amorphous state

Abstract Microcrystalline silicon ( μ c-Si) layers have been obtained by thermal annealing of amorphous films prepared by radio frequency (r.f.) magnetron sputtering. X-ray diffraction (XRD) and Raman spectra were measured. A systematic effect has been observed in these samples on both the diffraction lines and the Raman spectrum profiles, i.e., a distribution of the crystal size peaking at two different means. The diffraction pattern has tails superimposed on the 111, 220, 311 powder lines, while the Raman spectra have a shoulder on the low wave number side of the 520-cm −1 band at about 500 cm −1 . A relationship is established between this effect and the local order inhomogeneities observed in the initial amorphous state by XRD. The first halo of the diffraction pattern can be reproduced by two components, one being located on the low angle side (left side) of the theoretical 111 line of c-Si (relaxed domains), the other one on its right side (disordered domains). This bimodal size distribution is the result of heterogeneous nucleation and crystal growth process during the amorphous–crystalline transition. Relaxed domains favor a nucleation rate leading to small crystals, while disordered domains increase the nucleation activation energy, i.e., yield fewer nuclei and larger crystals.

Studies of evaporated amorphous GeSe2 films as a function of annealing

The optical properties of evaporated amorphous GeSe 2 films have been determined before and after annealing by transmission and photothermal deflection spectroscopy measurements. The results are analyzed together with those of X-ray photoemission and X-ray diffraction experimemts. The annealing effects are related to changes in medium-range order. The low-energy optical absorption shows a defect state density varying with deposition conditions and annealing

X-ray diffraction investigation of polymer-like hydrogenated amorphous carbon films

Abstract Structural properties of polymer-like amorphous carbon (a-C:H) films grown in a dual-plasma (microwave (MW) assisted radio frequency (RF)) reactor have been investigated. An interesting transition appears as the film density increases due to increasing ion energy: (1) in situ infrared ellipsometry shows a transition in the C–H bonding modes corresponding to carbon skeleton cross-linking, (2) a quenching of the photoluminescence (PL) efficiency is observed when film density is >1.3 g cm −3 . To analyze the origin of such an evolution, X-ray diffraction investigations have been performed on a-C:H powders with densities increasing from 0.9 to 1.7 g cm −3 . This paper reports on X-ray measurements performed in transmission geometry using the high photon flux at LURE facilities. The data show differences between the samples in the structure factor, S ( K ), and in the pair correlation function, G ( r ). X-ray spectra have pre-peaks in the vicinity of 1 A −1 , which change in position and shape with the density of the powders. The contraction of the first distances, C–C, is observed as the density increases, from 0.152±0.002 nm for transparent and soft films to 0.142±0.002 nm for the denser one. The evolution of C-skeleton structure is described in terms of local co-ordination, in relation with the C–H bonding.

An AWAXS study of CoErB ternary amorphous metallic alloys

Amorphous Co79 - x - yErxB21 + y alloys, with x < 10 at.% and y < 3 at.%, belong to the series of ternary transition metal-rare earth-metalloid glasses of great interest for their high coercivity and magnetization. An anomalous wide angle X-ray scattering study has been performed on a series of metallic glasses in order to relate their magnetic behaviour to their local and medium range order. Due to the large difference in size and electronic number, Z, between the three components, this technique allows the determination of the surroundings of the cobalt and erbium atoms and the discrimination of the CoCo, ErEr and CoEr correlations in the first coordination shell. A competition between the topological disorder and a chemical ordering in the short and medium range occurs when the Er content increases, which may influence their magnetic and thermodynamic properties.

Investigation of the structural disorder fluctuations in a a-Si:H films by coupled X-ray diffractometry and photodeflection spectroscopy

Abstract The full width at half maximum (FWHM) of the first diffraction peak and the width of the optical absorption edge E o (Urbach edge) have been measured on glow discharge (GD) and sputtered (SP) prepared a-Si:H samples. The coherence length L, derived from the FWHM has been plotted vs E o and also vs the optical gap E g . It is shown that L increases when E o decreases. The values of L are always found larger for GD samples than for SP films. The Si matrix relaxation by H atoms is demonstrated in GD materials through an increase of L with E g . This is not the case for SP materials.

Intermediate range order in pure and hydrogenated thin amorphous Si films

Abstract One micrometer thick pure and hydrogenated Si films have been prepared by DC triode sputtering onto Si single crystals for coupled X ray and Infra-red characterization. Topological features of the amorphous relaxation process and transition to the microcrystalline state are described and associated with modifications of the atomic population under the peaks of the radial distribution function corresponding to intermediate range order (I.R.O.). Hydrogenated material I.R.O. lies in between that observed in unrelaxed and relaxed pure a. Si films. The indirect effect of SiH bond conformation on the Si network structure is also investigated.

Structural inhomogeneities in amorphous silicon layers observed by X-ray diffraction and Raman scattering

Abstract Structural inhomogeneities in amorphous silicon layers, prepared by r.f. magnetron sputtering, were detected and characterized by X-ray diffraction (XRD) and Raman scattering using samples either as-deposited or post-annealed at increasing temperatures. These inhomogeneities, which can be interpreted in terms of disordered domains around the voids and which depend on the annealing temperature, are identified through analysis of the first halo profiles of XRD patterns as well as of the low-frequency part of the Raman spectra. The first halo profile has been well reproduced by using two components, one located at the low wave vector (left side) of the 111 line of c-Si (relaxed domains), the other one at the other side (disordered domains). The Raman spectra at low frequency (ω

Short-range order in CoErB metallic glasses

The anomalous wide-angle X-ray scattering (AWAXS) technique has been used for the determination of the total and differential structure factors of amorphous ternary Co 79-x Er x B 21 alloys. Three melt-spun ribbons with x=3.9, 7.5 and 9.5 at.% have been investigated. The experiment at the Co K edge has allowed us to extract the total and differential structure factor for each concentration and to calculate the differential distribution of pairs around cobalt. A preliminary analysis of the results shows that an important modification of the local order of Co atoms takes place in alloys with more than 7.5 at.% Er

Unusual magnetron sputtered a-Si:H materials obtained at high deposition rates as favourable precursors for the preparation of large-grain-size crystallized thin silicon films

Abstract This paper reports the great variations observed in the properties of both amorphous and thermally crystallized amorphous sputtered silicon on increasing the deposition rate. Unusual amorphous materials are obtained at high deposition rate ( r d >10 A /s ), which display a very low bandgap despite a high hydrogen content (a tauc gap = 1.50 eV when the hydrogen concentration is 20%). The increase of the deposition rate is shown to produce effects on bandgap, hydrogen bonding and content, strictly opposite to the effects observed in the case of the deposition by the PECVD of He-diluted silane. Upon crystallization, these high-rate-deposited a-Si:H films yield grains of drastically larger size (210 A) than the low-rate-deposited samples (85 A).

Structural, optical and transport properties of sputtered hydrogenated amorphous silicon films in relation to Si-H bonding configurations

Abstract The hypothesis of a relationship between the structural effects of hydrogen on the Si matrix and the electronic structure of hydrogenated a-Si has been tested on d.c, sputtered 1 μm thick a-Sit-x H x films, with x ranging from 0 to 9 at.%. Comparative optical, electrical and X-ray diffractometry measurements have been performed on samples in which different kinds of H distribution and Si-H bonds were achieved by varying the total pressure (P tot) of Ar and H2 and the substrate temperature (T s). For H concentrations in the range 0–5 at.%, materials with either a predominant 2000cm−1 or 2100cm−1 infrared (i.r.) absorption stretching band could be prepared (without the 890cm−1 bending mode). It has been observed that, for a given H content, the optical gaps of these two materials are the same, despite the fact that their atomic distribution functions (ADF) exhibit significant differences in the region 4–6 A. The behaviour of the dark conductivity α with temperature is sensitive to the type of H dis...