On the basis of the Brandt–Ritchie model, we use the calculated Valence Band Density Of electronic States to explain the selectivity of the chemical modifications induced by ion irradiation in cellulose nitrate and cellulose acetate. Some consequences pertaining to the characteristics of the valence band structure are deduced with a view to electronic applications. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 319–323, 1998

A physical model is presented that aims at rationalizing the selectivity of bond breakage observed when polymethylmethacrylate is irradiated by ions in the 10-500 keV energy range. This model, previously proposed by Brandt and Ritchie, is based on electronic collective effects. The coupling between the pure plasma oscillation at omega(p) and the oscillation of free electrons at [omega(k0)(2)](1/2) makes the whole electronic population resonant at the frequency omega(rp) = (omega(p)(2) + [omega(k0)(2)])(1/2). By computing the valence-band density of states, we are calculate [omega(k0)(2)] and then to deduce the theoretical value of omega(rp). On the other hand, we provide an experimental measurement of omega(rp) and study its dependence on ion fluence by electron-energy-loss spectroscopy. The validity of the model of Brandt and Ritchie is then discussed in the light of both theoretical and experimental data.

High energy argon ion implantation was used to form, in intentionally gold or platinum contamined silicon samples, a buried layer of efficient gettering sinks with low damage creation close to the surface. In any case, the implantation temperature was chosen to avoid partial or complete amorphization.Both nature and long term stability of these centers have been determined by Transmission Electron Microscopy (TEM) and channeling measurements. The kinetics of gold accumulation on these sinks was measured using high sensitivity Rutherford Backscattering (RBS) analysis as a function of implantation dose and annealing temperature. The effect of initial metallic contamination concentration was also investigated.The results are discussed using a model which takes into account a trapping-detrapping reaction and an impurity dependent annealing behaviour of the gettering sites.

The aim of the present work is to investigate by electron energy loss spectroscopy the structural differences between oxygen-doped aluminium nitride deposits (AlON) which are characterized by strong changes in their surface morphology. The deposits have been obtained by chemical vapour deposition using AlCl3 and NH3 as precursors. Progressive addition of N2O in the gas mixture makes possible the introduction of oxygen atoms in the 2H-AlN lattice. Quantitative analysis suggests that well-crystallized materials showing a feather-like surface morphology correspond to the insertion of oxygen atoms in the empty sites of the AlN structure, while for less-crystallized materials, associated with spherolitic surface morphology and a higher oxygen content, the oxygen atoms are substituted for nitrogen atoms. These two kinds of localization for the oxygen atoms can be deduced from the radial distribution function, which was determined by analysing the extended energy loss fine structure, observed on the aluminium, nitrogen and oxygen K-edges.

Oxidation tests were performed (at 500 < T < 900-degrees-C), on (a) as-received T300 fiber, (b) PyC-infiltrated tows, and (c) C/PvC/SiC composite. The goal was to assess which carbonaceous constituent exhibits the highest reactivity with oxygen in the composites. TGA and TEM were used to establish the relationship between the behaviour of the materials in oxygen and their nano/microtexture. In the as-processed state, the overall oxidation rate of the fiber is higher than that of the PyC-interphase, whereas both constituents behave in a similar way after an annealing treatment at 1600-degrees-C. Beyond 700-degrees-C, the rate-determining step in the oxidation of uncoated fibers is diffusion transport in the external stagnant boundary layer. Below 700-degrees-C, it is a mixed in-pore diffusion/surface reaction mode for the as-received fibers and mainly surface reaction for the annealed fibers. The oxidation of the fiber is selective. In cross-section, it occurs more rapidly in the outer zone, owing to the high porosity of this specific zone. The occurrence of a high porosity zone very near the PyC interphase plays a kev role in understanding the effect of environment on the mechanical behaviour of the composites.

Specimens of single-crystal alpha-Al2O3 in the [0001] orientation have been implanted at -185-degrees-C with either 4 x 10(16) Al cm-2 and 6 x 10(16) O cm-2 or with 4 x 10(16)Fe cm-2. In both cases, amorphous layers were produced which extended from the surface to a depth of approximately 170 nm. Investigation of the response of the amorphous material to post-implantation thermal treatments has revealed significant differences. When annealed for 1 h at 960-degrees-C in argon, the material made amorphous by implantation with a stoichiometric ratio of aluminium and oxygen recrystallized into a dual-phase microstructure consisting of gamma-Al2O3, a cubic transitional form, and epitactical alpha-Al2O3. In contrast, when treated under similar conditions, the material made amorphous by implantation with iron recrystallized completely to epitactical alpha-Al2O3. These differences suggest that fundamental structural and chemical differences exist in the as-implanted state. The analysis of extended energy loss fine structure (EXELFS) in electron energy loss spectra obtained using an analytical electron microscope has been used to investigate these differences. The Al-O interatomic distance measured in the material made amorphous by implantation with a stoichiometric ratio of aluminium and oxygen is 0.170 nm in agreement with the value measured for gamma-Al2O3, the form into which it first recrystallizes. Similarly, the Al-O interatomic distance measured for the material made amorphous by implantation with iron is 0.185 nm, which agrees with the value measured for alpha-Al2O3, the form into which it recrystallizes. The results of the EXELFS analyses confirm the existence of underlying structural differences in amorphous materials.

It is already established that a nitrogen content in carbon fibres induces poor high tensile strength properties of the fibres. Up to now the nitrogen localization in the fibre, particularly along the diameter, was not known, due to the small size of the fibres (7 μm) and the insufficient sensitivity of the usual analytical techniques, using X-rays or ion beam for instance, for such low atomic number elements (nitrogen and carbon). By using electron Energy Loss Spectroscopy (EELS) in a Philips EM 400T microscope equipped with a V.G. electron spectrometer, we have determined this distribution for the Toray 300 carbon fibre. The measurements have been made by using the carbon and nitrogen K edge intensity when EEL spectra correspond to thin enough samples, thickness ≤ 500 Å. The accuracy of this determination is on the order of 10%. In this way, we have measured a NC atomic concentration varying from 2 to 7%. For all the Toray 300 fibres a similar variation of the ratio is observed. The nitrogen content is low in the core of the fibre, about 2%. It remains practically constant in the whole center of the fibre and grows rapidly to 6–7% in the periphery. These measurements reveal a skin core concentration gradient effect in the high tensile strength fibres. They confirm that it is necessary to avoid this structure if one desires ultra-high mechanical properties for the fibres.

High tensile strength properties of carbon fibres used in composite materials are very dependent on the nitrogen distribution in the fibre, in spite of a few percent nitrogen content. The nitrogen concentration profile in the diameter of the fibre has been determined by quantitative EELS. It shows a particular distribution with a higher concentration near the surface of the fibre.

Aluminium oxalate decomposition at high temperature produces various allotropic forms of alumina. An extended electron energy loss fine structure (EXELFS) analysis above the oxygen and aluminium K edges has been applied to a study of these structures. By considering the distance associated with the first Al-O bond-length the gamma and alpha alumina phases have been characterized. For the crystalline samples, got by heating above 700-degrees-C, the EXELFS measurement are in very good agreement with crystallographic informations deduced from x-ray or electron diffraction. The EXELFS technique has allowed us to characterize the morphology of the amorphous alumina which are produced in the first phase of the decomposition at 400-degrees-C. An organization of the gamma-Al2O3 or alpha-Al2O3 types can be characterized depending on the atmosphere, air or H2, in which the aluminium oxalate decomposition is achieved. These results confirm the viability of the EXELFS technique in TEM.

The present developments of electron energy analysis in the microscopes by E.E.L.S. allow an accurate recording of the spectra and of their different complex structures associated with the inner shell electron excitation by the incident electrons (1). Among these structures, the Extended Energy Loss Fine Structures (EXELFS) are of particular interest. They are equivalent to the well known EXAFS oscillations in X-ray absorption spectroscopy. Due to the EELS characteristic, the Fourier analysis of EXELFS oscillations appears as a promising technique for the characterization of composite materials, the major constituents of which are low Z elements. Using EXELFS, we have developed a microstructural study of carbon fibers. This analysis concerns the carbon K edge, which appears in the spectra at 285 eV. The purpose of the paper is to compare the local short range order, determined by this way in the case of Courtauld HTS and P100 ex-polyacrylonitrile carbon fibers, which are high tensile strength (HTS) and high modulus (HM) fibers respectively.

The electron energy loss spectra can be considered as the result of the convolution of elementary inelastic scattering processes (1, 2). We have developed a procedure which allows to write the intensity of the spectrum as a function of the energy loss.These calculations take the electron angular scattering into account.The probability for an electron to suffer an energy loss E and to be deviated through an angle after a single electron-electron interaction of any kind is given by a normalized function D(E, ), which can be written with a good approximation as a product of two functions g(E) and f(), separately normalized. Assuming that the excitation probabilities of any interaction follows a Poisson distribution, for a collection angle θd the intensity of the spectrum can be written in the Fourier space :Gs(ω) is the Fourier transform of GS(E) which characterizes the transfer function of the experimental device.

In electron beam lithography the interactions between the incident electrons and the molecules of the resist lead to a chemical modification of the polymer. In order to understand the various processes which occur, we have used the technique of electron energy-loss spectroscopy (EELS). The detection of plasmons and characteristic signals associated with atomic deep level excitations in the high-energy region of the spectrum allows the chemical elements in a given volume of the specimen to be identified and localized. By measuring the intensity of the characteristic signal associated with a given element it is also possible to estimate the number of atoms of this element present in the volume analyzed. The evolution of the energy-loss spectrum during electron irradiation gives information on the structural modification and on the mass loss of the specimen as a function of the dose. In electron lithography the pattern dimensions vary with the energy deposited in the resist and consequently are related to the time exposure to the beam. The results obtained by EELS allow the evolution of the resist during irradiation to be followed.

Amorphous phases have been shown to influence properties of many metallic, semiconducting, and ceramic materials. However, analysis of these phases presents a difficult challenge since most conventional characterization techniques provide only limited qualitative information. Extended Energy Loss Fine Structure (EXELFS) analysis is a technique which is sensitive to both structure and composition within near neighbor distances of specific types of atoms in both crystalline and amorphous materials. The fine structure, which is present in the form of modulations on the core loss edges of electron energy loss spectra, results from diffraction of ejected core electrons by neighboring atoms. The ability to obtain EXELFS measurements with an analytical electron microscope allows direct observation of changes in composition, microstructure, and local atomic environment at a spatial resolution (<100 nm) not attainable by other techniques.Recently an investigation of the effects of ion implantation on the microstructure and properties of A12O3has revealed differences in the response of various forms of amorphous A12O3to post-implantation annealing.

The near edge fine structure and the extended energy loss fine structure are analyzed in the case of the boron and nitrogen K edges from boron nitride electron energy loss spectra. The analysis provides information relevant to the electronic states and structure of the material.

A general convolution procedure based on the Fourier transform is proposed for the prediction of electron energy loss spectra which may be described in terms of several characteristic inelastic scattering processes. The angular scattering and the instrument response are taken into account. The procedure is illustrated by considering the energy loss spectra of carbon films of different thicknesses and good agreement is found between observed and calculated spectra for energy losses less than about five hundred eV.