Publications

2007

• Intervalley scattering in GaAs: ab initio calculation of the effective parameters for Monte Carlo simulations
  
  • Sjakste J.
  • Tyuterev V.
  • Vast N.
  Applied physics. A, Materials science & processing, Springer Verlag, 2007, 86 (3), pp.301-307. (10.1007/s00339-006-3786-7)
  DOI : 10.1007/s00339-006-3786-7
• Positron annihilation characteristics in UO$_2$: For lattice and vacancy defects induced by electron irradiation
  
  • Barthe M.-F.
  • Labrim H.
  • Gentils A.
  • Desgardin P.
  • Corbel C.
  • Esnouf S.
  • Piron J.P.
  Physica Status Solidi C: Current Topics in Solid State Physics, Wiley, 2007, 4 (10), pp.3627-3632. Annealing of sintered polished UO$_2$ disks at high temperature (1700DC) has been performed in order to eliminate the defects created both during the sintering and the polishing of the disks. Several sets of such UO$_2$ disks coming from different origins have been studied in the bulk using positron lifetime spectroscopy, and near the surface using a slow positron beam coupled with Doppler broadening spectrometry. They appear homogeneous and similar using positron annihilation spectroscopy. Results show the presence of negative ions, that may be negatively charged oxygen atom located in interstitial site. The positrons annihilation characteristics of the UO$_2$ lattice have been determined and are equal to SL(UO$_2$) = 0.371, WL(UO$_2$)=0.078, $\tau_L$(UO$_2$)=169ps. (10.1002/pssc.200675752)
  DOI : 10.1002/pssc.200675752
• Identification of fullerene-like CdSe nanoparticles from optical spectroscopy calculations
  
  • Botti Silvana
  • Miguel A. L. Marques
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2007, 75, pp.035311. Semiconducting nanoparticles are the building blocks of optical nanodevices as their electronic states, and therefore light absorption and emission, can be controlled by modifying their size and shape. CdSe is perhaps the most studied of these nanoparticles, due to the efficiency of its synthesis, the high quality of the resulting samples, and the fact that the optical gap is in the visible range. In this article, we study light absorption of CdSe nanostructures with sizes up to 1.5 nm within density functional theory. We study both bulk fragments with wurtzite symmetry and fullerene-like core-cage structures. The comparison with recent experimental optical spectra allows us to confirm the synthesis of these fullerene-like CdSe clusters. (10.1103/PhysRevB.75.035311)
  DOI : 10.1103/PhysRevB.75.035311
• Origin of the Optical Contrast in Phase-Change Materials
  
  • Welnic W.
  • Botti Silvana
  • Reining L.
  • Wuttig M.
  Physical Review Letters, American Physical Society, 2007, 98, pp.236403. Several chalcogenide alloys exhibit a pronounced contrast between the optical absorption in the metastable rocksalt and in the amorphous phase. This phenomenon is the basis for their application in optical data storage. Here we present ab initio calculations of the optical properties of GeTe and Ge1Sb2Te4 in the two phases. The analysis of our computations and experimental data reveal the correlation between local structural changes and optical properties as well as the origin of the optical contrast in these materials. We find that the change in optical properties cannot be attributed to a smearing of transition energies as commonly assumed for amorphous semiconductors: the optical contrast between the two phases can only be explained by significant changes in the transition matrix elements. (10.1103/PhysRevLett.98.236403)
  DOI : 10.1103/PhysRevLett.98.236403
• Transformation of graphite into nanodiamond following extreme electronic excitations
  
  • Dunlop A.
  • Jaskierowicz G.
  • M. Ossi P.
  • Della Negra S.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2007, 76, pp.155403. Graphite targets have been irradiated at 90 K and 300 K with 850 MeV and 6 GeV lead ions and with 20–30 MeV fullerene cluster ions in a large range of fluences. Damage creation was studied both by transmission electron microscopy and Raman spectroscopy. The very strong energy density deposited in electronic processes generates a highly excited region around the projectile path. The relaxation of the deposited energy via hydrodynamic expansion and shock-wave propagation leads to the formation of small defective graphitic domains and of nanocrystalline diamond particles. (10.1103/PhysRevB.76.155403)
  DOI : 10.1103/PhysRevB.76.155403
• Raman bands of double-wall carbon nanotubes : comparison with single- and triple-wall carbon nanotubes, and influence of annealing and electron irradiation
  
  • Puech Pascal
  • Flahaut Emmanuel
  • Bassil A.
  • Juffmann T.
  • Beuneu Francois
  • Bacsa Wolfgang
  Journal of Raman Spectroscopy, Wiley, 2007, 38, pp.714. We compare the G and G'2D bands of single-, double- and triple-wall carbon nanotubes (CNTs). We observe that the band shape is sensitive to the number of walls of the CNTs. For single-wall carbon nanotubes (SWCNTs), the G band is composed of two distinct contributions G+ and G−, while the G band for double-wall nanotubes is composed of one band with twomain contributions from the inner and the outer tube. The G'2D band can be fitted with one Lorentzian for single-wall tubes, while two distinct contributions are observed for double-wall carbon nanotubes (DWCNTs). Considerable variations of the G'2D band are found with similar first order Raman spectra. Annealing influences the D- and RBM-band intensities. Electron irradiation has the effect of decreasing the G- and D-band wavenumbers but does not enhance the D-band intensity considerably. The down-shifts of the G- and D-band wavenumbers are correlated and are the same for two excitation wavelengths. This is consistent with the scattering of phonons around the K-point.
• Strongly enhanced laser absorption and electron acceleration via resonant excitation of surface plasma waves
  
  • Raynaud M.
  • Kupersztych J.
  • Riconda C.
  • Adam J. C.
  • Héron A.
  Physics of Plasmas, American Institute of Physics, 2007, 14 (9), pp.092702. Two-dimensional (2D) particle-in-cell numerical simulations of the interaction between a high-intensity short-pulse p-polarized laser beam and an overdense plasma are presented. It is shown that, under appropriate physical conditions, a surface plasma wave can be resonantly excited by a short-pulse laser wave, leading to strong relativistic electron acceleration together with a dramatic increase, up to 70%, of light absorption by the plasma. Purely 2D effects contribute to enhancement of electron acceleration. It is also found that the angular distribution of the hot electrons is drastically affected by the surface wave. The subsequent ion dynamics is shown to be significantly modified by the surface plasma wave excitation. (10.1063/1.2755969)
  DOI : 10.1063/1.2755969
• Ultra-fast relaxation of electrons in wide-gap dielectrics
  
  • Fitting Hans-Joachim
  • Kortov Vsevolod S.
  • Petite Guillaume
  Journal of Luminescence, Elsevier, 2007, 122-123, pp.542-545. Low-energy electrons scattered in the conduction band of a dielectric solid should behave like Bloch electrons and will interact with perturbations of the atomic lattice, i.e. with phonons. Thus the phonon-based description of low-energy scattering within an energy band structure of a solid bears certain advantages against common free-electron scattering mechanisms. Moreover, the inelastic scattering is described by the dielectric energy loss function. With these collective scattering models we have performed the simulation of excited electron relaxation and attenuation in the insulator SiO2. After excitation to a mean initial energy of several eV their energy relaxation occurs within a short time interval of 200 fs to full thermalization. There is a very rapid impact ionization cooling connected with cascading of electrons at the beginning during the first 10 fs, followed by much slower attenuation due to phonon losses in wide-gap dielectrics and insulators.
• Efficient calculation of van der Waals dispersion coefficients with time-dependent density functional theory in real time: Application to polycyclic aromatic hydrocarbons
  
  • A. L. Marques M.
  • Castro A.
  • Malloci G.
  • Mulas G.
  • Botti Silvana
  The Journal of Chemical Physics, American Institute of Physics, 2007, 127, pp.014107. The van der Waals dispersion coefficients of a set of polycyclic aromatic hydrocarbons, ranging in size from the single-cycle benzene to circumovalene (C66H20), are calculated with a real-time propagation approach to time-dependent density functional theory (TDDFT). In the nonretarded regime, the Casimir-Polder integral is employed to obtain C6, once the dynamic polarizabilities have been computed at imaginary frequencies with TDDFT. On the other hand, the numerical coefficient that characterizes the fully retarded regime is obtained from the static polarizabilities. This ab initio strategy has favorable scaling with the size of the system—as demonstrated by the size of the reported molecules—and can be easily extended to obtain higher order van der Waals coefficients. (10.1063/1.2746031)
  DOI : 10.1063/1.2746031
• Gradient Optics of subwavelength nanofilms,
  
  • Shvartsburg Alexander
  • Kuzmiak Vladimir
  • Petite Guillaume
  Physics Reports, Elsevier, 2007, 452 (2-3), pp.33-88. Propagation and tunneling of light through subwavelength photonic barriers, formed by dielectric layers with continuous spatial variations of dielectric susceptibility across the film are considered. Effects of giant heterogeneity-induced non-local dispersion, both normal and anomalous, are examined by means of a series of exact analytical solutions of Maxwell equations for gradient media. Generalized Fresnel formulae, visualizing a profound influence of gradient and curvature of dielectric susceptibility profiles on reflectance/transmittance of periodical photonic heterostructures are presented. Depending on the cutoff frequency of the barrier, governed by technologically managed spatial profile of its refractive index, propagation or tunneling of light through these barriers are examined. Nonattenuative transfer of EM energy by evanescent waves, tunneling through dielectric gradient barriers, characterized by real values of refractive index, decreasing in the depth of medium, is shown. Scaling of the obtained results for different spectral ranges of visible, IR and THz waves is illustrated. Potential of gradient optical structures for design of miniaturized filters, polarizers and frequency-selective interfaces of subwavelength thickness is considered. (10.1016/j.physrep.2007.07.003)
  DOI : 10.1016/j.physrep.2007.07.003
• Time-dependent density-functional theory for extended systems
  
  • Botti Silvana
  • Schindlmayr Arno
  • del Sole Rodolfo
  • Reining Lucia
  Reports on Progress in Physics, IOP Publishing, 2007, 70, pp.357. For the calculation of neutral excitations, time-dependent density functional theory (TDDFT) is an exact reformulation of the many-body time-dependent Schrödinger equation, based on knowledge of the density instead of the many-body wavefunction. The density can be determined in an efficient scheme by solving one-particle non-interacting Schrödinger equations—the Kohn–Sham equations. The complication of the problem is hidden in the—unknown—time-dependent exchange and correlation potential that appears in the Kohn–Sham equations and for which it is essential to find good approximations. Many approximations have been suggested and tested for finite systems, where even the very simple adiabatic local-density approximation (ALDA) has often proved to be successful. In the case of solids, ALDA fails to reproduce optical absorption spectra, which are instead well described by solving the Bethe–Salpeter equation of many-body perturbation theory (MBPT). On the other hand, ALDA can lead to excellent results for loss functions (at vanishing and finite momentum transfer). In view of this and thanks to recent successful developments of improved linear-response kernels derived from MBPT, TDDFT is today considered a promising alternative to MBPT for the calculation of electronic spectra, even for solids. After reviewing the fundamentals of TDDFT within linear response, we discuss different approaches and a variety of applications to extended systems. (10.1088/0034-4885/70/3/R02)
  DOI : 10.1088/0034-4885/70/3/R02
• Atomic structures of symmetrical and asymmetrical facets in a near Sigma=9 {221} tilt grain boundary in copper
  
  • Hardouin Duparc Olivier
  • Couzinié Jean-Philippe
  • Thibault-Pénisson Jany
  • Lartigue-Korinek Sylvie
  • Décamps Brigitte
  • Priester Louisette
  Acta Materialia, Elsevier, 2007, 55, pp.1791-1800. Atomic structures in a S=9 {221} tilt grain boundary (GB) grown by Bridgman solidification of a tricrystal are determined through high-resolution transmission electron microscopy and numerical simulation. Atomic models are simulated via molecular dynamics annealing using an n-body potential fitted on copper properties including its stacking fault energy. Symmetrical and asymmetrical facets are thus identified. Mainly asymmetrical facets are observed, viz S=9 and also small parts of incommensurate . The symmetrical facets are described by a quasi mirror plane atomic structure. A specific GB structural unit is recognized as a Lomer unit. Its GB Burgers vector depends on the GB structure itself. Further analyses of these models and of accommodating dislocations is successfully carried out at the atomic level within the framework of the continuous structural unit approach
• Ab initio Method for Calculating Electron-Phonon Scattering Times in Semiconductors: Application to GaAs and GaP
  
  • Sjakste Jelena
  • Vast Nathalie
  • Tyuterev Valeriy
  Physical Review Letters, American Physical Society, 2007, 99, pp.236405. We propose a fully ab initio approach to calculate electron-phonon scattering times for excited electrons interacting with short-wavelength (intervalley) phonons in semiconductors. Our approach is based on density functional perturbation theory and on the direct integration of electronic scattering probabilities over all possible final states with no ad hoc assumptions. We apply it to the deexcitation of hot electrons in GaAs, and calculate the lifetime of the direct exciton in GaP, both in excellent agreement with experiments. Matrix elements of the electron-phonon coupling, and their dependence on the wave vector of the final state and on the phonon modes, are shown to be crucial ingredients of the evaluation of electron-phonon scattering times
• Identification of fullerene-like CdSe nanoparticles from optical spectroscopy calculations
  
  • Botti Silvana
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2007, 75, pp.035311. Semiconducting nanoparticles are the building blocks of optical nanodevices as their electronic states, and therefore light absorption and emission, can be controlled by modifying their size and shape. CdSe is perhaps the most studied of these nanoparticles, due to the efficiency of its synthesis, the high quality of the resulting samples, and the fact that the optical gap is in the visible range. In this article, we study light absorption of CdSe nanostructures with sizes up to 1.5 nm within density functional theory. We study both bulk fragments with wurtzite symmetry and fullerene-like core-cage structures. The comparison with recent experimental optical spectra allows us to confirm the synthesis of these fullerene-like CdSe clusters
• Photopolymerization of Epoxy Coatings Containing Iron-Oxide Nanoparticles
  
  • Sangermano Marco
  • Priola Aldo
  • Kortaberria Galder
  • Jimeno Amaia
  • Garcia Ignacio
  • Mondragon Inaki
  • Rizza Giancarlo
  Macromolecular Materials and Engineering, Wiley-VCH Verlag, 2007, 292 (8), pp.956-961. Iron-oxide nanoparticles were functionalized with epoxy groups and were dispersed into a dicyclo-aliphatic epoxy resin to obtain organic-inorganic hybrid coatings via cationic ring-opening photopolymerization. TEM investigations confirmed that the filler has a size-distribution range between 5 to 20 nm, without the formation of aggregates. The influence of the presence of Fe2O3 on the rate of polymerization was investigated by real time FT-IR spectroscopy. Increasing the iron-oxide nanofiller in the photocurable resin induced an increase in the Tg values. By controlling the phase separation it was possible to obtain transparent iron-oxide nanostructured coatings, characterized by improved hardness
• Threshold displacement energy in yttria-stabilized zirconia
  
  • Costantini Jean-Marc
  • Beuneu Francois
  Physica Status Solidi C: Current Topics in Solid State Physics, Wiley, 2007, 4, pp.1258. We have studied the color center production in yttria-stabilized zirconia single crystals (i.e. ZrO2: Y with 9.5 mol% Y2O3) with the (100) orientation, by electron irradiations at energies ranging between 1.0 and 2.5 MeV. Electron paramagnetic resonance (EPR) measurements show that three paramagnetic centers are stable at room-temperature: i) an F+ -type center (singly ionized oxygen vacancy), ii) the so-called T-center (Zr 3+ in a trigonal oxygen environment), and iii) a hole center. The growth curves of F+ -type centers at variable electron energy cannot be rescaled versus the absorbed dose. These data confirm that F+-type center production is primarily governed by elastic collision processes with a threshold electron energy about 1.0 MeV. This can be correlated to a threshold displacement energy either about 120 eV for the O-atoms in the collision cascades, or about 80 eV for the Zr- (or Y-) atoms. In contrast, the growth curves of T-centers at variable electron energy are rescaled versus the absorbed dose.
• Effect of pulsed UV laser irradiation on the properties of crystalline YBa2Cu3O7− thin films
  
  • Abal'Oshev A.
  • Abal'Osheva I.
  • Gierłowski P.
  • J Lewandowski S.
  • Konczykowski M.
  • Rizza G.
  • Chromik Š
  Superconductor Science and Technology, IOP Publishing, 2007, 20 (5), pp.433. The influence of UV laser irradiation on the physical properties of epitaxial YBa2Cu3O7-δ (YBCO) thin (<1 µm) films fabricated by laser ablation was studied. The samples were irradiated by a pulsed excimer laser beam at different incident energy densities Eir≤160 mJ cm-2, i.e. 2–3 times below the ablation threshold of YBCO. Analysis of the sample cross-section using a transmission electron microscope (TEM) has shown that such irradiation results in a disordered layer on the top of the film. Independent confirmation of the film surface amorphization was also obtained by tunnelling experiments. Strong UV absorption in YBCO prevents further spreading of the amorphous region, which can be considered as a protective layer for the sample interior. Only a small reduction of the superconducting critical temperature Tc was observed in the irradiated samples. The transport measurements in the normal state indicate that at the interface between the disordered layer and the non-modified part of the film there exists a wide transitional region with reduced carrier concentration
• Swift heavy ion-induced swelling and damage in yttria-stabilized zirconia
  
  • Costantini Jean-Marc
  • Trautmann C.
  • Thomé L.
  • Jagielski J.
  • Beuneu Francois
  Journal of Applied Physics, American Institute of Physics, 2007, 101, pp.073501. Yttria-stabilized zirconia single crystals were irradiated with a variety of different swift heavy ions from 145 MeV C to 2.6 GeV U in a broad fluence range between 1011 and 1015 cm-2. Surface profilometry measurements show that the out-of-plane expansion of the samples increases versus ion fluence up to an asymptotic value of about 0.2%; the larger the ion mass, the smaller the fluence needed to reach saturation. Rutherford backscattering spectrometry data on irradiated crystals under channeling conditions give clear evidence of lattice damage creation for ions heavier than Br corresponding to a threshold electronic stopping power about 20 keV nm-1. In contrast, no threshold is found for the swelling data which scale fairly well with the number of displacements per atom except for the irradiation with U ions. In all cases we find a linear increase of the out-of-plane expansion versus the concentration of F+-type centers singly ionized oxygen vacancies measured by electron paramagnetic resonance spectroscopy in as-received and thermochemically reduced samples, regardless of crystal orientation. The nature of the lattice disorder and the respective effects of elastic collisions and electronic excitations on the ion-induced volume expansion and damage are discussed. (10.1063/1.2714651)
  DOI : 10.1063/1.2714651
• Efficient ab initio calculations of bound and continuum excitons in the absorption spectra of semiconductors and insulators
  
  • Sottile Francesco
  • Marsili Margherita
  • Olevano Valério
  • Reining Lucia
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2007, 76, pp.161103. We present calculations of the absorption spectrum of semiconductors and insulators comparing various approaches: (i) the two-particle Bethe-Salpeter equation of many-body perturbation theory; (ii) time-dependent density-functional theory using a recently developed kernel that was derived from the Bethe-Salpeter equation; and (iii) a mapping scheme that we propose in the present work and that allows one to derive different parameter-free approximations to (ii). We show that all methods reproduce the series of bound excitons in the gap of solid argon, as well as continuum excitons in semiconductors. This is even true for the simplest static approximation, which allows us to reformulate the equations in a way such that the scaling of the calculations with the number of atoms equals the one of the random phase approximation
• A combined spectroscopic and theoretical approach to investigate structural properties of Co(II)/Co(III) tris-cysteinato complexes in aqueous medium
  
  • Bresson Carole
  • Spezia Riccardo
  • Esnouf Stéphane
  • Solari Pier Lorenzo
  • Coantic Stéphanie
  • Auwer Christophe Den
  New Journal of Chemistry, Royal Society of Chemistry [1987-....], 2007, 31 (10), pp.1789. Physiological and toxicological effects of metallic ions depend on their speciation and on the structure of their associated bioligand complexes. In the field of chemical and/or nuclear toxicological studies, we are investigating cobalt complexes with biorelevant ligands such as amino acids or peptides. The aqueous reaction of cobalt dichloride with an excess of cysteine (Cys, C$_3$H$_5$NSO$_2$$^{2-}$) in a basic medium under an anaerobic atmosphere and subsequent oxidation by O$_2$ , afforded the mononuclear complexes Co(II):3Cys and Co(III):3Cys, respectively. A combination of X-ray absorption spectroscopy (XAS) measurements and Car-Parrinello molecular dynamics (CPMD) simulations allowed us to assess structural features of the already explored Co(III):3Cys complex. Inclusion of the temperature effects in the CPMD calculations gives an implicit access to disorder effects in the extended X-ray absorption fine structure (EXAFS) equation. The very good agreement between the measured and the simulated data showed the accuracy of these models provided by CPMD. The present investigation is completed by new UV-visible, X-ray absorption near edge structure (XANES) and electron paramagnetic resonance (EPR) data of Co(II):3Cys. These data are consistent with a Co(II) high-spin d$^7$ complex in a distorted octahedral geometry. This work contributes to the knowledge of topics such as metal-bioligand interaction which is of major interest in the field of bioinorganic chemistry. (10.1039/b707055a)
  DOI : 10.1039/b707055a
• Study of structural evolution in Ce- and Nd-doped aluminoborosilicate glasses under β-irradiation
  
  • Malchukova Evguenia
  • Boizot Bruno
  • Petite Guillaume
  • Ghaleb D.
  Physica Status Solidi C: Current Topics in Solid State Physics, Wiley, 2007, 4 (3), pp.1280-1283. The structural changes in aluminoborosilicate glasses under β-irradiation as a function of rare earth oxide content and the dose have been studied using Electron Paramagnetic Resonance (EPR) and luminescence spectroscopies. The EPR measurements at helium temperature (4 K) showed that β-irradiation affects valence state of cerium ions. According to concentration and dose dependences, the line with g ~ 2.89 can be attributed to paramagnetic Ce3+ ions resulting from Ce4+ reduction under irradiation. The effect of CeO2 content leads to the modifications of the EPR signal of defects at helium and the change in the relative proportion of electron and hole defects with the increase of the cerium doping level at room temperature. We observed also a decrease of the defect concentration as a function of the Nd doping into these glass compositions but by two orders less than for Ce-doped samples. Exposure to irradiation induced the appearance of a non-resolved EPR band in the region of defects. We can assume that possible dipolar interaction between Nd3+ ion and hole can result in not typical EPR resonance shape of paramagnetic defects at g ~ 2. Moreover, estimation of the ratio between splitted components of the 4F3/2 – 4I9/2 transition depending on the irradiation dose showed that dose increase leads to increase of this ratio suggesting that the nearest environment of Nd ions is expected to be changed (10.1002/pssc.200673803)
  DOI : 10.1002/pssc.200673803
• Consequences of external irradiation on the chemical durability of the $\beta$-thorium phosphate-diphosphate during leaching tests
  
  • Tamain C.
  • Özgümüs A.
  • Dacheux N.
  • Garrido F.
  • Thomé L.
  • Corbel C.
  • Mendès E.
  Journal of Radioanalytical and Nuclear Chemistry, Springer Verlag, 2007, 273, pp.597-601. The effect of external irradiation on $\beta$-thorium phosphate-diphosphate (tetravalent actini des bearing storage matrix) and the influence on its dissolution in aqueous media were studied. Highly energetic heavy ions were used to get the amorphization of the crystalline structure of the ceramic. The ex-situ dissolution expenments showed an increase of the dissolution versus amorphous fraction in several pH and temperature conditions. The in-situ dissolution experiments highlighted the primordial importance of radiolytic produced free radical species. From these results, the ceramic presents a good resistance to aqueous alteration even in amorphous state. (10.1007/s10967-007-0917-3)
  DOI : 10.1007/s10967-007-0917-3
• Developments of Organic-Inorganic Hybrid Free Radical-Cationic Dual Cured Coatings
  
  • Sangermano M.
  • Acosta Ortiz R.
  • Garcia Valdez A.E.
  • Berlanga Duarte L.
  • Amerio E.
  • Priola A.
  • Rizza G.
  Polymer Bulletin, Springer Verlag, 2007, 59 (6), pp.865-872. Organic-inorganic nanocomposite hybrid coatings were prepared through a dual-cure process involving free-radical and cationic photopolymerization of a methacrylic-epoxy functionalized resin and subsequent condensation of organo-alkoxysilane inorganic precursor. All the formulations investigated gave rise to photocured films characterized by a high gel content values. A lower decrease on glass transition temperature is observed in the presence of MEMO or GPTS compared with a monofunctional methacrylic monomer. The dual-cured hybrid films were optically transparent evidencing that the organic-inorganic phase separation is in the scale of smaller than 400 nm. The formation of nanometric size inorganic domains (in the range between 10–30 nm), both in the presence of MEMO or GPTS as silica precursor, were further confirmed by TEM analysis
• Nanoporous alumina wire templates for surrounding-gate nanowire transistors
  
  • L Wade Travis
  • Hoffer Xavier
  • Dughaim Mohammed Al
  • Dayen Jean-François
  • Pribat Didier
  • Wegrowe Jean-Eric
  Nanotechnology, Institute of Physics, 2007, 18, pp.125201. Aluminium wires are electrochemically sculptured into bi-directional templates for the templated growth and contacting of nanowires as three terminal devices. The use of this nanostructured template is demonstrated by a ZnO nanowire surrounding-gate field-effect transistor. This bottom-up approach to a 3D nanowire transistor is unique in that it can be almost entirely fabricated in a beaker using aqueous, room temperature electrochemistry. The fabrication procedures and preliminary device characteristics of this new approach to nanowire transistors are shown
• OPTICS OF SUBWAVELENGTH GRADIENT NANOFILMS
  
  • Shvartsburg A.B.
  • Kuzmiak V.
  • Petite G.
  Physics Reports, Elsevier, 2007, 452 (2-3), pp.33-88. Propagation and tunneling of light through subwavelength photonic barriers, formed by dielectric layers with continuous spatial variations of the dielectric susceptibility across the film are considered. Effects of giant heterogeneity-induced non-local dispersion, both normal and anomalous, are examined by means of a series of exact analytical solutions of the Maxwell equations for gradient media. Generalized Fresnel formulae, showing a profound influence of the gradient and curvature of dielectric susceptibility profiles on the reflectance/transmittance of periodic photonic heterostructures, are presented. Depending on the cutoff frequency of the barrier, governed by the technologically managed spatial profile of its refractive index, propagation or tunneling of light through it is examined. Non-attenuative transfer of electromagnetic energy by evanescent waves, tunneling through dielectric gradient barriers characterized by real values of the refractive index decreasing into the interior of the medium, is shown. Scaling of the results obtained for different spectral ranges of visible, IR and THz waves is illustrated. The potential of gradient optical structures for the design of miniaturized filters, polarizers and frequency–selective interfaces of subwavelength thickness is considered