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Tin diselenide (SnSe2) is a layered semiconductor with broad application capabilities in the fields of energy storage, photocatalysis, and photodetection. Here, we correlate the physicochemical properties of this van der Waals semiconductor to sensing applications for detecting chemical species (chemosensors) and millimeter waves (terahertz photodetectors) by combining experiments of high-resolution electron energy loss spectroscopy and X-ray photoelectron spectroscopy with density functional theory. The response of the pristine, defective, and oxidized SnSe2 surface towards H2, H2O, H2S, NH3, and NO2 analytes was investigated. Furthermore, the effects of the thickness were assessed for monolayer, bilayer, and bulk samples of SnSe2. The formation of a sub-nanometric SnO2 skin over the SnSe2 surface (self-assembled SnO2/SnSe2 heterostructure) corresponds to a strong adsorption of all analytes. The formation of non-covalent bonds between SnO2 and analytes corresponds to an increase of the magnitude of the transferred charge. The theoretical model nicely fits experimental data on gas response to analytes, validating the SnO2/SnSe2 heterostructure as a suitable playground for sensing of noxious gases, with sensitivities of 0.43, 2.13, 0.11, 1.06 [ppm]−1 for H2, H2S, NH3, and NO2, respectively. The corresponding limit of detection is 5 ppm, 10 ppb, 250 ppb, and 400 ppb for H2, H2S, NH3, and NO2, respectively. Furthermore, SnSe2-based sensors are also suitable for fast large-area imaging applications at room temperature for millimeter waves in the THz range.

Chemistry of materials 34(4), 1838 - 1853 (2022). doi:10.1021/acs.chemmater.1c04106, Misfit layered compounds (MLCs) MX-TX$_2$, where M, T = metal atoms and X = S, Se, or Te, and their nanotubes are of significant interest due to their rich chemistry and unique quasi-1D structure. In particular, LnX-TX$_2$ (Ln = rare-earth atom) constitute a relatively large family of MLCs, from which nanotubes have been synthesized. The properties of MLCs can be tuned by the chemical and structural interplay between LnX and TX$_2$ sublayers and alloying of each of the Ln, T, and X elements. In order to engineer them to gain desirable performance, a detailed understanding of their complex structure is indispensable. MLC nanotubes are a relative newcomer and offer new opportunities. In particular, like WS$_2$ nanotubes before, the confinement of the free carriers in these quasi-1D nanostructures and their chiral nature offer intriguing physical behavior. High-resolution transmission electron microscopy in conjunction with a focused ion beam are engaged to study SmS-TaS$_2$ nanotubes and their cross-sections at the atomic scale. The atomic resolution images distinctly reveal that Ta is in trigonal prismatic coordination with S atoms in a hexagonal structure. Furthermore, the position of the sulfur atoms in both the SmS and the TaS$_2$ sublattices is revealed. X-ray photoelectron spectroscopy, electron energy loss spectroscopy, and X-ray absorption spectroscopy are carried out. These analyses conclude that charge transfer from the Sm to the Ta atoms leads to filling of the Ta 5d$_z$$^2$ level, which is confirmed by density functional theory (DFT) calculations. Transport measurements show that the nanotubes are semimetallic with resistivities in the range of 10$^{���4}$ ����cm at room temperature, and magnetic susceptibility measurements show a superconducting transition at 4 K., Published by American Chemical Society, Washington, DC

The quantitative determination of the carbon hybridization is critical for establishing processing-structure-properties relationships for carbon-based materials, including amorphous carbon coatings. While several techniques have been employed to characterize the amount of sp$^{2}$ and sp$^{3}$ carbon in these materials, direct comparisons between analytical results are limited. Here, we compare near edge X-rayabsorptionfine structure (NEXAFS) spectra of a silicon- and oxygen-containing hydrogenated amorphouscarbon (a-C:H:Si:O) coating acquired in synchrotron-based scanning transmission X-ray microscopy (STXM) mode with electron energy loss spectra (EELS) obtained from the same a-C:H:Si:O lamella. While the fractions of sp$^{2}$ carbon computed from STXM and EELS spectra are in close agreement, the comparison of NEXAFS spectra acquired in STXM mode with NEXAFS spectra collected in partial electron yield mode on a flat a-C:H:Si:O surface indicated that the destructive preparation of thin lamellae for STXM analyses induces variations in the structure of a-C:H:Si:O, namely the breakage of carbon-siliconand carbon-hydrogen bonds, a change in ordering of sp$^{2}$-bonded carbon, and an increase in the sp$^{2}$ carbon fraction. These findings can help scientists in the careful interpretation of spectroscopic results obtained from the analysis of samples made of metastable materials after the destructive preparation ofspecimens for analytical purposes.

In order to accommodate an increasing demand for glassy carbon products with tailored characteristics, one has to understand the origin of their structure-related properties. In this work, through the use of high-resolution transmission electron microscopy, Raman spectroscopy, and electron energy loss spectroscopy it has been demonstrated that the structure of glassy carbon at different stages of the carbonization process resembles the curvature observed in fragments of nanotubes, fullerenes, or nanoonions. The measured nanoindentation hardness and reduced Young’s modulus change as a function of the pyrolysis temperature from the range of 600–2500 °C and reach maximum values for carbon pyrolyzed at around 1000 °C. Essentially, the highest values of the mechanical parameters for glassy carbon manufactured at that temperature can be related to the greatest amount of non-planar sp 2 -hybridized carbon atoms involved in the formation of curved graphene-like layers. Such complex labyrinth-like structure with sp 2 -type bonding would be rigid and hard to break that explains the glassy carbon high strength and hardness.

International audience; We report here triply differential cross sections (TDCSs) for 81 eV electron and positron-impact ionization of the combined (1b 1 + 3a 1 ) orbitals of the water molecule by using the second-order distorted wave Born approximation (DWBA2) for ejection electron and positron energies of 5 eV and 10 eV and different momentum transfer conditions. The electron-impact TDCS will be compared with the experimental data measured by Ren et al. [Phys. Rev. A 95, 022701 (2017)] and with the molecular 3-body distorted wave (M3DW) approximation results in the scattering plane as well as the perpendicular plane. The DWBA2 results are in better agreement with the experiment than the M3DW results for the scattering plane, and the M3DW results are somewhat better for the perpendicular plane. This observation is explained in terms of collision interactions. The electron and positron TDCSs are indistinguishable in the scattering plane. In the perpendicular plane, the positron results are similar in shape, but smaller in magnitude. However, the difference reduces with increasing projectile scattering angle and increasing ejected electron energy.

The features of the domain patterning in thin lithium niobate crystals were studied. It was shown that decrease in crystal plate thickness led to domain size increase due to limitation of forward growth. The domain size weakly depended on electron energy due to equality of screening charge value at the same doses and various accelerating voltages. The weak dependence of domain sizes on pattern period was attributed to absence of electrostatic interaction of domain walls. The possibility of creation of the through periodical domain structures with the vertical domain walls and period down to 2 μm in thin crystal was demonstrated. © 2019, © 2019 Taylor & Francis Group, LLC.

The Slater-type orbital basis with non-integer principal quantum numbers is a physically and mathematically motivated choice for molecular electronic structure calculations in both non-relativistic and relativistic theory. The non-analyticity of these orbitals at $$r=0$$ , however, requires analytical relations for multi-center integrals to be derived. This is nearly insurmountable. Previous papers by the present authors eliminated this difficulty. Highly accurate results can be achieved by the procedure described in these papers, which place no restrictions on quantum numbers in all ranges of orbital parameters. The purpose of this work is to investigate computational aspects of the formulae given in the previous paper. It is to present a method which helps to increase computational efficiency. In terms of the processing time, evaluation of integrals over Slater-type orbitals with non-integer principal quantum numbers is competitive with those over Slater-type orbitals with integer principal quantum numbers.

The work describes an investigation of afterglow of various luminophores under influence of pulsed X-ray radiation of nanosecond duration. As a source of radiation a pulsed X-ray "Yasen 01" apparatus is applied. Maximum impulse current of an X-ray tube is 300 A. Maximum electron energy is 120 keV. Half-height pulse duration of an X-ray burst is about 30 ns. A pulse repetition rate is up to 4 kHz. Two types of X-ray luminophores based on gadolinium oxysulfide Gd 2 O 2 S:Tb and cesium iodide CsI:Tl have been investigated. The novelty of the work is use of a fast-acting solid-state semiconductor photomultiplier. It allows recording changes of luminophores luminosity in the nanosecond time range. The photomultiplier is characterized by having two discreet outputs for measuring quickly and slowly time-changing light flows. Presence of two signal outputs allows recording changes of luminophores luminosity both during fast nanosecond excitation and during long-time afterglow. Obtained data about the nature of afterglow of investigated luminophores makes it possible to select the best one for use in conjunction with a pulsed X-ray apparatus with a high pulse repetition rate. © Published under licence by IOP Publishing Ltd.

An iron- plastic-scintillator shashlik calorimeter with a 4.3 $X_0$ longitudinal segmentation was tested in November 2016 at the CERN East Area facility with charged particles up to 5 GeV. The performance of this detector in terms of electron energy resolution, linearity, response to muons and hadron showers are presented in this paper and compared with simulation. Such a fine-grained longitudinal segmentation is achieved using a very compact light readout system developed by the SCENTT and ENUBET Collaborations, which is based on fiber-SiPM coupling boards embedded in the bulk of the detector. We demonstrate that this system fulfills the requirements for neutrino physics applications and discuss performance and additional improvements., 21 pages, 19 figures. To appear in JINST

1 pag., 1 fig. -- International Conference on Photonic, Electronic, and Atomic Collisions (ICPEAC) (30th. 2017. Cairns, Australia). -- Open Access funded by Creative Commons Atribution Licence 3.0, In the present study joint experimental and theoretical elastic differential cross sections for electron scattering from dichloromethane in the incident electron energy region 7 to 50eV are discussed.

The irradiation exposure experiments were carried out by means of the pulsed repetitive nanosecond accelerator URT-0.5 (electron energy of up to 500 keV, a pulse width of 50 ns, pulse repetition rate of up to 200pps). The determination of the distribution of the absorbed dose (AD) in the depth in the polyethylene was conducted by a gray wedge. The measurement of the electron beam AD on the surface of the shell (removed from the eggs) and under the shell, as well as beneath the absorber layer (polyethylene 80 microns thick) was also performed by the film dosimeter. Thermoluminescent dosimeters, TLD-500, were used to determine the distribution of the bremsstrahlung AD inside chicken eggs. These results lead to the conclusion that the irradiation of an electron beam with the AD level of 5 kGy is sufficient for complete disinfection on the surface of an egg. The AD inside of it will not exceed 8 cGy because of bremsstrahlung. © RAD Conference Proceedings. All rights reserved.

We present results from a measurement of double diffraction dissociation in $\bar pp$ collisions at the Fermilab Tevatron collider. The production cross section for events with a central pseudorapidity gap of width $\Delta\eta^0>3$ (overlapping $\eta=0$) is found to be $4.43\pm 0.02{(stat)}{\pm 1.18}{(syst) mb}$ [$3.42\pm 0.01{(stat)}{\pm 1.09}{(syst) mb}$] at $\sqrt{s}=1800$ [630] GeV. Our results are compared with previous measurements and with predictions based on Regge theory and factorization., Comment: 10 pages, 4 figures, using RevTeX. Submitted to Physical Review Letters

At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low Tc. We report the occurrence of high Tc superconductivity in the bilayer CaCuO2/SrTiO3, where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO2/SrTiO3 interface must be realized between the Ca plane of CaCuO2 and the TiO2 plane of SrTiO3. Only in this case extra oxygen ions can be incorporated in the interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO2 planes. A detailed hole doping spatial profile has been obtained by STEM/EELS at the O K-edge, clearly showing that the (super)conductivity is confined to about 1-2 CaCuO2 unit cells close to the interface with SrTiO3. The results obtained for the CaCuO2/SrTiO3 interface can be extended to multilayered high Tc cuprates, contributing to explain the dependence of Tc on the number of CuO2 planes in these systems., 14 pages, 4 figures

Irradiation of saturated monolayers of 3- and 4-substituted pyridyl diazoacetates on single-crystal Pt surfaces leads to either the corresponding reactive carbene or stable ketene intermediate with the chemoselectivity determined by the position of the photoreactive substituent on the pyridyl ring, which ultimately directs the available interactions with neighboring substrates.

Magnetic properties of carbon nanotubes (CNT) obtained by plasma-enhanced chemical vapour deposition (PECVD) have been studied. The growth of these nanotubes has been activated from Ni catalyst nanoparticles. Samples consist of Ni nanoparticles encapsulated at the tip of vertically aligned multiwalled carbon nanotubes (VACNTs) forming an homogeneous and dense large area monolayer of isolated (non-contacting) nanoparticles. The magnetic characterisation has been performed in the temperature range of 5-300 K with magnetic fields up to 9 T. The results show that the wide size range (30-180 nm) of the particles originates the coexistence of blocked and superparamagnetic particles and leads to the strong ferromagnetic behaviour of the whole assembly. The coercivity decreases monotonically with increasing temperature and the value for the intrinsic coercivity is 225 Oe. The encapsulation of Ni nanoparticles by VACNTs preserves them from aggregation. This makes possible to tune the coercivity by controlling size distribution of particle monolayers. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. This work was supported in part by the University of Oviedo under Grant No. UNOV-08-MA-100 and by the Spanish MEC through grant Ref. MAT2008-06784. Projects CSD2006-12 and DPI2006-03070 of the Spainsh MEDU and the Generalitat de Catalunya (project No. SGR2005-00666). The authors thank Serveis Cientifico-Tècnics of the Universitat de Barcelona (SCT-UB) for measurement facilities.

We report on a two-dimensional highly ordered self-assembled monolayer (SAM) directly grown on a bare polymer surface. Semiconducting SAMs are utilized in field-effect transistors and combined into integrated circuits as 4-bit code generators. The driving force to form highly ordered SAMs is packing of the liquid crystalline molecules caused by the interactions between the linear alkane moieties and the π-π stacking of the conjugated thiophene units. The fully functional circuits demonstrate long-range order over large areas, which can be regarded as the start of flexible monolayer electronics. © 2010 American Chemical Society.

cited By 1; International audience; At an implant biointerface, where an engineered material merges into a biological environment, complex biophysicochemical interactions occur. One typical biointerface is the bond between human bone and dental or orthopedic implants, which is based on the biomineralization of essential bone components such as hydroxyapatite, at the implant surface. However, the exact bonding mechanism between bone and implants is still unclear. The distribution of both the mineralized and organic components of bone at the interface, and their origins, requires improved characterization. Here, the first correlative characterization is reported using multiple-length-scale tomography and spectroscopy techniques to probe the chemical structure of the biointerface between human bone and commercial titanium dental implant down to the atomic scale in four dimensions (4D). The existence of an intervening transition zone bonding mature bone tissue is demonstrated to implant at multiple length scales, where the phase of bone mineral differs immediately adjacent to the implant and atomic-scale osseointegration is confirmed. The correlative 4D electron energy loss spectroscopy tomography and atom probe tomography workflow established herein is transferable to other applications in materials or biological sciences. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In this work, we use Langmuir monolayers of dipalmitoyl phosphatidylcholine (DPPC) as model systems to enhance the understanding of specific anion effects in physicochemical and biological systems. The 298 K isotherms (equation of state, EOS) of DPPC over solutions of a range of sodium salts depend strongly on the type and concentration of the salt in the subphase. We focus in particular on the liquid expanded phase region of the DPPC EOS and assume that the deviation of the isotherms over electrolyte solutions from that over pure water is due entirely to the charging of the lipid monolayer by the ions. We then examine the ability of a range of phenomenological continuum models to explain the pressure increase in the presence of electrolytes. The important finding is that insoluble lipid monolayers allow the discrimination between possible modes of ion-lipid interaction. Chemical binding models, simple or modified, cannot fit the range of data presented in this work. Both dispersion interaction and partitioning models fit most of the experimental isotherms and provide unique values for dispersion coefficients or ionic partitioning constants, respectively, even though the nature of these models is completely different (the former concentrates on the potential of mean force that acts on an ion in the double layer, while the latter concentrates on the treatment of interactions at the interface). Surprisingly, the respective fitting parameters are very highly correlated, reflecting, we believe, the effect of ion size on ionic properties and interactions. With sodium fluoride (NaF) as the subphase electrolyte, it is demonstrated that sodium exhibits a weak complexation-type interaction with the zwitterionic lipids. The simple dispersion and partitioning models cannot account for the NaF results, highlighting the need for more complex salt-lipid interaction models that account both for sodium binding and anion partitioning. This realization sets the stage for the companion paper. © 2009 American Chemical Society. 113 5 1447 1459 Cited By :43

Transforming growth factor beta (TGF beta) is often used in cartilage tissue engineering to increase matrix formation by cells with various phenotypes. However, adverse effects of TGF beta, such as extensive cross-linking in cultured fibroblasts, have also been reported. Our goal was to study effects of TGF beta on collagen cross-linking and evaluating the role of cellular phenotype and physical environment. We therefore used four different cell populations in two very different physical environments: primary and expanded chondrocytes and fibroblasts embedded in alginate gel and attached to tissue culture plastic. Matrix production, collagen cross-linking, and alpha-smooth muscle actin (alpha SMA) were analyzed during 4 weeks with or without 2.5 ng/mL TGF beta 2. TGF beta 2 did not affect collagen deposition by primary cells. In expanded cells, TGF beta 2 increased collagen deposition. Chondrocytes and fibroblasts in monolayer produced more collagen cross-links with TGF beta 2. In alginate, primary and expanded cells displayed an unexpected decrease in collagen cross-linking with TGF beta 2. aSMA was not present in alginate cultures and barelay upregulated by TGF beta 2. Organized alpha SMA fibers were present in all monolayer cultures and became more pronounced with TGF beta 2. This study demonstrates that the physical environment determined by the substrate used co-determines the response of cells to TGF beta. The presence of mechanical stress, determined with alpha SMA-staining, is probably responsible for the increase in collagen cross-linking upon addition of TGF beta.

A recently developed unified description of low-order above-threshold ionization (Becker et al 2014 J. Phys. B: At. Mol. Opt. Phys. 47 204022; 2015 J. Phys. B: At. Mol. Opt. Phys. 48 151001) is revisited and extended. By considering the rescattering electron energies and angles at the classical cutoffs and the contributions of particular quantum-orbit solutions, it is shown that summing both the backward- and the forward-scattering contributions, within the low-frequency approximation, it is possible to reproduce the observed features of the ATI spectra both for low and high energies and both on and off the laser-polarization axis in the momentum plane.

cited By 2; International audience; In spite of the current prevalence of the CVD-based processes, the electric arc remains an interesting process for the synthesis of carbon nanoforms, thanks to its versatility, robustness and easiness. It also allows performing in-situ substitution of carbon atoms by hetero-elements in the graphene lattice. Our work aims to establish a correlation between the plasma properties, type and chemical composition (and the substitution rate) of the obtained single-wall carbon nanotubes. The plasma was characterized by optical emission spectroscopy and the products were analyzed by high resolution transmission electron microscopy and core level Electron Energy-Loss Spectroscopy (EELS). Results show that a high boron content leads to a plasma temperature decrease and hinders the formation of nanotubes. This effect can be compensated by increasing the arc current and/or yttrium content. The optimal conditions for the synthesis of boron- and/or nitrogen-substituted nanotubes correspond to a high axial plasma temperature associated to a strong radial gradient. EELS analysis confirmed that the boron incorporates into the graphenic lattice.

Atomic data for electron impact ionization of all the elements from H to Ge are reviewed, the rates for these processes needing to be regularly updated following the publication of new experimental data and new theoretical calculations. Experimental cross sections, along with specific theoretical calculations when experimental data are missing, are fitted as functions of the electron energy, and from these fits ionization rate coefficients can be evaluated. It has been possible to take into account all elements but not all charge states of every element. Since the purpose of the paper is to update the ionization data evaluated and proposed in previous review papers, it is discussed if modifications are needed for the ions not considered. For highly ionized ions starting from the Ne- like iso- electronic sequence corrections do not appear necessary. On the other hand, except for Fe, for slightly ionized ions, specifically below the S- like iso- electronic sequence, the previously proposed data often underestimate the total ionization cross section, since only direct ionization channels have been considered and indirect processes have been neglected. Multiplicative correction coefficients are given to agree with recently published theoretical calculations. Experimental ionization data are considered, even when the presence of populated metastable levels ( related to the electron density inside the source) is reported in the ion beams involved in the cross- section data measurements. We deem such a procedure acceptable when the proposed rates have to be included in codes that simulate the impurity behaviour in magnetic- confinement fusion devices, i. e., when radial transport is added to ionization and recombination to predict spatially resolved charge- state distributions. On the other hand, for astrophysical plasmas the contributions of metastable levels to the experimental data may represent a serious problem since, generally, the values of the electron densities that are involved are much lower than those in the ion sources. However, we critically investigated this problem and we found that the presence of metastables does not significantly modify the rates of most of the ions apart from a dozen. For this set of ions we provide different, corrected rates. Recombination is not considered since a review has been recently published.

Cataloged from PDF version of article. In this study, electron energy relaxation mechanisms in HEMT structures with different InxGa1−xN-channel quantum well (QW) widths are investigated. Theoretical value of the inelastic scattering rates is carried out at electron temperatures between 30 K (−243 °C) < Te < 700 K (427 °C). We used both the experimentally determined and calculated electron temperatures to estimate the energy relaxation rates of non-equilibrium electrons. In wide InGaN QWs, power loss of an electron is shown to be significantly smaller than that in the narrower QWs. © 2015, The Minerals, Metals & Materials Society and ASM International.

We have developed a variational many-body description for few-electron systems in a parabolic quantum dot in an external magnetic field. The ground state energy of the electronic system has been theoretically investigated in a broad range of magnetic fields. The possibility of existence of a spin-singlet paired state in a QD in an external magnetic field is discussed. Analytical expressions for the spin-singlet phase and for the Wigner phase in a QD have been obtained and studied as a function of the magnetic field and QD confinement. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA. 3 1095 1098 Conference code: 67232 Cited By :3

The ground state total and correlation energies of a negative ion-electron and electron-electron systems in a parabolic QD with standard dispersion law are theoretically investigated in an external magnetic field by a variational approach. Both cases of finite and infinite potential barrier on the spherical surface of the QD are considered. The negative ion-electron system energies in a A3B5 semiconductor QD with nonparabolic (Kane's) dispersion law is also investigated. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA. 3 532 535 Conference code: 67231

We have previously established that, the vibration period T of a diatomic molecule, can be expressed as T=[4π 2 /( n i n j h)] g M 0 m e r 2 , where M 0 is the reduced mass of the nuclei, m e the mass of the electron , r the internuclear distance of the molecule at the given electronic state, h the Planck Constant , and g a dimensionless and relativistically invariant coefficient , which appears to be a characteristic of the electronic configuration of the molecule. Herein we validate this relationship, chiefly on the basis of vibrational data of H 2 molecule's electronic states , and achieve its calibration , vis-a-vis the quantum numbers that it is to involve. This, basically yields, the elucidation of the complete set of H 2 spectroscopic data . Thus, the composite quantum number n 1 n 2 along our finding is nothing but the ratio of the internuclear distance r at the given electronic state, to the internuclear distance r 0 at the ground state. This makes that for electronic states configured alike, for which g is expected to remain the same, T 2 versus r 3 , should exhibit a linear behavior . Our approach can well be applied to other molecules.

Photolimuniscence (PL) spectra of TlGaS2 layered crystals were studied in the wavelength region 500-1400 nm and in the temperature range 15-115 K. We observed three broad bands centered at 568 nm (A-band), 718 nm (B-band) and 1102 nm (C-band) in the PL spectrum. The observed bands have half-widths of 0.221, 0.258 and 0.067 eV for A-, B-, and C-bands, respectively. The increase of the emission band half-width, the blue shift of the emission band peak energy and the quenching of the PL with increasing temperature are explained using the configuration coordinate model. We have also studied the variations of emission band intensity versus excitation laser intensity in the range from 0.4 to 19.5 W cm -2 . The proposed energy-level diagram allows us to interpret the recombination processes in TlGaS2 crystals.

The O 1s excited states of formaldehyde have been investigated theoretically using the restricted open-shell Hartree-Fock method for electronic structure calculations and a linear vibronic coupling model for studying excited state nuclear dynamics. The results are compared with vibrationally resolved experimental data, published previously. In its 1B1(O 1s -> pi*) state the molecule is found to be unstable with respect to the out-of-plane bending mode v4(b1). The latter is a manifestation of vibronic coupling between the 1B1(O 1s -> pi*) state and the next excited state, 1A1(O 1s -> 3s). The dynamical calculations taking into account this interaction are in good agreement with experiment, whereas a simple Poisson intensity distribution reproduces only the main features of the spectral envelope of the 1B1(O 1s -> pi*) resonance. For the 1A1(O 1s -> 3s) state, the Poisson distribution gives poor agreement with experiment, whereas the vibronic coupling model yields a more satisfactory description.

At present the existing data on the cosmic ray electron energy spectra in the high energy range are fragmented, and the situation is exacerbated by their small number. In the satellite PAMELA experiment measurements at high energies are carried out by the calorimeter. The experimental data accumulated for more than 8 years of measurements, with the information of the calorimeter, the neutron detector and the scintillation counters made it possible to obtain the total spectrum of high-energy electrons and positrons in energy range 0.3-3 TeV.

Quantum confinement (QC) typically assumes a sharp interface between a nanostructure and its environment, leading to an abrupt change in the potential for confined electrons and holes. When the interface is not ideally sharp and clean, significant deviations from the QC rule appear and other parameters beyond the nanostructure size play a considerable role. In this work we elucidate the role of the interface on QC in Ge quantum dots (QDs) synthesized by rf-magnetron sputtering or plasma enhanced chemical vapor deposition (PECVD). Through a detailed electron energy loss spectroscopy (EELS) analysis we investigated the structural and chemical properties of QD interfaces. PECVD QDs exhibit a sharper interface compared to sputter ones, which also evidences a larger contribution of mixed Ge-oxide states. Such a difference strongly modifies the QC strength, as experimentally verified by light absorption spectroscopy. A large size-tuning of the optical bandgap and an increase in the oscillator strength occur when the interface is sharp. A spatially dependent effective mass (SPDEM) model is employed to account for the interface difference between Ge QDs, pointing out a larger reduction in the exciton effective mass in the sharper interface case. These results add new insights into the role of interfaces on confined systems, and open the route for reliable exploitation of QC effects. © The Royal Society of Chemistry.

International audience; A comprehensive study of atomic-layer deposited thulium oxide (Tm2O3) on germanium has been conducted using x-ray photoelectron spectroscopy (XPS), vacuum ultra-violet variable angle spectroscopic ellipsometry, high-resolution transmission electron microscopy (HRTEM), and electron energy-loss spectroscopy. The valence band offset is found to be 3.05±0.2eV for Tm2O3/p-Ge from the Tm 4d centroid and Ge 3p3/2 charge-corrected XPS core-level spectra taken at different sputtering times of a single bulk thulium oxide sample. A negligible downward band bending of ∼0.12eV is observed during progressive differential charging of Tm 4d peaks. The optical band gap is estimated from the absorption edge and found to be 5.77eV with an apparent Urbach tail signifying band gap tailing at ∼5.3eV. The latter has been correlated to HRTEM and electron diffraction results corroborating the polycrystalline nature of the Tm2O3 films. The Tm2O3/Ge interface is found to be rather atomically abrupt with sub-nanometer thickness. In addition, the band line-up of reference GeO2/n-Ge stacks obtained by thermal oxidation has been discussed and derived. The observed low reactivity of thulium oxide on germanium as well as the high effective barriers for holes (∼3eV) and electrons (∼2eV) identify Tm2O3 as a strong contender for interfacial layer engineering in future generations of scaled high-κ gate stacks on Ge. © 2015 AIP Publishing LLC.

A series of para-conjugatively coupled phenylenecarbenonitrenes {(4-nitrenophenyl)methylene (3a), (4-nitrenophenyl)fluoromethylene (3b), (4-nitrenophenyl)chloromethylene (3c), and (4-nitrenophenyl)bromomethylene (3d)} were generated in argon matrix at low temperature (10 or 13 K) and characterized by IR and UV/vis spectroscopy. Density functional theory (B3LYP/6-31G(d)) and ab initio (MCSCF, CASPT2) methods were used to study the ground- and some low-lying excited states of 3a-d. The experimental and computational data suggest that 3a-d have singlet ground states (S0) and can be thought of as quinonoidal biradicals. In all cases, the lowest triplet (T1) and quintet (Q1) states lie about 2 kcal mol-1 and 28-29 kcal mol-1, respectively, higher in energy than S0. On the other hand the substituent is found to have a significant effect on the relative energy of the second excited triplet (T2) state. This state tends to become relatively more stable as the ability of the substituent to enforce a closed-shell configuration at the carbene subunit increases. Interestingly, the energy difference between the T2 and S0 states in 3a-d is found to depend linearly on the S-T gap of the corresponding phenylcarbenes 7a-d. This relationship is helpful in predicting when a substituted p-phenylenecarbenonitrene may have a triplet ground state instead of a singlet one. 123 11 2628 2636 Cited By :28

We examine experimentally and computationally the nature of substitution of perylene in polycrystalline solid alkane matrices (Shpol’skii systems). The technique of low temperature excitation-emission matrix spectroscopy is used to determine all substitution sites in alkane matrices from hexane to decane. A theoretical method from the group of Jortner [Shalev et al., J. Chem. Phys. 95, 3147 (1991)], which was extended and applied by us to this problem in the past [Wallenborn et al., J. Chem. Phys. 112, 1995 (2000)], allows one to separate the perylene sites in all alkanes into normal and defective sites. Normal sites are obtained by direct substitution of two alkane molecules by a perylene molecule, while defective sites are derived from normal sites by eliminating one of the four nearest neighbors of perylene in the lattice planes parallel to the chromophore. We discuss the strengths and limitations of the present theoretical treatment, which can serve as a valuable supplement and guide to line-narrowing...

Non-radiative transitions cause changes in the generation of the intensity of the L lines. In order to investigate the physical quantities relevant to the L lines affected by the non-radiative transitions, experimental measurements were carried out using a Si(Li) x-ray spectrometer. Atomic L shell Coster-Kronig yields (f(12), f(13) and f(23)) for some elements in the atomic number range 59 less than or equal to Z less than or equal to 90 were determined. These selected measured semi-empirical values were also fitted by least squares to polynomials in Z of the form Sigma (n) a(n) Z(n) (except for f(13)) and compared with theoretical and with earlier fitted values.

We report the observation of the unusually weak decay of the N 1s --> pi* core-excited N-2 molecule to the (B) over tilde (2)Sigma(u)(+) final state of N-2(+), which is only detectable in an exp ...

The adsorption of germanium on the Bi/Si(001)-(2×5) surface [bismuth saturation coverage of 0.7 ML (monolayers)] was investigated by core-level photoemission spectroscopy. At submonolayer germanium coverage, the presence of a bulk component largely dominating the Ge 3d core level demonstrates that the favourite adsorption sites are the bismuth-terminated terraces, where Ge–Bi site exchange takes place. At larger germanium coverage, in addition to the previous process, the occurrence of a pure germanium epitaxy is indicated by the presence of the (2×1) surface components in the Ge 3d core level.