[en] The ageing of various glass forming materials (polycarbonate, polystyrene, polyvinyl acetate and triphenylethene) has been studied by differential scanning calorimetry. The variation of the relaxation enthalpy ΔH with the ageing time measured in a large domain of time is compared to the variation of volume ΔV reported in the literature. Simple and complex thermal treatments (memory effect) can be distinguished. In simple thermal treatments (annealing at a unique temperature) the following can be concluded. (a) The glass at equilibrium is a liquid: the relaxation time τ_f to reach equilibrium, the saturation of enthalpy, is the time predicted by the Vogel-Fulcher-Tamman (VFT) law and the heat capacity is equal to that of the liquid. (b) The kinetic laws giving the enthalpy, ΔH = k_H log t, and the volume, ΔV = k_V log t, are observed between the initial τ_i (H) and τ_i*(V) and final times τ_f (H) and τ_f* (V). For PS and PVAc we show that the times obtained by these two techniques are comparable, τ_i = τ_i* and τ_f = τ_f*. The initial relaxation times (or incubation times) follow the Arrhenius law and the final times (or equilibrium times) verify the VFT law. It is shown that for polymers the experimental slopes k_H and k_V can be deduced from this VFT (WLF) law, k_H = C₂ ΔC_p /C₁ and k_V = C₂ Δα/C₁, C₁ and C₂ being the coefficients of the WLF equation and ΔC_p and Δα being the jumps of the heat capacity and of the expansion coefficient at T_g. In complex thermal treatments (annealing at two different temperatures) the enthalpy relaxation is compared to the volume relaxation (the memory effects) studied by Kovacs and Struik. In any case the kinetics presents two regimes, which defines an equivalent time t_eq; this is the annealing time necessary to erase the previous thermal history of the glass; the origin of this time is discussed. Above t_eq the kinetics is not different from that of simple treatments; below t_eq no variation of ΔH is observed

[en] The freezing, melting and dynamics of supercooled water at different hydration of controlled porous glass with mean pore sizes 10 nm, 30 nm, 50 nm and 70 nm are studied using differential scanning calorimetry and deuteruim nuclear magnetic resonance (²H-NMR). For saturated samples, the melting temperature follows the Gibbs–Thomson relation despite a clear linear decrease of the melting enthalpy when the transition is shifted due to confinement. For partially filled porous glasses the crystallization and melting temperatures as well as enthalpies are lower than for the saturated samples. ²H-NMR confirms the existence of a non-crystallizable part of water adsorbed on the surface of pores. At room temperature, spin–lattice relaxation rate (1/T ₁) is proportional to the inverse of the mean pore size indicating that the relaxation is governed by a surface limited process. At low temperature relaxation rate follows the Vogel–Fulcher–Tammann (VFT) relation. (paper)

[en] We report on the charge spill-out and work function of epitaxial few-layer graphene on 6 H-SiC(0 0 0 1). Experiments from high-resolution, energy-filtered x-ray photoelectron emission microscopy (XPEEM) are combined with ab initio density functional theory calculations using a relaxed interface model. The work function values obtained from theory and experiments are in qualitative agreement, reproducing the previously observed trend of increasing work function with each additional graphene plane. Electron transfer at the SiC/graphene interface through a buffer layer (BL) causes an interface dipole moment which is at the origin of the graphene work function modulation. The total charge transfer is independent of the number of graphene layers, and is consistent with the constant binding energy of the SiC component of the C 1s core-level, measured by XPEEM. Charge leakage into a vacuum depends on the number of graphene layers, explaining why the experimental, layer-dependent C 1s graphene core-level binding energy shift does not rigidly follow that of the work function. Thus, a combination of charge transfer at the SiC/graphene interface and charge spill-out into the vacuum resolves the apparent discrepancy between the experimental work function and C 1s binding energy. (paper)

[en] By using numerical simulations and experimental campaigns on a small-scale laser facility, the concept of the focal spot imaging on harmonics of laser frequency is developed and implemented on the Laser MegaJoule (LMJ)/PETawatt Aquitaine Laser (PETAL) facility. The Two/Three omega Imaging System was activated and validated during the first 2017-2019 interaction campaigns of PETAL on the LMJ. It provides major information on focal spot characteristics on a target. Such an approach could be easily applied to any high-intensity facility in the relativistic intensity regime (≥10¹⁸ W cm^-2). (authors)

[en] Single crystalline bismuth is known to have a peculiar electronic structure which is very close to the topological phase transition. The modification of the surface states of Bi depending on the temperature are revealed by angle-resolved photoelectron spectroscopy. At low temperature, the upper branch of the surface state merged into the projected bulk conduction bands around the point of the surface Brillouin zone. In contrast, the same branch merged into the projected bulk valence bands at high temperature (400 K). Such behavior could be interpreted as a topological phase transition driven by the temperature, which might be applicable for future spin-thermoelectric devices. We discuss the possible mechanisms to cause such transition, such as the thermal lattice distortion and electron–phonon coupling. (paper)

[en] For certain conditions of layer thickness, the interface between GdTiO_3 (GTO) and SrTiO_3 (STO) in multilayer samples has been found to form a two-dimensional electron gas (2DEG) with very interesting properties including high mobilities and ferromagnetism. We have here studied two trilayer samples of the form [2 nm GTO/1.0 or 1.5 unit cells STO/10 nm GTO] as grown on (001) (LaAlO_3)_0_._3(Sr_2AlTaO_6)_0_._7, with the STO layer thicknesses being at what has been suggested is the critical thickness for 2DEG formation. We have studied these with Ti-resonant angle-resolved and angle-integrated photoemission and find that the spectral feature in the spectra associated with the 2DEG is present in the 1.5 unit cell sample, but not in the 1.0 unit cell sample. We also observe through core-level spectra additional states in Ti and Sr, with the strength of a low-binding-energy state for Sr being associated with the appearance of the 2DEG, and we suggest it to have an origin in final-state core-hole screening