Search results for "530"
showing 10 items of 1476 documents
Direct Imaging of Chiral Domain Walls and Néel‐Type Skyrmionium in Ferrimagnetic Alloys
2021
International audience; The evolution of chiral spin structures is studied in ferrimagnet Ta/Ir/Fe/GdFeCo/Pt multilayers as a function of temperature using scanning electron microscopy with polarization analysis (SEMPA). The GdFeCo ferrimagnet exhibits pure right-hand Néel-type domain wall (DW) spin textures over a large temperature range. This indicates the presence of a negative Dzyaloshinskii-Moriya interaction (DMI) that can originate from both the top Fe/Pt and the Co/Pt interfaces. From measurements of the DW width, as well as complementary magnetic characterization, the exchange stiffness as a function of temperature is ascertained. The exchange stiffness is surprisingly mostly const…
Chemical stability of the magnetic oxide EuO directly on silicon observed by hard x-ray photoemission spectroscopy
2011
We present a detailed study of the electronic structure and chemical state of high-quality stoichiometric EuO and O-rich ${\mathrm{Eu}}_{1}{\mathrm{O}}_{1+x}$ thin films grown directly on silicon without any buffer layer using hard x-ray photoemission spectroscopy (HAXPES). We determine the EuO oxidation state from a consistent quantitative peak analysis of $4f$ valence band and $3d$ core-level spectra. The results prove that nearly ideal, stoichiometric, and homogeneous EuO thin films can be grown on silicon, with a uniform depth distribution of divalent Eu cations. Furthermore, we identify the chemical stability of the EuO/silicon interface from Si $2p$ core-level photoemission. This work…
Heterogeneous and Homogeneous Diffusivity in an Ion-Conducting Glass
1999
The nature of ion diffusivity in the vitreous conductor 2Ca NO3 2 ? 3KNO3 (CKN) was studied by nonresonant dielectric hole burning. Spectral holes in the electric field relaxation are probed subsequent to a high electric sinusoidal burn field. For sufficiently high pump frequencies we are able to induce spectrally selective modifications in the relaxation of the electric modulus, indicating that ionic diffusivity is a spatially varying quantity in glassy CKN. Homogeneous behavior occurs in the regime of low pump frequencies, in which the resistivity approaches its steady state value. Thus, longer-ranged ionic motions lead to a spatial averaging over the heterogeneity of local ion diffusivit…
Impact of pump wavelength on terahertz emission of a cavity-enhanced spintronic trilayer
2018
We systematically study the pump-wavelength dependence of terahertz pulse generation in thin-film spintronic THz emitters composed of a ferromagnetic Fe layer between adjacent nonmagnetic W and Pt layers. We find that the efficiency of THz generation is essentially at for excitation by 150 fs pulses with center wavelengths ranging from 900 to 1500 nm, demonstrating that the spin current does not depend strongly on the pump photon energy. We show that the inclusion of dielectric overlayers of TiO2 and SiO2, designed for a particular excitation wavelength, can enhance the terahertz emission by a factor of of up to two in field.
The influence of steel fibres on compressive and tensile strength of ultra high performance concrete : A review
2020
Abstract This review paper presents the effects of steel fibre reinforcement regarding the compressive and tensile strength of UHPC. The intention is to give an overview of the research field and supply guidance for future research. Relevant papers were identified through a systematic literature search. An accumulation of the results shows that fibres have potential for improving the tensile strength of UHPC. The effect depends on fibre content, type and hybrid combinations. The effect of fibres on compressive strength seems to be questionable. Variations in test specimen geometry and other factors might also influence the results.
Graphene and graphene oxide on Ir(111) are transparent to wetting but not to icing
2021
Anti-icing coatings reduce the freezing onset temperature for water by changing the chemical and physical environment at the water-substrate interface to prevent ice nucleation and growth. Graphene oxide has several attributes that make it attractive as an anti-icing coating and it has been theoretically predicted that graphene oxide has a lower freezing onset temperature than pristine graphene. Here, we test this hypothesis using carefully prepared, well-characterized graphene oxide substrates. We compare the water contact angle for graphene and graphene oxide coatings, both prepared on iridium(111) surfaces. The results show both materials to be transparent to wetting, but indicate a lowe…
Parabolic pulse generation with active or passive dispersion decreasing optical fibers
2007
International audience; We experimentally demonstrate the possibility to generate parabolic pulses via a single dispersion decreasing optical fiber with normal dispersion. We numerically and experimentally investigate the influence of the dispersion profile, and we show that a hybrid configuration combining dispersion decrease and gain has several benefits on the parabolic generated pulses.
Photon assisted-inversion of majority charge carriers in molecular semiconductor-based organic heterojunctions
2021
International audience; Ambipolar molecular materials hold great promises as a building block of next generation highly efficient, less complex and low cost electronics devices. In this endeavor, the present work reports the fabrication of organic heterojunction devices based on halogenated copper Phthalocyanines (CuPc) and lutetium bisphthalocyanine (LuPc2) bilayer, investigates their structural and electrical properties and probes the ambipolar behavior by ammonia sensing. Microstructural analysis of the heterostructure thin films revealed compact and semicrystalline organization, depending on the number of halogen substituents in CuPc. The heterojunction devices reveal a non-linear I(V) …
Near-Field Distribution of Optical Transmission of Periodic Subwavelength Holes in a Metal Film
2000
Recent experimental discovery of the enhanced optical transmission through metal films with periodic subwavelength holes has given rise to a considerable interest in the optical properties of such structures due to their possible numerous applications in optics and optoelectronics as well as rich physics behind the phenomenon of the transmission enhancement [1–4]. The transmission of a subwavelength aperture is very low and proportional to the fourth power of the ratio of its diameter and light wavelength. However, if a metal film is perforated with a periodic array of such holes, the optical transmission can be significantly enhanced [1]. Being normalized to the total area of the illuminat…
Characterization of thin superconducting YBaCuO-films by Raman-spectroscopy
1988
We have investigated thin sputtered films of the high Tc material YBa2Cu3O7 by means of Raman spectroscopy at different stages of the preparation process. We find that the films are amorphous after sputtering. The Raman spectra indicate that random polycrystalline layers, as well as crystalline layers with preferred orientation, are obtained by an additional thermal treatment.