Magnetic reversal in ion-irradiated FePt thin films

International audiencePrevious work on ion irradiation control of FePt thin films magnetic anisotropy is extended to ultrathin films (2-10nm). The effects of 30keV He ion irradiation on the magnetic properties are explored as a function of ion fluence and film thickness. Depending on their growth conditions, the thinnest films exhibit different magnetic properties. Although this affects their final magnetic behaviour, we show that after irradiation at 300 @BULLET C the easy magnetization axis may rotate entirely from inplane to out-of-plane at very low fluences, e.g. 2×10 13 He + /cm 2 on 5 nm thick film. This demonstrates the extreme sensitivity of the magnetic anisotropy to ion-induced local L1 0 ordering. Under these conditions, ultrathin films may exhibit perfectly square hysteresis loops with 100% remnant magnetization and low coercivity

Deciphering Electron Interplay at the Fullerene/Sputtered TiOxInterface: A Barrier-Free Electron Extraction for Organic Solar Cells

Organic photovoltaics (OPVs) technology now offers power conversion efficiency (PCE) of over 18% and is one of the main emerging photovoltaic technologies. In such devices, titanium dioxide (TiOx) has been vastly used as an electron extraction layer, typically showing unwanted charge-extraction barriers and the need for light-soaking. In the present work, using advanced photoemission spectroscopies, we investigate the electronic interplay at the interface between low-temperature-sputtered TiOx and C70 acceptor fullerene molecules. We show that defect states in the band gap of TiOx are quenched by C70 while an interfacial state appears. This new interfacial state is expected to support the favorable energy band alignment observed, showing a perfect match of transport levels, and thus barrier-free extraction of charges, making low-temperature-sputtered TiOx a good candidate for the next generation of organic solar cells

Photoelectron Holographic Derivative Transform For Increased Range Of Atomic Images

A transform-k derivative spectra (KDS) transform—is introduced for construction of an atomic-structure image from photoelectron diffraction data. A phenomenological theory is used to show that the transform of spectrum derivatives enhances the image peaks by the square of the emitter-scatter distance when used in conjunction with the small cone method. In comparison with the standard transform used in photoelectron holography, the KDS transform allows more distant neighbors (scatterers) to be “seen” by the emitter and suppresses strong forward scattering. The ability to experimentally observe more neighbors of a photoelectron emitter expands the applicability of holographic imaging. The procedure is applied to experimental data obtained from the As/Si(111)-(1×1) and C2H4/Si(100)-(2×1) surface structures. The letter results show that C2H4 adsorption does not break the Si dimer bond

Growth mechanism of silicene on Ag ( 111 ) determined by scanning tunneling microscopy measurements and ab initio calculations

International audienceScanning tunneling microscopy has been used to real-time study the growth of silicene on Ag(111) in the200–533-K temperature range. We show that the growth mode depends strongly on the deposition temperatureT. At T = 300K and above, the formation of silicene results from the exchange between surface Ag atomsand Si atoms, which are inserted in the substrate top layer. Density functional theory calculations confirm thatSi insertion is thermodynamically favored, and we propose an energetic model for explaining the observedgrowth processes as a function of T . For T 400 K, ordered structures are observed as soon as silicene domainsare large enough. With increasing coverage, disordered and dotted phases progressively transform into stable(√13 ×√13)R13.9◦ and (4 × 4) structures

Photoelectron diffraction evidence for a surface substitutional site of Sb in the Sb-induced smooth growth of Ag on Ag(111)

International audienc

Relating localized electronic states to host band structure in rare-earth-activated optical materials

The energies of the rare-earth ions' electronic states relative to the host band states in optical materials were discussed. Resonant electron photoemission spectroscopy (REPS) was used. Results provide a model to describe the rare earth binding energies in optical materials with two parameters such as constant shifts and dependence of ionic radius.link_to_subscribed_fulltex

Surface reconstructions of epitaxial MnAs films grown on GaAs(111)B

This study makes reference to the surface structure of MnA

Stoichiometry-Dependent Chemical Activity of Supported MgO(100) Films

Here, we show that the stoichiometry and, consequently, the chemical activity toward hydroxylation of MgO(100) films grown by reactive deposition on Ag(100) strongly depend on the O(2) partial pressure during film growth. Oxygen-deficient films undergo dramatic relative oxygen uptake either by exposure to a partial pressure of water vapor or by aging in vacuum for a sufficiently long time. Conversely, on stoichiometric monolayer MgO islands, photoemission analysis of the O Is level and scanning tunneling microscopy images are consistent with the prediction that dissociative adsorption of water occurs only at the borders of the islands

Unveiling the Energy Alignment across Ultrathin 4P NPD Hole Extraction Interlayers in Organic Solar Cells

Molecular thin films of N,N amp; 8242; di 1 naphthalenyl N,N amp; 8242; diphenyl [1,1 amp; 8242; 4 amp; 8242;,1 amp; 8243; 4 amp; 8243;,1 amp; 8244; quaterphenyl] 4,4 amp; 8244; diamine 4P NPD have been demonstrated to function as efficient exciton blocking layers in organic solar cell devices, leading to improved device performance by minimizing exciton losses and by providing hole extraction selectivity. However, the exact mechanisms have been debated, as ultrathin thicknesses of less than 1 nm are required to observe optimized device performance improvements. In this work, we conduct photoelectron spectroscopy to gain information about core levels, HOMO LUMO levels, and work functions for the hole extraction side of an organic solar cell device consisting of the small molecule tetraphenyldibenzoperiflanthene DBP as an electron donor and 4P NPD for exciton blocking hole extraction, the latter being in contact with the hole transport layer MoOx. Using in situ deposition and characterization, we demonstrate that a negative HOMO energy offset increases with 4P NPD thickness on the DBP donor layer, which cannot account for the improvement observed in device performance. Investigation of the 4P NPD MoOx interface, on the other hand, reveals shifts of the electronic levels in 4P NPD and a band alignment that favors hole extraction while blocking for exciton electron leakage. This appealing behavior is enhanced for ultrathin 4P NPD films of less than 1 nm. Thus, the exciton blocking hole extraction behavior of 4P NPD interlayers in organic solar cell devices is confirmed and understood from the detailed energy level alignment across both interfaces, as extracted from the in situ photoelectron spectroscopy studie