The selective oxidation of the Fe0.85Al0.15 body-centred cubic (bcc) ferritic alloy has been studied in annealing conditions relevant for steel industry, i.e. a fast heating up to 800 degrees C under a N2-5vol% H2 reducing atmosphere containing traces of residual water acting as the oxidising agent (dew point of-60 degrees C, p(H2O) = 1.9 10-2 mbar). Single crystals with the three (110), (100) and (111) low-index orientations have been compared to a polycrystalline specimen to pinpoint the effect of crystallogaphic orientation and grain boundaries on the resulting oxide. Film thickness, morphology, composition, structure and epitaxy have been explored by a combination of techniques: x-ray reflectivity, atomic force microscopy, x-ray photoemission spectroscopy, x-ray diffraction and transmission electron microscopy. On all samples, the formation of a dense covering face-centred cubic (fcc) Al2O3 film having an orientation dependent thickness of 10-20 nm is evidenced. Neither other alumina polymorphs nor any Fe oxides are present. Compared to the nominal bulk composition, the alloy subsurface is not depleted in Al but instead enriched, thus demonstrating a rapid Al transport towards the surface under the present conditions. All the film/alloy orientations (Bain: Al2O3(100)[011] parallel to Fe0.85Al0.15(100)[001], Nishiyama-Wassermann: Al2O3(111)[110] parallel to Fe0.85Al0.15(110)[001] and Al2O3(11n)[n01] parallel to Fe0.85Al0.15(111)[110]) are driven by the alignment of the close-packed row of fcc and bcc lattices leading to a minimal mismatch. Present in the interface plane for Fe0.85Al0.15(100) and (110), it dictates the epitaxial orientation while on the (111) surface, it gives rise to an axiotaxy texture. While traces of metallic Fe are always present in the form of nanoparticles, likely because of the reduction of the initial iron oxide, an incipient internal oxidation was observed at grain boundaries.

The question of the intensity-energy response of photoemission spectrometers has been approached through a round-robin involving 13 instruments working with low (Al/Mg-K alpha) and high (Cr-K alpha) energy photon sources. An algorithm based on the analysis of inelastic background previously proposed [S. Guilet et al., J. Electron Spectrosc. Relat. Phenom. 285 (2022) 147225)] was intensively tested against calibrated Al/Mg-K alpha instruments and calculated relative sensitivity factors (RSFs) over the 15 core level peaks of coinage metals (Ag, Au, Cu). In both cases, the linear correlation within +/- 10 %, over two orders of magnitude in intensity and for kinetic energies ranging from similar to 400 to 1400eV, showed the consistency of the approach. All the contributions to RSFs (e.g. non-dipolar terms in the photo-ionization cross section, elastic scattering effects, surface excitations, beam polarization by the monochromator) were critically reviewed and taken into account using the state-of-the-art modellings and databases. Strong variations were evidenced among instruments, regarding not only the response functions, but also the theoretical RSFs due to different measurement geometries. For the Cr-K alpha hard x-ray instruments, the same analysis was performed with a set of different materials (Al, Si, Ge, Fe, Co, Ni, Cu, Zn, Nb, Mo, Ag, W, Au). A +/- 10 % satisfactory agreement against theoretical RSFs over 69 core levels spanning a large kinetic energy range (300-4000 eV) could be achieved with a common response function. Despite limitations that are reviewed, this work opens interesting perspectives for a systematic calibration of photoemission instruments.

In this study, we explore the catalytic activity of highly pure PdZn–ZnO nanopowder, synthesized via an innovative metal–organic chemical vapor synthesis (MOCVS) method.

A new method is proposed for the determination of the intensity/energy response function of a hemispherical electrostatic analyser as commonly used in photoemission spectroscopy. It only requires the measurement of a wide spectrum of a reference metallic sample. Based only on the knowledge of the Tougaard inelastic electron scattering cross section and an educated parametrization of the response function, the retrieval algorithm minimizes the area of the background subtracted primary spectrum with some constraints. Sound results for different metals (Ag, Au, Cu, Zn) are obtained (i) on two different photoemission instruments (ii) in both fixed analyser transmission and fixed retarding ratio modes (iii) for various lens and slits settings (iv) for both monochromated and unmonochromated x-ray sources. The linear correlation between core level areas and the product of tabulated inelastic mean free paths and of photo-ionization cross sections validates the approach.

Droplet based micro/nanofluidics has been demonstrated as a versatile tool in a wide range of fields. In particular, seeded growth of planar low-dimensional nanomaterials often relies on crawling metal droplets as catalytic media where nucleation and crystal growth proceed. However, direct observations of nanomaterials growth led by self-propelled droplet transport remain rare, which leaves many open questions on droplet behavior during growth. Here, we report in situ observations of in-plane Si nanowire growth in a transmission electron microscope, where an indium droplet migrates on a silicon nitride membrane coated by a layer of hydrogenated amorphous silicon (a-Si:H), dissolves the a-Si:H coating film on the membrane, and results in the production of a crystalline Si nanowire in its trail. This in situ observation, combined with the geometric investigation of the nanowires, presents nice consistency with de Gennes' theoretical prediction of reactive wetting induced droplet motion. Interestingly, we recorded a nanoflake-to-nanowire transition when the growth rate was increased by heating the membrane from 350 degrees C to 400 degrees C. This work directly unveils rich transport mechanism of catalytic droplets, which are expected to be a new platform for producing diverse low-dimensional nanomaterials and promote their potential applications in nanoscience and technologies.

The dry etching process of Fe, Cr and Fe-Cr alloys under a chlorine-based plasma is studied. The objective is to create new surface functionalities. The approach combines an experimental study of an ICP (Inductively Coupled Plasma) reactor with the development of a multi-scale etching model including kinetic, sheath and surface models. The results from plasma etching of substrates made of Fe, Cr and Fe-Cr alloys are presented. Optical emission spectroscopy and interferometry measurements show strong modifications of the plasma when Fe or Cr samples are present in the reactor. It is shown that Fe is easier to etch than Cr. The study highlights the role of chemical etching by the formation of volatile products such as FeCl3. The Cr content in Fe-Cr alloys has a strong impact on both the lateral and vertical etch rates, as well as on the roughness along the profile. For Fe-Cr alloys, the experimental and calculated values of etch rate are very similar. The concept of hard zones is introduced to get a better agreement between simulation results and experimental ones. This good agreement demonstrates the capability of the developed simulator to implement new phenomena.

In this paper, we present the results of plasma nitriding treatments on austenitic stainless steel substrates previously coated with a patterned silicon oxide layer. For this purpose, masks were made by PECVD for the deposition of a silicon oxide layer on polished austenitic AISI 316L samples. For the final nitriding treatment, we used a multi-dipolar plasma providing independent substrate polarization. The interactions between expanded austenite and fixed silicon oxide mask in different shapes (circular and square dots) are observed by atomic force microscopy (AFM) on the same area before and after the nitriding treatment. After this thermochemical treatment, we obtain strong distortions of the dots, in particular at the edges of the larger size dots. The role of elastic deformation, due to the expanded austenitic phase formed by the diffusion of nitrogen under the mask is of primary importance.

We demonstrate systematic resonance fluorescence recovery with near-unity emission efficiency in single quantum dots embedded in a charge-tunable device in a wave-guiding geometry. The quantum dot charge state is controlled by a gate voltage, through carrier tunneling from a close-lying Fermi sea, stabilizing the resonantly photocreated electron-hole pair. The electric field cancels out the charging/discharging mechanisms from nearby traps toward the quantum dots, responsible for the usually observed inhibition of the resonant fluorescence. Fourier transform spectroscopy as a function of the applied voltage shows a strong increase of the coherence time though not reaching the radiative limit. These charge controlled quantum dots act as quasi-perfect deterministic single-photon emitters, with one laser pulse converted into one emitted single photon.

Segmented strip-loaded waveguide arrays are investigated within a rigorous square lattice photonic crystal model. We derive a full multiband discrete diffraction approach for near-axial injection in the direction of a lattice vector. We obtain an effective waveguide array picture, with quasi-linear dependence on the segmentation ratio in a simplified single-band scheme. Our results are validated by beam deviation experiments. Such a diffraction framework allows for efficient shaping of the phase map in waveguide arrays and enriches the engineering toolkit of photonic crystals with the in-plane free propagation structures of discrete photonics.

We demonstrate sub-wavelength electromagnetic resonators operating in the THz spectral range, whose resonant properties and optical response can be engineered using lumped elements, similarly to what is done in electronic circuits and antennas. We discuss the device concept, and we experimentally study the tuning of the resonant frequency as a function of variable capacitances and inductances. The advantages of this 'circuit-tunable' platform to realize novel THz meta-devices featuring an ultra-small semiconductor core are then discussed. As an application, we show that these micro-resonators have a strong potential for ultra-fast THz detection, when combined to a tiny quantum well photodetector active core.

We present our systematic work on the in situ generation of In nanoparticles (NPs) from the reduction of ITO thin films by hydrogen (H2) plasma exposure. In contrast to NP deposition from the vapor phase (i.e., evaporation), the ITO surface can be considered to be a solid reservoir of In atoms thanks to H2 plasma reduction. On one hand, below the In melting temperature, solid In NP formation is governed by the island-growth mode, which is a self-limiting process because the H2 plasma/ITO interaction will be gradually eliminated by the growing In NPs that cover the ITO surface. On the other hand, we show that above the melting temperature In droplets prefer to grow along the grain boundaries on the ITO surface and dramatic coalescence occurs when the growing NPs connect with each other. This growth-connection-coalescence behavior is even strengthened on In/ITO bilayers, where In particles larger than 10 μm can be formed, which are made of evaporated In atoms and in situ released ones. Thanks to this understanding, we manage to disperse dense evaporated In NPs under H2 plasma exposure when inserting an ITO layer between them and substrate like c-Si wafer or glass by modifying the substrate surface chemistry. Further studies are needed for more precise control of this self-assembling method. We expect that our findings are not limited to ITO thin films but could be applicable to various metal NPs generation from the corresponding metal oxide thin films.

Single-mode diode lasers on an InP(001) substrate have been developed using InAs/In0.53Ga0.47As quantum dash (Qdash) active regions and etched lateral Bragg gratings. The lasers have been designed to operate at wavelengths near 2 μm and exhibit a threshold current of 65 mA for a 600 μm long cavity, and a room temperature continuous wave output power per facet >5 mW. Using our novel growth approach based on the low ternary In0.53Ga0.47As barriers, we also demonstrate ridge-waveguide lasers emitting up to 2.1 μm and underline the possibilities for further pushing the emission wavelength out towards longer wavelengths with this material system. By introducing experimentally the concept of high-duty-cycle lateral Bragg gratings, a side mode suppression ratio of >37 dB has been achieved, owing to an appreciably increased grating coupling coefficient of κ ∼ 40 cm−1. These laterally coupled distributed feedback (LC-DFB) lasers combine the advantage of high and well-controlled coupling coefficients achieved in conventional DFB lasers, with the regrowth-free fabrication process of lateral gratings, and exhibit substantially lower optical losses compared to the conventional metal-based LC-DFB lasers.

In this contribution, we demonstrate ultrafast sub-wavelength (λ/10) THz QWIP detectors based on a 3D split-ring geometry recently developed in our team [3]. The key idea is to exploit a miniaturized loop RF antenna as a coupler element to efficiently feed THz radiation (λ=100-200 μm) into an ultra-sub-wavelength (λ/25) QWIP active core (active volume ~20 μm 3) , as depicted in Fig. 1(a). The LC resonance of the device has been set by carefully selecting both the capacitor and inductor sizes in order to match the GaAs/AlGaAs QWIP response band (detection peak at ~3 THz) [4].

Terahertz (THz) and sub-THz frequency emitter and detector technologies are receiving increasing attention, underpinned by emerging applications in ultra-fast THz physics, frequency-combs technology and pulsed laser development in this relatively unexplored region of the electromagnetic spectrum. In particular, semiconductor-based ultrafast THz receivers are required for compact, ultrafast spectroscopy and communication systems, and to date, quantum-well infrared photodetectors (QWIPs) have proved to be an excellent technology to address this, given their intrinsic picosecond-range response. However, with research focused on diffraction-limited QWIP structures (lambda/2), RC constants cannot be reduced indefinitely, and detection speeds are bound to eventually meet an upper limit. The key to an ultra-fast response with no intrinsic upper limit even at tens of gigahertz (GHz) is an aggressive reduction in device size, below the diffraction limit. Here we demonstrate sub-wavelength (lambda/10) THz QWIP detectors based on a 3D split-ring geometry, yielding ultra-fast operation at a wavelength of around 100 mu m. Each sensing meta-atom pixel features a suspended loop antenna that feeds THz radiation in the similar to 20 mu m(3) active volume (V (eff)similar to 3 x 10(-4) (lambda/2)(3)). Arrays of detectors as well as single-pixel detectors have been implemented with this new architecture, with the latter exhibiting ultra-low dark currents below the nA level. This extremely small resonator architecture leads to measured optical response speeds-on arrays of 300 devices-of up to similar to 3 GHz and an expected device operation of up to tens of GHz, based on the measured S parameters on single devices and arrays. (c) 2017 Optical Society of America

We propose a new guide mode resonant photodiode demonstrating better sensitivity for the infrared imaging. This comprises a backside dielectric sub-wavelength periodic structure and an absorbing region as thin as 90 nm. In this study, electro-optical characterizations of individual InGaAs detector featuring focal-plane array-compatible geometries are fully explained by electro-magnetic simulations. In particular, we observe near perfect collection of the photo-carriers and external quantum efficiency of up to 71% around 1,55 μm.

We investigate a resonant photodiode transferred onto a gold mirror. This comprises a backside dielectric subwavelength periodic structure and an absorbing region as thin as 90 nm. Electrooptical characterizations of individual pixels featuring focal-plane array-compatible geometries are fully explained by electro-magnetic simulations. In particular, we observe a near perfect collection of the photo-carriers and external quantum efficiency of up to 71% around 1: 55 mu m. (C) 2016 AIP Publishing LLC.

Commissioned in May 2004 on the SLS machine, the LUCIA beamline was moved to the synchrotron SOLEIL during the summer of 2008. To take advantage of this new setting several changes to its design were introduced. Here, a review of the various improvements of the mechanics and, mostly, of the optics is given. Described in detail are the results of a new multilayer grating monochromator implemented on the Kohzu vessel already holding the two-crystal set-up. It consists of a grating grooved onto a multilayer (replacing the first crystal) associated to a multilayer (as a second crystal). It allows a shift of the low-energy limit of the beamline to around 500 eV with an energy resolution and a photon flux comparable with those of the previous couples of crystals (KTP and beryl).

We demonstrate single-pixel and 2D arrays of THz quantum-well photodetectors featuring extremely sub-wavelength, antenna-coupled resonators. Few-micron sized devices show photodetection in the 100-200 μm range, with a consequent dramatic reduction in the device dark current.

We derive an analytical diffraction relation and a numerical angular signature in segmented waveguide arrays. Our 2D effective index model matches our experiments and connects the photonic crystal picture with the diffraction management approach.