In this paper, embedded amorphous-silicon (a-Si) and titanium (Ti) ultrathin-films forming a multilayer structure is proposed as a new efficient absorber material for thin-film solar cells (TFSCs). Promising design strategy based on combining FDTD (finite difference time domain) with particle swarm optimization (PSO) was adopted to identify the a-Si/Ti multilayer structure offering the highest total absorbance efficiency (TAE). It is found that the proposed multilayer structure can serve as an effective absorber, yielding superb TAE exceeding 80%. The a-Si/Ti multilayer was then elaborated by successive growth of a-Si and Ti ultrathin layers using RF magnetron sputtering technique. The sputtered a-Si/Ti thin-film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-visible absorption spectroscopy. Measurements showed a unique optical behavior, promoting broadband absorbance over the visible and even NIR spectrum ranges. In particular, the prepared aSi/Ti absorber exhibits an optical band-gap of 1.36 eV, which is suitable for photovoltaic applications. A performance assessment of the elaborated absorber was investigated by extracting I-V characteristics and electrical parameters under dark and 1-sun illumination. It is revealed that the proposed absorber demonstrates outstanding electrical and sensing performances. Therefore, promoting enhanced resistive behavior and lightscattering effects, this innovative concept of optimized a-Si/Ti multilayer provides a sound pathway for designing promising alternative absorbers for the future development of a-Si-based TFSCs.

In this paper, a new cost-effective multispectral photodetector (PD) based on amorphous-silicon (a-Si)/titanium (Ti) multilayer structure, which achieves a high UV-Visible-NIR photoresponse is elaborated. A new design strategy based on combining FDTD (Finite Difference Time Domain) with GA (Genetic Algorithm) was used to determinate the a-Si/Ti multilayer geometry providing the highest photoresponsivity in UV, Visible and NIR regions. The optimized structure is then fabricated using RF magnetron sputtering technique. A comprehensive analysis of the photodetector electrical, optical and structural properties was carried out. The sputtered a-Si/Ti multilayer was characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and UV-visible-NIR absorption spectroscopy. The a-Si/Ti multilayer PD exhibits a high broadband absorbance of 80% over the UV and even NIR spectrum ranges [200-1100 nm]. Moreover, photoelectrical characterization showed that the developed device exhibits an improved responsivity under UV, Visible and NIR lights (1.9 A/W at 365 nm, 1.24 A/W at 550 nm and 0.93 A/W at 900 nm) and a high I-ON/I-OFF ratio of 68 dB. The broadband multispectral photodetection property offered by the proposed a-Si/Ti multilayer PD opens a new route for the fabrication of promising alternative photodetectors for future high-performance and cost-effective optoelectronic systems. (C) 2021 Elsevier B.V. All rights reserved.

Using a combination of top-down lithographic techniques, isolated, individual and oriented multi-wall carbon nanotubes (MWNTs) were grown on nickel or iron nanoscaled dots. In the first step of the process, micron-sized catalytic metallic dots ( either iron or nickel) were prepared using UV lithography. MWNTs were then synthesized from these catalysts using a direct current plasma-assistance and hot-filament-enhanced chemical vapor deposition (CVD) reactor. Samples were characterized by means of scanning electron microscopy. It turns out that the splitting up of the micron-sized dot is favored in the iron case and that the surface diffusion of the metal is enhanced using ammonia in the gaseous mixture during the CVD process. The results are discussed giving arguments for the understanding of the MWNT growth mechanism. In a second step, a focused ion beam ( FIB) procedure is carried out in order to reduce the initial dot size down to submicronic scale and subsequently to grow one single MWNT per dot. It is found that nickel is most appropriate to control the size of the dot. Dots of size 200 nm +/- 40 nm are then required to grow individual MWNTs.

Hydroxyapatite thin films were grown on layered structures by Pulsed Laser Deposition with the goal of investigating the interface of the ceramic film with the substrate. The latter consisted of Si/TiN/Ti sandwich structures. This multilayer substrate was also prepared by laser ablation earlier in the same experimental session.This particular type of structure was chosen in order to induce the in situ growth of hydroxyapatite directly onto freshly deposited Ti. We tried this way to avoid previous direct Ti exposure to air, hence its oxidation. The subsequent depositions of multilayers were performed with the aid of a carousel multi-target system mounted inside the irradiation chamber. This allowed for selecting in order the respective TiN, Ti and HA targets without opening the chamber between individual depositions.X-ray diffractometry, transmission electron microscopy and selected area electron diffractometry studies revealed the formation at the interface of a transition complex phase, 2 to 25 nm thick, consisting of a mixture of TiO2 and CaP phase. The specific growth of TiN and Ti phases was also investigated. (c) 2007 Elsevier B.V. All rights reserved.

Rutherford backscattering spectrometry was performed using 2 MeV alpha-particles, to characterize electroless platinum contacts on cadmium telluride CdTe(111) crystals, aiming to improve and to understand the structure of the metal electroless chemically deposited. In this paper we have studied the platinum metal contact as well as the interface material-contact. The thickness, the stoichiometry and the concentration profile of platinum, cadmium, tellurium and oxygen present in the surface layers were determined as a function of many parameters, especially the variation trend as function of the chloride solution pH. This work showed the important effect of the crystallographic direction on the growth of Pt on CdTe II-VI semiconductors. Furthermore, the process was more pH dependence at the metalloid Te face than the Cd one. (C) 2007 Elsevier B.V. All rights reserved.

Hydroxyapatite-based ceramics are largely applied as coatings on metallic components of prostheses for inducing osteoblasts apposition and subsequent regrowth. However the ceramics-metal interfaces are often the seat of residual stresses with amplitude primarily depending on the deposition technique and the coating conditions. The amplitude of this stress can stay at origin of failure mechanism at the interface. Our aim is to validate new methods of laser ablation deposition (PLD), allowing for control the residual stresses in ceramic layers and adherence to titanium substrates. We present a study of the growth of HA layers obtained by PLD.

The control of synthesis, stabilization, and organization of metallic nanoparticles is one of the most active subjects in condensed matter science because of possible applications in high performance technology. A route to prepare a collection of ordered nanoparticles in large quantities consists of using the original combination of soft chemistry and surface science. A metal thin film deposited onto a self-assembled two-dimensional silica bead array can restructure through annealing. Pure metallic nanoparticles do form in an ordered array offering the opportunity of studying properties of an individual nanoparticle, thanks to a natural amplifier effect.

L1(0)-ordered FeNiPt2(001) thin films were prepared by the interdiffusion of FePt(001) and NiPt(001) layers codeposited on MgO(001) substrates by molecular beam epitaxy (MBE). A large uniaxial magnetic anisotropy (K-u=9.10(5) J/m(3)) and a reduced magnetic transition temperature (T-c=400 K) were obtained. Growth at 700 K and a first annealing at 800 K result in a large long-range order parameter reflecting the concentration modulation along the growth direction. This high long-range order parameter is conserved in the FeNiPt2 layers after interdiffusion at 900 K, contrary to what is expected from a simple vacancy migration process. This experimental observation can be explained either by a 6-jump cycle mechanism or by the alternate diffusion of a double vacancy, which are both favored energetically over a second-nearest-neighbor jump mechanism or the simultaneous diffusion of a double vacancy as shown by quenched molecular dynamics simulations.

Hydroxyapatite-based ceramics are largely applied as coatings on metallic components of prostheses for inducing osteoblasts apposition and subsequent regrowth. However the ceramics-metal interfaces are often the seat of residual stresses with amplitude primarily depending on the deposition technique and the coating conditions. The amplitude of this stress can stay at origin of failure mechanism at the interface. Our aim is to validate new methods of laser ablation deposition (PLD), allowing for control the residual stresses in ceramic layers and adherence to titanium substrates. We present a study of the growth of HA layers obtained by PLD.

L10 ordered (Fe–Ni)50Pt50 alloy films with perpendicular magnetic anisotropy were successfully prepared by interdiffusing FePt(001) and NiPt(001) layers co-deposited on MgO(001) substrates by MBE. The [001] growth direction corresponds to the epitaxy of the alloy on the substrate and is the interesting growth orientation to get a perpendicular magnetization. The X-ray diffraction shows a high L10 chemical order (S=0.7±0.1). The easy magnetization direction is perpendicular for all samples. The MFM images display highly interconnected stripes corresponding to up and down orientations of the magnetization. Large uniaxial magnetic anisotropy (Ku=9.105J/m3) and suitable magnetic transition temperature (TC=400K) are obtained. The addition of Ni changes the spin–orbit interaction in the FePt compound system, hence causes a decrease of anisotropy, saturation magnetization and coercivity.

The low-temperature surface diffusion of isolated Cr adatoms on Au(111) has been determined using nonperturbing x rays. Changes in the x-ray magnetic circular dichroism spectral line shape together with Monte Carlo calculations demonstrate that adatom nucleation proceeds via quantum tunneling diffusion rather than over-barrier hopping for temperatures <40K. The jump rates are shown to be as much as 35 orders of magnitude higher than that expected for thermal over-barrier hopping at 10 K.

SURFACES, INTERFACES, LIQUIDS AND THIN FILMS C413angle was 0.7 or 0.9 times the critical angle for total reflection.Thus, a depth of 2 and 3 nm, respectively, of the top-layers was probed.For the bulk microstructure, no long-range order has been experimentally established in Pt-Rh owing to small interactions and sluggish kinetics.Only recently, weak diffuse maxima were found at 1 ½ 0 positions.For the near-surface microstructure, typically 600 positions were measured, with about 500 counts in 200 s.After calibration and subtraction of the inelastic scattering contributions, the remaining elastic scattering was decomposed into short-range order scattering, size-effect scattering, and Huang scattering.Local order was revealed for both surfaces, but there were differences, too.For the (110) surface, the diffuse maxima were located at 1 ½ 0 positions as for the bulk microstructure, for the (111) surface they were at ½ ½ ½ positions.In the evaluation, surface segregation was considered negligible, an assumption that seemed justified in view of the measured and calculated segregation profiles.

The effects of the bias current density and the filament-to-substrate distance on the nucleation of diamond on iridium buffer layers were investigated in a hot-filament chemical-vapor deposition (HFCVD) reactor. The nucleation density increased by several orders of magnitude with the raise of the bias current density. According to high-resolution field-emission gun scanning electron microscopy observation, diamond nuclei formed during bias-enhanced nucleation (BEN) did not show any preferred oriented growth. Moreover, the first-nearest-neighbor distance distribution was consistent with a random nucleation mechanism. This occurrence suggested that the diffusion of carbon species at the substrate surface was not the predominant mechanism taking place during BEN in the HFCVD process. This fact was attributed to the formation of a graphitic layer prior to diamond nucleation. We also observed that the reduction of the filament sample distance during BEN was helpful for diamond growth. This nucleation behavior was different from the one previously reported in the case of BEN-microwave chemical-vapor deposition experiments on iridium and has been tentatively explained by taking into account the specific properties and limitations of the HFCVD technique.

Hydroxylapatite layers were grown by pulsed laser deposition on a titanium nitride buffer deposited on silicon or a titanium alloy. Usually the layers are deposited in the presence of water vapors or in oxygen with partial pressures of several mbar. In this study depositions were carried out in vacuum of about 10-5 Torr in order to preserve the memory of the physicochemical state of the expelled material from the target under laser beam impact. This enabled us to study the morphology, the structure and the composition of deposited material by various investigation techniques (XRD, TEM, XPS, SEM). We observed that the deposition is made essentially of hydroxylapatite that have two well-known morphologies: (1) an homogeneous film made of grains of nanometric size without chemical interaction between them and which form a not very dense film; (2) particulates (droplets) where are ejected in solid, pasty or liquid state, accredited by characteristic morphologies and which have complex structures whose origins are the physicochemical transformation and decomposition of hydroxyplapatite during laser beam-target interaction. The physical conditions to obtain a continuous and dense hydroxylapatite film are discussed.

This study attempts to better understand the BEN effects on diamond nucleation on iridium buffer layers investigated by in situ electron spectroscopies (XPS, AES). The surface morphology is further characterised by AFM and SEM FEG. Nano-Auger experiments provide information about the chemical nature of the crystals. During the early stages of BEN, nano-Auger observations revealed a significant carbon sp 3 contribution within the bright crystals whereas the surrounding areas are mainly sp 2 . This emphasizes the BEN effect on the diamond nucleation. Moreover, AES experiments reveal the formation of graphite. The equivalent thickness of the graphite layer is estimated from XPS data, it is close to a monolayer. The graphite formation is not a proper effect of BEN because it is also obtained under CVD environment according to our study. Anisotrope crystals arranged along (110) directions have been characterized by HR-SEM and AFM.

We investigated the relative merits and limits of pulsed laser deposition from AlN targets in vacuum and low-pressure nitrogen in obtaining stoichiometric and crystalline aluminum nitride thin films. We used two UV excimer laser sources (λ=248 nm): a nanosecond system (τFWHM=30 ns) and, a subpicosecond (τFWHM=450 fs) system. The obtained structures were characterized by x-ray diffraction, electron microscopy in cross section, selected area electron diffraction, and profilometry. We demonstrated that the best results are obtained with the sub-ps laser source in vacuum and in low pressure nitrogen when the AlN thin films are very pure, crystalline, clearly exhibiting a tendency to epitaxy. Metallic Al is present in the films deposited with the ns laser source. We believe this is an effect of the gradual decomposition of AlN inside the crater on the target surface under multipulse laser irradiation.

Copper thin films of thickness 1000 Å are evaporated on (100) and (111) single crystal Si wafers in the presence of interfacial native silicon oxide (SiOx). The behavior of copper and the mechanism of compound formation at the Cu/Si interface are studied at different temperatures using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Rutherford backscattering (RBS). Annealing in the 600–750°C temperature range leads to the formation of islands of two copper-rich silicides Cu3Si and Cu4Si. On the Si(100), after annealing at 750°C, we observe epitaxially grown Cu3Si crystallites with square and rectangular shapes. However, on Si(111) annealing at the same temperature yields Cu3Si and Cu4Si crystallites with droplet-like shapes and no sign of epitaxy. The presence of oxygen, after heat treatment under vacuum, is closely related to the formation of copper silicide crystallites.

The possibility of achieving copper-to-cordierite cosintering using a eutectic bonding technique was investigated. Optimized cosintering conditions were determined, in particular the firing atmosphere and heating schedule. Clear correlations have been drawn between macroscopic properties on the one hand and copper diffusion, structural state of the ceramic and chemical composition at the interface on the other by means of electron microprobe, X-ray diffraction, scanning electron microscopy and electron spectroscopy for chemical analysis.

Copper and sol-gel processed cordierite were cosintered in oxidizing atmosphere using an eutectic bonding technique. Firing at low and high heating rates leads to interfaces which present different macroscopic properties. These interfaces were therefore investigated on a microscopic scale by SEM, XPS and STEM analyses. Copper diffusion as well as strong chemical and structural modifications were observed in the interface region. Although these interfaces have good adhesion properties, there was no evidence for the formation of some interfacial copper compound.