Normal grain growth (NGG) of a (111) textured Ni film on c-sapphire and abnormal grain growth (AGG) of (100) grains at the expense of this (111) texture has been studied as a function of temperature with and without a capping layer. The grain boundaries (GBs) in the Ni film are controlled by the preferred orientation relationships (ORs) adopted by the Ni grains on the sapphire substrate. The 2 variants of a single OR, Ni(111)<110>//Al2O3(0001)<1100>, form a (111) mazed bicrystal with Sigma(3) GBs. The (100) grains have a single OR, Ni(100)<010>//Al2O3(0001)<1100> with 3 variants; their GBs within the (111) grains have the (111)<110>//(100)<010> misorientation. (100) AGG within the (111) mazed bicrystal of the 100 nm Ni film takes place above 1023 K. The orientation transition is driven by the biaxial elastic modulus anisotropy which favors the growth of (100) grains over (111) grains, as this reduces the elastic strain energy induced by the thermal mismatch between Ni and sapphire. (100) AGG is suppressed and the NGG of the (111) texture is slowed down when the film is covered by a 10 nm amorphous alumina layer aimed at inhibiting surface diffusion. Thus, it is proposed that as long as the surface can act as a sink for the point defects diffusing along the GBs, the movement of the GBs is correlated to the diffusivity of atoms and vacancies, which is a function of their misorientation and crystallographic GB structure.

Previous studies have shown that the orientation relationships which develop in hetero-epitaxy are strongly influenced by the alignment of steps in the deposit with the pre-existing steps of the substrate. In this paper we use a combination of experiments with computer simulations to identify the important influence of substrate step structure on the eventual orientation relationships that develop in the deposit. We have made use of Ag deposited on Ni as it has been used extensively as a model system for the study of hetero-epitaxy. This system displays a large lattice mismatch of 16%. It is shown that on any surface vicinal to Ni(111), which has two possible kinds of 〈110〉 steps (A-steps with {100} ledges and B-steps with {111} ledges), a Ag deposit adopts a single orientation relationship because only A-steps remain stable in the presence of Ag.

Homogeneous face-centered cubic (fcc) polycrystalline CoCrFeNi films were deposited at room temperature on (0001)alpha-Al2O3 (c-sapphire). Phase and morphological stability of 200 to 670 nm thick films were investigated between 973 K and 1423 K. The fcc-phase persists while the original <111> texture of 30-100 nm wide columnar grains evolves into ~10 or ~1000 micron wide grains. Only the grains having specific orientation relationships to the sapphire grow; as in the case of pure fcc metal (M) films 4 orientation relationships (OR) are found: OR1 (M(111)[1-10]//alpha-Al2O3 (0001)[1-100]) and OR2 (M(111)[1-10]//alpha-Al2O3 (0001)[11-20]) and their twin-related variants (OR1t and OR2t). Below 1000 K, the film microstructure stabilizes into 10 micron wide OR1 and OR1t twin grains independent of film thickness. Above 1000 K, the OR2 and OR2t grains expand to sizes exceeding more than a 1000 times the film thickness. Upon annealing, the films either retain their integrity or break-up depending on the competing kinetics of grain growth and grain boundary grooving. Triple junctions of the grain boundaries, the major actors in film stability, were tracked. Thinner films and higher temperatures favor film break-up by dewetting from the holes grooved at the triple junctions down to the substrate. The grain boundaries of the OR2 and OR2t grains migrate fast enough to overcome the nucleation of holes from which break-up could initiate. The growth of the OR2 and OR2t grains in this complex alloy is faster than in pure fcc metals at equivalent homologous annealing temperatures.

The study of HEA in the form of thin films aims at providing missing data on HEA phase stability. Indeed, the small bulk volume of a film, combined with the presence of grain boundaries and interfaces, helps in achieving thermodynamic equilibration of these complex alloys. In addition, polycrystalline films can be used to test the role of grain boundaries on the mechanical properties of HEAs. Here we present a study of the stability of polycrystalline CoCrFeNi thin films, grown on (0001) α-Al2O3 (c-sapphire), with respect to annealing treatments. It has been found that extremely large grains can grow in the film depending on their orientation relationship to the c-sapphire substrate. Despite their complex chemistry, the grains in the 200 - 670 nm thick CoCrFeNi FCC films investigated, adopt the same orientation relationships as those of pure FCC metal films on c-sapphire. However, the grains in CoCrFeNi grow much larger at homologous annealing temperatures. The films have been synthesized at room temperature, using magnetron sputtering from four pure element targets in a chamber with UHV base vacuum. They consist of 30-100 nm wide columnar FCC grains with a texture. Upon annealing for 1 hour in the range 973 K to 1423 K under an Ar-H2 atmosphere, grain growth and grain boundary grooving compete to either stabilize or break-up the film. The microstructure evolves into larger grains and/or islands, of four different orientation relationships: OR1 (Me(111)[1-10]//α-Al2O3(0001)[1-100] and OR2 (Me(111)[1-10]//α-Al2O3(0001)[11-20] and their twins (OR1t and OR2t). Thinner films and higher temperatures favor the dewetting of the film to form single-crystalline islands. Dewetting initiates from holes which nucleate at grain boundary triple junction grooves, and which have deepened sufficiently to reach the substrate. At the highest temperatures, the OR2 and OR2t grains grow to sizes exceeding 1000 times the film thickness. The migration of the grain boundaries of these grains is fast enough to overcome both grooving and the nucleation of dewetting holes.

Nuclear reaction analysis (NRA) has been used for the determination of nitrogen content in diamond by monitoring the N-14(d,p(0))N-15 nuclear reaction from a 1.4 MeV deuteron beam incident on the diamond samples. Results obtained in bulk diamond are compared to those inferred from infrared optical transmission measurements. Furthermore, nitrogen content has also been measured by NRA in diamond nanoparticles and in the light of these results we evaluate the conversion of nitrogen to nitrogen-vacancy (NV) complexes in both bulk diamond and diamond nanoparticles after a 2.4 MeV-proton irradiation and subsequent thermal annealing.

Nano-crystalline Ni and Cu films deposited on the r-plane of sapphire (alpha-Al2O3) develop a <1 1 1> fiber-texture upon annealing, in which grains grow up to 300 to 500 times larger than the film thickness. Most of the largest grains, which have grown at the expense of others, display one of four preferred orientation relationships (ORs) to the substrate. The four preferred ORs are OR1r = Me(1 1 1)[1 (1) over bar 0]//alpha-Al2O3(1 (1) over bar 0 2)[1 1 (2) over bar 0], OR2r = Me(1 1 1)[1 (1) over bar 0]//alpha-Al2O3(1 (1) over bar 0 2)[(1) over bar 1 0 1] (Me = Ni or Cu), and their twins, which are rotated 60 degrees about the <1 1 1> axis perpendicular to the substrate. For these ORs, one of the densest <1 1 0> atomic rows that lies within the Me {1 1 1} interfacial plane, aligns with the direction of the step edges that form at the intersection of the r-plane with one of its neighboring facets on the equilibrium shape of sapphire (i.e. the c(0001), p-{1 1 (2) over bar 3} or s{1 0 (1) over bar 1}-planes). One of the ORs is most preferred when the steps at the interface are such that a {1 0 0}-type ledge of the Me {1 1 1} interfacial plane faces the ledge of the sapphire step. This observation provides a useful insight into the origin of the preferred ORs, and confirms the important role of surface steps in texture development. The evolution of Ni films of different thicknesses, ranging from 100 to 560 nm, was analyzed. Grain boundary grooving inhibits grain boundary motion and favors hole formation and dewetting in the thinnest films (100 nm). The crystals left behind after dewetting display ORs which may differ from the preferred ones. Large grains with the preferred ORs can grow at the expense of others when the film thickness is greater than 300 nm.

The removal of black crusts decaying the surface of artworks is an important concern for the conservation of cultural heritage. Nd:YAG laser cleaning of encrusted stones and plasters at 1064 nm is widely recognized as an effective restoration technique, but induces a noticeable yellowing of the treated surface. Several researches carried out on the effects of laser cleaning have been focused on the induced yellowing and how to visually mitigate this phenomenon. To this end, UV-B radiations were successfully used to lessen the laser-induced yellowing due to the removal of lamp black particles on gypsum. The mechanism at play for both the formation of the compounds yellowing the surface and their disappearance upon UV-B exposure remains, however, poorly understood. Within the frame of this research, we apply surface-sensitive characterization techniques to analyze the yellowed surface produced after Nd:YAG Q-Switched laser cleaning of lamp black deposit on a gypsum plate, and the same surface after UV-B exposure. A combination of X-ray photoelectron spectroscopy and Fourier-transformed infrared spectroscopy has been used to identify the residual carbon compounds responsible for the yellow coloration of the substrate. A nanoscale structural description of the ejected particles collected during the laser cleaning was finally performed with transmission electron microscopy. We found that the yellowing is due to partially oxidized hydrocarbons compounds deposited at the surface of the gypsum substrate. We propose that they form by reactions between carbon species emitted by the vaporization of the carbon particles, with hydrogen and oxygen produced by the dissociation of water molecules coming together from dehydration of the gypsum surface and from the water sprayed by the operator during cleaning. (C) 2019 Elsevier Masson SAS. All rights reserved.

We investigated the effect of laser fluence and spot size on the structure and composition of BiFeO3 (BFO) epitaxial thin films grown on SrTiO3 substrates by Pulsed Laser Deposition. X-ray diffraction shows that BFO's out of plane lattice parameter increases with the laser fluence. A coherent epitaxial film growth is observed for all tested laser fluences and spot sizes for thicknesses up to 16nm. The critical thickness at which relaxation occurs depends either on the laser fluence or spot size. The fluence dependence of the out of plane lattice parameter is accompanied with a cationic composition variation. Bi vacancies are evidenced at lower fluences while as Bi/Fe tends towards 1 a higher relaxation critical thickness is observed. An optimum Bi/Fe ratio is obtained for a fluence of 1.72J/cm2. This result was confirmed by wavelength-dispersive x-ray spectroscopy (WDS) scans over a 1cm2 film. An excellent thickness and composition uniformity is attained over the entire sample area.

12 MeV proton activation analysis is applied to a variety of archaeological specimens (glass, pottery, mortar and ivory) and its usefulness studied. The method is non-destructive and Ca, Ti, V, Cr, Fe, Cu, Zn, As, Sr, Y, Zr and Sb, ranging from percentage to parts per million (ppm) level were determined. The detection limits in archaeological glass for Ti, V, Cr, Fe, As, Sr, Y and Zr are at 1–10 ppm level; Cu, Zn and Sb at 20–35 ppm level, and Ca at 150 ppm level.

The question of the helium behavior in silicon carbide has been studied at the atomic scale by numerical simulations, but no experiment has been carried out to assess the results hitherto. This paper describes the first experiments allowing this comparison. 6H–SiC single crystals were implanted with 50-keV He ions at a fluence of 1015He/cm2 at room temperature. The as-received and as-implanted samples were analyzed by RBS and NRA in channeling mode along the main crystallographic planes and across three main axes. The measurements have shown that a portion of the He is located in the interstitial tetrahedral sites as predicted by the numerical simulations. The same measurements were performed on an implanted sample subsequently annealed at 400°C under Ar atmosphere. They have shown that the quantity of He detected in interstitial tetrahedral sites TSi and TC has not significantly changed whereas that of He detected in the main crystallographic plane and in the main axis has increased. This increase is likely caused by He atoms migration at 400°C toward interstitial positions located inside vacancies such as VSi and VSiVC. In parallel a partial recovery of the Si and C sublattices has been observed.

The piezoelectric properties of compositional spread (1 − x)BiFeO3-xGaFeO3 epitaxial thin films are investigated where Ga3+ substitution for Bi3+ is attempted in Bi1−xGaxFeO3 compounds. Ga content x was varied from 0 to 12% (atomic). Ferroelectric characterizations are reported at various length scales. Around 6.5% of Ga content, an enhancement of the effective piezoelectric coefficient d33eff is observed together with a change of symmetry of the film. Measured d33eff values in 135 nm thick films increased from 25 pm/V for undoped BiFeO3 to 55 pm/V for 6.5% Ga with no extrinsic contribution from ferroelastic domain rearrangement.

Li2TiO3 ceramic is one of the promising solid breeding candidates for fuel generation in deuterium–tritium Fusion reactors. The Tritium (T) release characteristics consist of a complex combination of gas diffusion stages inside the solid. Considering that this ceramic will produce high concentration of gaseous transmutation products (3H and 4He) when exposed to high-energy neutrons, there are considerable interests in studying 3He thermal evolution for the fundamental understanding of the light ion behavior in breeder blanket materials under reactor conditions. 3He atoms used to simulate the 4He incorporation were implanted by a 600keV ion beam at a fluence of 1017 at/cm2 and the 3He(d,α)1H nuclear reaction analysis (NRA) technique was subsequently used to study depth profiles evolution after different thermal annealing treatments. The release experiments showed that 3He outgassing is not effective at room temperature, remaining quite negligible till 300°C. After this temperature, the 3He content in the sample reduces steadily with increasing the annealing temperature, and less than 5% of the initial 3He concentration was found at 900°C after an isochronal annealing, without significant depth-profile broadening. Scanning and transmission electron microscopies characterization highlight the microstructural changes of the implanted and annealed ceramic within the nuclear cascades zone. The correlation of results obtained by electron microscopy and NRA technique leads to the conclusion that the helium release is governed by a transport mechanism that involves rapid migration/diffusion through interconnected gas cavities and resulting microcracks before reaching grain boundaries and opened pores.

Tungsten has been selected as the material of the divertor of the ITER fusion reactor. In operation, tungsten will be submitted to high alpha particles bombardment. The consequence of helium implantation is a major issue for the reliability of tungsten components. The aim of the study was to investigate the behavior of helium implanted in tungsten at low energy and low flux. 320eV Helium ions were introduced by plasma immersion at the flux of 2.5×1018ion/m−2/s−1. The helium behavior was investigated by Nuclear Reaction Analysis and the evolution of the tungsten lattice by Positron Annihilation Spectroscopy (PAS). Helium-implanted tungsten exhibits a low retention rate (13.6% at 9.4×1019Hem−2) which decreases with the implantation fluence. The desorption of helium starts at low temperature (<400K). SEM analysis after annealing over 973K shows sparse pores probably due to bubbles opening at the surface. The creation of helium-filled defects in the near surface layer (0.5 to ∼20nm) was followed by PAS. A low level of damages was introduced by 12MeV proton irradiation, prior to He introduction and allowed to examine the influence of pre-existing defects on the helium trapping. The PAS results suggest that the early stage of the formation of helium-filled vacancy clusters does not require the presence of pre-existing vacancy and thus proceed from the trap mutation phenomenon.

Fluorine was determined by particle induced gamma-ray emission (PIGE) technique with 2.3 MeV protons in elephant, mammoth, aquatic (walrus, pot whale, narwhal, hippopotamus) and archaeological ivory, with concentration varying between 55 ppm and 2.3 %. The characteristic variation of F concentration with species shows that it has the potential to serve as a marker in identifying different types of ivory. Additionally, Na concentration was also reported in all the analysed samples.

In this work, we report the investigation of a planar waveguide in a 2D periodically-poled lithium niobate (PPLN). The waveguide is fabricated by helium (He(+)) implantation at 2 MeV and a fluence of 1.5 x 10(16) ions/cm(2). Second harmonic generation (SHG) at 532 nm using a Q-switched laser and a CW laser diode at 1064 nm, was measured as a function of angular distribution and temperature. The experimental results show higher gain in SHG conversion efficiency in the waveguide than in the bulk 2D PPLN. In particular, SHGs from 2D reciprocal lattice vectors (RLV) are observed and studied.

The influence of post deposition annealing (PDA) up to temperatures of T-PDA = 900 degrees C on the morphology and agglomeration behavior of ambient temperature sputter deposited platinum onto anodic aluminum oxide templates is investigated. Both cluster agglomeration and diffusion processes occur on the surface and on the inner channel walls. When the annealing temperature is less than 400 degrees C, particles are diffusing inside the channels. Around T-PDA = 400 degrees C, a particle agglomeration process is taking place. A diffusion process is playing an important role and the Pt particles are able to reach a depth of 12 mu m. The surface morphology exhibits a remarkable change for annealing temperature above 600 degrees C, where Pt is migrating on the outermost surface for forming flat films. When further enhancing T-PDA to 900 degrees C, the particles on the surface and in the channels agglomerate together to form separated large flat islands. Moreover, the maximum channel depth where platinum is present is around 12 mu m. (C) 2012 Elsevier B.V. All rights reserved.

We prepared SrTiO3 (STO) to Ba0.6Sr0.4TiO3 (BST06) out-of-plane composition-graded films on STO (100) substrates by means of a dual-beam dual-target pulsed laser deposition technique. In the deposition system, a sliding mirror divides one KrF excimer laser beam into two, realizing the dual-beam of controlled intensity ratio. X-ray diffraction reciprocal space mapping has revealed that the graded films deposited under oxygen pressure at or lower than 1×10−3mbar were coherently strained with the same in-plane lattice parameter as the substrate. Their composition gradient along the growth direction was confirmed by Rutherford backscattering analysis to be uniform. We deposited BST06 top layers of various thickness on epitaxial composition-graded (ECG) buffer layers and examined their coherency and crystallinity. In comparison with the cases of STO homoepitaxial buffer layers, ECG buffer layers achieved better crystallinity of top BST06 layers, suggesting that the crystallinity of a heteroepitaxially-grown film is affected not only by the in-plane lattice matching but also by the out-of-plane lattice continuity with the substrate. ECG films that bridge compositions of substrate and top layer materials can be useful buffer layers for epitaxial growth of lattice-mismatched oxide films.

A study of the reactive sputtering of aluminum was carried out by coupling energy flux measurements at the substrate location with conventional diagnostics of the gas phase and analyses of the deposited films. The main purpose was to get some insight into the elementary mechanisms involved at the substrate surface during the film growth in the well known metal and oxide regimes and at the transitions from one to another. Measurements were carried out in front of a 10 cm Al target at a power of 400 W (i.e. 5 W/cm(2)) and a total pressure of 0.6 Pa. The flow rate ratio (O-2/O-2 + Ar) was varied in the range 0 to 50%. Different kinetics and values of energy transfer, denoting different involved mechanisms, were evidenced at metal-oxide (increasing flow rate) and oxide-metal (decreasing flow rate) transitions. The metal-oxide transition was found to be a progressive process, in agreement with optical emission spectroscopy and deposit analysis, characterized by an increase of the energy flux that could be due to the oxidation of the growing metal film. On the contrary, oxide-metal transition is abrupt, and a high energy is released at the beginning that could not be attributed to a chemical reaction. The possible effect of O- ions at this step was discussed. (C) 2013 Elsevier B.V. All rights reserved.