Fcc Films Research Articles

The role of microfaceting in heteroepitaxial interfaces

We investigate the effects of microfaceting on the orientation and interface structure of fcc films on fcc substrates by molecular dynamics simulations and atomic resolution electron microscopy. For (110) substrates, the simulations reveal a misorientation between film and substrate lattices that undergoes a sudden change when interfacial facets approach the “magic size”, where a lattice dislocation minimizes the strain energy by compensating the misfit between film and substrate. For a large misfit, the angle of misorientation varies between zero and several degrees, depending on the size and sequence of microfacets. Experimental observations of interfaces in Ag/Ni near the Ni(110) orientation uncover the presence of magic-size {111} facets and show how microfaceting controls the partitioning of misfit dislocations. For facets smaller than the magic size, misfit may be compensated by partial rather than perfect dislocations. In vicinal {hhl} interfaces, made of {111} terraces separated by single-layer steps, a partial dislocation per terrace leads to film growth in the heterotwin orientation. This concept explains a range of previous results on interface structures in a variety of heteroepitaxial systems.

Magnetic properties and structural phase transition in ultrathin fcc Fe(111) and bcc Fe(111) films: First-principles study

The aim of this work is to investigate the structural and magnetic characteristics of Fe thin films with a triangular (hexagonal) lattice surfaces (fcc (111) and bcc (111)). The properties of these structures have been calculated using density functional theory (DFT) implemented in the full-potential local-orbital (FPLO) code. The results indicate a structural phase transition from fcc to bcc structure when the film thickness exceeds 23 Fe atomic monolayers. The considered fcc films prefer the low-spin ferromagnetic state with an average magnetic moment of about 1.0 μB per atom. This moment decreases with increasing film thickness until the critical thickness, where, after the structural transition to the bcc phase, it reaches a value close to that of bulk bcc Fe. Moreover, the values of the magnetic anisotropy energy are positive (perpendicular magnetic anisotropy) for the entire thickness range of films with fcc structure (in ferromagnetic low-spin state) and systematically decrease with increasing film thickness. The presented computational results explain the experimentally observed structural transition and may help to select appropriate substrates with suitable lattice parameters for the deposition of ultrathin Fe(111) films.

The preferred growth orientation of Ti thin film on MgO(100) substrate

Understanding the preferred growth orientation of metal films is of great significance for optimizing film properties and preparing films with special structures. However, early works mainly focused on the preferred growth orientations of FCC and BCC metal films, the preferred growth orientation of HCP metal films and its formation mechanism are unclear. In this work, Ti film was deposited on MgO(100) substrate by magnetron sputtering at 523 K. The preferred growth orientation of Ti film and its formation mechanism were studied by experiment and first-principles calculation. XRD results found the preferred growth orientations of Ti film on MgO(100) substrate were Ti(001), Ti(100), and Ti(101), with Ti(001) being the most favored. First-principles calculation results showed the preferred growth orientation of the Ti film on the MgO(100) substrate was determined by a combination of interface separation work and lattice strain.

Selective corrosion mechanism of CoCrFeMoNi high-entropy alloy in the transpassive region based on the passive film characterization by ToF-SIMS

The selective corrosion mechanism of CoCrFeMoNi HEA in the transpassive region is investigated by electrochemical tests and ToF-SIMS. The results show that Mo and Cr oxides are more enriched in the local passive films formed on the μ and σ phases than those formed on the FCC phase. As the applied potential increases, the passive film thickens, while the Mo and Cr content decreases, which results in the passive film degradation. The local passive films formed on the FCC surface is easier to dissolve in the transpassive region than those formed on the μ and σ phases due to the lower content of Cr and Mo in the FCC films. Therefore, selective corrosion of FCC phase occurs in the transpassive region.

Orbital correlations in ultrathin films of late transition metals

We develop a two-orbital Hubbard model of electron correlations in ultrathin (111)-oriented fcc films of late transition metals such as Co and Ni. Our model indicates that the Mott-Hund's interaction results in ferromagnetic nearest-neighbor orbital correlations. Frustration associated with the mismatch between orbital and crystal symmetries prevents orbital ordering, resulting in the orbital liquid state. This state can be manifested in phenomena involving spin-orbit coupling, such as magnetic anisotropy.

Heteroepitaxy of FCC-on-FCC systems of large misfit

To understand the effects of lattice mismatch on heteroepitaxial growth, we have studied the equilibrium structure and orientation relationships (ORs) of FCC films grown epitaxially on FCC substrates, using molecular dynamics simulations in conjunction with embedded atom method potentials. Three film/substrate systems have been investigated, namely: Ag on Cu, Ag on Ni and Pb on Al. These systems cover a significant range of lattice mismatch, from 12.6% for Ag/Cu to 21.8% for Pb/Al. For each system, the ORs of films on six different substrate orientations, namely: (100), (511), (311), (211), (322) and (111), have been investigated. Films on these susbstrates cover a gradual transition from the oct-cube orientation relationship, which occurs only on (100) substrates, to the heterotwin orientation relationship, which often occurs on (111) substrates. It is found that the resulting ORs vary systematically with substrate orientation, but that the pattern of variation is almost identical for all three systems, and therefore largely independent of mismatch. However, the manner in which mismatch is accommodated does depend on the magnitude of mismatch. Simulations point to an important role for edge-to-edge matching and defects such as stacking faults. An analysis of these results in terms of transformation strains highlights the distinction between the ORs, which are largely independent of mismatch, and the local interfacial structure, which changes directly with mismatch.

Microstructure Characterization of Electrodeposited Invar Fe–Ni Alloy

In Fe–Ni alloys, coefficients of thermal expansion (CTEs) of Fe–Ni alloys with 30 to 40 mass% Ni are small compared to that of Fe (CTE = 12 ppm/K) or Ni (CTE = 13 ppm/K) at near room temperature. In particular, the Fe–Ni alloys with 36 mass% Ni exhibit the lowest CTE (approximately 1 ppm/K) among the Fe–Ni alloys. These Fe–Ni alloys with 30 to 40 mass% Ni are called “Invar alloys.” An Fe–Ni alloy electroplating can be used as the high-throughput Invar alloy fabrication process, furthermore, an Fe–Ni alloy electroforming process can provide precise micrometer-sized three-dimensional structures of Invar alloys with excellent thermal dimensional stability, e.g., MEMS (microelectromechanical systems).We already have prepared electrodeposited Invar Fe–Ni alloys with 36 mass% Ni from plating baths containing saccharin as a stress reducer and containing Fe2+ and Ni2+ ions with various concentration ratios. The electrodeposited Invar Fe–Ni alloys contained of small amount of S (~0.02 mass%) which was originated from saccharin.It was confirmed that as-deposited Invar Fe–Ni alloys were mainly composed of metastable bcc phases, resulting in larger CTEs. When the alloys were annealed at 400°C or above, the equilibrium fcc phases became the predominant phases, accompanied by a drastic decrease of the CTEs. The bcc-to-fcc transformation led to a decrease of the CTEs.In general, electrodeposited fcc Ni and Ni-rich Fe–Ni alloys containing small amounts of S are often embrittled upon annealing. An S (sulfide) in the as-deposited fcc films is dispersed at grain boundaries (2). During recrystallization and grain growth of the fcc grains by heat treatment, the S (sulfide) is extruded into recrystallized an fcc grain boundary with segregating as a thin layer form. The S thin layer coats the fcc grain boundaries and causes grain boundary weakening; therefore, distinct embrittlement occurs, and the embrittlement is promoted by rapid grain growth during annealing (3).With respect to our electrodeposited Invar Fe–Ni alloys with S, in contrast, ductile behavior was confirmed, irrespective of whether the alloys were heat-treated. Upon heat treatment at 400 to 500°C, the Invar Fe–Ni alloys exhibited high strength with good ductility, consistent with their low CTE (1). Moreover, we observed that the S in the Invar Fe–Ni alloys heat-treated at 600°C existed not as a filmy sulfide but as a granular sulfide at grain boundaries. However, the microstructures containing the granular sulfide generated in the film during heat treatment have not been sufficiently explored.In this study, we investigated microstructure of the electrodeposited Invar alloys with and without heat treatment in detail. In particular, morphology and composition of the sulfide were evaluated in the Invar alloys with changing of microstrucutre during an annealing.A galvanostatic electrolysis was conducted for preparation of the Invar Fe–Ni alloy film with 36 mass% Ni from the plating bath (1).A transmission electron microscopy (TEM) was are used for microstructure characterization of the obtained films. A focused-ion-beam (FIB) system have given choice to fabricate cross-sectional TEM specimen.From the results of cross-sectional TEM observation of the electrodeposited Invar Fe- 36 mass%Ni alloys with and without heat treatment at 300 to 600°C, it was found that the as-deposited bcc electrodeposited Invar alloys exhibited a columnar microstructure composed of micrometer-sized coarse grains and submicrometer-sized grains.After the heat treatment at 300 to 400°C, where the proportion of fcc phase increased, the columnar structure became indistinct and the fraction of the submicrometer-sized fine grains increased. Furthermore, no substantial segregated sulfide was detected at the Fe–Ni alloy from elemental mapping by energy dispersive spectroscopy (EDS) in TEM.Heat treatment at 500°C led to grain growth; the alloys treated at this temperature were fully composed of the fcc phase, accompanied by a decrease in the CTE.Our TEM results suggest that S in the Invar Fe-36 mass%Ni alloy became highly concentration upon heat treatment at 500°C and formed granular Fe-rich Fe–Ni–S in grain-boundary triple-points.In our research, the formation of granular sulfide in the film after heat treatment at 500 ° C and its composition were confirmed for the first time.Upon heat treatment at 600°C, Fe-Ni matrix grains grew up as recrystallized grains, accompanied by grain growth of the Fe–Ni–S compound in the matrix grains or grain-boundary triple-points. T. Nagayama, T. Yamamoto and T. Nakamura, Electrochim. Acta, 205, 178 (2016). I. Tabakovic, S. Riemer, K. Tabakovic, M. Sun and M. Kief, J. Electrochem. Soc., 153, C586 (2006). Y. M. Wang, S. Cheng, Q. M. Wei, E. Ma, T. G. Nieh and A. Hamza, Scripta Mater., 51, 1023 (2004).

Impact of crystalline anisotropy on the extrinsic spin Hall effect in ultrathin films

An efficient conversion of a charge current into a spin current is a crucial point for application of the spin Hall effect in practical spintronic devices. Recently, we revealed that this goal can be achieved by using ultrathin fcc (111) and (001) noble metal films doped with Bi impurities, which possess spin Hall angles up to 80%. Here, we show that the effect can be further amplified in monolayer films with a strong crystalline anisotropy. This is demonstrated by considering noble metal films with fcc (110) geometry. Our theoretical study predicts related spin Hall angles exceeding 100% especially when the crystalline anisotropy is increased, which tunes the Fermi surface topology.

Microstructural characterization of medium entropy alloy thin films

This study presents detailed microstructural investigations on single and bilayer thin films of two medium entropy alloys (MEAs) synthesized using magnetron sputter deposition. Single layer thin films of CoCrFeNi and AlCoCrFe show single-phase face-centered cubic (fcc) and body-centered (bcc) structure, respectively. The bilayer thin film consisting of CoCrFeNi (fcc) and AlCoCrFe (bcc) has a sharp interface between them with an equiatomic composition. Nanodiffraction was used to characterize planar defects in the fcc films. This first study on bilayer film of two MEAs is transformative to other systems and will help fundamental studies on high entropy alloys.

Microstructural Characterization of Medium Entropy Alloy Thin Films

This study presents detailed microstructural investigations on single and bilayer thin films of two medium entropy alloys (MEAs) synthesized using magnetron sputter deposition. Single layer thin films of CoCrFeNi and AlCoCrFe show single-phase face-centered cubic (fcc) and body-centered (bcc) structure, respectively. The bilayer thin film consisting of CoCrFeNi (fcc) and AlCoCrFe (bcc) has a sharp interface between them with an equiatomic composition. Nanodiffraction was used to characterize planar defects in the fcc films. Plausibly, this maiden study on bilayer film of two MEAs is transformative to other systems and will help fundamental studies on high entropy alloys.

Crystal structure and local ordering in epitaxial Fe100−xGax/MgO(001) films

In this work we present a study of the structural properties of Fe100−x Gax (x < 30) films grown by Molecular Beam Epitaxy on Mg0(100). We combine long range and local/chemically selective X-ray probes (X-ray Diffraction and X-ray absorption spectroscopy) together with real space imaging by means of Transmission Electron Microscopy and surface sensitive in situ Reflected High Energy Electron Diffraction. For substrate temperature Ts below 400 °C we obtain bcc films while, for x ≈ 24 and Ts ≥ 400oC the nucleation of the fcc phase is observed. For both systems a Ga anticlustering or local range ordering phenomenon appears. The Ga/Fe composition in the first and second coordination shells of the bcc films is different from that expected for a random Ga distribution and is close to a D03 phase, leading to a minimization of the number Ga-Ga pairs. On the other side, a long-range D03 phase is not observed indicating that atomic ordering only occurs at a local scale. Overall, the epitaxial growth procedure presented in this work, first, avoids the formation of a long range ordered D03 phase, which is known to be detrimental for magnetostrictive properties, and second, demonstrates the possibility of growing fcc films at temperatures much lower than those required to obtain bulk fcc samples.

A photoemission spectroscopy study of the initial oxidation of epitaxial fcc and bcc Fe films grown on Cu(100)

The initial oxidation of Fe is a fundamental issue due to its importance for corrosion and catalysis. In this study, we investigate the initial oxidation of epitaxial fcc and bcc Fe thin films grown on a Cu(100) substrate at room temperature. Fe thin films deposited with two different thicknesses on Cu(100) were prepared by molecular beam epitaxy in order to obtain the fcc Fe(100) and bcc Fe(110) surfaces. The structures and the chemical composition of the Fe films were evaluated by LEED and photoelectron spectroscopy, using the facilities at the TEMPO beamline of the Synchrotron SOLEIL. The Fe 2p and O 1s high-resolution spectra were collected during oxidation at a constant O2 pressure in order to build the kinetic curves, which are discussed taking into account the Fromhold-Cook theory. Our result revealed the different initial oxidation kinetics of the films and showed that bcc Fe(110) surface has a much higher reactivity with O2 than the fcc Fe(100). The Fe 2p peak analysis suggests the formation of Fe1−xO and an Fe3+-rich oxide on the bcc Fe(110) surface and Fe1−xO on the fcc Fe(100) surface.

High resolution electron energy loss spectroscopy of spin waves in ultra‐thin cobalt films

Electron energy loss spectroscopy has successfully established itself as the experimental method to study exchange‐dominated, high‐momentum spin waves in ultra‐thin films. Because of insufficient energy resolution, previous studies were limited to spin waves in the high energy range and to wave vectors larger than about q|| = 0.4 Å−1. In this regime, spin waves are strongly damped by decay into Stoner excitations. Furthermore, the spin wave signal of a multilayer film consists of several overlapping modes. After implementation of several technical modifications, our electron spectrometer now enables the study of spin waves with an energy resolution down to 2 meV, and thereby the discrimination of several spin wave modes in ultra‐thin films as well as the study of the intrinsic width of modes down to 1 meV. Examples are presented for fcc and hcp cobalt films and discussed in terms of current theoretical models. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Hydrogen Solubility of Magnetron Co-Sputtered FCC and BCC PdCuAu Thin Films

Palladium–copper–gold (PdCuAu) ternary alloy membranes are promising alternatives to pure palladium for the purpose of hydrogen separation processes. In the current work, PdCuAu ternary alloys were prepared by magnetron cosputtering deposition. All as-deposited samples showed face-centered cubic (fcc) structure in the composition range of study: 30 ≤ [Pd] ≤ 100, 0 ≤ [Cu] ≤ 66, and 0 ≤ [Au] ≤ 6 (in at%). The body-centered cubic (bcc) phase was prepared from the fcc samples by annealing for 4 h at 400 °C under Ar and was identified in alloys with Pd content between 40 and 46 at%. The hydrogen solubility was evaluated for both fcc and bcc phases using an electrochemical method and an electrochemical in situ X-ray diffraction method, respectively. The alloys’ hydrogen solubility increases with the lattice parameter and palladium content, and decreases with crystallite size and phase transition to bcc. In the same range of composition, the hydrogen solubility of the fcc and bcc phases vary in the same way with...

A thermodynamic model for predicting surface melting and overheating of different crystal planes in BCC, FCC and HCP pure metallic thin films

In order to predict as well as study the surface melting phenomena in contradiction to surface overheating, a generalized thermodynamics model including the surface free energy of solid and the melt state along with the interfacial energy of solid–liquid (melt on substrate) has been introduced. In addition, the effect of different crystal structures of surfaces in fcc, bcc and hcp metals was included in surface energies as well as in the atomistic model. These considerations lead us to predict surface melting and overheating as two contradictory melting phenomena. The results of the calculation are demonstrated on the example of Pb and Al thin films in three groups of (100), (110) and (111) surface planes. Our conclusions show good agreement with experimental results and other theoretical investigations. Moreover, a computational algorithm has been developed which enables users to investigate the surface melt or overheating of single component metallic thin film with variable crystal structures and different crystalline planes. This model and developed software can be used for studying all related surface phenomena.

Driving forces for texture transformation in thin Ag films

The well-known thickness-dependent (111)-to-(100) texture transformation in thin FCC films is usually attributed to a competition between interface and strain energies. In this model, thin films retain their (111) texture due to the lower energy of the (111) interface, while thick films transform to (100) due to the lower stiffness and thus strain energy of a (100) film. However, recent work has called this model into question, suggesting that neither the stress nor the interface energy play a dominant role in texture transformation. We investigated the driving forces involved in this transformation by using a bulge test apparatus to induce different stresses in thin Ag films under identical annealing conditions. In situ synchrotron XRD measurements show the change in texture during annealing, and reveal that applied stresses have no effect on the transformation. Stress analysis shows that differences in driving forces for texture transformation due to applied bulge pressure were significant (≈200 kJ/m3), suggesting that a different, much larger driving force must be responsible. Reduction in defect energy has been proposed as an alternative. However, vacancy and dislocation densities must be exceptionally high to significantly exceed the strain energy and do not provide obvious orientation selection mechanisms. Nanotwins in reported densities are shown to provide greater driving force (≈1000 kJ/m3) and may account for orientation selection. The large difference between the calculated strain and defect energies and the driving force for grain growth (21,100 kJ/m3) casts doubt on the applicability of a simple thermodynamic model of texture transformation.

Growth of thermally stable crystalline C60 films on flat-lying copper phthalocyanine

We observe thermally stable growth of fcc(111) films of fullerene-C60 on top of crystalline, flat-lying, CuPc film structures on graphite using combined grazing incidence wide-angle X-ray scattering and atomic force microscopy.

MECHANICAL AND TRIBOLOGICAL BEHAVIOR OF VN AND HfN FILMS DEPOSITED VIA REACTIVE MAGNETRON SPUTTERING

HfN and VN thin films were deposited onto silicon and 4140 steel substrates with r.f. reactive magnetron sputtering by using Hf and V metallic targets with 4-inch diameter and 99.9% purity in argon/nitrogen atmosphere, applying a substrate temperature of 250°C and a pressure of 1.2 × 10-3 mbar. In order to evaluate the structural, chemical, morphological, mechanical and tribological properties, we used X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM), scanning electron microscopy (SEM), nanoindentation, pin-on-disc and scratch tests. Film structure determined by XRD showed that FCC ( NaCl -type) films are formed in both the cases by δ- HfN and δ- VN phases. Hardness and elastic modulus values obtained for both the films were 21 and 224 GPa for the HfN film and 19 and 205 GPa for the VN film, respectively. Additionally, the films showed low friction coefficient of 0.44 for HfN and 0.62 for VN when these films were evaluated against 100 Cr 6 steel, and finally the critical load was found at 41 N for the HfN film and 34 N for the VN film.

Electrochemical control of composition and crystalline structure of CoNi nanowires and films prepared potentiostatically from a single bath

Using a single bath and controlling the deposition regime, it has been possible to grow electrochemically both CoNi films and nanowires of variable composition and crystalline structure. Low deposition potentials favour the formation of cobalt-rich hcp CoNi films, whereas fcc films (also cobalt-rich) can be obtained at more negative deposition potentials as a consequence of the faster deposition rate. By using membranes to grow CoNi nanowires, the control of the deposition rate is more difficult because the growth is strongly affected by the transport of the electroactive species into the channels: in this case, the structure of the nanowires is also affected by the type of the membrane used (nature, pore’s diameter and length). Short nanowires (between 2μm and 250nm length) in membranes with decreasing pore diameter (200, 100 and 20nm) have been electrodeposited in order to tend to monodomain magnetic nanowires. The magnetic properties of the different deposits related to size, shape, crystalline structure and composition were studied and interpreted.

Elastic fields of interacting point defects within an ultra-thin fcc film bonded to a rigid substrate

AbstractCertain physical and mechanical phenomena within ultra-thin face-centered cubic (fcc) films containing common types of interacting point defects are addressed. An atomic-scale lattice statics in conjunction with many-body interatomic potentials suitable for binary systems is conducted to analyze the effects of the depth on the: (1) formation energy and layer-by-layer displacements due to the presence of vacancy-octahedral self-interstitial atom (OSIA) ensemble, and (2) elastic fields as well as the free surface shape in the case of vacancy-dopant interaction. Moreover, the effects of the inter-defect spacing for various depths are also examined. To ensure reasonable accuracy and numerical convergence, the atomic interaction up to the second-nearest neighbor is considered.