Highly textured and twinned Cu films fabricated by pulsed electrodeposition

This paper reports the influence of substrates and peak current densities on: crystallographic textures; twin density, thickness, spacing and twin boundary orientations; and electrical transport and mechanical properties of Cu films fabricated by pulsed electrodeposition. Films of {3 1 1}, {1 0 0}, {1 1 0} and {1 1 1} out-of-plane textured Cu with a high density of {1 1 1} twins were synthesized. With increasing twin density and change of texture by selection of the peak current densities and substrates, the ultimate tensile strength, hardness and elongation monotonically increase. This paper also discusses the mechanisms for manipulation of texture and twin densities via changing both the peak current densities and substrates, and the correlation among the microstructure, electrical resistivity and mechanical properties.     

Twinning of CaMgSi phase in a cast Mg–1.0Ca–0.5Si–0.3Zr alloy

Two types of twins and an orientation domain (orientation twin) were found in CaMgSi particles formed in a Mg–Ca–Si alloy by transmission electron microscopy. The two types of twins were shown to be a (1 0 2) twin with the (1 0 2) plane serving as the twinning plane and a (0 1 1) twin with the (0 1 1) plane serving as the twinning plane. In addition to the frequently observed two-fold twin, two different three-fold twins were also observed in the (1 0 2) twinned CaMgSi particles; their crystallographic features are discussed in detail. The boundaries of both the (1 0 2) and (0 1 1) twins were found to be coincident with the twinning plane. The orientation domains were formed by one segment rotating 60° about the [1 0 0] axis relative to the other. The possible formation mechanisms of the twins and orientation domain are discussed based on a crystallographic consideration.     

Microtwinning in highly nonstoichiometric VOx thin films

Both pulsed-DC biased and commercial ion-beam sputtered VO_x thin films maintain a face-centered-cubic nanocrystalline phase, even for stoichiometries of x > 1.5, which is well outside the bulk equilibrium solubility range for cubic VO_x. Many of these highly nonstoichiometric films exhibit a high density of microtwins, which give rise to unusual fine structure in the selected-area electron diffraction patterns, namely: an additional defect ring; a significant broadening of the {2 0 0} ring; pairs of parallel rod features which are tangent to the additional defect ring; and additional fine-structure features between the {2 0 0} and {2 2 0} rings. The formation of the microtwins is correlated with the coalescence of vanadium vacancies along the {1 1 1} twin planes in the crystalline lattice.     

Structure of martensite in Ti-rich Ti–Ni–Cu thin films annealed at different temperatures

After annealing at different temperatures, there are different types of precipitates in Ti-rich Ti–Ni–Cu thin films: plate-like Guinier–Preston (GP) zones, Ti₂Cu precipitates and spherical Ti₂Ni precipitates. The (0 1 1) compound twins and (1 1 1) type I twins are dominant in Ti-rich Ti–Ni–Cu thin films annealed at different temperatures, which suggests that the precipitates do not change the twinning modes of the B19 martensite. However, the amount of the (0 1 1) compound twin increases with increasing annealing temperature due to its small twinning shear. In thin films with GP zones or Ti₂Ni precipitates, the amount of martensite with a single-pair morphology is less than that in thin films without precipitates. And in thin film with Ti₂Cu + Ti₂Ni precipitates, hardly any martensite with a single-pair morphology is observed. For the different types of precipitates at the different annealing temperatures, the obstacle of the precipitates to the growth of the B19 martensite plate also varies. The GP zones slightly hinder the growth in the width of martensite, resulting in wavy twin boundaries at the martensite variant tip. The Ti₂Cu precipitates can change both the width and the direction of the martensite plates. Ti₂Ni precipitates also significantly disturb or impede the growth of the martensite variants. These effects lead to a decrease in the maximum shape recoverable strain with increasing annealing temperature.     

Characterization of mobile type I and type II twin boundaries in 10M modulated Ni–Mn–Ga martensite by electron backscatter diffraction

Mobile type I and type II twin boundaries mediating the magnetic field-induced strain in five-layered modulated (10M) Ni–Mn–Ga martensite were analyzed by electron backscatter diffraction. Taking into account the slight monoclinic distortion of the pseudo-tetragonal lattice, the electron backscatter diffraction study reveals domains of 0.01–1 mm thickness adjacent to the type I and type II twin boundaries. The domains differing in the modulation direction are {1 0 0) compound twins and their effect on twinning stress is discussed. Detailed analysis of type II twin boundary reveals that the domains are further internally twinned by compound {1 1 0) twins 1–15 μm in size. An additional example of a complex twin microstructure combining type I and type II twin boundaries is presented.     

Microstructural characterizations of magnetron sputtered Ti films on glass substrate

Magnetron sputtered Ti thin films deposited on glass substrates under varying deposition parameters were characterized by X-Ray Diffraction, Scanning Electron Microscopy and Atomic Force Microscopy. The textures of the Ti films characterized by X-ray diffraction revealed the initial (1 0 0) preferred orientation but it transformed in to (0 0 2) and (1 0 1) orientation with increase in sputtering power and substrate temperature, respectively. The preferred orientations of (0 0 2) and (1 0 1) were observed for the films deposited with the sputtering pressure of 5 mTorr and 20 mTorr, respectively. The average surface roughness of the Ti films showed an increasing trend with power, pressure, and temperature from the Atomic Force Microscopy analysis. The dense film morphology was observed in the Scanning Electron Microcopy images of Ti thin films deposited with higher substrate temperature (500 °C). X-ray diffraction analysis revealed that the grain size of the Ti thin films exhibits an increasing trend with varying deposition parameters.     

Epitaxial Ni–Mn–Ga/MgO(1 0 0) thin films ranging in thickness from 10 to 100 nm

Thin films of Ni–Mn–Ga alloy ranging in thickness from 10 to 100 nm have been epitaxially grown on MgO(1 0 0) substrate. Temperature-dependent X-ray diffraction measurements combined with room-temperature atomic force microscopy and transmission electron microscopy highlight the structural features of the martensitic structure from the atomic level to the microscopic scale, in particular the relationship between crystallographic orientations and twin formation. Depending on the film thickness, different crystallographic and microstructural behaviours have been observed: for thinner Ni–Mn–Ga films (10 and 20 nm), the L2₁ austenitic cubic phase is present throughout the temperature range being constrained to the substrate. When the thickness of the film exceeds the critical value of 40 nm, the austenite-to-martensite phase transition is allowed. The martensitic phase is present with the unique axis of the pseudo-orthorhombic 7M modulated martensitic structure perpendicular to the film plane. A second critical thickness has been identified at 100 nm where the unique axis has been found both perpendicular and parallel to the film plane. Magnetic force microscopy reveals the out-of-plane magnetic domain structure for thick films. For the film thickness below 40 nm, no magnetic contrast is observed, indicating an in-plane orientation of the magnetization.     

The effect of film thickness on the failure strain of polymer-supported metal films

We perform uniaxial tensile tests on polyimide-supported copper films with a strong (1 1 1) fiber texture and with thicknesses varying from 50 nm to 1 μm. Films with thicknesses below 200 nm fail by intergranular fracture at elongations of only a few percent. Thicker films rupture by ductile transgranular fracture and local debonding from the substrate. The failure strain for transgranular fracture exhibits a maximum for film thicknesses around 500 nm. The transgranular failure mechanism is elucidated by performing finite element simulations that incorporate a cohesive zone along the film/substrate interface. As the film thickness increases from 200 to 500 nm, a decrease in the yield stress of the film makes it more difficult for the film to debond from the substrate, thus increasing the failure strain. As the thickness increases beyond 500 nm, however, the fraction of (1 0 0) grains in the (1 1 1)-textured films increases. On deformation, necking and debonding initiate at the (1 0 0) grains, leading to a reduction in the failure strain of the films.     

Effect of copper content and substrate bias on structure and mechanical properties of reactive sputtered CrCuN films

The CrCuN films with various Cu contents were deposited under different substrate bias by DC magnetron sputtering. The influence of Cu content and substrate bias was examined with regard to the microstructure, morphology, and mechanical properties of these films. The CrCuN films containing low Cu content (3.4 at.%) present distinctive columnar growth. Their preferred orientations change from (1 1 1) (?50 V bias) to (2 0 0) (?200 V bias) and surface morphology changes from porous to granular structure with increasing bias. However, when the copper content is increased to 15 at.%, CrCuN films remain (2 0 0) preferred growth independent of bias, while the film maximum hardness is reduced from 32 GPa to 20 GPa because of excess soft metal.     

Thin film epitaxy and structure property correlations for non-polar ZnO films

Heteroepitaxial growth and strain relaxation were investigated in non-polar a-plane (1 1 ?2 0)ZnO films grown on r-plane (1 0 ?1 2)sapphire substrates in the temperature range 200–700 °C by pulsed laser deposition. The lattice misfit in the plane of the film for this orientation varied from ?1.26% in [0 0 0 1] to ?18.52% in the [?1 1 0 0] direction. The alignment of (1 1 ?2 0)ZnO planes parallel to (1 0 ?1 2)sapphire planes was confirmed by X-ray diffraction θ?2θ scans over the entire temperature range. X-ray ?-scans revealed the epitaxial relationship:[0 0 0 1]ZnO6[?1 1 0 1]sap; [–1 1 0 0]ZnO6[?1 ?1 2 0]sap. Depending on the growth temperature, variations in the structural, optical and electrical properties were observed in the grown films. Room temperature photoluminescence for films grown at 700 °C shows a strong band-edge emission. The ratio of the band-edge emission to green band emission is 135:1, indicating reduced defects and excellent optical quality of the films. The resistivity data for the films grown at 700 °C shows semiconducting behavior with room temperature resistivity of 2.2 × 10^?3 Ω-cm.     

Orientation- and microstructure-dependent deformation in metal nanowires under bending

Device miniaturization requires the bending of nanowires (NWs) on the nanoscale. To explore the mechanical behavior the mechanisms of plastic deformation of nickel nanowires of different orientations, sizes and twin structures under bending were investigated by means of molecular dynamics simulation. We show that plastic deformation can be either homogeneous or heterogeneous, depending on the NW orientation. Bending 〈1 2 1〉 oriented NW leads to homogeneous plastic flow, attributed to the large capacity for storage of axial extended dislocations (AEDs). AEDs are formed by constriction and cross-slip of inclined extended dislocations to the neutral (1 1 1) planes. The stacking of AEDs forms new defect structures, such as micro-twins and small hcp embryos. More localized deformation appears in NWs with 〈1 1 1〉 and 〈0 1 0〉 orientations at large bending angles, which is mainly caused by the pile-up and escape of inclined dislocations. The mechanical behavior of NWs is altered by introducing preset nano-twins,. The strength increases monotonically as the twin boundary spacing decreases. Among the three orientations the 〈1 2 1〉 oriented NWs with twin structure have been demonstrated to possess both high strength and ductility. A theoretical model based on geometrically necessary dislocations is proposed to quantify the contribution of various defects to the plastic deformation under bending, which links the continuum theory and atomistic simulations.     

Highly (1 0 0)-textured Pb(Zr0.52Ti0.48)O3 film derived from a modified sol–gel technique using inorganic zirconium precursor

Highly (1 0 0)-textured Pb(Zr_0.52Ti_0.48)O₃ films have been prepared on platinized silicon substrate by a modified sol–gel technique using inorganic zirconium precursor. The X-ray diffraction analysis on the crystallinity and texture evolution of sol–gel lead zirconate titanate (PZT) films revealed that the films were well crystallized to perovskite phase when annealed at 550 °C, and that highly (1 0 0) preferred orientation dominated in the PZT films after annealed at 650 °C. The (1 0 0)-oriented PZT film exhibited the remnant polarization of 26.3 μC/cm² and the coercive field of 100 kV/cm.     

Preparation and characterization of sol–gel derived (1 0 0)-textured Pb(Zr,Ti)O3 thin films: PbO seeding role in the formation of preferential orientation

Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary region were deposited onto Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates using a sol–gel method. A seeding layer was introduced between the most underlying surface of the PZT film and the platinum electrode surface to control the texture of the PZT thin film. The lead oxide seeding layer resulted in the formation of a single-phase perovskite and absolutely (1 0 0)-textured PZT film. SEM, XRD, XPS, and AES were used to characterize the evolution of the lead oxide layer and the PZT thin films. The growth kinetic mechanism of the (1 0 0)-textured PZT thin films was proposed phenomenologically. The ferroelectric and piezoelectric properties of the PZT films were also evaluated and discussed in association with different preferential orientations.     

Phase transformation in an yttrium–hydrogen system studied by TEM

Phase transformations in Pd-capped epitaxial yttrium films grown on (0 0 0 1) sapphire substrates covered with a Ti buffer layer and hydrogenated for different times were studied using transmission electron microscopy (TEM). For short hydrogen charging times, the phase transformation from α-Y to β-YH₂ is associated with the nucleation and growth of two orientational variants, which after coalescence form twin-related lamellae of the β-YH₂ phase with twin interfaces parallel to the substrate plane. Shockley partial dislocations are present at the twin boundaries; their glides during phase transformation are responsible for the formation of the twin lamellae. Superlattice reflections were observed for β-YH₂, and the existence of a new long-range ordered superstoichiometric YH_2+x phase was suggested. A structural model of the ordering based on the occupation of octahedral interstitial sites by H in a doubled cell of Y-face-centered cubic was offered. For samples hydrogenated for longer times, β-YH₂-to-γ-YH₃ phase transformation was accompanied by cracking along the twin boundaries, which eventually developed into a network of pores and caused significant swelling of the films. No γ-YH₃ phase was observed directly in TEM because of its unstable nature under the high vacuum of a microscope column. The fully transformed YH₃ films have over a 60% increase in its thickness, which is mostly accounted for by the high volume fraction of pores.     

Texture transformations in Ag thin films

A thickness-dependent texture transformation during annealing of initially (1 1 1) fiber-textured face-centered-cubic metal thin films is phenomenologically well known: sufficiently thin films retain the (1 1 1) texture, while sufficiently thick films transform to a (1 0 0) fiber texture. This transformation has been explained based on minimization of strain and interface energies, but recent work calls into question the roles of both of these driving forces. A high-throughput experimental method for the study of this texture transformation has been developed and applied to thin silver films with and without Ti adhesion layers. More than 150 individual samples spanning a range of thicknesses and interface conditions were prepared in a single deposition run. The texture evolution of these samples was characterized using X-ray diffraction as a function of time and temperature during annealing. The transformation proceeds despite the fact that the stresses are too low according to the strain/interface energy model. For films with Ti adhesion layers, the transformation kinetics and extent of transformation depend on the film thickness in a surprising way with intermediate thickness films showing initially fast transformations and stable mixed textures, while thicker films show an incubation time but transform fully. The results are consistent with reduction in defect energy (e.g. dislocations or point defects) as the driving force for secondary grain growth in an environment in which only (1 0 0) recrystallization nuclei can form. The driving force increases with film thickness so the nonmonotonic variation in transformation rate implies that the density of (1 0 0) nuclei decreases with thickness.     

Size-independent stresses in Al thin films thermally strained down to −100 °C

Size and temperature dependencies of thermal strains of {1 1 1} textured Al thin films were determined by in situ X-ray diffraction (XRD) in the temperature range of −100 to 350 °C. The experiments were performed on 50–2000 nm thick Al films sputter-deposited on oxidized silicon (1 0 0) substrates. The in-plane stresses were assessed by measuring the {3 3 1} lattice plane spacing at each temperature in steps of 25 °C during thermal cycling. At high temperatures, the films could only sustain small compressive stresses. The obtained stress–temperature evolutions show the well-known increase of flow stresses with decreasing film thickness for films thicker than 400 nm. However, for thinner films, the measured stress on cooling is independent of the film thickness. This lack of size effect is caused by the flow stresses in the thinnest films exceeding the maximum stress that can be applied to these samples using thermomechanical loading down to −100 °C. Thus, the measured stresses of ∼770 MPa in the thinnest film represent a lower limit for the actual flow stresses. The observed stresses are also discussed taking microstructural information and possible constraints on dislocation processes into account.     

Structural and optical properties of epitaxial ZnO thin films on 4H–SiC (0 0 0 1) substrates prepared by pulsed laser deposition

Epitaxially grown ZnO thin films on 4H–SiC (0 0 0 1) substrates were prepared by using a pulsed laser deposition (PLD) technique at various substrate temperatures from room temperature to 600 °C. The crystallinity, in-plane relationship, surface morphology and optical properties of the ZnO films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) measurements, respectively. XRD analysis showed that highly c-axis oriented ZnO films were grown epitaxially on 4H–SiC (0 0 0 1) with no lattice rotation at all substrate temperatures, unlike on other hexagonal-structured substrates, due to the very small lattice mismatch between ZnO and 4H–SiC of ～5.49%. Further characterization showed that the substrate temperature has a great influence on the properties of the ZnO films on 4H–SiC substrates. The crystalline quality of the films was improved, and surfaces became denser and smoother as the substrate temperature increased. The temperature-dependent PL measurements revealed the strong near-band-edge (NBE) ultraviolet (UV) emission and the weak deep-level (DL) blue-green band emission at a substrate temperature of 400 °C.     

Reactively sputtered epitaxial γ′-Fe4N films: Surface morphology,microstructure, magnetic and electrical transport properties

Epitaxial γ′-Fe₄N films with (1 0 0) and (1 1 0) orientations have been fabricated by reactive sputtering; these films were characterized by X-ray θ–2θ and φ scans, pole figures and high-resolution transmission electron microscopy. The film surface is very smooth as the film is less than 58 nm thick. The films exhibit soft ferromagnetism, and the saturation magnetization decreases with an increase in temperature, following Bloch’s spin wave theory. The films also exhibit a metallic conductance mechanism. Below 30 K, magnetoresistance (MR) is positive and increases linearly with the applied field in the high-field range. In the low-field range, MR increases abruptly. Above 30 K, MR is negative, and its value increases linearly with the applied field.     

Pseudoelastic deformation and size effects during in situ transmission electron microscopy tensile testing of NiTi

The stress-induced B2–B19′ transformation in aged 51 at.% NiTi was investigated using in situ straining transmission electron microscopy (TEM). Increased applied strain along [1 1 0]_B2 transforms B2 into plates containing B19′ variants that are related by a (1 1 0)_B2 compound twin plane. This atypical twin plane is explained by relaxing the invariant plane constraint in the crystallographic theory of martensite (CTM) to an invariant line constraint. The relaxation is rationalized from the thin foil geometry. The relaxed CTM approach, coupled with conditions to maximize transformation strain along the loading axis and minimize elastic energy, predicts the observed twin interface, diffraction patterns, and interface with the B2 austenite. These results demonstrate subtleties in interpreting thin foil TEM results regarding martensitic transformations, and translating those results to bulk response.     

Misfit dislocations of anisotropic magnetoresistant Nd0.45Sr0.55MnO3 thin films grown on SrTiO3 (1 1 0) substrates

Nd_0.45Sr_0.55MnO₃ is an A-type antiferromagnetic manganite showing obvious angular-dependent magnetoresistance, which can be tuned by misfit strain. The misfit strain relaxation of Nd_0.45Sr_0.55MnO₃ thin films is of both fundamental and technical importance. In this paper, microstructures of epitaxial Nd_0.45Sr_0.55MnO₃ thin films grown on SrTiO₃ (1 1 0) substrates by pulsed laser deposition were investigated by means of (scanning) transmission electron microscopy. The Nd_0.45Sr_0.55MnO₃ thin films exhibit a two-layered structure: a continuous perovskite layer epitaxial grown on the substrate followed by epitaxially grown columnar nanostructures. An approximately periodic array of misfit dislocations is found along the interface with line directions of both 〈1 1 1〉 and [0 0 1]. High-resolution (scanning) transmission electron microscopy reveals that all the misfit dislocations possess a〈1 1 0〉-type Burgers vectors. A formation mechanism based on gliding or climbing of the dislocations is proposed to elucidate this novel misfit dislocation configuration. These misfit dislocations have complex effects on the strain relaxation and microstructure of the films, and thus their influence needs further consideration for heteroepitaxial perovskite thin film systems, especially for films grown on substrates with low-symmetry surfaces such as SrTiO₃ (1 1 0) and (1 1 1), which are attracting attention for their potentially new functions.