Preferred In-plane Orientation Research Articles

The Growth Mechanism of a Conductive MOF Thin Film in Spray-based Layer-by-layer Liquid Phase Epitaxy.

The layer-by-layer liquid-phase epitaxy (LBL-LPE) method is widely used in preparing metal-organic framework (MOF) thin films with the merits of controlling thickness and out-of-plane orientation for superior performances in applications. The LBL-LPE growth mechanism related to the grain boundary, structure defect, and orientation is critical but very challenging to study. In this work, a novel "in-plane self-limiting and self-repairing" thin-film growth mechanism is demonstrated by the combination study of the grain boundary, structure defect, and orientation of Cu3 (HHTP)2 -xC thin film via microscopic analysis techniques and electrical measurements. This mechanism results a desired high-quality MOF thin film with preferred in-plane orientations at its bottom for the first time and is very helpful for optimizing the LBL-LPE method, understanding the growth cycle-dependent properties of MOF thin film, and inspiring the investigations of the biomimetic self-repairing materials.

Sprayed Nanometer-Thick Hard-Magnetic Coatings with Strong Perpendicular Anisotropy for Data Storage Applications

The rapid growth of digital information in the world necessitates a big leap in improving the existing technologies for magnetic recording. For the best modern perpendicular recording, the highest coercivity materials with minimal volume are required. We present a study of a facile technology for establishing mono- and multilayer surfaces from various single-domain flat magnetic nanoparticles that exhibit a strong perpendicular-oriented magnetic moment on solid and flexible substrates. Surfactant-free, hard ferromagnetic, and single-domain anisotropic strontium hexaferrite SrFe12O19 nanoparticles with a perpendicular magnetic moment orientation and two different aspect ratios are self-ordered into magnetic thin nanofilms, exploiting the templating effect of cellulose nanofibrils and magnetic fields. Uniform magnetic coatings obtained by the scalable layer-by-layer spray deposition from a monolayer coverage up to thicknesses of a few tens of nanometers show a preferred in-plane orientation of the hard-magnetic nanoparticles. High coercivities of the films of up to 5 kOe and a high perpendicular anisotropy of Mr⊥/Ms > 80% are found. The application of the magnetic field during film deposition ensures additional improvement in perpendicular magnetic anisotropy and the appearance of residual magnetization in the film of up to 0.6Ms. For low-aspect-ratio nanoparticles stacked in periodic planar structures, the signs of the photonic band gap are revealed. The ability to create scalable, thin magnetic structures based on nanosized particles/building blocks opens great opportunities for their application in a wide variety of optoelectronic and magnetic storage devices.

Effect of Copper Line Geometry and Process Parameters on Interconnect Microstructure and Degradation Processes

Abstract The atomic transport processes which could cause degradation mechanisms in Cu interconnects are described. The influence of interconnect line width, barrier type and anneal process on the microstructure and reliability of the inlaid Cu lines are discussed. Grain size and texture measurements have been performed at blanket films and at arrays of Cu lines using advanced analytical techniques. The median grain size decreases with decreasing line width, and it can be influenced by heat treatments. The crystallographic texture is predominantly {111} out-of-plane with sidewall-oriented grains in narrow Cu lines. The grains have an in-plane preferred orientation with the 〈110〉 direction parallel to the sidewall normal. The Cu texture is influenced by barrier structure and thickness.

Polar in-plane surface orientation of a ferroelectric nematic liquid crystal: Polar monodomains and twisted state electro-optics

We show that surface interactions can vectorially structure the three-dimensional polarization field of a ferroelectric fluid. The contact between a ferroelectric nematic liquid crystal and a surface with in-plane polarity generates a preferred in-plane orientation of the polarization field at that interface. This is a route to the formation of fluid or glassy monodomains of high polarization without the need for electric field poling. For example, unidirectional buffing of polyimide films on planar surfaces to give quadrupolar in-plane anisotropy also induces macroscopic in-plane polar order at the surfaces, enabling the formation of a variety of azimuthal polar director structures in the cell interior, including uniform and twisted states. In a π-twist cell, obtained with antiparallel, unidirectional buffing on opposing surfaces, we demonstrate three distinct modes of ferroelectric nematic electro-optic response: intrinsic, viscosity-limited, field-induced molecular reorientation; field-induced motion of domain walls separating twisted states of opposite chirality; and propagation of polarization reorientation solitons from the cell plates to the cell center upon field reversal. Chirally doped ferroelectric nematics in antiparallel-rubbed cells produce Grandjean textures of helical twist that can be unwound via field-induced polar surface reorientation transitions. Fields required are in the 3-V/mm range, indicating an in-plane polar anchoring energy of w P ∼3 × 10-3 J/m2.

Efficient MAPbI3 Perovskite Solar Cells Employing Sputtered p-Type NiOx Hole Transport Layer on Dependence of Oxygen Partial Pressure

In this paper, the effect of NiO x thin film prepared by a radio-frequency sputtering process under different oxygen partial (Ar:O2 ratio) pressures on the photovoltaic properties of planar-type MAPbI3 perovskite solar cells (PSCs) was investigated. The electrical, optical, morphological, and structural properties of sputtered NiO x thin films deposited under varied process oxygen gas condition are scrutinized. In particular, this study demonstrates that the properties of NiO x thin film with Ni3+/Ni2+ ratio are dependent on process oxygen gas condition. The influence of Ni vacancies on the chemistry and electronic structure of NiO x thin films is investigated using X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The sputtered NiO x thin film with lower Ni3+/Ni2+ ratio exhibits appropriate conductivity, hole mobility, high transmittance, and uniform surface morphology as well as a preferred in-plane orientation of the (220) plane under pure Ar gas atmosphere. When 5% (Ar:O2=19:1) or 10% (Ar:O2=18:2) oxygen is injected during the process, the conductivity of NiO x thin films with higher Ni3+/Ni2+ ratio is higher, but at the expense of optical transmittance. Additionally, this work exhibits the effect of perovskite active layer crystallinity and device performance using sputtered NiO x thin film under different oxygen partial pressures (Ar:O2 ratio) as hole transport layer for PSCs. The power conversion efficiency (PCE) of PSC obtains the highest PCE of 15.74% at the optimized NiO x thin film under pure Ar atmosphere. Compared to that, the efficiencies of the PSCs using the NiO x thin films processed at 5% and 10% oxygen partial pressure is 4.17% and 1.39%, respectively. Therefore, this study elucidate the effect of NiO x thin films deposited under different oxygen partial (Ar:O2 ratio) pressures on the performance of PSCs.

Giant energy storage density in PVDF with internal stress engineered polar nanostructures

Abstract High power dielectric capacitors with high energy density are needed in order to develop modern electronic and electrical systems, including hybrid vehicles, telecommunication infrastructures and portable electronic devices. Relaxor ferroelectric polymers (RFP) are considered to be the most promising candidates for the next generation of capacitors owing to their relatively high energy storage density. However, the commercialization of RFP capacitors in power systems is hindered by their high cost and low dielectric breakdown strength. In this study, inexpensive, free-standing nano-crystalline (~3.3 nm) poly (vinylidene fluoride) (PVDF) films with high β phase content (~98%), “relaxor-like” ferroelectric behaviour and high breakdown strength (880 kV/mm) were fabricated using the facile Press & Folding (P&F) technique. An internal stress dominated polarization switching model is proposed to explain the origin of the relaxor-like ferroelectric behaviour. The internal stress generated during pressing alters the intermolecular chain distance of the (200) plane of β-PVDF from 4.24 A in internal stress free films to 4.54 A in P&F films, corresponding to a tensile strain and residual stress of 7.11% and 142 MPa, respectively. The internal stress acts to partially reverse the polarization on reversal of the applied electric field. This, combined with preferred in-plane orientation of the crystallites, results in a polar nanostructure with high polarization reversibility at high electric fields. A giant discharged energy storage density of 39.8 J/cm3 at 880 kV/mm was achieved for P&F films, which surpasses all previously reported polymer-based materials.

Influencing mechanisms of atomic diffusion and compositional distribution on the magnetic anisotropy of Cr/SmCo/(Cu)/Cr thin films

Rare earth (RE) permanent magnetic thin films, such as SmCo-based films, are promising candidates for future thermal-assisted magnetic recording media because of their supreme thermal stability and fine superparamagnetic critical size. Phase compositional distributions and crystallographic orientations can directly influence the magnetic domain evolutions and magnetic performance of SmCo films. However, these films often exist in multi-phases without well-defined distinct magnetic anisotropy, thereby causing difficulties in analyzing their functions. The effects of atomic diffusions induced by annealing on crystallization and magnetic anisotropy energy are poorly understood. In this work, the influence of doping Cu atoms via introducing Cu layer on magnetic anisotropy of Cr/SmCo/(Cu)/Cr films is investigated. Introducing a Cu layer and post-annealing lead to tunable magnetic anisotropy from isotropy to anisotropy and domain structure formation. Micromagnetic simulation is used to further analyze the effects of crystallization, anisotropy field and compositional distribution on the magnetization reversal behavior and coercivity variations in SmCo films. It reveals that the differences of anisotropy field of Co and amorphous phases could affect the domain wall motions and coercivity, which shows the analogous trend as an experimental result. Moreover, the elevated anisotropy constant of Sm(Co,Cu) alloy and the small fractions of SmCo5 boundary phases are also beneficial to the enhancement of coercivity derived by calculating domain wall energy. In-plane magnetic anisotropy is improved by the SmCo5 phase, which has an in-plane preferred orientation of the c axis. This work provides theoretical and experimental bases for the future fabrication of SmCo-based films by controlling atomic diffusion with optimized grain boundary phase distribution.

Joint improvement of conductivity and Seebeck coefficient in the ZnO:Al thermoelectric films by tuning the diffusion of Au layer

Joint improvement of the Seebeck coefficient S and conductivity σ is a pressing issue to overcome the limit of the figure of merit (ZT) enhancement of thermoelectric materials. This study presents a joint improvement in the ZnO:Al films by tuning the diffusion of Au layer via substrate temperature, using a radio frequency-assisted molecular beam vapor deposition method. The phenomenon occurs in the ZnO:Al films at the room temperature (RT) substrate deposited on a 10 nm Au layer (RT-ZnO:AuAl). The films have a hexagonal wurtzite structure with an in-plane (002) preferred orientation and smooth surface. The resistivity values of the films are at the same magnitude of the transparent conducting oxide (~10−6 Ω·m). The carrier concentration reaches 2.60 × 1021 cm−3 for the RT-ZnO:AuAl film. The S is about 29.5 μV/K at 240 °C. Joint improvement of conductivity and Seebeck coefficient makes the PF of the RT-ZnO:AuAl film reaches 3.58 × 10−5 Wm−1 K−2, which is two orders of magnitude larger than that of the RT-ZnO:Au film without joint improvement. The results indicate that the higher conductivity originates from the Au layer, in-plane (002) preferred orientation, and the easily excited carriers in the ZnO:Al due to the low binding energy of the Zn 2p electrons. The large S in the film is related to the high effective masses due to the impact of the diffusion of the Au layer on electronic interactions.

Molecular orientation in electrodeposited polypyrrole films

The molecular arrangement in electrodeposited polypyrrole films was studied by means of linear dichroism in the near-edge X-ray absorption fine structure (NEXAFS) spectra measured at the K absorption edges of carbon and nitrogen. It has been found that the change of the exciting radiation incidence from normal to grazing leads to an increase in the intensity of π*-related resonances with simultaneous decrease in the intensity of σ*-related resonances in the spectra. Similar changes in the spectra measured for both absorption edges indicate a pronounced conjugation of π-bonds in the polypyrrole chains in the grown films. Preferential in-plane orientation of pyrrole rings relative to the substrate surface is observed for all the deposited films. The linear dichroism is more pronounced at the initial stages of deposition (2D growth) than at later stages characterized by “cauliflower”-like morphology of the grown film.

Nucleation mechanism during WS2 plasma enhanced atomic layer deposition on amorphous Al2O3 and sapphire substrates

The structure, crystallinity, and properties of as-deposited two-dimensional (2D) transition metal dichalcogenides are determined by nucleation mechanisms in the deposition process. 2D materials grown by atomic layer deposition (ALD) in the absence of a template are polycrystalline or amorphous. Little is known about their nucleation mechanisms. Therefore, the nucleation behavior of WS2 during plasma enhanced ALD from WF6, H2 plasma, and H2S at 300 °C is investigated on amorphous ALD Al2O3 starting surface and on monocrystalline, bulk sapphire. Preferential interaction of the precursors with the Al2O3 starting surface promotes fast closure of the WS2 layer. The WS2 layers are fully continuous at WS2 content corresponding to only 1.2 WS2 monolayers. On amorphous Al2O3, (0002) textured and polycrystalline WS2 layers form with grain size of 5 to 20 nm due to high nucleation density (∼1014 nuclei/cm2). The WS2 growth mode changes from 2D (layer-by-layer) growth on the initial Al2O3 surface to three-dimensional (Volmer–Weber) growth after WS2 layer closure. Further growth proceeds from both WS2 basal planes in register with the underlying WS2 grain, and from or over grain boundaries of the underlying WS2 layer with different in-plane orientation. In contrast, on monocrystalline sapphire, WS2 crystal grains can locally align along a preferred in-plane orientation. Epitaxial seeding occurs locally albeit a large portion of crystals remain randomly oriented, presumably due to the low deposition temperature. The WS2 sheet resistance is 168 MΩ μm, suggesting that charge transport in the WS2 layers is limited by grain boundaries.

The importance of the electrical contact between specimen and testing fixture in evaluating the electromagnetic interference shielding effectiveness of carbon materials

The quality of the electrical contact between the specimen and electromagnetic interference (EMI) shielding testing fixture (coaxial cable method) is found to be critical to shielding effectiveness testing. The carbon fiber (CF) mat (0.15–0.42 mm thick) and carbon nanofiber (CNF) fiber mat (4.4–4.6 mm thick) are similar in the shielding effectiveness (68–70 dB), but the former is much superior in the effectiveness per unit thickness (200 vs. 15 dB/mm), due to the clinginess of the CF mat (resulting from short fiber protrusion) promoting good electrical contact, even at zero specimen-fixture fastening torque. Flexible graphite (0.13–0.38 mm thick) is superior to CF/CNF mats in both the shielding effectiveness (110 dB) and shielding effectiveness per unit thickness (560 dB/mm), partly due to its deformability promoting the electrical contact. For the CF mat, the shielding effectiveness decreases monotonically with increasing fastening torque, due to the increase in the degree of in-plane fiber preferred orientation and the consequent degradation of the electrical contact between the specimen and testing fixture. In contrast, for both CNF mat and flexible graphite, the torque enhances the shielding. The absorption loss per unit thickness reaches 165, 14 and 500 dB/mm for CF mat, CNF mat and flexible graphite, respectively.

Surface-induced orientation of pentacene molecules and transport anisotropy on nanogroove SiO2 dielectric layer by simple scratched method: The study of surface roughness and molecular alignment on the mobility of organic thin film transistors

We obtained preferential in-plane molecular orientation and charge-transport anisotropy in pentacene thin-film transistors (TFTs) on conventional SiO2/Si substrates. The nanoscale SiO2 grooves with depths of 1–3 nm were prepared by a simple scratching process with diamond powder to create a new type of alignment template for inducing the aligned growth of pentacene with in-plane anisotropy. Results of atomic force microscopy and grazing-incidence X-ray diffraction showed that the nanogrooved SiO2 structure could control the alignment and growth mode of pentacene, and it remarkably decreased the grain size of the pentacene crystals. The charge-carrier mobility along the parallel axis of the nanogrooved structure (0.392 ± 0.039 cm2/(V·s)) was more than four-fold higher than that perpendicular to the alignment (0.104 ± 0.048 cm2/(V·s)). In addition, we investigated the effect of nanogrooved SiO2's surface roughness on the electrical properties of the pentacene TFT and found out that the surface roughness of SiO2 dielectric layer was more crucial factor on the device performance compared to the preferential alignment of the pentacene molecule.

Structural transformations in highly oriented seven modulated martensite Ni–Mn–Ga thin films on an Al2O3 substrate

Abstract

The effect of the deposition rate on the crystallographic texture, microstructure evolution and magnetic properties in sputter deposited Ni-Mn-Ga thin films

The development of crystallographic texture (preferred orientation), structure and microstructure has been investigated and correlated with the magnetic properties of sputter-deposited Ni-Mn-Ga thin films. The overall compositions of the films were strongly dependent on the sputtering power. X-ray diffraction based crystallographic texture measurement and transmission electron microscopy have been performed to examine the preferred orientation and structure of the films. All the films exhibit strong 〈400〉 and 〈220〉 double fiber orientation with no sign of in-plane preferred orientation. The strengthening of 〈400〉 and weakening of 〈220〉 preferred orientation in the films are observed with an increase in sputtering power. The development of the texture in films is mainly governed by the minimization of surface energy and strain energy. All the films exhibit a uniform microstructure with an increase in grain size as the sputtering power increases. An analysis of the magnetic hysteresis of the films revealed that all the films are ferromagnetic in nature, irrespective of the sputtering power. However, coercivity and the saturation field are found to be dependent on the sputtering power, and lead to the crystallographic texture of the films.

Enhanced Stability of CH3NH3PbI3Thin Films Deposited on FTZO

Fluorine (F) and tin (Sn) codoped ZnO (FTZO) nanoparticles (NPs) were synthesized by sol–gel technique on indium tin oxide (ITO). The structural changes arising from CH3NH3PbI3 deposited on FTZO NPs layer during its degradation were characterized via in situ grazing incidence X-ray diffraction (GIXRD). It was indicated that the FTZO NPs layer helped reduce the degradation of the perovskite film during the annealing process. This film also exhibited enhanced crystallization and preferred in-plane orientation of the (110) plane after annealing.

Texture formation in iron particles using mechanical milling with graphite as a milling aid

Crystallographically anisotropic platelet iron particles were successfully prepared using a conventional ball mill with addition of graphite (Gp) particles. The morphological and structural changes resulting from the milling were investigated using scanning electron microscopy and X-ray diffraction. The spherical iron particles were plastically deformed into platelet shapes during the milling. Simultaneously, it is suggested that the size of the Gp particles decreased and adhered as nanoparticles on the surface of the iron particles. The adhered Gp particles affected the plastic deformation behavior of the iron particles: the {001} planes of α-iron were oriented parallel to the particle face, and no preferred in-plane orientation was observed. This study not only details the preparation of soft magnetic metal particles that crystallographically oriented to enhance their magnetic properties but also provides new insight into the activities of the well-established and extensively studied mechanical milling method.

CH₃NH₃PbI₃-based planar solar cells with magnetron-sputtered nickel oxide.

Herein we report an investigation of a CH3NH3PbI3 planar solar cell, showing significant power conversion efficiency (PCE) improvement from 4.88% to 6.13% by introducing a homogeneous and uniform NiO blocking interlayer fabricated with the reactive magnetron sputtering method. The sputtered NiO layer exhibits enhanced crystallization, high transmittance, and uniform surface morphology as well as a preferred in-plane orientation of the (200) plane. The PCE of the sputtered-NiO-based perovskite p-i-n planar solar cell can be further promoted to 9.83% when a homogeneous and dense perovskite layer is formed with solvent-engineering technology, showing an impressive open circuit voltage of 1.10 V. This is about 33% higher than that of devices using the conventional spray pyrolysis of NiO onto a transparent conducting glass. These results highlight the importance of a morphology- and crystallization-compatible interlayer toward a high-performance inverted perovskite planar solar cell.

Epitaxial Fe/Y2O3 interfaces as a model system for oxide-dispersion-strengthened ferritic alloys

The fundamental mechanisms underlying the superior radiation tolerance properties of oxide-dispersion-strengthened ferritic steels and nanostructured ferritic alloys are poorly understood. Thin film heterostructures of Fe/Y2O3 can serve as a model system for fundamental studies of radiation damage. Epitaxial thin films of Y2O3 were deposited by pulsed laser deposition on 8% Y:ZrO2 (YSZ) substrates with (100), (110), and (111) orientation. Metallic Fe was subsequently deposited by molecular beam epitaxy. Characterization by X-ray diffraction and Rutherford backscattering spectrometry in the channeling geometry revealed a degree of epitaxial or axiotaxial orientation for Fe(211) deposited on Y2O3(110)/YSZ(110). In contrast, Fe on Y2O3(111)/YSZ(111) was fully polycrystalline, and Fe on Y2O3(100)/YSZ(100) exhibited out-of-plane texture in the [110] direction with little or no preferential in-plane orientation. Scanning transmission electron microscopy imaging of Fe(211)/Y2O3(110)/YSZ(110) revealed a strongly islanded morphology for the Fe film, with no epitaxial grains visible in the cross-sectional sample. Well-ordered Fe grains with no orientation to the underlying Y2O3 were observed. Well-ordered crystallites of Fe with both epitaxial and non-epitaxial orientations on Y2O3 are a promising model system for fundamental studies of radiation damage phenomena. This is illustrated with preliminary results of He bubble formation following implantation with a helium ion microscope. He bubble formation is shown to preferentially occur at the Fe/Y2O3 interface.

Anomalous magnetic ground state in an LaAlO3/SrTiO3 interface probed by transport through nanowires.

Resistance as a function of temperature down to 20 mK and magnetic fields up to 18 T for various carrier concentrations is measured for nanowires made from the SrTiO3/LaAlO3 interface using a hard mask shadow deposition technique. The narrow width of the wires (of the order of 50 nm) allows us to separate out the magnetic effects from the dominant superconducting ones at low magnetic fields. At this regime hysteresis loops are observed along with the superconducting transition. From our data analysis, we find that the magnetic order probed by the giant magnetoresistance effect vanishes at TCurie=954±20 mK. This order is not a simple ferromagnetic state but consists of domains with opposite magnetization having a preferred in-plane orientation.

Anomalous epitaxial stability of (001) interfaces in ZrN/SiNx multilayers

Isostructural stability of B1-NaCl type SiN on (001) and (111) oriented ZrN surfaces is studied theoretically and experimentally. The ZrN/SiNx/ZrN superlattices with modulation wavelength of 3.76 nm (dSiNx∼0.4 nm) were grown by dc-magnetron sputtering on MgO(001) and MgO(111). The results indicate that 0.4 nm thin SiNx layers utterly influence the preferred orientation of epitaxial growth: on MgO(001) cube-on-cube epitaxy of ZrN/SiNx superlattices were realized whereas multilayers on MgO(111) surface exhibited an unexpected 002 texture with a complex fourfold 90°-rotated in-plane preferred orientation. Density functional theory calculations confirm stability of a (001) interface with respect to a (111) which explains the anomaly.