In-plane Relationship Research Articles

Epitaxial Single-Domain Cu-BTC Metal-Organic Framework Thin Films and Foils by Electrochemical Conversion of Cuprous Oxide.

Metal-organic frameworks (MOFs) are an important class of crystalline porous materials with extensive chemical and structural merits. However, the fabrication of MOF thin films oriented along all crystallographic axes to achieve well-aligned nanopores and nanochannels with uniform apertures remains a challenge. Here, we achieved highly crystalline single-domain MOF thin films with the [111] out-of-plane orientation by electrochemical conversion of cuprous oxide. Copper(II)-benzene-1,3,5-tricarboxylate, Cu3(BTC)2 (referred to as Cu-BTC), is a well-known metal-organic open framework material with a cubic crystal system. Epitaxial Cu-BTC(111) thin films were manufactured by electrochemical oxidation of Cu2O(111) films electrodeposited on single-crystal Au(111). The Cu-BTC(111) shows an in-plane antiparallel relationship with the precursor Cu2O(111) with a -0.91% coincidence site lattice mismatch. A plausible mechanism was proposed for the electrochemical conversion of Cu2O into Cu-BTC, indicating formation of intermediate CuO, growth of Cu-BTC islands, and termination with coalesce into a dense film with a limiting thickness of about 740 nm. The Faradaic efficiency for the electrochemical conversion was 63%. In addition, epitaxial Cu-BTC(111) foils were fabricated by epitaxial lift-off following the electrochemical etching of residual Cu2O underneath the Cu-BTC. It was also demonstrated that Cu-BTC(111) films with two in-plane domains and textured Cu-BTC(111) films can be achieved on a large scale using electrodeposited Au/Si and Au-coated glass as low-cost substrates.

Quasi-epitaxial growth of BaTiS3 films

Perovskite chalcogenides have emerged as a new class of semiconductors with tunable band gap in the visible-infrared region. High quality thin films are critical to understand the fundamental properties and realize the potential applications based on these materials. We report growth of quasi-epitaxial thin films of quasi one-dimensional (quasi-1D) hexagonal chalcogenide BaTiS$_3$ by pulsed laser deposition. We identified the optimal growth conditions by varying the growth parameters such as the substrate temperature and H2S partial pressure and examined their effects on the thin film structure. High resolution thin film X-Ray diffraction shows strong texture in the out-of-plane direction, whereas no evidence of in-plane relationship between the film and the substrate is observed. Grazing incidence wide-angle X-ray scattering and scanning transmission electron microscopy studies reveal the presence of weak epitaxial relationships of the film and the substrate, despite a defective interface. Our study opens up a pathway to realize quasi-1D hexagonal chalcogenide thin films and their heterostructures with perovskite chalcogenides.

Growth and characterization of heteroepitaxial (001) and (111) diamond on Ir/sapphire structures

We report the comparative study on the growth and characterization of heteroepitaxial (001) and (111) diamond on Ir/(112¯0) and (0001) sapphire using direct current plasma chemical vapor deposition, in order to understand differences in heteroepitaxial behavior in both crystal directions as a preliminary step for large-sized high quality heteroepitaxial (111) diamond growth. An Ir deposition and bias-enhanced nucleation treatment were followed by 60, 190, and 1500 s diamond growth, under the same process conditions. The growth behaviors, morphological, and structural properties of the two crystal directions were greatly different. The growth rates of (001) and (111) diamond were 500 and 60 nm/min, respectively. The epitaxial relationships of (001) and (111) diamond were confirmed to be (001) diamond//(001) Ir//(112¯0) sapphire and (111) diamond//(111) Ir//(0001) sapphire. Further, in-plane relationship of (001) diamond was [1¯10] diamond//[1¯10] Ir//[11¯00] sapphire. In the case of (111) diamond growth, 180°-rotated twins and penetration twins in diamond were observed. The atomic force microscopy and X-ray rocking curve measurements exhibited that the surface roughness and the crystalline quality of (111) diamond were inferior to those of (001) diamond. Consequently, the growth conditions of Ir and diamond in [111] direction need to be considerably modified for suppressing twins and surface roughening and obtaining a high growth rate and high crystalline quality.

Local photonic density of states in hyperbolic metasurfaces

In this work, we design and study an optical hyperbolic metamaterial of a few layers (i.e. metasurface), with a specific in-plane dispersion relationship that has a transition from open hyperbolic type I to type II. We will show that although there is no longer a topological transition from a closed curve to an open hyperbola in dispersion relationship, the local photonic density of state (PDOS) still can be significantly enhanced around the transition point, due to epsilon-near-zero (ENZ) modes. We also show a finite-size effect, which leads to the PDOS enhancement that is strongly dependent on the top layer of material. It is found a balance between the ENZ modes and surface plasmon polaritons for PDOS enhancement. Our results provide some insights for enhancing light–matter interactions via hyperbolic metasurfaces.

Low-Temperature Epitaxial Growth of AlN Thin Films on a Mo Electrode/Sapphire Substrate Using Reactive Sputtering

High-crystalline aluminum nitride (AlN) thin films are essential for device applications, and epitaxial growth is a promising approach to improve their crystalline quality. However, a high substrate temperature is usually required for the epitaxial growth, which is not compatible with the complementary metal-oxide-semiconductor (CMOS) process. Furthermore, it is very difficult to obtain epitaxial AlN thin films on the deposited metal layers that are sometimes necessary for the bottom electrodes. In this work, epitaxial AlN thin films were successfully prepared on a molybdenum (Mo) electrode/sapphire substrate using reactive sputtering at a low substrate temperature. The structural properties, including the out-of-plane and in-plane relationships between the AlN thin film and the substrate, were investigated using X-ray diffraction (XRD) 2θ-ω, rocking curve, and pole figure scans. Additional analyses using scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) were also carried out. It was shown that highly c-axis-oriented AlN thin films were grown epitaxially on the Mo/sapphire substrate with an in-plane relationship of AlN [112¯0]//sapphire [101¯0]. This epitaxial growth was attributed to the highly ordered and oriented Mo electrode layer grown on the sapphire substrate. In contrast, the AlN deposition on the Mo/SiO2/Si substrate under the same conditions caused poorly oriented films with a polycrystalline structure. There coexisted two different low-crystalline phases of Mo (110) and Mo (211) in the Mo layer on the SiO2/Si substrate, which led to the high mosaicity and polycrystalline structure of the AlN thin films.

Microstructural analysis of heteroepitaxial β-Ga2O3 films grown on (0001) sapphire by halide vapor phase epitaxy

(01)-oriented β-Ga2O3 films have been grown on (0001) sapphire substrates using the halide vapor phase epitaxy method. The as-grown β-Ga2O3 films exhibit highly textured with domain-like surface morphologies and the root-mean-square roughness is measured at 6.2 nm using atomic force microscopy. The microstructure characteristics of the β-Ga2O3 film have been investigated comprehensively to understand the origin for the domain-like morphologies. Two in-plane rational domains with mirror-symmetrical atomic arrangement have been identified along the [010] axis of β-Ga2O3 by high resolution transmission electron microscopy, which are caused by the (0001) sapphire substrate symmetry. Various defects, including twinned crystals, inversion domains and domain boundaries etc, have been observed, leading to the rough surfaces and poor crystalline quality of β-Ga2O3 grown on non-angled (0001) sapphire substrate. Schematic diagrams and the oxygen atomic arrangements of β-Ga2O3 on ∼7° off-angled (0001) sapphire substrate toward the 〈110〉 plane were proposed to illustrate the in-plane quasi-epitaxial relationships between the β-Ga2O3(400) film and the sapphire (113) substrate, and to explain the single domain growth mechanism. The results would be helpful for improving the surface morphologies and crystalline quality of heteroepitaxial Ga2O3 films.

High-Crystallinity Epitaxial Sb2Se3 Thin Films on Mica for Flexible Near-Infrared Photodetectors.

The V-VI binary chalcogenide, Sb2Se3, has attracted considerable attention for its applications in thin film optoelectronic devices because of its unique 1D structure and remarkable optoelectronic properties. Herein, we report an Sb2Se3 thin film epitaxially grown on a flexible mica substrate through a relatively weak (van der Waals) interaction by vapor transport deposition. The epitaxial Sb2Se3 thin films exhibit a single (120) out-of-plane orientation and a 0.25° full width at half-maximum of (120) rocking curve in X-ray diffraction, confirming the high crystallinity of the epitaxial films. The Sb2Se3(120) plane is epitaxially aligned on mica(001) surface with the in-plane relationship of Sb2Se3[2̅10]//mica[010] and Sb2Se3[001]//mica[100]. Compared to the photodetector made of a nonepitaxial Sb2Se3 film, the photocurrent of the epitaxial Sb2Se3 film photodetector is almost doubled. Furthermore, because of the flexibility and high sensitivity of the epitaxial Sb2Se3 film photodetector on mica, it has been successfully employed to detect the heart rate of a person. These encouraging results will facilitate the development of epitaxial Sb2Se3 film-based devices and potential applications in wearable electronics.

The nonlinear orthotropic material model describing biaxial tensile behavior of PVC coated fabrics

The nonlinear orthotropic material model describing the biaxial tensile behavior of PVC coated fabrics is developed in this paper. Based on energy function, the general nonlinear stress-strain relationship is derived and the second-order and third-order nonlinear equations are proposed due to the in-plane stress-strain relationship assumption. The Membrane Structures Association of Japan (MSAJ) standard testing method for elastic constants of membrane materials is adopted and three types of PVC coated fabrics are tested under five different load ratios. The measured stress-strain data are used to calculate the coefficients of proposed nonlinear equations using the Least-square method of minimizing strain. Then the stress-strain curves of five different load ratios are compared among MSAJ suggested linear orthotropic model, proposed second-order nonlinear model, third-order nonlinear model, and the test data, also the 3D strain surfaces are plotted to make an intuitive comparison. Results show that both two proposed nonlinear models have a better representation of the test data than the linear model. Finally, considering the convenience and simplicity of the calculation, the second-order nonlinear model was integrated into the finite element software and further prove its adaptability. Thus it is recommended to apply the second-order nonlinear model to engineering design and numerical calculation.

Lattice-matched GaN(0002)/LSAT(111) hetero-structures grown by PLD and analyzed by first-principles calculations

La0.3Sr1.7AlTaO6(LSAT), a desired substrate for GaN epitaxial growth with a lattice mismatch as small as 1%, has not been applied in growth of GaN films due to hetero-interface rotation in epitaxial growth. In this paper, high-quality GaN epitaxial films with a small FWHM for GaN(0002) X-ray rocking curve of 0.06° have been grown by pulsed laser deposition (PLD) with a lattice mismatch as small as 1% between GaN and LSAT, and the corresponding mechanism avoiding interface rotation has also been investigated by first-principles calculation. On the one hand, we found that GaN grown on LSAT by PLD shows an in-plane relationship of GaN[2-1-10]//LSAT[1-10], revealing a small lattice mismatch of 1%. On the other hand, the first-principles calculation based on density function theory reveals that GaN growth along GaN[2-1-10]//LSAT[1-10] shows a higher interface energy barrier compared with that along GaN[1-100]//LSAT[1-10] with a lattice mismatch of 12.5%. The high interface energy barrier can only be provided by PLD. Moreover, this work is of paramount importance for understanding the hetero-interface formation mechanism in a GaN/substrates system and will be beneficial to the development of GaN-based devices that require high-quality GaN epitaxial films.

Thermal chemical vapor deposition of epitaxial rhombohedral boron nitride from trimethylboron and ammonia

Epitaxial rhombohedral boron nitride (r-BN) films were deposited on α-Al2O3(001) substrates by chemical vapor deposition, using trimethylboron, ammonia, and a low concentration of silane in the growth flux. The depositions were performed at temperatures from 1200 to 1485 °C, pressures from 30 to 90 mbar, and N/B ratios from 321 to 1286. The most favorable conditions for epitaxy were a temperature of 1400 °C, N/B around 964, and pressures below 40 mbar. Analysis by thin film x-ray diffraction showed that most deposited films were polytype-pure epitaxial r-BN with an out-of-plane epitaxial relationship of r-BN[001]∥w-AlN[001]∥α-Al2O3[001] and with two in-plane relationships of r-BN[110]∥w-AlN[110]∥α-Al2O3[100] and r-BN[110]∥w-AlN[110]∥α-Al2O3[1¯00] due to twinning.

Floor Map Visualizations of Medical Volume Data

Typically, volumetric medical image data is examined by assessing each slice of an image stack individually. However, this enables observers to assess in-plane spatial relationships between anatomical structures only and requires them to keep track of relationships along the third anatomical plane mentally. Therefore, visualization techniques are researched to support this task by depicting spatial information along the third plane, but they can introduce a high degree of abstraction. To overcome this, we present a novel approach that transforms image stacks with labeled anatomical structures into maps with a three-dimensional layout, namely floor maps. Since this approach increases the visual complexity under certain conditions, some clinical application scenarios, e. g. diagnosis and therapy planning, probably will not benefit. Thus, the approach is mainly aimed to support student training and the generation of clinical reports. We also discuss how to enhance the slice-based exploration of medical image stacks via floor maps and present the results of an informal evaluation with three trained anatomists.

Synthesis and characterization of multicomponent (CrNbTaTiW)C films for increased hardness and corrosion resistance

Multicomponent carbide thin films of (CrNbTaTiW)C (30–40at.% C) with different metal contents were deposited at different temperatures using non-reactive DC magnetron sputtering. The lattice distortion for the metal lattice was estimated to vary from about 3 to 5%. Most films crystallized in the cubic B1 structure but Ta/W-rich films deposited at 600°C exhibited a tetragonal distortion. X-ray diffraction results show that near-equimolar films exhibited a strong (111) texture. In contrast, Ta/W-rich films exhibited a shift from (111) to (100) texture at 450°C. The in-plane relationship was determined to MC(111)[-12-1]//Al2O3(001)[110] with a lattice mismatch of about 11% along the Al2O3[110] direction. A segregation of Cr to the grain boundaries was observed in all films. The microstructure was found to be the most important factor for high hardness. Less dense Nb-rich and near-equimolar films deposited at low temperatures exhibited the lowest hardness (12GPa), while very dense Ta/W-rich high temperature films were found to be the hardest (36GPa). No correlation was found between the lattice distortion and the hardness. Corrosion studies revealed that the multicomponent films exhibited excellent corrosion resistance, superior to that of a reference hyper-duplex stainless steel, in 1.0M HCl.

Epitaxial growth of non-polar ZnO films on MgO substrate

The pulsed laser deposition of pure and doped (Nd or Fe) ZnO films on (001) oriented MgO substrates was investigated. Polar (alternate Zn and O planes along the main axis growth), or non-polar ZnO films were obtained according to the growth conditions, and epitaxial relationships were observed in both cases. For the non-polar films, different in-plane orientations were observed, and the domain matching epitaxy was used in order to describe the in-plane relationships of the film with respect to the MgO substrate. These relationships correspond to different angles between the in-plane [001]ZnO and [100]MgO directions and are different from those previously proposed for the epitaxy of non-polar ZnO on MgO. In addition to the lattice mismatch between film and substrate, an important parameter governing the in-plane orientation is the minimum size of the epitaxial domain which mainly determines the in-plane alignment. Indeed, for doped-ZnO films, the coherence length, i.e. the spatial extension of the crystallites is limited by the presence of the dopants. This leads to different epitaxial relationships with respect to undoped films, and which are related to the epitaxial domain size.

Epitaxial deposition of BaTiO3 on TiO2 buffered GaAs(001) substrate

Ferroelectric BaTiO3 thin films were epitaxially grown on rutile-TiO2 buffered GaAs(001) substrates by pulsed laser deposition system. The in-plane relationship of this heterostructure is 〈110〉BaTiO3//〈001〉TiO2//〈110〉GaAs and the out-plane relationship is BaTiO3(110)//TiO2(110)//GaAs(001). The surface of BaTiO3 is flat and the interfaces between each layer are clear. The oxygen vacancies were eliminated by ex-situ annealing in adequate O2. In short, a highly (110)-oriented BaTiO3 thin film was grown on TiO2 buffered GaAs (001) substrate with excellent electrical and structural properties. The BaTiO3(150nm)/TiO2(40nm)/GaAs system demonstrates hysteresis loops with a remnant polarization of 2.6μC/cm2 and a small leakage current density of 1×10−6A/cm2 both at 300kV/cm.

Evolution of the structural and microstructural characteristics of SrSn1 − xTixO3 thin films under the influence of the composition, the substrate and the deposition method

SrSn1−xTixO3 thin films were grown on R-sapphire and (100) LaAlO3 single crystal substrates by two different routes: chemical solution deposition (CSD) and pulsed laser deposition (PLD). Structural and microstructural characteristics of the films were determined by X-ray diffraction (θ–2θ, ω- and φ-scans) and field emission scanning electron microscopy. Pure perovskite phase was obtained for all of the compositions, whatever the method of deposition and the substrate nature. On R-sapphire, a randomly oriented growth (polycrystalline) was observed for all of the compositions deposited by CSD while (h00) preferential orientation was attained when deposition was done by PLD, in particular for SrTiO3 composition. The phi-scan performed on this sample revealed that the (100) oriented grains present an in-plane ordering (epitaxial growth) with respect to the substrate with an alignment of the [011] direction of the film along the 121¯ direction of the substrate, explained on the basis of misfit considerations and interface arrangements. All of the films grown on (100) LaAlO3 exhibited an epitaxial growth with an in-plane relationship ⟨010⟩film // ⟨010⟩substrate. As for the thin film microstructure, porosity, homogeneity, shape and size of the grains were strongly influenced by Ti content in the SrSn1−xTixO3 solid solution, and also by the nature of the substrate and by the deposition method. Moreover, the influence of the composition and thin film growth on the photoluminescence of SST films were also evaluated.

Heteroepitaxy of Ge on Cube-Textured Ni(001) Foils Through CaF2 Buffer Layer

ABSTRACTEpitaxial Ge films are useful as a substrate for high-efficiency solar cell applications. It is possible to grow epitaxial Ge films on low cost, cube textured Ni(001) sheets using CaF2(001) as a buffer layer. Transmission electron microscopy (TEM) analysis indicates that the CaF2(001) lattice has a 45o in-plane rotation relative to the Ni(001) lattice. The in-plane epitaxy relationships are CaF2[110]//Ni[100] and CaF2[$\bar 1$10]//Ni[010]. Energy dispersive spectroscopy (EDS) shows a sharp interface between Ge/CaF2 as well as between CaF2/Ni. Electron backscatter diffraction (EBSD) shows that the Ge(001) film has a large grain size (∼50 μm) with small angle grain boundaries (< 8o). The epitaxial Ge thin film has the potential to be used as a substrate to grow high quality III-V and II-VI semiconductors for optoelectronic applications.

Hard and elastic epitaxial ZrB2 thin films on Al2O3(0001) substrates deposited by magnetron sputtering from a ZrB2 compound target

Zirconium diboride (ZrB2) exhibits high hardness and high melting point, which is beneficial for applications in for e.g. metal cutting. However, there is limited data on the mechanical properties of ZrB2 films and no data on epitaxial films. In this study, ZrB2(0001) thin films, with thicknesses up to 1.2 μm, have been deposited on Al2O3(0001) substrates by direct current magnetron sputtering from a compound target. X-ray diffraction and transmission electron microscopy show that the films grow epitaxially with two domain types exhibiting different in-plane epitaxial relationships to the substrate. The out-of-plane epitaxial relationship was determined to ZrB2(0001)‖Al2O3(0001) and the in-plane relationships of the two domains to ZrB2[101¯0]‖Al2O3[101¯0] and ZrB2[112¯0]‖Al2O3[101¯0]. Mechanical properties of the films, evaluated by nanoindentation, showed that all films exhibit hardness values above 45 GPa, a reduced Young's modulus in the range 350–400 GPa, and a high elastic recovery of 70% at an applied load of 9000 μN.

Structural and optical characterization of nonpolar (10–10) m-InN/m-GaN epilayers grown by PAMBE

Plasma-assisted molecular beam epitaxy growth of (10–10) m-InN/(10–10) m-GaN was carried out on bare (10–10) m-sapphire substrate. The high resolution X-ray diffraction studies confirmed the orientation of the as-grown films. Nonpolar InN layer was grown at different growth temperatures ranging from 390°C to 440°C and the FWHM of rocking curve revealed good quality film at low temperatures. An in-plane relationship was established for the hetrostructures using phi-scan and a perfect alignment was found for the epilayers. Change of morphology of the films grown at different temperatures was observed using an atomic force microscopy technique showing the smoothest film grown at 400°C. InN optical band gap was found to be vary from 0.79–0.83eV from absorption spectra. The blue-shift of absorption edge was found to be induced by excess background electron concentration.

Structural and compositional evolutions of InxAl1−xN core–shell nanorods grown on Si(111) substrates by reactive magnetron sputter epitaxy

Catalystless growth of InxAl1−xN core–shell nanorods have been realized by reactive magnetron sputter epitaxy onto Si(111) substrates. The samples were characterized by scanning electron microscopy, x-ray diffraction, scanning transmission electron microscopy, and energy dispersive x-ray spectroscopy. The composition and morphology of InxAl1−xN nanorods are found to be strongly influenced by the growth temperature. At lower temperatures, the grown materials form well-separated and uniform core–shell nanorods with high In-content cores, while a deposition at higher temperature leads to the formation of an Al-rich InxAl1−xN film with vertical domains of low In-content as a result of merging Al-rich shells. The thickness and In content of the cores (domains) increase with decreasing growth temperature. The growth of the InxAl1−xN is traced to the initial stage, showing that the formation of the core–shell nanostructures starts very close to the interface. Phase separation due to spinodal decomposition is suggested as the origin of the resultant structures. Moreover, the in-plane crystallographic relationship of the nanorods and substrate was modified from a fiber textured to an epitaxial growth with an epitaxial relationship of InxAl1−xN[0001]//Si[111] and InxAl1−xN[11]//Si[1 by removing the native SiOx layer from the substrate.

X-ray photoelectron spectroscopy and diffraction investigation of a metal–oxide-semiconductor heterostructure: Pt/Gd2O3/Si(111)

Platinum thin films deposited by physical vapor deposition (PVD) on Gd2O3/Si(111) templates are investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray photoelectron diffraction (XPD). Both XRD and XPD give clear evidence that Gd2O3 grows (111)-oriented and single-domain on Si(111) with mirror epitaxial relationship viz., [1¯10] Gd2O3(111)//[11¯0] Si(111). On Gd2O3/Si(111), Pt is partially crystallized with (111) orientation. There are two epitaxial domains and a slightly visible (111) fiber texture. The in-plane relationships of these Pt(111) domains with Gd2O3(111) are a direct one: [11¯0] Pt(111)//[11¯0] Gd2O3(111) and a mirror one: [1¯10] Pt(111)//[11¯0] Gd2O3(111). XPS reveals that Pt4f exhibits a metallic behavior even for small amounts of Pt but very small chemical shifts suggest that Pt environment is different at the interface with Gd2O3. These XPS chemical shifts have been correlated with features in XPD azimuth curves, which could be related with the existence of hexagonal α-PtO2(0001)layer.