Uniform Crystallographic Orientation Research Articles

Homogeneously Oriented Organic Single-Crystalline Patterns Grown by Microspacing In-Air Sublimation.

Fabrication of single-crystalline organic semiconductor patterns is of key importance to enable practical applications. However due to the poor controllability on nucleation locations and the intrinsic anisotropic nature of single-crystals, growth of single-crystal patterns with homogeneous orientation is a big challenge especially by thevapor method. Herein a vapor growth protocol to achieve patterned organic semiconductor single-crystals with high crystallinity and uniform crystallographic orientation is presented. The protocol relies on the recently invented microspacing in-air sublimation assisted with surface wettability treatment to precisely pin the organic molecules at desired locations, and inter-connecting pattern motifs to induce homogeneous crystallographic orientation. Single-crystalline patterns with different shapes and sizes, and uniform orientation are demonstrated exemplarily by using 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT). Field-effect transistor arrays fabricate on the patterned C8-BTBT single-crystal patterns show uniform electrical performance: a 100% yield with an average mobility of 6.28cm2 V-1 s-1 and in a 5×8 array. The developed protocols overcome the uncontrollability of the isolated crystal patterns in vapor growth on non-epitaxial substrates, making it possible to align the anisotropic electronic nature of single-crystal patterns in large-scale devices integration.

Water-Immersion Laser-Scanning Annealing for Improving Polycrystalline Au Films.

A water-immersion laser-scanning annealing (WILSA) method was developed for the heat treatment of a deposited polycrystalline Au film on a glass. The material characterization using X-ray diffraction, field-emission scanning electron microscopy, and electron backscatter diffraction shows improved crystallinity with a more uniform crystallographic orientation of (111) and the grain growth of the annealed Au film. Additionally, the optical constants of the Au film before and after annealing were characterized by spectroscopic ellipsometry in the visible to near-infrared (NIR) regime, and the corresponding optical densities (ODs) were measured by transmittance spectroscopy. Our results show that the extinction coefficient and the OD of the annealed film are significantly reduced, particularly in the NIR regime. This is because the grain growth caused by the annealing reduces the density of grain boundaries, leading to the decrease of the loss of free electrons' scattering at grain boundaries. Hence, the damping effect of the surface plasmon is reduced. Additionally, the integrity of the WILSA-treated thin film is kept intact without pinholes, usually produced by the conventional thermal annealing. Based on the improved optical property of the WILSA-treated Au film, two performances of an insulator-metal-insulator (IMI) layered structure of biosensors are theoretically analyzed. Numerical results show that the propagation length of a long-range surface plasmon polariton along an IMI structure with an annealed Au film is significantly increased, compared to an unannealed film, particular in the NIR region. For the other application of using an IMI sensor to detect the shift of the surface-plasmon-resonance dip in the total internal reflection spectrum for the measurement of a change of the medium's refractive index, the sensitivity is also profoundly improved by the WILSA method. It is worth mentioning that the optimal heating conditions (laser wavelength, fluence, exposure time, and scanning step) depend on the thickness of the Au film. Our study provides a postprocess of WILSA to improve the optical properties of a deposited polycrystalline Au film for raising the sensitivity of the related biosensors.

(Invited, Digital Presentation) Epitaxial Organic Molecular Interfaces As Well-Ordered Model Systems for Molecular Semiconductor p-n Junctions for Optoelectronic Applications

Donor-acceptor molecular interfaces are nothing but p-n junctions for organic optoelectronic devices such as organic light emitting diodes and organic solar cells where an exciton forms or dissociates. Understanding about dominating factors determining the intermolecular assembly and charge carrier exchange processes are highly anticipated for the establishment of smart design strategies of practically efficient devices. Molecular heterojunctions built on single crystal organic semiconductors provide well-ordered model systems disentangling complex intermolecular contacts in real devices. Moreover, the p-n junctions of highly ordered molecular assembly lead to the enhancement of the mobility of charge carriers and excitons through the inter-molecular delocalization of the electronic states, which potentially opens a new route for efficient optoelectronic applications of molecular semiconductors. In this contribution, crystallographic and electronic structures of well-ordered molecular semiconductor homo- and hetero-epitaxial junctions are overviewed.One representative system is a “complementary” p-n junction of perfluoropentacene (C22F14) crystalline ad-layers formed on the single crystal pentacene (C22H14) [1]. Grazing-incidence X-ray diffraction (GIXD) analyses revealed hetero-epitaxial growth of perfluoropentacene in a uniform crystallographic orientation with respect to the surface lattice of the single crystal pentacene. The energy-momentum dispersions of inter-molecular electronic bands were successfully demonstrated by angle-resolved photoelectron spectroscopy (ARPES) for the hetero-epitaxial perfluoropentacene as well as for the single crystal pentacene, which strongly suggests realization of the delocalization of electrons and holes across this well-ordered molecular p-n junction.To further improve the crystallinity of the epitaxial molecular heterojunctions, the authors’ group proposed a new concept of “quasi-homoepitaxial organic semiconductor junctions”, at which a molecular species with nearly identical in-plane lattice constants to those of the substrate molecular single crystal surface is stacked [2]. Actually, quasi-homoepitaxial crystallites of bis(trifluoromethyl)dimethylrubrene was revealed to form highly-ordered interface of much improved mean crystallite size on the single crystal surface of (unsubstituted) rubrene by means of high-resolution GIXD. The electronic structures exhibiting spontaneous electron transfer at this inter-molecular contact and possible opto-electronic applications of this quasi-homoepitaxial junction are also discussed in this presentation.This contribution is supported by Grant-in Aids for Transformative Research Areas (A) “Dynamic Exciton: Emerging Science and Innovation” (JSPS-KAKENHI Grant Number JP21H05405).[1] Y. Nakayama, et al., J. Phys. Chem. Lett. 10 (2019) 1312.[2] K. Takahashi, et al., J. Phys. Chem. Lett. 12 (2021) 11430.

Microscopic origins of the crystallographically preferred growth in evaporation-induced colloidal crystals

Unlike crystalline atomic and ionic solids, texture development due to crystallographically preferred growth in colloidal crystals is less studied. Here we investigate the underlying mechanisms of the texture evolution in an evaporation-induced colloidal assembly process through experiments, modeling, and theoretical analysis. In this widely used approach to obtain large-area colloidal crystals, the colloidal particles are driven to the meniscus via the evaporation of a solvent or matrix precursor solution where they close-pack to form a face-centered cubic colloidal assembly. Via two-dimensional large-area crystallographic mapping, we show that the initial crystal orientation is dominated by the interaction of particles with the meniscus, resulting in the expected coalignment of the close-packed direction with the local meniscus geometry. By combining with crystal structure analysis at a single-particle level, we further reveal that, at the later stage of self-assembly, however, the colloidal crystal undergoes a gradual rotation facilitated by geometrically necessary dislocations (GNDs) and achieves a large-area uniform crystallographic orientation with the close-packed direction perpendicular to the meniscus and parallel to the growth direction. Classical slip analysis, finite element-based mechanical simulation, computational colloidal assembly modeling, and continuum theory unequivocally show that these GNDs result from the tensile stress field along the meniscus direction due to the constrained shrinkage of the colloidal crystal during drying. The generation of GNDs with specific slip systems within individual grains leads to crystallographic rotation to accommodate the mechanical stress. The mechanistic understanding reported here can be utilized to control crystallographic features of colloidal assemblies, and may provide further insights into crystallographically preferred growth in synthetic, biological, and geological crystals.

Wafer-scale single crystals: crystal growth mechanisms, fabrication methods, and functional applications

This review aims to elucidate relevant challenging issues on controllable wafer-scale preparation, additive patterning, and heterogeneous integration of van der Waals single crystals with uniform morphology and crystallographic orientation.

Effects of subtransus heat treatments on microstructure features and mechanical properties of wire and arc additive manufactured Ti–6Al–4V alloy

Post heat treatment is necessary to optimize the microstructure of additive manufactured Ti–6Al–4V to satisfy the aeronautical criterion. However, the relationship between the unique heat treated microstructure features and corresponding mechanical properties of wire and arc additive manufactured (WAAMed) Ti–6Al–4V has not been completely understood so far. In this study, five subtransus heat treatment regimes were used to the WAAMed Ti–6Al–4V alloy, and the different heat treated microstructure and the resultant mechanical properties were investigated. The microstructure was not substantially changed after heat treatment 600 °C/4 h/air cooling (AC). The α laths were coarsened after heat treatment 850 °C/2 h/AC, and the higher annealing temperature contributed to the appearance of αs. After solution and aging treatment, there were the discontinuous αGB, coarsened αp, and fine αs. There was the small Widmanstätten structural αs sharing the uniform crystallographic orientation after heat treatment 930 °C/1 h/AC + 550 °C/4 h/AC. The α′ martensite and extremely fine dispersed granular αs were obtained after heat treatment 930 °C/1 h/water quenching (WQ) + 550 °C/4 h/AC. The heat treatment 930 °C/1 h/WQ + 800 °C/2 h/AC was found to be the best heat treatment in this study. The discontinuous αGB, dispersed αs with various crystallographic orientations were obtained, which simultaneously increased the ultimate tensile strength (UTS) and elongation (EL) to 886 ± 8 MPa and 16.6 ± 1.6%, comparing to 847 ± 12 MPa and 12.2 ± 2.8% for the as-deposited specimen. Besides, the α/β interface phase distribution in the as-deposited and heat treated specimens was concerned. Two break-up mechanisms of αp, including boundary splitting and termination migration, were observed and discussed.

Understanding the Formation Mechanism of Magnetic Mesocrystals with (Cryo-)Electron Microscopy

Magnetite (Fe3O4) nanoaggregates with a flower-like morphology are considered promising materials in the field of magnetically induced hyperthermia in cancer therapy due to their good heating efficiency at low applied alternating magnetic fields. Although the structure and the magnetic state of such flower-like aggregates have been investigated previously, the mechanism that leads to the hierarchical morphology is still poorly understood. Here, we study the formation mechanism of Fe3O4 aggregates synthesized through the partial oxidation of ferrous hydroxide in the presence of poly(acrylic acid) by using cryogenic electron microscopy. The aggregates are formed through a multistep process involving first the conversion of ferrous hydroxide precursors in ∼5 nm primary particles that aggregate into ∼10 nm primary Fe3O4 crystals that finally arrange into the secondary mesocrystal structure. High-resolution electron tomography is used to show that the Fe3O4 mesocrystals are composed of ∼10 nm subunits, often showing a uniform crystallographic orientation resulting in single-crystal-like diffraction patterns. Furthermore, electron holography reveals that mesocrystals have a single magnetic domain despite polymeric interfaces between subunits being present throughout the mesocrystal. Our findings could be used to design materials with specific properties by modulating the morphology and/or magnetic state that is suitable for biomedical application.

Pulsed laser deposition of Ga doped ZnO films - Influence of deposition temperature and laser pulse frequency on structural, optical and electrical properties

The contribution deals with Ga doped ZnO films (deposited from a sintered target composed of 99.0 ZnO and 1.0 wt % of Ga2O3) prepared by pulsed laser deposition (PLD). Experimentally were compared the deposition parameters influence on structural, optical and electrical properties. The variable parameters were: deposition temperature (RT to 500 °C) and growth rate (controlled by laser pulsing repetition frequency in range 2–50 Hz). Investigation by SEM and XRD confirmed columnar structure of prepared films with highly uniform crystallographic orientation regardless of applied deposition parameters. Samples exhibited high optical transparency in VIS region with sharp absorption edge near 380 nm and band gap energies varied between 3.19 and 3.24 eV at room temperature. The best electrical properties (resistivity ∼5.96 × 10−4 Ω cm) was achieved at 400 °C and 10 Hz of laser frequency, however the application of deposition at RT or highest laser frequency (50 Hz) still maintain average resistivity at levels of 10−3 Ω cm. The results suggest that PLD can play an important role in production of high conductive transparent thin film deposited on temperature sensitive organic materials at RT deposition levels.

High mobility indium tin oxide thin film and its application at infrared wavelengths: model and experiment.

In this work, high mobility indium tin oxide (ITO) thin films with uniform crystallographic orientation are prepared. These films present a wide-range transmittance window and could be used as transparent electrodes at ultraviolet-visible-infrared wavelengths. In particular, the ITO thin film is characterized by low resistivity (5.1 × 10-4 Ωcm) and high infrared transmittance (88.5% at 2.5 μm) due to the improved mobility, achieving higher infrared performance than other transparent conductive materials. A model based on carrier's transport theory and Lorentz-Drude dielectric function is proposed to quantitatively calculate the optical performance of conductive thin films under the influence of plasma effect. The calculation demonstrates that ITO is a suitable electrode material for near/middle infrared optoelectronic applications.

Surface-Guided CsPbBr3 Perovskite Nanowires on Flat and Faceted Sapphire with Size-Dependent Photoluminescence and Fast Photoconductive Response.

All-inorganic lead halide perovskite nanowires have been the focus of increasing interest since they exhibit improved stability compared to their hybrid organic-inorganic counterparts, while retaining their interesting optical and optoelectronic properties. Arrays of surface-guided nanowires with controlled orientations and morphology are promising as building blocks for various applications and for systematic research. We report the horizontal and aligned growth of CsPbBr3 nanowires with a uniform crystallographic orientation on flat and faceted sapphire surfaces to form arrays with 6-fold and 2-fold symmetries, respectively, along specific directions of the sapphire substrate. We observed waveguiding behavior and diameter-dependent photoluminescence emission well beyond the quantum confinement regime. The arrays were easily integrated into multiple devices, displaying p-type behavior and photoconductivity. Photodetectors based on those nanowires exhibit the fastest rise and decay times for any CsPbBr3-based photodetectors reported so far. One-dimensional arrays of halide perovskite nanowires are a promising platform for investigating the intriguing properties and potential applications of these unique materials.

Contact resonance atomic force microscopy (CR-AFM) in applied mineralogy: the case of natural and thermally treated diaspore

Contact resonance atomic force microscopy (CR-AFM) is a nondestructive technique based on atomic force microscopy (AFM) that allows one to perform single-point measurements as well as surface mapping of the indentation modulus of a material. In this work, we demonstrate the potential of CR-AFM in applied mineralogy research. As a case study, we report the characterization of natural and thermally treated diaspore. Natural diaspore samples from the Ilbirdagi diasporic metabauxite (diasporite) deposit in the Milas (Mugla) region in Turkey were heat treated in a muffle furnace causing them to transform from diaspore to corundum. After the treatment, the samples had a polycrystalline structure with ordered micrometer-size rectangular grains of uniform crystallographic orientation. Nanomechanical characterization by CR-AFM allowed us to visualize inclusions with different mechanical properties and to determine the average indentation modulus of the surface of the thermally treated diaspore. Quantitative maps of the indentation modulus reveal the variation of the indentation modulus on the surface of single micro-grains with nanometer spatial resolution.

Glycothermal synthesis and photoluminescent properties of Ce3+-doped YBO3 mesocrystals

Abstract We report a glycothermal synthesis of Ce 3+ -doped YBO 3 mesocrystals and their Ce 3+ -concentration dependence of particulate and photoluminescent properties. Submicrometer-sized YBO 3 :Ce 3+ disk-like particles with Ce 3+ concentrations of 0–3 at.% were formed from trimethyl borate and acetates of yttrium and cerium(III) via a glycothermal reaction at 300 °C for 2 h in 1,4-butanediol. The size of the particles decreased from ∼1.5 μm to ∼150 nm with increasing the Ce 3+ concentration up to 1 at.%. Selected area electron diffraction revealed that each disk-like particle was a mesocrystal, i.e., an assembly of nanocrystals with a uniform crystallographic orientation, irrespective of the Ce 3+ concentration. The particles showed blue emission through 5d–4f transitions of Ce 3+ under near-UV excitation. Concentration quenching of the Ce 3+ emission for the glycothermally-prepared YBO 3 :Ce 3+ started from a lower Ce 3+ concentration than that of solid-state-prepared bulk YBO 3 :Ce 3+ , indicating an inhomogeneous distribution of Ce 3+ ions in the mesocrystals.

Angular dependence of the magnetoelectric effect in orthorhombic HoMnO3films

Epitaxial orthorhombic HoMnO${}_{3}$ films were grown on Nb-doped SrTiO${}_{3}$ $(001)$ single-crystal substrates. X-ray diffractometry showed a uniform crystallographic orientation with the $c$ axis along the substrate normal and an anisotropic compressive stress along the $b$ axis of the Pbnm structure. The magnetization of the films was dominated by the paramagnetism of the Ho${}^{3+}$ ions; the latter showed a strong anisotropy with respect to the in-plane and perpendicular-to-plane magnetic field direction. The rotational anisotropy of the magnetoelectric effect was measured for magnetic field rotation in the ${(110)}_{o}$, ${(1\overline{1}0)}_{o}$, and ${(001)}_{o}$ planes. Whereas magnetic field rotation in the ${(110)}_{o}$ and ${(1\overline{1}0)}_{o}$ planes showed a twofold pattern with the smallest magnetoelectric effect observed in magnetic fields along the $c$ axis, in-plane ${(001)}_{o}$ magnetic field rotations revealed an intricate rotational symmetry. A magnetic-field-induced crossover was observed from a low-field region with fourfold rotation patterns to a high-field region with rotation patterns up to the 12th order. This complex rotational symmetry arises from spin-orbit coupling of the Ho${}^{3+}$ moments that induces a modulation of the magnetoconductance as well as a magnetoelectric effect through the Maxwell-Wagner mechanism.

ChemInform Abstract: A Novel Route for the Synthesis of Mesoporous and Low‐Thermal Stability Materials by Coupled Dissolution‐Reprecipitation Reactions. Mimicking Hydrothermal Mineral Formation

AbstractReview: 55 refs.

A Novel Route for the Synthesis of Mesoporous and Low-Thermal Stability Materials by Coupled Dissolution-Reprecipitation Reactions: Mimicking Hydrothermal Mineral Formation

Replacement reactions ('pseudomorphism') commonly occur in Nature under a large range of conditions (T 25 to >600 degrees C; P 1 to >5 kbar). Whilst mineral replacement reactions are often assumed to proceed by solid-state diffusion of the metal ions through the mineral, many actually proceed via a coupled dissolution and reprecipitation (CDR) mechanism. In such cases, a starting mineral is dissolved into a fluid and this dissolution is coupled with the precipitation of a replacement phase across the reaction front. In cases where there are close relationships between the crystal structures of the parent and newly formed minerals, the replacement can be topotactic (interface-coupled dissolution and reprecipitation). The kinetics and chemistry of the CDR route are fundamentally different from solid-state diffusion and can be exploited i) for the synthesis of materials that are often difficult to synthesise via traditional methods and ii) to obtain materials with unique properties. This review highlights recent research into the use of CDR for such synthetic challenges. Emphasis has been given to i) the use of CDR to synthesise compounds with relatively low thermal stability such as the thiospinel mineral violarite ((Ni,Fe)(3)S(4)), ii) preliminary work into use of CDR for the production of roquesite (CulnS(2)), a potentially important photovoltaic component and, iii) examples where the textures resulting from CDR reactions are controlled by the nature and texture of the parent phase and the reaction conditions; these being the formation of micro-porous gold and three-dimensional ordered arrays of nanozeolite of uniform size and crystallographic orientation.

Ferroelectric Properties of KIO3 Nanorods Grown Inside Aluminum Oxide Pores

This paper reports the characterization and ferroelectric properties of a dense array of KIO 3 nanorods grown inside an aluminum oxide porous film. The pores are cylindrical, having an average diameter of 43 nm and a length of 1 micron. They are uniformly aligned in vertical to the film plane. The crystals grown inside the pores possess a uniform crystallographic orientation, where the normal to their (11) planes is aligned along the pore axis. Polarization vs. applied electric field measurements, made at room temperature along the direction of the pore axis, yield a ferroelectric hysteresis with a remanent polarization of about 0.55μC/cm 2 and a coercive field of about 50 kV/cm.

Three-Dimensional Ordered Arrays of Zeolite Nanocrystals with Uniform Size and Orientation by a Pseudomorphic Coupled Dissolution−Reprecipitation Replacement Route

We report a simple and facile hydrothermal pseudomorphic replacement route to synthesize three-dimensional (3D) ordered arrays of zeolite nanocrystals with uniform size and crystallographic orientation. We demonstrate this route by synthesizing analcime monoliths as an example using leucite crystals as precursors. The leucite crystals contain an inherent 3D ordered network of nanometer-sized lamellar twins. Such highly ordered 3D patterns were precisely preserved during hydrothermal pseudomorphic replacement reactions in pH buffered NaCl solutions, resulting in 3D ordered arrays of analcime nanocrystals. Moreover, these analcime nanocrystals have a uniform size and crystallographic orientation due to epitaxial nucleation and growth facilitated by the similarity of crystal lattice between leucite and analcime. The morphology of the nanocrystals is tunable by simply changing solution pH values. Mild acidic to mild alkaline conditions tend to produce cuboid-shaped nanocrystals, while strong alkaline conditio...

Reversible electric field induced nonferroelectric to ferroelectric phase transition in single crystal nanorods of potassium nitrate

Single-crystal rods of the α-phase of potassium nitrate were grown with [010] uniform crystallographic orientation inside a matrix of aluminum oxide nanopores. The pores were prepared by anodization of polished aluminum substrates. The potassium nitrate single crystals were grown inside the pores from a supersaturated aqueous solution at various temperatures. Dielectric polarization measurements of the porous film filled with the potassium nitrate crystals show an electric field induced reversible transition from the nonferroelectric α-phase to the ferroelectric γ-phase at about 200kV∕cm. The ferroelectric γ-phase has a coercive field of about 169kV∕cm and remnant polarization of about 0.216μC∕cm2.

Nucleation and growth of single crystals with uniform crystallographic orientation inside alumina nanopores

Single crystal rods, having nanometer-size diameter, were grown with uniform crystallographic orientation inside a matrix of alumina nanopores. The fabrication process of this nanocomposite structure consists of several stages. First, a highly dense array of alumina pores (about 1011cm−2 and an average diameter of about 35nm) is prepared by an electrochemical anodization process of pure Al substrate. Then, the pores are filled with a liquid solution aided by the pores’ capillary forces. Finally, the temperature of the liquid solution is slightly decreased to a supersaturated state where precipitation starts only at the pore bottom. The nucleation preference at the pore bottom is explained thermodynamically based on the contact angle, geometrical parameters of the nucleus, surface curvature, and pore diameter. In each pore the nucleus is grown to a single crystal that completely fills its volume. The crystallographic orientation of the single crystals inside the pores can be controlled by temperature and composition during growth. The nucleation and growth processes in the alumina nanopores are demonstrated with Rochelle salt (NaKC4H4O6∙4H2O) and potassium nitrate (KNO3).

Controlled growth and nucleation of ferroelectric and dielectric single-crystal nano-rods inside nano-porous aluminum oxide

Single-crystal rods of the ferroelectric materials potassium nitrate (PN) and Rochelle salt (RS) were grown inside a matrix of aluminum oxide nano-pores, having a nanometer-size diameter, with a uniform crystallographic orientation towards the longitudinal axis of the pores. The dense porous array is prepared by electro-chemical anodization of an Al substrate. A liquid solution of RS or PN is inserted into the pores using strong capillary forces. Finally, the liquid solution temperature is slowly reduced, to promote preferred nucleation of the solute at the pore bottom. This preference of nucleation at the pore bottom is explained thermodynamically, based on the geometrical parameters of the pore and the nucleus, such as surface curvature and diameter. The initial nucleus is grown to a single-crystal completely filling the pore volume. The crystallographic orientation of these single-crystal nano-rods can be readily controlled by altering the saturation temperature of the solution, and the cooling rate during nucleation and growth. Moreover, such a composite thin film exhibits pronounced polarization values and improved thermal stability of the ferroelectric phase in comparison to the bulk-size material, for the case of RS.