Preferred Crystalline Orientation Research Articles

Conversion of preferred crystalline orientation by annealing and its impacts on the structural, electronic, and optical properties of pulsed laser-deposited CdO thin films

The impact of annealing on the preferred crystalline orientation as well as the structural, electronic, and optical properties of pulsed laser-deposited 150 ± 3 nm thick cadmium oxide (CdO) films was studied. X-ray diffraction analysis revealed that the annealed CdO films have smaller crystallite sizes, as their molecules at the grain boundaries possessed enough kinetic energy to rearrange their preferred crystalline orientation between (111) and (200). The atomic force microscopy and field emission scanning electron microscopy analyses revealed an enhancement in the active surface area with optimized grain boundaries by annealing which facilitates gas adsorption/desorption. DC electrical conductivity depends on the annealing process and reveals two different conduction mechanisms. The direct optical energy gap was decreased from 3.41 eV to 2.76 eV by annealing at 473 K which is greater than the theoretical value, i.e. 2.2 eV, for bulk CdO. The findings agree with the Burstein-Moss effect as a result of the increased carrier concentration following the generation of numerous oxygen vacancy sites and Cd interstitials. However, mutual charge carrier-impurity interaction and charge carrier Columb interaction contributed to narrowing the band gap by increasing the annealing temperature. The enhanced values of Urbach energy, optical packing density, dispersion parameters, optical conductivity, dissipation factor, oscillator strength, and lattice dielectric constant supported the effectiveness of the annealing process on tailoring optoelectronic responses in the infrared region for the CdO thin films for use in optoelectronic devices. Moreover, the calculated linear optical susceptibility, and nonlinear constants (i.e. third-order optical susceptibility and nonlinear refractive index) were the highest for CdO films annealed at 473 K. The improved value of the figure of merit, solar material protection factor, and solar skin protection factor for the CdO films, annealed at 473 K supports its use in several photovoltaic applications, including solar cells.

The Effect of Lewis Acid-Base Additive on lead-free Cs2SnI6 thin film prepared by direct solution coating process

Abstract Inorganic Cs2SnI6 perovskite has exhibited substantial potential for light harvesting due to its exceptional optoelectronic properties and remarkable stability in ambient conditions. The charge transport characteristics within perovskite films are subject to modulation by various factors, including crystalline orientation, morphology, and crystalline quality. Achieving preferred crystalline orientation and film morphology via a solution-based process is challenging for Cs2SnI6 films. In this work, we employed thiourea as an additive to optimize crystal orientation, enhance film morphology, promote crystallization, and achieve phase purity. Thiourea lowers the surface energy of the (222) plane along the ＜111＞ direction, confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy studies, and density functional theory calculations. Varying thiourea concentration enables a bandgap tuning of Cs2SnI6 from 1.52 eV to 1.07 eV. This approach provides a novel method for utilizing Cs2SnI6 films in high-performance optoelectronic devices.

Ternary eutectic growth and associated tensile properties of directionally solidified Al87Si11Ni2 alloy

The directional growth mechanism and associated tensile properties of ternary Al87Si11Ni2 eutectic alloy were investigated within a wide growth velocity range from 1 to 120 μm s−1 at a constant temperature gradient of 380 K cm−1. If eutectic growth velocity was below 40 μm s−1, this alloy exhibited a ternary lamellar eutectic structure composed of Si plates, Al3Ni chips and αAl matrix. As growth velocity increased to faster regime, the microstructure evolved into a complex structure characterized by primary αAl dendrites plus ternary eutectics. Correspondingly, the preferred crystalline orientation along solidification direction transformed from 101αAl //010Al3Ni // 101Si to 001αAl // 010Al3Ni //113Si. The tensile strength initially increased with the rise of growth velocity until 40 μm s−1, primarily due to the refinement of eutectic structure, and then decreased beyond this threshold, mainly resulting from the coarsening of primary αAl phase.

Communication—Texture and Bandgap Tuning of Phase Pure Cu2O Thin Films Grown by a Simple Potentiostatic Electrodeposition Technique

Highly textured phase pure Cu2O thin films have been grown by a simple electrodeposition technique with varying deposition voltages (−0.3 to −1.0 V). The surface morphology characterized by Scanning Electron Microscopy (SEM) revealed that the deposited thin films coherently carpet the underlying substrate and are composed of sharp faceted well-defined grains of 0.5–1.0 μm sizes. XRD analyses showed that all films are composed of polycrystalline cubic Cu2O phase only and have average crystalline domain size in the range of 30–73 nm. The preferred crystalline orientation of phase pure Cu2O films was found to be changing from (200) to (111) with increasing cathodic voltages and showed the highest (111) and (200) crystalline texture coefficient while growing at −1.0 and −0.8 V respectively. The optical bandgap of the as-grown samples was calculated in the range of 1.95–2.20 eV using UV–vis Transmission data. The performance of Cu2O/FTO photocathodes was tested by estimating LED “ON/OFF” modulated surface photovoltage into a photoelectrochemical cell at a zero bias.

Sulfur‐Supplemented Vapor Transport Deposition of Sb2S3 and Sb2(S,Se)3 for High‐Performance Hydrogen Evolution Photocathodes

Chalcogen vacancy has long been recognized as a detrimental deep‐level defect that can induce severe charge recombination and diminish the quasi‐Fermi‐level splitting in Sb2S3 and Sb2Se3, especially when they are prepared by physical vapor deposition in vacuum. In order to counter this limitation, a sulfur‐supplemented vapor transport deposition technique is proposed, which intentionally introduces low pressure sulfur vapor and can thus afford low‐defect‐density antimony chalcogenide films. The resultant photocathodes modified with conformal TiO2 protection layer and Pt cocatalyst demonstrate a photocurrent as high as 20 mA cm−2 along with a much improved fill factor and onset potential, achieving an applied bias photoconversion efficiency above 1%. This work highlights the importance of the vacancy defect passivation and the preferential crystalline orientation in the film in promoting the photocathode performance.

Highly Transparent and Stable Flexible Electrodes Based on MgO/AgNW Nanocomposites for Transparent Heating Applications

AbstractTransparent electrodes (TE) based on silver nanowire (AgNW) exhibit good physical properties and constitute a promising alternative to transparent conductive oxides due to their low cost, flexibility, and low toxicity. Nevertheless, they suffer from stability issues over harsh conditions, and encapsulation allows to overcome these limitations. Herein, the low‐cost, scalable fabrication and study of transparent electrodes based on sprayed AgNW networks coated with MgO thin films deposited by atmospheric pressure spatial atomic layer deposition (AP‐SALD) at mild deposition temperature (≤220 °C) is reported. Fabrication of MgO thin films by AP‐SALD is reported here for the first time, and their deposition on different substrates is optimized. MgO exhibits a pure phase and conformal growth with a preferential (220) crystalline orientation and a higher growth rate as compared to conventional atomic layer deposition (ALD). Furthermore, thanks to the conformal coating of MgO on AgNW, the obtained nanocomposites exhibit great optical transparency of ≈85% and flexibility while maintaining high stability under thermal and electrical stress. Indeed, this study shows a clear enhancement of the stability of AgNW networks for thin MgO coatings of only a few nanometers thick. Finally, a proof‐of‐concept transparent heater is fabricated to melt a piece of cheese.

Effect of grain size on ferroelectric and dielectric properties of Bi3.25La0.75Ti3O12 thin films prepared by rf-magnetron sputtering

[Formula: see text][Formula: see text]Ti3[Formula: see text](BLT) thin films are promising materials used in non-volatile memories. In this work, BLT films were deposited on Pt(111)/Ti/SiO2/Si substrates by rf-magnetron sputtering method followed by annealing treatments. The microstructures of BLT thin films were investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). With the increase in annealing temperature, the grain size increased significantly and the preferred crystalline orientation changed. A well-saturated hysteresis loop with a superior remnant polarization of 15.4 [Formula: see text]C/cm2 was obtained for BLT thin films annealed at 700∘C. The results show that the dielectric constant decreased with the increase in grain sizes.

Structural, morphological and optical properties of Sn doped zinc oxide thin films synthesis by sol-gel method for photocatalytic applications

Undoped and tin (Sn)-doped ZnO thin films were synthesized via sol-gel technique and deposited onto the glass substrates using the spin-coating technique. The impact of Sn incorporation at various concentrations on the structural, morphological, and optical properties of ZnO films was studied x-ray diffraction revealed a hexagonal crystal structure for all samples with a preferential crystalline orientation along the (002) plane. The transparency of Sn-doped ZnO thin film in the visible region significantly increased from 75% to 90%. The morphological analysis revealed a decrease in the grain size from 21 nm to 15 nm with Sn content in the matrix of ZnO. The optical properties reveal the contribution of the Burstein-Moss effect and electron-impurity scattering to slightly widen the bandgap from 3.22 eV to 3.24 eV. Urbach energy values demonstrated that the presence of Sn dopant increased the tail-band width of the localized states. These observations suggest that the deposited Sn-ZnO thin films could have possible applications as a photocatalyst for methylene blue (MB) dye degradation.

Effects of B/C ratio on the structural and mechanical properties of TiBCN coating deposited by PACVD

TiBCN coating is known as a hard, self-lubricant and wear resistant coating which can be applied on industrial tools to increase their working life time under severe wear conditions. In this paper, TiBCN coatings with different B/C ratios were applied on H13 steel using plasma-assisted chemical vapor deposition from BBr3, TiCl4, CH4, N2 and H2 reactants at 500 °C. The results signified that the introduction of B and C elements to TiN changed its preferred crystalline orientation from (200) to (111) and decreased crystal size from 12 to 9 nm as a result of the formation of amorphous phases which constrain grain growth. The addition of B and C altered the coating's nucleation and growth mechanisms and generated a strong surface etching agent of HBr which significantly changed surface morphology and roughness. Increasing flow ratio of CH4 to BBr3 from 0.125 to 0.25 influenced the coating's mechanical properties and increased coating's hardness from 18.1 to 23.2 GPa and Young's modulus from 296 to 334.7 GPa. Rising coating's C content remarkably improved its nano-wear resistance and the coating with the highest C content exhibited a wear volume of 1*10−19 m3 which was about 63% lower than that of TiN coating.

Microstructure, properties and synergetic effect of graphene oxide-functionalized carbon nanotubes hybrid reinforced copper matrix composites prepared by DC electrodeposition

As the prospective carbon materials, graphene oxide (GO) and carbon nanotubes (CNTs) have attracted extensive attention in the fabrication of copper matrix composites (CMCs), but how their orientation and synergetic effect in Cu matrix affects the properties of composites has not been explored systematically. Herein, an efficient route to fabricate CMCs with GO-CNTs hybrid reinforcement had been reported, as well as the influence of different carbon reinforcement and different current densities on the texture orientation, microstructure and the comprehensive performance were investigated. From ultraviolet–visible results, it was found that one-dimensional CNTs bridge adjacent two-dimensional GO through π-π bonding to form an interconnected network structure. By adding GO-CNTs hybrid reinforcement to pure Cu sulfate, the preferred crystalline orientation of the GO-CNTs/Cu had been changed and a preferred orientation of (111) crystal plane was formed. Meanwhile, the EBSD results revealed that the GO-CNTs hybrid reinforcement had significant grain refinement effect and the average grain size of GO-CNTs/Cu composite reduced to 112 nm. According to TEM images, the lattice stripes between GO and CNTs indicate the formation of C–C covalent bonding. Owing to the synergistic effect and the C–C covalent bonding between GO and CNTs, the highest thermal conductivity reached to 527 W m−1 K−1, while, the highest hardness was up to 226.8 HV0.1, the friction coefficient reduced to 0.62and excellent corrosion resistance of the GO-CNTs/Cu composite were also achieved. This study suggested that the promising fabrication of high-oriented GO-CNTs/Cu composite may have the potential to obtain excellent performance.

Additive engineering in spray enables efficient methylammonium-free wide-bandgap perovskite solar cells

Spray coating is an emerging technique, paving the way for the commercialization of perovskite. However, it still faces challenges in the preparation of wide-bandgap (WBG) perovskite solar cells (PSCs) for tandem photovoltaic devices. Applying a two-step evaporate-spray method, and an additive engineering strategy, where n-propylammonium chloride is introduced in spray processing, we fabricate efficient and stable methylammonium-free (MA-free) WBG PSCs. The propylammonium cation plays a role in passivating grain boundaries, which resulted in the reduction of vacancy defects on the surface of films. Cl− plays a big part in the crystal growth process. After the addition of PACl, preferred crystalline orientation, larger grain size, and reduced trap density in perovskite films are obtained. Finally, the champion WBG PSC (Energy gap (Eg), Eg ≈ 1.68 eV) delivers a power conversion efficiency (PCE) over 19%, which is the highest efficiency of the WBG PSCs prepared by the evaporate-spray method, as compared to pristine devices with the highest PCE of 16.59%. Additionally, the barrier against moisture formed at the surface of films significantly enhances humidity stability of the photovoltaic (PV) device.

Strain‐Sensitive Flexible Magnetoelectric Ceramic Nanocomposites

AbstractMagnetoelectric (ME) oxide materials can convert magnetic input into electric output and vice versa, making them excellent candidates for advanced sensing, data storage, and communication. However, their application has been limited to rigid devices due to their brittle nature. Here, flexible ME oxide composite (BaTiO3/CoFe2O4) thin film nanostructures with distinct ME coupling coefficients are reported. In contrast to rigid bulk counterparts, these ceramic nanostructures display a flexible behavior after being released from the substrate, and can be transferred onto a stretchable substrate such as polydimethylsiloxane. These ceramic films possess high ME coefficients due to minimized clamping effect and preferred crystalline orientation, and exhibit reversibly tunable ME coupling via mechanical stretching thanks to their large elasticity (>4%). It is believed that the study can open up new avenues for integrating ceramic ME composites into micro‐/nanoelectromechanical system and soft robotic devices.

High performance LaNiO3-buffered, (001)-oriented PZT piezoelectric films integrated on (111) Si

Integration of high-performance lead zirconate titanate (PZT) piezoelectric films onto (111) Si substrates is beneficial for the development of piezoelectric micro-electro-mechanical systems (Piezo-MEMS) because of (111) Si's isotropic mechanical properties and desirable etching characteristics. These features will greatly reduce complications in micro-device fabrication and patterning of PZT/Si heterostructures. However, piezoelectric performance of a PZT film is usually dominated by its preferred crystalline orientation, with (001) being superior than (110) and (111). Such a vectorial dependence seriously restricts applications of PZT films grown on (111) Si, which are usually not (001)-textured. In this work, highly (001)-oriented PZT thick films (∼1.5 μm) with a 53/47 Zr/Ti ratio were prepared on (111) Si substrates via a multi-layer buffering technique, i.e., through the use of a (111)Pt/Ti bi-layer and a LaNiO3 buffer layer. The PZT films were sputter-deposited at a low temperature (350 °C) and then crystallized in a (001) texture via a rapid thermal annealing (RTA). The e31,f transverse piezoelectric coefficient was up to ∼11.6 C/m2 for PZT films with a RTA time of 2 minutes. Such an e31,f value is comparable to that of PZT films grown on (100) Si. This work opens up many possibilities for Piezo-MEMS by demonstrating the desirable combination of a large piezoelectricity in (001) PZT with a good patternability of (111) Si.

Highly Textured Zinc Thin Films through Novel Pulsed Electrodeposition Techniques and Their Applications

The electrodeposition of zinc thin films has been widely investigated with extensive applications in corrosion, battery electrodes, photo- and electro-catalysis. Traditionally, the direct current (DC) method of electroplating has been explored in terms of varying current density to obtain changes in morphology, grain size, preferred crystalline orientation, which in turn have significant consequences for properties such as catalysis and corrosion resistance. We have recently demonstrated [1] a novel, additive-free pulsed plating method to control the specific crystalline growth orientations and average grain size of zinc electrodeposited on steel substrates.Specifically, we have observed a transition of the preferential (002) facets at low peak current density (or low duty cycle) to (101) preferring facets at higher peak current density (or high duty cycle) as determined by the analysis of texture coefficients. Further analysis using scanning electron microscopy reveals a transition from the conventional hexagonal-shaped particles of zinc to needle-shaped structures, accompanied by a change in average crystallite size from 33 to 19 nanometers, determined from X-ray diffraction studies. The variation in morphology is also correlated to crystallographic textures through the analysis of texture coefficients and an understanding of crystallization mechanisms occurring during deposition.Herein, we report on an application of these highly textured zinc-coated steel substrates towards corrosion resistance, through accelerated electrochemical testing. Using industry-standard ASTM methods such as Linear Polarization Resistance (LPR), Linear sweep voltammetry (LSV) and electro-impedance spectroscopy (EIS) measurements, we report on preliminary findings of corrosion potential, current and corrosion rates expressed in mm per year as a function of crystalline texture of the zinc thin films.

Improving the Mechanical Resistance of Hydroxyapatite/Chitosan Composite Materials Made of Nanofibers with Crystalline Preferential Orientation.

The stability and mechanical properties of hydroxyapatite (HAp)/Chitosan composite materials depend on the dispersion of HAp aggregates in the chitosan matrix and on the chemical interaction between them. Therefore, hexagonal cross-sectioned HAp nanofibers were produced using a microwave-assisted hydrothermal method. Glutamic acid was used to control the HAp crystal growth; thereby, nanofibers were obtained with a preferential crystalline orientation, and they were grown along the “c” axis of HAp crystal structures. This morphology exposed the (300) and (100) crystal planes on the surface, and several phosphate groups and calcium ions were also exposed; they were able to form numerous chemical interactions with the amine, hydroxyl, and carbonyl groups of chitosan. Consequently, the final mechanical resistance of the composite materials was synergistically increased. Nanofibers were mixed with commercial chitosan using a sonotrode to improve their dispersion within the biopolymer matrix and prevent migration. The HAp nanofiber/Chitosan composite materials showed higher mechanical resistance than that observed in similar materials with the same chemical composition that were made of commercial HAp powders, which were used as reference materials. The mechanical resistance under tension of the composite materials made of nanofibers was similar to that reported for cortical bone.

A biomineralization-inspired strategy of self-encapsulation for perovskite solar cells

Solution-processed perovskite films are promising for the cost-effective fabrication of optoelectronic devices. However, the poor environmental stability of perovskite materials hampers their commercial development, and a challenge remains in the universal technology for self-encapsulating perovskite films through controlling the crystallization. Herein, we designed a strategy of crystal growth assisted by the polymer bottom-up dynamic diffusion and created the self-encapsulated perovskite films with preferred crystalline orientation by mimicking the typical process of biomineralization. Thin polymer distributed at the surface, buried interface, and grain boundaries facilitated the efficient defect passivation and self-encapsulation of the entire film, and also, the coordination interaction between polymer and perovskite aligned the interface energy band. These collaborative advantages endowed perovskite solar cells (PSCs) with power conversion efficiency (PCE) of 22.90 %. In addition, the self-encapsulated perovskite films exhibited negligible decomposition and PCE remained 90 % after being stored in ambient air (30–50 % humidity) for 90 days. This universal strategy of biomineralization-inspired polymer self-encapsulating opens up a new avenue for efficient and stable perovskite optoelectronics.

Crystalline structures and optoelectronic properties of orthorhombic CsPbBr3 polycrystalline films grown by the Co-evaporation method

In order to fabricate pure-phase CsPbBr3 films with high crystalline quality, the stoichiometry between precursors is of great importance. However, the precise control of the stoichiometry is difficult for solution processed methods, which is hindered by the poor solubility of CsBr in commonly used solvents. On the other hand, in terms of co-evaporation method, the stoichiometry of CsPbBr3 films can be easily modulated by controlling the deposition rates of precursors. Herein, the impact of deposition rate ratio between CsBr and PbBr2 on the crystalline quality and optoelectronic properties of orthorhombic CsPbBr3 polycrystalline films has been investigated. CsPbBr3 polycrystalline films with high crystalline quality and preferential crystalline orientation have been fabricated using co-evaporation method at the optimized deposition rate ratio. The reversible structural transformation from orthorhombic to cubic phase CsPbBr3 films is confirmed using temperature-dependent XRD characterizations. At the deposition ratio of 0.5:0.7, largest grain size of 7.82 × 104 nm2 along with a high uniformity is observed for CsPbBr3 films. Moreover, the longest lifetime of 24.0 ns for photo-generated exciton within CsPbBr3 films has also been revealed at the optimized deposition rate ratio. Because of the high crystalline quality and prolonged lifetime for photo-generated exciton, a photoresponsivity of 20.2 A/W and external quantum efficiency of 48.7% are achieved for CsPbBr3 based photodetector. Our findings demonstrate a facile approach for the growth of CsPbBr3 polycrystalline films with high crystalline quality and promote their applications in optoelectronic devices.

Influence of the carrier wafer during GaN etching in Cl2 plasma

In this study, we have performed a thorough characterization of the GaN surface after etching up to 100 nm in Cl2 plasma under various bias voltages and according to the carrier wafer used (Si, SiO2, Si3N4, and photoresist). The objective of this article is to evaluate the etch damage and contamination of the GaN surface when materials with other chemical nature are present during etching. The effects of etching conditions on surface morphology and chemical compositions of etched GaN films are studied in detail using XPS and AFM measurements. To this aim, a universal methodology is proposed to estimate accurately by XPS the stoichiometry of the GaN surface exposed to reactive plasmas when only an Al Kα x-ray source is available. The results indicate that the GaN etching mechanisms are very sensitive to the chlorine radical density present in the plasma, the latter being strongly influenced by the carrier wafer. Substrates that are more chemically reactive with Cl2 plasma such as silicon or photoresist compared to SiO2 or Si3N4 will lead to a greater loading of atomic chlorine, which in turn will lead to lower GaN etch rates. Moreover, the GaN surface contamination will depend on the etch by-products ejected by the carrier wafer. The GaN surface exposed to Cl2 plasma shows a Ga-depleted surface because of the more important reactivity of Cl with Ga rather than N, except in the SiO2 carrier wafer case. In this latter case, the formation of Ga–O bond limits the Ga removal. Regarding the surface roughness, it seems that the contaminants play a little role in the roughness formation except for the oxygen released by the SiO2 carrier wafer. On the other hand, the surface roughness evolution is clearly driven by the chlorine radical flux reaching the GaN surface. At low bias voltage, a preferential crystalline orientation etching driven by the Cl radicals leads to the formation of hexagonal shaped defects that are associated to screw-type threading dislocations already present in the pristine GaN material. At higher bias, the enlargement of the defects is limited, leading to a very low surface roughness value but to amorphized surfaces.

Structural, Morphological, Vibrational and Optical Properties of GaN Films Grown by Reactive Sputtering: The Effect of RF Power at Low Working Pressure Limit

This work reports the properties of GaN films grown onto c-Si (100) at relatively low substrate temperature (400°C) by reactive magnetron sputtering. The study depicts the effect of working pressure and RF power on the GaN film structural, vibrational and optical properties characterized by X-ray diffraction, atomic force and scanning electron microscopies, Raman spectroscopy and spectroscopic ellipsometry. Unusual low pressure deposition condition (0.40 Pa) was achieved by using a separated argon inlet directed to the Ga target surface, resulting in improved crystalline quality of the films. In this condition, the preferential crystalline orientation, the surface morphology and the optical gap of the GaN films show a strong dependence on the RF power applied to the Ga target, where low RF power (30-60 W) was responsible for increasing the c-axis orientation and the optical gap, while higher RF power (75-90 W) decreased the overall crystal quality and increased the surface roughness.

On some peculiar fractures observed in tests of the Upper-Cretaceous fossil echinoid Micraster

Many skeletons (“tests”) of the fossil echinoid Micraster from the marl limestone strata of the Upper Cretaceous formation of western Navarra (Spain) show small triangular holes on their surface, caused by the loss of a pyramidal fragment. The base of the pyramidal borings is often close to an equilateral triangle. The test of echinoids is a mosaic structure constituted of interlocking monocrystalline plates of bio-calcite which possess a preferred crystalline orientation. In the case of the genus Micraster, the surface of the plates is near-parallel to the basal calcite plane (0001). The geometry of the observed holes, at first sight surprising, is simply explained by the intersection of cracks along the three easy 101¯4 cleavage planes of the calcite single crystalline plates constitutive of the skeletons. The fracture process leading to the pyramidal fractures is most likely due to stresses of thermo-elastic origin induced by the heterogeneous dilatational response of the anisotropic tests adhered to the isotropic marly limestone in which they are embedded and which is constitutive of their inner molds.