C-axis Orientation Research Articles

Deterioration of apatite orientation in the cholecystokinin B receptor gene (Cckbr)-deficient mouse femurs.

The discrepancy between bone mineral density (BMD), the gold standard for bone assessment, and bone strength is a constraint in diagnosing bone function and determining treatment strategies for several bone diseases. Gastric hypochlorhydria induced by clinically used proton pump inhibitor (PPI) therapy indicates a discordance between changes in BMD and bone strength. Here, we used Cckbr-deficient mice with gastric hypochlorhydria to examine the effect of gastric hypochlorhydria on bone mass, BMD, and preferential orientation of the apatite crystallites, which is a strong indicator of bone strength. Cckbr-deficient mice were created, and their femurs were analyzed for BMD and preferential orientation of the apatite c-axis along the femoral long axis. Cckbr-deficient mouse femurs displayed a slight osteoporotic bone loss at 18weeks of age; however, BMD was comparable to that of wild-type mice. In contrast, apatite orientation in the femur mid-shaft significantly decreased from 9 to 18weeks. To the best of our knowledge, this is the first report demonstrating the deterioration of apatite orientation in the bones of Cckbr-deficient mice. Lesions in Cckbr-deficient mice occurred earlier in apatite orientation than in bone mass. Hence, bone apatite orientation may be a promising method for detecting hypochlorhydria-induced osteoporosis caused by PPI treatment and warrants urgent clinical applications.

Room-temperature deformation of single crystals of WC investigated by micropillar compression

The room temperature deformation behavior of single crystals of WC has been investigated as a function of crystal orientation and specimen size by micropillar compression tests. Plastic flow is successfully observed at room temperature by the operation of slip on {011¯0}〈21¯1¯3〉 when the specimen size is reduced to micrometer orders. This slip system is the only operative slip system in WC at room temperature, and thus plastic flow is not observed for crystal orientations close to the c-axis orientation. The bulk critical resolve shear stress (CRSS) is estimated to be 1.2 ± 0.3 GPa from the extrapolation of the size-dependent CRSS. The 1/3〈21¯1¯3〉 dislocation carrying slip on {011¯0} dissociates into two identical collinear partial dislocations separated by a stacking fault with the energy of 211∼264 mJ/m2. The preference of slip along 〈21¯1¯3〉 among possible directions (such as 〈21¯1¯0〉 and [0001]) on the {011¯0} prism plane is discussed in terms of dislocation self-energy based on anisotropic elasticity, stacking fault energy, dislocation dissociation and Peierls stress for dislocation motion. The lowest Peierls stress arising from the shorter Burgers vector (1/6〈21¯1¯3〉) of dislocations as a result of collinear dissociation of dislocations with b = 1/3〈21¯1¯3〉 on the {011¯0} slip plane is considered to be the main reason for the preference of the {011¯0}〈21¯1¯3〉 slip system.

RF-sputtered Z-cut electro-optic barium titanate modulator on silicon photonic platform

Epitaxial BaTiO3 integrated on Si or Si-on-insulator using off-axis radio frequency sputtering is a promising material platform for building electro-optic modulators based on the Pockels effect. Barium titanate thin films with c-axis orientation have been epitaxially integrated on silicon-on-insulator wafers. They exhibit excellent structural quality with Pockels coefficient (r33) > 130 pm/V and propagation loss <2 dB/cm. Our results show that off-axis sputtered BaTiO3 films yield electro-optic modulation similar to that of high-quality films grown by molecular beam epitaxy and that the material is suitable for implementation of low-power Mach–Zehnder interferometer electro-optic modulators integrated on silicon in a Z-cut configuration.

Influence of doping concentrations of Hf on structural and electrical properties of HfxZn1-xO thin films

HfxZn1−xO thin films (x=0, 2.5,3, 7.5, 10 and 15mol %) were deposited on glass substrates using Sol-gel process. The influence of the Hf concentration on the structural, electrical, and optical properties of the films was studied. It is found that Hf ions can be effectively doped into ZnO and all films crystallize in the hexagonal wurtzite structure with a preferred c-axis orientation. The lattice constants of HfxZn1−xO films increase with the Hf contents. The HfxZn1−xO thin films structures of high-Hf-content films remain after annealing at 600 °C for 20 min. The optical band gap increases with the Hf content, but it decreases with the annealing temperature. The reduction of bandgap partly results from grain growth, which is due to the quantum confinement effect of the small grains. Hf doping increases the resistivity of ZnO owing to the disorder of the material structure and the higher bandgap, which results in more carrier traps and less thermally excited carriers in the conduction bands. Two FTIR peaks centered at about 1432 and 1056 cm-1 coexist in the fluorescent spectra. With increasing the Hf contents, the intensity of fluorescent peaks enhances remarkably. The Minimum resistivity reached 6.1 * 10-2 Ὠ cm after annealing with 3% Hf content.

Photodetection Properties of CdS/Si Heterojunction Prepared by Pulsed Laser Ablation in DMSO Solution for Optoelectronic Application.

The high-quality n-type CdS on a p-type Si (111) photodetector device was prepared for the first time by a one-pot method based on an ns laser ablation method in a liquid medium. Cadmium target was ablated in DMSO solution, containing sulfur precursor, and stirred, assisting in 1D-growth, to create the sulfide structure as CdS nano-ropes form, followed by depositing on the Si-substrate by spin coating. The morphological, structural, and optical characteristics of the CdS structure were examined using X-ray diffraction, transmission, and scanning electron microscopy, photoluminescence, and UV-VIS spectroscopy. From X-ray diffraction analysis, the growing CdS spheres have a good crystal nature, with a high purity and desired c-axis orientation along the (002) plane, and the crystallinity was around 30 nm. According to optical characterization, high transparency was found in the visible-near-infrared areas of the electromagnetic spectrum, and the CdS spheres have a direct optical energy band gap of 3.2 eV. After that, the CdS/Si hetero-structured device was found to be improved remarkably after adding CdS. It showed that the forward current is constantly linear, while the dark current is around 4.5 µA. Up to a bias voltage of 4 V, there was no breakdown, and the reverse current of the heterojunctions somewhat increased with reverse bias voltage, while the photocurrent reached up to 580 and 690 µA for using 15 and 30 W/cm2 light power, respectively. Additionally, the ideal factors for CdS/Si heterojunction were 3.1 and 3.3 for 15 and 30 W/cm2 light power, respectively. These results exhibited high performance compared to the same heterojunction produced by other techniques. In addition, this opens the route for obtaining more enhancements of these values based on the changing use of sulfide structures in the heterojunction formation.

Controlling the shape of hexagonal structure by growth condition improves the thermoelectric properties of p-type Bi-Te films

Improving the thermoelectric (TE) properties of typical p-type Bi0.5Sb1.5Te3 film is crucial for power generation in film-based thermoelectric devices. The shape of the hexagonal structure in the Bi0.5Sb1.5Te3 film can be controlled by adjusting the magnetron sputtering parameters. The results indicate that a high nucleation rate under high sputtering power promotes island growth with a preferred orientation of (015). Thermal energy influences the growth in the in-plane direction along the (00 l) orientation and induces the c-axis orientation in the out-of-plane direction. Consequently, a dense layered hexagonal structure with a high grain boundary density is formed, leading to increased defect density, carrier concentration, and phonon scattering. In this case, the power factor reaches 3149.01 μW·m-1·K-2 at 480 K and the ZT value is 1.14 at 480 K. These results indicate that the film with a dense layered hexagonal structure enhances the TE properties.

Preparation and Laser-Induced Thermoelectric Voltage Effect of Bi2Sr2Co2Oy Thin Films Grown on Al2O3 (0001) Substrate.

Bi2Sr2Co2Oy thin films were grown on 10° vicinal-cut Al2O3 (0001) single crystalline substrates by pulsed laser-deposition techniques with in situ annealing, post-annealing and non-annealing process, respectively. The pure phase Bi2Sr2Co2Oy thin film was obtained with a non-annealing process. The result of X-ray diffraction showed that Bi2Sr2Co2Oy thin film was obviously c-axis preferred orientation. The laser-induced thermoelectric voltage signals were detected in Bi2Sr2Co2Oy thin films, which originated from the anisotropy of the Seebeck coefficient. The maximum peak value of laser-induced thermoelectric voltage was strong and could reach as large as 0.44 V and the response time was 1.07 μs when the deposition time was 6 min. Furthermore, the peak voltage enhanced linearly with the single-pulse laser energy. These characteristics demonstrate that Bi2Sr2Co2Oy thin film is also an excellent choice for laser energy/power detectors.

Nitrogen flow rate dependent atomic coordination, phonon vibration and surface analysis of DC magnetron sputtered nitrogen rich-AlN thin films

In this work, the effect on crystallite orientation, surface morphology, fractal geometry, structural coordination and electronic environment of DC magnetron sputtered AlN films were investigated. X-ray diffraction results disclosed that the c-axis orientation of AlN films increased with the preferred wurtzite hexagonal structure above 17% N2 flow. X-ray reflectivity data confirmed AlN film density increased with increasing N2 flow and was found to be 3.18 g/cm3 for 40% N2. The transition of electrons from N 1s to 2p states hybridized with Al 3p states because of π* resonance was obtained from X-ray absorption spectroscopy of the N K-edge. The semi-empirical coordination geometry of nitrogen atoms has been studied by deconvolution of N K-edge. The surface composition of AlN films at 40% N2 consists of 32.08, 51.94 and 15.97 at.% Al, N and O respectively. Blue-shifting of A1(LO) and E1(LO) modes in the Raman spectra at phonon energies 800 and 1051 cm−1 respectively was most likely due to the presence of oxygen bonds in the AlN films.

Inhomogeneity of the Backward Extruded NdFeB Ring Magnet Prepared from Amorphous Powders.

Back extrusion is an important process to prepare radially oriented NdFeB ring magnets. In this work, we fabricate the ring magnets using amorphous magnetic powders as the raw material. The microstructure, magnetic properties, corrosion resistance, and mechanical properties of the backward extruded magnet at different positions along the axial direction have been investigated, and the inhomogeneity of the magnet is clarified. The results showed that the grains in the middle region of the ring magnet exhibit a strong c-axis orientation, whereas the grains at the bottom and top regions are disordered with random orientation. The microstructure variation is related to the distribution of the grain boundary phase and the degree of grain deformation. Due to the microstructure difference, the magnetic properties, temperature stability, corrosion resistance, and mechanical properties in the middle region of the magnet are higher than those in the top and bottom regions. The exchange coupling between grains also varies in different regions, which is related to the grain size and grain boundary thickness. In addition, different Co element segregations were observed in different regions, which has a crucial effect on the Curie temperature and thermal stability of the magnet. The microstructure difference also leads to the variation of corrosion resistance and mechanical properties for the samples from different regions of the magnet. This work suggests that the amorphous powder can be used to directly prepare radially oriented ring magnets, and the inhomogeneity of the magnet should be fully understood.

Effect of atomic layer annealing in plasma-enhanced atomic layer deposition of aluminum nitride on silicon

The effect of adding an atomic layer annealing step to a plasma-enhanced atomic layer deposition process of aluminum nitride was investigated with commonly available materials. The refractive index, crystallinity, stoichiometry, and impurity concentrations were studied from films grown from trimethylaluminum and ammonia precursors at 300°C on Si(111) substrates. Additional energy provided by the atomic layer annealing step during each deposition cycle was found to enhance the crystallinity and stoichiometry and increase the refractive index and film density. A polycrystalline hexagonal film with a weak c-axis orientation was obtained on substrates with and without native oxide, which is promising for applications that require high quality films at low temperatures.

Facile preparation of α-calcium sulfate hemihydrate whisker from by-product gypsum in chloride-free salt solution system

Lactic acid gypsum (LAG), the by-product from lactic acid preparation, has caused land occupation and environmental pollution. Herein, hemihydrate gypsum (HHG) whisker, an inorganic material with excellent performance, prepared using LAG as the raw material via atmospheric pressure salt solution method was investigated. Nitrate enhanced the salt effect of the solution, which increased the solubility of dihydrate gypsum (DDG), and further accelerated the conversion into HHG. NaNO3 was proved to accelerate the formation of α- HHG whisker, while Mg(NO3)2 promoted its aspect ratio. The whiskers with an average length of 75.9 µm and aspect ratio of 17.8 were achieved under optimum conditions of NaNO3/Mg(NO3)2–0.5:1, mass fraction of LAG–15%, reagent concentration–40%, and the reaction temperature–100 °C. Mg2+ was found to bind with SO42- on the side of the whisker, promoting the growth of the whisker along the c-axis orientation and forming the morphology of high aspect ratios. Hence, it was feasible to achieve the recycling of salt medium by adding medicament containing Mg2+. By employing direct recycling, the salt medium was limited to be effective in two cycles. However, with the addition of the medicament, the salt medium can now be effectively recycled up to four times or more. Such technique realized the high-value utilization of industrial by-product gypsum, guided the HHG whisker preparation via the green and convenient method and reduced the environmental hazards.

Structural, Surface, and Optical Properties of AlN Thin Films Grown on Different Substrates by PEALD

Plasma-enhanced atomic layer deposition was employed to grow aluminum nitride (AlN) thin films on Si (100), Si (111), and c-plane sapphire substrates at 250 °C. Trimethylaluminum and Ar/N2/H2 plasma were utilized as Al and N precursors, respectively. The properties of AlN thin films grown on various substrates were comparatively analyzed. The investigation revealed that the as-grown AlN thin films exhibit a hexagonal wurtzite structure with preferred c-axis orientation and were polycrystalline, regardless of the substrates. The sharp AlN/substrate interfaces of the as-grown AlN are indicated by the clearly resolved Kiessig fringes measured through X-ray reflectivity. The surface morphology analysis indicated that the AlN grown on sapphire displays the largest crystal grain size and surface roughness value. Additionally, AlN/Si (100) shows the highest refractive index at a wavelength of 532 nm. Compared to AlN/sapphire, AlN/Si has a lower wavelength with an extinction coefficient of zero, indicating that AlN/Si has higher transmittance in the visible range. Overall, the study offers valuable insights into the properties of AlN thin films and their potential applications in optoelectronic devices, and provides a new technical idea for realizing high-quality AlN thin films with sharp AlN/substrate interfaces and smooth surfaces.

Stability of ferroelectric phase and structural characteristics in oriented PbTiO3 ceramic coating formed by aerosol deposition method

Temperature-dependent structural variations of ceramic coatings of lead titanate PbTiO3 (PT) formed at room temperature (RT) via aerosol deposition (AD) have been investigated to evaluate the stability of the ferroelectric phase. Synchrotron radiation x-ray diffraction experiments in the as-deposited state showed a polycrystalline film oriented preferentially along the c-axis of the perovskite-type ferroelectric tetragonal structure on the quartz glass substrate. The c-axis orientation may be attributed to the anisotropic structural characteristics of the crystal with a layered structure composed of a two-dimensional (2D) covalent bonding network in the ferroelectric phase at RT. The 2D interfaces of the ceramic particles in the aerosol, which are chemically activated by collision with the substrate, are most likely to recombine during the AD process and form a dense and hard coating at RT. When the PT film was heated to the paraelectric phase with a cubic structure at 1000 K, the c-axis orientation observed in the as-deposited state disappeared upon cooling owing to the degree of freedom in selecting the polar axis associated with the cubic-tetragonal phase transition. The spontaneous lattice distortion of the AD film at RT was smaller than that of the bulk ceramic. However, the phase transition temperature (TC) was approximately 100 K higher only during the first heating process from the c-oriented as-deposited state. The AD method stabilizes the ferroelectric phase up to a higher temperature, although the spontaneous polarization is suppressed. The ferroelectric ceramic materials synthesized mainly via particle collisions are assumed to have low ferroelectricity but high TC.

Improvement of the uniformity of structural and electrical properties of transparent conductive Al-doped ZnO thin films by inductively coupled plasma-assisted radio frequency magnetron sputtering

Transparent conductive Al-doped Zinc oxide thin films were deposited on glass substrates by conventional radio frequency magnetron sputtering (C-RFMS) and inductively coupled plasma-assisted radio frequency magnetron sputtering (ICP-RFMS) methods. The structural and electrical properties of films were studied as a function of the radial position (r) of the substrate in both methods. A good thickness uniformity was obtained in ICP-RFMS, while a significant decrease in film thickness was observed at r=30mm (erosion zone) in C-RFMS. The c-axis orientation was achieved in all positions in ICP-RFMS, while crystallinity was degraded at r≥25mm in C-RFMS. Low resistivity ρ of the order of 10−4Ωcm was obtained at all positions in ICP-RFMS, while ρ was rapidly increased at r≥30mm in C-RFMS. In ICP-RFMS, high-energy ion bombardment is suppressed due to the modified plasma density profile and lower space potential. As for transparency, the sample prepared at r=0mm in ICP-RFMS showed an average visible transmittance of 81%, higher than that in C-RFMS. Throughout the study, it was demonstrated that ICP-RFMS method was promising to improve the radial distribution of structural, electrical, and optical properties of Al-doped ZnO thin films.

Pulsed chemical vapor deposition for crystalline aluminum nitride thin films and buffer layers on silicon and silicon carbide

Low temperature aluminum nitride (AlN) deposition has applications ranging from serving as a heat spreading material to serving as a buffer layer for III-V semiconductors on silicon or silicon carbide (SiC) for radio frequency, power, and microLED devices. While crystalline AlN is traditionally deposited at high temperature (>800 °C), in the present study AlN is deposited on Si(100), Si(111), and 4H-SiC substrates by two modest temperature processes using a metal precursor with high thermal stability, tris(dimethylamido) aluminum (III), and a highly reactive nitrogen source, anhydrous hydrazine. A 580 °C pulsed chemical vapor deposition (CVD) process is compared to a more complex 400 °C atomic layer annealing process, in which the same precursors are utilized with periodic ion bombardment to induce film crystallinity. Films deposited by both processes template preferential c-axis orientation in subsequently sputtered AlN on unheated substrates. Both templating techniques demonstrate equivalent enhancements in crystallinity of the sputtered AlN relative to a non-templated sputtered film by x-ray diffraction and transmission electron microscopy studies. On 4H-SiC substrates, a comparison of sputtering directly and templating with the 580 °C pulsed CVD process reveals epitaxial deposition by the 580 °C pulsed CVD process which extends into the low temperature sputtered AlN.

Manipulating the optoelectronic characteristic of AZO films by magnetron sputtering power

We investigated the effects of sputtering power on the structure, morphology, electrical and optical properties of AZO films. The results show that all the films show typical hexagonal wurtzite structure with preferred c-axis orientation. When the sputtering power is 120 W, the film has the smallest FHWH value and the largest grain size (24.33 nm), and the AZO thin films obtained the best conductivity, the electrical characteristic parameters are ρ = 3.25 × 10−3 Ω cm， N = 3.512 × 1019 cm−3, μH = 8.642 cm2V−1s−1, respectively. With the increase of sputtering power, the carrier concentration and hall mobility are increasing, which are directly related to the improvement of crystal quality, that is, the higher the crystal quality of the film, the better the conductivity. The average transmittance of all samples is above 80%, and the band gaps increase first and then decreased. This work implies that the application of controllable growth AZO transparent conductive film in photovoltaic devices.

Fabrication of Well-Aligned ZnO Nanorods with Different Reaction Times by Chemical Bath Deposition Method Applying for Photocatalysis Application.

Zinc oxide nanorods were grown on an aluminum-doped zinc oxide seeds layer using the chemical bath deposition method. The effects of growth reaction time on the structural, optical, and photocatalytic properties of zinc oxide nanorods were investigated. It was clearly observed that the growth direction of zinc oxide nanorods were dependent on the crystallinity of the as-deposited aluminum-doped zinc oxide seed layer. The crystallinity of the obtained zinc oxide nanorods was improved with the increase in reaction times during the chemical bath deposition process. The mechanism of zinc oxide nanorod growth revealed that the growth rate of nanorods was influenced by the reaction times. With increasing reaction times, there were much more formed zinc oxide crystalline stacked growth along the c-axis orientation resulting in an increase in the length of nanorods. The longest nanorods and the high crystallinity were obtained from the zinc oxide nanorods grown within 5 h. The optical transmittance of all zinc oxide nanorods was greater than 70% in the visible region. Zinc oxide nanorods grown for 5 h showed the highest degradation efficiency of methyl red under ultraviolet light and had a high first-order degradation rate of 0.0051 min-1. The photocatalytic mechanism was revealed as well.

Self-assembled c-oriented Ni(OH)2 films for enhanced electrocatalytic activity towards the urea oxidation reaction.

This study investigates the electrocatalytic properties of the transparent c-oriented Ni(OH)2 films self-assembled from colloidal 2D Ni(OH)2 nanosheets for urea oxidation. The synthesis process yields highly uniform close-packed superlattices with a dominant c-axis orientation. The self-assembled c-oriented Ni(OH)2 films exhibit advantageous electrocatalytic performance in urea oxidation, presenting significantly lower overpotentials and higher current densities compared to randomly distributed Ni(OH)2 particles. In-depth in situ impedance analysis and Raman spectroscopy demonstrate that the c-oriented Ni(OH)2 films possess a higher propensity for a Ni valence transition from +2 to +3 during the urea oxidation process. This finding provides crucial insights into the catalytic behavior and electronic transformations of c-oriented Ni(OH)2 films, shedding light on their superior electrocatalytic activity for urea oxidation. Overall, this study advances our understanding of urea electrooxidation mechanisms and contributes to the design of efficient urea electrocatalysts.

Sputtering Process of ScxAl1−xN Thin Films for Ferroelectric Applications

Several key sputtering parameters for the deposition of ScxAl1−xN such as target design, sputtering atmosphere, sputtering power, and substrate temperature are reviewed in detail. These parameters serve a crucial role in the ability to deposit satisfactory films, achieve the desired stoichiometry, and meet the required film thickness. Additionally, these qualities directly impact the degree of c-axis orientation, grain size, and surface roughness of the deposited films. It is systematically shown that the electric properties of ScxAl1−xN are dependent on the crystal quality of the film. Although it is not possible to conclusively say what the ideal target design, sputtering atmosphere, sputtering power, and substrate temperature should be for all sputtering processes, the goal of this paper is to analyze the impacts of the various sputtering parameters in detail and provide some overarching themes that arise to assist future researchers in the field in quickly tuning their sputtering processes to achieve optimum results.

Influence of neutron/gamma irradiation on damage and scintillation of Ga-doped ZnO thin films

As a new type of inorganic scintillator, ZnO crystal doped with Ga has been used for Ultra-fast scintillating detectors with fast response to detect X-ray, gamma, neutron, and charged particles. Moreover, due to the large bandgap energy and high threshold displacement energy, ZnO: Ga has a strong radiation resistance in theory. However, there is a lack of experimental studies on the change of scintillation properties of ZnO: Ga under an intense irradiation environment. This study deposited thin Ga-doped ZnO films on α-Al2O3(0001) substrate by dual-target reactive magnetron sputtering. The ZnO: Ga samples were irradiated by neutrons from 1010 to 7.1 × 1014 neutrons/cm2 (1 MeV neutron equivalent fluence) and γ rays from 500 to 10,000 Gy, respectively. The structural and optical properties of all irradiated samples were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), optical transmittance (TS), and effective light output at room temperature. The results indicated that all the irradiated samples are still in both hexagonal wurtzite structure and c-axis orientation. Compared with unirradiated samples, it is found that the samples' optical transmittance, energy resolution, and effective light output have little change due to irradiation, which has fully proved that the ZnO: Ga scintillation films have good radiation resistance under neutron and gamma irradiation. Hence, ZnO: Ga is an attractive candidate for radiation detectors with ultra-fast responses under extreme radiation environments.