Protein adsorption on single-crystal hydroxyapatite particles with preferred orientation to a(b)- and c-axes

Adsorption of bovine serum albumin (BSA) and lysozyme (LSZ) proteins with preferred orientation to a(b)- and c-axes of single-crystal hydroxyapatite (HAp) particles, was investigated. Fiber-like HAp single crystal particles (aHAp) and plate-like HAp single crystal particles (cHAp) were used as models for a(b)-plane and c-plane oriented HAps, respectively, together with randomly shaped HAp particles (iHAp) as a control. The selective adsorption behaviors of negatively charged BSA and positively charged LSZ on these HAp particles were examined in a phosphate buffered saline at pH 7.3 and 25 °C for 48 h. The amount of BSA adsorption, normalized for specific surface area, was in the order of aHAp > iHAp > cHAp; however, the order for LSZ was reversed as cHAp > iHAp ≒ aHAp. These results indicate that the a(b)- and c-planes of HAp crystal have high specificity for the adsorption of acidic or basic proteins.     

Biomimetic synthesis of enamel-like hydroxyapatite on self-assembled monolayers

Hydroxyapatite (HAp) crystals mimicking tooth enamel in chemical composition and morphology were formed on sulfonic-terminated self-assembled monolayer (SAM) in 1.5SBF with F⁻ at 50 °C for 7 days. F⁻ ions showed a marked effect on the composition and morphology of deposited HAp crystals. In the absence of F⁻ ions, HAp containing CO₃²⁻ were formed on SAM, and worm-like crystals of 200–300 nm in length aggregated to form a spherical morphology. When F⁻ was added, HAp crystals containing both CO₃²⁻ and F⁻ were formed on SAM. Needle-shaped crystals of high aspect ratio and 1–2 μm in length grew elongated along the c-axial direction. In addition, these needle-shaped crystals grew in bundles, mimicking HAp crystals in tooth enamel. After the process of ripening, the needles in bundle grew to large size of up to 10 μm in length, and still kept no crystal–crystal fusion like enamel HAp crystals. The formation of enamel-like HAp can be attributed to the substitute of F⁻ for OH⁻ by disturbing the normal progress of HAp formation on SAM. The results suggest potential applications in preparing a novel dental material by a simple method.     

Microstructure and electrical properties of YBCO thin films

Microstructures of c-axis oriented YBCO thin films made by high-pressure d.c. sputtering on LaAlO₃ and MgO substrates were examined by TEM. The a-axis oriented grains, second phases and micro-twins were frequently observed in the film. The a-axis oriented grains expanded along their c-axis directions during film growth. The a- and b-axis misorientations were observed in the film on MgO due to serious lattice mis-match between YBCO and MgO. The second phases were often accompanied with a-axis oriented grains suggesting they act as nuclei. These observed results were correlated with the measured T _c and J _c of the films.     

Thermal expansion of β-FeSi2 at low temperatures

We present the temperature dependence of the lattice constants (a, b, c) of β-FeSi₂ single crystals at low temperatures. a showed the largest temperature dependence of 0.14% and the relationship of a>c>b did not change at 8-300 K. The linear thermal expansion coefficients α showed remarkable anisotropy. α along the a-axis (αa) was much larger than αb and αc, and showed negative thermal expansion at temperatures below 60 K. From these results, we estimated the temperature dependence of the lattice mismatches at β-FeSi₂/Si heterojunctions.     

Crystalline thin films of β-phase poly(9,9-dioctylfluorene)

The detailed structure of crystalline β-phase poly(9,9-dioctylfluorene) (PFO) films was studied by polarized optical measurements, transmission electron microscopy, and grazing-incidence X-ray diffraction. Crystalline β-phase PFO thin films were fabricated by a friction transfer technique and subsequent vapor treatment. Compared to the α-phase, the lattice parameters of the β-phase crystals shrank along the a-axis (film thickness direction) and elongated along the b-axis (side-chain direction), but the period along the c-axis (main-chain direction) remained nearly equal. These changes in molecular packing were consistent with a planar conformational change from the α-phase to the β-phase of PFO.     

Magnetoresistance of UPt3

We have performed measurements of the temperature dependence of the magnetoresistance up to 9 T in bulk single crystals of UPt₃ with the magnetic field along the b-axis, the easy magnetization axis. We have confirmed previous results for transverse magnetoresistance with the current along the c-axis, and report measurements of the longitudinal magnetoresistance with the current along the b-axis. The presence of a linear term in both cases indicates broken orientational symmetry associated with magnetic order. With the current along the c-axis the linear term appears near 5 K, increasing rapidly with decreasing temperature. For current along the b-axis the linear contribution is negative.     

Electric-field-induced orientation control of organic semiconductor rubrene crystals

The electric field-induced orientation of rubrene single crystals was observed in a nonpolar solvent. Rubrene single microcrystals responded to an AC electric field beyond a crystal-size dependent threshold. The longitudinal axis, i.e., b-axis, of rubrene single crystals on a SiO₂/Si substrate was aligned almost parallel to the direction of the applied electric field. Field-effect transistors with these orientated crystals exhibited low variability of the carrier mobility.     

High-Field Magnetism of the S=5/2 Kagome-Lattice Antiferromagnet KFe3(OH)6(SO4)2 for the Magnetic Field in the Kagome-Plane

We have performed electron spin resonance (ESR) and magnetization measurements on single crystals of K-Fe-jarosite along the a-axis (in the kagome-plane). We have calculated the resonance branches and the magnetization curve using a spin Hamiltonian including the interlayer exchange and the Dzyaloshinsky-Moriya (DM) interactions. By putting the same parameter values for the analyses along the c-axis (normal to the kagome plane), the calculated results show satisfactory agreement with the experimental ones. As a result, we have successfully explained all the experimental results with one set of the intra- and the inter-plane exchange and the DM interaction parameters.     

Preparation and properties of polycrystalline films of (TTF)(TCNQ)

Thin films of the highly conductive organic complex tetrathiofulvalinium tetracyanoquinodimethane (TTF)(TCNQ) have been prepared on a variety of substrate materials and at substrate temperatures in the range 77–310 K by thermal sublimation of bulk crystals in vacuum. Analysis of the chemical and physical structure of the films indicates that this method of film deposition yields polycrystalline (TTF)(TCNQ) with the grain size and crystalline orientation sensitively dependent on the substrate temperature. In-plane electrical conductivity of the films as a function of temperature and pressure shows behavior indicative of an appropriately weighted average of the single crystal a-axis and b-axis conductivities, with the temperature dependence above the metal-insulator transition temperature influenced by a weakly activated process attributed to crystalline grain boundaries. Comparison of our results with those for sublimation of 1:1 mixtures of TTF with TCNQ suggests that (TTF)(TCNQ) vaporizes primarily as a complex rather than as the individual neutral components.     

Reflection electron diffraction study of oblique textures in CdS thin films produced by electron bombardment evaporation

Reflection electron diffraction studies have been made of obliquely deposited CdS films. The films were produced by electron bombardment evaporation on polished corundum single-crystal substrates at room temperature. The orientation of the uppermost layer of the film was determined for different growth conditions from reflection electron diffraction patterns and the progress in the inclination of the c-axis was studied. It was seen that for the deposition conditions used the c-axis tilted increasingly towards the vapour beam direction for thicknesses ranging from 700 to 10 000 Å. A growth orientation occured, predominantly a two degree orientation in which there was also an a-axis alignment. The influence of the deposition rate and of the angle of incidence were studied.     

Effects of the Ar–N2 sputtering gas mixture on the preferential orientation of sputtered Ru films

We have investigated the influence of N₂ addition to the Ar sputtering gas on the crystal orientation of sputtered Ru films. An rf magnetron sputtering apparatus with a Ru target (99.9%) and a glass substrate heated to 100 °C or 300 °C was used for the deposition. The crystal structure, chemical composition and electrical properties of the resultant films were investigated. X-ray diffraction (XRD) revealed the dominant orientation at 0% N₂ to be the c-axis. With increasing proportion of N₂ in the sputtering gas at a substrate temperature of 100 °C, the intensity of the (002) peak decreased, finally disappearing at 50% N₂. This c-axis-suppressed Ru film sputtered at 50% N₂ was found to contain nitrogen by Auger electron spectroscopy (AES), but by annealing the film in vacuum at 400 °C, the nitrogen in the film was completely removed. The film orientation remained the same as before annealing. Thus, we have demonstrated a new method for depositing Ru films with a controlled preferential orientation of either c-axis oriented or c-axis suppressed.     

Fabrication of crystal-oriented barium-bismuth titanate ceramics in high magnetic field and subsequent reaction sintering

High magnetic field was applied to fabricate novel lead-free piezoelectric ceramics with a textured structure. A compact of crystallographically oriented grains was prepared by dry forming in a high magnetic field from a mixed slurry of bismuth titanate and barium titanate powders. Bismuth titanate particles with a size of about 1 μ m were used as the host material. In the forming process, the slurry was poured into a mold and set in a magnetic field of 10 T until completely dried. Bismuth titanate particles were highly oriented in the slurry under the magnetic field. The dried powder compact consisted of highly oriented bismuth titanate particles and randomly oriented barium titanate particles. Barium bismuth titanate ceramics with a- and b-axis orientations were successfully produced from the dried compact by sintering at temperatures above 1100 ° C.     

Shape-controlled synthesis of hydroxyapatite from α-tricalcium bis(orthophosphate) in organic-aqueous binary systems

Hydrolyses of -tricalcium bis(orthophosphate) Ca₃(PO₄)₂ (-TCP) were carried out in a heterogeneous solvent system (hydrophobic organic solvent-water). The hydroxyapatites (HAp) formed were deficient in calcium (Ca/P = 1.56–1.61, a-axis = 0.9440 nm, c-axis = 0.6880 nm) and contained acid phosphate (and sometimes carbonate depending on the organic solvent used). The HAp was in the form of needles with a length (1–4 m) that depended on the polarity of the hydrophobic organic solvent. The aspect ratio was highest in 1-octanol with a polarity of E _T = 48.3. On the other hand, in a hydrophobic organic solvent system without OH groups such as n-octane (E _T = 31.1), HAp formed fine particles that are similar to HAp prepared in a system without an organic solvent. Thus, hydrophobicity and OH groups of organic solvents affect the crystal growth of HAp.     

High quality c-axis oriented thin ZnO film obtained at very low pre-heating temperature

Highly oriented ZnO thin film has been obtained at a very low pre-heating temperature, with the spin-coating sol-gel technique. The dependence of the c-axis orientation on the pre-heating temperature has been studied with experimental design and response surface techniques to optimize the deposition process with respect to c-axis orientation, and surface uniformity. The optimization variables selected for this study are: pre-heating temperature, spin-coating speed and number of coating layers. The films are probed with X-ray diffraction and electron microscopy.     

Crystal growth of Bi-Sr-Ca-Cu-O from Sr-Ca-Cu-O thin films

Bi-Sr-Ca-Cu-O crystals have been prepared from amorphous Sr-Ca-Cu-O thin films by annealing at 890 °C in the presence of bismuth oxide vapour. Sr_0.8Ca_0.2CuO₂ (08021) and Bi₂(Sr, Ca)₂CuO₆ (2201) crystals initially appeared. On further annealing, needle crystals of Sr_14?xCa_xCu₂₄O₄₁ (14?x) grew. These 14?x needle crystals gradually changed to 2201 needle crystals, which further changed to crystals of the nominal composition Bi-Sr-Ca-Cu-O with ac-axis length of 1.69 nm.     

Transmission electron microscopic observation of a metastable phase on the thermal decomposition process of Ca-deficient hydroxyapatite

Calcium-deficient hydroxyapatite (Ca-def HAp) decomposes to stoichiometric hydroxyapatite (HAp) and β-tricalcium phosphate (β-TCP) at high temperature. In a previous study, we reported that a metastable phase with a high Ca/P molar ratio appeared in the temperature range from 700 to 800°C. In the present study, the formation process of a metastable phase and the crystallographic relationship between the Ca-rich metastable phase and HAp matrix were investigated by high-resolution transmission electron microscopy (HRTEM). Ca-def HAp was annealed at 600–850°C for 2 or 6 h in air. TEM observations were performed before and after annealing Ca-def HAp. Based on analysis of image of Ca-def HAp before annealing, several HAp crystals with different aspect ratios agglomerated. The metastable phases grew thicker by long-term annealing. HRTEM image suggested that the Ca-rich metastable phase was formed by migration to the interface and continuous accumulation of calcium ions from HAp crystals with a small aspect ratio. From HRTEM images and results of the analysis of selected area electron diffraction patterns along the [010], [110] and [001] zone axes, lattice constants of the metastable phases were determined to be a = 2.86 nm, b = 0.94 nm, and c = 0.69 nm with orthorhombic crystals system.     

Microstructures ofa-axis oriented YBa2Cu3O7-δ thin films prepared by low temperature and template processes

Highly a-axis oriented epitaxial thin films of YBa₂Cu₃O_7– have been prepared by both a low temperature process and also a self-template technique. Films deposited at low temperature showed good crystallinity whereas films grown on a template exhibited a high transition temperature into the superconducting state. Detailed transmission electron microscopic investigations have been performed on these two kinds ofa-axis oriented films. Significant differences have been found in the microstructures of these films. The dominant defects formed in these films are misoriented grains which mainly show ac-axis orientation. The origin of the nucleation of misoriented grains is attributed to surface defects of the substrate. No boundary between the template layer and upper layer could be distinguished for films made by the self-template process. A thinc-axis intermediate layer with a thickness of 2–5 unit cells was observed at the interface between thea-axis film and the SrTiO₃ substrate for both kinds of films. The formation and influence of such an intermediate layer needs further study.     

Effect of mechanical deformation and annealing on the evolution of c-axis texture of Bi1.6Pb0.4Sr2Ca2Cu3O z superconductor hot-isostatic-press cladded onto a Ag substrate

A systematic study was undertaken of the mechanical deformation and annealing effects on the c-axis texture evolution of a Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O _z (BSCCO) superconductor cladded onto a Ag substrate. As the amount of cold-rolling reduction (%) increased, a tighter clustering of the (001 l4) poles around the surface normal indicated that randomly oriented grains from the initial hot-isostatic-press (HIP) cladded surface are progressively oriented nearly perpendicularly to the plane of the tape. Conventional X-ray diffraction (XRD), and X-ray pole-figure studies support a basal-plane sliding mechanism of plastic deformation. In samples annealed for 100 h, the superconductor (BSCCO) material near the BSCCO/Ag interface appears to undergo incipient melting, and there is a layer-like growth (c-axis texture), which extends macroscopically from the Ag interface. The sample-orientation distribution of short-term (5 h) annealed samples showed a strong c-axis texture, with the c-axis aligned nearly perpendicularly to the plane of the tape with no preferred alignment of the a- and b-axes.     

Study on the doping effect of Li-doped ZnO film

Zinc oxide (ZnO) is an excellent piezoelectric material with simple composition. ZnO film is applied to the piezoelectric devices because it has high resistivity and highly oriented direction at c-axis. Structural and electrical properties in ZnO films are influenced by deposition conditions. Lithium-doped ZnO (LZO) films were deposited by RF magnetron sputtering method using Li-doped ZnO ceramic target with various ratios (0 to 10 wt.% LiCl dopant). LZO films revealed high resistivity of above 10⁷ Ω cm with smooth surface when they were deposited with 4% LiCl-doped ZnO target under room temperature. However, their c-axis orientation was worse than the c-axis orientation of pure ZnO films. We have also studied on structural, optical and electrical properties of the ZnO films by XRD, AFM, SEM, XPS, and 4-point probe analyses. We concluded that LZO films were deposited with 4 wt.% LiCl-doped ZnO target and were apposite for piezoelectrical application.     

Anisotropic Thermal Expansion of <Emphasis Type="Italic">p</Emphasis>-Terphenyl: a Self-Assembled Supramolecular Array of Poly-<Emphasis Type="Italic">p</Emphasis>-phenyl Nanoribbons

The recent discovery of superconductivity in a metallic aromatic hydrocarbon, alkali-doped p-terphenyl, has attracted considerable interest. The critical temperature T _c ranges from few to 123 K, the record for organic superconductors, due to uncontrolled competition of multiple phases and dopants concentrations. In the proposed mechanism of Fano resonance in a superlattice of quantum wires with coexisting polarons and Fermi particles, the lattice properties play a key role. Here, we report a study of the temperature evolution of the parent compound p-terphenyl crystal structure proposed to be made of a self-assembled supramolecular network of nanoscale nanoribbons. Using temperature-dependent synchrotron X-ray diffraction, we report the anisotropic thermal expansion in the ab plane, which supports the presence of a nanoscale network of one-dimensional nanoribbons running in the b-axis direction in the P21/a structure. Below the enantiotropic phase transition at 193 K, the order parameter of the C-1 structure follows a power law behavior with the critical exponent α =?0.34 ± 0.02 and the thermal expansion of the a-axis and b-axis show major changes supporting the formation of a two-dimensional bonds network. The large temperature range of the orientation fluctuations in a double well potential of the central phenyl has been determined.