Control Of Crystal Orientation Research Articles

Beta tricalcium phosphate ceramics with controlled crystal orientation fabricated by application of external magnetic field during the slip casting process

Beta tricalcium phosphate (β-TCP) is a resorbable bioceramic that has hitherto been utilized in the medical field. Since it crystallizes in the anisotropic hexagonal system, properties such as chemical and physical ones are expected to depend on its crystal axis direction and/or on its crystal plane (anisotropy). Control of crystal orientation is thus important when used in polycrystalline form. Meanwhile, application of a strong magnetic field has been found to be a promising technique to control crystal orientation of anisotropic shape or structured crystals. In this work, we attempted to fabricate β-TCP ceramics with controlled crystal orientation by applying an external magnetic field during the slip casting process and subsequently sintering them at 1050°C, below the β–α transition temperature. Application of a vertical magnetic field increased intensities of planes perpendicular to c-plane on the top surface, while a horizontal one with simultaneous mechanical mold rotation decreased it. These results indicated that crystal orientation of β-TCP ceramics were successfully controlled by the external magnetic field and together that the magnetic susceptibility of β-TCP is χc⊥>χc//.

Facile synthesis and catalytic oxidation property of palygorskite/mesocrystalline Ce1−xMnxO2 nanocomposites

We have developed a one-pot chemical approach to prepare palygorskite (PG) supported mesocrystalline Ce1−xMnxO2 oxides with controllable surface coverage, crystal orientation and dopant fraction. Transmission electron microscopy reveals that the surface is composed of a single phase based on the face-centered cubic CeO2 and the crystals are highly oriented with the axis [100] parallel to the longitudinal direction of PG as if the Mn3+ molar fraction x is 0.2 or less. However, when the Mn3+ molar fraction is larger than 0.2, a mixture of face-centered cubic (fcc) CeO2 and body-centered cubic (bcc) α-Mn2O3 forms and the preferential crystal orientation disappears as revealed by XRD and Raman measurements. The acetate group and PG support are believed to play significant role in the mesoscally oriented attachment. The effects of the molar fraction of Mn3+ on the degradation rate of methyl orange are investigated. Results show that PG/Ce1−xMnxO2 composite has remarkably enhanced catalytic activity as compared with pure PG and PG/CeO2, and the maximum degradation rate of methyl orange reaches 98% when the molar fraction x is 0.2, due to the unique mesocrystalline structure with adequate oxygen vacancies as well as predominant exposure of highly active {200} planes.

SEM study of semi‐oriented tube microstructures of Serpulidae (Polychaeta, Annelida): Implications for the evolution of complex oriented microstructures

Semi-oriented microstructures represent an intermediate state between isotropic and complex oriented microstructures of serpulids. Semi-oriented microstructures are apparently unique to serpulids, indicating that there may have been unique aspects in the evolution of their biomineralization system. The occurrence of semi-oriented microstructures in serpulids supports the hypothesis that complex oriented microstructures are derived from isotropic microstructures via evolution of a biochemical crystal orientation control mechanism.

Controllable Growth Orientation of Ag2O and Cu2O Films by Electrocrystallization from Aqueous Solutions

We demonstrate that Ag2O and Cu2O polycrystal films with a cubic cuprite structure can be grown on F:SnO2 substrates with controllable crystal orientation between ⟨111⟩ and ⟨100⟩ directions by galvanostatic electrocrystallization from aqueous electrolytes. The Ag2O and Cu2O films have been electrodeposited at different applied current densities determined by linear-sweep voltammetry (LSV) measurements, and their crystal structure and morphology were characterized with X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The XRD results show the preferred growth orientation changed from ⟨111⟩ to ⟨100⟩ with increasing and decreasing current density for Ag2O and Cu2O, respectively. The surface morphology, especially for the Cu2O films, was also changed from a three-sided pyramidal shape to a four-sided pyramidal shape corresponding to the orientation. We also give a reasonable explanation for the observed trend in the growth orientation by considering the formation rate of AgOH an...

Orientation and Structure of Controllable GaAs Nanowires Grown on GaAs (311)B Substrates by Molecular Beam Epitaxiy

GaAs nanowires (NWs) are grown on GaAs (311)B substrates by gold assisted molecular beam epitaxy technology. Combined scanning and transmission electron microscopy analyses, the crystallographic orientations of NWs are studied. It is found that crystallographic orientations of NWs are closely related to their crystal structures: NWs of zinc blende structure grow along 〈001〉 directions and NWs of wurtzite structure grow along 〈0001〉 directions. The influence of impinging Ga flux on morphology and crystal structure of the NWs is also discussed. It is observed that NWs prefer to grow along zinc blende 〈001〉 directions at lower Ga flux, while NWs tend to grow along the wurtzite 〈0001〉 directions with only a small portion along the zinc blende 〈001〉 direction at a higher Ga flux. The control of crystal structure and orientation of NWs can be achieved effectively by changing the Ga flux.

Controlled crystal orientation in fluorine-free superconducting YBa2Cu3O7−δ films

The opportunity to control crystal orientation is a serious benefit in the multidisciplinary application field of YBa2Cu3O7−δ (YBCO) thin films. c-Axis aligned YBCO thin films are used in cable industry, while a-axis alignment is required for Josephson junctions. Within this study, we succeeded to control the crystal orientation in fluorine-free YBCO thin films obtained by chemical solution deposition (CSD). Using a direct annealing process, a c-axis aligned YBCO thin film was obtained. In order to increase the flexibility of incorporation into an industrial approach, a preceding burn-out step was introduced. After the introduction of a burn-out process, a-axis oriented films were obtained. If however, CO2 was added during heating towards the annealing temperature, c-axis aligned films were achieved. These observations were linked to the corresponding reaction mechanism leading to an explanation of this orientation alignment. Using the CO2 controlled process, an YBCO thin film with a Tc,onset of 92K and a Jc of 1.25MAcm−2 was obtained. Sustainable YBCO films were therefore generated from a fluorine-free water-based precursor.

OS7-1-3 金属触媒とポーラスアルミナを用いた垂直シリコンナノワイヤ配列の形成(OS7 最先端材料が拓くマイクロ・ナノ工学の新展開(1))

Control of crystal orientation and diameter of vertically grown epitaxial Si nanowire arrays on Si substrate has been demonstrated using a combination of an anodic aluminum oxide (AAO) template and vapor - liquid - solid (VLS) growth using electrolessplated Au in AAO pores as a catalyst. The crystal orientation of the nanowire was investigated by transmission electron microscopy. A growth direction of the nanowire arrays was guided perpendicular to the surface of the substrate by the AAO template, and the crystal orientation of the nanowire arrays was selected using the single crystal Si substrate properly cut in desired orientation.

Crystal orientation control of polycrystalline TiN thin films using ZnO under layers deposited by magnetron sputtering

The effect of ZnO under layers on crystal growth of TiN thin films was investigated. TiN single layers and double-layered ZnO/TiN thin films were deposited on soda-lime-silicate glass substrates by magnetron sputtering. XRD analysis indicated that TiN single layers exhibited {111} preferred orientation on glass substrates; on the other hand, the TiN thin films with {100} preferred orientation were obtained using ZnO under layers and crystallized better than the TiN single layers. This crystal orientation change of TiN thin films should come from heteroepitaxial-like growth because the TiN{100} and ZnO{001} crystal lattice planes have similar atomic arrangements. Besides, the possible mismatch between TiN and ZnO atomic arrangements was estimated to be 7.8%. Furthermore, the resistivity and optical absorbance of TiN thin films decreased when they were deposited on ZnO under layers. It can be considered that electrical and optical properties should be improved due to the well-crystallization of TiN thin films using ZnO under layers.

Seed-Free Fabrication of Highly Bi-Axially Oriented Poly-Si Thin Films by Continuous-Wave Laser Crystallization with Double-Line Beams

Highly bi-axially oriented poly-Si thin films with very long grains (>100 μm) were successfully fabricated on quartz substrates by continuous wave laser crystallization with parallel double-line beams, without seed crystals. The newly-developed technique restricts crystal nucleation time and enhances growth of crystal nuclei of a specific orientation selectively, which is preferentially generated. The technique achieved highly-oriented silicon grains having (110), (111) and (211) crystal orientations in the laser lateral crystallized plane, the transverse side plane and the surface plane, respectively. All the silicon grains were elongated in the laser-scanning direction and linearly arranged with a length of over 100 μm and a width of 0.7 μm. The laser-crystallized poly-Si films were crystallographically investigated precisely, and electrically inactive CSL Σ3 twin boundaries were typically observed. This technique enables simultaneous enhancement of grain size and control of crystal orientation.

A Review of the Measurement of Single Crystal Orientation Parameters of Nickel Castings

Control of single crystal orientation in modern gas turbine components is a critical quality control issue for optimum reliable behaviour, and an increasingly important aspect of trade. This paper reviews industrial practice for the determination of primary crystal orientation and for the determination of 'disorientation' (R-value) between sub-grains. Different techniques and measurement conventions are compared, and the errors of measurement have been assessed through a European round-robin. Causes of poor reproducibility in 'disorientation' measurement have been identified by EBSD investigations. Recommendations for unified practice have been made in a Good Practice Guide as a precursor to a new industry-wide standard.

Polymorph Switching in the Calcium Carbonate System by Well-Defined Alginate Oligomers

Functional biominerals formed in living organisms require high control of inorganic phase crystal polymorphs, morphology, size, and orientation. Such control is often governed by both soluble and insoluble functional molecules, where the soluble ones usually are highly negatively charged proteins and polymers. Here, the effect of alginate and well-defined alginate oligomers on calcium carbonate crystallization is explored, by seeded and unseeded experiments, to separate the effects of the additive on the crystal growth process from the effect on nucleation. The experiments were done at well-defined activity-based levels of supersaturation, controlled pH and temperature. In the seeded experiments, crystal growth of calcite, aragonite, and vaterite were studied separately, and the observations were used to explain a switch in polymorphism when alginate oligomers were present during the crystallization process. Unseeded experiments showed that low concentrations of G-blocks (oligomers of α-l-guluronic acid) ...

Fabrication of Crystalline Semiconductor Nanowires by Vapor-Liquid-Solid Glancing Angle Deposition (VLS-GLAD) Technique

ABSTRACTVapor-liquid-solid (VLS) method has become one of the few and most powerful bottom-up single crystal nanowire growth techniques in nanotechnology due to its easy scalability from micro to nano feature sizes, high throughput, relatively low cost, and its applicability to various semiconductor materials. On the other hand, control of growth direction and crystal orientation of nanowires, which determine their electrical, optical, and mechanical properties, stand as major issues in VLS technique. In this study, we demonstrate a new vapor-liquid-solid glancing angle deposition (VLS-GLAD) fabrication approach to produce crystalline semiconductor nanowires with controlled geometry. VLS-GLAD is a physical vapor deposition nanowire fabrication approach based on selective deposition of nanowire source atoms onto metal catalyst nanoislands placed on a crystal wafer. In this technique, collimated obliquely incident flux of source atoms selectively deposit on catalyst islands by using “shadowing effect”. Geometrical showing effect combined with conventional VLS growth mechanism leads to the growth of tilted crystalline semiconductor nanowire arrays. In this study, we report morphological and structural properties of tilted single crystal germanium nanowire arrays fabricated by utilizing a conventional thermal evaporation system. In addition to the tilted geometry, by introducing substrate rotation, nanowires with various morphologies including helical, zig-zag, or vertical shapes can be fabricated. Engineering crystalline nanowire morphology by using VLS-GLAD have the potential of enabling control of optical, electrical, and mechanical properties of these nanostructures leading to the development of novel 3D nano-devices.

Effect of the electrode structure on the electrical properties of alkoxide derived ferroelectric thin film

Effect of the thermal expansion coefficient of electrode on the electrical properties in lead zirconate titanate (PZT) with morphotropic phase boundary (Pb(Zr 0.53,Ti 0.47)O 3: MPB) composition film was demonstrated in this paper. The lanthanum nickel oxide (LaNiO 3: LNO) and lanthanum strontium cobalt oxide ((La 0.5,Sr 0.5)CoO 3: LSCO) was deposited by chemical solution deposition (CSD) as bottom electrode on Si wafer. Highly (100)-oriented LSCO layers were successfully prepared by CSD on Si wafer using (100)-oriented LNO layers as seeding layer for the crystal orientation control. As a result, (100) and (001) oriented PZT film was also successfully prepared on LSCO/LNO/Si stacking structure. The obtained dielectric and ferroelectric properties changed according to the thermal stress which was influenced by the bottom electrode thickness.

Control of crystal orientation in soft nanostructures by nanoimprint lithography

Nanoimprint lithography (NIL) is a low-cost and high resolution technique consisting of replicating the nanofeatures of a hard mold by pressing it into a film of a soft material, in order to create nanostructures of virtually any shape. When NIL is applied to materials capable to self-organize, it may also control their crystallographic orientation and morphology provided imprinting conditions are appropriately selected. The principles governing this ordering involve a decreased nucleation probability in the nanostructures, graphoepitaxial alignment, rheological chain alignment, nanoconfinement in the cavities of the mold, and the effect of pressure on the microstructure of soft materials. The ordering can be rationalized based on the knowledge of the structure of the material and more specifically on the notion of basic structural element of the material. The control over the internal structure of nanomolded materials afforded by NIL translates into improved performance of soft functional nanodevices, as is demonstrated in this highlight.

Deposition and Growth Mechanism of Low-Temperature Crystalline Silicon Films on Inexpensive Substrates

of the deposition parameters on the crystallinity and the preferred crystal orientation of the samples on glass were investigated, and films with adjustable crystallinity and controllable preferred crystal orientation were obtained at a substrate temperature of 350 C. A new approach of aluminum-induced crystallization growth was developed to prepare highly-crystallized Si films at room temperature. A growth mechanism was suggested and demonstrated by the subsequent experimental results. Crystalline Si films with (111)-preferred orientation were deposited on Al-coated polyethylene napthalate at room temperature by optimizing the deposition parameters. The achievement of highly-crystallized Si films could be attributed to the promotion of nucleation in the incubation layer with the assistance of the Al layer.

Ferroelectric properties of epitaxial Pb(Zr,Ti)O3 thin films on silicon by control of crystal orientation

Crystalline Pb(Zr,Ti)O3 (PZT) thin films between metallic-oxide SrRuO3 (SRO) electrodes were prepared using pulsed laser deposition on CeO2/yttria-stabilized zirconia buffered silicon (001) substrates. Different deposition conditions for the initial layers of the bottom SRO electrode result in an orientation switch. Either (110)- or (001)-oriented SRO thin films are obtained and the PZT films deposited on the bottom electrode continued both growth directions. The ferroelectric characteristics of the SRO/PZT/SRO capacitors are found to be strongly dependent on their crystalline orientation: PZT (001)-oriented thin films showed stable, high quality ferroelectric response, while the remnant polarization of the PZT (110)-oriented thin films only show high response after multiple switching cycles.

Control of crystal orientation of CdTe epitaxial layers grown on (0 0 1) GaAs with ZnSe buffer layer by molecular beam epitaxy

CdTe layers were grown on (001) GaAs substrates with a ZnSe buffer layer by molecular beam epitaxy. The high-quality ZnSe (001) epitaxy on GaAs allows us to control the II–VI/III–V heterovalent interface prior to the CdTe deposition. By subsequently adjusting the interface between ZnSe and CdTe, it was possible to selectively obtain the growth of either (001) or (111) CdTe epitaxial layers on the (001) ZnSe/GaAs substrate. Reflection high energy electron diffraction indicates that the nucleation of the CdTe epitaxial layers turns two-dimensional within a few seconds of initiating the growth. X-ray diffraction and photoluminescence measurements indicate that both the (111) and the (001) CdTe films are of high structural quality despite the large lattice constant mismatch of 14.6% between CdTe and the (001) ZnSe/GaAs substrate.

Magnetically tunable left handed metamaterials by liquid crystal orientation

The tunability of an omega-type left handed metamaterial was demonstrated at microwave frequencies via the magnetic control of liquid crystal (LC) orientation. From the experimental and simulation results, it is shown that the left handed pass-band can be tuned by 220 MHz by changing the orientation of LC molecules by 90 degrees. A maximum index variation of 0.25 was obtained in the negative index regime with a measured LC birefringence of 0.05 in the 10 - 12 GHz frequency band.

Prospective crystallization of amorphous Si films for new Si TFTs

AbstractProspective crystallization results of amorphous silicon film are reviewed and are discussed. Silicon TFTs are playing an important role for Active‐Matrix Flat Panel Displays (AM‐FPD) based on amorphous or poly‐Si thin‐film transistors (TFTs). Poly‐Si TFTs provide a possibility to develop highly functional system on pane (SoP) applications. In order to get a high performance TFT, large poly‐crystal grains or high cystallinity for the film is required. Two basic crystallization techniques namely solid phase crystallization (SPC) and excimer laser crystallization (ELC) are reviewed and relating issues are described. A grain growth technique has been developed based on the two crystallization techniques, so far. In order to mount a poly‐Si TFT system on a flexible panel such as a plastic, an excimer laser of UV pulse beam has an advantage for the TFT channel as well as for the source and drain contacts as a ultra‐low temperature poly‐Si (U‐LTPS) process. To realize a high performance TFT of uniform and high carrier mobility, location control crystallization had been proposed. Some of the distinctive results for crystal orientation control of (100) and (111) face using the laser crystallization techniques are described. In the future, single‐crystalline Si TFT of a functional 3D structure is expected to realize an advanced SoP for ubiquitous electronics era. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Enhanced performance of α-Al 2O 3 coatings by control of crystal orientation

α-Al 2O 3 coatings with (101̄2), (101̄4), (0001) and (101̄0) textures were obtained using chemical vapour deposition. The textured coatings were compared with α-Al 2O 3 obtained through the κ→α phase transformation. The coating microstructures were studied by scanning electron microscopy and transmission electron microscopy and residual stress and texture were determined by X-ray diffraction using Cr K α and Cu K α radiation, respectively. Microtexture was investigated using electron back-scatter diffraction. Wear properties of the α-Al 2O 3 coatings were evaluated in turning of cast iron and steel. All the studied coatings were under a tensile stress of the order of 0.2–0.7 GPa. The cutting tests confirmed substantial texture effects especially in cutting of steel. The best performance was exhibited by the (0001) textured coatings i.e. when the basal planes of α-Al 2O 3 grains were nearly parallel to the coating surface. As compared with the other textured coatings, the (0001) textured coating showed a clearly enhanced ability to undergo uniform plastic deformation. The present work also established that the texture of α-Al 2O 3 coatings could be controlled by process data during deposition.