Planes Of Al2O3 Research Articles

The influences of internal interactions and functional groups on the adsorption of graphene and graphene oxide with alumina substrate

Molecular dynamics is used to simulate the adsorption process of graphene and graphene oxide fragments with different sizes on the (0001) crystal plane of Al2O3. The results reveal that the influence of internal interaction and functional groups on graphene and graphene oxide adsorbed by the alumina surface. From the atomic simulation, it can be found that the Coulomb interaction between graphene and the substrate can enhance the interaction between graphene oxide and the substrate after oxidation. It also promotes the spontaneous adsorption of graphene oxide to the substrate, and its influence on the process is much greater than that of the van der Waals force interaction. Before graphene was oxidized, the Coulomb interaction and van der Waals force interaction inhibited the desorption of graphene, but the Coulomb interaction was relatively weak. In addition, the increase of the size of graphene and graphene oxide can reduce the adhesion energy and desorption free energy, resulting in the instability of adsorption state, which is more unfavorable to the occurrence of the adsorption process. In graphene oxide, the oxidized carbon atom bears most of the potential energy and induces the instability of the structure. Its three functional groups, carboxyl, hydroxyl and epoxy, play a role in reducing the overall potential energy of graphene oxide and stabilizing the structure of graphene. Therefore, compared with pristine graphene, graphene oxide with a high degree of oxidation can form a much stable coating on the alumina substrate. By means of multiscale modelling and simulation, this article may theoretically contribute to the application of graphene coating on the aluminum alloy surface and gives guiding opinions for enhancing the strength of graphene coating.

Toward Innovative Hemocompatible Surfaces: Crystallographic Plane Impact on Platelet Activation.

The anticoagulation treatment of cardiovascular patients, which is mandatory after implantation of heart valves or stents, has significantly adverse effects on life quality. This treatment can be reduced or even circumvented by developing novel antithrombogenic surfaces of blood-contacting implants. Thus, we aim to discover materials exhibiting outstanding hemocompatibility compared to other available synthetic materials. We present promising surficial characteristics of single crystalline alumina in terms of platelet activation inhibition. In order to elucidate the relation between its crystallographic properties including the plane orientation and blood cell behavior, we examined endothelialization, cytocompatibility, and platelet activation at the blood-alumina interfaces in a controlled experimental setup. We observed that the cell response is highly sensitive to the plane orientation and differs significantly for (0001) and (11-20) planes of Al2O3. Our results reveal for the first time the dependence of platelet activation on crystallographic orientation, which is assumed to be a critical condition controlling the thrombogenicity. Additionally, we used an endothelial cell monolayer as an internal control since endothelial cells have an impact on vessel integrity and implant acceptance. We successfully demonstrate that Al2O3(11-20) exhibits enhanced hemocompatibility in contrast to Al2O3(0001) and is comparable to the physiological endothelial monolayer in vitro.

Digestion mechanism and crystal simulation of roasted low-grade high-sulfur bauxite

Low-grade high-sulfur bauxite was pretreated via suspension roasting and muffle furnace roasting to remove sulfur and enhance digestion properties. The results show that sulfur can be efficiently removed, and the alumina digestion properties are significantly improved after suspension roasting. Under optimal conditions (t=70 min, T=280 °C, w(CaO)=8% and Nk=245 g/L), the digestion ratios are 94.45% and 92.08% for the suspension-roasted and muffle-roasted ore, respectively, and the apparent activation energies are 63.26 and 64.24 kJ/mol, respectively. Two crystal models were established by Materials Studio based on the XRD patterns. The DFT simulation shows that the existing Al—O bands after suspension roasting can improve alumina digestion. The (104) and (113) planes of Al2O3 after suspension roasting are found to combine with NaOH more easily than those of Al2O3 treated in a muffle furnace.

Microstructure of nanocomposite wurtzite-spinel (Fe:ZnO)-(Zn:Fe3O4) epitaxial films

Abstract Pulsed-laser ablation of zinc and iron-based oxide targets leads to the growth on c-cut sapphire substrates of nanocomposite films constituted by randomly distributed wurtzite (Fe:ZnO) and spinel (Zn:Fe3O4) phases. By the complementary use of Rutherford backscattering spectrometry, X-ray diffraction and transmission electron microscopy, the nature and composition of the phases, their structure and microstructure were investigated. Both phases are textured, (0001) and (111) for the wurtzite and spinel, respectively. The epitaxial relationships with the sapphire substrate were determined: the wurtzite crystallites present the classical 30° rotation of the hexagon of their (0001) plane with respect to the hexagon of the (000l) Al2O3 plane. The spinel crystallites show two in-plane orientations, one corresponding to the 30° rotation of the hexagon of their (111) planes, the other one being at 0°. These two in-plane epitaxial orientations were observed for spinel crystallites directly grown on (000l) Al2O3 as well as for spinel crystallites inside the nanocomposite films. They are shown to be related to differences in the Zn concentration inside the spinel. A high Zn concentration (>33%) leads to the hexagon on hexagon 0° epitaxy while a lower concentration leads to the 30° rotation. This lead us to conclude in differences in the epitaxy of the inverse spinel (low Zn concentration in the crystallite) and of the normal spinel (high Zn concentration).

Epitaxy of gold films on the structured (0001) sapphire surface

The oriented growth of gold films from vapor phase occurs on (0001) sapphire substrates heated to 500°C. Epitaxy is observed when gold nanocrystals reach a certain size under fixed external conditions. In the case of weak adhesion between a crystal and substrate, gold is crystallized on the edges of atomically smooth steps of the substrate in the form of a nanocrystals, mainly with the following three epitaxial relationships maintained: the (111), (100), and (211) planes with high atomic density are oriented parallel to the (0001)Al2O3 plane. At lower temperatures, gold is crystallized on substrates in the form of nanocrystals 100–120 nm in size, ordered along the step edges and having no preferred orientation.

Quantification of ordering at a solid-liquid interface using plasmon electron energy loss spectroscopy

We present an in situ electron energy loss spectroscopy (EELS) study of ordering of liquid Al at various Al-Al2O3 interfaces. This technique utilizes precise measurements of the shifts in bulk plasmon resonance and their sensitivity to the valence electron density. Plasmon EELS combined with high resolution transmission electron microscopy provides information regarding the chemical composition in liquid Al at Al-Al2O3 interfaces. Preferential oxygen segregation to the (0006) Al2O3 plane was verified, and the (101¯2) Al2O3 plane was found to contain the lowest amount of segregated species.

Pseudo-hexagonal in-plane alignment of rutile (100)Nb:TiO2 on hexagonal (0001)Al2O3 plane

Nb-doped TiO2 (Nb:TiO2) films were grown on a hexagonal (0001)Al2O3 substrate at 650°C and ∼10−5Torr. The Nb:TiO2 film had a small resistivity of ∼8×10−4Ωcm at room temperature and a behavior of a slightly increasing resistance upon cooling. In addition, the Nb:TiO2 film had an optical transmittance of about 60% in the visible range. A careful analysis of the in-plane atomic structure suggests that the rutile Nb:TiO2 film on the hexagonal (0001)Al2O3 can be re-interpreted by a certain pseudo-hexagonal structure, which is discriminated from the in-plane rectangular one of the tetragonal (100)Nb:TiO2. The pseudo-hexagonal properties of the Nb:TiO2 film were characterized by negligible mosaic structure at the interface, the same electron diffraction pattern as the hexagonal Al2O3 substrate, and perfect six-fold symmetries in the pole figure and ϕ-scan XRD patterns.

Cost Effective Deposition of Aluminium Oxide Layers

Al2O3 surface-layers were deposited on Al substrates by thermal evaporation technique. Samples were treated for different (1 h, 2 h, 3 h, 4 h and 5 h) treatment time in open air environment by keeping the temperature (550oC) of the evaporator plate constant. XRD patterns revealed the emergence of Al2O3 H2O (111), Al (OH)3 (214) and Al2O3 (20 6) planes. Crystallinity of the above mentioned phases was attributed with treatment time. However, minimum treatment time to break oxygen hydrogen bonds and the formation of Al2O3 plane was 5 h. Crystallite size and compressive stress found in Al2O3 (2 0 6) plane were 14.31 nm 0.53 GPa respectively. SEM microstructure features revealed the formation of rounded grains, irregular patches and rods. AFM analysis exhibited the formation of dome shapes microstructures. The grain size and surface roughness were increased from 1 ?m to 2.5 ?m and from 35 nm to 115 nm respectively. This variation in surface roughness and grain sizes was associated with treatment time.

X‐ray pole figure analysis of ZnTe layers grown on lattice mismatched substrates

AbstractThe electro‐optical effect of ZnTe is recently highlighted, and various device structures utilizing ZnTe are explored. ZnTe substrates are recently commercially available, and high quality homoepitaxial layers can be grown. On the other hand, the cost of the substrate could be a concern for the practical device application. In this study, Si and Al2O3 substrates were used since they are widely used for many kinds of device applications. The lattice mismatch between those substrate materials and ZnTe is above 10% and those mismatch strain should be carefully considered. ZnTe layers were nucleated on chemically treated substrate surfaces. (111), (110), (211) oriented Si substrates and (0001), (11‐20), and (10‐10) planes of Al2O3 were used. By taking the pole figure data and studying the crystal symmetry of the domain, detail information associated with the formation of domains in the layer was discussed. The pole figure analysis revealed that several kinds of (110) oriented ZnTe domains rotated 60 degrees each other were formed on (110) oriented Si surface. On the other hand, preferentially oriented single domain of (111) was confirmed for the layer grown on the (0001) plane of Al2O3. ZnTe layers grown on (10‐10) plane Al2O3exhibited a unique domain formation. Pole figure data combined with the conventional theta‐2theta measurement indicated that (211) oriented plane of ZnTe was a dominant domain formed on the (10‐10) plane Al2O3. These crystallographic features would be related to the interface valency as well as the interfacial bond structure. X‐ray pole figure method was a useful and powerful method to study the domain formation of the severely lattice mismatched structures. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

InN nanorods and nanowires grown on different substrates

AbstractTransmission Electron Microscopy was applied to study InN nanorods grown by non‐catalytic, template‐free hydride metal‐organic vapor phase epitaxy (solid‐vapor mechanism) and nanowires grown by a vapor‐liquid‐solid growth (VLS) mechanism in a MOVPE reactor. The nanorods and nanowires were grown on different planes of Al2O3, (0002) GaN/ Al2O3, and (001) Si. The majority of nanorods have a high structural perfection and exhibit abrupt side walls, but some of them show formation of the planar defects. Depend‐ ing on the substrate used, the size, shape and tips of the nanorods vary from hexagonal to pencil‐like. Nanowires, however have very corrugated surfaces along their side‐walls and tips, and depending on the V/III flow ratio these nanowires can have either a constant diameter or taper‐off. Their length can extend up to 100 μm. Bending and branching of nanowires was observed, but this phenomenon was never observed for nanorods. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure of cubic polytype indium nitride layers on top of modified sapphire substrates

AbstractThe occurrence of cubic indium nitride thin layers grown by molecular beam epitaxy on top of c‐plane sapphire substrates modified by an intermediate layer of cubic indium oxide is reported. An orientation relationship between the (0001) plane of Al2O3 and both (001) surfaces of body‐centered cubic In2O3 and zinc‐blende InN is demonstrated by means of electron and X‐ray diffraction and by transmission electron microscopy. We propose that the demonstrated approach is able to stabilize the non equilibrium phase of InN (i. e., the cubic polytype) due to a low lattice mismatch together with a four fold surface atomic arrangement of the indium oxide‐indium nitride interface. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural and compositional characterization of a Co∕Re multilayer and superlattice

The structure and composition of a Co∕Re trilayer and a 19-period superlattice were characterized by high-resolution transmission electron microscopy (TEM) and scanning TEM (STEM). Low-angle x-ray reflectivity measurements were performed and compared with the TEM results. The Re and Co layers are epitaxial with their (101¯0) planes parallel to the (112¯0) plane of Al2O3, and the [001] direction of Re and Co layers coincides with that of the Al2O3. The in-plane lattice parameters for Co, Re, and Al2O3 are approximately 0.24 and 0.43nm, 0.26 and 0.44nm, and 0.24 and 0.44nm, respectively, in the superlattice. The lattice spacing of Al2O3 corresponds to a∕2 and c∕3, where a and c are lattice parameters of the Al2O3. High-angle and low-angle annular-dark-field STEM and nanoscale electron energy loss spectroscopy line analysis exhibit very weak interdiffusion between Co and Re layers; therefore, very sharp interfaces are maintained in the superlattice. The initial interface roughness between the Re buffer layer and the first Co layer is amplified during the subsequent growth of the superlattices. Layer thickness fluctuations are much smaller in the Re∕Co superlattice than the interface roughness, which suggests that interface roughness plays a more important role in the giant magnetoresistance effect than thickness fluctuations of the spacer layer.

Atomic-scale structural analyses of epitaxial Co∕Re superlattices

High-resolution transmission electron microscopy and scanning transmission electron microscopy (STEM) have been used to investigate atomic-scale structural properties of Co∕Re trilayers and superlattices grown via magnetron sputtering. The sample growth was epitaxial with the (101¯0) plane of Co and Re parallel to the (112¯0) plane of Al2O3, and the [001] direction of Re and Co coinciding with that of the Al2O3. Both low-angle and high-angle Z-contrast STEM images show a very uniform layer thickness. However, the interface roughness between the Re and Co layers monotonically increases with interface distance from the substrate. These results strongly imply that, in the epitaxial Re∕Co superlattice system, interface roughness plays a more important role in the giant magnetoresistance effect than thickness fluctuations of the spacer layer. Previous anisotropic magnetoresistance measurements can be explained in terms of the observed atomic-scale structure.

Structure and interface-controlled growth kinetics of ZnAl2O4 formed at the (112̄0) ZnO/(011̄2) Al2O3 interface

The solid state reaction between metalorganic chemical vapor deposition grown epitaxial ZnO films and the R-plane sapphire substrate after annealing at 1000 °C for various times in an O2/N2 atmosphere was studied in detail. Multiple epitaxial relationships between the reaction product (ZnAl2O4) and the reactants were observed, as determined by cross-sectional transmission electron microscopy. In the dominant epitaxial relationship (A1), the (22̄0) plane of ZnAl2O4 was parallel to the (1̄101) plane of Al2O3. A twin (A2) of orientation A1, i.e. (22̄0) ZnAl2O4//(101̄1) Al2O3, and a closely related orientation (B) wherein the (22̄0) ZnAl2O4 plane is parallel to the (1̄21̄0) ZnO plane (which is equivalent to a 5° clockwise rotation about the [1̄1̄2] ZnAl2O4 or [0001] ZnO zone axis relative to A2), were also observed. Enhanced growth was observed at grain boundaries. It was necessary to measure the spinel growth rate from grains with the same orientation far away from grain boundaries because the growth rate was observed to be influenced by the orientation of the grains in addition to the enhanced growth at grain boundaries. The growth rate was observed to follow a linear rate law during early stages (for grains with orientation A1), suggesting an interface-controlled reaction. The structures of the ZnO/Al2O3, ZnO/ZnAl2O4 and ZnAl2O4/Al2O3 interfaces were studied for grains with this orientation (A1). The 13.7% lattice mismatch between ZnO and ZnAl2O4 was relieved by a series of misfit dislocations spaced five to six (11̄00) ZnO planes apart. Due to the small lattice misfit (2.1%) at the ZnAl2O4/Al2O3 interface, very few misfit dislocations were present. This interface was faceted and the sapphire surface had a series of single steps. It is expected that the reaction at the ZnAl2O4/ZnO interface is the rate-controlling step due to the necessity for a dislocation climb (of a large number of misfit dislocations) for movement of this interface.

Activities of SiO2 and Al2O3 and activity coefficients of FetO and MnO in CaO-SiO2-Al2O3-MgO slags

The activities of SiO2 and Al2O3 in CaO-SiO2-Al2O3-MgO slags were determined at 1873 K along the liquidus lines saturated with 2CaO · SiO2, 2(Mg,Ca)O · SiO2, MgO, and MgO · Al2O3 phases using a slag-metal equilibration technique. Based on these and previous results obtained in ternary and quaternary slags, the isoactivity lines of SiO2 and Al2O3 over the liquid region on the 0, 10, 20, 30, and 40 mass pct Al2O3 planes and those on the 10 and 20 mass pct MgO planes were determined. The activity coefficients of FetO and MnO, the phase boundary, and the solubility of MgO were also determined.

Formation of ZnAl2O4 and MgAl2O4 Spinel in Al2O3 by Ion Implantation

AbstractZnAl2O4 spinel has been formed in Al2O3 by ion implantation. Sequential implantation of Zn and 0 in overlapping profiles followed by annealing in Ar + H2 gives rise to a nearly continuous epitaxial layer of ZnAl2O4 oriented with (111) planes parallel to (0001) planes of Al2O3. If only Zn is implanted, then discrete bands of ZnAl2O4 oriented with (422) planes parallel to (0001) planes of Al2O3 are produced. By similar methods, oriented MgAl2O4 spinel also has been produced in Al2O3 by sequential Mg + O implantation.

Quantitative Transmission Electron Microscopy Investigation of the Relaxation by Misfit Dislocations Confined at the Interface of GaN/Al2O3(0001)

A quantitative transmission electron microscopy (TEM) investigation of the relaxation of GaN grown on Al2O3(0001) has been carried out. Terminating {112̄0}-substrate fringes observed at the interface of the highly mismatched system have been characterized and the efficiency of the relaxation was measured. Wurtzite type GaN was grown by plasma induced molecular beam epitaxy (MBE) on the (0001) basal plane of Al2O3. The in-plane orientation between GaN and substrate reveals a high lattice misfit of f=-13.9% and therefore the critical thickness of dislocation formation is reached when the first monolayer of GaN is grown. An expected interfacial relaxation process is characterized by the results of high resolution transmission electron microscopy (HRTEM) which reveals misfit dislocations confined in the GaN/Al2O3 interface region. The quantitative evaluation of the HRTEM images on the one hand and Moiré pattern on the other hand shows the effectiveness of the observed relaxation process: here a degree of relaxation δ=(-11.8±0.9)% and a residual strain of εr=(-2.1±0.9)% was measured, and it seems that only εr causes a dislocation density of estimately 1010 cm-2 in the GaN epilayer.

Pulsed Laser Deposition of Bi4Ti3O12 Thin Films on Sapphire Substrates

ABSTRACTUsing pulsed laser deposition, Bi4Ti3O12 thin films were grown on (0001) and (1102) surfaces of Al2O3. Substrate temperature from 700 to 800 °C and oxygen pressure from 50 to 1000 mtorr were varied, and their effects on Bi4Ti3O12 film growth behavior was investigated. Only for a narrow range of deposition parameters, can highly oriented Bi4Ti3O12(104) films be grown on Al2O3(0001). Further, epitaxial BTO(004) films can be grown on Al2O3(1102). The growth behavior of preferential BTO film orientations can be explained in terms of atomic arrangements in the Bi4Ti3O12 and the Al2O3 planes.

Impurity segregation to the surfaces of corundum-structured oxides

Atomistic computer simulation methods have been used to calculate iso-and alio-valent segregation energies in the corundum-structured oxides Al2O3 and Cr2O3. The results show that the assumption made in the Langmuir isotherm, i.e. that the heat of segregation is coverage-independent, is not generally valid and that segregation is often both coverage-dependent and highly surface specific. The heats of segregation for Ca at the basal and prism planes of Al2O3 and Y at low index, and Mg and Fe at basal plane of Cr2O3 are given. Comparison with available experimental data is given, showing good agreement for Ca on the prism plane of Al2O3.