Increase In Domain Size Research Articles

Dynamical downscaling: Assessment of value retained and added using the Regional Atmospheric Modeling System (RAMS)

The value restored and added by dynamical downscaling is quantitatively evaluated by considering the spectral behavior of the Regional Atmospheric Modeling System (RAMS) in relation to its domain size and grid spacing. A regional climate model (RCM) simulation is compared with NCEP Reanalysis data regridded to the RAMS grid at each model analysis time for a set of six basic experiments. At large scales, RAMS underestimates atmospheric variability as determined by the column integrated kinetic energy and integrated moisture flux convergence. As the grid spacing increases or domain size increases, the underestimation of atmospheric variability at large scales worsens. The model simulated evolution of the kinetic energy relative to the reanalysis regridded kinetic energy exhibits a decrease with time, which is more pronounced with larger grid spacing. Additional follow‐on experiments confirm that the surface boundary forcing is the dominant factor in generating atmospheric variability for small‐scale features and that it exerts greater control on the RCM solution as the influence of lateral boundary conditions diminish. The sensitivity to surface forcing is also influenced by the model parameterizations, as demonstrated by using a different convection scheme. For the particular case considered, dynamical downscaling with RAMS in RCM mode does not retain value of the large scale which exists in the larger global reanalysis. The utility of the RCM, or value added, is to resolve the smaller‐scale features which have a greater dependence on the surface boundary. This conclusion regarding RAMS is expected to be true for other RCMs as well.

Raman and Electron Spin Resonance Investigations of as Prepared and Thermal Annealed Cluster Beam Deposited Carbon Thin Films

ABSTRACTNanostructured amorphous carbon thin films deposited by a Low Energy Carbon Cluster Beam Deposition technique have been characterized by Raman spectroscopy and Electron Spin Resonance (ESR). This study focuses on the correlation between carbon cluster structure and sp2 related defects. The ESR spectrum of as prepared and thermally annealed carbon clusters is a single line located near the free electron g-factor. Resonance lines were accurately fitted by a single line symmetric and narrow Lorentzian line. The resonance line parameters (line position, line amplitude, and line width) were found to be extremely sensitive to the thermal treatment of the as deposited samples. The paramagnetic centres are randomly distributed and correlated with the nanosized nature of the investigated system. The absence of the resonance line asymmetry, typical for the ESR spectra of conducting carbaceneous materials, confirms the small size of carbon nanoclusters and indicates poor electrical contacts between them. The resonance line parameters (position, intensity, and width) are not affected by the orientation of the carbon cluster film relative to the direction of the external magnetic field. The evolution of the ESR signal upon thermal treatments is sensitive to the increase of the sp2 average domain size as revealed by Raman spectroscopy. The Raman spectrum of as obtained and thermally annealed carbon clusters, in the domain 1000 cm−1 to 2000 cm−1 shows two Lorentzian lines located at 1300 cm−1 and 1550 cm−1 representing the D and G bands. The position and amplitude of these lines were found to be affected by thermal annealing.

Structural and Morphological Changes during UV Irradiation of the Crystalline Helical Form of Syndiotactic Polypropylene

Syndiotactic polypropylene films, in the most usual crystallographic modification (form I), were exposed to accelerated weathering in a UV device at 45 °C for increasing times. A different series of films characterized by the same structural organization were annealed at 45 °C to discern the thermal effects from those due to UV irradiation. The influence of UV irradiation and thermal treatments on the structural changes in terms of phase composition, crystallite sizes, and chain conformations was investigated. The analyzed samples were crystallized from the melt at 25 °C, obtaining the disordered crystalline form I, with chains in helical conformations, in large amounts, and a small fraction of mesophase with chains in trans-planar conformations. Diffractometric and thermal analysis have shown that UV radiation causes a strong increase in the crystallinity degree within the first 170 h of treatment. Such an increase mainly occurs by an increase in the coherent crystalline domain size in the direction perpendicular to the (200) planes. Spectroscopic data (FTIR) confirm that the increase in the crystallinity degree occurs not only by a strong reduction of the amorphous phase and a consistent increase of the conformational order of the chains in helical conformation but also by a reduction of the domains with chains in the trans-planar conformation. The trans-planar domains, very small and arranged in the amorphous matrix, are attached by UV radiation together with the amorphous phase. The observed phenomena are to be attributed to the effects of chain scission due to the photooxidation. Samples only annealed at 45 °C show only small effects of physical aging within the first 10 h of treatment.

Effects of milling, doping and cycling of NaAlH 4 studied by vibrational spectroscopy and X-ray diffraction

The effects of milling and doping NaAlH 4 with TiCl 3, TiF 3 and Ti(OBu n ) 4, and of cycling doped NaAlH 4 have been investigated by infrared (IR) and Raman spectroscopy and X-ray powder diffraction. Milling and doping produce similar effects. Both decrease the crystal domain size (∼900 Å for milled and ∼700 Å for doped, as compared to ∼1600 Å for unmilled and undoped NaAlH 4) and increase anisotropic strain (by a factor >2.5, mainly along c). They also influence structure parameters such as the axial ratio c/ a, cell volume and atomic displacement amplitudes. They show IR line shifts by ∼15 cm −1 to higher frequencies for the Al–H asymmetric stretching mode ν 3, and by ∼20 cm −1 to lower frequencies for one part of the H–Al–H asymmetric bending mode ν 4, thus suggesting structural changes in the local environment of the [AlH 4] − units. The broad ν 3 bands become sharpened which suggests a more homogeneous local environment of the [AlH 4] − units, and there appears a new vibration at 710 cm −1. The Raman data show no such effects. Cycling leads to an increase in domain size (1200–1600 Å), IR line shifts similar to doped samples (except for TiF 3: downward shift by ∼10 cm −1) and a general broadening of the ν 3 mode that depend on the nature of the dopants. These observations support the idea that some Ti diffusion and substitution into the alanate lattice does occur, in particular during cycling, and that this provides the mechanism through which Ti-doping enhances kinetics during re-crystallisation.

The predictability of deep convection in cloud‐resolving simulations over land

AbstractCloud‐resolving models (CRMs) can be used to provide subgrid information for use in improving the representation of convection in large‐scale models. However, it is shown here that, for a 24‐hour simulation of convection over land, the total daily rainfall and instant rain rates can often be hard to predict. An ensemble of 2D CRM runs, which differ only in the initial white‐noise temperature perturbations added to the lowest 200 m, show a large spread of results. The size of the spread is shown to be dependent on the nature and strength of the forcing with the most significant differences between ensemble members when only a small number of convective cells exist in the domain. Further sensitivity experiments show that stronger forcing or increased domain size can reduce the spread of results due to an increased number of clouds. However, in all the simulations described in this paper, convection tended to organize into fewer but larger clouds during the day and, as this occurs, the ensemble members began to diverge even with a domain size of 1000 km. © Crown copyright, 2004.

Poly(Ethylene Oxide)/Organosolv Lignin Blends: Relationship between Thermal Properties, Chemical Structure, and Blend Behavior

Blends of poly(ethylene oxide) with organosolv lignin (Alcell) were prepared by thermal blending. Excellent fiber spinning was achieved over the entire blend ratio. The good thermal properties of the Alcell lignin arise from its unique chemical structure. HMQC 2D NMR analysis revealed the presence of alkoxyl chains at the Cα and Cγ positions of the Alcell lignin side chain structure acting as internal plasticizers and enhancing the thermal mobility of the lignin. The addition of a small amount of Alcell lignin to PEO resulted in an increase of the PEO crystalline domain size. However, both PEO crystallinity and crystalline domain size decreased with lignin incorporation beyond 25 wt %. A negative polymer−polymer interaction energy density “B” was calculated on the basis of the melting point depression of PEO and a negative deviation of Tg from the weighted average values observed. Good prediction of the Tg-composition behavior was obtained indicating the presence of favorable interactions between blend components. FT-IR analysis revealed the formation of a strong hydrogen-bonding system between Alcell lignin and PEO, supporting that hydrogen-bonding interactions are an important factor in the formation of miscible lignin-based polymer blends.

Effect of nitrogen doping into SiO2 studied by photoemission spectroscopy

Photoemission spectroscopy using synchrotron radiation has been performed on ultrathin Si oxynitride films on Si(001) to investigate a change of the energy-band structure by nitrogen doping. The valence-band spectra obtained by subtracting the contribution of the Si substrate clearly show the difference in nitrogen doping and two valence-band maxima, assigned as SiO2 and Si3N4, are deduced. The chemical analysis in N 1s spectra suggests a possibility that two phases, SiO2 and Si3N4, are separated in the SiOxNy films, since the sample with high nitrogen concentration (1.7×1022 cm−3) shows a valence-band maximum similar to Si3N4. A change of the valence-band maximum by nitrogen doping can be explained by an increase of the Si3N4 domain size in the SiOxNy film.

Structure and support effects on the selective oxidation of dimethyl ether to formaldehyde catalyzed by MoO x domains

The selective oxidation of dimethyl ether (CH 3OCH 3) to formaldehyde (HCHO) was carried out on MoO x species with a wide range of MoO x surface density and structure supported on MgO, Al 2O 3, ZrO 2, and SnO 2. Raman and X-ray absorption spectroscopies were used to probe the structure of these MoO x domains, as they evolved from monomeric species into two-dimensional polymolybdate domains and MoO 3 clusters with increasing MoO x surface density. Primary HCHO synthesis rates (per Mo atom) initially increased with increasing MoO x surface density (1.5–7 Mo/nm 2) on all supports, indicating that MoO x domain surfaces become more active as two-dimensional monolayers form via oligomerization of monomer species. The incipient formation of MoO 3 clusters at higher surface densities led to inaccessible MoO x species and to lower HCHO synthesis rates (per Mo). Areal rates reached constant values as polymolybdate monolayers formed. These areal rates depend on the identity of the support; they were highest on SnO 2, lowest on Al 2O 3, and undetectable on MgO, indicating that the surface properties of polymolybdate structures are strongly influenced by their atomic attachment to a specific support. The catalytic behavior of MoO x domains reflects their ability to delocalize electron density during the formation of transition states required for rate-determining CH bond activation steps within redox cycles involved in HCHO synthesis from dimethyl ether. These conclusions are consistent with the observed parallel increase in the rates of HCHO synthesis and of incipient stoichiometric reduction of MoO x domains by H 2 as the domain size increases and as the supports become less insulating and more reducible, and as the energy required for ligand-to-metal electronic transitions in the UV–visible spectrum decreases. HCHO selectivities increased with increasing MoO x domain size; they were highest on Al 2O 3 and lowest on SnO 2 supports. The Lewis acidity of the support cations appears to influence HCHO binding energy. HCHO reactions leading to CO x and methyl formate via primary and secondary pathways are favored on weaker Lewis acids (with stronger conjugate bases). The MoO–support linkages prevalent at low surface densities also favor primary and secondary pathways to CO x and methyl formate. When reported on a CH 3OH-free basis, because of the pathways available for CH 3OH oxidation to HCHO and for CH 3OCH 3CH 3OH interconversion, primary HCHO selectivities reached values greater than 95% on Al 2O 3-supported polymolybdate monolayers.

Reaction-diffusion dynamics in an oscillatory medium of finite size: Pseudoreflection of waves

Wave propagation in an oscillatory reaction-diffusion, one-dimensional domain of finite size with Dirichlet boundary conditions is analyzed. For sizes below a certain threshold length, the medium cannot sustain wave motion. Above this threshold we find that for a relatively small domain extent, a strong correlation exists between the dynamics of the system and its size. This correlation gradually disappears with increasing domain size. For still larger sizes, we observe an effect of wave pseudo reflection near the boundary. It is shown both numerically and analytically that pseudoreflected waves are periodically generated inside the medium by a fast, self-generated "source" near the boundary.

Structural Studies of Extension-Induced Mesophase Formation in Poly(diethylsiloxane) Elastomers: In Situ Synchrotron WAXS and SAXS

Amorphous poly(diethylsiloxane) (PDES) elastomers undergo a transition to an aligned mesomorphic state when subjected to uniaxial tension. The structural changes associated with this transition and the kinetics of its formation have been investigated by in-situ synchrotron wide-angle and small-angle X-ray scattering. In the mesomorphic state, the PDES elastomers are biphasic, consisting of aligned mesophase domains and amorphous material. Because of the well-defined structure of the networks used, we were able to determine that the mesophase domain size is governed by the precursor chain length and is unaffected by trapped entanglements. The observed increase in mesophase content with increase in extension ratio in a fully necked sample is caused by an increase in the number of mesophase domains rather than an increase in domain size. In the extended state, PDES elastomers attain a very high degree of segment orientation comparable to that of mesogen-containing liquid crystalline elastomers.

Mechanical properties and morphology of PA6/EVA blends

AbstractThe mechanical properties of blends of polyamide6 (PA6) and ethylene vinyl acetate (EVA) at a blending composition of 0–50 wt % EVA were studied. The notched Izod impact strength of PA6 increased with the incorporation of EVA, the increase being more than 100% compared to PA6 at 10% EVA. The tensile strength and the tensile modulus of the blends decreased steadily as the weight percent of EVA increased. Analysis of the tensile data using predictive theories indicated the extent of the interaction of the dispersed phase and the matrix up to 20 wt % EVA. SEM studies of the cryogenically fractured surfaces indicated increase in the dispersed phase domain size with EVA concentrations. On the other hand, impact fractured surfaces of PA6/EVA blends indicated debonding of EVA particles, leaving hemispherical bumps, indicating inadequate interfacial adhesion between PA6 and EVA. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1593–1606, 2002

Phase separation and physical properties of PEO-containing poly(ether ester amide)s

Poly(ether ester amide) (PEEA) copolymers based on poly(ethylene glycol) (PEG), 1,4- butanediol, and dimethyl-7,12-diaza-6,13-dione-1,18-octadecanedioate (a diester-diamide monomer) were synthesized by a two-step polycondensation reaction. The obtained segmented copolymers are hydrophilic, with a water uptake of 24–340%. PEEA copolymers showed microphase separation, as observed by differential scanning calorimetry (DSC). The long spacing determined by small-angle X-ray scattering shows an increase in the hydrophilic domain size with increasing PEO content. By varying the copolymer composition, the E-modulus of PEEA could be varied between 61 and 427 MPa, with tensile strengths ranging from 12 to 39 MPa. The elongation at break can reach values up to 850%. The mechanical properties decrease with the uptake of water. However, PEEAs with a relatively low content of PEO still retain good tensile properties and are, in principle, suitable for biomedical applications.

Optimization of mechanical properties of a Ni–Mo–Cr alloy by structural modifications induced by changes in heat treatment

The influence of modifications of heat treatment applied to a commercial Ni–25 wt.%Mo–8 wt.%Cr age-hardenable alloy (HAYNES® 242™) on microstructure and mechanical properties were investigated. The standard heat treatment (aging at 650°C for 72 h), producing coherent long-range ordered domains with the Ni 2(Mo, Cr) stoichiometry, was modified by short duration thermal exposures at temperatures at between 760 and 980°C (preceding the alloy's aging). The intermediate heat treatment (IHT) affected the size of the long-range order domains and produced precipitations of a μ phase on the grain boundaries. The size of the ordered domains depended on the temperature of the IHT. The largest domains occurred after the IHT at 760°C. With the increase in the IHT temperature, the domain size decreased. The yield strength of the alloy increased with increasing domain size. The amount of grain boundary particles, and not the size of the ordered domains, controlled the ductility of the material subjected to the IHT: The more grain boundary precipitates there were, the lower tensile ductility. Optimization of the tensile properties (strength and ductility) of the examined alloy occurred when the conventional aging was preceded by the IHT at 760°C.

Studies of Domain Size of Hexagonal Liquid Crystals in C12EO8/Water/Alcohol Systems

The broadening of the most intense lines observed in the X-ray diffraction patterns has been used to determine the domain sizes of hexagonal liquid crystals in C12EO8/water/alcohol systems. A linear “master” relationship between the sizes and the distance to the isotropic phase-transition boundary line (H1 → Wm) was observed as the temperature, surfactant, and glycerol volume fractions were varied. This linear relationship is interpreted as the feature of a “glassy” state formed by the crystallites, which grow until their glass-transition temperature is attained. The master relationship indicates that both temperature and volume fraction induce the glass transition, hindering a further growth of the crystal domains. A fractal dimension close to one for these cylindrical domains is obtained, and an estimation of the number of bounded cylinders inside a domain has been made. For systems containing propylene glycol and propanol, the observed increase in domain size on approaching the phase boundary is much larger than for glycerol systems, which seems to be related to the different influence of the alcohols on the surfactant aggregation and its structure, as it was previously reported for these alcohols. A large increase of the domain sizes by aging the samples, as it is usually observed for common glassy systems, is also reported.

Reactively compatibilised polymer blends: a case study on PA6/EVA blend system

Reactive compatibilisation of immiscible polymers is becoming increasingly important and a representative study with PA6/EVA system is the focus of this paper. Morphological studies and crystallization behaviour of uncompatibilised and compatibilised blends of PA6/EVA were studied as functions of dispersed phase concentration (EVA or EVA-g-MA) and maleic anhydride (MA) content. Impact properties of the compatibilised PA6/EVA blends were studied as a function of MA content at fixed dispersed phase concentration. SEM studies of cryogenically fractured surfaces showed an increase in average domain size with increase in EVA level. On contrary, the average domain size and the domain size distributions reduced significantly in the presence of EVA-g-MA. This observation is found consistent with increase in EVA-g-MA concentration at a fixed MA level and also at a fixed concentration of dispersed phase with different level of MA in binary and ternary compositions. Morphological observations also revealed that the phenomenon of coalescence is slower in the presence of EVA-g-MA indicating the formation of in situ graft co-polymer at the interface. Impact strength of the compatibilised PA6/EVA blends increased significantly as compared to uncompatibilised PA6/EVA blends. Crystallization studies indicate that PA6 and EVA (or EVA-g-MA) crystallize separately at their bulk crystallization temperature. The degree of crystallinity is reduced marginally with increase in EVA level, whereas, the decrease in crystallinity is more in the presence of EVA-g-MA. SAXS studies indicate the superposition of PA6 and EVA lamellar scattering and the possible mode of insertion is random in nature. In case of reactive systems, SAXS studies also revealed the hindered crystal growth of PA6 and EVA due to the interfacial reaction.

Spatiotemporal chaos in spatially extended systems

To address finite-size effects in the use of the decay mutual information to characterize spatiotemporal chaotic dynamics, we modify the dispersion of the nonlinear Schrödinger equation to obtain a model system for which the number of unstable modes remains fixed while the domain size increases. Our numerical study of the model system clearly establishes that spatiotemporal chaos arises in the presence of only two unstable modes. In this spatially extended system, the spatiotemporal chaos is characterized by chaotic dynamics in time and by an exponential decay in space of mutual information, with the decay rate becoming system-size independent in the large system-size limit.

Structure and Properties of Oxidative Dehydrogenation Catalysts Based on MoO3/Al2O3

The effects of MoOx structure on propane oxidative dehydrogenation (ODH) rates and selectivity were examined on Al2O3-supported molybdenum oxide catalysts with a wide range of Mo surface density (0.4–12 Mo/nm2). X-ray diffraction and Raman, UV-visible, and X-ray absorption spectroscopies showed that the structure of dispersed molybdena depends strongly on the Mo surface density. Two-dimensional MoOx oligomers formed preferentially for Mo surface densities below 4 Mo/nm2. At higher surface densities, these MoOx oligomers coexist on Al2O3 surfaces with three-dimensional MoO3. UV-visible edge energies decrease with increasing Mo surface density, consistent with the growth of MoOx structures. The evolution of near-edge spectral features in the X-ray absorption spectra and the gradual appearance of a Mo–Mo scattering peak in the radial structure function confirmed the growth of MoOx domains with increasing surface density. ODH rates per Mo atom increased with increasing Mo surface density and reached a maximum value for samples with ∼4.5 Mo/nm2; this behavior reflects an increase in the reactivity of surface Mo species, because all MoOx species are exposed at domain surfaces in this surface density range. As also shown for VOx-based catalysts, turnover rates are higher on two-dimensional domains than on isolated monomers and they increase as the MoOx domain size increases. The rates of reduction of MoOx species in H2 or C3H8 were probed using kinetic and X-ray absorption methods; these reduction rates increased in parallel with ODH rates as the MoOx surface density increased, apparently as a result of the ability of larger domains to delocalize the higher electron density that accompanies the reduction process. As the surface density increased above 4.5 Mo/nm2, ODH rates (per Mo atom) decrease, as a result of the loss of accessibility caused by the formation of MoO3 crystallites. For these latter samples, the ODH rate per BET surface area approached a constant value as the surface density increased, because all exposed surfaces in these samples reside within two- or three-dimensional MoOx structures with similar reactivity. The ratio of rate constants for propane ODH and propane combustion reactions increased with increasing surface density and then remained constant for values above 5 Mo/nm2. These effects appear to reflect the tendency of Al–O–Mo species to adsorb alkoxide intermediates and favor their sequential oxidation to COx. Propene combustion rate constants also decreased relative to those for propane ODH as two-dimensional structures form with increasing Mo surface density.

Nonlinear Analysis of Juxtacrine Patterns

We investigate a discrete mathematical model for a type of cell-cell communication in early development which has the potential to generate a wide range of spatial patterns. Our previous work on this model has highlighted surprising differences between the predictions of linear analysis and the results of numerical simulations. In particular, there is no quantitative agreement between the unstable modes derived from linear analysis and the patterns observed numerically. In this paper, we look at the nonlinear model on a domain of two cells with the aim of gaining an insight into behavior in larger systems. We study the existence and stability of spatially heterogeneous steady-state solutions, which correspond to patterns of alternating cell fate on larger domains, as we vary two key parameters. These parameters are measures of the strength of positive feedback in the biological system. By reducing the problem to two coupled nonlinear algebraic equations, we show that a patterned solution exists and is stable on a 2-cell domain for a significant part of parameter space. We compare these results to those obtained from linear analysis and conclude that the behavior of the nonlinear 2-cell system gives a better insight into the results of numerical simulations on large arrays of cells. Furthermore, we conduct a bifurcation analysis of the model on domains of various sizes: we demonstrate that as the domain size increases, the 2-cell pattern becomes unstable for certain parameters, and overall the number of stable patterns increases. This leads us to speculate that on large domains there are many stable patterned solutions to the model of approximately the same periodicity, which is typical of the fine-grained patterns that one sees during early development. Our work predicts that this is a feature of the patterning dynamics rather than a consequence of environmental heterogeneity.

Effect of Processing Conditions on the Formation of Aggregates and Phase Domains in Monolayers of the Hemicyanine Dye, 4-(4-(Dihexadecylamino)styryl)-N-methylpyridinium Iodide

Epifluorescence microscopy and tapping mode AFM measurements were used to study the morphology of Langmuir−Blodgett monolayers of the hemicyanine dye, 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide, I, prepared under conditions of varying spreading solution concentration, compression speed, aging, subphase composition, and deposition pressure. The morphology, which is the result of coexisting liquid-expanded (LE) and liquid-condensed (LC) phases, is very sensitive to film preparation conditions but relatively insensitive to deposition pressure for a given film preparation protocol. Emission images reveal the following: domain size and shape are unaffected by deposition pressure; increasing spreading solution concentration while maintaining a constant number of molecules on the surface results in increased domain size; emission from the LC domains is more highly variegated as compression speed increases; and incorporation of I- in the subphase results in an entirely new morphology, in contrast to Cl- which only reduces domain size slightly. Far-field fluorescence from films of I is nearly constant as a function of pressure, indicating that aggregation occurs long before the compression process, perhaps even persisting from the spreading solution. This suggests that for monolayers of I, unlike monolayers of fatty acids, both aggregates and phase domains are seeded early in the Langmuir process. This is corroborated by the observation of aggregate formation at the air−water interface before compression takes place. A third phase was also observed and shown to be tens of monolayers in thickness and ca. 1 μm in lateral size by atomic force microscopy. This phase is likely associated with local film collapse and the presence of small bright regions in the epifluorescence images.

Effects of a low-temperature buffer layer on structural properties of ZnO epilayers grown on (1 1 1)CaF 2 by two-step MBE

ZnO epitaxial layers are grown on (1 1 1)CaF 2 substrates by the two-step MBE, in which a 80 nm thick low-temperature buffer layer was predeposited onto CaF 2. Structural properties of ZnO layers have been investigated in detail with high-resolution four-crystal diffractometry to get insight into three-dimensional lattice ordering in the epilayers. The results are compared with a ZnO layer grown on CaF 2 without a low-temperature buffer layer and reported data of ZnO layers grown on Al 2O 3. It is found that the low-temperature buffer layer is effective for reducing mosaicity in the layers. The domain size increases and inhomogeneous lattice strain along the growth direction is reduced in ZnO layers grown by two-step MBE. Although the low-temperature buffer layer is effective for improving the in-plane lattice ordering and the ordering along the growth direction, it is more effective for the lattice ordering along the growth direction.