Miscut Angle Research Articles

Anisotropy of Ag Diffusion on Vicinal Si Surfaces

Photoemission electron microscopy (PEEM) is used to study Ag surface diffusion on vicinal Si surfaces. The diffusion field is represented by Iso-Coverage Zones around Ag islands during desorption. By analyzing the shape and radius of the Iso-Coverage Zone we can determine diffusion parameters. For anisotropic diffusion the zone has an elliptical shape and the aspect ratio gives a measure for the anisotropy. Using this technique, we study the degree of anisotropy of Ag diffusion on vicinal Si(001) and Si(111). With increasing miscut angles, starting from Si(001) as well as from Si(111), we find a gradually increasing anisotropy, caused by the higher step density. On higher index surfaces, like Si(119), Si(115) and Si(113), we find isotropic diffusion for surfaces with comparable dimer and (double) step structure as on Si(001)-4°, where diffusion is strongly anisotropic. [DOI: 10.1380/ejssnt.2010.372]

Fabrication and surface characterization of single crystal PtBi and PtPb (100) and (001) surfaces

High quality single crystal PtM (M = Bi or Pb) (100) and (001) surfaces have been generated from solid state bulk materials. The specific orientation was determined via X-ray Laue back-reflection and the miscut angles of the single crystal surfaces were ∼0.3° which was limited by instrumental resolution. The PtM (001) electrode had a Pt termination based on cyclic voltammetric (CV) profiles. The surface structure and composition of single crystal PtM surfaces have been studied by synchrotron-based in situ X-ray grazing incidence diffraction (GID) under active electrochemical control. Cycling of the potential to increasingly high values resulted in dramatic changes to the surface crystalline structure and composition of these single crystal electrodes. Well-defined Pt nano-domains in a hexagonal pattern with a 23° offset angle to the substrate were formed on the PtM (001) surface after electrochemical pretreatment in supporting electrolyte (0.1M H(2)SO(4)), especially for E(ulp) (E(ulp) = upper limit potential) of +0.80 V or beyond. From an analysis of the diffraction peaks, the size of the Pt domains was estimated to be ∼15 nm. The Pt domain formation on the single crystal surfaces, similar to results on polycrystalline intermetallic phases, was due to leaching of the less-noble elements (Bi or Pb) from the intermetallic matrix and sintering of the Pt atoms on the surfaces. On the other hand, Pt domains with a preferential direction but no offset angle to the substrate were formed on PtM (100) surface after similar electrochemical pretreatment. PtBi and PtPb single crystal surfaces exhibited different anisotropic electrocatalytic activities towards the electrooxidation of formic acid and other potential fuels for fuel cell applications. The reactivities of these single crystal electrodes towards the oxidation of small organic molecules were a function of E(ulp) values and maximal activities were around +0.60 V for PtBi(001) surface which might be due to formation of partially oxidized surfaces but around +1.20 V for PtPb(100) and (001) surfaces which might be due to the increasing boundary lines of Pt and PtPb grains.

Superconducting weak link generated on a linear array of substrate steps in ultrathin films ofYBa2Cu3O7−δ

We have studied a three-unit-cell-thick YBa2Cu3O7-x (YBCO) superconducting film grown on a slightly vicinal SrTiO3 substrate that was polished from the (001) plane by a small miscut angle (less than 0.5 degrees). This produced, on its surface, a linear array of single-unit-cell-height steps with a period larger than 40 nm. A characteristic fault, with a displacement corresponding to one-third of the c-axis length of YBCO, is generated in the film on each substrate step, as observed by atomic force microscopy. Transport measurements with current flows parallel and perpendicular to the fault show that the fault serves as a superconducting weak link, as well as a unique one-dimensional flux-pinning center in an applied magnetic field. In addition, a characteristic fine structure is found in the flux-flow resistivity as a function of magnetic field, the origin of which may be ascribed to a matching effect between the periodically aligned faults and the flux lattice.

Surface structure and magnetic properties of MnAs epilayers grown on vicinal GaAs(001) substrates

In this study, we have investigated the influence of the vicinality on the surface morphology of MnAs/GaAs(001) epilayers at the nanoscale. The microscopic structure of the MnAs surface is strongly affected by the miscut angle of the substrate, while the characteristic MnAs α−β micronic self-organized stripes pattern remains largely unaffected. Even though the surface morphology is quite different from epilayers deposited on nominal substrates (no miscut), the magnetic properties of the films grown on vicinal substrates are nearly unaltered. That is, the temperature for the onset of the β phase, for decreasing temperature, the coercive field, and the remnant magnetization are similar to films grown on nominal substrates. These findings open interesting prospects concerning the use of MnAs/GaAs(001) epilayers as temperature-dependent striped templates for the subsequent growth of magnetic thin films and the formation of a great variety of nanostructures.

Nanostructured sapphire vicinal surfaces as templates for the growth of self-organized oxide nanostructures

Vicinal substrates of sapphire with miscut angle of 10° from the (0 0 1) planes towards the [1 1 0] direction have been annealed in air in the range from 1000 to 1500 °C. The behaviour of these surfaces has been characterized as a function of the temperature and the thermal treatment time by Atomic Force Microscopy observations. A thermal treatment at 1250 °C allows to stabilize a surface made of periodically spaced nanosized step-bunches. Such stepped surfaces were used as template to grow self-patterned epitaxial oxide nanoparticles by thermal annealing of yttria-stabilized zirconia thin films produced by sol–gel dip-coating. Grazing Incidence Small Angle X-ray Scattering and High-Resolution Transmission Electron Microscopy were used to study the morphology of the nanoparticles and their epitaxial relationships with the substrate.

Step-step interaction on vicinal Si(001) surfaces studied by scanning tunneling microscopy

We report on measurements of step-step interaction on a flat Si(111)−(7×7) surface and on vicinal Si(001) surfaces with miscut angles ranging between 0.2° and 8°. Starting from scanning tunneling microscopy images of these surfaces and describing steps profile and interactions by the continuum step model, we measured the self-correlation function of single steps and the distribution of terrace widths. Empirical parameters, such as step stiffness and step-step interaction strength, were evaluated from the images. The present experiment allows to assess the dependence of the step-step repulsion on miscut angle, showing how parameters drawn from tunneling images can be used to interpolate between continuum mesoscopic models and atomistic calculations of vicinal surfaces.

Two-dimensional interface structures of epitaxial (Ba,Sr)TiO 3 film on miscut (001) MgO

We report on the effect of substrate miscut on the 2-dimensional interfacial structure and dielectric properties of the epitaxial Ba 0.6Sr 0.4TiO 3/MgO. Epitaxial Ba 0.6Sr 0.4TiO 3 films on vicinal (001) MgO grown by pulsed-laser ablation were studied using transmission electron microscopy (TEM). Plan-view TEM showed that the films grown on the substrate with miscut angles of 1.2°, 3.5°, and 5.3° have lattice mismatches of − 5.6%, − 6.0% and − 5.7% at the interface, larger than the values (− 5.4%, − 5.7% and − 5.5%, respectively) obtained using cross-section TEM. The films grown on 1.2° and 5.3° miscut substrates consist of commensurate domains with sizes about 30 to 40 nm at the interface, significantly larger than those of 10 to 20 nm obtained for the films grown on the 3.5° miscut substrate. The films with larger commensurate domains at the interface exhibit about 30% higher dielectric constant and dielectric tunability than those with smaller commensurate domains. Initial measurements show that their interfacial differences have a tremendous effect on the dielectric properties of the films.

Microstructural Characterization of ${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{7-{\rm x}}$ Films With ${\rm BaZrO}_{3}$ Nanorods Grown on Vicinal ${\rm SrTiO}_{3}$ Substrates

When grown on miscut SrTiO3 substrates, significant microstructural changes are observed in BaZrO3-doped YBa2Cu3O7-x thin films when compared to those on non-vicinal substrates. Scanning Electron Microscopy indicates a surface morphology strongly influenced by the vicinal angle, and an accumulation of BaZrO3 particles is observed near the step edges. Cross-sectional Transmission Electron Microscopy reveals that while the columnar formations of BaZrO3 rods typically seen on non-vicinal substrates are present, a significant increase in planar defects in a 10deg vicinal film are observed. The effects observed with increasing miscut angle indicate that the modulated surface provided by the vicinal substrate influences the crystalline quality of the YBCO matrix and BZO columnar formation through the thickness of the film.

Self-organization processes in highly epitaxial La2/3Sr1/3MnO3 thin films grown on SrTiO3 (001) substrates

We report on the growth of highly epitaxial La2/3Sr1/3MnO3 thin films on SrTiO3 (001) oriented substrates by rf magnetron sputtering. It is shown that structural strain caused by lattice mismatch between film and substrate and kinetics growing instabilities may offer unique opportunities to control the film morphologies. By increasing growth rate, the surface morphology undergoes a dramatic transformation: from very smooth surface through arrays of mounds or antidots to hatched morphology. All nano-objects form long-range ordered arrays running in the steps direction defined by the miscut angle of underlying substrate. These self-assembled structures are of high interest envisaging a new route for the fabrication of oxide-based magnetoelectronic devices by using a bottom-up approach.

Towards Large Area (111)3C-SiC Films Grown on Off-Oriented (111)Si

The choice of off-axis (111) Si substrates is poorly reported in literature despite of the ability of such an oriented Si substrate in the reduction of stacking faults generation and propagation. The introduction of off-axis surface would be relevant for the suppression of incoherent boundaries. We grew 3C-SiC films on (111) Si substrates with a miscut angle from 3° to 6° along <110> and <11 >. The film quality was proved to be high by X-Ray diffraction (XRD) characterization. Transmission electron microscopy was performed to give an evaluation of the stacking fault density while pole figures were conducted to detect microtwins. Good quality single crystal 3C-SiC films were finally grown on 6 inch off-axis (111)Si substrate. The generated stress on both 2 and 6 inch 3C-SiC wafers has been analyzed and discussed.

Strain‐Driven Self‐Assembled Network of Antidots in Complex Oxide Thin Films

Structural strain due to lattice mismatch is used to promote the formation of a self-assembled network of antidots in highly epitaxial La(2/3)Sr(1/3)MnO(3) thin films grown on (001) oriented SrTiO(3) substrates by radiofrequency magnetron sputtering. Size, depth, and separation between antidots can be controlled by changing deposition parameters and the miscut angle of the substrate. This morphology exhibits a remarkable magnetic anisotropy and offers unique opportunities for versatile nanostencils for the preparation of nano-object networks that can be of major relevance for the fabrication of oxide-based magnetic and magnetoelectronic devices.

STEP-FLOW GROWTH OF HETEROEPITAXIAL SrRuO3 THIN FILMS ON 0.04° SrTiO3 (001) VICINAL SUBSTRATES

We have grown epitaxial SRO thin films of thickness of about 50 nm on the STO (001) substrates with a small miscut angle of 0.04° by step-flow mode. A mode transition from two-dimensional mixed growth of layer-by-layer and step-flow growth to complete step-flow growth was observed, which is associated with the change in the surface mobility of adatoms and the rate of edge diffusion along the steps.

Step formation on hydrogen-etched 6H-SiC{0 0 0 1} surfaces

The formation of step bunches and/or facets on hydrogen-etched 6H-SiC(0 0 0 1) and ( 0 0 0 1 ¯ ) surfaces has been studied, using both nominally on-axis and intentionally miscut ( i.e. vicinal) substrates. It is found that small miscuts on the (0 0 0 1) surface produce full unit-cell high steps, while half unit-cell high steps are observed on the ( 0 0 0 1 ¯ ) surface. The observed step normal direction is found to be 〈 1 1 ¯ 0 0 〉 for both surfaces. Hence, for intentionally miscut material, a miscut oriented towards this direction produces much better order in the step array compared to a miscut oriented towards a 〈 1 1 2 ¯ 0 〉 direction. For (0 0 0 1) vicinal surfaces that are miscut towards the 〈 1 1 ¯ 0 0 〉 direction, the formation of surface ripples is observed for 3° miscut and the development of small facets (nanofacets) is found for higher miscut angles. Much less faceting is observed on miscut ( 0 0 0 1 ¯ ) surfaces. Additionally, the (0 0 01) surface is found to have a much larger spatial anisotropy in step energies than the ( 0 0 0 1 ¯ ) surface.

Step-flow growth of homoepitaxial ZnO thin films by ultrasonic spray-assisted MOVPE

Homoepitaxial zinc oxide thin films with atomically flat surfaces have successfully been grown on Zn-polar (0 0 0 1) ZnO substrates with the step-flow growth mode by ultrasonic spray-assisted metalorganic vapor phase epitaxy. The surfaces of the grown layers were composed of terraces and steps, where the step height was mainly 0.26 nm originated from half of a c-axis lattice parameter of hexagonal ZnO crystal, at the optimizing growth conditions. The step-flow growth required the higher growth temperature (for example, at 950 °C), while at lower temperatures (for example, at 875 °C) the growth mode was a mixture of layer-by-layer and step-flow growths. In order for the step-flow growth maintaining the monolayer steps, the miscut angles of substrates should be so small that the terrace lengths were about 200 nm or more in our experimental conditions.

Effect of c‐plane sapphire misorientation on the growth of AlN by high‐temperature MOVPE

AbstractAlN layers were directly grown on sapphire substrates with slightly different miscut angles from the c‐plane by metalorganic vapor phase epitaxy at 1300 °C. By X‐ray diffraction analysis, the structural quality was found to improve with the increase in substrate off‐angle. When the substrate off‐angle was 0.5°, the X‐ray rocking curve (XRC) full widths at half maximum (FWHMs) of symmetric and asymmetric planes were 170 and 550 arcsec, respectively. At smaller off‐angle, XRC‐FWHMs were wider. When the substrate off‐angle was zero, the XRC‐FWHM was considerably inferior to that on 0.5o‐off‐angle sapphire. The surface morphology was investigated. Atomic steps were observed on the substrates with a small misorientation. In contrast, macro steps appeared on larger‐off‐angle sapphire substrates. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In-plane magnetic anisotropies inFe3O4films on vicinal MgO(100)

Ferromagnetic resonance was used to study the influence of vicinal (miscut) angle and film thickness on in-plane fourfold and uniaxial magnetic anisotropies in epitaxial ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ films grown on vicinal MgO(100) surfaces. The in-plane fourfold anisotropy constant ${K}_{4\ensuremath{\parallel}}$ is approximately the same for all films but the dominant in-plane uniaxial constant ${K}_{2\ensuremath{\parallel}}$ varies linearly with the inverse ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ layer thickness and approximately quadratically with the vicinal angle. A second, weaker, in-plane uniaxial term is evident for the film on a larger miscut (10\ifmmode^\circ\else\textdegree\fi{}) substrate. The easy axis of the dominant in-plane uniaxial term is perpendicular to the step edges. The dominant in-plane uniaxial anisotropy has one term inversely proportional to the film thickness that is associated with anisotropy localized at the interface and a second term that is independent of film thickness; the latter may arise from the preferential alignment of antiphase boundaries with the step edges.

Tuning reactive epitaxy of silicides with surface steps: Silicide quantum dot arrays on Si(111)

We have studied the nucleation and growth of cobalt silicides on vicinal silicon surfaces. The latter exhibit one-dimensional arrays of steps with narrow terrace widths ranging from 20 Å to 40 Å (miscut angle between 9 ∘ and 4.6 ∘, respectively). Submonolayer amounts of Co were deposited by thermal evaporation on such vicinal Si(111) surfaces by reactive thermal deposition, and the resulting silicide structures were analysed by scanning tunnelling microscopy. The presence of narrow terraces in the system notably alters the usual nucleation process of cobalt silicide on flat Si(111). It is observed that by varying the Co coverage and vicinal angle, the size and amount of the hexagonal silicide clusters can be controlled producing a dense array of quantum dots. This behaviour contrasts to that observed on flat substrates, where nanocluster structures are notably scarce.

Magnetization processes in ultrathin Au∕Co∕Au films grown on a bifacial Mo(110)/Mo(540) single crystal

We studied magnetization reversal processes and magnetic anisotropy in ultrathin Au∕Co∕Au films deposited on a bifacial Mo(110)/(540) single crystal. The influence of the Co thickness and miscut angle on the spin reorientation from out-of-plane into in-plane magnetization were investigated by means of the magneto-optical Kerr effect (MOKE). In the case of Co grown on a vicinal Au∕Mo(540) substrate, the perpendicular magnetization component was found throughout the 1–8nm Co thickness range. The canted orientation of magnetization was deduced from vectorial MOKE magnetometry. The out-of-plane switching field, which is 160Oe for the perpendicular magnetization, increases to about 960Oe as observed at 8nm Co thickness on the vicinal part. The experimental data are discussed taking into account both uniaxial out-of-plane and in-plane magnetic anisotropy energy terms. The results indicate the possibility of tuning the perpendicular magnetization component with the use of vicinal substrates, and are important from both a surface physics and magnetic memory media point of view.

LEEM / PEEM Study of Anisotropic Diffusion Fields in the Ag/Si(001) System

AbstractWe used direct imaging of diffusion fields in photoemission electron microscopy to study the diffusion (an)isotropy of Ag on flat and vicinal Si(001) surfaces with miscut angles between 0.2° and 4° in the [110] direction. While the diffusion field, represented by its iso-coverage zone, is isotropic on flat Si(001), it becomes elongated on the vicinal surface. The aspect ratio of the iso-coverage zone is used as a measure of the effective diffusion anisotropy on the surface. The aspect ratio of the iso-coverage zone increases continuously with the miscut angle, up to the maximum miscut that was studied. For the 4° miscut surface we find that the shape of the diffusion field is independent of the kink density of the substrate. From the temperature dependence of the aspect ratio, we determine an effective energy of ΔEani ∼ 0.7 eV for the activation energy responsible for the anisotropy.

Ultrasonic spray assisted Mist-CVD method for high-quality crystalline and amorphous oxide semiconductors growth

ABSTRACTThe growth of high-quality crystalline ZnO thin films on ZnO bulk substrates and of amorphous In-Ga-O and Ga-Al-O thin films has been demonstrated by using the solution-based cost-effective and environmental friendly ultrasonic spray assisted mist-CVD method. The homoepitaxial ZnO thin films with atomically flat surfaces were successfully grown on Zn-polar ZnO substrates via a step-flow growth mode, in spite of different miscut angles of the substrate, at the furnace temperature of 1000°C. The compositions and optical absorption edges of the amorphous In-Ga-O and Ga-Al-O thin films were controlled by means of the concentration ratios of [In]/([In]+[Ga]) and [Al]/([Al]+[Ga]) in the starting solutions.