Regular Array Of Steps Research Articles

Lateral confinement effects of [formula omitted]-point Tamm state in vicinal Cu(100) surfaces

Vicinal Cu(100) surfaces with different miscut angles and terrace widths are studied by angle resolved photoemission spectroscopy. The Tamm M¯-point d-like surface state is strongly affected by the super periodic potential induced by the regular array of steps, as it shifts away from the Fermi level and its bandwidth is reduced. For smaller terraces, several replicas are observed, proving that the Tamm surface state is sensitive to the new superperiodic potential. For the largest terraces, the Tamm state starts splitting into incipient and non-dispersing quantum well states, indicating that a transition into a localized regime takes place as a function of terrace width. The results are rationalized using a Kronig–Penney model to simulate the step superperiodicity.

Two-Dimensional Motion of Unstable Steps Induced by Flow in Solution

By carrying out Monte Carlo simulation, we study step instabilities during crystal growth from solution. In previous studies [M. Sato: J. Phys. Soc. Jpn. 79 (2010) 064606; M. Sato: J. Cryst. Growth 318 (2011) 5; M. Sato: J. Phys. Soc. Jpn. 80 (2011) 024604], we used a one-dimensional model, so that we were unable to study another type of instability, step wandering. In this research, we use a two-dimensional model to study both step wandering and step bunching. When the flow of solutes is in the step-down direction, a regular array of steps is unstable and bunches of steps are formed. Owing to the step bunching, fluctuations along the steps are enlarged and step wandering is induced. If the direction of flow is opposite, a regular array of steps is stable and step bunching does not occur. Although a single straight step is unstable in the case of long-wavelength fluctuations, step wandering does not occur on a vicinal face. Thus, with a step-up flow, the vicinal face is stable against both step bunching a...

Thermally Induced Surface Reorganization of 3C-SiC(111) Epilayers Grown on Silicon Substrates

We investigate by means of Atomic Force Microscopy and Scanning Electron Microscopy the surface modifications of 3C-SiC(111)/Si epilayers induced by thermal annealing performed under hydrogen or argon atmosphere. We explore the effects of these treatments both on as grown and polished epilayers. Owing to an important initial surface roughness, the annealing has few impact on as grown films. On polished epilayers, a surface reorganization via the formation of a regular array of steps is evidenced. The proper effect of each gas on the surface reorganization is discussed.

Regular stepped structures on clean Si(hhm)7×7 surfaces

Regular single and triple step arrays with different periodicities have been fabricated in ultrahigh vacuum on clean Si(557) surfaces at various thermal treatment procedures. The atomic structure of the triple step staircases has been studied with high resolution scanning tunneling microscopy (STM). The results of atomically resolved STM experiments demonstrate a number of possible triple step configurations on Si(hhm) surfaces. The triple step models consistent with atomically resolved STM data obtained on regular Si(223) and Si(556) triple step staircases are presented. Possible driving forces for self-assembling regular step arrays on large scale areas are discussed.

Fabrication of rubrene nanowires on vicinal (0 0 0 1) sapphire surfaces

Morphology of high-vacuum deposited rubrene thin films on the annealed (0 0 0 1) vicinal sapphire surfaces was studied by atomic force microscopy in non-contact mode. Atomic force microscopy images of rubrene thin films indicate that a regular array of steps on the sapphire surface acts as a template for the growth of the arrays of rubrene nanosize wires. To further demonstrate that morphological features of a substrate are crucial in determining the morphology of rubrene layers we have grown rubrene on the sapphire surfaces that were characterized by the terrace-and-step morphology with islands. We have found preferential nucleation of rubrene molecules at the intersection between a terrace and a step, as well as around the islands located on terraces.

Surface preparation of [formula omitted]-SiC for the epitaxial growth of 3C–SiC

In this paper, we present a study of the surface preparation of on-axis, Si face 6H–SiC(0 0 0 1) and 4H–SiC(0 0 0 1) substrates for the growth of 3C–SiC heteroepitaxial layers. The treatments were performed in a vertical cold-wall reactor, at temperatures ranging from 1350 to 1650 °C for 10–30 min, under H 2 or H 2+C 3H 8 atmospheres. By atomic force microscopy investigation, the 4H–SiC surfaces were always found to be rougher than the 6H–SiC ones so that we mainly studied the use of 6H–SiC. All the samples displayed a more or less regular surface covered with small steps (up to 1 nm height). Si droplet formation was observed in some specific conditions, which, hence, are to be avoided. The most regular array of steps (∼0.7 nm height) was obtained on 6H–SiC seeds under H 2 treatment at 1450 °C for 10 min. On such surfaces, 3C–SiC growth was performed using a mixture of SiH 4+C 3H 8 at 1450 °C with a C/Si ratio of 3 in the gas phase.

The instability of vicinal electrode surfaces against step bunching II: Theory

It is shown that vicinal surfaces with a regular step array in contact with an electrolyte are intrinsically unstable against a phase separation into areas of flat terraces and areas of step bunches. The effect is caused by the step dipole moment which lowers the potential of zero charge (pzc) of stepped surfaces. Specific calculations performed for vicinal surfaces of silver are qualitatively in keeping with experimental observations. Step bunching is likewise expected for vicinal surfaces of gold and platinum.

Electronic states at vicinal surfaces

Vicinal noble metal surfaces with regular arrays of steps and terraces are very convenientmodel systems to test the electronic properties of lateral nanostructures. Usingangle-resolved photoemission with synchrotron radiation we thoroughly characterizeelectronic states and wavefunctions in a variety of vicinal Cu(111) and Au(111)surfaces. By tuning the terrace width, we can observe the fundamental transitionfrom arrays of non-interacting nano-objects (terraces), where electron states areconfined, to lateral coupling between terraces, which leads to superlattice states.

Vicinal metal surfaces as nanotemplates for the growth of low-dimensional structures

Vicinal surfaces, which exhibit a regular array of steps, introduce defined arrangements ofsurface defects, which have the potential to create specific functionalities of the surface. Inparticular they can be used as templates for the growth of one-dimensional structures usingselective step decoration. In this article we discuss the properties of vicinal metal surfacesand how they can be used as nanotemplates. The requirements for the growth oflow-dimensional adsorbate structures at step edges of the vicinal (997) and (779)surfaces of platinum will be discussed in detail. Here energetics determined by thedifferent adsorption sites and the kinetics present through the diffusion processesplay an essential role. In order to obtain stable arrangements the propensity ofthe elements for alloy formation must be taken into account. Examples for theproperties of the structures obtained and their role in studying one-dimensionalsystems are discussed, and we give a short outlook on how the principles of stepdecoration might be extended to a kind of atomic assembly of more complex surfacenanostructures.

Gd disilicide nanowires attached to Si(111) steps

Self-assembled electronic devices, such as quantum dots or switchable molecules,need self-assembled nanowires as connections. We explore the growth of Gddisilicide nanowires at step arrays on Si(111). Atomically smooth wires with largeaspect ratios are formed at low coverage and high growth rate (length ≥ 1μm, width 10 nm, height 0.6 nm). They grow parallel to the steps in the [1 1̄0] direction, which is consistent with a lattice match of 0.8% with thea-axisof the hexagonal silicide, together with a large mismatch in all other directions.This mechanism is similar to that observed previously on Si(100). In contrast toSi(100), the wires are always attached to step edges on Si(111) and can thus begrown selectively on regular step arrays.

Growth mode of Pb films on vicinal Si( [formula omitted

Vicinal surfaces of silicon are good candidates as substrate for nanowires of metals by deposition on regular step arrays, since silicon surfaces may be prepared with very regular step arrays and silicon is insulating at low temperatures for conductance measurements of the wires. Using high resolution low-energy electron diffraction we have studied clean vicinal Si(7 7 9) and (5 5 7) surfaces and the deposition of metallic Pb films on these surfaces. We confirmed that both types of the clean vicinal surfaces are triple step surfaces. The triple step shows a separate superstructure, different from the superstructure on the (1 1 1) terraces. Pb films show a small inclination (<1°) towards the Si(1 1 1) plane due to the misfit between Pb and Si. Depending on the annealing temperatures Pb grows on the clean surface with one or two inclinations towards the Si(1 1 1) plane. The tendency of forming nanowires depends on the conditions of deposition and annealing.

Image-potential states on stepped Cu (001) surfaces

Image-potential states on Cu (117) and Cu (119) surfaces were studied by means of two-photon photoelectron spectroscopy. The regular array of steps generates a lateral potential on the vicinal surfaces, which modifies the surface-electronic structure. Compared to Cu (001), the band bottom of the n=1 image-potential states shifts by 40 meV to lower binding energy. The periodicity of the step-induced superlattice manifests itself as back-folding of the n=1 and 2 dispersion bands. At the surface Brillouin zone boundary a mini-gap opens with a width of 135 meV for the first image-potential state on Cu (117). On the vicinal surfaces the lifetime of the image-potential states is reduced by a factor of three as compared to Cu (001). This is attributed to a narrowing of the surface-projected bulk-band gap when projected along the [11n] direction. While the dephasing rate of the first image-potential state is close to the decay rate, higher members of the Rydberg-like series show negligible dephasing.

Thermal relaxation of isolated silicon pyramids on the Si([formula omitted])2×1 surface

Silicon mounds fabricated on the Si(100)2×1 surface by a tip of a scanning tunneling microscope (STM) have been observed by STM at substrate temperature of 770 K. The shape of the mound is a quadrangular pyramid with facets of regular array of steps with double layer height. For all the step, the dimer rows are perpendicular to the step edges, so called the DB step. Just after the fabrication, the pyramid begins to decay immediately layer-by-layer. During decay, the DB steps move scarcely, but only the SB steps at the bottom layer move due to attachment and detachment of atoms which are detached from the upper layers. For a single layer mound, the aspect ratio of the mound oscillates between about 2.5 and 1.5.

Adatom dynamics in a periodic potential under time-periodic bias

We study the dynamics of a Brownian particle in a 1D external potential under the influence of a time-periodic bias with an amplitude small with respect to the potential barriers. We consider both a periodic potential corresponding to a smooth crystal surface and a regular array of steps with an extra Ehrlich–Schwoebel barrier for step crossing. For the smooth surface, we extend our previous work in the high friction limit to the low friction case and find that the oscillating bias enhances the diffusion coefficient D T due to the broadening of the jump length distribution. In the case of a stepped surface with terraces of length L, the bias induces a non-zero average current J ave in the direction of descending steps as long as the driving frequency is smaller than a threshold frequency Ω T≈ L −1. The current shows a maximum as a function of temperature for fixed L. However, no evidence of stochastic resonance type of enhancement can be found either in D T or J ave.

Cu induced step bunching on a Si(111) vicinal surface studied by reflection electron microscopy

Step bunching induced by Cu adsorption on a Si(111) vicinal surface was studied by reflection electron microscopy. A surface with a regular array of steps changes to wide (111) terraces and step bands due to the formation of the incommensurate (IC) Cu-adsorbed structure on the Si(111) terraces. The maximum terrace width of the IC domains depends on the deposition conditions of Cu, and is wider at higher temperature and at lower deposition rate. (441) and (331) facets are formed on a vicinal Si(111) surface inclined towards the 〈112〉 direction, while no facet with definite index is noticed on a vicinal surface inclined towards the 〈110〉 direction.

Influence of miscut on crystal truncation rod scattering

X-rays can be used to measure the roughness of a surface by the study of crystal truncation rod scattering. It is shown that for a simple cubic lattice the presence of a miscut surface with a regular step array has no effect on the scattered intensity of a single rod and that a distribution of terrace widths on the surface is shown to have the same effect as adding roughness to the surface. For a perfect crystal without miscut, the scattered intensity is the sum of the intensity from all the rods with the same in-plane momentum transfer. For all real crystals, the scattered intensity is better described as that from a single rod. It is shown that data-collection strategies must correctly account for the sample miscut or there is a potential for improperly measuring the rod intensity. This can result in an asymmetry in the rod intensity above and below the Bragg peak, which can be misinterpreted as being due to a relaxation of the surface. The calculations presented here are compared with data for silicon (001) wafers with 0.1 and 4° miscuts.

Explanation of multiplet spots in low-energy electron diffraction patterns of clean GaN surfaces

Clean, ordered, and stoichiometric GaN\(\) surfaces are obtained after exposure to a Ga-flux followed by annealing in ultrahigh vacuum (UHV), after desorption of a Ga layer deposited at room-temperature or after nitrogen ion-bombardment and annealing in UHV. Samples annealed at temperatures above approximately \(\) display \(\) low-energy electron diffraction patterns. As a function of electron energy, the normal-order spots split into circular sextets. These multiplet rings periodically expand and coalesce. This observation is explained by oppositely oriented, regular step arrays in the [1000]-, [0100]- and [0010]-directions on the GaN\(\) surfaces. Quantitative analysis of the data gives terrace widths of \(\)A and step heights of \(\)A. The observations suggest faceting or the “development” of growth spirals with steps heights of two Ga-N bilayers by thermal etching.

Electrochemical behavior and structural changes of a reconstructed Pt(100) electrode in sulfuric acid: a comparison with Pt(100)-(1×1)

The structural changes of a reconstructed Pt(100) surface after electrochemical treatments are characterized by LEED/RHEED under UHV conditions. It is found that the reconstructed Pt(100) structure is stable in the range of −0.2↔+0.4 V (vs. Ag/AgCl) in 0.01 M H 2SO 4 solution, though slightly disordered by hydrogen adsorption. It transforms to a (1×1) structure through an intermediate phase if the electrode potential is scanned to the oxide formation region (>0.9 V). At intermediate potentials, regular arrays of steps running along the [011] direction perpendicular to the fivefold periodicity are formed with a mean spacing of 2.8 nm that is only detected by RHEED. The structural transitions conform to the concurrent changes of the voltammetric features. The cyclic voltammogram of the reconstructed surface is intrinsically different from that of an unreconstructed surface, the latter being almost identical to that of a Pt(100)-(1×1) surface prepared by Ar +-sputtering at room temperature without any annealing above 300 K.

Formation of regular step arrays on Si(111)7×7

Highly regular arrays of steps are produced on vicinal Si(111)7×7 surfaces. A tilt of the surface normal from (111) toward (1̄1̄2) produces single steps (0.3 nm high and typically 15 nm apart). The opposite tilt toward (112̄) produces bunched steps with adjustable height (1–5 nm) and a spacing of 70 nm. Preparation criteria for straight edges and regular spacings are determined, taking into account the miscut angle (azimuthal and polar), annealing sequence, current direction, and applied stress.

Regular step arrays on silicon

Highly regular arrays of steps are produced on vicinal Si(111)7×7. The step edges are atomically straight for up to 2×104 lattice sites. The terraces are single domain, which produces a minimum kink width of 2.3 nm (half a 7×7 unit cell) and thus a high barrier for creating kinks. Criteria for obtaining optimum step arrays are established, such as the miscut [≈1° towards (1̄1̄2)] and an annealing sequence which passes through step bunching regions quickly.