Vicinal SiC Surfaces Research Articles

Energetics of the surface step and its morphology on the 3C-SiC(111) surface clarified by the density-functional theory

We report first-principles calculations that clarify the atomic structures and the energetics of all the possible atomic steps on 3C-SiC(111) surfaces. The calculated formation energies of the atomic steps reveal the origin of the experimentally observed variation of the step morphology, i.e., the emergence of either the straight or the meandering step edge, depending on the inclined direction of the vicinal SiC surfaces. We find that the peculiar reconstructions near the steps play decisive roles in the step energetics. The calculated formation energy of the meandering step edge shows that the straight step edges along particular directions are energetically unfavorable.

Carbon-Based Aromatic-Like Nanostructures on the Vicinal SiC Surfaces Induced by Ba Adsorption

The electronic structure of the SiC/Si(111)-8° and SiC/Si(111)-4° epitaxial layers with adsorbed Ba submonolayers is thoroughly studied in situ in ultrahigh vacuum by synchrotron-based photoemission spectroscopy. The SiC epitaxial layers were grown on the vicinal Si(111)-8°, Si(111)-4° surfaces by the original method of substitution of atoms. The C 1s and Si 2p сore level spectra are investigated in relation to the different Ba coverages. A substantial change in the C 1s spectra induced by Ba adsorption is revealed. It is found that the effect results from the formation of a new, previously unknown carbon-based structure consist of nanoclusters on the surface. Experimental data show that the nanoclusters can be created exclusively on the vicinal SiC surfaces in the presence of stabilizing adsorbed metal atoms, specifically, Ba atoms. Density functional theory using the basis of plane waves with the pseudopotential approximation is applied to calculate the spatial configuration of this clusters structure. It is shown that the surface nanoclusters are formed due to local interaction between silicon vacancies, carbon atoms and Ba adatoms. It is established that the carbon clusters is composed of carbon rings, in which the chemical bonds are close in nature to the bonds inherent in aromatic-like compounds.

Publisher’s Note: Graphene nanoribbons on vicinal SiC surfaces by molecular beam epitaxy [Phys. Rev. B87, 121407(R) (2013)

Publisher’s Note: Graphene nanoribbons on vicinal SiC surfaces by molecular beam epitaxy [Phys. Rev. B<b>87</b>, 121407(R) (2013)

Graphene nanoribbons on vicinal SiC surfaces by molecular beam epitaxy

We present a method of producing a densely ordered array of epitaxial graphene nanoribbons (GNRs) using vicinal SiC surfaces as a template, which consists of ordered pairs of (0001) terraces and nanofacets. Controlled selective growth of graphene on approximately 10 nm wide (0001) terraces with 10 nm spatial intervals allows GNR formation. By selecting the vicinal direction of SiC substrate, [1$\overline{1}$00], well-ordered GNRs with predominantly armchair edges are obtained. These structures, the high-density GNRs, enable us to observe the electronic structure at $K$ points by angle-resolved photoemission spectroscopy, showing a clear band-gap opening of at least 0.14 eV.

Nanoscale structural characterization of epitaxial graphene grown on off-axis 4H-SiC (0001)

In this work, we present a nanometer resolution structural characterization of epitaxial graphene (EG) layers grown on 4H-SiC (0001) 8° off-axis, by annealing in inert gas ambient (Ar) in a wide temperature range (Tgr from 1600 to 2000°C). For all the considered growth temperatures, few layers of graphene (FLG) conformally covering the 100 to 200-nm wide terraces of the SiC surface have been observed by high-resolution cross-sectional transmission electron microscopy (HR-XTEM). Tapping mode atomic force microscopy (t-AFM) showed the formation of wrinkles with approx. 1 to 2 nm height and 10 to 20 nm width in the FLG film, as a result of the release of the compressive strain, which builds up in FLG during the sample cooling due to the thermal expansion coefficients mismatch between graphene and SiC. While for EG grown on on-axis 4H-SiC an isotropic mesh-like network of wrinkles interconnected into nodes is commonly reported, in the present case of a vicinal SiC surface, wrinkles are preferentially oriented in the direction perpendicular to the step edges of the SiC terraces. For each Tgr, the number of graphene layers was determined on very small sample areas by HR-XTEM and, with high statistics and on several sample positions, by measuring the depth of selectively etched trenches in FLG by t-AFM. Both the density of wrinkles and the number of graphene layers are found to increase almost linearly as a function of the growth temperature in the considered temperature range.

Tight-Binding Approach to Initial Stage of the Graphitization Process on a Vicinal SiC Surface

Tight-Binding Approach to Initial Stage of the Graphitization Process on a Vicinal SiC Surface

Tight-Binding Approach to Initial Stage of the Graphitization Process on a Vicinal SiC Surface

We study the process of growth of graphene by the SiC surface decomposition method to improve the technique of growing graphene. In this study, the initial stage of the graphitization process on a periodically faceted SiC surface is investigated by the Naval Research Laboratory tight-binding approach. The results suggest that the decomposition of the SiC surface started by the desorption of Si atoms at the step edge. It is also found that released C atoms are trapped at the step-edge sites and that neighboring Si atoms are subsequently desorbed. These results suggest that graphene nucleation on the SiC surface proceeds in a negative step-flow mode.

Self-ordering of nanofacets on vicinal SiC surfaces.

Vicinal 4H and 6H-SiC(0001) surfaces have been investigated using atomic force microscopy and cross-sectional high-resolution transmission electron microscopy. We observed the characteristic self-ordering of nanofacets on any surface, regardless of polytypes and vicinal angles, after gas etching at high temperature. Two facet planes are typically revealed: (0001) and high index (112;n) that are induced by equilibrium surface phase separation. A (112;n) plane may have a free energy minimum due to attractive step-step interactions. The differing ordering distances in 4H and 6H polytypes imply the existence of SiC polytypic dependence on nanofaceting. Thus, it should be possible to control SiC surface nanostructures by selecting a polytype, a vicinal angle, and an etching temperature.

Structural anisotropy in GaN films grown on vicinal 4H-SiC surfaces by metallorganic molecular-beam epitaxy

GaN grown directly on 4H-SiC substrates by metallorganic molecular-beam epitaxy is investigated in terms of nucleation, coalescence, and growth front evolution. The effects of SiC surface configurations such as step and terrace structures on GaN film growth physics are examined in detail. Comparative studies using on-axis and vicinal SiC surfaces indicate distinguishable differences in structural and morphological characteristics. An anisotropic x-ray characteristic is observed for the GaN film deposited on the vicinal stepped SiC surfaces. This is due to preferential nucleation and coalescence of GaN islands along step edges, which are induced by the confinement of adatoms on the narrow terraces on the vicinal SiC surface.

Characterization of structural defects in wurtzite GaN grown on 6H SiC using plasma-enhanced molecular beam epitaxy

Thin wurtzite GaN films have been grown by plasma-enhanced molecular beam epitaxy on the basal plane of 6H SiC, with and without AlN buffer layers. Threading defects, identified from high-resolution electron micrographs as double-positioning boundaries (DPBs), originate at the substrate–buffer and/or buffer–film interfaces. The density of these faults seems to be related to the smoothness of the substrate, so that their occurrence emphasizes the importance of adequate substrate preparation. Stacking faults within the GaN are often visible parallel to the SiC substrate basal plane, sometimes terminating at the DPBs. These faults are related to the particular growth conditions, with greatly decreased density obtained for lower plasma power during GaN deposition. Growth of high quality GaN without stacking faults was achieved without using AlN buffer layers by deposition directly onto a vicinal SiC surface having a miscut angle of 4°. Such stepped substrates represent a potentially useful means for controlled growth of the DPBs, which could then serve as suitable stress-relieving defects in lieu of misfit dislocations.