Realization of post-CMOS graphene electronics requires production of semiconducting graphene, which has been a labor-intensive process. We present tailoring of silicon carbide crystals via conventional photolithography and microelectronics processing to enable templated graphene growth on 4H-SiC{1-10n} (n = 8) crystal facets rather than the customary {0001} planes. This allows self-organized growth of graphene nanoribbons with dimensions defined by those of the facet. Preferential growth is confirmed by Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) measurements, and electrical characterization of prototypic graphene devices is presented. Fabrication of > 10,000 top-gated graphene transistors on a 0.24 cm2 SiC chip demonstrates scalability of this process and represents the highest density of graphene devices reported to date.
We performed electronic structure calculations based on the first-principles many-body theory approach in order to study quasiparticle band gaps, and optical absorption spectra of hydrogen-passivated zigzag SiC nanoribbons. Self-energy corrections are included using the GW approximation, and excitonic effects are included using the Bethe-Salpeter equation. We have systematically studied nanoribbons that have widths between 0.6 $\text{nm}$ and 2.2 $\text{nm}$. Quasiparticle corrections widened the Kohn-Sham band gaps because of enhanced interaction effects, caused by reduced dimensionality. Zig…
We present electronic structure calculations of few-layer epitaxial graphene nanoribbons on SiC(0001). Trough an atomistic description of the graphene layers and the substrate within the extended Hückel Theory and real/momentum space projections we argue that the role of the heterostructure's interface becomes crucial for the conducting capacity of the studied systems. The key issue arising from this interaction is a Fermi level pinning effect introduced by dangling interface bonds. Such phenomenon is independent from the width of the considered nanostructures, compromising the importance of c…
Thermal decomposition of vicinal 6H-SiC(0001) surfaces with off-angles toward the $[1\bar{1}00]$ direction results in the appearance of pairs of (0001) macroterraces and $(1\bar{1}0n)$ macrofacets covered with graphene, as follows. A carpet-like carbon layer grows on the surface, covering both the macroterraces and macrofacets; it forms $(6\sqrt{3} \times 6\sqrt{3})$ buffer layer on the former ones, whereas its partial periodic bonding with the SiC steps on the latter ones generates a pseudo-graphene nanoribbon (pseudo-GNR) array. The nanoribbons have a width of 2 nm and are aligned in the $[1…
A first principles many-body approach is employed to calculate the band structure and optical response of nanometer sized ribbons of SiC. Many-body effects are incorporated using the GW approximation, and excitonic effects are included using the Bethe-Salpeter equation. Both unpassivated and hydrogen passivated armchair SiC nanoribbons are studied. As a consequence of low dimensionality, large quasiparticle corrections are seen to the Kohn-Sham energy gaps. In both cases quasiparticle band gaps are increased by up to 2 eV, as compared to their Kohn-Sham energy values. Inclusion of electron-hol…
Electronic structures of SiC nanoribbons have been studied by spin-polarized density functional calculations. The armchair nanoribbons are nonmagnetic semiconductor, while the zigzag nanoribbons are magnetic metal. The spin polarization in zigzag SiC nanoribbons is originated from the unpaired electrons localized on the ribbon edges. Interestingly, the zigzag nanoribbons narrower than $\sim$4 nm present half-metallic behavior. Without the aid of external field or chemical modification, the metal-free half-metallicity predicted for narrow SiC zigzag nanoribbons opens a facile way for nanomateri…
Using ab initio calculations based on density-functional theory we have performed a theoretical investigation of substitutional boron and nitrogen impurities in silicon carbide (SiC) nanoribbons. We have considered hydrogen terminated SiC ribbons with zigzag and armchair edges. In both systems we verify that the boron and nitrogen atoms energetically prefer to be localized at the edges of the nanoribbons. However, while boron preferentially substitutes a silicon atom, nitrogen prefers to occupy a carbon site. In addition, our electronic-structure calculations indicate that (i) substitutional b…
We propose a natural way to create quantum-confined regions in graphene in a system that allows large-scale device integration. We show, using first-principles calculations, that a single graphene layer on a trenched region of $[000\bar{1}]$ $SiC$ mimics i)the energy bands around the Fermi level and ii) the magnetic properties of free-standing graphene nanoribbons. Depending on the trench direction, either zigzag or armchair nanoribbons are mimicked. This behavior occurs because a single graphene layer over a $SiC$ surface loses the graphene-like properties, which are restored solely over the …
We present a new method of producing a densely ordered array of epitaxial graphene nanoribbons (GNRs) using vicinal SiC surfaces as a template, which consist of ordered pairs of (0001) terraces and nanofacets. Controlled selective growth of graphene on approximately 10 nm wide of (0001) terraces with 10 nm spatial intervals allows GNR formation. By selecting the vicinal direction of SiC substrate, [1-100], 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 photoem…
Using ab-initio calculations based on density functional theory, we investigate the effects of vacancies on the electronic and magnetic properties of zigzag SiC nanoribbons (Z-SiCNR). Single (V_C and V_Si) and double (V_SiV_Si and V_SiV_C) vacancies are observed to induce magnetism in Z-SiCNRs. The presence of a single V_Si does not affect the half-metallic behavior of pristine Z-SiCNRs; however, a single V_C leads to a transition from half-metallic to metallic behavior in Z-SiCNRs due to the edge Si p orbitals and the atoms surrounding the vacancy. The interactions of vacancies with foreign i…
We present a minimal but crucial microscopic theory for epitaxial graphene and graphene nanoribbons on the 4H-SiC(0001) surface -- protopypical materials to explore physical properties of graphene in large scale. Coarse-grained model Hamiltonians are constructed based on the atomic and electronic structures of the systems from first-principles calculations. From the theory, we unambiguously uncover origins of several intriguing experimental observations such as broken-symmetry states around the Dirac points and new energy bands arising throughout the Brillouin zone, thereby establishing the ro…
We demonstrate that the confocal laser scanning microscopy (CLSM) provides a non-destructive, highly-efficient characterization method for large-area epitaxial graphene and graphene nanostructures on SiC substrates, which can be applied in ambient air without sample preparation and is insusceptible to surface charging or surface contamination. Based on the variation of reflected intensity from regions covered by interfacial layer, single layer, bilayer, or few layer graphene, and through the correlation to the results from Raman spectroscopy and SPM, CLSM images with a high resolution (around …
We present a study of mechanical, electronic and magnetic properties of two dimensional (2D), monolayer of silicon carbide (SiC) in honeycomb structure and its quasi 1D armchair nanoribbons using first-principles plane wave method. In order to reveal dimensionality effects, a brief study of 3D bulk and 1D atomic chain of SiC are also included. Calculated bond-lengths, cohesive energies, charge transfers and band gaps display a clear dimensionality effect. The stability analysis based on the calculation of phonon frequencies indicates that 2D SiC monolayer is stable in planar geometry. We found…
Three single-layer tetragonal silicon carbides (SiC), termed as T1,T2 and T3, are proposed by density functional theory (DFT) computations. Although the three structures have the same topological geometry, they show versatile electronic properties from semiconductor (T1), semimetal (T2) to metal (T3).The versatile properties are originated from the rich bonds between Si and C atoms. The nanoribbons of the three SiC also show interesting electronic properties. Especially, T1 nanoribbons possess exotic edge states, where electrons only distribute on one edge's silicon or carbon atoms. The band g…
We demonstrate the preparation of both armchair and zigzag epitaxial graphene nanoribbons (GNRs) on 4H-SiC using a polymer-assisted, sublimation growth method. Historically, the preparation of GNRs depended on the quality, or smoothness, of the surface changes during growth. The physical phenomenon of terrace step formation introduces the risk of GNR deformation along sidewalls, but the risk is heavily mitigated by this polymer-assisted sublimation method. Two widths (100 nm and 50 nm) are examined electrically and optically for both armchair and zigzag GNRs. Our electrical results support the…
Graphene electronics has motivated much of graphene science for the past decade. A primary goal was to develop high mobility semiconducting graphene with a band gap that is large enough for high performance applications. Graphene ribbons were thought to be semiconductors with these properties, however efforts to produce ribbons with useful bandgaps and high mobility has had limited success. We show here that high quality epitaxial graphene nanoribbons 40 nm in width, with annealed edges, grown on sidewall SiC are not semiconductors, but single channel room temperature ballistic conductors for …
Quantum spin Hall insulators have one-dimensional (1D) spin-momentum locked topological edge states (ES) inside the bulk band gap, which can serve as dissipationless channels for the practical applications in low consumption electronics and high performance spintronics. However, the clean and atomically sharp ES serving as ideal 1D conducting channels are still lack. Here, we report the formation of the quasi-1D Bi4I4 nanoribbons on the surface of Bi(111) with the support of the graphene-terminated 6H-SiC(0001) and the direct observations of the topological ES at the step edge by scanning tunn…
