Ab initio investigation of the electronic properties of graphene on InAs(111)A
05 Dec 2012-Journal of Physics: Condensed Matter (IOP Publishing)-Vol. 24, Iss: 48, pp 485004-485004
TL;DR: There is a re-distribution of the charge density around the graphene sheet, which leads to the development of a dipole moment along the surface normal, and scanning tunnelling microscopy images suggest that the InAs(111) substrate is visible through the graphene layer.
Abstract: The equilibrium geometry and electronic structure of graphene on the most stable In-vacancy InAs(111)A surface has been investigated using the density functional and pseudopotential theories. The equilibrium distance between graphene and InAs(111) is found to be 3.05 A with adsorption energy approximately 38 meV/C atom. According to our electronic band calculation, there is a re-distribution of the charge density around the graphene sheet, which leads to the development of a dipole moment along the surface normal. Scanning tunnelling microscopy image simulations suggest that the InAs(111) substrate is visible through the graphene layer.
01 Feb 2012
TL;DR: In this paper, the authors show that the inclusion of the many-body collective response of the substrate electrons inside the inorganic bulk enables them to reliably predict the HIOS geometries and energies.
Abstract: The electronic properties and the function of hybrid inorganic-organic systems (HIOS) are intimately linked to their interface geometry. Here we show that the inclusion of the many-body collective response of the substrate electrons inside the inorganic bulk enables us to reliably predict the HIOS geometries and energies. This is achieved by the combination of dispersion-corrected density-functional theory (the DFTþ van der Waals approach) [Phys. Rev. Lett. 102, 073005 (2009)], with the Lifshitz-Zaremba-Kohn theory for the nonlocal Coulomb screening within the bulk. Our method yields geometries in remarkable agreement (� 0:1 � A) with normal incidence x-ray standing wave measurements for the 3, 4, 9, 10-perylene-tetracarboxylic acid dianhydride (C24O6H8, PTCDA) molecule on Cu(111), Ag(111), and Au(111) surfaces. Similarly accurate results are obtained for xenon and benzene adsorbed on metal surfaces.
TL;DR: In this article, the properties of pristine, free-standing graphene monolayers prepared by mechanical exfoliation of graphite are investigated by means of spatially resolved Raman spectroscopy of the G-, D-, and 2D-phonon modes.
Abstract: The properties of pristine, free-standing graphene monolayers prepared by mechanical exfoliation of graphite are investigated. The graphene monolayers, suspended over open trenches, are examined by means of spatially resolved Raman spectroscopy of the G-, D-, and 2D-phonon modes. The G-mode phonons exhibit reduced energies (1580 cm-1) and increased widths (14 cm-1) compared to the response of graphene monolayers supported on the SiO2 covered substrate. From analysis of the G-mode Raman spectra, we deduce that the free-standing graphene monolayers are essentially undoped, with an upper bound of 2x10^11 cm-2 for the residual carrier concentration. On the supported regions, significantly higher and spatially inhomogeneous doping is observed. The free-standing graphene monolayers show little local disorder, based on the very weak Raman D-mode response. The two-phonon 2D mode of the free-standing graphene monolayers is downshifted in frequency compared to that of the supported region of the samples and exhibits a narrowed, positively skewed line shape.
TL;DR: In this paper, the authors investigated the electronic and optical properties of two heterostructures, namely, graphene/InAs and MoS2/INAs, and found that the interfacial structure, coupling, and transfer charges are crucial to enhance the electronic properties and optical adsorption of the two materials.
Abstract: Vertical heterostructures of two-dimensional materials have recently emerged as a promising application in designing novel electronic and optoelectronic devices. By using first principles methods, we investigated the electronic and optical properties of two heterostructures, graphene/InAs and MoS2/InAs. The results reveal that the interfacial structure, coupling, and transfer charges are crucial to enhance the electronic properties and optical adsorption of heterostructures. We found obvious electron–hole pair separation and an in-built polarized electric field at the interface in graphene/InAs heterostructures. In particular, the strong interface electronic coupling opens a 15 meV band gap in graphene after the adsorption on an InAs slab substrate. Benefiting from the interfacial coupling and transfer charge, the optical properties of graphene/InAs heterostructures are slightly enhanced compared to those of isolated composites of heterostructures. Remarkably, MoS2/InAs heterostructures were found to have a larger redistribution of charge, a smaller interlayer distance, and a stronger interfacial interaction than graphene/InAs heterostructures. The calculated optical absorption of MoS2/InAs heterostructures shows more significant absorption properties in the visible region than that of graphene/InAs heterostructures. The mechanisms to understand these phenomena are suggested.
TL;DR: In this paper, the authors investigated the electronic and transport properties of InAs/graphene heterostructures by using both ab initio electronic calculations and quantum transport simulations.
Abstract: Vertical heterostructures of two-dimensional (2D) materials are excellent candidates for designing next-generation electronic devices with superior performance. By using both ab initio electronic calculations and quantum transport simulations, we investigated the electronic and transport properties of InAs/graphene heterostructure. The results reveal that electrons and holes accumulate at different layers after the adsorption of InAs layer, forming the built-in electronic field at the interface. The electrostatic potential energy of InAs layer is higher than that of graphene, and it favors more electrons transferring from InAs to graphene layer. Comparing the comment methods by introducing impurity and carriers' injection, rectifying and negative differential resistance behaviors can also be realized by the combined effects of electron-hole distribution, interfacial hybridization, and contact barrier in InAs/graphene heterostructure device. It shows that the rectifying ration gradually increases with bias voltage, and the negative differential resistance effect happens at either positive or at negative bias voltage regions. Electrostatic potential distribution and contact barrier play important roles in determining transport properties. Increasing interfacial hybridization is helpful for transmission enhancement in the weak interlayer interaction van der Waals heterostructure.
TL;DR: In this article, the pseudo-van der Waals epitaxy (vdWE) growth parameter space for heterogeneous integration of InAs nanowires (NWs) with continuous films of single layer graphene via metalorganic chemical vapor deposition (MOCVD) is investigated.
Abstract: Heterogeneous self-assembly of III–V nanostructures on inert two-dimensional monolayer materials enables novel hybrid nanosystems with unique properties that can be exploited for low-cost and low-weight flexible optoelectronic and nanoelectronic device applications. Here, the pseudo-van der Waals epitaxy (vdWE) growth parameter space for heterogeneous integration of InAs nanowires (NWs) with continuous films of single layer graphene (SLG) via metalorganic chemical vapor deposition (MOCVD) is investigated. The length, diameter, and number density of NWs, as well as areal coverage of parasitic islands, are quantified as functions of key growth variables including growth temperature, V/III ratio, and total flow rate of metalorganic and hydride precursors. A compromise between self-assembly of high aspect ratio NWs comprising high number density arrays and simultaneous minimization of parasitic growth coverage is reached under a selected set of optimal growth conditions. Exploration of NW crystal structures formed under various growth conditions reveals that a characteristic polytypic and disordered lattice is invariant within the explored parameter space. A growth evolution study reveals a gradual reduction in both axial and radial growth rates within the explored timeframe for the optimal growth conditions, which is attributed to a supply-limited competitive growth regime. Two strategies are introduced for further growth optimization. Firstly, it is shown that the absence of a pre-growth in situ arsine surface treatment results in a reduction of parasitic island coverage by factor of ∼0.62, while NW aspect ratio and number densities are simultaneously enhanced. Secondly, the use of a two-step flow-modulated growth procedure allows for realization of dense fields of high aspect ratio InAs NWs. As a result of the applied studies and optimization of the growth parameter space, the highest reported axial growth rate of 840 nm min−1 and NW number density of ∼8.3 × 108 cm−2 for vdWE of high aspect ratio (>80) InAs NW arrays on graphitic surfaces are achieved. This work is intended to serve as a guide for vdWE of self-assembled III–V semiconductor NWs such as In-based ternary and quaternary alloys on functional two-dimensional monolayer materials, toward device applications in flexible optoelectronics and tandem-junction photovoltaics.
TL;DR: Monocrystalline graphitic films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands and they exhibit a strong ambipolar electric field effect.
Abstract: We describe monocrystalline graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are found to be a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar electric field effect such that electrons and holes in concentrations up to 10 13 per square centimeter and with room-temperature mobilities of ∼10,000 square centimeters per volt-second can be induced by applying gate voltage.
TL;DR: In this article, a method for generating sets of special points in the Brillouin zone which provides an efficient means of integrating periodic functions of the wave vector is given, where the integration can be over the entire zone or over specified portions thereof.
Abstract: A method is given for generating sets of special points in the Brillouin zone which provides an efficient means of integrating periodic functions of the wave vector. The integration can be over the entire Brillouin zone or over specified portions thereof. This method also has applications in spectral and density-of-state calculations. The relationships to the Chadi-Cohen and Gilat-Raubenheimer methods are indicated.
TL;DR: Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena can now be mimicked and tested in table-top experiments.
Abstract: Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.
TL;DR: A new density functional of the generalized gradient approximation (GGA) type for general chemistry applications termed B97‐D is proposed, based on Becke's power‐series ansatz from 1997, and is explicitly parameterized by including damped atom‐pairwise dispersion corrections of the form C6 · R−6.
Abstract: A new density functional (DF) of the generalized gradient approximation (GGA) type for general chemistry applications termed B97-D is proposed. It is based on Becke's power-series ansatz from 1997 and is explicitly parameterized by including damped atom-pairwise dispersion corrections of the form C(6) x R(-6). A general computational scheme for the parameters used in this correction has been established and parameters for elements up to xenon and a scaling factor for the dispersion part for several common density functionals (BLYP, PBE, TPSS, B3LYP) are reported. The new functional is tested in comparison with other GGAs and the B3LYP hybrid functional on standard thermochemical benchmark sets, for 40 noncovalently bound complexes, including large stacked aromatic molecules and group II element clusters, and for the computation of molecular geometries. Further cross-validation tests were performed for organometallic reactions and other difficult problems for standard functionals. In summary, it is found that B97-D belongs to one of the most accurate general purpose GGAs, reaching, for example for the G97/2 set of heat of formations, a mean absolute deviation of only 3.8 kcal mol(-1). The performance for noncovalently bound systems including many pure van der Waals complexes is exceptionally good, reaching on the average CCSD(T) accuracy. The basic strategy in the development to restrict the density functional description to shorter electron correlation lengths scales and to describe situations with medium to large interatomic distances by damped C(6) x R(-6) terms seems to be very successful, as demonstrated for some notoriously difficult reactions. As an example, for the isomerization of larger branched to linear alkanes, B97-D is the only DF available that yields the right sign for the energy difference. From a practical point of view, the new functional seems to be quite robust and it is thus suggested as an efficient and accurate quantum chemical method for large systems where dispersion forces are of general importance.
TL;DR: This study reports an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation and reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions.
Abstract: Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrodinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.