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Register a new userChemical doping-induced gap opening and spin polarization in graphene
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Added by
Antonio Gomes de Souza Filho
Publication date
2007
fields
Physics
and research's language is
English
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By using first principles calculations we report a chemical doping induced gap in graphene. The structural and electronic properties of CrO$_3$ interacting with graphene layer are calculated using ab initio methods based on the density functional theory. The CrO$_3$ acts as an electron acceptor modifying the original electronic and magnetic properties of the graphene surface through a chemical adsorption. The changes induced in the electronic properties are strongly dependent of the CrO$_3$ adsorption site and for some sites it is possible to open a gap in the electronic band structure. Spin polarization effects are also predicted for some adsorption configurations.
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Graphene grown on metal surface, Cu(111), with a boron nitride(BN) buffer layer is studied for the first time. Our first-principles calculations reveal that charge is transferred from the copper substrate to graphene through the BN buffer layer which results in a n-doped graphene in the absence of a gate voltage. More importantly, a gap of 0.2 eV which is comparable to that of a typical narrow gap semicondutor opens just 0.5 eV below the Fermi-level at the Dirac point. The Fermi-level can be easily shifted inside this gap to make graphene a semiconductor which is crucial for graphene-based electronic devices. A graphene based p-n junction can be realized with graphene eptaxially grown on metal surface.
Graphene has shown great application potentials as the host material for next generation electronic devices. However, despite its intriguing properties, one of the biggest hurdles for graphene to be useful as an electronic material is its lacking of an energy gap in the electronic spectra. This, for example, prevents the use of graphene in making transistors. Although several proposals have been made to open a gap in graphenes electronic spectra, they all require complex engineering of the graphene layer. Here we show that when graphene is epitaxially grown on the SiC substrate, a gap of ~ 0.26 is produced. This gap decreases as the sample thickness increases and eventually approaches zero when the number of layers exceeds four. We propose that the origin of this gap is the breaking of sublattice symmetry owing to the graphene-substrate interaction. We believe our results highlight a promising direction for band gap engineering of graphene.
Graphene has attracted increasing interests due to its remarkable properties, however, the zero band gap of monolayer graphene might limit its further electronic and optoelectronic applications. Herein, we have successfully synthesized monolayer silicon-doped graphene (SiG) in large area by chemical vapor deposition method. Raman spectroscopy and X-ray photoelectron spectroscopy measurements evidence silicon atoms are doped into graphene lattice with the doping level of 3.4 at%. The electrical measurement based on field effect transistor indicates that the band gap of graphene has been opened by silicon doping, which is around 0. 28 eV supported by the first-principle calculations, and the ultraviolet photoelectron spectroscopy demonstrates the work function of SiG is 0.13 eV larger than that of graphene. Moreover, the SiG/GaAs heterostructure solar cells show an improved power conversion efficiency of 33.7% in average than that of graphene/GaAs solar cells, which are attributed to the increased barrier height and improved interface quality. Our results suggest silicon doping can effectively engineer the band gap of monolayer graphene and SiG has great potential in optoelectronic device applications.
The phase diagram of isotropically expanded graphene cannot be correctly predicted by ignoring either electron correlations, or mobile carbons, or the effect of applied stress, as was done so far. We calculate the ground state enthalpy (not just energy) of strained graphene by an accurate off-lattice Quantum Monte Carlo (QMC) correlated ansatz of great variational flexibility. Following undistorted semimetallic graphene (SEM) at low strain, multi-determinant Heitler-London correlations stabilize between $simeq$8.5% and $simeq$15% strain an insulating Kekule-like dimerized (DIM) state. Closer to a crystallized resonating-valence bond than to a Peierls state, the DIM state prevails over the competing antiferromagnetic insulating (AFI) state favored by density-functional calculations which we conduct in parallel. The DIM stressed graphene insulator, whose gap is predicted to grow in excess of 1 eV before failure near 15% strain, is topological in nature, implying under certain conditions 1D metallic interface states lying in the bulk energy gap.
We report on the energy spectrum of electrons in twisted bilayer graphene (tBLG) obtained by the band-unfolding method in the tight-binding model. We find the band-gap opening at particular points in the reciprocal space, that elucidates the drastic reduction of the Fermi-level velocity with the tiny twisted angles in tBLGs. We find that Moir`e pattern caused by the twist of the two graphene layers generates interactions among Dirac cones, otherwise absent, and the resultant cone-cone interactions peculiar to each point in the reciprocal space causes the energy gap and thus reduced the Fermi-level velocity.
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