Ultrapure multilayer graphene in bromine-intercalated graphite (original) (raw)
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Supermetallic conductivity in bromine-intercalated graphite
Exposure of highly oriented pyrolytic graphite to bromine vapor gives rise to in-plane charge conductivities which increase monotonically with intercalation time toward values ͑for ϳ6 at % Br͒ that are significantly higher than Cu at temperatures down to 5 K. Magnetotransport, optical reflectivity and magnetic susceptibility measurements confirm that the Br dopes the graphene sheets with holes while simultaneously increasing the interplanar separation. The high-room-temperature mobility ͑ϳ5 ϫ 10 4 cm 2 / V·s͒ and resistance anisotropy together with the reduced diamagnetic susceptibility of the intercalated samples suggests that the observed supermetallic conductivity derives from a parallel combination of weakly coupled hole-doped graphene sheets.
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The electronic and optical properties of monolayer and bilayer graphene are investigated to verify the effects of interlayer interactions and external magnetic field. Monolayer graphene exhibits linear bands in the low-energy region. Then the interlayer interactions in bilayers change these bands into two pairs of parabolic bands, where the lower pair is slightly overlapped and the occupied states are asymmetric with respect to the unoccupied ones. The characteristics of zero-field electronic structures are directly reflected in the Landau levels. In monolayer and bilayer graphene, these levels can be classified into one and two groups, respectively. With respect to the optical transitions between the Landau levels, bilayer graphene possesses much richer spectral features in comparison with monolayers, such as four kinds of absorption channels and double-peaked absorption lines. The explicit wave functions can further elucidate the frequency-dependent absorption rates and the comple...
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For full reference please see: Phys. Rev. B 83, 045411, 2011 We present a density functional theory study of low density bromination of graphene and graphite, finding significantly different behaviour in these two materials. On graphene we find a new Br2 form where the molecule sits perpendicular to the graphene sheet with an extremely strong molecular dipole. The resultant Br + -Br − has an empty pz-orbital located in the graphene electronic π-cloud. Bromination opens a small (86meV) band gap and strongly dopes the graphene. In contrast, in graphite we find Br2 is most stable parallel to the carbon layers with a slightly weaker associated charge transfer and no molecular dipole. We identify a minimum stable Br2 concentration in graphite, finding low density bromination to be endothermic. Graphene may be a useful substrate for stabilising normally unstable transient molecular states. PACS numbers: 31.15.A-73.22.Pr 81.05.uf 37.30.+i
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The linear and nonlinear optical susceptibilities of bilayer pristine graphene (BLPG) and H 2 S single molecule adsorbed at three different sites on a single graphene sheet of BLPG are calculated to obtain further insight into the electronic properties. Calculations show that the adsorption of H 2 S on the bridge and top sites open a gap around the Fermi level, while adsorption of H 2 S on the hollow site closes the energy gap, resulting in significant changes in the linear and nonlinear optical susceptibilities. This is attributed to the fact that the adsorbed H 2 S onto a single graphene sheet of BLPG cause significant changes in the electronic structure. The calculated linear optical susceptibilities show a huge anisotropy confirming that the graphene has unusual and interesting optical properties. We find that the absorption spectrum of graphene is quite flat extending from 300-2500 nm with an absorption peak in the UV region (∼270 nm), which is in excellent agreement with the experimental data. The pristine graphene shows a strong saturable absorption because of a large absorption and Pauli blocking. We have calculated the nonlinear optical susceptibilities of BLPG and the three configurations and found that they possess a huge second harmonic generation. We have also calculated the microscopic hyperpolarizability, ijk , for BLPG.
Electronic transport properties monitored by selective functionalization in Bernal bilayer graphene
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Jouda Jemaa Khabthani, ∗ Ahmed Missaoui, 3, † Didier Mayou, ‡ and Guy Trambly de Laissardière § Laboratoire de Physique de la Matière Condensée, Département de Physique, Faculté des Sciences de Tunis, Université de Tunis El Manar, Campus universitaire 1060 Tunis, Tunisia Laboratoire de Spectroscopie Atomique Moléculaire et Applications, Département de Physique, Faculté des Sciences de Tunis, Université de Tunis El Manar, Campus universitaire 1060 Tunis, Tunisia Laboratoire de Physique Théorique et Modélisation, CY Cergy Paris Université, CNRS, 95302 Cergy-Pontoise, France Univ. Grenoble Alpes, Inst NEEL, F-38042 Grenoble, France CNRS, Inst NEEL, F-38042 Grenoble, France (Dated: May 7, 2021)
Georgakilas/Functionalization Of Graphene, 2014
Carbon takes its name from the latin word carbo meaning charcoal. This element is unique in that its unique electronic structure allows for hybridization to build up sp 3 , sp 2 , and sp networks and, hence, to form more known stable allotropes than any other element. The most common allotropic form of carbon is graphite which is an abundant natural mineral and together with diamond has been known since antiquity. Graphite consists of sp 2 hybridized carbon atomic layers which are stacked together by weak van der Waals forces. The single layers of carbon atoms tightly packed into a two-dimensional (2D) honeycomb crystal lattice is called graphene. This name was introduced by Boehm, Setton, and Stumpp in 1994 [1]. Graphite exhibits a remarkable anisotropic behavior with respect to thermal and electrical conductivity. It is highly conductive in the direction parallel to the graphene layers because of the in-plane metallic character, whereas it exhibits poor conductivity in the direction perpendicular to the layers because of the weak van der Waals interactions between them [2]. The carbon atoms in the graphene layer form three σ bonds with neighboring carbon atoms by overlapping of sp 2 orbitals while the remaining p z orbitals overlap to form a band of filled π orbitals-the valence band-and a band of empty π* orbitals-the conduction band-which are responsible for the high in-plane conductivity. The interplanar spacing of graphite amounts to 0.34 nm and is not big enough to host organic molecules/ions or other inorganic species. However several intercalation strategies have been applied to enlarge the interlayer galleries of graphite from 0.34 nm to higher values, which can reach more than 1 nm in some cases, depending on the size of the guest species. Since the first intercalation of potassium in graphite, a plethora of chemical species have been tested to construct what are known as graphite intercalation compounds (GICs). The inserted species are stabilized between the graphene layers through ionic or polar interactions without influencing the graphene structure. Such compounds can be formed not only with lithium, potassium, sodium, and other alkali metals, but also with anions such as nitrate, bisulfate, or halogens.
Determination of the electronic structure of bilayer graphene from infrared spectroscopy
Physical Review B, 2008
We present an experimental study of the infrared conductivity, transmission, and reflection of a gated bilayer graphene and their theoretical analysis within the Slonczewski-Weiss-McClure ͑SWMc͒ model. The infrared response is shown to be governed by the interplay of the interband and the intraband transitions among the four bands of the bilayer. The position of the main conductivity peak at the charge-neutrality point is determined by the interlayer tunneling frequency. The shift of this peak as a function of the gate voltage gives information about less known parameters of the SWMc model such as those responsible for the electron-hole and sublattice asymmetries. These parameter values are shown to be consistent with recent electronic structure calculations for the bilayer graphene and the SWMc parameters commonly used for the bulk graphite.
Functionalizing Single- and Multi-layer Graphene with Br and Br 2
The Journal of Physical Chemistry C, 2010
The structural and electronic properties of Br 2 /Br adsorption and intercalation of single-layer graphene (SLG) and multi-layer graphene (MLG) are studied by density-functional theory. As a result of charge transfer, the Br atom is found to be stable as adsorbed on the vertex or near bridge sites of graphene whereas the Br 2 molecule will be more stable when adsorbed perpendicularly on graphene. Because of the interactions between Br 2 molecules, the stable configurations of Br 2 on graphene or intercalated in MLG are parallel to graphene. With the analysis of charge difference, the experimental observation that the lowest stage of Br 2 intercalated graphite is the stage 2 compound is ascribed to the effect of localized dipoles on graphene induced by Br 2 . Although only slightly disturbing the orbitals of graphene atoms, the existence of Br 2 molecules or Br atoms will still affect the electronic structures of both materials. As adsorbed on the single surface of graphene, Br 2 will open its bandgap at the K (K′) point. While present on both surfaces, Br 2 molecules will induce a much larger bandgap of graphene with the Fermi level shifted down into the valence bands. If Br atoms are absorbed on graphene, the significant amount of charge will transfer from graphene to Br atoms because of the strong electronegativity of Br. More importantly, the electronic properties of SLG/MLG with the absorbed Br 2 molecules can be controlled by the ultraviolet light that decomposes the Br 2 on SLG/MLG.