Raman Evidence for Pressure-Induced Formation of Diamondene
Total Page：16
File Type：pdf, Size：1020Kb
Raman evidence for pressure-induced formation of diamondene The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Martins, Luiz Gustavo Pimenta et al. “Raman Evidence for Pressure- Induced Formation of Diamondene.” Nature Communications 8, 1 (July 2017) © 2017 The Author(s) As Published http://dx.doi.org/10.1038/S41467-017-00149-8 Publisher Nature Publishing Group Version Final published version Citable link http://hdl.handle.net/1721.1/113640 Terms of Use Creative Commons Attribution 4.0 International License Detailed Terms https://creativecommons.org/licenses/by/4.0/ ARTICLE DOI: 10.1038/s41467-017-00149-8 OPEN Raman evidence for pressure-induced formation of diamondene Luiz Gustavo Pimenta Martins1,7, Matheus J.S. Matos 2, Alexandre R. Paschoal3, Paulo T.C. Freire3, Nadia F. Andrade4, Acrísio L. Aguiar5, Jing Kong6, Bernardo R.A. Neves 1, Alan B. de Oliveira2, Mário S.C. Mazzoni1, Antonio G. Souza Filho3 & Luiz Gustavo Cançado1 Despite the advanced stage of diamond thin-film technology, with applications ranging from superconductivity to biosensing, the realization of a stable and atomically thick two-dimensional diamond material, named here as diamondene, is still forthcoming. Adding to the outstanding properties of its bulk and thin-film counterparts, diamondene is predicted to be a ferromagnetic semiconductor with spin polarized bands. Here, we provide spectro- scopic evidence for the formation of diamondene by performing Raman spectroscopy of double-layer graphene under high pressure. The results are explained in terms of a break- down in the Kohn anomaly associated with the finite size of the remaining graphene sites surrounded by the diamondene matrix. Ab initio calculations and molecular dynamics simulations are employed to clarify the mechanism of diamondene formation, which requires two or more layers of graphene subjected to high pressures in the presence of specific chemical groups such as hydroxyl groups or hydrogens. 1 Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, MG 30123-970, Brazil. 2 Departamento de Física, Universidade Federal de Ouro Preto, Ouro Preto, MG 35400-000, Brazil. 3 Departamento de Física, Universidade Federal do Ceará, Fortaleza, CE 60455-900, Brazil. 4 Instituto Federal de Educação, Ciência e Tecnologia do Ceará, Tianguá, CE 62320-000, Brazil. 5 Departamento de Física, Universidade Federal do Piauí, Teresina, PI 64049-550, Brazil. 6 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. 7Present address: Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA. Correspondence and requests for materials should be addressed to L.G.C. (email: cancado@fisica.ufmg.br) NATURE COMMUNICATIONS | 8: 96 | DOI: 10.1038/s41467-017-00149-8 | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/s41467-017-00149-8 – iamond is the hardest and least compressible material1 3 have monitored the charge injection into mono- and bi-layer as well as the best bulk heat conductor4. In addition, it is graphene with increasing tip-force interaction and different water D 5 22 chemically inert , highly refractive at optical wavelengths, contents on the graphene surface . and transparent to ultraviolet6. Unlike graphite, another bulk Here we provide spectroscopic evidence of the formation of carbon allotrope that can easily exfoliate due to its layered such a 2D-diamond structure, which we shall denote as hexagonal structure7, 8, diamond does not present a stable diamondene, by performing Raman spectroscopy of double-layer two-dimensional (2D) counterpart to date, and this is mostly due graphene under high pressure conditions using water as the to its tetrahedral structure. Nevertheless, many of the outstanding pressure transmission medium (PTM). The results are explained physical properties of graphene (the 2D version of graphite) in terms of a breakdown in the Kohn anomaly associated with the rely on its dimensionality7, 9 the same as with other 2D materi- finite size of remaining sp2 sites inside the rehybridized 2D als10, such as phosphorene11, silicene12, 13, 2D transition metal matrix. Ab initio calculations and molecular dynamics (MD) dichalcogenides14, and 2D transition metal carbides or nitrides15. simulations are employed to clarify the formation mechanism in Given the technological advances in the diamond thin-film pro- the present experimental conditions tested. Additional experi- – duction and applications5, 16 21 the systematic realization of an ments performed in single-layer graphene using water as PTM, atomically thin 2D diamond structure is highly desirable. and also in double-layer graphene using mineral oil as PTM A first step was recently given by Barboza et al.,22 who pro- indicate that the pressure-induced formation of diamondene is posed and provided experimental evidence for the existence of a drastically favored by the stacking of two or more layers of 2D diamond crystal formed when two or more layers of graphene graphene surrounded by specific chemical groups such as are subjected to high pressures in the presence of chemical hydroxyl groups and hydrogens. groups. With the assumption that the chemical groups are hydroxyl radicals, the compound was named diamondol, and was characterized as a 2D ferromagnetic semiconductor with spin Results polarized bands22. These unique properties, which arise from Raman analysis. Figure 1a shows the schematic of the experi- the periodic array of dangling bonds at the bottom layer, make mental setup. The sample was placed into a diamond anvil cell diamondol a promising candidate for spintronics. Thus far, the (DAC) capable of operating up to ≈15 GPa. The details about the existence of this 2D rehybridized carbon material has been experimental conditions are provided in the Methods section. demonstrated by electric force microscopy experiments, which Figure 1b shows the evolution of the first-order Raman-allowed a bc1st run 2nd run 0 GPa 0 GPa 2.7 GPa Spectrometer/ Focusing 3.0 GPa CCD lens 5.9 GPa 6.1 GPa 11.0 GPa decrease 10.2 GPa P Longpass decrease 12.5 GPa P filter 13.4 GPa 11.6 GPa Incident 12.4 GPa 11.1 GPa laser beam Scattered field 11.9 GPa 10.4 GPa 10.9 GPa 9.5 GPa Dichroic 10.3 GPa 9.4 GPa mirror 8.8 GPa 9.7 GPa 8.4 GPa 9.2 GPa 8.0 GPa 8.8 GPa 7.0 GPa Objective 7.9 GPa 6.5 GPa lens units) Intensity (arb. units) Intensity (arb. 7.2 GPa 5.1 GPa 6.6 GPa 3.7 GPa 6.2 GPa 2.7 GPa 5.4 GPa 2.2 GPa increase Diamond increase 1.8 GPa P Gasket 4.8 GPa P anvil Teflon substrate 4.3 GPa 1.4 GPa 3.4 GPa 1.0 GPa Ruby 2.8 GPa 0.7 GPa crystal Sample 0.3 GPa 1.4 GPa PTM 0 GPa 0 GPa Graphene 1550 1600 1650 1700 1750 1550 1600 1650 1700 1750 Raman shift (cm-1) Raman shift (cm-1) Fig. 1 Experimental setup and Raman spectra. a Schematic of the experimental setup. The sample was placed into a diamond anvil cell (DAC) capable of operating up to ≈15 GPa. The details about the experimental conditions are provided in the Methods section. b, c Evolution of the G band with increasing pressure (up to ≈14 GPa) using water as PTM. The respective applied pressure is indicated on the right side of each respective spectrum. The sample used in this experiment was a double-layer graphene transferred to a Teflon substrate (G/G/T). Two spectra are shown for each pressure level, one obtained with an excitation laser energy EL = 2.33 eV (green symbols), and the other with EL = 2.54 eV (blue symbols). The solid lines are Voigt fit to the experimental data. All intensities were normalized to show approximately the same peak height. The data shown in (b) and (c) were obtained in two distinct measurement runs (first and second, respectively), performed in two distinct G/G/T samples 2 NATURE COMMUNICATIONS | 8: 96 | DOI: 10.1038/s41467-017-00149-8 | www.nature.com/naturecommunications NATURE COMMUNICATIONS | DOI: 10.1038/s41467-017-00149-8 ARTICLE bond-stretching G band with increasing pressure (up to ≃14 GPa) conducted on graphite indicate that this material undergoes a − using water as PTM. Due to the superposition of the D (~1350 cm 1) phase transition for pressure values between 10–20 GPa, turning − and 2D (~2700 cm 1) bands with the first- and second-order into a diamond-like material in which sp2 and sp3 hybridizations – bond-stretching peaks of diamond, respectively, the G band was coexist28 30. This sp2/sp3 mixed phase has been confirmed the only clearly observable Raman feature from graphene in the through other experimental techniques, such as inelastic X-ray high-pressure experiments. The sample used in this experiment scattering31, optical transmittance32, and electrical resistivity33. was a double-layer chemical vapor deposition (CVD)-grown Several theoretical models have been proposed to explain these – graphene transferred to a Teflon substrate (G/G/T)23. It should be experimental findings28, 31, 34 37, and the general consensus is noted that what we call double-layer graphene is, in fact, a that this diamond-like phase originates from the formation of structure formed by the deposition of a single layer of graphene sp3 bonds, favored by the enhanced interlayer interaction induced on top of another single layer of graphene. This is different from by high pressure. High-pressure Raman experiments were also – the traditional bilayer graphene with AB stacking. conducted in mono- and few-layer graphene samples26, 27, 38 40 Two spectra are shown in Fig. 1b for each pressure level, and a phase transformation has been observed in graphene = 38 one obtained with an excitation laser energy EL 2.33 eV nanoplates at 15 GPa .