Evidence for formation of multi-quantum dots in hydrogenated graphene
© Chuang et al.; licensee Springer. 2012
Received: 26 June 2012
Accepted: 10 August 2012
Published: 16 August 2012
We report the experimental evidence for the formation of multi-quantum dots in a hydrogenated single-layer graphene flake. The existence of multi-quantum dots is supported by the low-temperature measurements on a field effect transistor structure device. The resulting Coulomb blockade diamonds shown in the color scale plot together with the number of Coulomb peaks exhibit the characteristics of the so-called ‘stochastic Coulomb blockade’. A possible explanation for the formation of the multi-quantum dots, which is not observed in pristine graphene to date, was attributed to the impurities and defects unintentionally decorated on a single-layer graphene flake which was not treated with the thermal annealing process. Graphene multi-quantum dots developed around impurities and defect sites during the hydrogen plasma exposure process.
KeywordsMulti-quantum dots Single-layer graphene flake Coulomb peaks
Graphene, a mono-layer of carbon atoms arranged in a honeycomb lattice, has extraordinary electrical properties, such as the gapless linear dispersion[1–4]. In order to realize graphene-based nanoelectronic device applications, many research groups tried to open the energy bandgap in the gapless linear dispersion in different ways, for instance, graphene nanoribbons[5, 6] and bilayer graphene applied by the electric field[7–9]. Recently, hydrogenated graphene attracts a great deal of attention because of its bandgap behavior driven by the chemical functionalization[10–17]. The adsorbed atomic hydrogen atoms form three-dimensional C-H sp3 covalent bonds with carbon atoms by interrupting C-C sp2 bonds, thus, removing the conducting π bonds and opening a bandgap[11, 18, 19]. In 2010, Singh and co-workers proposed that graphane could form natural host for graphene multi-quantum dots, clusters of vacancies in hydrogen sublattice. According to the surface dynamics, thermally energetic hydrogen atoms adsorbed on graphene could be desorbed from the graphene surface or migrate to the proper bonding sites or nucleate randomly (due to short diffusion length) to form dense islands of coexisting two-dimensional phases, C-H and C-C[14, 20, 21]. On the other hand, some reports proposed that the multi-quantum dots were unintentionally formed by impurities or defects in single-wall carbon nanotubes, which belong to the same honeycomb lattice as single-layer graphene[22–24].
In this study, we propose a possible explanation based on the aforementioned mechanism for the formation of multi-quantum dots on our single-layer graphene flake and supported by the low-temperature electrical transport measurements.
An Oxford top-loading He4 cryostat was used to carry out the two-terminal conductance measurements using standard AC lock-in technique at 77 Hz with a DC bias at the temperature range between 1.3 and 40 K.
Results and discussion
Figure 1a shows the source-drain current (ISD) dependence on the back gate voltage (VBG) measured at the charge neutrality point, VNP = 74 V, with a fixed source-drain voltage VSD = 0.1 mV at T = 1.32 K before the hydrogen plasma treatment. The charge neutrality point, which is far from the zero voltage, can be attributed to the hole-doping impurities left on the graphene flake[27, 28]. Figure 1b shows the ISDVBG measurement after hydrogen plasma treatment. Strong suppression of the source-drain current in the Coulomb blockade oscillation region (between the dashed lines) with a fixed source-drain voltage VSD = 20 mV at T = 1.41 K is observed. To assure the Coulomb peaks in the Coulomb blockade oscillation region, we examined the Coulomb peaks with a fixed VSD = 1 mV at T = 1.32 K shown in the inset to Figure 1b. To further investigate the Coulomb blockade effect, the Coulomb blockade color scale plot of the conductance G in a VBGVSD plane was adopted for a better illustration of the existence of multi-quantum dots in our graphene flake sample; overlapped diamond-shape pattern was expected.
Two-dimensional multi-quantum dots can be realized on a mechanically exfoliated graphene flake followed by the hydrogen plasma treatment without executing post-exfoliation thermal annealing. The overlapped Coulomb blockade diamonds observed from the electrical measurements, as well as the monotonic increase of the number of Coulomb peaks with the ascending temperature, suggest the formation of two-dimensional multi-quantum dots that is unprecedented on the annealed graphene flakes with similar hydrogenation processes. Therefore, we suggest a defect (or vacancy) and impurity-related mechanism to account for the formation of the multi-quantum dots discovered on our device. Further characterizations, such as AFM or SEM, on the atomic structure of un-annealed graphene layers might shed light on the origin of the quantum dot formation, whereas the degree of post-growth annealing could be utilized to engineer the quantum dots in terms of its size, density, shape, or charging states in a cost-effective way for quantum chip device applications.
CC obtained his B.Sc. degree in Physics at NCUE in 2006 and M.Sc. degree in Physics at NTNU in 2009. He is currently pursuing his Ph.D. degree in Physics at NTU. RKP is currently pursuing his Ph.D. degree at the Cavendish Laboratory, University of Cambridge. MRC is currently a postdoctoral research worker at the Cavendish Laboratory, University of Cambridge. STL obtained his B.Sc. degree at NTU in 2010 and is pursuing his Ph.D. degree at the Graduate Institute of Applied Physics, NTU. He won the Dr. An-Tai Chen Scholarship, Mr. Ming Kao Scholarship, and college students participating in special research project of Creative Award provided by the NSC in 2009. HDL obtained his B.S. degree at Chinese Culture University, Taiwan and his Ph.D. degree at Mississippi State University, USA, and currently works as a project engineer at Electronics Testing Center, Tao-Yuan, Taiwan (R.O.C). TMC obtained his B.Sc. degree and M.Sc. degree at NTU, Taiwan and obtained his Ph.D. degree at Cambridge University, UK. He is currently an assistant professor at the Department of Physics, NCKU. CGS obtained his Ph.D. degree at Cambridge University, UK and is currently a professor of Physics at Cambridge University, UK. CTL obtained his B.Sc. degree at NTU in 1990 and his Ph.D. degree in Physics at Cambridge University, UK in 1996 and is currently a professor of Physics at NTU. He is also a topical editor for Current Applied Physics.
This work was funded by the Initiative Research Cooperation among top universities between UK and Taiwan (grant no.: NSC 99-2911-I-002-126), the NSC (grant no: NSC 101-2923-M-002-003-MY3), and National Taiwan University (grant no: 101R7552-2). CC, TMC, and CTL would like to thank the hospitality of the Semiconductor Physics Group, Cavendish Laboratory. CTL thanks Tina Liang, Valen Liang, and Eva Liang for their support.
- Geim AK, Novoselov KS: The rise of graphene. Nat Mate 2007, 6: 183.View Article
- Castro Neto AH, Guinea F, Peres NMR, Novoselov KS, Geim AK: The electronic properties of graphene. Rev Mod Phys 2009, 81: 109. 10.1103/RevModPhys.81.109View Article
- Zhao S, Lv Y, Yang X: Layer-dependent nanoscale electrical properties of graphene studied by conductive scanning probe microscopy. Nano Res Letts 2011, 6: 498. 10.1186/1556-276X-6-498View Article
- Ishikawa R, Bando M, Morimoto Y, Sandhu A: Doping graphene films via chemically mediated charge transfer. Nano Res Letts 2011, 6: 111. 10.1186/1556-276X-6-111View Article
- Han MY, Özyilmaz B, Zhang Y, Kim P: Energy band-gap engineering of graphene nanoribbons. Phys Rev Lett 2007, 98: 206805.View Article
- Son Y-W, Cohen ML, Louie SG: Energy gaps in graphene nanoribbons. Phys Rev Lett 2006, 97: 216803.View Article
- Castro EV, Novoselov KS, Morozov SV, Peres NMR, Santos JMB L, Nilsson J, Guinea F, Geim AK, Castro Neto AH: Biased bilayer graphene: semiconductor with a gap tunable by the electric field effect. Phys Rev Lett 2007, 99: 216802.View Article
- Ohta T, Bostwick A, Seyller T, Horn K, Rotenberg E: Controlling the electronic structure of bilayer graphene. Science 2006, 313: 951. 10.1126/science.1130681View Article
- Oostinga JB, Heersche HB, Liu X, Morpurgo AF, Vandersypen LMK: Gate-induced insulating state in bilayer graphene devices. Nature 2008, 7: 151. 10.1038/nmat2082View Article
- Elias DC, Nair RR, Mohiuddin TMG, Morozov SV, Blake P, Halsall MP, Ferrari AC, Boukhvalov DW, Katsnelson MI, Geim AK, Novoselov KS: Control of graphene's properties by reversible hydrogenation: evidence for graphane. Science 2009, 323: 610. 10.1126/science.1167130View Article
- Sofo JO, Chaudhari AS, Barber GD: Graphane: a two-dimensional hydrocarbon. Phys Rev B 2007, 75: 153401.View Article
- Boukhvalov DW, Katsnelson MI: Chemical functionalization of graphene. J Phys Condens Matter 2009, 21: 344205. 10.1088/0953-8984/21/34/344205View Article
- Ryu S, Han YM, Maultzsch J, Heninz TF, Kim P, Steigerwald ML, Brus LE: Reversible basal plane hydrogenation of graphene. Nano Lett 2008, 8: 4597. 10.1021/nl802940sView Article
- Balog R, JØrgensen B, Nilsson L, Andersen M, Rienks E, Bianchi M, Fanetti M, Lægsgaard E, Baraldi A, Lizzit S, Sljivancanin Z, Besenbacher F, Hammer B, Pedersen TG, Hofmann P, Hornekær L: Bandgap opening in graphene induced by patterned hydrogen adsorption. Nat Mater 2010, 9: 315. 10.1038/nmat2710View Article
- Dikin DA, Stankovich S, Zimney EJ, Piner RD, Dommett GHB, Evmenenko G, Nguyen ST, Ruoff RS: Preparation and characterization of graphene oxide paper. Nature 2007, 448: 457. 10.1038/nature06016View Article
- Park S, Ruoff RS: Chemical methods for the production of graphenes. Nat Nanotechnol 2009, 4: 217. 10.1038/nnano.2009.58View Article
- Chuang C, Puddy RK, Lin H-D, Lo S-T, Chen T-M, Smith CG, Liang C-T: Experimental evidence for efros-shklovskii variable range hopping in hydrogenated graphene. Solid State Commun 2012, 152: 905. 10.1016/j.ssc.2012.02.002View Article
- Boukhvalov DW, Katsnelson MI, Lichtenstein AI: Hydrogen on graphene: electronic structure, total energy, structural distortions and magnetism from first-principles calculations. Phys Rev B 2008, 77: 035427.View Article
- Withers F, Russo S, Dubois M, Craciun MF: Tuning the electronic transport properties of graphene through functionalisation with fluorine. Nano Res Letts 2011, 6: 526. 10.1186/1556-276X-6-526View Article
- Singh AK, Penev ES, Yakobson BI: Vacancy clusters in graphane as quantum dots. ACS Nano 2010, 4: 3510. 10.1021/nn1006072View Article
- Luth H: Surface and Interfaces of Solid Materials. New York: Springer Press; 1995.View Article
- Suzuki M, Ishibashi M, Ida T, Aoyagi Y: Quantum dot formation in single-wall carbon nanotubes. Jpn J Appl Phys 1915, 2001: 40.
- McEuen PL, Bockrath M, Cobden DH, Yoon Y-G, Louie SG: Disorder, pseudospins, and backscattering in carbon nanotubes. Phys Rev Lett 1999, 83: 5098. 10.1103/PhysRevLett.83.5098View Article
- Zhou C, Kong J, Yenilmez E, Dai H: Modulated chemical doping of individual carbon nanotubes. Science 2000, 290: 1552.View Article
- Novoselov KS, Geim AK, Morozov SV, Jiang D, Zhang Y, Dubonos SV, Grigorieva IV, Firsov AA: Electric field effect in atomically thin carbon films. Science 2004, 306: 666. 10.1126/science.1102896View Article
- Luo Z, Yu T, Kim K-J, Ni Z, You Y, Lim S, Shen Z, Wang S, Lin J: Thickness-dependent reversible hydrogenation of graphene layers. ACS Nano 2009, 3: 1781. 10.1021/nn900371tView Article
- Ponomarenko LA, Yang R, Mohiuddin TM, Katsnelson MI, Novoselov KS, Morozov SV, Zhukov AA, Schedin F, Hill EW, Geim AK: Effect of a high-κ environment on charge carrier mobility in graphene. Phys Rev Lett 2009, 102: 206603.View Article
- Connolly MR, Chiou KL, Smith CG, Anderson D, Jones GAC, Lombardo A, Fasoli A, Ferrari AC: Scanning gate microscopy of current-annealed single layer graphene. Appl Phys Lett 2010, 96: 113501. 10.1063/1.3327829View Article
- Ponomarenko LA, Schedin F, Katsnelson MI, Yang R, Hill EW, Novoselov KS, Geim AK: Chaotic dirac billiard in graphene quantum dots. Science 2008, 320: 356. 10.1126/science.1154663View Article
- Nazarov YV, Blanter YM: Quantum Transport Introduction to Nanoscience. Cambridge: Cambridge University Press; 2009.View Article
- Ruzin IM, Chandrasekhar V, Levin EI, Glazman LI: Stochastic Coulomb blockade in a double-dot system. Phys Rev B 1992, 45: 13469. 10.1103/PhysRevB.45.13469View Article
- Kemerink M, Molenkamp LW: Stochastic Coulomb blockade in a double quantum dot. Appl Phys Lett 1994, 65: 1012. 10.1063/1.112209View Article
- Ishibashi K, Suzuki M, Ida T, Aoyagi Y: Formation of coupled quantum dots in single-wall carbon nanotubes. Appl Phys Lett 1864, 2001: 79.
- Notargiacomo A, Gaspare LD, Scappucci G, Mariottini G, Evangelisti F, Giovine E, Leoni R: Single-electron transistor based on modulation-doped SiGe heterostructures. Appl Phys Lett 2003, 83: 302. 10.1063/1.1592883View Article
- Guttinger J, Stampfer C, Fery T, Ihn T, Ensslin K: Transport through a strongly coupled graphene quantum dot in perpendicular magnetic field. Nano Res Letts 2011, 6: 253.View Article
- Liu XL, Hug D, Vandersypen MK: Gate-defined graphene double quantum dot and excited state spectroscopy. Nano Letts 2010, 10: 1623. 10.1021/nl9040912View Article
- Molitor F, Dröscher S, Güttinger J, Jacobsen A, Stamper C, Ihn T, Ensslin K: Transport through graphene double dots. Appl Phys Letts 2009, 94: 222107. 10.1063/1.3148367View Article
- Ishigami M, Chen JH, Cullen WG, Fuhrer MS, Williams EW: Atomic structure of graphene on SiO2. Nano Lett 2007, 7: 1643. 10.1021/nl070613aView Article
- Schedin F, Geim AK, Morozov SV, Hill EW, Blake P, Katsnelson MI, Novoselov KS: Detection of individual gas molecules adsorbed on graphene. Nat Mate 2007, 6: 652. 10.1038/nmat1967View Article
- Hashimoto A, Suenage K, Gloter A, Urita K, Iijima S: Direct evidence for atomic defects in graphene layers. Nature 2004, 430: 870. 10.1038/nature02817View Article
- Joung D, Zhai L, Khondaker SI: Coulomb blockade and hopping conduction in graphene quantum dots array. Phys Rev B 2011, 83: 115323.View Article
- Nielsen MA, Chuang IL: Quantum Computation and Quantum Information. Cambridge: Cambridge University Press; 2000.
- Loss D, DiVincenzo DP: Quantum computation with quantum dots. Phys Rev A 1998, 57: 120. 10.1103/PhysRevA.57.120View Article
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