Tunable Coulomb blockade in nanostructured graphene

Stampfer, Christoph; Güttinger, J.; Molitor, F.; Graf, David; Ihn, Thomas; Ensslin, Klaus

doi:10.1063/1.2827188

Cited by 280 publications

(289 citation statements)

References 22 publications

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“…For the detailed fabrication process and the * Corresponding author, e-mail: stampfer@phys.ethz.ch single-layer graphene verification we refer to Refs. [14,18,19]. Fig.…”

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confidence: 97%

Tunable Graphene Single Electron Transistor

et al. 2008

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We report electronic transport experiments on a graphene single electron transistor. The device consists of a graphene island connected to source and drain electrodes via two narrow graphene constrictions. It is electrostatically tunable by three lateral graphene gates and an additional back gate. The tunneling coupling is a strongly nonmonotonic function of gate voltage indicating the presence of localized states in the barriers. We investigate energy scales for the tunneling gap, the resonances in the constrictions and for the Coulomb blockade resonances. From Coulomb diamond measurements in different device configurations (i.e. barrier configurations) we extract a charging energy of ≈ 3.4 meV and estimate a characteristic energy scale for the constriction resonances of ≈ 10 meV. The recent discovery of graphene [1,2], filling the gap between quasi 1-dimensional (1-D) nanotubes and 3-D graphite makes truly 2-D crystals accessible and links solid state devices to molecular electronics [3]. Graphene, which exhibits unique electronic properties including massless carriers near the Fermi level and potentially weak spin orbit and hyperfine couplings [4,5] has been proposed to be a promising material for spin qubits [6], high mobility electronics [7,8] and it may have the potential to contribute to the downscaling of state-ofthe-art silicon technology [9]. The absence of an energy gap in 2-D graphene and phenomena related to Klein tunneling [10,11] make it hard to confine carriers electrostatically and to control transport on the level of single particles. However, by focusing on graphene nanoribbons, which are known to exhibit an effective transport gap [7,8,12,13] this limitation can be overcome. It has been shown recently that such a transport gap allows to fabricate well tunable graphene nanodevices [14,15,16]. Here we investigate a fully tunable single electron transistor (SET) that consists of a width modulated graphene structure exhibiting spatially separated transport gaps. SETs consist of a conducting island connected by tunneling barriers to two conducting leads. Electronic transport through the device can be blocked by Coulomb interaction for temperatures and bias voltages lower than the characteristic energy required to add an electron to the island [17]. The sample is fabricated based on single-layer graphene flakes obtained from mechanical exfoliation of bulk graphite. These flakes are deposited on a highly doped silicon substrate with a 295 nm silicon oxide layer [1]. Electron beam (e-beam) lithography is used for patterning the isolated graphene flake by subsequent Ar/O 2 reactive ion etching. Finally, an additional e-beam and lift-off step is performed to pattern Ti/Au (2 nm/50 nm) electrodes. For the detailed fabrication process and the * Corresponding author, e-mail: stampfer@phys.ethz.ch single-layer graphene verification we refer to Refs. [14,18,19]. Fig. 1a shows a scanning force micrograph of the investigated device. Both the metal electrodes and the graphene structure are highlighted. In Fig....

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“…For the detailed fabrication process and the * Corresponding author, e-mail: stampfer@phys.ethz.ch single-layer graphene verification we refer to Refs. [14,18,19]. Fig.…”

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Tunable Graphene Single Electron Transistor

et al. 2008

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“…In close analogy to single-layer graphene nanodevices we observe a region of suppressed current separating the hole (left inset) from the electron transport regime (right inset). This so-called transport gap [8], which extends for the investigated device from roughly 32 V to 48 V is expected to be mainly caused by the local tunneling barriers formed by the three 30 nm narrow constrictions (see illustration in Figure 1d) [14,17]. The reproducible sharp conductance resonances in and around the transport gap region are due to localized states in the constrictions whereas the overall hole-doping is most likely due to atmospheric O 2 binding [32].…”

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Electronic Excited States in Bilayer Graphene Double Quantum Dots

et al. 2011

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We report tunneling spectroscopy experiments on a bilayer graphene double quantum dot device that can be tuned by all-graphene lateral gates. The diameter of the two quantum dots are around 50 nm and the constrictions acting as tunneling barriers are 30 nm in width. The double quantum dot features addition energies on the order of 20 meV. Charge stability diagrams allow us to study the tunable interdot coupling energy as well as the spectrum of the electronic excited states on a number of individual triple points over a large energy range. The obtained constant level spacing of 1.75 meV over a wide energy range is in good agreement with the expected single-particle energy spacing in bilayer graphene quantum dots. Finally, we investigate the evolution of the electronic excited states in a parallel magnetic field.Keywords: graphene, bilayer graphene, quantum dot, double quantum dot, excited states Graphene quantum dots (QDs) are interesting candidates for spin qubits with long coherence times [1]. The suppressed hyperfine interaction and weak spin-orbit coupling [2, 3] make graphene and flat carbon structures in general, promising for future quantum information technology [4]. Significant progress has been made recently in the fabrication and understanding of graphene quantum devices. A "paper-cutting" technique enables the fabrication of graphene nanoribbons [5][6][7][8][9][10][11][12][13], quantum dots [14][15][16][17][18][19], and double quantum dot devices [20][21][22][23], where a disorder-induced energy gap allows confinement of individual carriers in graphene. These devices allowed the experimental investigation of excited states [16,21], spin states [19] and the electron-hole crossover [17]. However, all of these studies were based on single-layer graphene and showed a number of device limitations related to the presence of disorder, vibrational excitations and to the fact that the missing band gap makes it difficult to realize soft confinement potentials and "well-behaving" tunneling barriers. In particular, it has been shown that intrinsic ripples and corrugations in single-layer graphene can lead to unintended vibrational degrees of freedom [24] and to a coherent electron-vibron coupling in graphene QDs [25]. Bilayer graphene is a promising candidate to overcome some of these limitations. In particular it allows to open a band gap by an out-of-plane electric field [26][27][28], which may enable a soft confinement potential and may reduce the influence of localized edge states. More importantly, it has been shown that ripples and substrate-induced disorder are reduced in bilayer graphene [29], which increases the mechanical stability and suppresses unwanted vibrational modes.Here, we present a bilayer graphene double quantum dot (DQD) device, with a number of lateral gates. These local gates allow to tune transport from hole to electron dominated regimes and they enable to access different device configurations. We focus on the DQD configuration and show characteristic honeycomb-like charge stability dia...

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“…For instance, fabricating narrow constrictions in graphene layers is of interest for electronic property engineering. [15][16][17][18][19][20][21][22][23] Structures made by electron-beam irradiation are stable and do not evolve over time. Furthermore, we find that extensive removal of carbon does not introduce significant long-range distortions of the graphene sheet.…”

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Electron beam nanosculpting of suspended graphene sheets

Fischbein

Drndić

2008

Applied Physics Letters

559

450

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We demonstrate high-resolution modification of suspended multi-layer graphene sheets by controlled exposure to the focused electron beam of a transmission electron microscope. We show that this technique can be used to realize, on timescales of a few seconds, a variety of features, including nanometer-scale pores, slits, and gaps that are stable and do not evolve over time. Despite the extreme thinness of the suspended graphene sheets, extensive removal of material to produce the desired feature geometries is found to not introduce long-range distortion of the suspended sheet structure

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Tunable Coulomb blockade in nanostructured graphene

Cited by 280 publications

References 22 publications

Tunable Graphene Single Electron Transistor

Tunable Graphene Single Electron Transistor

Electronic Excited States in Bilayer Graphene Double Quantum Dots

Electron beam nanosculpting of suspended graphene sheets

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