Transport measurements on an etched graphene nanoribbon are presented. It is shown that two distinct voltage scales can be experimentally extracted that characterize the parameter region of suppressed conductance at low charge density in the ribbon. One of them is related to the charging energy of localized states, the other to the strength of the disorder potential. The lever arms of gates vary by up to 30% for different localized states which must therefore be spread in position along the ribbon. A single-electron transistor is used to prove the addition of individual electrons to the localized states. In our sample the characteristic charging energy is of the order of 10 meV, the characteristic strength of the disorder potential of the order of 100 meV.PACS numbers: 71.15. Mb, 78.30Na, 81.05.Uw, 63.20.Kr Graphene nanoribbons [1,2,3,4,5] and narrow graphene constrictions [6,7,8] display unique electronic properties based on truly two-dimensional (2D) graphene [9] with potential applications in nanoelectronics [10] and spintronics [11]. Quasi-1D graphene nanoribbons and constrictions are of interest due to the presence of an effective energy gap, overcoming the gap-less band structure of graphene and leading to overall semiconducting behavior, most promising for the fabrication of nanoscale graphene transistors [5], tunnel barriers, and quantum dots [6,7,8]. On the other hand, ideal graphene nanoribbons [12,13] promise interesting quasi-1D physics with strong relations to carbon nanotubes [14]. Zonefolding approximations [13], π-orbital tight-binding models [15,16], and first principle calculations [17,18] predict an energy gap E g scaling as E g = α/W with the nanoribbon width W , where α ranges between 0.2-1.5 eV×nm, depending on the model and the crystallographic orientation of the nanoribbon [4]. However, these theoretical estimates can neither explain the experimentally observed energy gaps of etched nanoribbons of widths beyond 20 nm, which turn out to be larger than predicted, nor do they explain the large number of resonances found inside the gap [1,2,8]. This has led to the suggestion that localized states (and interactions effects) due to edge roughness, bond contractions at the edges [20] and disorder may dominate the transport gap. Several mechanisms have been proposed to describe the observed gap, including re-normalized lateral confinement [2], quasi-1D Anderson localization [21], percolation models [22] and many-body effects (incl. quantum dots) [19], where substantial edge disorder is required. Recently, it has been shown that also moderate amounts of edge roughness can substantially suppress the linear conductance near the charge neutrality point [23], giving rise to localized states relevant for both single particle and many-body descriptions.In this paper we show experimental evidence that the transport gap in an etched graphene nanoribbon (see schematic in Fig. 1a) is primarily formed by local resonances and quantum dots along the ribbon. We employ lateral graphene gates to show that size...

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We performed radiofrequency (RF) reflectometry measurements at 2−4 GHz on electrolyte-gated graphene field-effect transistors (GFETs) utilizing a tunable stub-matching circuit for impedance matching. We demonstrate that the gate voltage dependent RF resistivity of graphene can be deduced even in the presence of the electrolyte which is in direct contact with the graphene layer.The RF resistivity is found to be consistent with its DC counterpart in the full gate voltage range. Furthermore, in order to access the potential of high-frequency sensing for applications, we demonstrate time-dependent gating in solution with nanosecond time resolution. PACS numbers: 73.61.Cw, 73.40.Mr 1 arXiv:1401.0381v1 [cond-mat.mes-hall] 2 Jan 2014Owing to its atomically thin structure and exceptional high mobilities, 1-3 graphene is potentially well suited to radiofrequency (RF) applications. This prospect is reinforced by the relative openness of the RF-electronics industry to new materials without the requirement of a high on/off current ratio, which limits the application of graphene for digital applications. 4 Much of the research conducted so far on graphene RF transistors has focused on the cut-off frequency, f T , which is the highest frequency at which a field-effect transistor (FET) is useful in RF applications. 5-10 For instance, graphene FETs (GFETs) with an intrinsic cut-off frequency of f T = 100 − 300 GHz have been demonstrated, 6,8 which are superior to the best silicon MOSFETs with similar gate lengths. Graphene full-wave rectification and consequently frequency conversion with high efficiency have also been demonstrated by making use of the ambipolar conduction properties. 11,12 The cyclotron motion of the charge carriers of graphene in a magnetic field suggests further applications in non-reciprocal components. 13,14 Moreover, the microwave properties of graphene antennas and transmission line have also been investigated. 15,16 Recently, there is also growing interest in applying graphene RF transistors to biochemical sensing applications. 17,18 But in spite of the rapid advances in recent years, our understanding of the RF properties of graphene, especially with regards to sensing in a liquid environment, is still incomplete. Although it is known that atomically thin large area graphene behaves as a wideband resistor due to negligible skin effect and kinetic inductance, 19 it is difficult to measure the device resistance directly at RF. This is due to the large shunt capacitance in conventional back or top-gated graphene RF transistors having a significant influence on the RF performance, hindering (if not preventing) the extraction of the intrinsic parameters of graphene.In contrast to conventional oxide based back or top gating, electrolyte gating can be used to tune the properties of GFETs without shunting the propagating RF signal. This is because of the unique frequency dependent properties of the electrolyte. At DC and relatively low frequency 10 MHz the ions in the electrolyte can instantly respond to ...

Incorporating a variable capacitance diode into a radio-frequency matching circuit allows us to in-situ tune the resonance frequency of an RF quantum point contact, increasing the versatility of the latter as a fast charge sensor of a proximal quantum circuit. The performance of this method is compared in detail to conventional low-frequency charge detection. The approach is also applicable to other RF-detection schemes, such as RF-SET circuits.

In situ-tunable radio-frequency charge detection is used for the determination of the tunneling rates into and out of a graphene single quantum dot connected to only one lead. An analytical model for calculating these rates in the multi-level tunneling regime is presented and found to correspond very well to our experimental observations.