The ultimate aim of any detection method is to achieve such a level of sensitivity that individual quanta of a measured entity can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity. The fundamental reason limiting the resolution of such sensors is fluctuations due to thermal motion of charges and defects, which lead to intrinsic noise exceeding the sought-after signal from individual molecules, usually by many orders of magnitude. Here, we show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphene's surface. The adsorbed molecules change the local carrier concentration in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chemical detectors but also for other applications where local probes sensitive to external charge, magnetic field or mechanical strain are required.

Microfabrication of graphene devices used in many experimental studies currently relies on the fact that graphene crystallites can be visualized using optical microscopy if prepared on top of silicon wafers with a certain thickness of silicon dioxide. We study graphene's visibility and show that it depends strongly on both thickness of silicon dioxide and light wavelength. We have found that by using monochromatic illumination, graphene can be isolated for any silicon dioxide thickness, albeit 300 nm (the current standard) and, especially, approx. 100 nm are most suitable for its visual detection. By using a Fresnel-law-based model, we quantitatively describe the experimental data without any fitting parameters.Comment: Since v1: minor changes to text and figures to improve clarity; references added. Submitted to Applied Physics Letters, 30-Apr-07. 3 pages, 3 figure

The exceptional electronic properties of graphene and its formidable potential in various applications have ensured a rapid growth of interest in this new material [1,2]. One of the most discussed and tantalizing directions in research on graphene is its use as the base material for electronic circuitry that is envisaged to consist of nanometer-sized elements. Most attention has so far been focused on graphene nanoribbons (see [3][4][5][6][7][8][9] and references therein). In this Letter, we report quantum dot (QD) devices made entirely from graphene, including their central islands (CI), quantum barriers, source and drain contacts and side-gate electrodes. We have found three basic operational regimes for such devices, depending on their size. For relatively large (submicron) CIs, size quantization plays an insignificant role, and our devices were found to operate as orthodox singleelectron transistors (SET) exhibiting periodic Coulomb blockade (CB) oscillations. The CB regime has been extensively studied previously using metallic and semiconducting materials [10,11] and, more recently, the first SET devices made from graphite [12] and graphene [1,13,14] were also demonstrated. The all-graphene SETs reported here are technologically simple, reliable and robust and can operate above liquid-helium temperatures T, which makes them attractive candidates for use in various charge-detector schemes [10]. For intermediate CI sizes (less than ∼100nm), we enter into the quantum regime, in which the confinement energy δE >10meV exceeds the charging energy E c . Such a strong quantization for relatively modest confinement is unique to massless fermions [1,2] and related to the fact that their typical level spacing δE ≈v F h/2D in a quantum box of size D is much larger than the corresponding energy scale ≈h 2 /8mD 2 for massive carriers in other materials (v F ≈10 6 m/s is the Fermi velocity in graphene, h the Planck constant and m the effective mass). This means that level splitting in graphene-based 100-nm devices should be tens and hundreds times larger than in typical semiconducting and metal QDs, respectively. This regime is probably most interesting from the fundamental physics point of view, allowing studies of relativistic-like quantum effects in confined geometries [15][16][17][18][19][20][21]. In particular, we have observed a strong level repulsion in QDs, which is a clear signature of quantum chaos (so-called "neutrino billiards" [15]). Conductance of our smallest devices is dominated by individual constrictions with sizes down to ∼1nm, which exhibit δE ∼0.5eV and a good-quality transistor action at room T. It is remarkable that these molecular-scale structures survive microfabrication procedures, remain mechanically and chemically stable and highly conductive under ambient conditions and sustain large (nA) currents. Our devices were made from graphene crystallites prepared by micromechanical cleavage on top of an oxidized Si wafer (300nm of SiO 2 ) [22]. By using high-resolution electron-beam lithography, we de...

Graphene is only one atom thick, optically transparent, chemically inert, and an excellent conductor. These properties seem to make this material an excellent candidate for applications in various photonic devices that require conducting but transparent thin films. In this letter, we demonstrate liquid crystal devices with electrodes made of graphene that show excellent performance with a high contrast ratio. We also discuss the advantages of graphene compared to conventionally used metal oxides in terms of low resistivity, high transparency and chemical stability.