Self-assembled monolayers of aromatic molecules on copper substrates can be converted into high-quality single-layer graphene using low-energy electron irradiation and subsequent annealing. This two-dimensional solid state transformation is characterized on the atomic scale and the physical and chemical properties of the formed graphene sheets are studied by complementary microscopic and spectroscopic techniques and by electrical transport measurements. As substrates, Cu(111) single crystals and the technologically relevant polycrystalline copper foils are successfully used.

Non-destructive chemical functionalization of graphene for applications in electronic devices (e.g., sensors or transducers) is achieved via assembly of carbon nanomembrane (CNM)/single-layer graphene (SLG) van der Waals heterostructures. The CNMs are 1 nm-thick, dielectric molecular sheets terminated with functional amino groups. The structure and performance of heterostructured field-effect transistors (FETs) are characterized by photoelectron/Raman spectroscopy and by electric transport measurements in vacuum, ambient conditions and water.

We demonstrate a device concept to fabricate resistance standards made of quantum Hall series arrays by using p-type and n-type graphene. The ambipolar nature of graphene allows fabricating series quantum Hall resistors without complex multi-layer metal interconnect technology, which is required when using conventional GaAs two-dimensional electron systems. As a prerequisite for a precise resistance standard we confirm the vanishing of longitudinal resistance across a p-n junction for metrological relevant current levels in the range of a few microamperes.Graphene is an electronic material which, since its discovery in 2004, has triggered an avalanche of theoretical and experimental studies. 1 Its band structure gives rise to a number of fascinating properties, making it a promising material for next generation electronic devices. 2 Especially for electrical metrology graphene has unique advantages: since the quantum Hall effect persists up to room temperature, 3 and since the Landau level spacing in a small magnetic field B decreases only with the square root of B, graphene offers the exciting possibility of a resistance standard working at 4.2 K or higher, and in a magnetic field of only 1 or 2 Tesla. 4,5 In metrology the quantum Hall effect is used to realize a value of electrical resistance with relative measurement uncertainty of a few parts in 10 9 or better, typically employing GaAs based heterostructures hosting a 2-dimensional electron system (2DES). Parallel or series quantum Hall arrays could cover a wider resistance scale than just the singular value of 12.9 kΩ. Such quantum Hall arrays are technically feasible, but they are not used in practice, mainly due to the technical difficulties to produce arrays which reliably allow a low measurement uncertainty. Here we present a device concept which avoids these difficulties by exploiting the unique feature of graphene that it can support a 2-dimensional hole system (2DHS) as well as a 2-dimensional electron system in the same device. We support our concept by demonstrating that the prerequisite for a quantum Hall series resistance standard, the vanishing of longitudinal resistance across the series connection, is met even at the high current levels required in practice.The technique of connecting quantum Hall devices in series or in parallel, to obtain multiples or fractions of the resistance h/2e², was first demonstrated by Delahaye. 6 For the case of a series connection, the principle is illustrated in FIG. 1(a). Twice the value of the single-Hall-bar resistance R H = h/2e² is measured between terminals 5 and 5' because the voltage drop in the connection (2-2') is practically zero as can be shown by an equivalent circuit model of a quantum Hall device. 7 The model predicts that in Hall-bars with multiple inter-connections the current in each additional connection is smaller than in the preceding one by a factor ε/(ε+2) with ε = R c /R H , where R c is the interconnect resistance. When ε << 1, three interconnects between successive Hall bars already suffi...

We show that quantum resistance standards made of transferred graphene reach the uncertainty of semiconductor devices, the current reference system in metrology. A large graphene device (150 \times 30 \mum2), exfoliated and transferred onto GaAs, revealed a quantization with a precision of (-5.1 \pm 6.3) \times 10-9 accompanied by a vanishing longitudinal resistance at current levels exceeding 10 \muA. While such performance had previously only been achieved with epitaxially grown graphene, our experiments demonstrate that transfer steps, inevitable for exfoliated graphene or graphene grown by chemical vapor deposition (CVD), are compatible with the requirements of high quality quantum resistance standards

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