Electrical transport and low-temperature scanning tunneling microscopy of microsoldered graphene

Using the recently developed technique of microsoldering, we perform a systematic transport study of the influence of PMMA on graphene flakes revealing a doping effect of up to 3.8x10^12 1/cm^2, but a negligible influence on mobility and gate voltage induced hysteresis. Moreover, we show that the microsoldered graphene is free of contamination and exhibits a very similar intrinsic rippling as has been found for lithographically contacted flakes. Finally, we demonstrate a current induced closing of the previously found phonon gap appearing in scanning tunneling spectroscopy experiments, strongly non-linear features at higher bias probably caused by vibrations of the flake and a B-field induced double peak attributed to the 0.Landau level of graphene.Comment: 8 pages, 3 figure

High On/Off Ratios in Bilayer Graphene Field Effect Transistors Realized by Surface Dopants

The unique property of bilayer graphene to show a band gap tunable by external electrical fields enables a variety of different device concepts with novel functionalities for electronic, optoelectronic and sensor applications. So far the operation of bilayer graphene based field effect transistors requires two individual gates to vary the channel's conductance and to create a band gap. In this paper we report on a method to increase the on/off ratio in single gated bilayer graphene field effect transistors by adsorbate doping. The adsorbate dopants on the upper side of the graphene establish a displacement field perpendicular to the graphene surface breaking the inversion symmetry of the two graphene layers. Low temperature measurements indicate, that the increased on/off ratio is caused by the opening of a mobility gap. Beside field effect transistors the presented approach can also be employed for other bilayer graphene based devices like photodetectors for THz to infrared radiation, chemical sensors and in more sophisticated structures such as antidot- or superlattices where an artificial potential landscape has to be created.Comment: 4 pages, 4 figure

Non-volatile switching in graphene field effect devices

The absence of a band gap in graphene restricts its straight forward application as a channel material in field effect transistors. In this letter, we report on a new approach to engineer a band gap in graphene field effect devices (FED) by controlled structural modification of the graphene channel itself. The conductance in the FEDs is switched between a conductive "on-state" to an insulating "off-state" with more than six orders of magnitude difference in conductance. Above a critical value of an electric field applied to the FED gate under certain environmental conditions, a chemical modification takes place to form insulating graphene derivatives. The effect can be reversed by electrical fields of opposite polarity or short current pulses to recover the initial state. These reversible switches could potentially be applied to non-volatile memories and novel neuromorphic processing concepts.Comment: 14 pages, 4 figures, submitted to IEEE ED