Showing papers by "Hang Zhang published in 2011"

Aryl functionalization as a route to band gap engineering in single layer graphene devices.

Abstract: Chemical functionalization is a promising route to band gap engineering of graphene. We chemically grafted nitrophenyl groups onto exfoliated single-layer graphene sheets in the form of substrate-supported or free-standing films. Our transport measurements demonstrate that nonsuspended functionalized graphene behaves as a granular metal, with variable range hopping transport and a mobility gap ∼0.1 eV at low temperature. For suspended graphene that allows functionalization on both surfaces, we demonstrate tuning of its electronic properties from a granular metal to a semiconductor in which transport occurs via thermal activation over a transport gap ∼80 meV from 4 to 300 K. This noninvasive and scalable functionalization technique paves the way for CMOS-compatible band gap engineering of graphene electronic devices.

Suspension and measurement of graphene and Bi2Se3 thin crystals.

Abstract: Coupling high-quality suspended atomic membranes to specialized electrodes enables the investigation of many novel phenomena, such as spin or Cooper pair transport in these two-dimensional systems. However, many electrode materials are not stable in the acids that are used to dissolve underlying substrates. Here we present a versatile and powerful multilevel lithographical technique to suspend thin crystals, which can be applied to the vast majority of substrate, crystal and electrode materials. Using this technique, we fabricated suspended graphene devices with Al electrodes and a mobility of 5500 cm(2) V(-1) s(-1). We also demonstrate, for the first time, fabrication and measurement of a free-standing thin Bi(2)Se(3) crystal, which has low contact resistance to electrodes and a mobility of approximately > 580 cm(2) V(-1) s(-1).

Magnetoconductance Oscillations in High-Mobility Suspended Bilayer and Trilayer Graphene

Abstract: We report pronounced magnetoconductance oscillations observed on suspended bilayer and trilayer graphene devices with mobilities up to 270,000 cm/Vs. For bilayer devices, we observe conductance minima at all integer filling factors ν between 0 and -8, as well as a small plateau at ν=1/3. For trilayer devices, we observe features at ν=-1, -2, -3 and -4, and at ν~0.5 that persist to 4.5K at B=8T. All of these features persist for all accessible values of Vg and B, and could suggest the onset of symmetry breaking of the first few Landau (LL) levels and fractional quantum Hall states.