Time: Sep 10th 10:00

Place:A429

1.Graphene Nanoribbons: Synthesis, Properties and Electronics

Xinran Wang

Stanford University, USA

 Abstract：Graphene nano-electronics has been very attractive due to

high carrier mobility. The semi-metallic nature of bulk graphene

requires width confinement down to ~sub-10nm in order to induce adequate

bandgap for room temperature logic applications. In this talk, I will

present our recent works on graphene (nanoribbon) electronics.

 First, we developed a unique chemical route to synthesize high

quality, ultra-smooth graphene nanoribbons (GNRs) with width below 10nm.

Transport measurements show that the bandgap scales inversely with GNR

widths, indicating that bandgap opens in narrow GNRs due to quantum

confinement. The first room temperature p-type graphene field-effect

transistor (FET) is demonstrated with our chemically derived sub-10nm

GNR.

 We next access the performance of chemically derived sub-10nm GNR

FETs. At on state, the current density could be as high as ~2000uA/um,

with on/off ratio ~ 106, subthreshold slope ~210mV/dec. The performance

of sub-10nm GNR FETs is comparable to small diameter (d<1.2nm) carbon

nanotube (CNT) FETs. The intrinsic carrier mobility and scattering mean

free path is ~200cm2/Vs and ~10nm, respectively. We discuss the possible

scattering mechanisms in the GNRs.

 Compared to CNTs, GNRs have open edges with high chemical reactivity.

We can take advantage of this fact and chemically modify the GNR edges

to change the electronic properties. We found that individual GNRs could

be covalently functionalized by nitrogen species through high-power

electrical joule heating in NH3 gas, leading to n-type electronic doping

consistent with theory. The formation of C-N bond occurs mostly at the

edges of graphene where chemical reactivity is high. We fabricated an n-

type N-doped graphene field-effect transistor (FET) that operates at

room temperature.

2.Ripple texturing of suspended graphene atomic membranes

 Wenzhong Bao

 University of California, Riverside

 Abstract： We investigate one-dimensional (1D) and 2D periodic ripples

in suspended graphene sheets, using spontaneously and thermally induced

longitudinal strains on patterned substrates. By in-situ SEM imaging, we

provide the first measurement of graphene’s thermal expansion

coefficient, which is anomalously large and negative, ~-7x10-6 K-1 at

300K. Latest progress towards transport measurement in these devices

will be discussed