Brian Larade

I-V characteristics and differential conductance fluctuations of Au nanowires

Electronic transport properties of the Au nanostructure are investigated using both experimental and theoretical analysis. Experimentally, stable Au nanowires were created using a mechanically controllable break junction in air, and simultaneous current-voltage (I-V) and differential conductance δI/δV data were measured. The atomic device scale structures are mechanically very stable up to bias voltage V b ∼0.6 V and have a lifetime of a few minutes. Facilitated by a shape function data analysis technique which finger prints electronic properties of the atomic device, our data show clearly differential conductance fluctuations with an amplitude > 1 % at room temperature and a nonlinear I-V characteristics. To understand the transport features of these atomic scale conductors, we carried out ah initio calculations on various Au atomic wires. The theoretical results demonstrate that transport properties of these systems crucially depend on the electronic properties of the scattering region, the leads, and most importantly the interaction of the scattering region with the leads. For ideal, clean Au contacts, the theoretical results indicate a linear I-V behavior for bias voltage V b <0.5 V. When sulfur impurities exist at the contact junction, nonlinear I-V curves emerge due to a tunneling barrier established in the presence of the S atom. The most striking observation is that even a single S atom can cause a qualitative change of the I-V curve from linear to nonlinear. A quantitatively favorable comparison between experimental data and theoretical results is obtained. We also report other results concerning quantum transport through Au atomic contacts.

Current-triggered vibrational excitation in single-molecule transistors

Abstract We investigate the possibility of inducing nuclear dynamics in single-molecule devices via inelastic, resonance-mediated tunneling current. Our method is based on the combination of a theory of current-triggered dynamics in molecular heterojunctions and a nonequilibrium Greens function approach of computing electron transport properties. The scheme is applied to study current-induced dynamics in single-molecule Au–C 60 –Au transistors.

Ab Intio Simulations of Quatum Transport: Si Clusters and Fullerene Chains

The I-V characteristics of small Si n clusters and short C 20 chains between atomistic Al leads were calculated using a new ab initio transport code based on a nonequilibrium Greens function formalism. All of the Si diaplay metallic I-V characteristics with typical conductances ranging between tow and three (units G o = 2e 2 /h). The transport properties of these molecular devices may be understood in terms of both the bandstructure ofelectrodes, and the molecular levels of the clusters as modified by the lead environment. Turning to the short C 20 chains, these behave as short C 20 chains, these behave as short nanowires whose tranmission depends sensitively on the orientation and distance between the individual C 20 molecules. Transport through the molecular chains is accompained by a significant amount of charge transfer, which however remains localized at the electrode/molecular interface.