Vincent Meunier

Electronic and field emission properties of boron nitride/carbon nanotube superlattices

BN/C nanotube superlattices are quasi one-dimensional heterostructures that show unique physical properties derived from their peculiar geometry. Using state-of-the-art ab initio calculations, we show that BN/C systems can be used for effective band-offset nanodevice engineering, polarization-based devices, and robust field emitters with an efficiency enhanced by up to two orders of magnitude over carbon nanotube systems.

Single electron tunneling of nanoscale TiSi2 islands on Si

Nanoscale TiSi2 islands are formed by electron beam deposition of a few monolayers of titanium on an atomically clean silicon surface followed by in situ annealing at high temperatures (800–1000u200a°C). The lateral diameter of typical islands are ∼5 nm, and they form a nanoscale metal–semiconductor interface. Direct probing of the electrical characteristics of these islands on both p- and n-type Si substrates was performed using ultrahigh vacuum scanning tunneling microscopy and scanning tunneling spectroscopy. With the vacuum between the tip and the island as a second tunnel junction, we thus form a double-junction system for observation of single electron tunneling (SET) effects. Moreover, the small dimensions of the system allow room temperature observation. The results showed features in the I–V spectra attributed to single electron tunneling. Features were more evident when the island–Si junction was in reverse bias. For substrates with a thin epitaxial layer of intrinsic Si, the tunneling related featu...

Large-scale simulations of advanced materials and nanoscale devices

Recent advances in theoretical methods and parallel supercomputing allow for reliable ab initio simulations of the properties of complex materials. We describe two current applications: pyro- and piezoelectric properties of BN nanotubes and optical signatures of organic molecules on Si(001) surface. BN nanotubes turn out to be excellent piezoelectrics, with response values significantly greater than those of piezoelectric polymers. However, their symmetry leads to exact cancellation of the total spontaneous polarization in ideal, isolated nanotubes. Breaking of this symmetry induces spontaneous polarization comparable to those wurtzite semiconductors. Turning to organics on Si(100), we calculated the atomic structure and the optical signatures of a cyclopentene overlayer on Si(001). Cyclopentene can be used to attach a variety of organic molecules to Si devices, including DNA, and can therefore form a basis of a sensor structure. The spectra turn out to be highly structure-dependent and can therefore be used to monitor interface formation.

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.