Molecular Electronics researches the innovative use of molecules as sensors and device elements. This requires an understanding of the mechanisms that influence current conduction at the molecular level, including the role of contacts and aspects of self assembly. We have tried to understand how orientation, packing and order in the self assembled monolayer (SAM) affect current transport through it. This movie shows atomic resolution images of alkanethiol and molecular wire SAMs obtained with a scanning tunneling microscope and their current-voltage behavior. Our research has shown that reducing the fluctuations and dynamics in the monolayer by ensuring an ordered packing of the molecules is crucial for reliable transport measurements. Our research also highlights the fact that molecular electronic devices have to be made tolerant to such stochastic variations inherently present in these soft systems.Reference: Geetha R Dholakia, Wendy Fan, Jessica Koehne, Jie Han and M. Meyyappan, “Transport in self-assembled molecular wires: Effect of packing and order”, Phys. Rev. B, Vol. 69, p.153402 (2004).

The branching networks in biological dendritic neural trees provide signal switching and processing operations at the locations of the branching. A similar concept, therefore can be proposed to fabricate branching networks similar to dendritic neurons, but made of single- or multi-wall branched carbon nanotube networks. For example, here we show a model of a 4-level dendrictic neural tree that has been made of 14 carbon nanotube Y-junctions, or networks with single branching. The Y junctions at each level of branching are shown in a single color. The contribution of a single Y-junction to a complex branching network, as indicated by the blue highlighted structure, is shown here. Recently, such single Y-junctions have been fabricated at various laboratories within the United States and abroad. Our quantum conductance simulations show that they have robust ballistic switching and rectification behavior. In the future, artificial nanoscale dendritic trees made of carbon nanotubes, could be grown in experiments that would serve as biomimetic models of computing architecture base on dendritic neurons in a biological system.

Design and operation of a carbon nanotube based - nanoscale - gear is shown in several videoclips. The gearshaft is a carbon nanaotube which may be just 1 to 10 nanometers in diameter. Benzyne molecules (as teeth) are attached to carbon nanotubes (shafts) to form gears that can operate at GHz frequencies. The early clips show how to attach a benzyne molecule to a buckyball or buckytube. The later clips in this sequence show how the gear rotates. Our theoretical investigations of the structure and operationg conditions of such machines show that the gear is very robust and can operate under adverse conditions such as slipping, conditions in which an ordinary macro-scale gear would fall apart. Computer simulations also show that nanogears, or other machines, in the future could be powered through lasers or externally controlled electric fields.

Though when we first designed this and showed its opeartion through computer simulations, we were not sure if anyone can actually attach molecules to the side of a nanotube or how difficult a job it would be. But recently, research groups have succeeded in attaching atoms and molecules to nanotubes. This is promising. We believe then a gear of this type can actually be made in the lab.

For further reading:

J. Han, A. Globus, R. Jaffe and Glenn Deardorff, "Molecular Dynamics Simulation of Carbon Nanotube Based Gears", Nanotechnology, Vol. 8, pp. 95-102 (1997).

D. Srivastava,"A Phenomenological Model of the Rotation Dynamics of Carbon Nanotube Gears with Laser Electric Fields", Nanotechnology, Vol. 8, pp. 186-192 (1997).

Carbon nanotube based, and other nanodesigned materials are expected to provide extraordinarily strong but light-weight composites for future structural applications. To realize these applications, we first need to know a lot more about these materials: especially, how strong is this nanotube? How stiff ? What happens if you bend it ? Twist it ? Stretch it ? Compress it ? To answer these, we have done computer simulations. Video clips show single-wall and multi-wall nanotubes undergoing axial compression, bending and torsional twisting. Simulations and experiments have shown that single-wall nanotubes are strongest known fiber so far and can withstand 10-50 times more deformation before they break. Simulations also show that nanotubes under extreme deformation remain elastic to a large extent.For further reading:D. Srivastava, M. Menon and K. Cho, "Nano-plasticity of Single-wall Carbon Nanotubes Under Uniaxial Compression" Physical Review Letters, Vol. 83 (15), pp. 2973-2976 (1999).Contributors: Deepak Srivastava and Steve Barnard

A carbon nanotube can be used as a tip in an atomic force microscope (AFM).Such a tip in an AFM can be used to create nanoscale patterns i.e. nanolithograpghy or to etch material away from a surface in the fabrication of semiconductor chips(i.e. the tip acts like a " nanotweezer " to remove atoms from the surface).

In the above scenerios, one is then concerned with the interaction between the carbon nanotube tip and a surface. We look at two kinds of surfaces: silicon and diamond. The videoclips show real-time dynamics of interaction between carbon nanotube tips and silicon and diamond surfaces. Two interaction regimes are considered: etching (the nanotube barely touches the surface) and indentation (the nanotube is pushed into the surface to make "nano-holes"). Computer simulations show that in the first regime the nanotube tip is able to selectively extract several silicon atoms off the surface of silicon, and in the second regime it is able to penetrate the silicon surface without much hindrance. That is, the nanotube tip does a good job of both a " nanotweezer " and a " nano hole-puncher " with silicon. But with diamond, the harder diamond surface destroys the nanotube.