Pages

September 28, 2008

Nanotechnology roundup: Graphene production and Copying Electric eel cells for implantable batteries

1. Two independent teams have shown that it is possible to produce stable suspensions of single-layer graphene from graphite crystals using chemical techniques.

2. A numerical model of a cell from the electric eel shows that artificial cells can be built to have higher power output densities and greater energy conversion efficiencies than natural cells, allowing them to potentially power medical implants and other devices.

Designing artificial cells to harness the biological ion concentration gradient
Jian Xu & David A. Lavan

Cell membranes contain numerous nanoscale conductors in the form of ion channels and ion pumps that work together to form ion concentration gradients across the membrane to trigger the release of an action potential. It seems natural to ask if artificial cells can be built to use ion transport as effectively as natural cells. Here we report a mathematical calculation of the conversion of ion concentration gradients into action potentials across different nanoscale conductors in a model electrogenic cell (electrocyte) of an electric eel. Using the parameters extracted from the numerical model, we designed an artificial cell based on an optimized selection of conductors. The resulting cell is similar to the electrocyte but has higher power output density and greater energy conversion efficiency. We suggest methods for producing these artificial cells that could potentially be used to power medical implants and other tiny devices.






3. Graphene devices: The first observation of saturating transistor characteristics in a graphene field–effect transistor is reported, demonstrating the feasibility of graphene devices for analogue and radio–frequency circuit applications without the need for bandgap engineering.

Current saturation in zero-bandgap, top-gated graphene field-effect transistors
Inanc Meric, Melinda Y. Han, Andrea F. Young, Barbaros Ozyilmaz, Philip Kim & Kenneth L. Shepard

The novel electronic properties of graphene including a linear energy dispersion relation and purely two-dimensional structure, have led to intense research into possible applications of this material in nanoscale devices. Here we report the first observation of saturating transistor characteristics in a graphene field-effect transistor. The saturation velocity depends on the charge-carrier concentration and we attribute this to scattering by interfacial phonons in the SiO2 layer supporting the graphene channels. Unusual features in the current–voltage characteristic are explained by a field-effect model and diffusive carrier transport in the presence of a singular point in the density of states. The electrostatic modulation of the channel through an efficiently coupled top gate yields transconductances as high as 150 microS microm-1 despite low on–off current ratios. These results demonstrate the feasibility of two-dimensional graphene devices for analogue and radio-frequency circuit applications without the need for bandgap engineering.

blog comments powered by Disqus