Porous Material With Nanoholes Lead To Efficient Thermoelectric Devices

Scientists from the National Center for Scientific Research Demokritos in Athens, Greece have discovered that using materials filled with tiny holes can lead to the improvement of thermoelectrics as a viable alternative for harvesting wasted heat.

Porous materials (materials filled with holes) have a direct correlation to thermal conductivity. The more porous a material is, the lower the thermal conductivity. This results in a better thermoelectric material since there is lower heat dissipation/loss.

The also researchers found that the smaller the pores and the closer they're packed together, the lower the thermal conductivity. They also show that, in principle, micro-nano porous materials can be several times better at converting heat to electricity than if the material had no pores.

The image above, This is a schematic illustration of the multilayer configuration with layers of different porosity (graded porous material). Each layer contains a concentration of periodically distributed pores of the same size (only one set of such particles is shown). Image Credit: APL Materials

Thermoelectric Clathrate Material and the Kondo Effect Turns Industrial Waste Heat into Electricity

Clathrates: Tiny cages enclosing single atoms are shown.
Credit: TU Vienna

Researchers at the Vienna University of Technology (TU Vienna) have developed a material that can turn waste heat generated by machines into electricity using the Kondo effect and clathrates.

Researchers have designed a material that traps cesium atoms inside a lattice structure (clathrate). When the material is exposed to heat, the trapped atoms start vibrating within its lattice 'cage' and electricity is generated. This is due to the Kondo effect.

Named after Jun Kondo, a theoretical physicist from Japan, the Kondo effect describes how the electrical resistance of a metal increases when the temperature is lowered up to a certain point, known as the Kondo temperature.

The current research shows that the Kondo effect can also apply to very high temperatures.

What this means is that applications can be developed that will take advantage of waste heat produced by machines that can turn it into useful electrical energy rather than it being dissipated into the environment.

Heat Dissipation at the Atomic Level Studied Through Nanotechnology

Researchers at the University of Michigan are studying the effects of heat at the nanoscale; between atoms. This study will help in understanding how heat behaves in nanoscale systems.

Moore's Law states that the number of transistors on integrated circuits doubles approximately every two years. This equates to computing processing power doubling every two years. For the last 50 years, the trend in computers and electronics adheres to Moore's law but technological evolution is fast approaching to the limit of transistors that can fit into a single silicon chip.

At last count, the current record for most number of transistors put on a chip is 2 billion.

With circuit boards getting smaller and smaller, one factor that scientists and engineers look at is heat. As devices get smaller and smaller, the laws of thermodynamics particularly in heat transfer and heat dissipation gets complicated.

The UM researchers are looking at measuring this process at the nanoscale which is the behavior of heat between individual atoms. This study can help develop devices that are smaller, energy efficient, and faster than those currently available. This is a major hurdle for Moore's Law since technology is now going towards atomic scale nano-electronics.

Because of this, the International Technology Roadmap for Semiconductors in 2010 adjusted the law and changed the period from every two years to every three years.

MIT News: Bending Light To Cloak Objects Lead To Better Electron Transfer For Thermoelectric Devices

A new approach that allows objects to become “invisible” has now been applied to an entirely different area: letting particles “hide” from passing electrons, which could lead to more efficient thermoelectric devices and new kinds of electronics.

Diagram shows the 'probability flux' of electrons, a representation of the paths of electrons as they pass through an 'invisible' nanoparticle. While the paths are bent as they enter the particle, they are subsequently bent back so that they re-emerge from the other side on the same trajectory they started with — just as if the particle wasn't there.
Image courtesy Bolin Liao et al.

The concept — developed by MIT graduate student Bolin Liao, former postdoc Mona Zebarjadi (now an assistant professor at Rutgers University), research scientist Keivan Esfarjani, and mechanical engineering professor Gang Chen — is described in a paper in the journal Physical Review Letters.