News in NanoCarbon TeK

This week in PhysOrg the recent news in nanocarbon technology:

'Unzipped' carbon  nanotubes  could  help  energize  fuel  cells,  batteries

This drawing shows the damaged outer wall of a carbon nanotube with nanosized graphene pieces (white patches), which facilitate the formation of catalytic sites made of iron (yellow) and nitrogen (red) atoms. The catalyst reduces oxygen to water. Credit: Guosong Hong

Multi-walled carbon nanotubes riddled with defects and impurities on the outside could replace some of the expensive platinum catalysts used in fuel cells and metal-air batteries, according to scientists at Stanford University. Their findings are published in the May 27 online edition of the journal Nature Nanotechnology. (here)

Scientists  take  steps  toward  creating  artificial  graphene

(Phys.org) -- Researchers first observed graphene in 2004 by extracting the single-atom-thick sheets of carbon from bulk graphite. While graphene’s electrical and optical properties have proven to have extraordinary potential for many applications, creating atomically precise structures out of graphene remains challenging. In an effort to improve graphene’s usability, scientists have been searching for a way to fabricate artificial graphene, which could serve as a helpful structure where devices can be easily tested before their implementation with natural graphene. Now in a new study, scientists have identified all the main criteria required to make artificial graphene, which could provide a guide for experimentally realizing the material. (here)

Researchers  find  new  properties  of  the  carbon  material  graphene

Graphene has caused a lot of excitement among scientists since the extremely strong and thin carbon material was discovered in 2004. Just one atom thick, the honeycomb-shaped material has several remarkable properties combining mechanical toughness with superior electrical and thermal conductivity. (here)

Nanostructures could make high-efficiency solar cells easier to fabricate

Showing data from four different crescent-shaped nanostructures, this figure demonstrates the strong dependence of SP excitations on crescent shape. Most significantly, the study shows that nanostructures can have a continuous light absorption spectrum even when having blunt edges, greatly simplifying fabrication requirements. Image credit: Yu Luo, et al. ©2012 American Physical Society

(PhysOrg.com) -- One of the most promising methods for increasing the efficiency of solar cells consists of coating the cells’ surfaces with a thin layer of metal nanoparticles. The nanoparticles scatter incoming light in different directions, which allows the solar cells to absorb more light than they otherwise would. The scattering occurs when the incoming light stimulates the nanoparticles’ surface plasmons (SPs), which are coherent electron oscillations in the metal atoms that can reach a resonance mode when the electrons’ frequency matches the photons’ frequency. Under these conditions, the resulting “surface plasmon resonance” induces light scattering and enhances the light absorption of the surface.

in PhysOrg

Ohm's law in atomic scale

Atomic wire made of phosphorus. It links to silicon atoms.
Credit: Physics World

Ohm's Law

Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equation that describes this relationship:

 where I is the current through the conductor in units of amperes, V is the potential difference measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms. More specifically, Ohm's law states that the R in this relation is constant, independent of the current.

The law was named after the German physicist Georg Ohm, who, in a treatise published in 1827, described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire. He presented a slightly more complex equation than the one above to explain his experimental results. The above equation is the modern form of Ohm's law.

In physics, the term Ohm's law is also used to refer to various generalizations of the law originally formulated by Ohm. The simplest example of this is:

where J is the current density at a given location in a resistive material, E is the electric field at that location, and σ is a material dependent parameter called the conductivity. This reformulation of Ohm's law is due to Gustav Kirchhoff.

Microscopic origins of Ohm's law

The dependence of the current density on the applied electric field is essentially quantum mechanical in nature; (see Classical and quantum conductivity.) A qualitative description leading to Ohm's law can be based upon classical mechanics using the Drude model developed by Paul Drude in 1900.

The Drude model treats electrons (or other charge carriers) like pinballs bouncing between the ions that make up the structure of the material. (read more in Wikipedia).

An atomic scale experiment results 

"A new technique for embedding atomic-scale wires within crystals of silicon has revealed that Ohm's law can hold true for wires just four atoms thick and one atom tall. The result comes as a surprise because conventional wisdom suggests that quantum effects should cause large deviations from Ohm's law for such tiny wires. Paradoxically, the researchers hope the finding will aid the development of quantum computers."

in Physics World (click to read entire article)

A team of Arizona State University created a channel in the silicon by removing layers of silicon atoms, by using the tip of a scanning probe microscope. The surface was then exposed to phosphorus gas, followed by the deposition of silicon atoms. The result was a chain of phosphorus atoms embedded inside a silicon crystal – an atomic wire. The team found that the resistivity of those wires was constant. That means the resistance of such a wire is proportional to its length and inversely proportional to its area, just as we seen in Ohm's law.

Implications

The discovery has several implications, including:

• For engineers it could provide a roadmap to future nanoscale computational devices where atomic sizes are at the end of Moore's law. The theory shows that a single dense row of phosphorus atoms embedded in silicon will be the ultimate limit of downscaling.

• For computer scientists, it places donor-atom based silicon quantum computing closer to realization.

• And for physicists, the results show that Ohm's Law, which demonstrates the relationship between electrical current, resistance and voltage, continues to apply all the way down to an atomic-scale wire.

in ScienceDaily

A new method to measure nanoparticles

Precise measurement of the molecular weight, size and density of a nanoparticle in a single procedure is now possible, thanks to an ultracentrifugation method, dusted off by Swiss scientists at EPFL.

An innovative method for measuring nanoparticles

Precise measurement of the molecular weight, size and density of a nanoparticle in a single procedure is now possible, thanks to an ultracentrifugation method, dusted off by Swiss scientists at EPFL.

Read more here and here.

Carbon nanotube structure changes

Carbon nanotube structures changed by 'attack' from within, researchers discover
(PhysOrg.com) -- A team of researchers involving scientists from The University of Nottingham has shown for the first time that chemical reactions at the nano-level which change the structure of carbon nanotubes can be sparked by an 'attack' from within.

"The discovery challenges previous scientific thinking that the internal surface of the hollow nanostructures is chemically unreactive, largely restricting their use to that of an inert container or a ‘nano-reactor’ inside which other chemical reactions can take place.
Their research, published in the journal Nature Chemistry, shows that carbon nanotubes that have had their structures changed are exciting new materials that could be useful in the development of new technologies for gas storage devices, chemical sensors and parts of electronic devices such as transistors."

Read full article in PhysOrg.com

Biofuel performance increase with nano particles

Nanoparticles increase biofuel performance

How to put more bang in your biofuels? Nanoparticles! A new study in the Journal of Renewable and Sustainable Energy shows that the addition of alumina nanoparticles can improve the performance and combustion of biodiesel, while producing fewer emissions.

in PhysOrg.com

A new quantum state of water

Credits: physicsworld.com

A recent publication scientist discovered that "water is confinned on scales of 20 A, this wave function responds to the details of the confi nement, corresponds to a strongly anharmonic local potential, shows evidence in some cases of coherent delocalization in double wells, and involves changes in zero point kinetic energy of the protons from -40 to +120 meV di erence from that of bulk water at room temperature. This behavior appears to be a generic feature of nanoscale confi nement."

from ArXiv.org

From physicsworld.com:

George Reiter of the University of Houston and colleagues study in detail the key to water's unusual properties – the hydrogen bond. This is the bond between water molecules, connecting the oxygen atom of one molecule to the hydrogen atom in another.[...]They found that the momentum distribution of the protons was strongly temperature dependent, with as much as 50% more kinetic energy than the electrostatic model predicts at low temperatures and 20% more kinetic energy at room temperature. The electrostatic model gives broadly the correct values for bulk water at room temperature.The team argues that this is evidence that the protons exist in a previously unobserved quantum state when water is confined to a very tiny volume – a state that is not described by the electrostatic model.[...]

read the full article in physicsworld.com