Using light to build nanoparticles into superstructures

March 15, 2011
Using light to build nanoparticles into superstructures
A structured, mesocale filament of gold and carbon nanoparticles formed via ODA in water intentionally resembles the Chinese character for “king.”

Scientists in the Center for Nanoscale Materials and Argonne's Biosciences Division have demonstrated a remarkably simple, elegant, and cost-effective way of assembling nanoparticles into larger structures of any desired shape and form at will via a process called "optically directed assembly."

Optically directed assembly (ODA) involves suspensions of gold and carbon in water. A small droplet of the suspension is placed on a glass slide, and a low-power laser is focused onto a small region within the droplet near its surface. Through a complex process involving optical trapping, heating, , convective fluid flow, and chemical interactions, the nanoparticles fuse near the laser focus and as the experimenter moves the laser focus around in the droplet, a continuous filament of the fused material follows.

Gold-carbon nanoparticle interactions. (a) TEM image of the tip of a gold-carbon filament; (b) TEM image of encapsulated gold nanoparticles within the tip; (c) Initial gold-carbon nanoparticle configuration for a molecular dynamics simulation; and (d) molecular dynamics result after 10 ns showing wetting of a gold nanoparticle by carbon atoms in the 450K range. These results indicate the possibility of encapsulation of gold nanoparticles by carbon.

These remarkable structures remain completely intact even after the fluid is drained off. In this manner “handcrafted” filaments of up to millimeter lengths and 10-60 times wider than the original nanoparticles can be formed with arbitrary shape and design. The resulting hierarchical architectures may be useful for a variety of applications, including biological sensing, electronics, optics, and emerging energy technologies. As a first demonstration, the researchers handcrafted a microscopic glyph -- the Chinese symbol for “king.”

Irreversible metal-metal aggregation is observed only when carbon is present. Scientists in CNM's Theory & Modeling Group used molecular dynamics simulations to model gold-carbon nanoparticle configurations and wetting behavior.

Explore further: Highlight: Damping of acoustic vibrations in gold nanoparticles

More information: J. T. Bahns et al., “Optically Directed Assembly of Continuuous Mesocale Filaments,” Phys. Rev. Lett., 106, 095501 (2011). (online) DOI: 10.1103/PhysRevLett.106.095501

Related Stories

Chemists make breakthrough in nanoscience research

July 12, 2010

A team of scientists led by Eugenia Kumacheva of the Department of Chemistry at the University of Toronto has discovered a way to predict the organization of nanoparticles in larger forms by treating them much the same as ...

Ultrashort laser ablation enables novel metal films

September 21, 2010

Laser ablation is well known in medical applications like dermatology and dentistry, and for more than a decade it has been used to vaporize materials that are difficult to evaporate for high-tech applications like deposition ...

Microfabrication: The light approach

March 4, 2011

Materials that conduct electricity but which are also transparent to light are important for electronic displays, cameras and solar cells. The industry’s standard material for these applications is indium tin oxide (ITO), ...

Recommended for you

Meet the high-performance single-molecule diode

July 29, 2015

A team of researchers from Berkeley Lab and Columbia University has passed a major milestone in molecular electronics with the creation of the world's highest-performance single-molecule diode. Working at Berkeley Lab's Molecular ...

Reshaping the solar spectrum to turn light to electricity

July 28, 2015

When it comes to installing solar cells, labor cost and the cost of the land to house them constitute the bulk of the expense. The solar cells—made often of silicon or cadmium telluride—rarely cost more than 20 percent ...

Could stronger, tougher paper replace metal?

July 24, 2015

Researchers at the University of Maryland recently discovered that paper made of cellulose fibers is tougher and stronger the smaller the fibers get. For a long time, engineers have sought a material that is both strong (resistant ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.