Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Nanomaterials: Bringing crystals into line

26.10.2012
The temperature-controlled alignment of tiny crystals could help harness their collective properties for nanotechnology applications.

The unique magnetic properties of cobalt phosphide nanowires stand them in good stead as future components of high-performance devices. Unlike bulk materials, these ultrasmall elongated crystals consist of single-domain structures that account for their superparamagnetism — a temperature-induced magnetism that arises in a magnetic field.


Schematic representations (top) and transmission electron microscopy images (bottom) of randomly oriented and vertically and horizontally aligned cobalt phosphide nanowires. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

To maintain and fully exploit this behavior, scientists must generate materials composed of precisely positioned and oriented building blocks. Such superstructures are now available, thanks to the development of a method that uses temperature changes to align individual nanowires. Ming-Yong Han from the A*STAR Institute of Materials Research and Engineering, Sinapore, led the research.

Current nanocrystal self-assembly approaches involve depositing a crystal suspension on a solid surface, and then slowly evaporating the solvent. Theoretically, the evaporation enhances the relatively weak attraction forces that exist between the nanocrystals, forcing them to align. However, high degrees of alignment of anisotropic structures — those exhibiting direction-dependent physical properties — remain difficult to achieve.

“We took a distinct pathway from the slow evaporation approach,” says Han. His team’s strategy followed similar principles to those used in chemical synthesis. First, they reacted a cobalt derivative with the phosphide precursor trioctylphosphine (TOP) at high temperature. This produced TOP-coated nanowires. Next, they stored the solution in which the nanowires formed at various temperatures. These storage, or ‘aging’, temperatures produced larger, well-defined superstructures with different alignments.

Washing the nanowires without the latter step resulted in random arrangements or small assemblies (see image). After cooling and aging the reaction mixture at room temperature for two hours, the team observed superstructures composed of nearly one million vertically standing nanowires. In this arrangement, each nanowire was surrounded by six others in a honeycomb pattern. When cooled to room temperature and then refrigerated, the reaction mixture produced extended sheets of nanowires aligned side-by-side horizontally.

The superstructures resisted any high temperature, ultrasound, or organic solvent treatment, indicative of strong cohesive forces between the nanowires. Further investigations revealed that, during the self-assembly, the TOP molecules continually adsorbed and desorbed from the nanowires, bringing them in close contact. This caused irreversible chemical bonds to form between the nanocrystals, facilitating and enhancing their alignment.

The team is currently testing the performance of the superstructures against that of the randomly oriented nanowires to explore their potential use as sensors or electrical components called inductors. “We are also trying to extend this methodology to self-assemble other systems, with a hope to establish a more universal method for aligning anisotropic nanocrystals,” adds Han.

The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering

References

Zhang, S.-Y., Ye, E., Liu, S., Lim, S. H., Tee, S. Y., Dong, Z. & Han, M.-Y. Temperature and chemical bonding-directed self-assembly of cobalt phosphide nanowires in reaction solutions into vertical and horizontal alignments. Advanced Materials 24, 4369–4375 (2012).

A*STAR Research | Research asia research news
Further information:
http://www.a-star.edu.sg
http://www.researchsea.com

More articles from Materials Sciences:

nachricht Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern
20.07.2018 | Princeton University

nachricht Relax, just break it
20.07.2018 | DOE/Argonne National Laboratory

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Future electronic components to be printed like newspapers

A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.

The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

A smart safe rechargeable zinc ion battery based on sol-gel transition electrolytes

20.07.2018 | Power and Electrical Engineering

Reversing cause and effect is no trouble for quantum computers

20.07.2018 | Information Technology

Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern

20.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>