Nanotechnology Now

Our NanoNews Digest Sponsors





Heifer International

Wikipedia Affiliate Button


android tablet pc

Home > Press > Light can induce twisting in semiconductor nanoribbons

Figure 2. Straight nanoribbons formed in complete darkness.
Figure 2. Straight nanoribbons formed in complete darkness.

Abstract:
A novel approach using ambient-light irradiation can produce twisted nanostructures of variable pitch length with many potential applications.

By Sudhanshu Srivastava and Nicholas A. Kotov

Light can induce twisting in semiconductor nanoribbons

Bellingham, WA | Posted on June 23rd, 2010

Self-organization of nanoparticles (NPs) can create advanced architectures such as nanowires (NWs), nanosheets (NSes), nanotubes, and nanoplates. They have many possible applications in electronic-device development, biomedicine, and other areas. Different mechanisms and routes have been reported that use noncovalent interactions between NPs to create these morphologies. An interesting topic to investigate regarding their assembly is the way that changes in physical conditions, such as ambient light, can affect their overall structural shape.

We have investigated self-assembly of cadmium telluride (CdTe) NPs under controlled conditions of visible-light irradiation, producing helically twisted nanoribbons (TRs)1 with pitch lengths ranging from 1500 to 250nm under varying degrees of illumination. In contrast, we did not observe any twisting when the ribbons were assembled in complete darkness. Although light is known to affect matter, the use of ambient-light illumination to twist or bend wires by a few nanometers has not been reported before.

The dipolar interactions involved in the self-assembly of CdTe NPs can create 1D NWs2 and 2D NSs.3 Using the same concept, we prepared an aqueous solution of CdTe NPs with thioglycolic acid (TGA) as a capping agent. We used a Cd2+/TGA ratio close to unity instead of the typical value of 2.4 used for 1D NW formation. The lower amount of TGA is expected to reduce the local concentration on the tetrahedral corners of NPs and increase the dipole of the particles.

We first precipitated CdTe NPs in methanol and centrifuged them. They were then redispersed in water at pH 9 (pH: Measure of acidity or basicity of a solution). The orange color of the initial NP solution turned to dark green in three days in the presence of ambient light. We analyzed the samples under scanning-electron microscopy (SEM) and transmission-electron microscopy (TEM) and found that TRs had formed.1 The TRs were 1 to 2ěm in length, with a helical pitch length of ~400nm (see Figure 1). We examined the direction of helicity for some 100 TRs and observed a racemic distribution of left- and right-handed ribbons. Under high-resolution TEM (HRTEM), the TRs showed a polycrystalline structure composed of both CdTe and cadmium sulfide (CdS) NPs. Because less TGA was used in the fabrication of the CdTe NPs, the particles were more exposed to Te oxidation. In this process, Te2− is oxidized and the excess of Cd2+ present in the particles reacts with the remaining S2− resulting from TGA decomposition to form CdS. This explains the composition of the resulting TRs.

Interestingly, the same procedure, when carried out in complete darkness, showed the same polycrystalline structure composed of CdTe/CdS NPs, but with no twisting (straight ribbons): see Figure 2. Because both CdTe and CdS are sensitive to light, the twisting is believed to be related to the exposure to ambient light.

To further investigate the effect of light illumination on the assembly of CdTe NPs into TRs, we exposed the solution described above to various levels of light illumination. The resulting TRs showed a sequential alteration in pitch length from 250 to 1500nm with increasing illumination. HRTEM observations showed that all TRs exhibited the same polycrystalline structure composed of CdTe/CdS NPs. The results clearly indicate the importance of ambient light. The wires prepared in the dark were also wider than the TRs prepared under ambient light.

The intermediate stages of sample preparation also supported the suggestion that photo-oxidation caused the twisted structures. We found unusual shapes (such as ellipsoids, dumbbell shapes, and bunches of ribbons) as intermediate stages and TRs finally emerged from these multiparticle assemblies. To further confirm that the pitch length of the TRs is controlled by ambient light, we also examined the duration of the illumination rather than its intensity. The CdTe samples were initially kept in complete darkness to form straight ribbons and then introduced to irradiation with ambient light for one day. The results showed a sequential change in pitch length from straight to ~600 and 400nm after 12 and 24hr, respectively, under ambient light. Theoretical calculations and simulations revealed that the resulting geometry and dimensionality are also controlled by electrostatic attraction and repulsion in the NP assemblies.

TRs with variable pitch length provide a new shape for use in nanotechnology. Nanoscale twisted propellers inspired by nature mimic the alpha-helical structures found in biomolecules such as proteins and DNA. Helical TRs similar to biomolecules could thus be used to control drug delivery as well as in microfluidic systems used in experiments to simulate the body. This newly discovered twisting effect could also be applied to create variable micro-electromechanical systems that are controlled by visible light. Similarly, the TRs could be used in lithography technologies and in designing microchips. Semiconductor materials can be applied as superchiral structures, which may have smart applications in the field of negative-refractive-index materials. We are currently investigating methods to construct chiral structures twisted in one direction for application as metamaterials. To further use this morphology for metamaterials with negative refractive index, we are also investigating new procedures to use them as templates for creating metallic wires with a similar twisted morphology.

Sudhanshu Srivastava
University of Michigan
Ann Arbor, MI

Sudhanshu Srivastava works as a research fellow with Nicholas Kotov. His research focuses on the spontaneous assembly of nanoparticles for construction of nanowires, nanoribbons, and other advanced architectures. He is also investigating exponential layer-by-layer assembly for loading and unloading of nanomaterials.

Nicholas Kotov
Departments of Chemical Engineering, Materials Science, and Biomedical Engineering
University of Michigan
Ann Arbor, MI

Nicholas Kotov is a professor. His research interests include nanocolloids, their assembled structures, layer-by-layer assembly, ultrastrong materials from carbon nanotubes and clays, nanomaterials for energy storage, interfacing neural tissues with nanomaterials, and diagnostics with nanoparticles.

References:
1. S. Srivastava, A. Santos, K. Critchley, K. S. Kim, P. Podsiadlo, K. Sun, J. Lee, C. Xu, G. D. Lilly, S. C. Glotzer, N. A. Kotov, Light-controlled self-assembly of semiconductor nanoparticles into twisted ribbons, Science 327, pp. 1355, 2010.
2. Z. Tang, N. A. Kotov, M. Giersig, Spontaneous organization of single CdTe nanoparticles into luminescent nanowires, Science 297, pp. 237, 2002.
3. Z. Tang, Z. Zhang, Y. Wang, S. C. Glotzer, N. A. Kotov, Self-assembly of CdTe nanocrystals into free-floating sheets, Science 314, pp. 274, 2006.

####

About International Society for Optical Engineering
SPIE is the international society for optics and photonics founded in 1955 to advance light-based technologies. Serving more than 177,000 constituents from 168 countries, the Society advances emerging technologies through interdisciplinary information exchange, continuing education, publications, patent precedent, and career and professional growth.

SPIE annually organizes and sponsors approximately 25 major technical forums, exhibitions, and education programs in North America, Europe, Asia, and the South Pacific.

In 2009, the Society provided more than $2 million in support of scholarships, grants, and other education programs around the world.

For more information, please click here

Copyright © International Society for Optical Engineering

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Iranian Researchers Present New Model to Strengthen Superconductivity at Higher Temperatures April 19th, 2014

Iranian Researchers Produce New Anti-Cancer Drug from Turmeric April 19th, 2014

'Exotic' material is like a switch when super thin April 18th, 2014

Innovative strategy to facilitate organ repair April 18th, 2014

Possible Futures

Virus structure inspires novel understanding of onion-like carbon nanoparticles April 10th, 2014

Local girl does good March 22nd, 2014

Surface Characteristics Influence Cellular Growth on Semiconductor Material March 12th, 2014

The "Tipping Point" February 12th, 2014

Self Assembly

Roomy cages built from DNA: Self-assembling cages are the largest standalone 3-D DNA structures yet, and could one day deliver drugs, or house tiny bioreactors or photonic devices March 13th, 2014

Cypress’s TrueTouch® Touchscreen Controllers Compatible with Cima NanoTech’s SANTE® Silver Nanoparticle-Based Touch Sensors: Supporting Designs for Advanced Touch Applications March 5th, 2014

Coupled carbon and peptide nanotubes achieved for the first time: twins nanotubes March 1st, 2014

A potentially revolutionnary material: Scientists produce a novel form of artificial graphene February 15th, 2014

Nanotubes/Buckyballs

Effects of Carbon Nanotubes Studied on Pregnant Mothers April 12th, 2014

Nanotech Business Review 2013-2014 April 9th, 2014

Scientists Succeed in Simultaneous Determination of Acetaminophen, Codeine in Drug Samples April 9th, 2014

Rebar technique strengthens case for graphene: Rice University lab makes hybrid nanotube-graphene material that promises to simplify manufacturing April 7th, 2014

Nanomedicine

Iranian Researchers Present New Model to Strengthen Superconductivity at Higher Temperatures April 19th, 2014

Iranian Researchers Produce New Anti-Cancer Drug from Turmeric April 19th, 2014

Innovative strategy to facilitate organ repair April 18th, 2014

High-temperature plasmonics eyed for solar, computer innovation April 17th, 2014

Discoveries

Iranian Researchers Present New Model to Strengthen Superconductivity at Higher Temperatures April 19th, 2014

Iranian Researchers Produce New Anti-Cancer Drug from Turmeric April 19th, 2014

'Exotic' material is like a switch when super thin April 18th, 2014

Innovative strategy to facilitate organ repair April 18th, 2014

Announcements

Iranian Researchers Present New Model to Strengthen Superconductivity at Higher Temperatures April 19th, 2014

Iranian Researchers Produce New Anti-Cancer Drug from Turmeric April 19th, 2014

'Exotic' material is like a switch when super thin April 18th, 2014

Innovative strategy to facilitate organ repair April 18th, 2014

Nanobiotechnology

Targeting cancer with a triple threat: MIT chemists design nanoparticles that can deliver three cancer drugs at a time April 15th, 2014

Biologists Develop Nanosensors to Visualize Movements and Distribution of Plant Stress Hormone April 15th, 2014

In latest generation of tiny biosensors, size isn't everything: UCLA researchers overturn conventional wisdom on nanowire-based diagnostic devices April 11th, 2014

Virus structure inspires novel understanding of onion-like carbon nanoparticles April 10th, 2014

NanoNews-Digest
The latest news from around the world, FREE







  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More














ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







© Copyright 1999-2014 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE