Nanotechnology Now

Our NanoNews Digest Sponsors





Heifer International

Wikipedia Affiliate Button


android tablet pc

Home > Press > Gold Solution for Enhancing Nanocrystal Electrical Conductance

Image (a) is a transmission electron micrograph of a cadmium-selenide nanocrystal before gold tip growth in solution and image (b) is after tips have been added. Image (c) is a scanning electron micrograph of a single nanocrystal two-terminal device.
Image (a) is a transmission electron micrograph of a cadmium-selenide nanocrystal before gold tip growth in solution and image (b) is after tips have been added. Image (c) is a scanning electron micrograph of a single nanocrystal two-terminal device.

Abstract:
In a development that holds much promise for the future of solar cells made from nanocrystals, and the use of solar energy to produce clean and renewable liquid transportation fuels, researchers with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have reported a technique by which the electrical conductivity of nanorod crystals of the semiconductor cadmium-selenide was increased 100,000 times.

Gold Solution for Enhancing Nanocrystal Electrical Conductance

Berkeley, CA | Posted on September 10th, 2009

"The key to our success is the fabrication of gold electrical contacts on the ends of cadmium-selenide rods via direct solution phase-growth of the gold tips," says Paul Alivisatos, interim-Director of Berkeley Lab, who led this research. "Solution-grown contacts provide an intimate, abrupt nanocrystal-metal contact free of surfactant, which means that unlike previous techniques for adding metal contacts, ours preserves the intrinsic semiconductor character of the starting nanocrystal."

Alivisatos is a chemist who holds joint appointments with Berkeley Lab's Materials Sciences Division, and with the University of California-Berkeley where he is the Larry and Diane Bock professor of Nanotechnology. He is an internationally-recognized authority on nanocrystal growth and the corresponding author of a paper published in the on-line edition of NanoLetters entitled: "Enhanced Semiconductor Nanocrystal Conductance via Solution Grown Contacts."

Co-authoring the paper with Alivisatos were Matthew Sheldon and Paul-Emile Trudeau, members of Alivisatos' research group; Taleb Mokari, of Berkeley Lab's Molecular Foundry; and Lin-Wang Wang, in Berkeley Lab's Computational Research Division.

With the world demand for energy projected to more than double by 2050 and more than triple by the end of the 21st century, it is imperative that sustainable and carbon-neutral energy technologies be developed. The use of sunlight to generate electricity as well as to split water molecules for the production of fuels is envisioned as an ideal energy source, and nanocrystals could be pivotal to the success of this vision. Electrical conductance in semiconductor nanocrystals is a critical element for both solar electricity and solar fuel technologies.

"Standard contacting procedures that deposit metal onto semiconductor nanocrystals directly, such as those used in commercial wafer-scale chip fabrication, cause alloying and chemical reactions at the metal-semiconductor interface," says Sheldon, who was the lead author on the NanoLetters paper. "This means that the finished electrical device is actually made of a different material than the starting nanocrystal."

Sheldon notes that while chemical treatments, such as etching off surfactant, have been shown to enhance the conductivity of thin film nanocrystal solids, these treatments will often alter the semiconductor's electrical properties, for example switching the material from n-type to p-type or altering the density of surface states. Furthermore, he says, previous studies have not explained why electrical conductance was enhanced, other than acknowledging the removal of surfactant coverage.

In this new study, Sheldon, Alivisatos and their co-authors used single nanostructure electrical measurements to make systematic comparisons between cadmium-selenide nanorods with and without gold tips. The solution-grown tipping process started with the addition of gold salt to a solution of toluene and cadmium-selenide nanorods, which resulted in gold metal being selectively deposited on the nanorod tips. A silicon wafer test chip was then dipped in this nanorod solution. After submersion, the evaporation of the toulene solvent oriented individual cadmium-selenide nanorods across pre-defined gold electrodes, which were fabricated through electron beam lithography. The results were gold-tipped cadmium-selenide heterostructure devices whose electrical conductance was characterized in a two-terminal geometry as a function of source-drain voltage and temperature.

Says Alivisatos, "Our study shows that the superior performance of gold-tipped cadmium-selenide heterostructures results from a lower Schottky barrier and that solution grown contacts do not alter the chemical composition of the semiconductor. Further, our work demonstrates the increasing sophistication of high-quality electrical devices that can be achieved through self-assembly and verifies this process as an excellent route to the next generation of electronic and optoelectronic devices utilizing colloidal nanocrystals."

Adds Sheldon, "We believe our approach is an ideal strategy for making future devices from nanocrystals because it preserves the semiconductor character of the nanocrystal as synthesized with the precise control of their synthesis developed over the past decades."

Sheldon says the next step in this work will be to determine if the dramatic improvements in electrical behavior can translate to improvements in nanocrystal-based energy production. Initially, the group plans to investigate the use of solution grown contacts in photovoltaic applications.

This research was primarily funded by the DOE Office of Science through Berkeley Lab's Helios Solar Energy Research Center.

Additional Information

For more information about the research of Paul Alivisatos visit the Website at www.cchem.berkeley.edu/pagrp/

For more information about the Helios Solar Energy Research Center, visit the Website at www.lbl.gov/LBL-Programs/helios-serc/index.html

####

About Lawrence Berkeley National Laboratory
Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research for DOE’s Office of Science and is managed by the University of California. Visit our Website at www.lbl.gov/

For more information, please click here

Contacts:
Lynn Yarris
(510) 486-5375

Copyright © Lawrence Berkeley National Laboratory

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

Govt.-Legislation/Regulation/Funding/Policy

Nanostructured metal-oxide catalyst efficiently converts CO2 to methanol: Highly reactive sites at interface of 2 nanoscale components could help overcome hurdle of using CO2 as a starting point in producing useful products July 31st, 2014

Carnegie Mellon Chemists Create Nanofibers Using Unprecedented New Method July 31st, 2014

Pressure probing potential photoelectronic manufacturing compound July 31st, 2014

Watching Schrödinger's cat die (or come to life): Steering quantum evolution & using probes to conduct continuous error correction in quantum computers July 30th, 2014

Possible Futures

IBM Announces $3 Billion Research Initiative to Tackle Chip Grand Challenges for Cloud and Big Data Systems: Scientists and engineers to push limits of silicon technology to 7 nanometers and below and create post-silicon future July 10th, 2014

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

Announcements

Industrial Nanotech, Inc. to Publish PCAOB Audited Financials July 31st, 2014

Nanostructured metal-oxide catalyst efficiently converts CO2 to methanol: Highly reactive sites at interface of 2 nanoscale components could help overcome hurdle of using CO2 as a starting point in producing useful products July 31st, 2014

Carnegie Mellon Chemists Create Nanofibers Using Unprecedented New Method July 31st, 2014

Pressure probing potential photoelectronic manufacturing compound July 31st, 2014

Environment

Nature inspires a greener way to make colorful plastics July 30th, 2014

Iranian Scientists Use Waste Cotton Fibers to Produce Cellulose Nanoparticles July 29th, 2014

Production of Toxic Gas Sensor Based on Nanorods July 28th, 2014

Researchers Use Various Zinc Oxide Nanostructures to Boost Efficiency of Water Purification Process July 13th, 2014

Energy

Nanostructured metal-oxide catalyst efficiently converts CO2 to methanol: Highly reactive sites at interface of 2 nanoscale components could help overcome hurdle of using CO2 as a starting point in producing useful products July 31st, 2014

From Narrow to Broad July 30th, 2014

Oregon chemists eye improved thin films with metal substitution: Solution-based inorganic process could drive more efficient electronics and solar devices July 21st, 2014

Steam from the sun: New spongelike structure converts solar energy into steam July 21st, 2014

Solar/Photovoltaic

From Narrow to Broad July 30th, 2014

Steam from the sun: New spongelike structure converts solar energy into steam July 21st, 2014

Making dreams come true: Making graphene from plastic? July 2nd, 2014

Shrinky Dinks close the gap for nanowires July 1st, 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