(NanoRealm)- Welding uses heat to join pieces of metal in everything from circuits to skyscrapers. But Rice University researchers have found a way to beat the heat on the nanoscale.

Jun Lou, an assistant professor in mechanical engineering and materials science, and his group have discovered that gold wires between three-billionths and 10-billionths of a meter wide weld themselves together quite nicely – without heat.

They report in today's online edition of the journal Nature Nanotechnology that clean gold nanowires with identical atomic structures will merge into a single wire that loses none of its electrical and mechanical properties. The process works just as well with silver nanowires, which bond with each other or with gold.

This cold-welding process has been observed on the macro scale for decades, Lou said. Clean, flat pieces of similar metals can be made to bond under high pressure and in a vacuum. But only Lou and his colleagues have seen the process happen on the nanoscale, under an electron microscope.

As so often happens in basic research, that's not what they were looking for at all. Lou and Rice graduate student Yang Lu, with collaborators at Sandia National Laboratories and Brown University, were trying to determine the tensile strength of gold nanowires by attaching one end of a wire to a probe in a transmission electron microscope (TEM) and the other to a tiny cantilever spring called an atomic force microscopy (AFM) probe.

Pulling the wire apart gave the team a measurement of its strength. What they didn't expect to see was the broken wire mending itself when its ends or sides touched. Measurements showed the reconnected wire was as strong as before.

"Before you can actually stretch something, you need to clamp it well," said Lou, who received a Young Investigators Research Program grant from the Air Force Office of Sponsored Research last year. "During the manipulation process, we observed this type of welding behavior all the time.

"Initially, we didn't pay attention to it because it didn't seem significant. But after doing a little research on the field, I realized we discovered something that may be useful."

In testing, Lou found the nanowires could be snapped and welded many times. Mended wires never broke again at the same spot; this attests to the strength of the new bond.

The wire's electrical properties also seemed unaffected by repeated breaking and welding. "We'd break a wire and reweld it 11 times and check the electrical properties every time. All the numbers were very close," he said.

The keys to a successful weld are the nanowire's single crystalline structure and matching orientation. "There are a lot of surface atoms, very active, that participate in the diffusion at the nanoscale," Lou said. "We tried gold and silver, and they weld in the same way as long as you satisfy the crystalline-orientation requirement."

Lou sees the discovery opening new paths for researchers looking at molecular-scale electronics. He said teams at Harvard and Northwestern are working on ways to pattern arrays of nanowires, and incorporating cold welding could simplify their processes. "If you're building high-density electronic devices, these kinds of phenomena will be very useful," he said, noting that heat-induced welds on the nanoscale run the risk of damaging the materials' strength or conductivity.

Lou said the discovery has caused a stir among the few he's told. "Different people see different aspects: Electrical engineers see the application side. Theory people see some interesting physics behind this behavior. We hope this paper will encourage more fundamental study."

---

The paper's co-authors include Jian Yu Huang, a scientist at the Center for Integrated Nanotechnologies at Sandia National Laboratories; and Professor Shouheng Sun and former graduate student Chao Wang of Brown University.

The National Science Foundation and the Air Force Office of Sponsored Research supported the project.

---

Source: Rice University (web)

Paper: "Cold welding of ultrathin gold nanowires" by Yang Lu, Jian Yu Huang, Chao Wang, Shouheng Sun & Jun Lou

Material scientists at the Nano/Bio Interface Center of theUniversity of Pennsylvania have demonstrated the transduction of optical radiation to electrical current in a molecular circuit. The system, an array of nano-sized molecules of gold, respond to electromagnetic waves by creating surface plasmons that induce and project electrical current across molecules, similar to that of photovoltaic solar cells.

The results may provide a technological approach for higher efficiency energy harvesting with a nano-sized circuit that can power itself, potentially through sunlight. Recently, surface plasmons have been engineered into a variety of light-activated devices such as biosensors.

It is also possible that the system could be used for computer data storage. While the traditional computer processor represents data in binary form, either on or off, a computer that used such photovoltaic circuits could store data corresponding to wavelengths of light.

Because molecular compounds exhibit a wide range of optical and electrical properties, the strategies for fabrication, testing and analysis elucidated in this study can form the basis of a new set of devices in which plasmon-controlled electrical properties of single molecules could be designed with wide implications to plasmonic circuits and optoelectronic and energy-harvesting devices.

Dawn Bonnell, a professor of materials science and the director of the Nano/Bio Interface Center at Penn, and colleagues fabricated an array of light sensitive, gold nanoparticles, linking them on a glass substrate. Minimizing the space between the nanoparticles to an optimal distance, researchers used optical radiation to excite conductive electrons, called plasmons, to ride the surface of the gold nanoparticles and focus light to the junction where the molecules are connected. The plasmon effect increases the efficiency of current production in the molecule by a factor of 400 to 2000 percent, which can then be transported through the network to the outside world.


In the case where the optical radiation excites a surface plasmon and the nanoparticles are optimally coupled, a large electromagnetic field is established between the particles and captured by gold nanoparticles. The particles then couple to one another, forming a percolative path across opposing electrodes. The size, shape and separation can be tailored to engineer the region of focused light. When the size, shape and separation of the particles are optimized to produce a “resonant” optical antennae, enhancement factors of thousands
might result.

Furthermore, the team demonstrated that the magnitude of the photoconductivity of the plasmon-coupled nanoparticles can be tuned independently of the optical characteristics of the molecule, a result that has significant implications for future nanoscale optoelectronic devices.

“If the efficiency of the system could be scaled up without any additional, unforeseen limitations, we could conceivably manufacture a one-amp, one-volt sample the diameter of a human hair and an inch long," Bonnell said.

The study, published in the current issue of the journal ACS Nano, was conducted by Bonnell, David Conklin and Sanjini Nanayakkara of the Department of Materials Science and Engineering in the School of Engineering and Applied Science at Penn; Tae-Hong Park of the Department of Chemistry in the School of Arts and Sceicnes at Penn; Parag Banerjee of the Department of Materials Science and Engineering at the University of Maryland; and Michael J. Therien of the Department of Chemistry at Duke University.

This work was supported by the Nano/Bio Interface Center, National Science Foundation, the John and Maureen Hendricks Energy Fellowship and the U.S. Department of Energy.

---

Source: University of Pennsylvania(web)

World Gold Council Research Paper Demonstrates Important Applications in Development Using Gold Nanoparticles

World Gold Council (WGC) has today published 'Gold for Good: Gold and nanotechnology in the age of innovation', a research paper detailing new scientific and technological innovations using gold. The report, which was produced in conjunction with Cientifica Ltd, the world's leading source of global business and investor intelligence about nanotechnologies, demonstrates how gold nanoparticles offer the potential to overcome many of the serious issues facing mankind over the coming decades.

Gold nanoparticles exhibit a variety of unique properties which, when harnessed and manipulated effectively, lead to materials whose uses are both far-ranging in their potential and cost effective. This report explores the many different applications that are being developed across the fields of health, environment and technology.

Trevor Keel, Nanotechnology Project Manager at World Gold Council said:
"The opportunities and possibilities identified in this report are just a subset of the amazing scope to use gold in the era of nanotechnology. As a readily available and well understood material, gold nanoparticles are ideal for use in a vast array of applications that improve our lives. WGC is looking to promote and invest in the development of gold-based innovations through Innovations Partnerships, so that the full benefits of gold nanotechnology can be realized."


Tim Harper, founder of Cientifica Ltd, said:
"Over the last decade, almost $50 billion of government funding has been invested into nanotechnologies, and this investment is now starting to bear fruit with a steady stream of commercially viable nanotechnologies which are positively impacting human health, the environment and technology. This paper demonstrates the many varied applications in which gold nanotechnology can improve society's standard of living."

Health: 
Gold has a long history in the biomedical field stretching back almost five thousand years. However the dawn of the 'nano-age' has really broadened the potential of gold in biomedical applications and today, gold nanoparticles are being employed in entirely novel ways to achieve therapeutic effects.

Tumor targeting technologies which exploit gold's inherent bio-compatibility are being developed to deliver drugs directly into cancerous tumours. Additionally, simple, cost effective and sensitive diagnostic tests are being developed for the early detection of prostate and other cancers.

Environment: 
Environmental concerns have never been more prominent - energy and clean water scarcity, global warming and pollution are all major issues that need to be addressed. Gold nano-particle based technologies are showing great promise in providing solutions to a number of environmentally important issues from greener production methods of the chemical feedstocks, to pollution control and water purification.

Gold-based catalysts are being developed that can effectively prevent the release of highly toxic forms of mercury into the atmosphere, the reduction of chemicals from green feedstock, and also for water purification and contaminant detection. In addition, gold is being used in meeting the challenge of constructing cost effective and efficient fuel cells, a key 'clean-energy' technology of the future.


Advanced technology: 
Gold is already a well established material in the electronics industry and the use of gold can only increase as the worlds of electronics and nanotechnology interact further in the future. Gold is being developed for conductive nanoparticle inks for plastic electronics because of its material compatibility, inherent durability and proven track record of reliability. Gold nanotechnologies have also been shown to offer functional benefits for visual display technologies like touch sensitive screens and potentially for use in advanced data storage technologies including advanced flash memory devices.

The full paper can be downloaded from:
http://www.gold.org/assets/file/rs_archive/gold_and_nanotechnology_in_the_age_of_innovation.pdf
(Due to the length of this URL, it may be necessary to copy and paste this hyperlink into your Internet browser's URL address field. Remove the space if one exists.)

http://cientifica.eu/blog/white-papers/gold/

---

Innovation Partnerships
World Gold Council works directly with partner companies via Innovation Partnerships. These support research and development of new practical applications for the metal, drawing on a genuine commercial market requirement for innovation. Partner organisations include (but are not limited to) precious metal, chemical, electronics, materials and biomedical companies, ranging from small enterprises through to established international businesses. Interested companies are invited to contact World Gold Council for further details.

During 2009-2010 World Gold Council is particularly interested in receiving proposals relating to the following areas:

• Industrial catalysts (including catalysts for pollution control and chemical processing)
  
• Biomedical applications (including medical diagnostics, therapeutics and materials)
  
• Advanced electronics (including any technology or component likely to be used in next-generation devices)
  
• Fuel cell systems (including applications both within the fuel cell structure and hydrogen processing infrastructure)
  
• Optical materials (including nanotechnology, chemicals and coatings)

Companies interested in collaborating with World Gold Council are invited to make contact.

---

Notes to Editors:
World Gold Council
World Gold Council's mission is to stimulate and sustain the demand for gold and to create enduring value for its stakeholders. It is funded by the world's leading gold mining companies. For further information please visit http://www.gold.org.

Cientifica
Cientifica Ltd, based in London, is one of the world's best-respected consultancy companies in the field of emerging technologies and technology commercialization. It provides global business intelligence and strategic consulting services to industry, governments and investors worldwide.
http://www.cientifica.eu