Nanostructures made of pure gold

Date:

November 4, 2016
Source:
Vienna University of Technology, TU Vienna
Summary:
The idea is reminiscent of the ancient alchemists’ attempts to create gold from worthless substances: Researchers have discovered a novel way to fabricate pure gold nanostructures using an additive direct-write lithography technique. An electron beam is used to turn an auriferous organic compound into pure gold. This new technique can now be used to create nanostructures, which are needed for many applications in electronics and sensor technology. Just like with a 3D-printer on the nanoscale, almost any arbitrary shape can be created.


The idea is reminiscent of the ancient alchemists’ attempts to create gold from worthless substances: Researchers from TU Wien (Vienna) have discovered a novel way to fabricate pure gold nanostructures using an additive direct-write lithography technique. An electron beam is used to turn an auriferous organic compound into pure gold. This new technique can now be used to create nanostructures, which are needed for many applications in electronics and sensor technology. Just like with a 3D-printer on the nanoscale, almost any arbitrary shape can be created.

The long search for the right production process

“Gold is not only a noble metal of exceptional beauty, but also a highly desired material for functional nanostructures”, says Professor Heinz Wanzenböck from TU Wien. Especially patterned gold nanostructures are key enabling structures in plasmonic devices, for biosensors with immobilized antibodies and as electrical contacts. For decades the fabrication of pure gold nanostructures on non-planar surfaces as well as of 3-dimensional gold nanostructures has been the bottleneck. Up to now, only 2-dimensional gold nanostructures on planar surfaces were achievable by resist based lithography.

The new technology, developed at TU Wien, can now solve this problem. The principle is the local decomposition of a metalorganic precursor by the focused electron beam of an electron microscope. With extremely high precision, the electron beam can decompose the organic compound at exactly the right position, leaving behind a 3D-trail of solid gold.

The final obstacle was getting the material purity right, as the electron-induced decomposition of metalorganic precursors has typically yielded metals with high carbon contaminations. This last bottleneck on the road to custom-designed, pure gold nanostructures has now been overcome as described in the work on “Highly conductive and pure gold nanostructures grown by electron beam induced deposition” published in Scientific Reports.

While conventional gold deposition usually contains about 70 atomic % carbon and only 30 atomic % gold, the new approach developed by a research group lead by Dr. Heinz Wanzenboeck at TU Wien has allowed to fabricate pure gold structures by in-situ addition of an oxidizing agent during the gold deposition. “The whole community has been working hard for the last 10 years to directly deposit pure gold nanostructures”, says Heinz Wanzenböck. At last, the group’s expertise in engineering and chemical reactions paid off and direct deposition of pure gold was successful. “It’s a bit like discovering the legendary philosopher’s stone that turns common, ignoble material into gold” joked Wanzenboeck.

This deposited pure gold structure exhibits extremely low resistivity near that of bulk gold. Generally, a FEBID gold structure has a resistivity around 1-Ohm-cm which is about 1 million times worse than the resistivity of purest bulk gold. However, this specially enhanced FEBID process produces a resistivity of 8.8 micro-Ohm-cm which is only a factor 4 away from the bulk resistivity of purest gold (2.4 micro-Ohm-cm).

The authors of the paper Dr. Mostafa Moonir Shawrav and Dipl.Ing. Philipp Taus stated, “This highly conductive and pure gold structure will open a new door for novel nanoelectronic devices. For example, it will be easier to produce pure gold structures for nanoantennas and biomolecule immobilization which will change our everyday life”. Dr. Shawrav added “it is remarkable how a regular SEM (Scanning Electron Microscope) nowadays can deposit nanostructures compared to 20 years back when it was only a characterization device”. And with pure gold direct deposition available now, he expects nanodevices to be deposited directly and utilized in many different applications for technological revolution. Concluding, this work is a giant leap forward for 3D nano-printing of gold structures which will be the core part of nanoplasmonics and bioelectronics devices

Story Source:

Materials provided by Vienna University of Technology, TU ViennaNote: Content may be edited for style and length.

Advertisements

Microfibers fabricated for single-cell studies, tissue engineering

Source:Iowa State University

Summary:
Researchers have created a new way to design and fabricate microfibers that support cell growth and could be useful tools for reconnecting nerves and regenerating other damaged tissues.

Neural stem cells on our polymer fibers could survive, differentiate and grow,” said Nastaran Hashemi, an Iowa State assistant professor of mechanical engineering and leader of an Iowa State team producing microfibers with the help of microfluidics, the study of fluids moving through channels just a millionth of a meter wide.

“These new fibrous platforms could also be used for cell alignment which is important in applications such as guiding nerve cell growth, engineered neurobiological systems and regenerating blood vessels, tendons and muscle tissue,” Hashemi said.

The research team’s findings were recently published in Biomacromolecules, a journal of the American Chemical Society. In addition to Hashemi, co-authors are Donald Sakaguchi, a professor of genetics, development and cell biology; Reza Montazami, an assistant professor of mechanical engineering; first author Farrokh Sharifi, a doctoral student in mechanical engineering; Bhavika Patel, a doctoral student in genetics, development and cell biology; and Adam Dziulko, a graduate who earned a 2015 bachelor’s degree in genetics.

The project has been supported by a two-year, $202,000 grant from the Office of Naval Research. The early stage of the project was supported by the Iowa State Presidential Initiative for Interdisciplinary Research and the U.S. Army Medical Research and Materiel Command.

Hashemi said the Office of Naval Research is supporting the project because it wants to learn more about traumatic brain injury.

“We are interested in understanding how shock waves created by blows to the head can create microbubbles that collapse near the nerve cells, or neurons in the brain, and damage them,” Hashemi said.

The Iowa State researchers are working to build a microfiber scaffold to support the cells and allow them to survive for the Navy’s studies of brain injuries. One day, the scaffold technology could help repair nerves or tissues damaged by injuries or disease.

“Our approach to fiber fabrication is unique,” Hashemi said. “There is no high voltage, high pressure or high temperatures. And so one day I think we can encapsulate cells within our fibers without damaging them.”

The Iowa State researchers have developed an approach that uses microfluidic fabrication methods to pump polycaprolactone (PCL) through tiny channels to produce microfibers. The fibers are 2.6 to 36.5 millionths of a meter in diameter. Their shapes can be controlled. So can their surface patterns. They’re also flexible, biocompatible and biodegradable.

“The novelty here is the fabrication method,” Hashemi said. “We employ hydrodynamic forces to influence the orientation of molecules for the fabrication of these fiber structures that have different properties along different directions.”

The Iowa State researchers demonstrated that neural stem cells were able to attach and align on the microfiber scaffold.

“In this study, cell death was minimal, and cell proliferation was affected by changing the features of the fibrous scaffold,” the researchers reported in their paper.

That finding has the researchers thinking their technology could be a tool that helps tissue engineers find ways to regenerate nerve cells and other tissues:

“By mimicking the microenvironment of the nervous system, regeneration can be enhanced due to biological and chemical cues in the environment,” the researchers wrote in their paper. “In addition, the PCL fibers can be applied in regeneration of other tissues such as muscle, tendons and blood vessels.”

A temperature below absolute zero: Atoms at negative absolute temperature are the hottest systems in the world. 

Summary:

On the absolute temperature scale, which is used by physicists and is also called the Kelvin scale, it is not possible to go below zero – at least not in the sense of getting colder than zero kelvin. According to the physical meaning of temperature, the temperature of a gas is determined by the chaotic movement of its particles – the colder the gas, the slower the particles. At zero kelvin (minus 273 degrees Celsius) the particles stop moving and all disorder disappears. Thus, nothing can be colder than absolute zero on the Kelvin scale. Physicists have now created an atomic gas in the laboratory that nonetheless has negative Kelvin values. These negative absolute temperatures have several apparently absurd consequences: although the atoms in the gas attract each other and give rise to a negative pressure, the gas does not collapse – a behavior that is also postulated for dark energy in cosmology. 
Full story. 

Temperature as a game of marbles: The Boltzmann distribution states how many particles have which energy, and can be illustrated with the aid of spheres distributed in a hilly landscape. At positive temperatures (left image), most spheres lie in the valley at minimum potential energy and barely move; they therefore also possess minimum kinetic energy. States with low total energy are therefore more likely than those with high total energy – the usual Boltzmann distribution. At infinite temperature (centre image) the spheres are spread evenly over low and high energies in an identical landscape. Here, all energy states are equally probable. At negative temperatures (right image), however, most spheres move on top of the hill, at the upper limit of the potential energy. Their kinetic energy is also maximum. Energy states with high total energy thus occur more frequently than those with low total energy – the Boltzmann distribution is inverted.

Credit: LMU and MPG Munich

A Backpack That Charges Your IPod?

Summary:

The stress and strain absorbed by your backpack could one day recharge your cell phone. Researchers have designed a strap that will capture the energy generated by the up-and-down movement of a hiker’s pack and turn it into enough voltage to power small electrical devices. 
Full:

Researchers at Michigan Technological University have designed a strap that will capture the energy generated by the up-and-down movement of a hiker’s pack and turn it into enough voltage to power small electrical devices.

“It’s pretty cool,” says Henry Sodano, an adjunct professor of engineering “mechanical engineering — engineering mechanics, who recently accepted a faculty appointment at Arizona State University. “We are harnessing free energy that would normally be lost.”

With mechanical engineering graduate students Jonathan Granstrom and Joel Feenstra, Sodano designed straps made of a piezoelectric material that can convert mechanical strain into electrical energy.

You probably wouldn’t be able to plug a TV into your backpack; the system is designed for use with devices that require small amounts of electricity, such as a GPS unit. Alternatively, a hiker could charge up a headlamp while walking during the day and then turn it on after dark. Or the backpack could generate enough power to recharge a handheld computer.

The straps are made of a nylon-like polymer that produces a fluctuating, AC current that could be stored in a battery or a capacitor. The researchers teamed up with the Blacksburg, Va., company NanoSonic Inc. to develop a specialized electrode grown on the surface of the strap using nanotechnology.

The beauty of the design is that it requires no extra effort on the part of the user, unlike other devices that transform mechanical energy into electricity, such as wind-up flashlights. It’s part of a new field called “energy harvesting.”

“We’re trying to capture free power. You don’t need watts of energy for many modern electronics,” Sodano said. “We’re not trying to generate significant levels of power, just enough to perform a useful function.”

Someone shouldering a heavy pack, such as a soldier in the field, could generate 45.6 milliwatts of power walking two or three miles per hour. That’s enough wattage to power small electronics. Or, it could be accumulated for later use.

“In general, we want to accumulate the power before using it; for example you could walk for 20 minutes then have enough power to talk for 2.5 minutes on your cell phone,” Sodano says.

The research was funded by the Office of Naval Research, which is investigating power sources for Marines in the field. The researchers hope to receive additional support to develop a prototype and then to commercialize their innovation.

Source:

Michigan Technological University