Tag Archives: Indian Institute of Science

Flat gallium (gallenene) and nanoelectronics

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Another day, another 2D material. A March 9, 2018 news item on ScienceDaily announced the latest thin material from Rice university,

Scientists at Rice University and the Indian Institute of Science, Bangalore, have discovered a method to make atomically flat gallium that shows promise for nanoscale electronics.

The Rice lab of materials scientist Pulickel Ajayan and colleagues in India created two-dimensional gallenene, a thin film of conductive material that is to gallium what graphene is to carbon.

Extracted into a two-dimensional form, the novel material appears to have an affinity for binding with semiconductors like silicon and could make an efficient metal contact in two-dimensional electronic devices, the researchers said.

A March 9, 2018 Rice University news release (also on EurekAlert), which originated the news item, describes the process for creating gallenene,

Gallium is a metal with a low melting point; unlike graphene and many other 2-D structures, it cannot yet be grown with vapor phase deposition methods. Moreover, gallium also has a tendency to oxidize quickly. And while early samples of graphene were removed from graphite with adhesive tape, the bonds between gallium layers are too strong for such a simple approach.

So the Rice team led by co-authors Vidya Kochat, a former postdoctoral researcher at Rice, and Atanu Samanta, a student at the Indian Institute of Science, used heat instead of force.

Rather than a bottom-up approach, the researchers worked their way down from bulk gallium by heating it to 29.7 degrees Celsius (about 85 degrees Fahrenheit), just below the element’s melting point. That was enough to drip gallium onto a glass slide. As a drop cooled just a bit, the researchers pressed a flat piece of silicon dioxide on top to lift just a few flat layers of gallenene.

They successfully exfoliated gallenene onto other substrates, including gallium nitride, gallium arsenide, silicone and nickel. That allowed them to confirm that particular gallenene-substrate combinations have different electronic properties and to suggest that these properties can be tuned for applications.

“The current work utilizes the weak interfaces of solids and liquids to separate thin 2-D sheets of gallium,” said Chandra Sekhar Tiwary, principal investigator on the project he completed at Rice before becoming an assistant professor at the Indian Institute of Technology in Gandhinagar, India. “The same method can be explored for other metals and compounds with low melting points.”

Gallenene’s plasmonic and other properties are being investigated, according to Ajayan. “Near 2-D metals are difficult to extract, since these are mostly high-strength, nonlayered structures, so gallenene is an exception that could bridge the need for metals in the 2-D world,” he said.

Co-authors of the paper are graduate student Yuan Zhang and Associate Research Professor Robert Vajtai of Rice; Anthony Stender, a former Rice postdoctoral researcher and now an assistant professor at Ohio University; Sanjit Bhowmick, Praveena Manimunda and Syed Asif of Bruker Nano Surfaces, Minneapolis; and Rice alumnus Abhishek Singh of the Indian Institute of Science. Ajayan is chair of Rice’s Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry.

The Air Force Office of Scientific Research sponsored the research, with additional support from the Indo-US Science and Technology Forum, the government of India and a Rice Center for Quantum Materials/Smalley-Curl Postdoctoral Fellowship in Quantum Materials.

Here’s a link to and a citation for the paper,

Atomically thin gallium layers from solid-melt exfoliation by Vidya Kochat, Atanu Samanta, Yuan Zhang, Sanjit Bhowmick, Praveena Manimunda, Syed Asif S. Asif, Anthony S. Stender, Robert Vajtai, Abhishek K. Singh, Chandra S. Tiwary, and Pulickel M. Ajayan. Science Advances 09 Mar 2018: Vol. 4, no. 3, e1701373 DOI: 10.1126/sciadv.1701373

This paper appears to be open access.

Recycle electronic waste by crushing it into nanodust

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Given the issues with e-waste this work seems quite exciting. From a March 21, 2017 Rice University news release (also on EurekAlert), Note: Links have been removed,

Researchers at Rice University and the Indian Institute of Science have an idea to simplify electronic waste recycling: Crush it into nanodust.

Specifically, they want to make the particles so small that separating different components is relatively simple compared with processes used to recycle electronic junk now.

Chandra Sekhar Tiwary, a postdoctoral researcher at Rice and a researcher at the Indian Institute of Science in Bangalore, uses a low-temperature cryo-mill to pulverize electronic waste – primarily the chips, other electronic components and polymers that make up printed circuit boards (PCBs) — into particles so small that they do not contaminate each other.

Then they can be sorted and reused, he said.

Circuit boards from electronics, like computer mice, can be crushed into nanodust by a cryo-mill, according to researchers at Rice and the Indian Institute of Science. The dust can then be easily separated into its component elements for recycling.

Circuit boards from electronics, like computer mice, can be crushed into nanodust by a cryo-mill, according to researchers at Rice and the Indian Institute of Science. The dust can then be easily separated into its component elements for recycling. Courtesy of the Ajayan Research Group

The process is the subject of a Materials Today paper by Tiwary, Rice materials scientist Pulickel Ajayan and Indian Institute professors Kamanio Chattopadhyay and D.P. Mahapatra. 

The researchers intend it to replace current processes that involve dumping outdated electronics into landfills, or burning or treating them with chemicals to recover valuable metals and alloys. None are particularly friendly to the environment, Tiwary said.

“In every case, the cycle is one way, and burning or using chemicals takes a lot of energy while still leaving waste,” he said. “We propose a system that breaks all of the components – metals, oxides and polymers – into homogenous powders and makes them easy to reuse.”

The researchers estimate that so-called e-waste will grow by 33 percent over the next four years, and by 2030 will weigh more than a billion tons. Nearly 80 to 85 percent of often-toxic e-waste ends up in an incinerator or a landfill, Tiwary said, and is the fastest-growing waste stream in the United States, according to the Environmental Protection Agency.

The answer may be scaled-up versions of a cryo-mill designed by the Indian team that, rather than heating them, keeps materials at ultra-low temperatures during crushing.

Cold materials are more brittle and easier to pulverize, Tiwary said. “We take advantage of the physics. When you heat things, they are more likely to combine: You can put metals into polymer, oxides into polymers. That’s what high-temperature processing is for, and it makes mixing really easy.

A transparent piece of epoxy, left, compared to epoxy with e-waste reinforcement at right. A cryo-milling process developed at Rice University and the Indian Institute of Science simplifies the process of separating and recycling electronic waste.

A transparent piece of epoxy, left, compared to epoxy with e-waste reinforcement at right. A cryo-milling process developed at Rice University and the Indian Institute of Science simplifies the process of separating and recycling electronic waste. Courtesy of the Ajayan Research Group

“But in low temperatures, they don’t like to mix. The materials’ basic properties – their elastic modulus, thermal conductivity and coefficient of thermal expansion – all change. They allow everything to separate really well,” he said.

The test subjects in this case were computer mice – or at least their PCB innards. The cryo-mill contained argon gas and a single tool-grade steel ball. A steady stream of liquid nitrogen kept the container at 154 kelvins (minus 182 degrees Fahrenheit).

When shaken, the ball smashes the polymer first, then the metals and then the oxides just long enough to separate the materials into a powder, with particles between 20 and 100 nanometers wide. That can take up to three hours, after which the particles are bathed in water to separate them.

“Then they can be reused,” he said. “Nothing is wasted.”

Here’s a link to and a citation for the paper,

Electronic waste recycling via cryo-milling and nanoparticle beneficiation by C.S. Tiwary, S. Kishore, R. Vasireddi, D.R. Mahapatra, P.M. Ajayan, K. Chattopadhyay. Materials Today         http://dx.doi.org/10.1016/j.mattod.2017.01.015 Available online 20 March 2017

This paper is behind a paywall.

Identifying performance problems in nanoresonators

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Use of nanoelectromechanical systems (NEMS) can now be maximised due to a technique developed by researchers at the Commissariat a l’Energie Atomique (CEA) and the University of Grenoble-Alpes (France). From a March 7, 2016 news item on ScienceDaily,

A joint CEA / University of Grenoble-Alpes research team, together with their international partners, have developed a diagnostic technique capable of identifying performance problems in nanoresonators, a type of nanodetector used in research and industry. These nanoelectromechanical systems, or NEMS, have never been used to their maximum capabilities. The detection limits observed in practice have always been well below the theoretical limit and, until now, this difference has remained unexplained. Using a totally new approach, the researchers have now succeeded in evaluating and explaining this phenomenon. Their results, described in the February 29 [2016] issue of Nature Nanotechnology, should now make it possible to find ways of overcoming this performance shortfall.

A Feb. 29, 2016 CEA press release, which originated the news item, provides more detail about NEMS and about the new technique,

NEMS have many applications, including the measurement of mass or force. Like a tiny violin string, a nanoresonator vibrates at a precise resonant frequency. This frequency changes if gas molecules or biological particles settle on the nanoresonator surface. This change in frequency can then be used to detect or identify the substance, enabling a medical diagnosis, for example. The extremely small dimensions of these devices (less than one millionth of a meter) make the detectors highly sensitive.

However, this resolution is constrained by a detection limit. Background noise is present in addition to the wanted measurement signal. Researchers have always considered this background noise to be an intrinsic characteristic of these systems (see Figure 2 [not reproduced here]). Despite the noise levels being significantly greater than predicted by theory, the impossibility of understanding the underlying phenomena has, until now, led the research community to ignore them.

The CEA-Leti research team and their partners reviewed all the frequency stability measurements in the literature, and identified a difference of several orders of magnitude between the accepted theoretical limits and experimental measurements.

In addition to evaluating this shortfall, the researchers also developed a diagnostic technique that could be applied to each individual nanoresonator, using their own high-purity monocrystalline silicon resonators to investigate the problem.

The resonant frequency of a nanoresonator is determined by the geometry of the resonator and the type of material used in its manufacture. It is therefore theoretically fixed. By forcing the resonator to vibrate at defined frequencies close to the resonant frequency, the CEA-Leti researchers have been able to demonstrate a secondary effect that interferes with the resolution of the system and its detection limit in addition to the background noise. This effect causes slight variations in the resonant frequency. These fluctuations in the resonant frequency result from the extreme sensitivity of these systems. While capable of detecting tiny changes in mass and force, they are also very sensitive to minute variations in temperature and the movements of molecules on their surface. At the nano scale, these parameters cannot be ignored as they impose a significant limit on the performance of nanoresonators. For example, a tiny change in temperature can change the parameters of the device material, and hence its frequency. These variations can be rapid and random.

The experimental technique developed by the team makes it possible to evaluate the loss of resolution and to determine whether it is caused by the intrinsic limits of the system or by a secondary fluctuation that can therefore by corrected. A patent has been applied for covering this technique. The research team has also shown that none of the theoretical hypotheses so far advanced to explain these fluctuations in the resonant frequency can currently explain the observed level of variation.

The research team will therefore continue experimental work to explore the physical origin of these fluctuations, with the aim of achieving a significant improvement in the performance of nanoresonators.

The Swiss Federal Institute of Technology in Lausanne, the Indian Institute of Science in Bangalore, and the California Institute of Technology (USA) have also participated in this study. The authors have received funding from the Leti Carnot Institute (NEMS-MS project) and the European Union (ERC Consolidator Grant – Enlightened project).

Here’s a link to and a citation for the paper,

Frequency fluctuations in silicon nanoresonators by Marc Sansa, Eric Sage, Elizabeth C. Bullard, Marc Gély, Thomas Alava, Eric Colinet, Akshay K. Naik, Luis Guillermo Villanueva, Laurent Duraffourg, Michael L. Roukes, Guillaume Jourdan & Sébastien Hentz. Nature Nanotechnology (2016) doi:10.1038/nnano.2016.19 Published online 29 February 2016

This paper is behind a paywall.

Asia’s research effort in nano-, bio-, and information technology integrated in Asian Research Network

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The Feb. 29, 2012 news item by Cameron Chai on Azonano spells it out,

An Asian Research Network (ARN) has been formed by the Hanyang University of Korea and RIKEN of Japan in collaboration with other institutes and universities in Asia. This network has been launched to reinforce a strong education and research collaboration throughout Asia.

The Asian Research Network website is here. You will need to use your scroll bars as it appears to be partially constructed (or maybe my system is so creaky that I just can’t see everything on the page). Towards the bottom (right side) of the home page,there are a couple of red buttons for PDFs of the ARN Pamphlet and Research Articles.

From page 2 of the ARN pamphlet, here’s a listing of the member organizations,

KOREA

Hanyang University
Samsung Electronics
Electronics and Telecommunication Research Institute
Seoul National University
Institute of Pasteur Korea
Korea Research Institute of Chemical Technology
Korea Advanced Nano Fab Center

JAPAN

RIKEN

INDIA

National Chemical Laboratory
Shivaji University
Indian Institutes of Science Education and Research
Pune University
Indian Institute of Technology-Madras (In Progress)
Indian Institute of Science (In Progress)

USA

University of Texas at Dallas
UCLA (In Progress)
f d i i ( )

CHINA

National Center for Nanoscience and Technology
Peking University

SINGAPORE

National University of Singapore
Nanyang Technological University (In Progress)
Stanford University In Progress)
University of Maryland (In Progress)

ISRAEL

Weizmann Institute of Science (In Progress)
Hebrew University Jerusalem

THAILAND

National Science and Technology Development Agency (In Progress)

I was a little surprised to see Israel on the list and on an even more insular note, why no Canada?

Getting back to the ARN, here are their aims, from page 2 of the ARN pamphlet,

We are committed to fostering talented human resources, creating a research network in which researchers in the region share their knowledge and experiences, and establishing a future-oriented partnership to globalize our research capabilities. To this end, we will achieve excellence in all aspects of education, research, and development in the area of fusion research between BT [biotechnology] and IT [information technology] based on NT [nanotechnology] in general. We will make a substantial contribution to the betterment of the global community as well as the Asian society.

I look forward to hearing more from them in the future.