Category Archives: Packaging Materials

A new class of carbon nanotubes could be the next-generation clean-up crew for toxic sludge and contaminated water, say researchers at Rochester Institute of Technology.

Single-walled carbon nanotubes filter dirty water in experiments at RIT. Credit: John-David Rocha and Reginald Rogers

Single-walled carbon nanotubes filter dirty water in experiments at RIT. Credit: John-David Rocha and Reginald Rogers

Enhanced single-walled carbon nanotubes offer a more effective and sustainable approach to water treatment and remediation than the standard industry materials–silicon gels and activated carbon–according to a paper published in the March issue of Environmental Science Water: Research and Technology.

RIT researchers John-David Rocha and Reginald Rogers, authors of the study, demonstrate the potential of this emerging technology to clean polluted water. Their work applies carbon nanotubes to environmental problems in a specific new way that builds on a nearly two decades of nanomaterial research. Nanotubes are more commonly associated with fuel-cell research.

“This aspect is new–taking knowledge of carbon nanotubes and their properties and realizing, with new processing and characterization techniques, the advantages nanotubes can provide for removing contaminants for water,” said Rocha, assistant professor in the School of Chemistry and Materials Science in RIT’s College of Science.

Rocha and Rogers are advancing nanotube technology for environmental remediation and water filtration for home use.

“We have shown that we can regenerate these materials,” said Rogers, assistant professor of chemical engineering in RIT’s Kate Gleason College of Engineering. “In the future, when your water filter finally gets saturated, put it in the microwave for about five minutes and the impurities will get evaporated off.”

Carbon nanotubes are storage units measuring about 50,000 times smaller than the width of a human hair. Carbon reduced to the nanoscale defies the rules of physics and operates in a world of quantum mechanics in which small materials become mighty.

“We know carbon as graphite for our pencils, as diamonds, as soot,” Rocha said. “We can transform that soot or graphite into a nanometer-type material known as graphene.”

A single-walled carbon nanotube is created when a sheet of graphene is rolled up. The physical change alters the material’s chemical structure and determines how it behaves. The result is “one of the most heat conductive and electrically conductive materials in the world,” Rocha said. “These are properties that only come into play because they are at the nanometer scale.”

The RIT researchers created new techniques for manipulating the tiny materials. Rocha developed a method for isolating high-quality, single-walled carbon nanotubes and for sorting them according to their semiconductive or metallic properties. Rogers redistributed the pure carbon nanotubes into thin papers akin to carbon-copy paper.

“Once the papers are formed, now we have the adsorbent–what we use to pull the contaminants out of water,” Rogers said.

The filtration process works because “carbon nanotubes dislike water,” he added. Only the organic contaminants in the water stick to the nanotube, not the water molecules.

“This type of application has not been done before,” Rogers said. “Nanotubes used in this respect is new.”

For the last few decades, microchip manufacturers have been on a quest to find ways to make the patterns of wires and components in their microchips ever smaller, in order to fit more of them onto a single chip and thus continue the relentless progress toward faster and more powerful computers. That progress has become more difficult recently, as manufacturing processes bump up against fundamental limits involving, for example, the wavelengths of the light used to create the patterns.

Now, a team of researchers at MIT and in Chicago has found an approach that could break through some of those limits and make it possible to produce some of the narrowest wires yet, using a process that could easily be scaled up for mass manufacturing with standard kinds of equipment.

The new findings are reported this week in the journal Nature Nanotechnology, in a paper by postdoc Do Han Kim, graduate student Priya Moni, and Professor Karen Gleason, all at MIT, and by postdoc Hyo Seon Suh, Professor Paul Nealey, and three others at the University of Chicago and Argonne National Laboratory. While there are other methods that can achieve such fine lines, the team says, none of them are cost-effective for large-scale manufacturing.

The new approach uses a self-assembly technique in which materials known as block copolymers are covered by a second polymer. They are deposited on a surface by first heating the precursor so it vaporizes, then allowing it to condense on a cooler surface, much as water condenses on the outside of a cold drinking glass on a hot day.

“People always want smaller and smaller patterns, but achieving that has been getting more and more expensive,” says Gleason, who is MIT’s associate provost as well as the Alexander and I. Michael Kasser (1960) Professor of Chemical Engineering. Today’s methods for producing features smaller than about 22 nanometers (billionths of a meter) across generally require building up an image line by line, by scanning a beam of electrons or ions across the chip surface — a very slow process and therefore expensive to implement at large scale.

The new process uses a novel integration of two existing methods. First, a pattern of lines is produced on the chip surface using standard lithographic techniques, in which light shines through a negative mask placed on the chip surface. That surface is chemically etched so that the areas that were illuminated get dissolved away, leaving the spaces between them as conductive “wires” that connect parts of the circuit.

Then, a layer of material known as a block copolymer — a mix of two different polymer materials that naturally segregate themselves into alternating layers or other predictable patterns — is formed by spin coating a solution. The block copolymers are made up of chain-like molecules, each consisting of two different polymer materials connected end-to-end.

“One half is friendly with oil, the other half is friendly with water,” Kim explains. “But because they are completely bonded, they’re kind of stuck with each other.” The dimensions of the two chains predetermine the sizes of layers or other patterns they will assemble themselves into when they are deposited.

Finally, a top, protective polymer layer is deposited on top of the others using chemical vapor deposition (CVD). This top coat, it turns out, is a key to the process: It constrains the way the block copolymers self-assemble, forcing them to form into vertical layers rather than horizontal ones, like a layer cake on its side.

The underlying lithographed pattern guides the positioning of these layers, but the natural tendencies of the copolymers cause their width to be much smaller than that of the base lines. The result is that there are now four (or more, depending on the chemistry) lines, each of them a fourth as wide, in place of each original one. The lithographed layer “controls both the orientation and the alignment” of the resulting finer lines, explains Moni.

Because the top polymer layer can additionally be patterned, the system can be used to build up any kind of complex patterning, as needed for the interconnections of a microchip.

Most microchip manufacturing facilities use the existing lithographic method, and the CVD process itself is a well-understood additional step that could be added relatively easily. Thus, implementing the new method could be much more straightforward than other proposed methods of making finer lines, such as the use of extreme ultraviolet light, which would require the development of new light sources and new lenses to focus the light. With the new method, Gleason says, “you wouldn’t need to change all those machines. And everything that’s involved are well-known materials.”

Hydrogen is both the simplest and the most-abundant element in the universe, so studying it can teach scientists about the essence of matter. And yet there are still many hydrogen secrets to unlock, including how best to force it into a superconductive, metallic state with no electrical resistance.

“Although theoretically ideal for energy transfer or storage, metallic hydrogen is extremely challenging to produce experimentally,” said Ho-kwang “Dave” Mao, who led a team of physicists in researching the effect of the noble gas argon on pressurized hydrogen.

It has long been proposed that introducing impurities into a sample of molecular hydrogen, H2, could help ease the transition to a metallic state. So Mao and his team set out to study the intermolecular interactions of hydrogen that’s weakly-bound, or “doped,” with argon, Ar(H2)2, under extreme pressures. The idea is that the impurity could change the nature of the bonds between the hydrogen molecules, reducing the pressure necessary to induce the nonmetal-to-metal transition. Previous research had indicated that Ar(H2)2 might be a good candidate.

Surprisingly, they discovered that the addition of argon did not facilitate the molecular changes needed to initiate a metallic state in hydrogen. Their findings are published by the Proceedings of the National Academy of Sciences.

The team brought the argon-doped hydrogen up to 3.5 million times normal atmospheric pressure–or 358 gigapascals–inside a diamond anvil cell and observed its structural changes using advanced spectroscopic tools.

What they found was that hydrogen stayed in its molecular form even up to the highest pressures, indicating that argon is not the facilitator many had hoped it would be.

“Counter to predictions, the addition of argon did not create a kind of ‘chemical pressure’ on the hydrogen, pushing its molecules closer together. Rather, it had the opposite effect,” said lead author Cheng Ji.

Transition metal oxides (TMO) are extensively studied, technologically important materials, due to their complex electronic interactions, resulting in a large variety of collective phenomena. Memory effects in TMO’s have garnered a huge amount of interest, being both of fundamental scientific interest and technological significance.

Dr. Amos Sharoni of Bar-Ilan University’s Department of Physics, and Institute of Nanotechnology and Advanced Materials (BINA), has now uncovered a new kind of memory effect, unrelated to memory effects previously reported.

Dr. Sharoni, together with his student Naor Vardi, and supported by theoretical modelling by Yonatan Dubi of Ben-Gurion University in the Negev, utilized a simple experimental design to study changes in the properties of two TMOs, VO2 and NdNiO3, which undergo a metal-insulator phase-transition. Their results, just published in the journal Advanced Materials, not only demonstrate a new phenomenon but, importantly, also provide an explanation of its origin.

Ramp reversal memory

Metal-insulator transitions are transitions from a metal (material with good electrical conductivity of electric charges) to an insulator (material where conductivity of charges is quickly suppressed). These transitions can be achieved by a small variation of external parameters such as pressure or temperature.

In Sharoni’s experiment, when heated the studied TMOs transit from one state to another, and their properties undergo a change, beginning in a small area where “islands” develop and then grow, and vice-versa during cooling, similar to the coexistence of ice and water during melting. Sharoni cooled his samples while transition was in process, and then examined what happened when they were reheated. He found that when the reheated metal-oxide reached the temperature point at which re-cooling had occurred, that is, in the phase coexistence state – an increase in resistance was measured. And this increase in resistance was observed at each different point at which cooling was initiated. This previously unknown and surprising phenomenon demonstrates the creation of a “memory”.

Sharoni explains: “When the temperature ramp is reversed, and the sample is cooled rather than heated, the direction change creates a “scar” wherever there is a phase-boundary between the conducting and insulating islands. The ramp reversal sequence “encrypts” in the TMO a “memory” of the reversal temperature, which is manifested as increased resistance”. Moreover, it is possible to create and store more than one “memory” in the same physical space.

Sharoni likens the creation of a “scar” to the motion of waves on the seashore. A wave rushes up the beach and as it recedes it leaves a small sandy mound at the furthest point that it reached. When the wave returns it slows and brakes as it reaches the mound obstacle in its path. However, if a strong wave follows, it rushes over the mound and destroys it. Similarly, Sharoni found that further heating the TMO enables it to complete transition and to cross the scarred boundaries, “healing” the scars and immediately erasing the memory. In contrast cooling does not erase them.

Technology and security

The results of Sharoni’s work will have important impact on additional research, both experimental and theoretical, and the simplicity of the experimental design will enable other groups studying relevant systems to perform similar measurements with ease.

The multi-state nature of the memory effect, whereby more than one piece of information can coexist in the same space, could be harnessed for memory technology. And while deleted computer data is not secure and can be recovered, at least partially, by talented hackers, the “erase-upon-reading” property of this system could make an invaluable contribution to security technologies.

Princeton researchers have discovered a new form of the simple compound GeSe that has surprisingly escaped detection until now. This so-called beta-GeSe compound has a ring type structure like graphene and its monolayer form could have similarly valuable properties for electronic applications, according to the study published in the Journal of the American Chemical Society.

Graphene has been hailed as a two-dimensional wonder material for electronics but its lack of a band gap has hindered its development for devices. As such, a closely related material, black phosphorus, has been receiving intense research attention because it has a small band gap and a high charge carrier mobility, and can easily be reduced to nanometer thicknesses. The researchers calculated that GeSe is highly analogous to black phosphorus and can be considered a pseudo-group-V element.

This is the building blocks of graphene, black phosphorus, α-GeSe, and β-GeSe. Credit: Cava lab

This is the building blocks of graphene, black phosphorus, α-GeSe, and β-GeSe. Credit: Cava lab

Under extreme pressure, black phosphorus is transformed into a simple cubic form, so the team wondered if the same could be done to GeSe and heated the abundant alpha-GeSe form of the compound to 1200 °C under 6 GPa of pressure or 60,000 times atmospheric pressure.

“What we found was not only a new kind of GeSe–which is already unconventional by itself in that you rarely find new binary compounds anymore–but that it has this uncommon ‘boat’ conformation that we were amazed by,” said first author of the study Fabian von Rohr, a postdoctoral researcher in the laboratory of Robert Cava, the Russell Wellman Moore Professor of Chemistry.

beta-GeSe’s rare “boat” form is likely stabilized by the slightly smaller distance between its layers, while black phosphorus and alpha-GeSe exist in standard “chair” conformations. The difference in structures gives rise to the compounds’ different electronic properties. The researchers found that beta-GeSe possesses a band gap size in between that of black phosphorus and alpha-GeSe, which could prove promising for future applications. GeSe is also an attractive material for electronics because it’s robust under ambient conditions while black phosphorus is reactive to both air and water.

This article originally appeared on SemiMD.com and was featured in the March 2017 issue of Solid State Technology.

By Ed Korczynski, Sr. Technical Editor

As detailed in Part 1 of this article published last month by SemiMD, the inaugural Critical Materials Council (CMC) Conference happened May 5-6 in Hillsboro, Oregon. Held just after the yearly private CMC meeting, the public CMC Conference provides a forum for the pre-competitive exchange of information to control the supply-chain of critical materials needed to run high-volume manufacturing (HVM) in IC fabs. The next CMC Conference will happen May 11-12 in Dallas, Texas.

At the end of the 2016 conference, a panel discussion moderated by Ed Korczynski was recorded and transcribed. The following is Part 2 of the conversation between the following industry experts:

  • Jean-Marc Girard, CTO and Director of R&D, Air Liquide Advanced Materials,
  • Jeff Hemphill, Staff Materials R&D Engineer, Intel Corporation,
  • Jonas Sundqvist, Sr. Scientist, Fraunhofer IKTS; and co-chair of ALD Conference, and
  • John Smythe, Distinguished Member of Technical Staff, Micron Technology.

KORCZYNSKI:  We heard from David Thompson [EDITOR’S NOTE:  Director of Process Chemistry, Applied Materials presented on “Agony in New Material Introductions –  Minimizing and Correlating Variabilities”] today on what we must control, and he gave an example of a so-called trace-contaminant that was essential for the process performance of a precursor, where the trace compound helped prevent particles from flaking off chamber walls. Do we need to specify our contaminants?

GIRARD:  Yes. To David’s point this morning, every molecule is different. Some are very tolerant due to the molecular process associated with it, and some are not. I’ll give you an example of a cobalt material that’s been talked about, where it can be run in production at perhaps 95% in terms of assay, provided that one specific contaminant is less than a couple of parts-per-million. So it’s a combination of both, it’s not assay OR a specification of impurities. It’s a matter of specifying the trace components that really matter when you reach the point that the data you gather gives you that understanding, and obviously an assay within control limits.

HEMPHILL:  Talking about whether we’re over-specifying or not, the emphasis is not about putting the right number on known parameters like assay that are obvious to measure, the emphasis is on identifying and understanding what makes up the rest of it and in a sense trying over-specify that. You identify through mass-spectrometry and other techniques that some fraction of a percent is primarily say five different species, it’s finding out how to individually monitor and track and control those as separate parameters. So from a specification point of view what we want is not necessarily the lowest possible numbers, but it’s expanding how many things we’re looking at so that we’re capturing everything that’s there.

KORCZYNSKI:  Is that something that you’re starting to push out to your suppliers?

HEMPHILL:  Yes. It depends on the application we’re talking about, but we go into it with the assumption that just assay will not be enough. Whether a single molecule or a blend of things is supposed to be there, we know that just having those be controlled by specification will not be sufficient. We go under the assumption that we are going to identify what makes up the remaining part of the profile, and those components are going to need to be controlled as well.

KORCZYNSKI:  Is that something that has changed by node? Back when things were simpler say at 45nm and larger, were these aspects of processing that we could safely ignore as ‘noise’ but are now important ‘signals’?

HEMPHILL:  Yes, we certainly didn’t pay as close attention just a couple of generations ago.

KORCZYNSKI:  That seems to lead us to questions about single-sources versus dual-sourcing. There are many good reasons to do both, but not simultaneously. However, it seems that because of all of the challenges we’re heard about over the last day-and-a-half of this conference it creates greater burden on the suppliers, and for critical materials the fabs are moving toward more single-sourcing over time.

SMYTHE:  I think that it comes down to more of a concern over geographic risk. I’ll buy from one entity if that entity has more than one geographic location for the supply, so that I’m not exposed to a single ‘Act of God’ or a ‘random statistical occurrence of global warming.’ So for example I  need to ask if a supplier has a place in the US and a place in France that makes the same thing, so that if something bad happens in one location it can still be sourced? Or do you have an alternate-supply agreement that if you can’t supply it you have an agreement with Company-X to supply it so that you still have control? You can’t come to a Micron and say we want to make sure that we get at minimum 25% no matter what, because what typically happens with second-sourcing is Company-A gets 75% of the business while Company-B gets 25%. There are a lot of reasons that that doesn’t work so well, so people may have an impression that there’s a movement toward single-source but it’s ‘single flexible-source.’

HEMPHILL:  There are a lot of benefits of dual- or multiple-sourcing. The commercial benefits of competition can be positive and we’re for it when it works. The risk is that as things are progressing and we’re getting more sensitive to differences in materials it’s getting harder to maintain that. We have seen situations where historically we were successful with dual-sourcing a raw material coming from two different suppliers or even a single supplier using two different manufacturing lines and everything was fine and qualified and we could alternate sources invisibly. However, as our sensitivity has grown over time we can start to detect differences.

So the concept of being ‘copy-exactly’ that we use in our factories, we really need production lines to do that, and if we’re talking about two different companies producing the same material then we’re not going to get them to be copy-exactly. When that results in enough of a variation in the material that we can detect it in the factory then we cannot rely upon two sources. Our preference would be one company that maintains multiple production sites that are designed to be exactly the same, then we have a high degree of confidence that they will be able to produce the same material.

GIRARD:  I can give you a supplier perspective on that. We are seeing very different policies from different customers, to the point that we’re seeing an increase in the number of customers doing single-sourcing with us, provided we can show the ability to maintain business continuity in case of a problem. I think that the industry became mature after the tragic earthquake and tsunami in Japan in 2011 with greater understanding of what business continuity means. We have the same discussions with our own suppliers, who may say that they have a dedicated reactor for a certain product with another backup reactor with a certain capacity on the same site, and we ask what happens if the plant goes on strike or there’s a fire there?

A situation where you might think the supply was stable involved silane in the United States. There are two large silane plants in the United States that are very far apart from each other and many Asian manufacturers dependent upon them. When the U.S. harbors went on strike for a long time there was no way that material could ship out of the U.S. customers. So, yes there were two plants but in such an event you wouldn’t have global supply. So there is no one way to manage our supply lines and we need to have conversations with our customers to discuss the risks. How much time would it take to rebuild a supply-chain source with someone else? If you can get that sort of constructive discussion going then customers are usually open to single-sourcing. One regional aspect is that Asian customers tend to favor dual-sourcing more, but that can lead to IP problems.

[DISCLOSURE:  Ed Korczynski is co-chair of the CMC Conference, and Marketing Director of TECHCET CA the advisory services firm that administers the Critical Materials Council (CMC).]

—E.K.

To realize the next generation of devices for information processing based on new phenomena such as spintronics, multiferroics, magnetooptics, and magnonics, their constituent materials need to be developed. Recent rapid progress in nanotechnology allows us to fabricate nanostructures that are impossible to obtain in nature.

However, complex magnetic oxides are one of the most complicated material systems in terms of development and analysis. In addition, the detailed mechanism is unknown by which changes in atomic composition that do not affect overall structure lead to drastic changes in material characteristics even though the material structure is similar.

Now, researchers at Spin Electronics Group at Toyohashi Tech and at Myongji University, Harbin Institute of Technology, Massachusetts Institute of Technology, Universidad Técnica Federico Santa María, University of California, San Diego, and Trinity College Dublin found that nanoscale pillar-shaped distribution of iron in strontium titanate (STF) changes its magnetic and magnetooptical response drastically. Surprisingly, the polycrystalline sample showed stronger magnetism than single crystalline film.

Image of nanopillar-like poly-crystalline STF film obtained by transmission electron microscopy. Credit: TOYOHASHI UNIVERSITY OF TECHNOLOGY.

Image of nanopillar-like poly-crystalline STF film obtained by transmission electron microscopy.
Credit: TOYOHASHI UNIVERSITY OF TECHNOLOGY.

“In usual oxide systems, magnetic and magnetooptical effects are stronger in highly ordered structures. In other words, single crystalline material is better for obtaining better magnetic properties,” explains Assistant Professor Taichi Goto, “However, iron-substituted strontium titanate deposited at certain oxygen pressure is different.”

The STF films were prepared by pulsed laser deposition at various pressures directly on silicon substrate, and crystalline structure and magnetic properties were characterized systematically. A sample deposited at a certain pressure showed significantly stronger magnetism and larger Faraday rotation angle (magnetooptical effects) at room temperature. Several tests analyzing the oxygen stoichiometry and the corresponding Fe valence states, the structure and strain state, and the presence of small-volume fractions of iron revealed that the nanostructure and clustering of the elements enhanced magnetism.

These results show the broad possibility of polycrystalline films being used in silicon-based devices. In this paper, the integration of STF film with 0.1 mm scale optical resonator was demonstrated. Further, the integration of such novel oxides with conventional device concepts would pave a way for interesting systems in the future.

In electronics, the race for smaller is huge.

Physicists at the University of Cincinnati are working to harness the power of nanowires, microscopic wires that have the potential to improve solar cells or revolutionize fiber optics.

University of Cincinnati physicist Hans-Peter Wagner is exploring nanowire semiconductors to harness the power of light at the nano level. Credit: Andrew Higley/UC Creative Services

University of Cincinnati physicist Hans-Peter Wagner is exploring nanowire semiconductors to harness the power of light at the nano level. Credit: Andrew Higley/UC Creative Services

Nanotechnology has the potential to solve the bottleneck that occurs in storing or retrieving digital data – or could store data in a completely new way. UC professors and their graduate students presented their research at the March 13 conference of the American Physical Society in New Orleans, Louisiana.

Hans-Peter Wagner, associate professor of physics, and doctoral student Fatemesadat Mohammadi are looking at ways to transmit data with the speed of fiber optics but at a significantly smaller scale.

Wagner and lead author Mohammadi are studying this field, called plasmonics, with researchers from three other universities. For the novel experiment, they built nanowire semiconductors with organic material, fired laser pulses at the sample and measured the way light traveled across the metal; technically, the excitations of plasmon waves.

“So, if we succeed in getting a better understanding about the coupling between the excitations in semiconductor nanowires and metal films, it could open up a lot of new perspectives,” Wagner said.

The successful harnessing of this phenomenon — called plasmon waveguiding — could allow researchers to transmit data with light at the nano level.

Universities around the world are studying nanowires, which have ubiquitous applications from biomedical sensors to light-emitting diodes or LEDs. Four UC papers on the topic are among more than 150 others by nanowire researchers around the world to be presented at the March conference.

“You’re trying to optimize the physical structure on something approaching the atomic scale. You can make very high efficiency devices like lasers,” said Leigh Smith, head of UC’s Department of Physics. Smith and UC Physics Professor Howard Jackson also presented papers on nanowires at the conference. Virtually everyone benefits from this line of research, even if the quantum mechanics underlying the latest biosensors exceed a casual understanding. For example, home pregnancy tests use gold nanoparticles – the indicator that turns color. People use technologies all the time that they don’t understand,” Smith said.

Gordon Moore, co-founder of Intel Corp., observed that the number of transistors used in a microchip has roughly doubled every two years since the 1970s. This phenomenon, now called Moore’s Law suggests that computer processing power improves at a predictable rate.

Some computer scientists predicted the demise of Moore’s Law was inevitable with the advent of microprocessors. But nanotechnology is extending that concept’s lifespan, said Brian Markwalter, senior vice president of research and technology for the Consumer Technology Association. His trade group represents 2,200 members in the $287 billion U.S. tech industry.

“It’s not a race to be small just to be the smallest. There’s a progression of being able to do more on smaller chips. The effect for consumers is that every year they get better and better products for the same price or less,” he said.

Nanotechnology is opening a universe of new possibilities, Markwalter said.

“It’s almost magical. They get better, faster, cheaper and use less power,” he said.

Markwalter said UC professor Wagner’s research is exciting because it shows promise in using optical switches to address a bottleneck in data transmission that occurs whenever you try to store or remove data.

“It’s really a breakthrough area to merge the semiconductor world and the optical world,” Markwalter said. “[Wagner’s] working at the intersection of fiber optics and photonics.”

But even nanotechnology has its limits, Smith said.

“We’re running toward the limits of what’s physically possible with present technologies,” Smith said. “The challenges are pretty immense. In 10 or 20 years there has to be a fundamental paradigm shift in how we make structures. If we don’t we’ll be caught at the same place we are now.”

How one UC experiment works:

UC graduate student Fatemesadat Mohammadi and Associate Physics Professor Hans-Peter Wagner fire laser pulses at semiconductor nanowires to excite electrons (called excitons) that potentially serve as an energy pump to guide plasmon waves over a coated metal film just a few nanometers thick without losing power, a nettlesome physical property called resistivity

They measure the resulting luminescence of the nanowire to observe how light couples to the metal film. By sending light over a metal film, a process called plasmonic waveguiding, researchers one day could transmit data with light at the nano level.

“The luminescence is our interest. So we coat them and see: How does the photoluminescence characteristic change?” Mohammadi said.

To make the semiconductor, they use a technique called high-vacuum organic molecular beam deposition (pictured above) to spread organic and metal layers on gallium-nitride nanorods.

The use of organic film is unique to the UC experiment, Wagner said. The film works as a spacer to control the energy flow between excitons in the nanowire and the oscillation of metal electrons called plasmons.

The organic material has the added benefit of also containing excitons that, arranged properly, could support the energy flow in a semiconductor, he said.

Coating the nanorods with gold significantly shortens the lifetime of the exciton emission resulting in what’s called a quenched photoluminescence. But by using organic spacers between the nanorod and the gold film, the researchers are able to extend the emission lifetime to nearly the equivalent of nanorods without a coating.

Once the gold-coated sample is prepared, they take it to an adjacent lab room and subject it to pulses of laser light.

Mohammadi said it took days of painstaking work to arrange the small city of mirrors and beam splitters bolted at precise angles to a workbench for the experiment (pictured above left).

The reactions in the nanowire take just 10 picoseconds (which is a trillionth of a second.) And the laser pulses are faster still — 20 femtoseconds (a figure that has 15 zeros following it or a quadrillionth of a second.)

The UC project used a gold coating so that experiments could be replicated at a later date without risk of oxidation. But traditional coatings such as silver, Mohammadi said, hold even more promise.

Entegris Inc. (NASDAQ: ENTG), a manufacturer of specialty chemicals and advanced materials handling solutions for the microelectronics industry, today announced it has signed an agreement with Spectrum Materials (Fujian) Co., Ltd. to expand its presence in China. According to the agreement, Spectrum Materials, a manufacturer and distributor of specialty chemicals, will manufacture Entegris specialty chemicals products at Spectrum Materials’ Quanzhou facility.

“We are excited about this partnership, as it will significantly improve our capabilities to meet growing demands for specialty chemicals in the industries we serve,” stated Entegris Senior Vice President of Specialty Chemicals and Engineered Materials, Stuart Tison. “Spectrum Materials is a well-established company in China that has experience supplying related high-purity chemicals and shares our expectations for quality and manufacturing standards. As we have done in other global regions, we continue to look for ways to better serve our customers and to add value with local collaboration, business processes and resources.”

Entegris currently manufactures specialty chemicals in both the U.S. and South Korea and has business operations in Beijing, Shanghai and Xi’an, China. The partnership with Spectrum Materials will expand its capability in China and shorten its supply chain for Chinese customers. This relationship is part of a broader strategic commitment by Entegris to support the growing semiconductor and related microelectronics industries in China.

“We are pleased to partner with Entegris in the manufacturing of its industry-leading specialty chemical products in China,” said President of Spectrum Materials, Guofu Chen. “Our new expansion, combined with Entegris manufacturing technology, establishes a world-class facility for the production of Entegris’ semiconductor grade specialty chemicals in China.”

Spectrum Materials will use a copy-exact manufacturing process to match existing Entegris processes and equipment and will implement the same quality control system in the manufacturing process.

Metamaterials don’t exist in nature, but their ability to make ultra-thin lenses and ultra-efficient cell phone antennas, bend light to keep satellites cooler and let photovoltaics absorb more energy mean they offer a world of possibilities.

Formed by nanostructures that act as “atoms,” arranged on a substrate to alter light’s path in ways no ordinary material can achieve, these surrogate substances can manipulate an incoming light beam to enable the creation of more efficient versions of ubiquitous, valuable devices — optical filters, lasers, frequency converters and devices that steer beams, for example.

But extensive commercial use of metamaterials has been restrained by the limitations imposed by the materials comprising them. Metal-based metamaterials are “lossy” (lose energy) at shorter wavelengths and can operate effectively only at low frequencies, such as the radio frequencies used by radar, before being overwhelmed by their own absorption. Silicon doesn’t emit light and can transmit it only in a limited wavelength range because of its narrow working range (bandgap). So neither class of material can create a metamaterial that will operate in the infrared and optical ranges, where most military and commercial applications would take place.

This three-resonator-thick III-V metasurface of cylindrical resonators illustrates three possible uses: The left light beam changes color as it passes through the metasurfaces, signifying that nonlinear harmonic generation is taking place that converts the light beam to a shorter wavelength. The blue trace in the middle shows a train of pulses passing through the surface. As they pass, the pulse width decreases due to pulse compression, which requires that the phase of the transmitted optical wave vary with the wavelength. The multilayer metasurfaces are able to achieve the correct phase variation -- something not possible with single layer metasurfaces. The beam on the right signifies that these metasurfaces can act as efficient emitters of light. Click on the thumbnail for a high-resolution image. Credit: (Illustration courtesy of Sandia National Laboratories)

This three-resonator-thick III-V metasurface of cylindrical resonators illustrates three possible uses: The left light beam changes color as it passes through the metasurfaces, signifying that nonlinear harmonic generation is taking place that converts the light beam to a shorter wavelength. The blue trace in the middle shows a train of pulses passing through the surface. As they pass, the pulse width decreases due to pulse compression, which requires that the phase of the transmitted optical wave vary with the wavelength. The multilayer metasurfaces are able to achieve the correct phase variation — something not possible with single layer metasurfaces. The beam on the right signifies that these metasurfaces can act as efficient emitters of light. Click on the thumbnail for a high-resolution image. Credit: (Illustration courtesy of Sandia National Laboratories)

Optical metamaterials enter the arena

Sandia National Laboratories researchers are helping lead the way to the use of III-V semiconductors as the building blocks of metamaterials. (III-V refers to elements in those columns in the periodic table.) Sandia researchers have published technical papers, including three in the past year, on work featuring materials like gallium-arsenide and aluminum-arsenide, which are more efficient than metals for optical metamaterial applications, with wider bandgap ranges than silicon. The work is promising enough to have been featured on the covers of two technical journals.

“There is very little work worldwide on all-dielectric metamaterials using III-V semiconductors,” said Sandia researcher Igal Brener, who leads the Sandia work with researchers Mike Sinclair and Sheng Liu. “Our advantage is Sandia’s vast access to III-V technology, both in growth and processing, so we can move pretty fast.”

Shinier than gold

The new Sandia dielectric materials — a kind of electrical insulator — offer more than just efficiency. They lose little incoming energy and can even be fabricated in multiple layers to form complex, three-dimensional meta-atoms that reflect more light than shiny gold surfaces, usually considered the ultimate in infrared reflectivity. The III-V materials also emit photons when excited — something that silicon, which can reflect, transmit and absorb — can’t do.

Another advantage is their highly variable outputs, across the color spectrum so they might be used to extend the wavelength range of lasers or for generating “entangled photons” for quantum computing.

Sandia’s approach also is attractive for its relatively simple method of forming the artificial atoms, known as resonators, that are the guts of the metamaterial.

Created under the supervision of Liu, the meta-atoms are a few hundred nanometers in diameter and made of many actual atoms. One of Liu’s improvements was to oxidize these tiny groupings around their perimeters to create layered coatings with a low index of refraction, rather than use a more expensive, time-consuming “flip-chip” bonding process. The complexity of previous methods was an obstacle to cost- and time-efficiency. Other Sandia researchers had used a variant of his simplification previously to make lasers, but not metamaterials, he said.

The oxidized, low-index surface surrounds the high-index core “like in wintertime, you have a coat surrounding you,” Liu said. “To confine light, you need a high refractive-index contrast.” Put another way, interior light bumping into the low-indexed oxide surface is herded back by the refractive difference so it travels along the high-index core.

Liu’s Sandia colleague Gordon Keeler achieved controlled oxidation simply by putting III-V materials in a hot oven and flowing water vapor over the sample. “It will oxidize at a certain rate,” Liu says. “The more material, the longer it takes.”

The man-made meta-atoms are sculpted in place during a lithographic process that permits researchers to make any pattern they chose for the placement of the metamaterial components. “We use simulations to direct us,” Liu said. Spacing is determined to some extent by the size of the manmade atoms.

Fractured cubic nanostructures store unusually large amounts of energy

The researchers experimented with cylindrical and cubic nanostructures, reducing the symmetry of the latter to achieve even better properties.

“Cylinders are much easier to fabricate and typically can be used for conventional metasurfaces,” said Brener. “But broken-symmetry cubes are crucial to obtain very sharp resonances. That’s the key issue of the paper.”

The idea of intentionally reducing the symmetry of a cubic resonator nanostructure originated five or six years ago, said Sinclair, with a serendipitous design that happened to break the intentionally symmetrical shape of the meta-atoms when the team tried to mimic a particular manufacturing flaw.

“During a Laboratory Directed Research and Development [LDRD] Metamaterials Grand Challenge, when we were first fabricating cubic resonators in our effort to see if we could get beyond microwaves into infrared and optical metamaterials, we were playing with the shape of resonators to try to simulate the effect of lithography errors. In one simulation, we happened to cut a corner of the cube and all of a sudden very sharp reflection bands appeared,” Sinclair said.

Prior to that discovery, dielectric resonator metamaterials only showed broad bands that didn’t trap much energy. The researchers found the new sharp resonances allowed greater energy storage — beneficial for efficient frequency conversion, and perhaps even for light emission and lasing.

Exploration of the crimped resonator had to wait for a later project, sponsored by the Department of Energy’s Office of Science. Salvatore Campione, building on previous work by Lorena Basilio, Larry Warne and William Langston — all of Sandia — used electromagnetic simulations to unravel precisely how the cubes trap light. Sandia’s Willie Luk measured the cubes’ reflective properties. Another LDRD grant currently supports research into metamaterial lasing.

“We feel we’ve created a pretty flexible platform for a lot of different kinds of devices,” Sinclair said.

The ongoing work is aided by Sandia’s John Reno, nationally known for growing extremely precise crystalline structures, who contributed the III-V wafers.

Three patents on aspects of the work have been submitted.