Nature Materials: Smallest lattice structure worldwide

The smallest lattice in the world is visible under the microscope only. Struts and braces are 0.2 µm in diameter. Total size of the lattice is about 10 µm. Photo: J. Bauer / KIT

KIT scientists now present the smallest lattice structure made by man in the Nature Materials journal. Its struts and braces are made of glassy carbon and are less than 1 µm long and 200 nm in diameter. They are smaller than comparable metamaterials by a factor of 5. The small dimension results in so far unreached ratios of strength to density. Applications as electrodes, filters or optical components might be possible. (DOI: 10.1038/nmat4561)

"Lightweight construction materials, such as bones and wood, are found everywhere in nature," Dr.-Ing. Jens Bauer of Karlsruhe Institute of Technology (KIT), the first author of the study, explains. "They have a high load-bearing capacity and small weight and, hence, serve as models for mechanical metamaterials for technical applications."

Metamaterials are materials, whose structures of some micrometers (millionths of a meter) in dimension are planned and manufactured specifically for them to possess mechanical or optical properties that cannot be reached by unstructured solids. Examples are invisibility cloaks that guide light, sound or heat around objects, materials that counterintuitively react to pressure and shear (auxetic materials) or lightweight nanomaterials of high specific stability (force per unit area and density).

The smallest stable lattice structure worldwide presented now was produced by the established 3D laser lithography process at first. The desired structure of micrometer size is hardened in a photoresist by laser beams in a computer-controlled manner. However, resolution of this process is limited, such that struts of about 5 - 10 µm length and 1 µm in diameter can be produced only. In a subsequent step, the structure was therefore shrunk and vitrified by pyrolysis. For the first time, pyrolysis was used for manufacturing microstructured lattices. The object is exposed to temperatures of around 900°C in a vacuum furnace. As a result, chemical bonds reorient themselves. Except for carbon, all elements escape from the resist. The unordered carbon remains in the shrunk lattice structure in the form of glassy carbon. The resulting structures were tested for stability under pressure by the researchers.

"According to the results, load-bearing capacity of the lattice is very close to the theoretical limit and far above that of unstructured glassy carbon," Prof. Oliver Kraft, co-author of the study, reports. Until the end of last year, Kraft headed the Institute for Applied Materials of KIT. This year, he took over office as KIT Vice President for Research. "Diamond is the only solid having a higher specific stability."

Microstructured materials are often used for insulation or shock absorption. Open-pored materials may be used as filters in chemical industry. Metamaterials also have extraordinary optical properties that are applied in telecommunications. Glassy carbon is a high-technology material made of pure carbon. It combines glassy, ceramic properties with graphite properties and is of interest for use in electrodes of batteries or electrolysis systems.

KIT

Argonne-UChicago researchers work to annihilate nanoscale defects in semiconductors

Researchers from the University of Chicago and Argonne use the supercomputing resources at the Argonne Leadership Computing Facility to predict the path molecules must follow to find defect-free states. They designed a process that delivers industry-standard nanocircuitry that can be scaled down to smaller densities without defects.
Courtesy of Argonne National Laboratory

Target dates are critical when the semiconductor industry adds small, enhanced features to consumer devices by integrating advanced materials onto the surfaces of computer chips. Missing a target means postponing a device’s release, which could cost a company millions of dollars or the loss of competitiveness and an entire industry.

But meeting target dates can be challenging because the final integrated devices, which include billions of transistors, must be flawless—less than one defect per 100 square centimeters.

Researchers at the University of Chicago and Argonne National Laboratory, led by Profs. Juan de Pablo and Paul Nealey, may have found a way for the semiconductor industry to hit miniaturization targets on time and without defects.

To make microchips, de Pablo and Nealey’s technique includes creating patterns on semiconductor surfaces that allow block copolymer molecules to self-assemble into specific shapes, but thinner and at much higher densities than those of the original pattern. The researchers can then use a lithography technique to create nano-trenches where conducting wire materials can be deposited.

This is a stark contrast to the industry practice of using homo-polymers in complex “photoresist” formulations, where researchers have “hit a wall,” unable to make the material smaller.

Before they could develop their new fabrication method, however, de Pablo and Nealey needed to understand exactly how block copolymers self-assemble when coated onto a patterned surface—their concern being that certain constraints cause copolymer nanostructures to assemble into undesired metastable states. To reach the level of perfection demanded to fabricate high-precision nanocircuitry, the team had to eliminate some of these metastable states.

Using the Argonne Leadership Computing Facility, UChicago and Argonne researchers have found a way miniaturize microchip components using a technique producing zero defects. This advance will allow semiconductor manufacturers to meet miniaturization target dates to produce smaller components with added functionality for consumer devices.
Courtesy of Argonne National Laboratory

To imagine how block copolymers assemble, it may be helpful to picture an energy landscape consisting of mountains and valleys, in which some valleys are deeper than others. The system prefers defect-free stability, which can be characterized by the deepest (low-energy) valleys, if they can be found. However, systems can get trapped inside higher (medium-energy) valleys, called metastable states, which have more defects.

To move from a metastable to stable state, block copolymer molecules must find ways to climb over the mountains and find lower energy valleys.

“Molecules in these metastable states are comfortable, and they can remain in that state for extraordinarily long periods of time,” said de Pablo.

“In order to escape such states and attain a perfect arrangement, they need to start rearranging themselves in a manner that allows the system to climb over local energy barriers, before reaching a lower energy minimum. What we have done in this work is predict the path these molecules must follow to find defect-free states and designed a process that delivers industry-standard nanocircuitry that can be scaled down to smaller densities without defects.”

Supported by a DOE leadership computing grant, de Pablo and his team used the Mira and Fusion supercomputers at the Argonne Leadership Computing Facility. The team generated molecular simulations of self-assembling block polymers along with sophisticated sampling algorithms to calculate where barriers to structural rearrangement would arise in the material. 

After all the calculations were done, the researchers could precisely predict the pathways of molecular rearrangement that block copolymers must take to move from a metastable to stable state. They could also experiment with temperatures, solvents and applied fields to further manipulate and decrease the barriers between these states.

To test these calculations, de Pablo and Nealey partnered with IMEC, an international consortium located in Belgium. Their commercial-grade fabrication and characterization instruments helped the researchers perform experiments under conditions that are not available in academic laboratories.

An individual defect measures only a handful of nanometers; “finding a defect in a 100-square centimeter area is like finding a needle in hay stack, and there are only a few places in the world where one has access to the necessary equipment to do so,” said de Pablo.

“Manufacturers have long been exploring the feasibility of using block copolymer assembly to reach the small critical dimensions that are demanded by modern computing and higher data storage densities,” de Pablo said. “Their biggest challenge involved evaluating defects; by following the strategies we have outlined, that challenge is greatly diminished.”

John Neuffer, president and CEO of the Semiconductor Industry Association, said industry is relentlessly focused on designing and building chips that are smaller, more powerful and more energy-efficient.

“The key to unlocking the next generation of semiconductor innovation is research,” he said. “SIA commends the work done by Argonne National Laboratory and the University of Chicago, as well as other critical scientific research being done across the United States.”

De Pablo, Nealey and their team will continue their investigations with a wider class of materials, increasing the complexity of patterns and characterizing materials in greater detail while also developing methods based on self-assembly for fabrication of three-dimensional structures.

Their long-term goal, with support from the DOE’s Office of Science, is to arrive at an understanding of directed self-assembly of polymeric molecules that will enable creation of wide classes of materials with exquisite control over their nanostructure and functionality for applications in energy harvesting, storage and transport.

University of Chicago

A ‘printing press’ for nanoparticles

This new technique could facilitate use of gold nanoparticles in electronic, medical applications

Gold nanoparticles have unusual optical, electronic and chemical properties, which scientists are seeking to put to use in a range of new technologies, from nanoelectronics to cancer treatments.

Some of the most interesting properties of nanoparticles emerge when they are brought close together – either in clusters of just a few particles or in crystals made up of millions of them.  Yet particles that are just millionths of an inch in size are too small to be manipulated by conventional lab tools, so a major challenge has been finding ways to assemble these bits of gold while controlling the three-dimensional shape of their arrangement.

One approach that researchers have developed has been to use tiny structures made from synthetic strands of DNA to help organize nanoparticles. Since DNA strands are programmed to pair with other strands in certain patterns, scientists have attached individual strands of DNA to gold particle surfaces to create a variety of assemblies. But these hybrid gold-DNA nanostructures are intricate and expensive to generate, limiting their potential for use in practical materials. The process is similar, in a sense, to producing books by hand.

Enter the nanoparticle equivalent of the printing press. It’s efficient, re-usable and carries more information than previously possible. In results reported online in Nature Chemistry, researchers from McGill’s Department of Chemistry outline a procedure for making a DNA structure with a specific pattern of strands coming out of it; at the end of each strand is a chemical “sticky patch.”  When a gold nanoparticle is brought into contact to the DNA nanostructure, it sticks to the patches. The scientists then dissolve the assembly in distilled water, separating the DNA nanostructure into its component strands and leaving behind the DNA imprint on the gold nanoparticle. (See illustration.)

“These encoded gold nanoparticles are unprecedented in their information content,” says senior author Hanadi Sleiman, who holds the Canada Research Chair in DNA Nanoscience. “The DNA nanostructures, for their part, can be re-used, much like stamps in an old printing press.”

From stained glass to optoelectronics

Some of the properties of gold nanoparticles have been recognized for centuries.  Medieval artisans added gold chloride to molten glass to create the ruby-red colour in stained-glass windows – the result, as chemists figured out much later, of the light-scattering properties of tiny gold particles. 

Now, the McGill researchers hope their new production technique will help pave the way for use of DNA-encoded nanoparticles in a range of cutting-edge technologies. First author Thomas Edwardson says the next step for the lab will be to investigate the properties of structures made from these new building blocks. “In much the same way that atoms combine to form complex molecules, patterned DNA gold particles can connect to neighbouring particles to form well-defined nanoparticle assemblies.”

These could be put to use in areas including optoelectronic nanodevices and biomedical sciences, the researchers say. The patterns of DNA strands could, for example, be engineered to target specific proteins on cancer cells, and thus serve to detect cancer or to selectively destroy cancer cells. 

Financial support for the research was provided by the Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, the Centre for Self-Assembled Chemical Structures, the Canada Research Chairs Program and the Canadian Institutes of Health Research.

“Transfer of molecular recognition information from DNA nanostructures to gold nanoparticles,” Thomas G. W. Edwardson et al, Nature Chemistry, Jan. 4, 2016. DOI: 10.1038/nchem.2420
http://www.nature.com/nchem/journal/vaop/ncurrent/full/nchem.2420.html

McGill University

The world's fastest nanoscale photonics switch

International team of researchers from Lomonosov Moscow State University and the Australian National University in Canberra created an ultrafast all-optical switch on silicon nanostructures.

This device may become a platform for future computers and permit to transfer data at an ultrahigh speed. The article with the description of the device was published in Nano Letters journal and highlighted in Nature Materials.

This work belongs to the field of photonics - an optics discipline which appeared in the 1960-s, simultaneously with the invention of lasers. Photonics has the same goals as electronics does, but uses photons--the quanta of light--instead of electrons. The biggest advantage of using photons is the absence of interactions between them. As a consequence, photons address the data transmission problem better than electrons. This property can primarily be used for in computing where IPS (instructions per second) is the main attribute to be maximized. The typical scale of eletronic transistors--the basis of contemporary electronic devices--is less than 100 nanometers, wheres the typical scale of photonic transistors stays on the scale of several micrometers.

Nanostructures that are able to compete with the electronic structures--for example, plasmonic nanoparticles--are characterized by low efficiency and significant losses. Therefore, coming up with a compact photonic switch was a very challenging task.

Three years ago several groups of researchers simultaneously discovered an important effect: they found out that silicon nanoparticles are exhibit strong resonances in the visible spectrum - the so-called magnetic dipole resonances. This type of resonance is characterized by strong localization of light waves on subwavelength scales, inside the nanoparticles. This effect turned out to be interesting to researches, but, according to Maxim Shcherbakov, the first author of the article published in Nano Letters, nobody thought that this discovery could create a basis for development of a compact and very rapid photonic switch.

Nanoparticles were fabricated in the Australian National University by e-beam lithography followed by plasma-phase etching. It was done by Alexander Shorokhov, who served an internship in the University as a part of Presidential scholarship for studying abroad. The samples were brought to Moscow, and all the experimental work was carried out at the Faculty of Physics of Lomonosov Moscow State University, in the Laboratory of Nanophotonics and Metamaterials.

"In our experimental research me and my colleague Polina Vabishchevich from the Faculty used a set of nonlinear optics methods that address femtosecond light-matter, -- explains Maxim Shcherbakov. -- We used our femtosecond laser complex acquired as part of the MSU development program".

Eventually, researches developed a "device": a disc 250 nm in diameter that is capable of switching optical pulses at femtosecond rates (femtosecond is a one millionth of one billionth of a second). Switching speeds that fast will allow to create data transmission and processing devices that will work at tens and hundreds terabits per second. This can make possible downloading thousands of HD-movies in less than a second.

The operation of the all-optical switch created by MSU researchers is based on the interaction between two femtosecond pulses. The interaction becomes possible due to the magnetic resonance of the silicon nanostructures. If the pulses arrive at the nanostructure simultaneously, one of them interacts with the other and dampers it due to the effect of two-photon absorption. If there is a 100-fs delay between the two pulses, the interaction does not occur, and the second pulse goes through the nanostructure without changing.

"We were able to develop a structure with the undesirable free-carrier effects are suppressed, -- says Maxim Shcherbakov. -- Free carriers (electrons and electron holes) place serious restrictions on the speed of signal conversion in the traditional integrated photonics. Our work represents an important step towards novel and efficient active photonic devices-- transistors, logic units, and others. Features of the technology implemented in our work will allow its use in silicon photonics. In the nearest future, we are going to test such nanoparticles in integrated circuits".

http://www.nanotechnologyworld.org/#!The-worlds-fastest-nanoscale-photonics-switch/c89r/565dba120cf2c000e929c875 

Lomonosov Moscow State University

Nanoplasmonics makes the impossible possible

Over a five-year period, Alexander Dmitriev and his research team at Chalmers will take on a task that until now has been deemed impossible: creating strong interaction between light and magnetic fields and determining ways to control light with magnetism on the nanoscale. The Harnessing light and spins through plasmons at the nanoscale project has received close to SEK 38 million from the Knut and Alice Wallenberg Foundation, and may eventually lead to more effective ways to process and store information with light and create different types of optical elements.

"The entire field is still fairly unknown, and we are one of only a few research teams in the world currently looking specifically into light as nanoplasmonic resonances combined with magnetic nanostructures," says Alexander Dmitriev, associate professor of physics at Chalmers.

For a long time it has been deemed impossible to combine light and magnetism because of a frequency gap where light moves 10,000 times faster than magnetism reacts, which means they do not feel each other and cannot integrate. By capturing the light in what are known as nanoantennas, which are built over a surface, it is possible for the two to interact on the nanoscale. There are nanoplasmons in this artificially created surface of nanoantennas – in other words small units of electrons that when exposed to visible light, move or oscillate collectively and thus create enhanced and localised electromagnetic fields that can then be connected with magnetic materials via different types of magneto-optical effects.  

"We want to attempt to force the light to become steerable using magnetism, and vice versa, and thus eliminate the frequency gap," says Alexander Dmitriev.

Steerable optical components

When the project ends in five years, the team hopes to have obtained a fundamental understanding of the field and be better equipped to build the specific nanostructures needed to achieve the desired properties. By bringing internationally leading research teams from Chalmers and the universities in Uppsala and Gothenburg together, it will be possible to utilise expertise within both theoretical and experimental physics in nanoplasmonics, nanomagnetism and spintronics. However, even if the project has a purely fundamental character, Alexander Dmitriev sees clear areas of application where it will hopefully be possible to use the methods in the future.

"This technology could enable steerable and adaptable optical components that are not easily controlled with electric current, for example three-dimensional holograms that move in real time. Thanks to the enhanced interaction we want to create between light and magnetism on the nanoscale, it will be possible to use low-intensity magnetic fields similar to those found in regular refrigerator magnets, and it will be quick, energy-efficient and easy to integrate with electronics.  

Chalmers University of Technology

Newly Discovered ‘Design Rule’ Brings Nature-Inspired Nanostructures One Step Closer

Snakes on a plane: This atomic-resolution simulation of a two-dimensional peptoid nanosheet reveals a snake-like structure never seen before. The nanosheet’s layers include a water-repelling core (yellow), peptoid backbones (white), and charged sidechains (magenta and cyan). The right corner of the top layer of the nanosheet has been “removed” to show how the backbone’s alternating rotational states give the backbones a snake-like appearance (red and blue ribbons). Surrounding water molecules are red and white. (Credit: Ranjan Mannige, Berkeley Lab)

Computer sims and microscopy research at Berkeley Lab yield first atomic-resolution structure of a peptoid nanosheet

Scientists aspire to build nanostructures that mimic the complexity and function of nature’s proteins, but are made of durable and synthetic materials. These microscopic widgets could be customized into incredibly sensitive chemical detectors or long-lasting catalysts, to name a few possible applications.

But as with any craft that requires extreme precision, researchers must first learn how to finesse the materials they’ll use to build these structures. A discovery by scientists from the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), and reported Oct. 7 in the advance online publication of the journal Nature, is a big step in this direction.

The scientists discovered a design rule that enables a recently created material to exist. The material is a peptoid nanosheet. It’s a flat structure only two molecules thick, and it’s composed of peptoids, which are synthetic polymers closely related to protein-forming peptides.

The design rule controls the way in which polymers adjoin to form the backbones that run the length of nanosheets. Surprisingly, these molecules link together in a counter-rotating pattern not seen in nature. This pattern allows the backbones to remain linear and untwisted, a trait that makes peptoid nanosheets larger and flatter than any biological structure.

The Berkeley Lab scientists say this never-before-seen design rule could be used to piece together complex nanosheet structures and other peptoid assemblies such as nanotubes and crystalline solids.

What’s more, they discovered it by combining computer simulations with x-ray scattering and imaging methods to determine, for the first time, the atomic-resolution structure of peptoid nanosheets.

“This research suggests new ways to design biomimetic structures,” says Steve Whitelam, a co-corresponding author of the Nature paper. “We can begin thinking about using design principles other than those nature offers.”

Whitelam is a staff scientist in the Theory Facility at the Molecular Foundry, a DOE Office of Science user facility located at Berkeley Lab. He led the research with co-corresponding author Ranjan Mannige, a postdoctoral researcher at the Molecular Foundry; and Ron Zuckermann, who directs the Molecular Foundry’s Biological Nanostructures Facility. They used the high-performance computing resources of the National Energy Research Scientific Computing Center (NERSC), another DOE Office of Science user facility located at Berkeley Lab.

The Molecular Foundry scientists who helped discover a new nano design rule. From left, Ellen Robertson, Alessia Battigelli, Ron Zuckermann, Caroline Proulx, Stephen Whitelam, and Ranjan Mannige. (Credit: Roy Kaltschmidt, Berkeley Lab)

Peptoid nanosheets were discovered by Zuckermann’s group five years ago. They found that under the right conditions, peptoids self assemble into two-dimensional assemblies that can grow hundreds of microns across. This “molecular paper” has become a hot prospect as a protein-mimicking platform for molecular design.

To learn more about this potential building material, the scientists set out to learn its atom-resolution structure. This involved feedback between experiment and theory. Microscopy and scattering data gathered at the Molecular Foundry and the Advanced Light Source, also a DOE Office of Science user facility located at Berkeley Lab, were compared with molecular dynamics simulations conducted at NERSC.

The research revealed several new things about peptoid nanosheets. Their molecular makeup varies throughout their structure, they can be formed only from peptoids of a certain minimum length, they contain water pockets, and they are potentially porous when it comes to water and ions.

These insights are intriguing on their own, but when the scientists examined the structure of the nanosheets’ backbone, they were surprised to see a design rule not found in the field of protein structural biology.

Here’s the difference: In nature, proteins are composed of beta sheets and alpha helices. These fundamental building blocks are themselves composed of backbones, and the polymers that make up these backbones are all joined together using the same rule. Each adjacent polymer rotates incrementally in the same direction, so that a twist runs along the backbone.

This rule doesn’t apply to peptoid nanosheets. Along their backbones, adjacent monomer units rotate in opposite directions. These counter-rotations cancel each other out, resulting in a linear and untwisted backbone. This enables backbones to be tiled in two dimensions and extended into large sheets that are flatter than anything nature can produce.

“It was a big surprise to find the design rule that makes peptoid nanosheets possible has eluded the field of biology until now,” says Mannige. “This rule could perhaps be used to build many more unrealized structures.”

Adds Zuckermann, “We also expect there are other design principles waiting to be discovered, which could lead to even more biomimetic nanostructures.”

A simulation of a peptoid nanosheet, shown first from a top-down view with the peptoid backbones colored to highlight their snake-like structure. The view then rotates to the side, and finally transitions to an all-atom representation. (Credit: Ron Zuckermann and Ranjan Mannige, Berkeley Lab)

Other Molecular Foundry scientists who contributed to this research are Thomas Haxton, Caroline Proulx, Ellen Robertson, and Alessia Battigelli.

This research was conducted at the Molecular Foundry, a DOE Office of Science user facility located at Berkeley Lab. The work was supported by the Defense Threat Reduction Agency, with additional funding provided by the Natural Sciences and Engineering Research Council of Canada. Part of this research was carried out through a User Project at the Molecular Foundry led by New York University’s Glenn Butterfoss.

Berkeley Lab

Nanotechnology World Association