Tag Archives: letter-dd-tech

The 64th annual IEEE International Electron Devices Meeting(IEDM), to be held at the Hilton San Francisco Union Square hotel December 1-5, 2018, has issued a Call for Papers seeking the world’s best original work in all areas of microelectronics research and development.

The paper submission deadline this year is Wednesday, August 1, 2018. Authors are asked to submit four-page camera-ready papers. Accepted papers will be published as-is in the proceedings. A limited number of late-news papers will be accepted. Authors are asked to submit late-news papers announcing only the most recent and noteworthy developments. The late-news submission deadline is September 10, 2018.

At IEDM each year, the world’s best scientists and engineers in the field of microelectronics gather to participate in a technical program consisting of more than 220 presentations, along with a variety of panels, special sessions, Short Courses, a supplier exhibit, IEEE/EDS award presentations and other events highlighting leading work in more areas of the field than any other conference.

This year, special emphasis is placed on the following topics:

  • Neuromorphic computing/AI
  • Quantum computing devices and links
  • Devices for RF, 5G, THz and mmWave
  • Advanced memory technologies
  • More-than-Moore devices and integrations
  • Technologies for advanced logic nodes
  • Non-charge-based devices and systems
  • Sensors and MEMS devices
  • Package-device level interactions
  • Electron device simulation and modeling
  • Advanced characterization, reliability and noise
  • Optoelectronics, displays and imaging systems

Overall, papers in the following areas of technology are encouraged:

  • Circuit and Device Interaction
  • Characterization, Reliability and Yield
  • Compound Semiconductor and High-Speed Devices
  • Memory Technology
  • Modeling and Simulation
  • Nano Device Technology
  • Optoelectronics, Displays and Imagers
  • Power Devices
  • Process and Manufacturing Technology
  • Sensors, MEMS and BioMEMS

Further information

For more information, interested persons should visit the IEDM 2018 home page at www.ieee-iedm.org.

An international research team from Russia, France, and Germany has proposed a new method for orienting liquid crystals. It could be used to increase the viewing angle of liquid-crystal displays. The paper was published in the journal ACS Macro Letters.

“This is first and foremost a fundamental study exploring the mechanisms of liquid crystal orientation,” says Dimitri Ivanov, the head of the Laboratory of Functional Organic and Hybrid Materials at MIPT. “That said, we expect that these mechanisms might have applications in new LCD technology.”

Subpixel structure in a twisted nematic LCD. Credit: Lion_on_helium/MIPT Press Office

Subpixel structure in a twisted nematic LCD. Credit: Lion_on_helium/MIPT Press Office

Liquid crystals

Most solids are crystals. In a crystal, molecules or atoms form an ordered three-dimensional structure. Unlike solids, liquids lack this internal long-range order, but they can flow. Matter in a liquid-crystal state has properties that are intermediate between those of liquids and crystals: It possesses both the molecular order and the ability to flow. A liquid crystal can thus be viewed as an “ordered” liquid.

Not all materials can exhibit a liquid crystalline state, and the phase transition mechanisms may vary. Among other things, the molecules of an LC material have to be anisometric — that is, rod- or disk-shaped. Some compounds become LCs in a certain temperature range. These are called thermotropic. By contrast, lyotropic LCs adopt the liquid crystalline state when a solvent is added.

The properties of an LC material vary depending on the direction. For example, polarized light propagates in a liquid crystal at different speeds along different directions. Also, in an electric or magnetic field, the orientation of LCs can rapidly change. This phenomenon is known as the Fréedericksz transition. Thanks to the optical properties of LCs and their ability to be easily realigned, they are widely used in the electronic displays of TVs, computers, phones, and other devices.

Liquid-crystal displays

In an LCD, the image is generated by changing the intensity of light in each pixel via an electric field, which realigns liquid crystals. There are several LCD configurations, but the one most commonly used is based on twisted nematic LCs. These are rod-shaped thermotropic liquid crystals that can adopt a twisted configuration by using special aligning substrates. Applying an electric field to these LCs can untwist them. This reproducible and predictable response can be used to control light intensity.

Each pixel in a color LCD consists of three subpixels: red, green, and blue. By varying their intensities, any color can be displayed. A subpixel in a twisted nematic-based LCD (figure 1) consists of a light source, a color filter, two polarizers, and an LC cell between two glass plates with electrodes. If the liquid crystals were not there, no light would pass through the cell, because whatever light is let through by the vertical polarizer would be blocked by the horizontal polarizer before reaching the color filter. However, special substrates with groovy surfaces can be used to twist LCs in a spiral between two polarizers so as to turn the light precisely by the amount needed to pass through the second polarizer. The fully illuminated state of the subpixel is actually its “off” state. When voltage is applied, the liquid crystals untwist, changing the light polarization to a lesser degree. As a result, some of the light is blocked. Eventually, as some voltage no light can reach the color filter, and the subpixel goes dark.

One of the limitations of this technology is the viewing angle of a display: From a sideways perspective, the LCD will not render the colors accurately. This is due to the co-alignment of liquid crystals. The issue can be solved using multidomain displays, in which pixels belong to a number of domains, whose LC orientations are different. This means that at least some of the domains are always oriented in the right way. The international team of researchers led by Professor Dimitri Ivanov, who heads MIPT’s Laboratory of Functional Organic and Hybrid Materials, has proposed a brand new solution for multidomain display design.

Going orthogonal

The authors of the paper reported in this story worked with liquid-crystal polymers. These are substances composed of long molecules with chainlike repetitive structure. It turned out that a slight variation in the structure of polymers can drastically alter their orientation on the substrate. The polymers used in the study are poly(di-n-alkylsiloxanes), or PDAS. Each molecule is a chain containing alternating silicon and oxygen atoms. The silicon atoms in PDAS bear two symmetric hydrocarbon side chains (figure 2). The n in the name of the compound stands for the length of the side chains, which was varied between 2 and 6.

In the experiment, polymers from the PDAS family were deposited on a Teflon-rubbed aligning surface with a regular pattern of grooves. Generally, crystalline polymers are known to align on such substrates, but only when the lattice parameters of the substrate match those of the deposited polymer. The researchers examined the orientation of the liquid-crystal polymer chains relative to the direction of the grooves on the aligning surface. The side chain length n was increased in steps of just one methylene group (CH?) at a time.

It was found that, contrary to expectations, the liquid-crystal orientation varied depending on side-chain length. At n equal to 2, the needlelike polymer superstructures known as lamellae co-aligned with the Teflon grooves. Because lamellae are known to be perpendicular to the polymer chains, the researchers concluded that the polymer chains are perpendicular to the grooves on the substrate (figure 3, left). When n was increased to 3, the orientation of the lamellae changed by 90 degrees, making them perpendicular to the grooves. As a result, the LC polymer chains were now oriented parallel to the grooves (figure 3, right). At n equal to 4, no further change in orientation was observed. However, when the side-chain length was further increased to 5 and 6, the lamellae again co-aligned with the Teflon grooves.

The researchers have thus found that by merely adding one methylene group to the side chain of the polymer, they could switch the LC orientation, which is crucial for most applications of liquid crystals, including LCDs. According to the authors, the effect they discovered could be used to design LCDs with improved viewing angles. This could be achieved using a multidomain technology that works by orienting subpixels of one color in different directions. As a result, the pixels compensate one another when the display is viewed at an angle, improving color rendition. The researchers expect this technology to be considerably simpler and cheaper than other multidomain approaches that are currently used.

Engineering and physics researchers at North Carolina State University have developed a new technology for steering light that allows for more light input and greater efficiency – a development that holds promise for creating more immersive augmented-reality display systems.

At issue are diffraction gratings, which are used to manipulate light in everything from electronic displays to fiber-optic communication technologies.

“Until now, state-of-the-art diffraction gratings configured to steer visible light to large angles have had an angular acceptance range, or bandwidth, of about 20 degrees, meaning that the light source has to be directed into the grating within an arc of 20 degrees,” says Michael Escuti, a professor of electrical and computer engineering at NC State and corresponding author of a paper on the work. “We’ve developed a new grating that expands that window to 40 degrees, allowing light to enter the grating from a wider range of input angles.

“The practical effect of this – in augmented-reality displays, for example – would be that users would have a greater field of view; the experience would be more immersive,” says Escuti, who is also the chief science officer of ImagineOptix Corp., which funded the work and has licensed the technology.

The new grating is also significantly more efficient.

“In previous gratings in a comparable configuration, an average of 30 percent of the light input is being diffracted in the desired direction,” says Xiao Xiang, a Ph.D. student at NC State and lead author of the paper. “Our new grating diffracts about 75 percent of the light in the desired direction.”

This advance could also make fiber-optic networks more energy efficient, the researchers say.

The new grating achieves the advance in angular bandwidth by integrating two layers, which are superimposed in a way that allows their optical responses to work together. One layer contains molecules that are arranged at a “slant” that allows it to capture 20 degrees of angular bandwidth. The second layer is arranged at a different slant, which captures an adjacent 20 degrees of angular bandwidth.

The higher efficiency stems from a smoothly varying pattern in the orientation of the liquid crystal molecules in the grating. The pattern affects the phase of the light, which is the mechanism responsible for redirecting the light.

“The next step for this work is to take the advantages of these gratings and make a new generation of augmented-reality hardware,” Escuti says.

The paper, “Bragg polarization gratings for wide angular bandwidth and high efficiency at steep deflection angles,” is published in the journal Scientific Reports. The paper was co-authored by Jihwan Kim, a research assistant professor of electrical and computer engineering at NC State.

Japanese researchers have developed a new method to build large areas of semiconductive material that is just two molecules thick and a total of 4.4 nanometers tall. The films function as thin film transistors, and have potential future applications in flexible electronics or chemical detectors. These thin film transistors are the first example of semiconductive single molecular bilayers created with liquid solution processing, a standard manufacturing process that minimizes costs.

Top surface view of 3-D computer model (left) and Atomic Force Microscopy image (right) of the new film made by University of Tokyo scientists. The well-organized structure of the molecules is visible in both the 3-D computer model and microscope image as a herringbone or cross-hair pattern. The color differences in the microscopy image are a result of the different lengths of the molecules' tails; the length differences cause the geometric frustration that prevents layers from stacking. pm = picometers, nm = nanometers. Credit: Shunto Arai and Tatsuo Hasegawa

Top surface view of 3-D computer model (left) and Atomic Force Microscopy image (right) of the new film made by University of Tokyo scientists. The well-organized structure of the molecules is visible in both the 3-D computer model and microscope image as a herringbone or cross-hair pattern. The color differences in the microscopy image are a result of the different lengths of the molecules’ tails; the length differences cause the geometric frustration that prevents layers from stacking. pm = picometers, nm = nanometers. Credit: Shunto Arai and Tatsuo Hasegawa

“We want to give electronic devices the features of real cell membranes: flexible, strong, sensitive, and super thin. We found a novel way to design semiconductive single molecular bilayers that allows us to manufacture large surface areas, up to 100 square centimeters (39 square inches). They can function as high performance thin film transistors and could have many applications in the future,” said Assistant Professor Shunto Arai, the first author on the recent research publication.

Professor Tatsuo Hasegawa of the University of Tokyo Department of Applied Physics led the team that built the new film. The breakthrough responsible for their success is a concept called geometric frustration, which uses a molecular shape that makes it difficult for molecules to settle in multiple layers on top of each other.

The film is transparent, but the forces of attraction and repulsion between the molecules create an organized, repeated herringbone pattern when the film is viewed from above through a microscope. The overall molecular structure of the bilayer is highly stable. Researchers believe it should be possible to build the same structure out of different molecules with different functionalities.

The individual molecules used in the current film are divided into two regions: a head and a tail. The head of one molecule stacks on top of another, with their tails pointing in opposite directions so the molecules form a vertical line. These two molecules are surrounded by identical head-to-head pairs of molecules, which all together form a sandwich called a molecular bilayer.

Researchers discovered they could prevent additional bilayers from stacking on top by building the bilayer out of molecules with different length tails, so the surfaces of the bilayer are rough and naturally discourage stacking. This effect of different lengths is referred to as geometric frustration.

Standard methods of creating semiconductive molecular bilayers cannot control the thickness without causing cracks or an irregular surface. The geometric frustration of different length tails has allowed researchers to avoid these pitfalls and build a 10cm by 10cm (3.9 inches by 3.9 inches) square of their film using the common industrial method of solution processing.

The semiconductive properties of the bilayer may give the films applications in flexible electronics or chemical detection.

Semiconductors are able to switch between states that allow electricity to flow (conductors) and states that prevent electricity from flowing (insulators). This on-off switching is what allows transistors to quickly change displayed images, such as a picture on an LCD screen. The single molecular bilayer created by the UTokyo team is much faster than amorphous silicon thin film transistors, a common type of semiconductor currently used in electronics.

The team will continue to investigate the properties of geometrically frustrated single molecular bilayers and potential applications for chemical detection. Collaborators based at the National Institute of Advanced Industrial Science and Technology, the Nippon Kayaku Company Limited, Condensed Matter Research Center, and High Energy Accelerator Research Organization also contributed to the research.

Thousands of miles of fiber-optic cables crisscross the globe and package everything from financial data to cat videos into light. But when the signal arrives at your local data center, it runs into a silicon bottleneck. Instead of light, computers run on electrons moving through silicon-based chips — which, despite huge advances, are still less efficient than photonics.

To break through this bottleneck, researchers are trying to integrate photonics into silicon devices. They’ve been developing lasers — a crucial component of photonic circuits — that work seamlessly on silicon. In a paper appearing this week in APL Photonics, from AIP Publishing, researchers from the University of California, Santa Barbara write that the future of silicon-based lasers may be in tiny, atomlike structures called quantum dots.

Such lasers could save a lot of energy. Replacing the electronic components that connect devices with photonic components could cut energy use by 20 to 75 percent, Justin Norman, a graduate student at UC Santa Barbara, said. “It’s a substantial cut to global energy consumption just by having a way to integrate lasers and photonic circuits with silicon.”

Silicon, however, does not have the right properties for lasers. Researchers have instead turned to a class of materials from Groups III and V of the periodic table because these materials can be integrated with silicon.

Initially, the researchers struggled to find a functional integration method, but ultimately ended up using quantum dots because they can be grown directly on silicon, Norman said. Quantum dots are semiconductor particles only a few nanometers wide — small enough that they behave like individual atoms. When driven with electrical current, electrons and positively charged holes become confined in the dots and recombine to emit light — a property that can be exploited to make lasers.

The researchers made their III-V quantum-dot lasers using a technique called molecular beam epitaxy. They deposit the III-V material onto the silicon substrate, and its atoms self-assemble into a crystalline structure. But the crystal structure of silicon differs from III-V materials, leading to defects that allow electrons and holes to escape, degrading performance. Fortunately, because quantum dots are packed together at high densities — more than 50 billion dots per square centimeter — they capture electrons and holes before the particles are lost.

These lasers have many other advantages, Norman said. For example, quantum dots are more stable in photonic circuits because they have localized atomlike energy states. They can also run on less power because they don’t need as much electric current. Moreover, they can operate at higher temperatures and be scaled down to smaller sizes.

In just the last year, researchers have made considerable progress thanks to advances in material growth, Norman said. Now, the lasers operate at 35 degrees Celsius without much degradation and the researchers report that the lifetime could be up to 10 million hours.

They are now testing lasers that can operate at 60 to 80 degrees Celsius, the more typical temperature range of a data center or supercomputer. They’re also working on designing epitaxial waveguides and other photonic components, Norman said. “Suddenly,” he said, “we’ve made so much progress that things are looking a little more near term.”

UC Berkeley engineers have built a bright-light emitting device that is millimeters wide and fully transparent when turned off. The light emitting material in this device is a monolayer semiconductor, which is just three atoms thick.

The device opens the door to invisible displays on walls and windows – displays that would be bright when turned on but see-through when turned off — or in futuristic applications such as light-emitting tattoos, according to the researchers.

Gif of the device in action. Probes inject positive and negative charges in the light emitting device, which is transparent under the campanile outline, producing bright light. Credit: Javey lab.

Gif of the device in action. Probes inject positive and negative charges in the light emitting device, which is transparent under the campanile outline, producing bright light. Credit: Javey lab.

“The materials are so thin and flexible that the device can be made transparent and can conform to curved surfaces,” said Der-Hsien Lien, a postdoctoral fellow at UC Berkeley and a co-first author along with Matin Amani and Sujay Desai, both doctoral students in the Department of Electrical Engineering and Computer Sciences at Berkeley.

Their study was published March 26 in the journal Nature Communications. The work was funded by the National Science Foundation and the Department of Energy.

The device was developed in the laboratory of Ali Javey, professor of Electrical Engineering and Computer Sciences at Berkeley. In 2015, Javey’s lab published research in the journal Science showing that monolayer semiconductors are capable of emitting bright light, but stopped short of building a light-emitting device. The new work in Nature Communicationsovercame fundamental barriers in utilizing LED technology on monolayer semiconductors, allowing for such devices to be scaled from sizes smaller than the width of a human hair up to several millimeters. That means that researchers can keep the thickness small, but make the lateral dimensions (width and length) large, so that the light intensity can be high.

Commercial LEDs consist of a semiconductor material that is electrically injected with positive and negative charges, which produce light when they meet. Typically, two contact points are used in a semiconductor-based light emitting device; one for injecting negatively charged particles and one injecting positively charged particles. Making contacts that can efficiently inject these charges is a fundamental challenge for LEDs, and it is particularly challenging for monolayer semiconductors since there is so little material to work with.

The Berkeley research team engineered a way to circumvent this challenge by designing a new device that only requires one contact on the semiconductor. By laying the semiconductor monolayer on an insulator and placing electrodes on the monolayer and underneath the insulator, the researchers could apply an AC signal across the insulator. During the moment when the AC signal switches its polarity from positive to negative (and vice versa), both positive and negative charges are present at the same time in the semiconductor, creating light.

The researchers showed that this mechanism works in four different monolayer materials, all of which emit different colors of light.

This device is a proof-of-concept, and much research still remains, primarily to improve efficiency. Measuring this device’s efficiency is not straightforward, but the researchers think it’s about 1 percent efficient. Commercial LEDs have efficiencies of around 25 to 30 percent.

The concept may be applicable to other devices and other kinds of materials, the device could one day have applications in a number of fields where having invisible displays are warranted. That could be an atomically thin display that’s imprinted on a wall or even on human skin.

“A lot of work remains to be done and a number of challenges need to be overcome to further advance the technology for practical applications,” Javey said. “However, this is one step forward by presenting a device architecture for easy injection of both charges into monolayer semiconductors.”

A new progress in the scaling of semiconductor quantum dot based qubit has been achieved at Key Laboratory of Quantum Information and Synergetic Innovation Center of Quantum Information & Quantum Physics of USTC. Professor GUO Guoping with his co-workers, XIAO Ming, LI Haiou and CAO Gang, designed and fabricated a quantum processor with six quantum dots, and experimentally demonstrated quantum control of the Toffoli gate. This is the first time for the realization of the Toffoli gate in the semiconductor quantum dot system, which motivates further research on larger scale semiconductor quantum processor. The result was published as ‘Controlled Quantum Operations of a Semiconductor Three-Qubit System ‘ (Physical Review Applied 9, 024015 (2018)).

This is the Toffoli Gate in a three-qubit system. Credit: University of Science and Technology of China

This is the Toffoli Gate in a three-qubit system. Credit: University of Science and Technology of China

Developing the scalable semiconductor quantum chip that is compatible with modern semiconductor-techniques is an important research area. In this area, the fabrication, manipulation and scaling of semiconductor quantum dot based qubits are the most important core technologies. Professor GUO Guoping’s group aims to master these technologies and has been devoted to this area for a long time. Before the demonstration of the three-qubit gate, they have realized ultrafast universal control of the charge qubit based on semiconductor quantum dots in 2013(Nature Communications. 4:1401 (2013)), and achieved the controlled rotation of two charge qubits in 2015(Nature Communications. 6:7681 (2015)).

The Toffoli gate is a three-qubit operation that changed the state of a target qubit conditioned on the state of two control qubits. It can be used for universal reversible classical computation and also forms a universal set of qubit gates in quantum computation together with a Hadamard gate. Furthermore, it is a key element in quantum error correction schemes. Implementation of the Toffoli gate with only single- and two-qubit operations requires six controlled-NOT gates and ten single-qubit operations.

As a result, a single-step Toffoli gate can reduce the number of quantum operations dramatically, which can break the limit of coherence time and improve the efficiency of quantum computing. Researchers from Guo’s group found the T-shaped six quantum dot architecture with openings between control qubits and the target qubit can strengthen the coupling between qubits with different function and minimize it between qubits with the same function, which satisfies the requirements of the Toffoli gate well. Using this architecture with optimized high frequency pulses, researchers demonstrated the Toffoli gate in semiconductor quantum dot system in the world for the first time, which paves the way and lays a solid foundation for the scalable semiconductor quantum processor.

The reviewer spoke highly of this work, and thought this is an important progress in the field of semiconductor quantum dot based quantum computing.”The work is detailed and clearly demonstrates a high level of experimental technique and would be of high interest to people working in the field of electrostatically defined quantum dots for quantum computation”.

 

Researchers have developed an imaging technique that uses a tiny, super sharp needle to nudge a single nanoparticle into different orientations and capture 2-D images to help reconstruct a 3-D picture. The method demonstrates imaging of individual nanoparticles at different orientations while in a laser-induced excited state.

The findings, published in The Journal of Chemical Physics, brought together researchers from the University of Illinois and the University of Washington, Seattle in a collaborative project through the Beckman Institute for Advanced Science and Technology at the U. of I.

Nanostructures like microchip semiconductors, carbon nanotubes and large protein molecules contain defects that form during synthesis that cause them to differ in composition from one another. However, these defects are not always a bad thing, said Martin Gruebele, the lead author and an Illinois chemistry professor and chair.

“The term ‘defect’ is a bit of a misnomer,” Gruebele said. “For example, semiconductors are manufactured with intentional defects that form the ‘holes’ that electrons jump into to produce electrical conductivity. Having the ability to image those defects could let us better characterize them and control their production.”

As advances in technology allow for smaller and smaller nanoparticles, it is critical for engineers to know the precise number and location of these defects to assure quality and functionality.

The study focused on a class of nanoparticles called quantum dots. These dots are tiny, near-spherical semiconductors used in technology like solar panels, live cell imaging and molecular electronics – the basis for quantum computing.

The team observed the quantum dots using a single-molecule absorption scanning tunneling microscope fitted with a needle sharpened to a thickness of only one atom at its tip. The needle nudges the individual particles around on a surface and scans them to get a view of the quantum dot from different orientations to produce a 3-D image.

The researchers said there are two distinct advantages of the new SMA-STM method when compared with the current technology – the Nobel Prize-winning technique called cryogenic electron tomography.

For a video related to this research can be found here.

“Instead of an image produced using an average of thousands of different particles, as is done with CryoET, SMA-STM can produce an image from a single particle in about 20 different orientations,” Gruebele said. “And because we are not required to chill the particles to near-absolute zero temperatures, we can capture the particles at room temperature, not frozen and motionless.”

The researchers looked at semiconductor quantum dots for this study, but SMA-STM can also be used to explore other nanostructures such as carbon nanotubes, metal nanoparticles or synthetic macromolecules. The group believes the technique can be refined for use with soft materials like protein molecules, Gruebele said.

The researchers are working to advance SMA-STM into a single-particle tomography technique, meaning that they will need to prove that method is noninvasive.

“For SMA-STM to become a true single-particle tomography technique, we will need to prove that our nudges do not damage or score the nanoparticle in any way while rolled around,” Gruebele said. “Knocking off just one atom can fundamentally alter the defect structure of the nanoparticle.”

Engineers at Rutgers University-New Brunswick and Oregon State University are developing a new method of processing nanomaterials that could lead to faster and cheaper manufacturing of flexible thin film devices – from touch screens to window coatings, according to a new study.

The “intense pulsed light sintering” method uses high-energy light over an area nearly 7,000 times larger than a laser to fuse nanomaterials in seconds. Nanomaterials are materials characterized by their tiny size, measured in nanometers. A nanometer is one millionth of a millimeter, or about 100,000 times smaller than the diameter of a human hair.

The existing method of pulsed light fusion uses temperatures of around 250 degrees Celsius (482 degrees Fahrenheit) to fuse silver nanospheres into structures that conduct electricity. But the new study, published in RSC Advances and led by Rutgers School of Engineering doctoral student Michael Dexter, showed that fusion at 150 degrees Celsius (302 degrees Fahrenheit) works well while retaining the conductivity of the fused silver nanomaterials.

The engineers’ achievement started with silver nanomaterials of different shapes: long, thin rods called nanowires in addition to nanospheres. The sharp reduction in temperature needed for fusion makes it possible to use low-cost, temperature-sensitive plastic substrates like polyethylene terephthalate (PET) and polycarbonate in flexible devices, without damaging them.

“Pulsed light sintering of nanomaterials enables really fast manufacturing of flexible devices for economies of scale,” said Rajiv Malhotra, the study’s senior author and assistant professor in the Department of Mechanical and Aerospace Engineering at Rutgers-New Brunswick. “Our innovation extends this capability by allowing cheaper temperature-sensitive substrates to be used.”

Fused silver nanomaterials are used to conduct electricity in devices such as radio-frequency identification (RFID) tags, display devices and solar cells. Flexible forms of these products rely on fusion of conductive nanomaterials on flexible substrates, or platforms, such as plastics and other polymers.

“The next step is to see whether other nanomaterial shapes, including flat flakes and triangles, will drive fusion temperatures even lower,” Malhotra said.

In another study, published in Scientific Reports, the Rutgers and Oregon State engineers demonstrated pulsed light sintering of copper sulfide nanoparticles, a semiconductor, to make films less than 100 nanometers thick.

“We were able to perform this fusion in two to seven seconds compared with the minutes to hours it normally takes now,” said Malhotra, the study’s senior author. “We also showed how to use the pulsed light fusion process to control the electrical and optical properties of the film.”

Their discovery could speed up the manufacturing of copper sulfide thin films used in window coatings that control solar infrared light, transistors and switches, according to the study. This work was funded by the National Science Foundation and The Walmart Manufacturing Innovation Foundation.

Nowadays, zinc oxide nanoparticles are one of the most commonly used nanomaterials. They seem to be safe for humans, but there are still no standards for their toxicity and despite intense investigations, the toxicological impact of ZnO nanomaterials still remains ambiguous. Researchers from the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) in Warsaw and the Faculty of Chemistry of the Warsaw University of Technology (PW) have recently developed a method for producing defect-free ZnO quantum dots with physicochemical properties that are particularly interesting and do not change over time, such as monodispersity, a relatively high quantum efficiency, record-long luminescence lifetimes and EPR silence under standard conditions. The unique features of the tightly coordinated and impermeable organic shells stabilizing the surface make the new ZnO quantum dots resistant to both chemical and biological environments.

“The zinc oxide nanocrystals of unprecedented high quality obtained by us are characterized by significantly better chemical and physical properties than their counterparts currently being produced by the most popular sol-gel method involving inorganic precursors”, emphasizes Prof. Janusz Lewinski (IPC PAS, PW). “The luminescence lifetime, or luminance, in the case of our quantum dots is much longer – by even up to several orders of magnitude! Moreover, until now only short ZnO photoluminescence decays have been observed, of the order of a few to a dozen-or-so picoseconds characteristic for sol-gel nanoparticles, or slightly longer, nanosecond ones, typical only for ZnO monocrystals. What we have is a luminescent material that can be used, for example, as a new generation optical marker for biomedical applications.”

Combined with biologically active molecules, the new nanoparticles could be used in biology or medicine, e.g. for imaging cells and tissues, which would enable much more accurate monitoring of disease development and efficacy of treatment. In a recent publication in the well-known scientific journal Chemistry – A European Journal, the Warsaw scientists, in collaboration with a group from the Jagiellonian University in Cracow, showed that their zinc oxide nanoparticles are indeed safe. The research, funded by the TEAM grant from the Foundation for Polish Science and the OPUS grant of the Polish National Science Centre, allows us to realistically think about rapid introduction of the new ZnO quantum dots into, among others, biological and medical laboratories.

ZnO nanocrystals manufactured in a classic manner by the sol-gel method are not well stabilized or isolated from the environment. For example, interactions that occur at the interface between the inorganic ZnO core and the biological environment can lead to the generation of reactive oxygen species or the dissolution and release of potentially toxic zinc cations.

“Zinc oxide is generally considered as a relatively safe and biocompatible material. However, many toxicological studies of ZnO concern nanoparticles that are heterogeneous in size and also too large to be able to penetrate into cells. We also realized that in practice many of the characteristics of nanoparticles depend not only on their size, but also on the surface properties of both the nanocrystalline ZnO and the organic stabilizing layer. Therefore, we decided to modify our one-pot self-supporting organometallic method of synthesis, so that the ZnO nanoparticles resulting from it behave as neutrally as possible in the interior of the cells,” explains Dr. Malgorzata Wolska-Pietkiewicz (PW).

Prof. Lewinski’s team produces quantum dots of zinc oxide from organometallic compounds (precursors). When the purpose is biological applications, the end result is stable nanoparticles with a shape that is similar to a sphere, consisting of a crystalline ZnO core with a diameter of 4-5 nanometres surrounded by a shell of organic ligands. This shell increases the size of the nanoparticles (their hydrodynamic diameter is about 12 nm) and has protective functions: on the one hand it protects the inorganic core from degradation due to interaction with what is often a very reactive biological environment, on the other hand it eliminates the influence of ZnO itself on this environment.

“Nanoparticles with core sizes below 10 nm penetrate inside the cells particularly easily. Such particles are considered to be potentially the most toxic. Interestingly, the ZnO nanoparticles created by us, contrary to popular opinion indicating that the smaller the systems, the greater their toxicity, showed extremely low harmful effects in in vitro model tests. The recent results as well as the studies carried out simultaneously in the parent team provided further evidence of the unique character of the nanocrystalline ZnO obtained as a result of the transformation of organometallic molecular precursors,” notes Dr. Wolska-Pietkiewicz.

The research on ZnO quantum dots gives hope for numerous applications. However, there are concerns about their biological and environmental impacts. Nanoparticles can enter the body and among others, the respiratory tract is frequently exposed to elevated concentrations of different nanomaterials and becomes the primary target site for toxicity. Therefore, A549 and MRC-5 cell lines were selected as in vitro models for internal malignancies and normal lung cells, respectively. Researchers from the IPC PAS and PW showed that the organic layer surrounding the improved nanoparticles is indeed impermeable: zinc ions are not released into the environment, and reactive oxygen species are not formed. Even at high concentrations, the toxicity of the new ZnO nanoparticles turned out to be negligible.

“Our ‘recipe’ for the production of ZnO quantum dots means that they simply do not interact with the biological environment. So we have a strong foundation on which to start working on their applications. Not only in medical imaging, but also in other areas in which nanoparticles could potentially interact with the human body, for example, as one of the components of paint. We are also developing a new technology for the synthesis of ZnO quantum dots and searching for potential applications as a part of NANOXO, a start-up company”, summarizes Prof. Lewinski.