Berkeley Lab, UC Berkeley scientists discover unique thermoelectric properties in cesium tin iodide
JULY 31, 2017
A newly discovered collective rattling effect in a type of crystalline semiconductor blocks most heat transfer while preserving high electrical conductivity – a rare pairing that scientists say could reduce heat buildup in electronic devices and turbine engines, among other possible applications.
A team led by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) discovered these exotic traits in a class of materials known as halide perovskites, which are also considered promising candidates for next-generation solar panels, nanoscale lasers, electronic cooling, and electronic displays.
These interrelated thermal and electrical (or “thermoelectric”) properties were found in nanoscale wires of cesium tin iodide (CsSnI3). The material was observed to have one of the lowest levels of heat conductivity among materials with a continuous crystalline structure.
Image – Rattling structures of halide perovskites: cesium tin iodide (left) and cesium lead iodide (right). (Credit: Berkeley Lab/UC Berkeley)
This so-called single-crystal material can also be more easily produced in large quantities than typical thermoelectric materials, such as silicon-germanium, researchers said.
“Its properties originate from the crystal structure itself. It’s an atomic sort of phenomenon,” said Woochul Lee, a postdoctoral researcher at Berkeley Lab who was the lead author of the study, published the week of July 31 in the Proceedings of the National Academy of Sciences journal. These are the first published results relating to the thermoelectric performance of this single crystal material.
Researchers earlier thought that the material’s thermal properties were the product of “caged” atoms rattling around within the material’s crystalline structure, as had been observed in some other materials. Such rattling can serve to disrupt heat transfer in a material.
“We initially thought it was atoms of cesium, a heavy element, moving around in the material,” said Peidong Yang, a senior faculty scientist at Berkeley Lab’s Materials Sciences Division who led the study.
Jeffrey Grossman, a researcher at the Massachusetts Institute of Technology, then performed some theory work and computerized simulations that helped to explain what the team had observed.
Researchers also used Berkeley Lab’s Molecular Foundry, which specializes in nanoscale research, in the study.
“We believe there is essentially a rattling mechanism, not just with the cesium. It’s the overall structure that’s rattling; it’s a collective rattling,” Yang said. “The rattling mechanism is associated with the crystal structure itself,” and is not the product of a collection of tiny crystal cages. “It is group atomic motion,” he added.
Within the material’s crystal structure, the distance between atoms is shrinking and growing in a collective way that prevents heat from easily flowing through.
But because the material is composed of an orderly, single-crystal structure, electrical current can still flow through it despite this collective rattling. Picture its electrical conductivity is like a submarine traveling smoothly in calm underwater currents, while its thermal conductivity is like a sailboat tossed about in heavy seas at the surface.
Yang said two major applications for thermoelectric materials are in cooling, and in converting heat into electrical current. For this particular cesium tin iodide material, cooling applications such as a coating to help cool electronic camera sensors may be easier to achieve than heat-to-electrical conversion, he said.
A challenge is that the material is highly reactive to air and water, so it requires a protective coating or encapsulation to function in a device.
Cesium tin iodide was first discovered as a semiconductor material decades ago, and only in recent years has it been rediscovered for its other unique traits, Yang said. “It turns out to be an amazing gold mine of physical properties,” he noted.
SEM images of suspended micro-island devices. Individual AIHP NW is suspended between two membranes. (Credit: Berkeley Lab/UC Berkeley)
To measure the thermal conductivity of the material, researchers bridged two islands of an anchoring material with a cesium tin iodide nanowire. The nanowire was connected at either end to micro-islands that functioned as both a heater and a thermometer.
Researchers heated one of the islands and precisely measured how the nanowire transported heat to the other island.
They also performed scanning electron microscopy to precisely measure the dimensions of the nanowire. They used these dimensions to provide an exacting measure of the material’s thermal conductivity. The team repeated the experiment with several different nanowire materials and multiple nanowire samples to compare thermoelectric properties and verify the thermal conductivity measurements.
“A next step is to alloy this (cesium tin iodide) material,” Lee said. “This may improve the thermoelectric properties.”
Also, just as computer chip manufacturers implant a succession of elements into silicon wafers to improve their electronic properties – a process known as “doping” – scientists hope to use similar techniques to more fully exploit the thermoelectric traits of this semiconductor material. This is relatively unexplored territory for this class of materials, Yang said.
The research team also included other scientists from Berkeley Lab’s Materials Sciences Division and the Molecular Foundry, the Kavli Energy NanoScience Institute at UC Berkeley and Berkeley Lab, and UC Berkeley’s Department of Chemistry.
The Molecular Foundry is a DOE Office of Science User Facility that provides free access to state-of-the-art equipment and multidisciplinary expertise in nanoscale science to visiting scientists from all over the world.
This work was supported by the Department of Energy’s Office of Basic Energy Sciences.
More information about Peidong Yang’s research group: http://nanowires.berkeley.edu/.
Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel Prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit http://www.lbl.gov.
DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
A European research project has made an important step towards the further miniaturisation of nanoelectronics, using a highly-promising new material called silicene. Its goal: to make devices of the future vastly more powerful and energy efficient.
Silicene, a new semiconducting material combining properties of silicon and graphene, is one of the most promising candidates for manufacturing even tinier electronic circuitry for future smart devices.
‘Electronics are currently embedded in many layers of silicon atoms. If they can be manufactured in a single layer, they can be shrunk down to much smaller sizes and we can cut down on power leakage, at the same time making devices more powerful and energy efficient,’ explained Dr Athanasios Dimoulas, coordinator of the EU’s 2D-NANOLATTICES project.
Graphene is an interesting substance in that it occurs in a single layer of atoms, but does not have the ‘energy gap’ needed to be a semiconductor material. Silicene, a 2D form of silicon, brings its semiconductor properties into the world of 2D materials. The problem with silicene, however, is it is modified in contact with other substances such as metals.
Electronics that are 100 times smaller
Condensing electronics into a single layer of silicene and retaining electronic performance has proved a difficult task for researchers – until now that is. The 2D-NANOLATTICES project has achieved a significant innovation worldwide by making a Field Effect Transistor (FET) out of the material to operate at room temperature.
FETs are a key switching component in electronic circuitry. Embedding it into just one layer of silicon atoms (in silicene structure), then transferring the layer, grown on a silver substrate, to one made of a more neutral substance, silicon dioxide, is a considerable success. ‘Tests showed that performance of silicene is very, very good on the non-metal substrate,’ enthused Dr Dimoulas, of Demokritos, Greece’s National Center for Scientific Research.
‘The fact that we have this one transistor made of just one single layer of material like silicon has not been done before and this is really something that can be described as a breakthrough. On the basis of this achievement, it could be possible to make transistors up to 100 times smaller in the vertical direction,’ Dr Dimoulas added.
Seeing the potential
Now that the transistor has been shrunk vertically into just one 2D layer of atoms, the dimensions can be shrunk laterally, too, meaning the same area on a chip could accommodate up to 25 times more electronics, Dr Dimoulas calculated.
Additionally, the use of a single, narrow channel to conduct electrical current reduces power leakages, a problem that has been worrying the semiconductor industry for some time: how to go even smaller without devices overheating in the form of power leakage.
This is good news for chip manufacturers, as the race to produce the next wave of communications technologies hots up with the advent of 5G mobile networks.
Researchers from the University of Alabama in Huntsville and the University of Oklahoma have found a new way to control the properties of quantum dots, those tiny chunks of semiconductor material that glow different colors depending on their size. Quantum dots, which are so small they start to exhibit atom-like quantum properties, have a wide range of potential applications, from sensors, light-emitting diodes, and solar cells, to fluorescent tags for biomedical imaging and qubits in quantum computing.
A key property of quantum dots that makes them so useful is their fluorescence. Scientists can “tune” quantum dots to emit a specific color of light by adjusting their size—small dots glow blue and large dots glow red. However, the dots’ ability to glow can change over time with exposure to light and air.
Seyed Sadeghi, a physicist at the University of Alabama in Huntsville, wondered if it would be possible to better control how quantum dots react to their environment. His team had previously found that placing quantum dots of a certain type on nanometer-thin layers of chromium and aluminum oxides significantly altered the dots’ behavior: the aluminum oxide increased their emission efficiency, while the chromium oxide increased the dots’ degradation rate when exposed to air. The researchers decided to extend their investigations to quantum dots with different structures.
Quantum dots come in a variety of shapes, sizes, and materials. For Sadeghi and his colleagues’ most recent studies, published in the Journal of Applied Physics, the researchers probed the behavior of four different types of commercially available quantum dots. Some of the quantum dots had protective shells, while others did not. Additionally, some of the dots had cores made of binary materials (two types of semiconductors), while others had ternary material cores (three types of semiconductors). All of the quantum dots had been manufactured by chemical synthesis.
The researchers found that ultrathin aluminum oxide could make quantum dots glow brighter and that the effect was much more significant for quantum dots without protective shells. They also found that while quantum dots with both binary and ternary cores shrink after reacting with the oxygen in air, ternary core dots placed on aluminum oxide glowed brighter despite the shrinkage. This observation surprised the researchers, Sadeghi said, and while they don’t yet have an explanation for the difference, they are continuing to study it.
“The results of these studies can serve to enhance emission efficiency of quantum dots, which is an important feature for many applications such as light emitting devices, sensors, detectors, photovoltaic devices, and the investigation of a wide range of quantum and nano-scale physical phenomena,” Sadeghi said. Quantum dots have already helped increase the efficiencies of many optical devices, he noted, and the further development and application of quantum dots’ unique properties, including in the fields of biological imaging and medicine, continues to be a prime focus of scientific study. As a next step in their own research, Sadeghi and his colleagues plan to investigate how metal oxides might affect the behavior of quantum dots when they are close to metallic nanoparticles.
More information: “Probing the structural dependency of photoinduced properties of colloidal quantum dots using metal-oxide photo-active substrates,” by K. Patty, S. M. Sadeghi, Q. Campbell, N. Hamilton, R. G. West, and C. B. Mao, Journal of Applied Physics, September 16, 2014. DOI: 10.1063/1.4894445
Rice’s silicon oxide memories catch manufacturers’ eye: Use of porous silicon oxide reduces forming voltage, improves manufacturability
Houston, TX | Posted on July 10th, 2014
Rice University’s breakthrough silicon oxide technology for high-density, next-generation computer memory is one step closer to mass production, thanks to a refinement that will allow manufacturers to fabricate devices at room temperature with conventional production methods.
First discovered five years ago, Rice’s silicon oxide memories are a type of two-terminal, “resistive random-access memory” (RRAM) technology. In a new paper available online in the American Chemical Society journal Nano Letters, a Rice team led by chemist James Tour compared its RRAM technology to more than a dozen competing versions.
“This memory is superior to all other two-terminal unipolar resistive memories by almost every metric,” Tour said. “And because our devices use silicon oxide — the most studied material on Earth — the underlying physics are both well-understood and easy to implement in existing fabrication facilities.” Tour is Rice’s T.T. and W.F. Chao Chair in Chemistry and professor of mechanical engineering and nanoengineering and of computer science.
Tour and colleagues began work on their breakthrough RRAM technology more than five years ago. The basic concept behind resistive memory devices is the insertion of a dielectric material — one that won’t normally conduct electricity — between two wires. When a sufficiently high voltage is applied across the wires, a narrow conduction path can be formed through the dielectric material.
The presence or absence of these conduction pathways can be used to represent the binary 1s and 0s of digital data. Research with a number of dielectric materials over the past decade has shown that such conduction pathways can be formed, broken and reformed thousands of times, which means RRAM can be used as the basis of rewritable random-access memory.
RRAM is under development worldwide and expected to supplant flash memory technology in the marketplace within a few years because it is faster than flash and can pack far more information into less space. For example, manufacturers have announced plans for RRAM prototype chips that will be capable of storing about one terabyte of data on a device the size of a postage stamp — more than 50 times the data density of current flash memory technology.
The key ingredient of Rice’s RRAM is its dielectric component, silicon oxide. Silicon is the most abundant element on Earth and the basic ingredient in conventional microchips. Microelectronics fabrication technologies based on silicon are widespread and easily understood, but until the 2010 discovery of conductive filament pathways in silicon oxide in Tour’s lab, the material wasn’t considered an option for RRAM.
Since then, Tour’s team has raced to further develop its RRAM and even used it for exotic new devices like transparent flexible memory chips. At the same time, the researchers also conducted countless tests to compare the performance of silicon oxide memories with competing dielectric RRAM technologies.
“Our technology is the only one that satisfies every market requirement, both from a production and a performance standpoint, for nonvolatile memory,” Tour said. “It can be manufactured at room temperature, has an extremely low forming voltage, high on-off ratio, low power consumption, nine-bit capacity per cell, exceptional switching speeds and excellent cycling endurance.”
This scanning electron microscope image and schematic show the design and composition of new RRAM memory devices based on porous silicon oxide that were created at Rice University.
Credit: Tour Group/Rice University
In the latest study, a team headed by lead author and Rice postdoctoral researcher Gunuk Wang showed that using a porous version of silicon oxide could dramatically improve Rice’s RRAM in several ways. First, the porous material reduced the forming voltage — the power needed to form conduction pathways — to less than two volts, a 13-fold improvement over the team’s previous best and a number that stacks up against competing RRAM technologies. In addition, the porous silicon oxide also allowed Tour’s team to eliminate the need for a “device edge structure.”
“That means we can take a sheet of porous silicon oxide and just drop down electrodes without having to fabricate edges,” Tour said. “When we made our initial announcement about silicon oxide in 2010, one of the first questions I got from industry was whether we could do this without fabricating edges. At the time we could not, but the change to porous silicon oxide finally allows us to do that.”
Wang said, “We also demonstrated that the porous silicon oxide material increased the endurance cycles more than 100 times as compared with previous nonporous silicon oxide memories. Finally, the porous silicon oxide material has a capacity of up to nine bits per cell that is highest number among oxide-based memories, and the multiple capacity is unaffected by high temperatures.”
Tour said the latest developments with porous silicon oxide — reduced forming voltage, elimination of need for edge fabrication, excellent endurance cycling and multi-bit capacity — are extremely appealing to memory companies.
“This is a major accomplishment, and we’ve already been approached by companies interested in licensing this new technology,” he said.
Study co-authors — all from Rice — include postdoctoral researcher Yang Yang; research scientist Jae-Hwang Lee; graduate students Vera Abramova, Huilong Fei and Gedeng Ruan; and Edwin Thomas, the William and Stephanie Sick Dean of Rice’s George R. Brown School of Engineering, professor in mechanical engineering and materials science and in chemical and biomolecular engineering.
(Nanowerk Spotlight) Carbon comes in many different forms, from the graphite found in pencils to the world’s most expensive diamonds. In 1980, we knew of only three basic forms of carbon, namely diamond, graphite, and amorphous carbon. Then, fullerenes and carbon nanotubes were discovered and, in 2004, graphene joined the club. Graphene is an atomic-scale honeycomb lattice made of carbon atoms. Existing forms of carbon basically consist of sheets of graphene, either bonded on top of each other to form a solid material like the graphite in your pencil, or rolled up into carbon nanotubes (think of a single-walled carbon nanotube as a graphene cylinder) or folded into fullerenes.
Mother of all graphitic forms. Graphene is a 2D building material for carbon materials of all other dimensionalities. It can be wrapped up into 0D buckyballs, rolled into 1D nanotubes or stacked into 3D graphite. (Artistic impression of a corrugated graphene sheet: Jannik Meyer) The reason nanotechnology researchers are so excited is that graphene and other two-dimensional crystals – it’s called 2D because it extends in only two dimensions: length and width; as the material is only one atom thick, the third dimension, height, is considered to be zero – open up a whole new class of materials with novel electronic, optical and mechanical properties. Early experiments with graphene have revealed some fascinating phenomena that excite researchers working towards molecular electronics. For instance, it was found that graphene remains capable of conducting electricity even at the limit of nominally zero carrier concentration because the electrons don’t seem to slow down or localize. The electrons moving around carbon atoms interact with the periodic potential of graphene’s honeycomb lattice, which gives rise to new quasiparticles that have lost their mass, or ‘rest mass’ (so-called massless Dirac fermions). That means that graphene never stops conducting. It was also found that they travel far faster than electrons in other semiconductors. Graphene is undoubtedly emerging as one of the most promising nanomaterials because of its unique combination of superb properties, which opens a way for its exploitation in a wide spectrum of applications ranging from electronics to optics, sensors, and biodevices. Watch a great introductory video on graphene:
Graphene production The quality of graphene plays a crucial role as the presence of defects, impurities, grain boundaries, multiple domains, structural disorders, wrinkles in the graphene sheet can have an adverse effect on its electronic and optical properties. In electronic applications, the major bottleneck is the requirement of large size samples, which is possible only in the case of CVD process, but it is difficult to produce high quality and single crystalline graphene thin films possessing very high electrical and thermal conductivities along with excellent optical transparency. Another issue of concern in the synthesis of graphene by conventional methods involves the use of toxic chemicals and these methods usually result in the generation hazardous waste and poisonous gases. Therefore, there is a need to develop green methods to produce graphene by following environmentally friendly approaches. The preparation methods for graphene should also allow for in-situ fabrication and integration of graphene-based devices with complex architecture that would enable eliminating the multi step and laborious fabrication methods at a lower production cost (read more: “Mass production of high quality graphene: An analysis of worldwide patents”). Currently, the most common techniques available for the production of graphene are shown schematically below, which includes micromechanical cleavage, chemical vapor deposition, epitaxial growth on SiC substrates, chemical reduction of exfoliated graphene oxide, liquid phase exfoliation of graphite and unzipping of carbon nanotubes. However, each of these methods can have its own advantages as well as limitations depending on its target application(s). In order to surmount these barriers in commercializing graphene, concerted efforts are being made by researchers at various R&D institutes, universities and companies from all over the globe to develop new methods for large scale production of low-cost and high quality graphene via simple and eco-friendly approaches.
A schematic showing the conventional methods commonly used for the synthesis of graphene along with their key features, and the current and future applications. (Image: CKMNT) (click image to enlarge)
These examples highlight the four major energy-related areas where graphene will have an impact: solar cells, supercapacitors, lithium-ion batteries, and catalysis for fuel cells. An excellent review paper (“Chemical Approaches toward Graphene-Based Nanomaterials and their Applications in Energy-Related Areas”) gives a brief overview of the recent research concerning chemical and thermal approaches toward the production of well-defined graphene-based nanomaterials and their applications in energy-related areas. The authors note, however, that before graphene-based nanomaterials and devices find widespread commercial use, two important problems have to be solved: one is the preparation of graphene-based nanomaterials with well-defined structures, and the other is the controllable fabrication of these materials into functional devices. Read more about graphene nanotechnology in energy applications.
Flexible, stretchable and foldable electronics Graphene has a unique combination of properties that is ideal for next-generation electronics, including mechanical flexibility, high electrical conductivity, and chemical stability. Combine this with inkjet printing and you get an inexpensive and scalable path for exploiting these properties in real-world technologies (“Inkjet printing of graphene for flexible electronics”). In contrast to flexible electronics, which rely on bendable substrates, truly foldable electronics require a foldable substrate with a very stable conductor that can withstand folding, i.e. an edge in the substrate at the point of the fold, which develops creases, and the deformation remains even after unfolding. That means that, in addition to a foldable substrate like paper, the conductor that is deposited on this substrate also needs to be foldable. To that end, researchers have demonstrated a fabrication process for foldable graphene circuits based on paper substrates.
Photographs of applications. a,b,c) Operation of a LED chip with graphene circuits on a paper substrate under -180° folding and 180° folding. d) Array of LED chips on a three-dimensional circuit board including negative and positive angle folding. e,f,g) Operation of a LED chip on the paper-based circuit board before and after crumpling. (Reprinted with permission from Wiley-VCH Verlag)
Graphene’s remarkable conductivity, strength and elasticity has made it a promising choice for stretchable electronics — a technology that aims to produce circuits on flexible plastic substrates for applications like bendable solar cells or robotic-like artificial skin. Scientists have devised a chemical vapor deposition (CVD) method for turning graphene sheets into porous three-dimensional foams with extremely high conductivity. By permeating this foam with a siloxane-based polymer, the researchers have produced a composite that can be twisted, stretched and bent without harming its electrical or mechanical properties (“Graphene: Foaming for stretchable electronics”).
Nanoelectronics Some of the most promising applications of graphene are in electronics (as transistors and interconnects), detectors (as sensor elements) and thermal management (as lateral heat spreaders). The first graphene field-effect transistors (FETs) – with both bottom and top gates – have already been demonstrated. At the same time, for any transistor to be useful for analog communication or digital applications, the level of the electronic low-frequency noise has to be decreased to an acceptable level (“Graphene transistors can work without much noise”). Transistors on the basis of graphene are considered to be potential successors for the some silicon components currently in use. Due to the fact that an electron can move faster through graphene than through silicon, the material shows potential to enable terahertz computing. In the ultimate nanoscale transistor – dubbed a ballistic transistor – the electrons avoid collisions, i.e. there is a virtually unimpeded flow of current. Ballistic conduction would enable incredibly fast switching devices. Graphene has the potential to enable ballistic transistors at room temperature. While graphene has the potential to revolutionize electronics and replace the currently used silicon materials (“High-performance graphene transistor with high room-temperature mobility”), it does have an Achilles heel: pristine graphene is semi-metallic and lacks the necessary band gap to serve as a transistor. Therefore it is necessary to engineer band gaps in graphene. Experiments have demonstrated the benefits of graphene as a platform for flash memory which show the potential to exceed the performance of current flash memory technology by utilizing the intrinsic properties of graphene.
Photodetectors Researchers have demonstrated that graphene can be used for telecommunications applications and that its weak and universal optical response might be turned into advantages for ultrafast photonics applications. They also found that graphene could be potentially exploited as a saturable absorber with wide optical response ranging from ultra-violet, visible, infrared to terahertz (“The rise of graphene in ultra-fast photonics”). There is a very strong research interest in using graphene for applications in optoelectronics. Graphene-based photodetectors have been realized before and graphene’s suitability for high bandwidth photodetection has been demonstrated in a 10 GBit/s optical data link (“Graphene photodetectors for high-speed optical communications”). One novel approach is based on the integration of graphene into an optical microcavity. The increased electric field amplitude inside the cavity causes more energy to be absorbed, leading to a significant increase of the photoresponse (“Microcavity vastly enhances photoresponse of graphene photodetectors”).
Coatings Coating objects with graphene can serve different purposed. For instance, researchers have now shown that it is possible to use graphene sheets to create a superhydrophobic coating material that shows stable superhydrophobicity under both static as well as dynamic (droplet impact) conditions, thereby forming extremely water repelling structures.
Snapshots of a water droplet impacting the surface of the Teflon coated graphene foam. The impact velocity just prior to the droplet striking the surface was ∼76 cm/sec. The sequence of snapshots shows the deformation time history of the droplet upon impact. The droplet spreads, then retracts and successfully rebounds off the surface. The coefficient of restitution (i.e. ratio of droplet impacting velocity to ejecting velocity) is ∼0.37 for the Teflon coated foam. (Reprinted with permission from Wiley-VCH Verlag)
Research findings also have established graphene as the world’s thinnest known coating for protecting metals against corrosion. It was found that graphene, whether made directly on copper or nickel or transferred onto another metal, provides protection against corrosion. Another novel coating application is the the fabrication of polymeric AFM probes covered by monolayer graphene to improving AFM probe performance.
Other uses Researchers have exploited the extraordinary electrical and mechanical properties of graphene to create a very efficient electrical/sound transducer. This experimental graphene loudspeaker, without any optimized acoustic design, is simple to make and already performs comparably to or better than similar sized commercial counterparts, and with much lower power consumption. Recent research also points to an opportunity to replacing antibiotics with graphene-based photothermal agents to trap and kill bacteria. Graphene appears to be a most effective material for electromagnetic interference (EMI) shielding. Experiments suggests the feasibility of manufacturing an ultrathin, transparent, weightless, and flexible EMI shield by a single or a few atomic layers of graphene. Due to rapidly increasing power densities in electronics, managing the resulting heat has become one of the most critical issues in computer and semiconductor design. As a matter of fact, heat dissipation has become a fundamental problem of electronic transport at the nanoscale. This is where graphene comes in – it conducts heat better than any other known material (“‘Cool’ graphene might be ideal for thermal management in nanoelectronics”). Thermal interface materials (TIMs) are essential ingredients of thermal management and researchers have achieved a record enhancement of the thermal conductivity of TIMs by addition of an optimized mixture of graphene and multilayer graphene (“Graphene sets new record as the most efficient filler for thermal interface materials”).
The concept of plasmonic cloaking is based on the use of a thin metamaterial cover to suppress the scattering from a passive object. Research shows that even a single layer of atoms, with the exciting conductivity properties of graphene, may achieve this functionality in planar and cylindrical geometries. This makes a single layer of graphene the thinnest possible invisibility cloak. Over the last decade, various solid lubricant materials, micro/nano patterns, and surface treatment processes have been developed for efficient operation and extended lifetime in MEMS/NEMS applications, and for various fabrication processes such as nanoimprint lithography and transfer printing. One of the important considerations in applying a solid lubricant at the micro- and nanoscale is the thickness of the lubricant and the compatibility of the lubricant deposition process with the target product. Graphene, with its atomically thin and strong structural with low surface energy, is a good candidate for these applications (“Graphene – the thinnest solid lubricant”).
In the decades-old quest to build artificial muscles, many materials have been investigated with regard to their suitability for actuator application (actuation is the ability of a material to reversibly change dimensions under the influence of various stimuli). Besides artificial muscles, potential applications include microelectro-mechanical systems (MEMS), biomimetic micro-and nanorobots, and micro fluidic devices. In experiments, scientists have shown that graphene nanoribbons can provide actuation. A relatively new method of purifying brackish water is capacitive deionization (CDI) technology. The advantages of CDI are that it has no secondary pollution, is cost-effective and energy efficient. Researchers have developed a CDI application that uses graphene-like nanoflakes as electrodes for capacitive deionization. They found that the graphene electrodes resulted in a better CDI performance than the conventionally used activated carbon materials (“Water desalination with graphene”). Researchers demonstrated the use of graphene as a transparent conductive coating for photonic devices and show that its high transparency and low resistivity make this two-dimensional crystal ideally suitable for electrodes in liquid crystal devices (LCDs).
IBM researchers have created a graphene-based circuit that they say performs 10,000 times better than existing options; It was reliable enough that they used it to send and receive a text message. They plan to publish their work in Nature Communications today.
The circuit performs 10,000 times better than existing options and builds on an earlier proof-of-concept circuit IBM made in 2011.
Graphene is an atom-thick sheet of carbon atoms renowned for its strength and conductivity. It is heralded as a possible alternative to silicon, which currently dominates electronics production. One of the major potential applications for graphene is transistors, which control the flow of electricity in circuits. The more transistors you can fit onto a chip, the more powerful it can be. Researchers should be able to pack far more atom-thick graphene transistors into a chip than the bulkier silicon alternative. Graphene also transports electricity 200 times faster than silicon.
A completed graphene integrated circuit chip. Photo courtesy of IBM.
The IBM team integrated graphene into a radio frequency receiver; a device that translates radio waves into understandable information that can be sent back and forth. They tested it by sending a text message that read “IBM” with no distortion.
“This is the first time that someone has shown graphene devices and circuits to perform modern wireless communication functions comparable to silicon technology,” IBM Research director of physical sciences Supratik Guha said in a release.
IBM created the first graphene-based integrated circuit back in 2011. The accomplishment proved that graphene could be used in electronics, but researchers also found that the circuits’ performance was negatively impacted by the harsh manufacturing process. That was a big problem considering nothing will replace silicon unless it can be safely manufactured in massive quantities. IBM scientists have been working since then on tweaking fabrication methods to better protect the graphene.
The circuit announced today was made by adding the graphene only after the rest of the circuit was assembled, which means it is never exposed to the manufacturing steps that could damage it. It included three graphene transistors, whereas the 2011 circuit used just one.
A view of the integrated circuit seen through a scanning electron microscope. The graphene transistors are located in the purple area marked GFET. Photo courtesy of IBM.
The team is particularly interested in how the technology could be used in wireless communications systems, though graphene could be integrated into any silicon-based technology. Mobile devices would potentially be able to transmit data more quickly at a lower cost using less power.
One of the big remaining challenges is bringing the cost of graphene manufacturing down to the level of silicon. The IBM team manufactured graphene in an oven; a common technique. At high temperatures, graphene naturally pulls out of the air and deposits itself on surfaces. But it would be much cheaper if manufacturers could make graphene in larger batches at room temperature. Techniques like roll-to-roll manufacturing could soon make that a reality.
Title: Quantum Dots Market by Product (QD Displays, Lasers, Medical Devices, Solar Cells, Chip, Sensor), Application (Healthcare, Optoelectronics, Sustainable Energy), Material (Cadmium Selenide, Sulfide, Telluride), and Geography – Forecast & Analysis (2013 – 2020).
Quantum Dots (QD) are the types of semiconductor nanoparticles, which find their usage in multiple applications like healthcare, electronics, and so on. The current market of QD is at the pre-commercialized stage; most of the researchers are working on the “application aspects” of the QD technology, and deriving the products based on QD.
Researchers have studied the quantum dots in transistors, solar cells, LEDs, and diode lasers. They have also investigated quantum dots as agents for medical imaging and, soon, the QDs will be used as ‘qubits’ in quantum computing.
This report deals with all the driving factors, restraints, and opportunities for the QD technology market, which are helpful in identifying the trends and key success factors for the industry. The report also profiles companies that are active in the field of QD technology. It also highlights the winning imperatives and burning issues pertaining to the QD technology industry.
The Quantum Dots market is expected to grow from the $108.41 million that it accounts for, currently, in 2013 to $3,414.54 million in 2020, at a CAGR of 71.13% from 2014 to 2020. Optoelectronics application is expected to be the major market share holder, with an expected revenue generation of $2,458.47 million in 2020.
PALO ALTO, Calif. — Not long after Gordon E. Moore proposed in 1965 that the number of transistors that could be etched on a silicon chip would continue to double approximately every 18 months, critics began predicting that the era of “Moore’s Law” would draw to a close.
More than ever recently, industry pundits have been warning that the progress of the semiconductor industry is grinding to a halt — and that the theory of Dr. Moore, an Intel co-founder, has run its course.
If so, that will have a dramatic impact on the computer world. The innovation that has led to personal computers, music players and smartphones is directly related to the plunging cost of transistors, which are now braided by the billions onto fingernail slivers of silicon — computer chips — that may sell for as little as a few dollars each.
But Moore’s Law is not dead; it is just evolving, according to more optimistic scientists and engineers. Their contention is that it will be possible to create circuits that are closer to the scale of individual molecules by using a new class of nanomaterials — metals, ceramics, polymeric or composite materials that can be organized from the “bottom up,” rather than the top down.
For instance, semiconductor designers are developing chemical processes that can make it possible to “self assemble” circuits by causing the materials to form patterns of ultrathin wires on a semiconductor wafer. Combining these patterns of nanowires with conventional chip-making techniques, the scientists believe, will lead to a new class of computer chips, keeping Moore’s Law alive while reducing the cost of making chips in the future.
“The key is self assembly,” said Chandrasekhar Narayan, director of science and technology at IBM’s Almaden Research Center in San Jose, Calif. “You use the forces of nature to do your work for you. Brute force doesn’t work any more; you have to work with nature and let things happen by themselves.”
To do this, semiconductor manufacturers will have to move from the silicon era to what might be called the era of computational materials. Researchers here in Silicon Valley, using powerful new supercomputers to simulate their predictions, are leading the way. While semiconductor chips are no longer made here, the new classes of materials being developed in this area are likely to reshape the computing world over the next decade.
“Materials are very important to our human societies,” said Shoucheng Zhang, a Stanford University physicist who recently led a group of researchers to design a tin alloy that has superconductinglike properties at room temperature. “Entire eras are named after materials — the stone age, the iron age and now we have the silicon age. In the past they have been discovered serendipitously. Once we have the power to predict materials, I think it’s transformative.”
Pushing this research forward is economics — specifically, the staggering cost semiconductor manufacturers are expecting to pay for their next-generation factories. In the chip-making industry this has been referred to as “Moore’s Second Law.”
Two years from now new factories for making microprocessor chips will cost from $8 to $10 billion, according to a recent Gartner report — more than twice as much as the current generation. That amount could rise to between $15 and $20 billion by the end of the decade, equivalent to the gross domestic product of a small nation.
The stunning expenditures that soon will be required mean that the risk of error for chip companies is immense. So rather than investing in expensive conventional technologies that might fail, researchers are looking to these new self-assembling materials.
In December, researchers at Sandia National Laboratories in Livermore, Calif., published a Science paper describing advances in a new class of materials called “metal-organic frameworks” or MOFs. These are crystalline ensembles of metal ions and organic molecules. They have been simulated with high-performance computers, and then verified experimentally.
What the scientists have proven is that they can create conductive thin films, which could be used in a range of applications, including photovoltaics, sensors and electronic materials.
The scientists said that they now see paths for moving beyond the conductive materials, toward creating semiconductors as well.
According to Mark D. Allendorf, a Sandia chemist, there are very few things that you can do with conventional semiconductorsto change the behavior of a material. With MOFs he envisions a future in which molecules can be precisely ordered to create materials with specific behaviors.
“One of the reasons that Sandia is well positioned is that we have huge supercomputers,” he said. They have been able to simulate matrixes of 600 atoms, large enough for the computer to serve as an effective test tube.
In November, scientists at the SLAC National Accelerator Laboratory, writing in the journal Physical Review Letters, described a new form of tin that, at only a single molecule thick, has been predicted to conduct electricity with 100 percent efficiency at room temperature. Until now these kinds of efficiencies have only been found in materials known as superconductors, and then only at temperatures near absolute zero.
The material would be an example of a new class of materials called “topological insulators” that are highly conductive along a surface or edge, but insulating on their interior. In this case the researchers have proposed a structure with fluorine atoms added to a single layer of tin atoms.
The scientists, led by Dr. Zhang, named the new material stanene, combining the Latin name for tin — stannum — with the suffix used for graphene, another material based on a sheet of carbon atoms a single molecule thick.
The promise of such a material is that it might be easily used in conjunction with today’s chip-making processes to both increase the speed and lower the power consumption of future generations of semiconductors.
The theoretical prediction of the material must still be verified, and Dr. Zhang said that research is now taking place in Germany and China, as well as a laboratory at U.C.L.A.
It is quite possible that the computational materials revolution may offer a path toward cheaper technologies for the next generation of computer chips.
That is IBM’s bet. The company is now experimenting with exotic polymers that automatically form into an ultrafine web and can be used to form circuit patterns onto silicon wafers.
Dr. Narayan is cautiously optimistic, saying there is a good chance that bottoms-up self-assembly techniques will eliminate the need to invest in new lithographic machines, costing $500 million, that use X-rays to etch smaller circuits. .
“The answer is possibly yes,” he said, in describing a lower cost path to denser computer chips.
Samsung is reportedly planning to unveil its secret weapon, the V1 Bomb, a high-definition TV called Quantum-dot LED TV (QLED TV) at the 2014 International CES, the world’s biggest electronics show in Las Vegas in January.
According to an industry source on January 3, Samsung Electronics is considering showcasing the Quantum-dot display of QLED TV in the upcoming 2014 International CES. QLED TV is a TV that is designed to use self-luminous quantum dots in nanoscale crystals of semiconductor chips that enable the display of colors without any more parts. The model that is expected to be introduced is a type of QLED that uses Quantum Dot Enhancement Film (QDEF) technology instead of a traditional backlighting unit. In that sense it is by definition not a true QLED, but its viability as a commercial product is immense, since manufacturing a large screen display using QLED technology is much easier then using an existing Organic Light-Emitting Diode, or OLED.
In 2011, Samsung succeeded in developing the world’s first full-color display using quantum dots. LG Electronics followed suit by forming a Memorandum of Understanding with US nanotechnology company QD Vision to build its own QLED TV. In the first half of last year, 3M and Nanosis introduced a prototype of QDEF targeted at LCD manufacturers. Japanese manufacturers such as Sony and Panasonic have suspended competition with Samsung and LG’s OLED products, and have reportedly been concentrating their efforts on developing QLED technology to be used in UHD TV. Taiwan’s LCD manufacturer AU Optronics is also said to be working on its own color-enhanced QLED using QDEF.
A source close to the electronics manufacturing industry said, “3M, the primary developer of QDEF, is right now supplying 85-inch QDEF products to LCD makers.” As of 3Q and 4Q of 2012, there were several manufacturers in the 85-inch LCD TV market, of which Samsung owned a 72 percent share. Considering Samsung’s lofty position, it is highly likely that it will introduce a prototype product at the 2014 CES.
On whether or not Samsung will unveil its QLED TV at 2014 CES, another source said, “CES is not necessarily an exhibit for finished products. Rather, it is a platform for manufacturers to showcase their latest technologies. Thus it is possible and likely that we will see Samsung’s QLED at the show.”
Samsung Advanced Institute of Technology, the core R&D incubator for Samsung Electronics, has developed a new transistor structure utilizing graphene, touted as the “miracle material.”
As published online in the journal Science on Thursday, 17th May, this research is regarded to have brought us one step closer to the development of transistors that can overcome the limits of conventional silicon.
Currently, semiconductor devices consist of billions of silicon transistors. To increase the performance of semiconductors (the speed of devices), the options have to been to either reduce the size of individual transistors to shorten the traveling distance of electrons, or to use a material with higher electron mobility which allows for faster electron velocity. For the past 40 years, the industry has been increasing performance by reducing size. However, experts believe we are now nearing the potential limits of scaling down.
Since graphene possesses electron mobility about 200 times greater than that of silicon, it has been considered a potential substitute. Although one issue with graphene is that, unlike conventional semiconducting materials, current cannot be switched off because it is semi-metallic. This has become the key issue in realizing graphene transistors. Both on and off flow of current is required in a transistor to represent “1” and “0” of digital signals. Previous solutions and research have tried to convert graphene into a semi-conductor. However, this radically decreased the mobility of graphene, leading to skepticism over the feasibility of graphene transistors.
By re-engineering the basic operating principles of digital switches, Samsung Advanced Institute of Technology has developed a device that can switch off the current in graphene without degrading its mobility.The demonstrated graphene-silicon Schottky barrier can switch current on or off by controlling the height of the barrier. The new device was named Barristor, after its barrier-controllable feature.
In addition, to expand the research into the possibility of logic device applications, the most basic logic gate (inverter) and logic circuits (half-adder) were fabricated, and basic operation (adding) was demonstrated.
Samsung Advanced Institute of Technology owns 9 major patents related to the structure and the operating method of the Graphene Barristor.
As demonstrated in this research, the institute has solved the most difficult problem in graphene device research and has opened the door to new directions for future studies. This breakthrough continues to keep Samsung Advanced Institute of Technology at the forefront of graphene-related industries.
*Schottky Barrier: Named after a German physicist Walter H Schottky, it is a potential (energy) barrier formed at a metal-semiconductor interface. It prevents an electric charge to flow from metal to silicon. Generally, metal-semiconductor junction would have fixed work function and Schottky barrier height, but as for graphene, Schottky barrier height can be controlled through the work function.
*Work Function: The minimum energy needed to take an electron out of material.
*Inverter: A basic logic gate that converts a digital signal into the opposite level; “0” into “1” or vice versa.
*Half-Adder: A logical circuit that performs addition of two binary digits.
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