NT/ Researchers improve cement with shrimp shell nanoparticles
Nanotechnology & nanomaterials biweekly vol.28, 25th July — 8th August
TL;DR
- Putting nanoparticles from shrimp shells into cement paste made the material significantly stronger — an innovation that could lead to reduced seafood waste and lower carbon emissions from concrete production.
- Scientists at the University of Virginia School of Medicine and their collaborators have used DNA to overcome a nearly insurmountable obstacle to engineering materials that would revolutionize electronics.
- Constructing a tiny robot from DNA and using it to study cell processes invisible to the naked eye… You would be forgiven for thinking it is science fiction, but it is in fact the subject of serious research. This highly innovative ‘nano-robot’ should enable a closer study of the mechanical forces applied at microscopic levels, which are crucial for many biological and pathological processes.
- Graphene scientists from The University of Manchester have created a novel ‘nano-petri dish’ using two-dimensional (2D) materials to create a new method of observing how atoms move in liquid.
- Carbon nano-onions (CNOs), a form of carbon nanostructure with excellent electrical and thermal conductivities, find several applications in biomedicine, bioimaging, energy conversion, and electronics. However, conventional methods to produce them suffer from high complexity, toxicity, and energy consumption. Fortunately, scientists have now found a convenient and eco-friendly way to synthesize high-quality CNOs using scales from fish waste and microwave pulses. This novel approach could open doors to the adoption of CNOs in next-generation technologies.
- A team of researchers has developed a new kind of Atomic Force Microscopy (AFM) probes in true three-dimensional shapes they call 3DTIPs. AFM technology allows scientists to observe, measure, and manipulate samples and micro and nanoscale entities with unprecedented precision. The new 3DTIPs, which are manufactured using a single-step 3D printing process, can be utilized for a wider variety of applications — and potential observations and discoveries — than standard, more limited silicon-based probes that are considered state-of-the-art in our current time.
- Knowledge of the atomic-level structures of materials is extremely important for correlating the properties and functions of material in any scientific discipline, including chemistry, biology, and physics. However, the determination of the structures of the magic-sized nanoclusters, which typically serve as nuclei of the semiconductor nanocrystals, remains highly challenging largely due to instability and inhomogeneity. In a recent finding, the researchers identified that the tertiary diamine and halide ligands can overcome these hurdles together, and revealed the core-cage structure in a subnanometer-sized 27-atom semiconductor cadmium selenide nanocluster, Cd14Se13.
- Researchers have designed smart, color-controllable white light devices from quantum dots — tiny semiconductors just a few billionths of a meter in size — which are more efficient and have better color saturation than standard LEDs, and can dynamically reproduce daylight conditions in a single light.
- An international team of researchers has developed a new type of strong and elastic two-dimensional (2D) membrane. The invention could prove useful, for instance, in detecting remnants of antibiotics from water.
- Nanodiamonds’ repertoire of applications expands constantly, including everything from ultra-fine coatings to precise drug delivery.nNow, Kyoto University and Daicel Corporation have developed nanodiamonds to detect temperatures on the nanoscale inside cells and organelles.
- And more!
Nanotech Market
Nanotechnology deals with the ability to see, understand, measure, predict, produce or control matter at the nanoscale (below 100 nanometers). The realm of nanotechnology lies between 0.1 and 100 nanometers, wherein a nanometer is defined as one-thousandth of a micron. As a versatile technology with widespread applications in a wide range of end-use sectors, nanotechnology is currently facing a mixed bag of challenges and opportunities as the COVID-19 pandemic continues to spread across the globe. With the world fighting its biggest public health crisis in history, nanotechnology healthcare applications are storming into the spotlight led by the focus on nano intervention in terms of designing effective ways to identify, diagnose, treat and eliminate the spread of COVID-19 infections. Their role as nanocarriers has the potential to design risk-free and effective immunization strategies. In the post-COVID-19 period, the use of nanotechnology solutions in the production of a multitude of devices & products will continue to grow.
Amid the COVID-19 crisis, the global market for Nanotechnology estimated at US$42.2 Billion in the year 2020, is projected to reach a revised size of US$70.7 Billion by 2026, growing at a CAGR of 9.2% over the analysis period. Nanocomposites, one of the segments analyzed in the report, is projected to record a 8.7% CAGR and reach US$35.4 Billion by the end of the analysis period. After a thorough analysis of the business implications of the pandemic and its induced economic crisis, growth in the Nanomaterials segment is readjusted to a revised 10.1% CAGR for the next 7-year period.
Global nanotechnology market to reach US $126.8 billion by the year 2027. Amid the COVID-19 crisis, the global market for Nanotechnology is estimated at US $54.2 billion in the year 2020, and is projected to reach a revised size of US $126 billion.
Latest News & Research
Insights into setting time, rheological and mechanical properties of chitin nanocrystals- and chitin nanofibers-cement paste
by Md Mostofa Haider, Guoqing Jian, Tuhua Zhong, Hui Li, Carlos A. Fernandez, Leonard S. Fifield, Michael Wolcott, Somayeh Nassiri in Cement and Concrete Composites
Putting nanoparticles from shrimp shells into cement paste made the material significantly stronger — an innovation that could lead to reduced seafood waste and lower carbon emissions from concrete production.
Reporting in the journal Cement and Concrete Composites, a team of Washington State University and Pacific Northwest National Laboratory researchers created nanocrystals and nanofibers of chitin, the second most abundant biopolymer in nature, from waste shrimp shells. When these tiny bits of chitin, which are about 1,000 times smaller than a human hair, were added to cement paste, the resulting material was up to 40% stronger. Set time for the cement, or how long it takes to harden, was also delayed by more than an hour, a desired property for long-distance transport and hot weather concrete work.
“The concrete industry is under pressure to reduce its carbon emissions from the production of cement,” said Somayeh Nassiri, an associate professor at the University of California, Davis, who led the research at WSU. “By developing these novel admixtures that enhance the strength of concrete, we can help reduce the amount of required cement and lower the carbon emissions of concrete.”
Concrete is used around the world in critical infrastructure such as building, bridges and roads. It is the most used material on earth after water. Cement production is carbon intensive, requiring the use of fossil fuels to reach the required high temperatures (1500°C). The limestone used in its production also goes through decomposition that produces additional carbon dioxide. Cement production comprises about 15% of industrial energy consumption and about 5% of total greenhouse gas emissions worldwide. High consumption of the material is also partly driven by the challenge of durability — concrete cracks easily and must be repaired or replaced often, says Nassiri.
Meanwhile, seafood waste is a significant problem for the fishing industry, which generates between 6 million and 8 million pounds of waste annually worldwide. Most of that waste is dumped into the sea, says Hui Li, research assistant professor in WSU’s Composite Materials and Engineering Center and a corresponding author on the paper.
“In the current world, dealing with climate change through the circular economy, we want to use waste materials as much as possible. One person’s waste is another person’s treasure,” he said.
Researchers have worked to improve concrete with a similar common biopolymer, cellulose. Sometimes cellulose additives would help the concrete, and sometimes they wouldn’t. The researchers were flummoxed as to why.
In their work, the WSU team studied the chitin materials at the nanoscale. Crab, shrimp and lobster shells are made up of about 20–30% chitin with much of the rest being calcium carbonate, another useful additive for cement. Compared to cellulose, chitin at the molecular scale happens to have an additional set of atoms — a functional group — that allows the researchers to control the charge on the surface of the molecules and, consequently, how they behave in the cement slurry.
“Being able to control the charge on the surface is an important piece to controlling how they function in cement. We could do that quite simply on the chitin because of the carboxyl group that sits in the chitin polymer,” said WSU Regents Professor Michael Wolcott, a corresponding author on the paper.
The success in strengthening the cement paste came down to how the particles suspend themselves within the cement slurry and how they interact with the cement particles.
“The chitin nanoparticles repel individual cement particles enough so that it changes the hydration properties of the cement particle within the system,” he said.
As they added the processed nanocrystals of chitin to the cement, they were able to improve and target its properties, including its consistency, setting time, strength and durability. They saw a 40% increase in strength in how the concrete can bend and a 12% improvement in the ability to compress it.
“Those are very significant numbers,” Wolcott said. “If you can reduce the amount that you use and get the same mechanical function or structural function and double its lifetime, then you’re able to significantly reduce the carbon emissions of the built environment.”
The researchers are now hoping to scale up the work to begin producing the additive on a large scale. The research also needs to continue to achieve the same level of enhancements seen at the cement paste scale at the concrete scale.
DNA-guided lattice remodeling of carbon nanotubes
by Zhiwei Lin, Leticia C. Beltrán, Zeus A. De los Santos, Yinong Li, Tehseen Adel, Jeffrey A Fagan, Angela R. Hight Walker, Edward H. Egelman, Ming Zheng in Science
Scientists at the University of Virginia School of Medicine and their collaborators have used DNA to overcome a nearly insurmountable obstacle to engineering materials that would revolutionize electronics.
One possible outcome of such engineered materials could be superconductors, which have zero electrical resistance, allowing electrons to flow unimpeded. That means that they don’t lose energy and don’t create heat, unlike current means of electrical transmission. Development of a superconductor that could be used widely at room temperature — instead of at extremely high or low temperatures, as is now possible — could lead to hyper-fast computers, shrink the size of electronic devices, allow high-speed trains to float on magnets and slash energy use, among other benefits.
One such superconductor was first proposed more than 50 years ago by Stanford physicist William A. Little. Scientists have spent decades trying to make it work, but even after validating the feasibility of his idea, they were left with a challenge that appeared impossible to overcome. Until now.
Edward H. Egelman, PhD, of UVA’s Department of Biochemistry and Molecular Genetics, has been a leader in the field of cryo-electron microscopy (cryo-EM), and he and Leticia Beltran, a graduate student in his lab, used cryo-EM imaging for this seemingly impossible project.
“It demonstrates,” he said, “that the cryo-EM technique has great potential in materials research.”
One possible way to realize Little’s idea for a superconductor is to modify lattices of carbon nanotubes, hollow cylinders of carbon so tiny they must be measured in nanometers — billionths of a meter. But there was a huge challenge: controlling chemical reactions along the nanotubes so that the lattice could be assembled as precisely as needed and function as intended.
Egelman and his collaborators found an answer in the very building blocks of life. They took DNA, the genetic material that tells living cells how to operate, and used it to guide a chemical reaction that would overcome the great barrier to Little’s superconductor. In short, they used chemistry to perform astonishingly precise structural engineering — construction at the level of individual molecules. The result was a lattice of carbon nanotubes assembled as needed for Little’s room-temperature superconductor.
“This work demonstrates that ordered carbon nanotube modification can be achieved by taking advantage of DNA-sequence control over the spacing between adjacent reaction sites,” Egelman said.
The lattice they built has not been tested for superconductivity, for now, but it offers proof of principle and has great potential for the future, the researchers say.
“While cryo-EM has emerged as the main technique in biology for determining the atomic structures of protein assemblies, it has had much less impact thus far in materials science,” said Egelman, whose prior work led to his induction into the National Academy of Sciences, one of the highest honors a scientist can receive.
Egelman and his colleagues say their DNA-guided approach to lattice construction could have a wide variety of useful research applications, especially in physics. But it also validates the possibility of building Little’s room-temperature superconductor. The scientists’ work, combined with other breakthroughs in superconductors in recent years, could ultimately transform technology as we know it and lead to a much more “Star Trek” future.
“While we often think of biology using tools and techniques from physics, our work shows that the approaches being developed in biology can actually be applied to problems in physics and engineering,” Egelman said. “This is what is so exciting about science: not being able to predict where our work will lead.”
A modular spring-loaded actuator for mechanical activation of membrane proteins
by A. Mills, N. Aissaoui, D. Maurel, J. Elezgaray, F. Morvan, J. J. Vasseur, E. Margeat, R. B. Quast, J. Lai Kee-Him, N. Saint, C. Benistant, A. Nord, F. Pedaci, G. Bellot in Nature Communications
Constructing a tiny robot from DNA and using it to study cell processes invisible to the naked eye… You would be forgiven for thinking it is science fiction, but it is in fact the subject of serious research by scientists from Inserm, CNRS and Université de Montpellier at the Structural Biology Center in Montpellier. This highly innovative “nano-robot” should enable a closer study of the mechanical forces applied at microscopic levels, which are crucial for many biological and pathological processes. It is described in a new study published in Nature Communications.
Our cells are subject to mechanical forces exerted on a microscopic scale, triggering biological signals essential to many cell processes involved in the normal functioning of our body or in the development of diseases.
For example, the feeling of touch is partly conditional on the application of mechanical forces on specific cell receptors (the discovery of which was this year rewarded by the Nobel Prize in Physiology or Medicine). In addition to touch, these receptors that are sensitive to mechanical forces (known as mechanoreceptors) enable the regulation of other key biological processes such as blood vessel constriction, pain perception, breathing or even the detection of sound waves in the ear, etc.
The dysfunction of this cellular mechanosensitivity is involved in many diseases — for example, cancer: cancer cells migrate within the body by sounding and constantly adapting to the mechanical properties of their microenvironment. Such adaptation is only possible because specific forces are detected by mechanoreceptors that transmit the information to the cell cytoskeleton.
At present, our knowledge of these molecular mechanisms involved in cell mechanosensitivity is still very limited. Several technologies are already available to apply controlled forces and study these mechanisms, but they have a number of limitations. In particular, they are very costly and do not allow us to study several cell receptors at a time, which makes their use very time-consuming if we want to collect a lot of data.
In order to propose an alternative, the research team led by Inserm researcher Gaëtan Bellot at the Structural Biology Center (Inserm/CNRS/Université de Montpellier) decided to use the DNA origami method. This enables the self-assembly of 3D nanostructures in a pre-defined form using the DNA molecule as construction material. Over the last ten years, the technique has allowed major advances in nanotechnology.
This enabled the researchers to design a “nano-robot” composed of three DNA origami structures. Of nanometric size, it is therefore compatible with the size of a human cell. It makes it possible for the first time to apply and control a force with a resolution of 1 piconewton, namely one trillionth of a Newton — with 1 Newton corresponding to the force of a finger clicking on a pen. This is the first time that a human-made, self-assembled DNA-based object can apply force with this accuracy.
The team began by coupling the robot with a molecule that recognizes a mechanoreceptor. This made it possible to direct the robot to some of our cells and specifically apply forces to targeted mechanoreceptors localized on the surface of the cells in order to activate them.
Such a tool is very valuable for basic research, as it could be used to better understand the molecular mechanisms involved in cell mechanosensitivity and discover new cell receptors sensitive to mechanical forces. Thanks to the robot, scientists will also be able to study more precisely at what moment, when applying force, key signaling pathways for many biological and pathological processes are activated at the cell level.
“The design of a robot enabling the in vitro and in vivo application of piconewton forces meets a growing demand in the scientific community and represents a major technological advance. However, the biocompatibility of the robot can be considered both an advantage for in vivo applications but may also represent a weakness with sensitivity to enzymes that can degrade DNA. So our next step will be to study how we can modify the surface of the robot so that it is less sensitive to the action of enzymes. We will also try to find other modes of activation of our robot using, for example, a magnetic field,” emphasizes Bellot.
Tracking single adatoms in liquid in a Transmission Electron Microscope
by Nick Clark, Daniel J. Kelly, Mingwei Zhou, Yi-Chao Zou, Chang Woo Myung, David G. Hopkinson, Christoph Schran, Angelos Michaelides, Roman Gorbachev, Sarah J. Haigh in Nature
Graphene scientists from The University of Manchester have created a novel ‘nano-petri dish’ using two-dimensional (2D) materials to create a new method of observing how atoms move in liquid
Publishing in the journal, Nature, the team led by researchers based at the National Graphene Institute (NGI) used stacks of 2D materials like graphene to trap liquid in order to further understand how the presence of liquid changes the behavior of the solid.
The team was able to capture images of single atoms ‘swimming’ in liquid for the first time. The findings could have a widespread impact on the future development of green technologies such as hydrogen production.
When a solid surface is in contact with a liquid, both substances change their configuration in response to the proximity of the other. Such atomic scale interactions at solid-liquid interfaces govern the behaviour of batteries and fuel cells for clean electricity generation, as well as determining the efficiency of clean water generation and underpinning many biological processes.
One of the lead researchers, Professor Sarah Haigh, commented: “Given the widespread industrial and scientific importance of such behaviour it is truly surprising how much we still have to learn about the fundamentals of how atoms behave on surfaces in contact with liquids. One of the reasons information is missing is the absence of techniques able to yield experimental data for solid-liquid interfaces.”
Transmission electron microscopy (TEM) is one of only a few techniques that allow individual atoms to be seen and analyzed. However, the TEM instrument requires a high vacuum environment and the structure of materials changes in a vacuum.
The first author, Dr Nick Clark explained: “In our work, we show that misleading information is provided if the atomic behaviour is studied in a vacuum instead of using our liquid cells.”
Professor Roman Gorbachev has pioneered the stacking of 2D materials for electronics but here his group has used those same techniques to develop a ‘double graphene liquid cell’. A 2D layer of molybdenum disulphide was fully suspended in liquid and encapsulated by graphene windows. This novel design allowed them to provide precisely controlled liquid layers, enabling unprecedented videos to be captured showing the single atoms ‘swimming’ around surrounded by liquid.
By analyzing how the atoms moved in the videos and comparing them to theoretical insights provided by colleagues at Cambridge University, the researchers could understand the effect of the liquid on atomic behavior. The liquid was found to speed up the motion of the atoms and also change their preferred resting sites with respect to the underlying solid.
The team studied a material that is promising for green hydrogen production but the experimental technology they have developed can be used for many different applications.
Dr Nick Clark said: “This is a milestone achievement and it is only the beginning — we are already looking to use this technique to support development of materials for sustainable chemical processing, needed to achieve the world’s net zero ambitions.”
Fabrication of ultra-bright carbon nano-onions via a one-step microwave pyrolysis of fish scale waste in seconds
by Yunzi Xin, Kai Odachi, Takashi Shirai in Green Chemistry
Thanks to their low toxicity, chemical stability, and remarkable electrical and optical properties, carbon-based nanomaterials are finding more and more applications across electronics, energy conversion and storage, catalysis, and biomedicine. Carbon nano-onions (CNOs) are certainly no exception. First reported in 1980, CNOs are nanostructures composed of concentric shells of fullerenes, resembling cages within cages. They offer multiple attractive qualities such as a high surface area and large electrical and thermal conductivities.
Unfortunately, conventional methods for producing CNOs have some serious drawbacks. Some require harsh synthesis conditions, such as high temperatures or vacuum, while others demand a lot of time and energy. Some techniques can circumvent these limitations but instead call for complex catalysts, expensive carbon sources, or dangerous acidic or basic conditions. This greatly limits the potential of CNOs.
Fortunately, not all hope is lost. In a recent study published in Green Chemistry (available online on April 25, 2022, and published in issue 10 on May 21, 2022), a team of scientists from Nagoya Institute of Technology in Japan found a simple and convenient way to turn fish waste into extremely high-quality CNOs. The team, which included Assistant Professor Yunzi Xin, Master’s student Kai Odachi, and Associate Professor Takashi Shirai, developed a synthesis route in which fish scales extracted from fish waste after cleaning are converted into CNOs in mere seconds through microwave pyrolysis.
But how can fish scales be converted into CNOs so easily? While the exact reason is not altogether clear, the team believes that it has to do with the collagen contained in fish scales, which can absorb enough microwave radiation to produce a fast rise in temperature. This leads to thermal decomposition or “pyrolysis,” which produces certain gases that support the assembly of CNOs. What is remarkable about this approach is that it needs no complex catalysts, nor harsh conditions, nor prolonged wait times; the fish scales can be converted into CNOs in less than 10 seconds!
Moreover, this synthesis process yields CNOs with very high crystallinity. This is remarkably difficult to achieve in processes that use biomass waste as a starting material. Additionally, during synthesis, the surface of the CNOs is selectively and thoroughly functionalized with (−COOH) and (−OH) groups. This is in stark contrast to the surface of CNOs prepared with conventional methods, which is typically bare and has to be functionalized through additional steps.
This “automatic” functionalization has important implications for applications of CNOs. When the CNO surface is not functionalized, the nanostructures tend to stick together owing to an attractive interaction known as pi−pi stacking. This makes it difficult to disperse them in solvents, which is necessary for any application requiring solution-based processes. However, since the proposed synthesis process produces functionalized CNOs, it allows for excellent dispersibility in various solvents.
Yet another advantage associated with functionalization and high crystallinity, is that of exceptional optical properties. Dr. Shirai explains: “The CNOs exhibit ultra-bright visible-light emission with efficiency (or quantum yield) of 40%. This value, which has never been achieved before, is about 10 times higher than that of previously reported CNOs synthesized via conventional methods.”
To showcase some of the many practical applications of their CNOs, the team demonstrated their use in LEDs and blue-light-emitting thin films. The CNOs produced a highly stable emission, both inside solid devices and when dispersed in various solvents, including water, ethanol, and isopropanol.
“The stable optical properties could enable us to fabricate large-area emissive flexible films and LED devices,” speculates Dr. Shirai. “These findings will open up new avenues for the development of next-generation displays and solid-state lighting.”
Furthermore, the proposed synthesis technique is environmentally friendly and provides a straightforward way to convert fish waste into infinitely more useful materials. The team believes their work would contribute to the fulfillment of several of UN’s Sustainable Development Goals. Additionally, if CNOs make their way into next-generation LED lighting and QLED displays, they could greatly help reduce their manufacturing costs.
3D Generation of Multipurpose Atomic Force Microscopy Tips
by Ayoub Glia, Muhammedin Deliorman, Mohammad A. Qasaimeh in Advanced Science
A team of researchers from NYU Abu Dhabi’s Advanced Microfluidics and Microdevices Laboratory (AMMLab) has developed a new kind of Atomic Force Microscopy (AFM) probes in true three-dimensional shapes they call 3DTIPs. AFM technology allows scientists to observe, measure, and manipulate samples and micro and nanoscale entities with unprecedented precision. The new 3DTIPs, which are manufactured using a single-step 3D printing process, can be utilized for a wider variety of applications — and potential observations and discoveries — than standard, more limited silicon-based probes that are considered state-of-the-art in our current time.
Atomic force microscopy (AFM) is a technique for characterizing samples by scanning a physical probe across surfaces, producing impressive resolutions 1,000 times higher than optical microscopy can achieve. AFM is a fundamental instrument in many disciplines including biomedical sciences, with applications ranging from characterizing viable bacteria and mammalian cells, analyzing DNA molecules, studying proteins in real time, and imaging molecules down to sub-atomic resolution.
The AFM probe, comprising a tiny cantilever beam with a miniature tip at its end, is the core of the technology. It senses and feels sample surfaces through forces of attraction and repulsion, in the same way, we use our fingertips, but with a resolution down to the atomic level. Commercial AFM probes are made out of silicon, using conventional semiconductor manufacturing processes, typical in the microelectronics industry, that are limited by 2D designs and lengthy production steps. These current state-of-the-art probes are rigid, brittle, and only available in certain shapes. They are non-ideal for probing soft matter, such as mammalian cells.
In the paper, the researchers present their proprietary technology for producing next generation AFM probes based on two-photon polymerization 3D printing. The resulting 3DTIPs are softer than their silicon-based counterparts, which makes them more suitable for AFM applications involving gentler interactions with cells, proteins, and DNA molecules. Importantly, the material properties of 3DTIPs make it possible to achieve scans that are more than 100 times faster than regular silicon probes of similar dimensions. Therefore, 3DTIPs might open the door for acquiring videos that capture bioactivities of proteins, DNA and even smaller molecules in real time.
“We have developed a novel technology for next-generation AFM probes with new materials, improved designs and production processes, novel shapes in 3D, and customized prototyping for a seamless production cycle for application-focused AFM probes,” said Mohammad Qasaimeh, the principal investigator of the project and Associate Professor of Mechanical Engineering and Bioengineering at NYUAD. “The ability to generate customized AFM probes with innovative 3D designs in a single step provides endless multidisciplinary research opportunities.”
“Our 3DTIPs are capable of obtaining high-resolution, high-speed AFM imaging using common AFM modes, and under air and liquid environments,” said Dr. Ayoub Glia, the first author of the study and postdoctoral associate at the AMMLab. “Refining the tip end of the 3DTIPs by focused ion beam etching and carbon nanotube inclusion substantially extends their functionality in high-resolution AFM imaging, reaching angstrom scales.”
The authors of the study hope that the multifunctional capabilities of the 3DTIPs could bring next-generation AFM tips to routine and advanced AFM applications and expand the fields of high-speed AFM imaging and biological force measurements.
Structure of a subnanometer-sized semiconductor Cd14Se13 cluster
by Megalamane S. Bootharaju, Woonhyuk Baek, Guocheng Deng, Kamalpreet Singh, Oleksandr Voznyy, Nanfeng Zheng, Taeghwan Hyeon in Chem
A semiconductor is a material whose conductivity lies somewhere between that of a conductor and an insulator. This property allows semiconductors to serve as the base material for modern electronics and transistors. It is no understatement that the technological progress in the latter part of the 20th century was largely spearheaded by the semiconductor industry.
Today, technological advancements in semiconductor nanocrystals are currently ongoing. For example, quantum dots and wires from semiconducting materials are of great interest in displays, photocatalytic, and other electronic devices. However, numerous aspects of the colloidal nanocrystals are still remaining to be understood at the fundamental level. An important one among them is the elucidation of the molecular-level mechanisms of the formation and growth of the nanocrystals.
These semiconducting nanocrystals are grown starting from tiny individual precursors made of a small number of atoms. These precursors are called “nanoclusters.” Isolation and molecular structure determination of such nanoclusters (or simply clusters) have been the subject of immense interest in the past several decades. The structural details of clusters, typical nuclei of the nanocrystals, are anticipated to provide critical insights into the evolution of the properties of the nanocrystals.
Different ‘seed’ nanoclusters result in the growth of different nanocrystals. As such, it is important to have a homogenous mixture of identical nanoclusters if one wishes to grow identical nanocrystals. However, the synthesis of nanoclusters often results in the production of clusters with all sorts of different sizes and configurations, and purifying the mixture to obtain only the desirable particles is very challenging.
Therefore, producing nanoclusters with homogenous sizes is important. “Magic-sized nanoclusters, MSCs,” which are preferably formed over random sizes in a uniform manner, possess size range from 0.5 to 3.0 nm. Among these, MSCs composed of non-stoichiometric cadmium and chalcogenide ratio (non 1:1) are the most studied. A new class of MSCs with a 1:1 stoichiometric ratio of metal-chalcogenide ratio has been under spotlight owing to the prediction of intriguing structures. For example, Cd13Se13, Cd33Se33 and Cd34Se34, which consist of an equal number of cadmium and selenium atoms have been synthesized and characterized.
Recently, researchers at the Center for Nanoparticle Research (led by Professor HYEON Taeghwan) within the Institute for Basic Science (IBS) in collaboration with the teams at Xiamen University (led by Professor Nanfeng ZHENG) and at the University of Toronto (led by Professor Oleksandr VOZNYY) reported the colloidal synthesis and atomic-level structure of stoichiometric semiconductor cadmium selenide (CdSe) cluster. This is the smallest nanocluster synthesized as of today.
Synthesis of Cd14Se13 was accomplished after numerous previous failures with Cd13Se13, which always ended up in undesirable assemblies, making them impossible to characterize. Director Hyeon stated, “We found that the tertiary diamine and halocarbon solvent play a crucial role in achieving nearly single-sized, stoichiometric clusters. The tertiary diamine (N,N,N’,N’-tetramethylethylenediamine) ligands not only provide rigid binding with appropriate steric constraints but also disable the intercluster interactions due to the short carbon chain, leading to the formation of soluble Cd14Se13 clusters, instead of undesired insoluble lamellar Cd13Se13 assemblies.”
The dichloromethane solvent supplies chloride ions in situ to simultaneously achieve charge-balancing of the 14th cadmium ion, which allows for the self-assembly of the clusters to form (Cd14Se13Cl2)n. As a result, single crystals of adequate quality could be obtained for the researchers to determine the structure of the clusters. The composition of the clusters obtained from the single crystal X-ray diffraction data analysis was in very good agreement with the mass spectrometry and nuclear magnetic resonance data. The overall shape of the cluster was spherical with a size of about 0.9 nm.
While most other MSCs with non 1:1 metal-chalcogenide ratios tend to have supertetrahedral geometry, the new Cd14Se13 was found to possess a core-cage arrangement of constituent atoms. Specifically, the cluster comprised a central Se atom encapsulated by a Cd14Se12 cage with an adamantane-like CdSe arrangement. Such a unique arrangement of atoms opens the possibility of growing nanocrystals with unusual structures, which needs to be further explored in the future.
The optical properties of the cluster showed the presence of quantum-confinement effects with band-edge photoluminescence. However, the photoluminescence features related to defect states were prominent due to the ultra-small size of the clusters. The structure and the absorption peaks observed in the experiments were well supported by the density functional theory calculations.
The researchers created the Cd14Se13 cluster through an intermediate Cd34Se33 cluster, which is the next known large-sized stoichiometric cluster. Interestingly, both of these two clusters could be doped via substitution with a maximum of two Mn atoms, which illustrates the potential to realize dilute magnetic semiconductors with tailored photoluminescence properties. The computational results showed that the Cd sites bound to halides were more susceptible to Mn substitution.
The implications of this study may go well beyond the synthesis of single-sized semiconductor clusters, as the tertiary diamines of different chemical structures may be extended to other clusters. Synthesis and determination of the atomic-level structure of other clusters may eventually help understand the molecular-level growth mechanism of the semiconductor nanocrystals.
It was shown that the Cd34Se33 cluster could be kinetically stabilized through a ligand-exchange-induced size conversion process developed in this work. However, more efforts and new strategies are needed to improve the solution-state stability for the structure determination of the next large-sized cluster Cd34Se33, which is the critical nuclei for the cadmium selenide-based nanocrystal growth. It is hoped that further studies of the size-, structure-, and dopant-dependencies on the optoelectronic, photocatalytic and spintronic applications may open new directions to scientific research on the semiconductor clusters.
Optoelectronic System and Device Integration for Quantum-Dot Light-Emitting Diode White Lighting with Computational Design Framework
in Nature Communications
Researchers have designed smart, color-controllable white light devices from quantum dots — tiny semiconductors just a few billionths of a meter in size — which are more efficient and have better color saturation than standard LEDs, and can dynamically reproduce daylight conditions in a single light.
The researchers, from the University of Cambridge, designed the next-generation smart lighting system using a combination of nanotechnology, color science, advanced computational methods, electronics and a unique fabrication process.
The team found that by using more than the three primary lighting colors used in typical LEDs, they were able to reproduce daylight more accurately. Early tests of the new design showed excellent color rendering, a wider operating range than current smart lighting technology, and wider spectrum of white light customization. The results are reported in the journal Nature Communications.
As the availability and characteristics of ambient light are connected with well-being, the widespread availability of smart lighting systems can have a positive effect on human health since these systems can respond to individual mood. Smart lighting can also respond to circadian rhythms, which regulate the daily sleep-wake cycle, so that light is reddish-white in the morning and evening, and bluish-white during the day.
When a room has sufficient natural or artificial light, good glare control, and views of the outdoors, it is said to have good levels of visual comfort. In indoor environments under artificial light, visual comfort depends on how accurately colors are rendered. Since the color of objects is determined by illumination, smart white lighting needs to be able to accurately express the color of surrounding objects. Current technology achieves this by using three different colors of light simultaneously.
Quantum dots have been studied and developed as light sources since the 1990s, due to their high color tunability and color purity. Due to their unique optoelectronic properties, they show excellent color performance in both wide color controllability and high color rendering capability.
The Cambridge researchers developed an architecture for quantum-dot light-emitting diodes (QD-LED) based next-generation smart white lighting. They combined system-level color optimization, device-level optoelectronic simulation, and material-level parameter extraction.
The researchers produced a computational design framework from a color optimization algorithm used for neural networks in machine learning, together with a new method for charge transport and light emission modeling.
The QD-LED system uses multiple primary colors — beyond the commonly used red, green and blue — to more accurately mimic white light. By choosing quantum dots of a specific size — between three and 30 nanometers in diameter — the researchers were able to overcome some of the practical limitations of LEDs and achieve the emission wavelengths they needed to test their predictions.
The team then validated their design by creating a new device architecture of QD-LED based white lighting. The test showed excellent color rendering, a wider operating range than current technology, and a wide spectrum of white light shade customisation.
The Cambridge-developed QD-LED system showed a correlated color temperature (CCT) range from 2243K (reddish) to 9207K (bright midday sun), compared with current LED-based smart lights which have a CCT between 2200K and 6500K. The color rendering index (CRI) — a measure of colors illuminated by the light in comparison to daylight (CRI=100) — of the QD-LED system was 97, compared to current smart bulb ranges, which are between 80 and 91.
The design could pave the way to more efficient, more accurate smart lighting. In an LED smart bulb, the three LEDs must be controlled individually to achieve a given color. In the QD-LED system, all the quantum dots are driven by a single common control voltage to achieve the full-color temperature range.
“This is a world-first: a fully optimized, high-performance quantum-dot-based smart white lighting system,” said Professor Jong Min Kim from Cambridge’s Department of Engineering, who co-led the research. “This is the first milestone toward the full exploitation of quantum-dot-based smart white lighting for daily applications.”
“The ability to better reproduce daylight through its varying color spectrum dynamically in a single light is what we aimed for,” said Professor Gehan Amaratunga, who co-led the research. “We achieved it in a new way through using quantum dots. This research opens the way for a wide variety of new human responsive lighting environments.”
The structure of the QD-LED white lighting developed by the Cambridge team is scalable to large area lighting surfaces, as it is made with a printing process and its control and drive are similar to that in a display. With standard point source LEDs requiring individual control, this is a more complex task.
Strong and Elastic Membranes via Hydrogen Bonding Directed Self‐Assembly of Atomically Precise Nanoclusters,
by Anirban Som et al in Small
An international team of researchers has developed a new type of strong and elastic two-dimensional (2D) membrane. The invention could prove useful, for instance, in detecting remnants of antibiotics from water.
Two-dimensional materials are ultrathin and composed of either single- or few-layer atoms. Recently, nanoparticle-based 2D materials have gained tremendous interest among researchers and industry due to their mechanical strength, flexibility, and optical and electronic properties which could make them key components, for instance, in emerging optoelectronic devices, sensors, and next-generation computing technologies. So far, though, no commercial applications exist due to problems with both scalability and obtaining uniform products from one batch to another.
A research team led by Nonappa, associate professor at Tampere University and adjunct professor at Aalto University, has now been able to fabricate a large 2D monolayer membrane using metal nanoparticles that surpasses some of these difficulties.
“These membranes are mechanically robust and can be transferred on to any substrate of interest for desired applications. Our approach enables the rapid, scalable, and efficient fabrication of large-area ultrathin membranes,” Nonappa says.
Unlike routinely used nanoparticles, the team used silver nanoparticles with a precisely defined molecular structure. The macroscopic membranes were prepared using a self-assembly approach.
“The membranes show elastic behavior, making them potentially useful, for example, in flexible transistors and memory devices in wearable electronics and displays. The experimental results on their mechanical properties are highly reproducible and reliable,” describes postdoctoral researcher Alessandra Griffo from Saarland University.
The research team has also explored the suitability of the newly-developed membranes as substrates for detecting antibiotics in water. With the increased use of pharmaceuticals and consequent contamination of surface and groundwater with antibiotics, there is an urgent need for rapid and reliable detection.
“We can detect extremely low amounts of antibiotics dissolved in water with a high degree of reproducibility,” postdoctoral researcher Anirban Som from Aalto University explains.
In the future, the team will focus on adapting the membrane fabrication methods to other types of nanoparticles, utilizing them as components in, for instance, flexible memory devices and smart e-skin applications.
All-optical nanoscale thermometry based on silicon-vacancy centers in detonation nanodiamonds
by Masanori Fujiwara et al in Carbon
Nanodiamonds’ repertoire of applications expands constantly, including everything from ultra-fine coatings to precise drug delivery. Now, Kyoto University and Daicel Corporation have developed nanodiamonds to detect temperatures on the nanoscale inside cells and organelles.
“The functions and activities of living cells will closely relate to the non-uniform temperature distribution and localized temperature changes within these biosystems,” notes author Norikazu Mizuochi.
Nanodiamonds with silicon-vacancy color centers, or SiV centers, are of a new generation that can detect temperature changes inside cells by gaging luminescence.
“The peak wavelength of the luminescence spectrum shifts linearly, which is mostly consistent with the spectral behavior of SiVs in bulk diamonds and shows us the possible future of all-optical nanoscale thermometry,” says the author.
Alternatively, color-center-containing nanodiamonds, especially nitrogen-vacancy centers, demonstrate high-temperature sensitivity when using laser light and microwave irradiation, and are advantageous in biological applications for their low cytotoxicity and stable luminescence.
Typically, temperature-measurable nanoparticles are larger than 100 nm — relatively massive in the nanoscale — potentially damaging cells. Mizuochi’s team, however, has succeeded in creating the smallest nanodiamond thermometry with a mean size of 20 nm, including other color centers such as NV centers. This nanoparticle enables smoother entry into organelles as well as temperature sensing to sub-kelvin precision.
“To investigate the temperature response of our polymer-coated and size-selected SiV-containing nanodiamonds, or SiV-DNDs, we used a temperature-controlled microscope to measure the luminescence spectrum of an array of SiV-DNDs,” adds Mizuochi.
Combining this technology with multi-color imaging and improving temperature sensing by optimizing the number of SiV centers per particle is part of the next stage in the research team’s development of high-precision nanodiamonds.
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