Advanced Mechanics Materials Cook Young Pdf Printer

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The new scopes increase the differentiation between these excellent sister polymer science titles and take effect from 1 January 2018. Polymer is our largest and broadest scope polymer journal.

Aug 26, 2011. Brain injury. She is scheduled to graduate in June 2012 with an advanced studies diploma. Complete task analyses of specific skills required for the adult life environments in which young. My high school career and technical education program are giving me the training I need to be an auto mechanic. Textbooks: 1. Advanced Mechanics of Materials; 4th Edition, A.P. Boresi and O.M. Sidebottom, John Wiley & Sons, 1985. Advanced Mechanics of Materials; 2nd Edition, R.D. Cook and W.C. Prentice Hall, 1999. Theory of Elastic Stability; 2nd Edition, S.P. Timoshenko and J.M. McGraw-Hill, 1963.

Advanced Mechanics Materials Cook Young Pdf PrinterAdvanced Mechanics Materials Cook Young Pdf Printer

It is ranked No.11 in the JCR subject category Polymer Science, its 2016 Impact Factor is 3.684 and it publishes over 900 articles per year. Polymer is an interdisciplinary journal dedicated to publishing innovative and significant advances in Polymer Physics, Chemistry and Technology. It welcomes submissions on polymer hybrids, nanocomposites, characterization and self-assembly. Polymer also publishes work on the technological application of polymers in Energy and optoelectronics. Polymer, will continue to publish the leading research across the full spectrum of Polymer Science including Polymer Chemistry, with an increased focus on fundamental advances in Polymer Physics, Polymer Physical Chemistry and the technological application of polymers.

Submissions on bio-based or renewable monomers and polymers, stimuli-responsive systems, polymer bio-hybrids and the biomedical application of polymers will now be considered by EPJ only. European Polymer Journal (EPJ) is ranked No. 13 in the JCR subject category Polymer Science, its 2016 Impact Factor is 3.531 and it publishes over 500 articles per year. EPJ is dedicated to publishing work on fundamental and applied polymer chemistry and macromolecular materials.

The journal covers all aspects of polymer synthesis, including polymerization mechanisms and chemical functional transformations, with a focus on novel polymers and the relationships between molecular structure and polymer properties. In addition, it welcome submissions on bio-based or renewable polymers, stimuli-responsive systems and polymer bio-hybrids. EPJ also publishes research on the biomedical application of polymers, including drug delivery and regenerative medicine.

EPJ will no longer publish Polymer Physics papers. Instead EPJ will an increased focus on fundamental advances in Polymer Chemistry, Polymer Materials and the biological application of polymers. Authors that submit work to either journal that is no longer within scope will be offered the opportunity to transfer their paper to the sister title via our Article Transfer Service.

Our Article Transfer Service, means you do not have to resubmit or reformat your manuscript, you just have to accept or decline the transfer offer. We hope that these new scopes will increase the clarity of the coverage of each journal and that this will better support our authors, readers and the wider international polymer science community. This is an illustration of an ultrashort laser light striking a lanthanum strontium nickel oxide crystal, triggering the melting of atomic-scale stripes. The charges (yellow) quickly become mobile while the crystal distortions react only with delay, exposing the underlying interactions. Image: Robert Kaindl/Berkeley Lab.

Stripes can be found everywhere, from zebras roaming in the wild to the latest fashion statement. In the world of microscopic physics, periodic stripe patterns can be formed by electrons within so-called quantum materials. Scientists at the US Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) have now disentangled the intriguing dynamics of how such atomic-scale stripes melt and form, providing fundamental insights that could be useful in the development of novel energy materials. In strongly correlated quantum materials, interactions between the electrons reign supreme.

The complex coupling of these electrons with each other – and with electron spins and crystal vibrations – results in exotic phases such as charge ordering or high-temperature superconductivity. 'A key goal of condensed matter physics is to understand the forces responsible for complex phases and the transitions between them,' said Robert Kaindl, a principal investigator and staff scientist at Berkeley Lab's Materials Sciences Division. 'But in the microscopic world, interactions are often extremely fast. If we just slowly heat or cool a material to change its phase, we can miss out on the underlying action.'

Kaindl and his colleagues have been using ultrafast laser pulses to tease apart the microscopic dynamics of correlated quantum materials to access the interactions electrons have with each other and with the crystal's atomic lattice in the time domain. For this study, the researchers worked with lanthanum nickelate, a quantum material and model stripe compound. In particular, the researchers investigated the electronic charges that form the stripe pattern and how they couple to the crystal lattice.

How charges interact with the crystal is a key ingredient to stripe physics, the researchers said. 'The crystal lattice strongly distorts around the charge stripes,' explained Giacomo Coslovich, who did the work while he was a postdoctoral researcher at Berkeley Lab. 'This change of the crystal symmetry results in new lattice vibrations, which we can in turn detect with light at terahertz frequencies.' Kaindl and Coslovich are corresponding authors of a paper reporting these results in. In their experiments, the material is optically excited by a near-infrared laser pulse with a duration of 50 femtoseconds, and then probed with a terahertz pulse with variable time delay. A femtosecond is one millionth of one billionth of a second.

The researchers found unexpected dynamics when using the laser to disrupt the microscopic order. 'The interesting thing is that while the laser immediately excited the electrons, the vibrational distortions in the crystal initially remained frozen,' said Coslovich, who is now associate staff scientist at SLAC National Accelerator Laboratory. 'The stripe-phase vibrations disappeared only after several hundred to a few thousand femtoseconds. We also concluded that the speed depends on the direction of the interactions.' The interpretation of the experiments was supported by simulations of the phonon dispersion conducted by Alexander Kemper at North Carolina State University. The results provide important insight into the interactions, or ‘glue’, that couple electrons to lattice vibrations in the lanthanum nickelate. However, their broader relevance stems from recent observations of charge order in high-temperature superconductors – materials where electrical currents can flow without resistance at temperatures above the boiling point of liquid nitrogen.

While the mechanism remains puzzling, recent studies demonstrated the ability to induce superconductivity by suppressing stripes with short light pulses. 'Fluctuating stripes are thought to occur in unconventional superconductors. Our study puts a speed limit on how fast such patterns can change,' said Kaindl. 'It highlights the importance of considering both the spatial and temporal structure of the glue.' This story is adapted from material from, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier..

Snapshots of softness fields and particle arrangements for the oligomer pillar simulation and the granular pillar experiment, two of the systems investigated in the Science paper. Image: University of Pennsylvania. Dropping a smartphone on its glass screen, which is made of atoms jammed together with no discernible order, could result in it shattering. Unlike metals and other crystalline material, glass and many other disordered solids cannot be deformed significantly before failing and, because of their lack of crystalline order, it is difficult to predict which atoms will change during failure. 'In order to understand how a system chooses its rearrangement scenario,' said Douglas Durian, professor of physics and astronomy at the University of Pennsylvania, 'we must make connection with the underlying microscopic structure.

For crystals, it's easy; rearrangements are at topological defects such as dislocations. For disordered solids, it's a very hard 40-year-old problem that we're now cracking: what and where are structural defects in something that's disordered?' To find a link between seemingly disparate disordered materials, an interdisciplinary collaboration between Penn researchers in the School of Arts and Sciences and the School of Engineering and Applied Science studied an unprecedented range of disordered solids with constituent particles ranging from individual atoms to river rocks. Understanding materials failure on a fundamental level could pave the way for designing more shatter-resistant glasses or predicting geological phenomena like landslides. In a paper published in, the Penn researchers revealed commonalities among these disordered systems, defining a counterpart to the ‘defects’ implicated in the failure of crystalline materials.

This so-called ‘softness’ in disordered systems predicts the location of defects, which are the collection of particles most likely to change when the material fails. The paper is the culmination of years of research conducted at Penn's Materials Research Science & Engineering Center (MRSEC), which is hosted by the Laboratory for Research on the Structure of Matter. Andrea Liu, professor of physics in Penn's School of Arts and Sciences. And Robert Carpick, professor and chair in mechanical engineering and applied mechanics at Penn, were co-leaders of the MRSEC's integrated research group focused on the mechanics of disordered packings. A dozen of the group's faculty members, along with students and postdoctoral researchers from their labs, contributed to the study, providing data from 15 simulations and experiments on different types of disordered systems. The particles in those systems ranged in size from carbon atoms that make up wear-resistant engine coatings to centimeter-sized plastic spheres in a model riverbed. Using machine learning, the researchers collected hundreds of quantities that characterize the arrangements of particles in each system, quantities that individually might not be expected to reveal much.

Importantly, they found the combination of these quantities that correlates strongly with the dynamics. This produced a microscopic structural property called softness. If the softness is known, the behavior of the disordered material and how likely its constituent particles are to rearrange can be predicted. The systems the researchers studied were rearranging due to random thermal fluctuations or to different kinds of applied stress such as squeezing or stretching. In all cases, the technique worked well, and the researchers were able to predict with high accuracy the probability that the systems would rearrange. The researchers then compared properties across systems.

They found that the length scale over which softness was correlated was identical to the size of the rearrangements, or the number of particles that move when failure occurs. Remarkably, they found that this number is almost identical in all of these systems, regardless of the size of the particles and how they interact. 'People have been talking about what sets the size of localized rearrangements in disordered solids for 40 years,' said Liu.

'They speculated about localized defects that they called shear transformation zones in disordered systems where rearrangements are likely to occur, but no one had seen this directly. They couldn't predict ahead of time where rearrangements would be likely to occur. With the machine learning, we're saying, 'Let's train the system.

Let's look at the rearrangements and the structures and see if we can figure out what's important and then use that.' It's conceptually very straightforward, but it turns out to be very powerful.' The researchers also measured the yield strain, or how much the solid can be deformed before it starts to plastically deform. They found that the yield strain is approximately the same for all disordered solids over systems spanning 13 orders of magnitude in their mechanical stiffness. By comparison, the yield strains for different crystalline materials can vary by a hundred- or thousand-fold. Now that the researchers have shown that, up to and around when stress is applied, all these systems look the same, the next step of the effort is co-led by Durian and Paulo Arratia, professor of mechanical engineering and applied mechanics in the School of Engineering and Applied Science.

Their goal is to go beyond the yield strain, where all becomes chaos and the systems begin to look extremely different. Some systems fracture, others show shear bands, and others, like foams, can smoothly flow forever. 'When a rearrangement happens, the softnesses of the nearby particles all change,' Durian said, 'but, due to long-range elastic couplings, so can the softnesses of particles even quite far away, as illustrated by this data. Thus, a rearrangement has a nontrivial effect on where the next rearrangements are likely to occur. In particular, will nearby rearrangements be encouraged and hence promote shear banding, or will they be discouraged and hence promote toughness? We believe that understanding and ultimately controlling the complex interplay between rearrangements, stress and structure – here quantified by softness – is the key to improving toughness.' If the researchers can understand why different systems behave differently beyond yield, they may be able to control softness and how it evolves when it's under stress.

This could lead to tougher coatings and materials, such as more durable glass screens for phones. 'Disordered solids have a lot of great properties,' Liu said. 'You can mold them into any shape you want or create surfaces that are atomically smooth, which you can't really do with crystalline systems. But they tend to shatter easily. If we can understand what controls that and how to prevent it, then the concepts start to have real applications.

In an ideal case, we want to develop new, tougher materials that aren't as brittle or don't fall apart as catastrophically.' This story is adapted from material from the, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.. Physics graduate student Julian Irwin checks equipment in the lab of Chang-Beom Eom, where researchers have produced a material that could exhibit the best qualities of both solid-state and spinning-disk digital storage. Photo: Sarah Page/UW-Madison College of Engineering. Smartphones and computers wouldn't be nearly as useful without room for lots of apps, music and videos. These devices tend to store that information in two ways: through electric fields (as in a flash drive) or through magnetic fields (as in a computer's spinning hard disk).

Each method has advantages and disadvantages, but in the future our electronics could benefit from the best of both. 'There's an interesting concept,' says Chang-Beom Eom, professor of materials science and engineering at the University of Wisconsin-Madison. 'Can you cross-couple these two different ways to store information? Could we use an electric field to change the magnetic properties? Then you can have a low-power, multifunctional device.

We call this a 'magnetoelectric' device.' In a paper published in, Eom and his collaborators describe not only their unique process for making a high-quality magnetoelectric material, but exactly how and why it works. Magnetoelectric materials – which have both magnetic and electrical functionalities, or ‘orders’ – already exist. Switching one functionality induces a change in the other. 'It's called cross-coupling,' says Eom.

'Yet, how they cross-couple is not clearly understood.' Gaining that understanding requires studying how the magnetic properties change when an electric field is applied.

Up to now, this has been difficult due to the complicated structure of most magnetoelectric materials. In the past, says Eom, people studied magnetoelectric properties using very ‘complex’ materials, or those that lack uniformity. In his approach, Eom simplified not only the research, but also the material itself. Drawing on his expertise in material growth, he developed a unique process that used atomic ‘steps’ to guide the growth of a homogenous, single-crystal thin film of bismuth ferrite. Atop that, he added cobalt, which is magnetic; on the bottom, he placed an electrode made of strontium ruthenate.

The bismuth ferrite material was important because it made it much easier for Eom to study the fundamental magnetoelectric cross-coupling. 'We found that in our work, because of our single domain, we could actually see what was going on using multiple probing, or imaging, techniques. The mechanism is intrinsic. It's reproducible – and that means you can make a device without any degradation, in a predictable way.' To image the changing electric and magnetic properties switching in real time, Eom and his colleagues used the powerful synchrotron light sources at Argonne National Laboratory, as well as synchrotrons in Switzerland and the UK. 'When you switch it, the electrical field switches the electric polarization.

If it's 'downward,' it switches 'upward,' he says. 'The coupling to the magnetic layer then changes its properties: a magnetoelectric storage device.' That change in direction allows the researchers to take the next steps needed to add programmable integrated circuits – the building blocks that are the foundation of our electronics – to the material. While the homogenous material enabled Eom to answer important scientific questions about how magnetoelectric cross-coupling happens, it could also enable manufacturers to improve their electronics.

'Now we can design a much more effective, efficient and low-power device,' he says. This story is adapted from material from the, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.. These images show the graphene nanoribbons lying across the gold substrate. Graphene ribbons that are only a few atoms wide, so-called graphene nanoribbons, have special electrical properties that make them promising candidates for the nanoelectronics of the future. While graphene – a one-atom thick, honeycomb-shaped carbon layer – is normally a conductive material, it can become a semiconductor when in the form of nanoribbons. Graphene nanoribbons have a sufficiently large energy or band gap where no electron states can exist, which means they can be turned on and off – and thus could become a key component of nanotransistors.

Scientists know that the smallest details in the atomic structures of these graphene bands can have massive effects on the size of the energy gap and thus on how well-suited nanoribbons are as components of transistors. The energy gap depends on both the width of the graphene nanoribbons and on the structure of their edges. Since graphene consists of equilateral carbon hexagons, the edges may have a zigzag or a so-called ‘armchair’ shape, depending on the orientation of the ribbons. While bands with a zigzag edge behave like metals and are electrically conductive, bands with an armchair edge are semiconductors. This poses a major challenge for the production of nanoribbons.

If the ribbons are cut from a layer of graphene or made by cutting carbon nanotubes, the edges may be irregular and thus the graphene ribbons may not exhibit the desired electrical properties. Researchers at Empa in Switzerland, in collaboration with the Max Planck Institute for Polymer Research in Mainz, Germany, and the University of California at Berkeley have now succeeded in growing ribbons exactly nine atoms wide with a regular armchair edge from precursor molecules.

As they report in a paper in, the specially prepared molecules are first evaporated in an ultra-high vacuum. After several process steps, they are then combined like puzzle pieces on a gold base to form the desired nanoribbons of about 1nm in width and up to 50nm in length. These structures, which can only be seen with a scanning tunneling microscope, have an energy gap that is relatively large and precisely defined, allowing the researchers to go one step further and integrate the graphene ribbons into nanotransistors. Initially, however, their first attempts were not very successful: measurements showed that the difference in the current flow between the ‘on’ state (with applied voltage) and the ‘off’ state (without applied voltage) was far too small. This turned out to be caused by the dielectric layer of silicon oxide, which connects the semiconducting layers to the electrical switch contact. In order to have the desired properties, this layer needed to be 50nm thick, which in turn influenced the behavior of the electrons.

To solve this problem, the researchers massively reduced the thickness of the dielectric layer by replacing the silicon oxide with hafnium oxide (HfO 2). As this layer is just 1.5nm thick, the ‘on’-current is orders of magnitudes higher. Another problem was incorporating the graphene ribbons into the transistor.

In the future, the ribbons shouldn’t lie across the transistor substrate, but should instead be aligned along the transistor channel. This would significantly reduce the currently high level of non-functioning nanotransistors. This story is adapted from material from, with editorial changes made by Materials Today.

The views expressed in this article do not necessarily represent those of Elsevier.. A collection of the objects and test samples printed on the new 3D printer, including a miniature chair, a simplified model of Building 10 at MIT, eyeglasses frames, a spiral cup and a helical bevel gear. Image: Chelsea Turner (using images provided by the researchers). Engineers at Massachusetts Institute of Technology (MIT) have developed a new desktop 3D printer that performs up to 10 times faster than existing commercial counterparts. Whereas the most common printers may fabricate a few Lego-sized bricks in one hour, the new design can print similarly sized objects in just a few minutes.

The key to the team's nimble design lies in the printer's compact printhead, which incorporates two new, speed-enhancing components. These are: a screw mechanism that feeds polymer material through a nozzle at high force; and a laser, built into the printhead, that rapidly heats and melts the material, allowing it to flow faster through the nozzle. The team demonstrated its new design by printing various detailed, handheld 3D objects, including small eyeglasses frames, a bevel gear and a miniature replica of the MIT dome – each, from start to finish, within several minutes. Anastasios John Hart, associate professor of mechanical engineering at MIT, says the new printer demonstrates the potential for 3D printing to become a more viable production technique. 'If I can get a prototype part, maybe a bracket or a gear, in five to 10 minutes rather than an hour, or a bigger part over my lunch break rather than the next day, I can engineer, build and test faster,' says Hart, who is also director of MIT's Laboratory for Manufacturing and Productivity and the Mechanosynthesis Group. 'If I'm a repair technician and I could have a fast 3D printer in my vehicle, I could 3D-print a repair part on-demand after I figure out what's broken.

I don't have to go to a warehouse and take it out of inventory.' Hart adds that he envisions 'applications in emergency medicine, and for a variety of needs in remote locations.

Fast 3D printing creates valuable new ways of working and enables new market opportunities.' Hart and Jamison Go, a former graduate researcher in Hart's lab, report their results in a paper in. In a previous paper, Hart and Go set out to identify the underlying causes limiting the speed of the most common desktop 3D printers, which extrude plastic, layer by layer, in a process referred to in the industry as ‘fused filament fabrication’. 'Every year now, hundreds of thousands of desktop printers that use this process are sold around the world,' Hart says. 'One of the key limitations to the viability of 3D printing is the speed at which you can print something.'

Hart and Go had previously determined that, on average, commercial desktop extrusion 3D printers print at a rate of about 20cm 3, or several Lego bricks' worth of structures, per hour. 'That's really slow,' Hart notes. The team identified three factors limiting a printer's speed: how fast a printer can move its printhead, how much force a printhead can apply to a material to push it through the nozzle, and how quickly the printhead can transfer heat to melt a material and make it flow. 'Then, given our understanding of what limits those three variables, we asked how do we design a new printer ourselves that can improve all three in one system,' Hart says. 'And now we've built it, and it works quite well.'

In most desktop 3D printers, plastic is fed through a nozzle via a ‘pinch-wheel’ mechanism, in which two small wheels within the printhead rotate and push the plastic, or filament, forward. This works well at relatively slow speeds, but if more force were applied to speed up the process, at a certain point the wheels would lose their grip on the material – a ‘mechanical disadvantage’, as Hart puts it, that limits how fast the printhead can push material through. Hart and Go chose to do away with the pinch-wheel design, replacing it with a screw mechanism that turns within the printhead. The team fed a textured plastic filament onto the screw, and as the screw turned it gripped onto the filament's textured surface and was able to feed the filament through the nozzle at higher forces and speeds.

'Using this screw mechanism, we have a lot more contact area with the threaded texture on the filament,' Hart says. 'Therefore, we can get a much higher driving force, easily 10 times greater force.' The team added a laser downstream of the screw mechanism, which heats and melts the filament before it passes through the nozzle.

In this way, the plastic is more quickly and thoroughly melted, compared with conventional 3D printers, which use conduction to heat the walls of the nozzle to melt the extruding plastic. Hart and Go found that, by adjusting the laser's power and turning it quickly on and off, they could control the amount of heat delivered to the plastic. They integrated both the laser and the screw mechanism into a compact, custom-built printhead about the size of a computer mouse. Finally, they devised a high-speed gantry mechanism – an H-shaped frame powered by two motors, connected to a motion stage that holds the printhead. The gantry was designed and programmed to move nimbly between multiple positions and planes. In this way, the entire printhead was able to move fast enough to keep up with the extruding plastic's faster feeds.

'We designed the printhead to have high force, high heating capacity, and the ability to be moved quickly by the printer, faster than existing desktop printers are able to,' Hart says. 'All three factors enable the printer to be up to 10 times faster than the commercial printers that we benchmarked.' The researchers printed several complex parts with their new printer, each produced within five to 10 minutes, compared with an hour for conventional printers. However, they ran up against a small glitch in their speedier design: the extruded plastic is fed through the nozzle at such high forces and temperatures that a printed layer can still be slightly molten by the time the printer is extruding a second layer.

'We found that when you finish one layer and go back to begin the next layer, the previous layer is still a little too hot. So we have to cool the part actively as it prints, to retain the shape of the part so it doesn't get distorted or soften,' Hart says.

That's a design challenge that the researchers are currently taking on, in combination with the mathematics by which the path of the printhead can be optimized. They will also explore new materials to feed through the printer. 'We're interested in applying this technique to more advanced materials, like high strength polymers, composite materials. We are also working on larger-scale 3D printing, not just printing desktop-scale objects but bigger structures for tooling, or even furniture,' Hart says. 'The capability to print fast opens the door to many exciting opportunities.' This story is adapted from material from, with editorial changes made by Materials Today.

The views expressed in this article do not necessarily represent those of Elsevier.. Carbon is not just the most important element for life, it also has fascinating properties of its own.

Graphene – a pure carbon sheet just one atom thick – is one of the strongest materials known; roll graphene into a cylinder and you get carbon nanotubes (CNTs), the key to many emerging technologies. Now, in a paper published in, researchers at Kyushu University in Japan report learning how to control the fluorescence of CNTs, potentially leading to new applications.

CNTs are naturally fluorescent – when placed under light, they respond by releasing light of their own, a process called photoluminescence. The wavelength (color) of this fluorescence depends on the tubes' structure, including the angle at which they are rolled up. So far, fluorescent CNTs have been studied for use in LED lighting and medical imaging. The Kyushu team wanted to gain finer control over the emission wavelength.

'Fluorescence occurs when electrons use energy from light to jump into higher orbitals around atoms,' the lead authors explain. 'They sink back to a lower orbital, then release excess energy in the form of light. The wavelength of emitted light differs from the input light, depending on the energy of the emitting orbital.' CNTs naturally fluoresce at infrared wavelengths, which are invisible to the eye but can be detected by sensors.

The researchers used chemistry to tether organic molecules – hexagons of carbon atoms – onto the CNTs, which pushed their orbitals up or down, thus tuning the fluorescence. One of the six atoms in each hexagon was bonded to a CNT, anchoring the molecule to the tube, while another was bonded to an extra group of atoms, termed the substituent. Because of the molecule’s hexagonal shape, the two bonded carbons could be adjacent to each other (denoted ‘o’), separated by a single carbon atom (‘m’), or by two carbon atoms (‘p’). Most studies use the ‘p’ arrangement, where the substituent points away from the CNT, but the Kyushu team compared all three. They found that the ‘o’ arrangement produced very different fluorescence from the ‘m’ and ‘p’ arrangements.

Instead of one infrared wavelength, the CNTs now emitted two, as result of the substituents distorting the tubes as they were squeezed against the tube walls. For the ‘m’ and ‘p’ arrangements, the energies depended on which elements were in the substituent. For example, nitrogen dioxide (NO 2) produced bigger gaps between the orbitals than bromine.

This was no surprise, as NO 2 is better at attracting electrons and thus creating an electric field (dipole). However, the size of the effect differed between the ‘m’ and ‘p’ arrangements. 'The variation in orbital energies with different substituents gives us fine control of the emission wavelength of CNTs over a broad range,' the authors say. 'The most important outcome is to understand how dipoles influence fluorescence, so we can rationally design CNTs with the very precise wavelengths needed by biomedical devices. This could be very important for the development of bioimaging in the near future.'

This story is adapted from material from, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier..

The top row of photos shows a particle that melts the surface on impact and bounces away without sticking. The bottom row shows a similar particle that does not melt and does stick to the surface. Arrows show impact sprays that look like liquid, but are actually solid particles. Image courtesy of the researchers. When bonding two pieces of metal, either the metals must melt a bit where they meet or some molten metal must be introduced between the pieces. A solid bond then forms when the metal solidifies again.

But researchers at Massachusetts Institute of Technology (MIT) have found that, in some situations, melting can actually inhibit metal bonding rather than promote it. This surprising and counterintuitive finding could have serious implications for the design of certain coating processes or for 3D printing, which both require getting materials to stick together and stay that way. The research, carried out by postdocs Mostafa Hassani-Gangaraj and David Veysset and professors Keith Nelson and Christopher Schuh, is reported in two papers in and. Schuh, who is professor of metallurgy and head of the Department of Materials Science and Engineering, explains that one of the papers outlines 'a revolutionary advance in the technology' for observing extremely high-speed interactions, while the other makes use of that high-speed imaging to reveal that melting induced by impacting metal particles can impede bonding. The optical setup, with a high-speed camera that uses 16 separate charged-coupled device (CCD) imaging chips and can record images in just 3 nanoseconds, was primarily developed by Veysset. The camera is so fast that it can track individual particles being sprayed onto a surface at supersonic velocities, a feat that was previously not possible.

The team used this camera, which can shoot up to 300 million frames per second, to observe a spray-painting-like process similar to ones used to apply a metallic coating to surfaces in many industries. While such processes are widely used, until now their characteristics have been determined empirically, since the process itself is so fast 'you can't see it, you can't tell what's happening, and no one has ever been able to watch the moment when a particle impacts and sticks,' Schuh says.

As a result, there has been ongoing controversy about whether the metal particles actually melt as they strike the surface to be coated. The new technology means that now the researchers 'can watch what's happening, can study it, and can do science,' he says.

The new images make it clear that, under some conditions, the particles of metal being sprayed at a surface really do melt the surface – and that, unexpectedly, prevents them from sticking. The researchers found that the particles bounce away in much less time than it takes for the surface to re-solidify, so they leave the surface while it is still molten. If engineers find that a coating material isn't bonding well, they may be inclined to increase the spray velocity or temperature in order to increase the chances of melting. However, the new results show the opposite: melting should be avoided. It turns out the best bonding happens when the impacting particles and impacted surfaces remain in a solid state but ‘splash’ outward in a way that looks like liquid. It was 'an eye-opening observation,' according to Schuh. This phenomenon 'is found in a variety of these metal-processing methods,' he says.

Now, it is clear that 'to stick metal to metal, we need to make a splash without liquid. A solid splash sticks, and a liquid one doesn't.' With the new ability to observe the process, Hassani-Gangaraj says, 'by precise measurements, we could find the conditions needed to induce that bond.'

The findings could be relevant for processes used to coat engine components in order to reuse worn parts rather than relegating them to the scrap-metal bin. 'With an old engine from a large earth-moving machine, it costs a fortune to throw it away, and it costs a fortune to melt and recast it,' Schuh says. 'Instead, you can clean it off and use a spray process to renew the surface.' But that requires that the sprayed coating remains securely bonded. In addition to coatings, the new information could also help in the design of some metal-based additive manufacturing systems, also known as 3D printing.

There, as with coatings, it is critical to make sure that one layer of the printing material adheres solidly to the previous layer. 'What this work promises is an accurate and mathematical approach' to determining the optimal conditions to ensure a solid bond, Schuh says. 'It's mathematical rather than empirical.' This story is adapted from material from, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.. Please log in/ register and complete the fields below to submit your nomination. We are seeking nominations for the inaugural Rising Stars in Computational Materials Science special issue and prize.

The aim of this initiative is to recognize the accomplishments and promise of researchers in the early stages of their independent careers and draw international attention to the work they are doing. Once the nominations have been received, the editors of Computational Materials Science will invite a selection of the nominees to submit a short review paper outlining their work and the impact it has made on the field.

The papers invited for inclusion in the Rising Stars initiative will feature in a special issue of Computational Materials Science. All authors in this issue will receive a certificate outlining their selection, and there will be one recipient of the overall prize of $500 who will also be invited to join the Editorial Board of Computational Materials Science. The criteria for the prize will be based on degree of scientific innovation outlined in the review, impact of the research, and the overall quality of the paper. • Candidates should be within 10 years of receiving their PhD, • Candidates are active in the area of computational materials science and engineering. All aspects of modern materials modeling are of interest, including quantum chemical methods, density functional theory, semi-empirical and classical approaches, statistical mechanics, atomic-scale simulations, mesoscale modeling, and phase-field techniques. The nominee's work may involve properties of materials or phenomena associated with their design, synthesis, processing, characterization, and utilization.

Most materials are of interest, including metals, ceramics, electronic materials, polymers, and composites. Research that focuses on computational molecular or nanocluster chemistry, biochemistry or biomedical modeling, continuum level mechanics of materials, or structural materials, such as concrete, will generally fall outside the scope of this award. • Candidate must be nominated through MaterialsToday.com (self-nominations are accepted). The nomination must include: • Short CV of nominated person • Year of completion of PhD and additional supporting information if more than 10 years ago (e.g. Career break, etc) • Area of research nominee is involved in • 31 st March 2018: Deadline for nominations • 1 st May 2018: The editors of Computational Materials Science will invite a selection of the nominees to submit a short review on their specific area of research..

• 31 st October: deadline for invited nominees to submit their reviews. • Jan-March 2019: reviews will be published in a special section in Computational Materials Science and MaterialsToday.com. • 31 st March 2019: Editorial Board of Computational Materials Science will select the recipient of the overall prize. For more information on Computational Materials Science please visit:. Scientists at the University of Surrey in the UK have developed a new and cost-effective catalyst to recycle two of the main causes of climate change – carbon dioxide (CO 2) and methane (CH 4).

In a study published in, the scientists describe how they created an advanced nickel-based catalyst strengthened with tin and ceria, and used it to transform CO 2 and CH 4 into a synthesis gas that can be used to produce fuels and a range of valuable chemicals. The project is part of the UK Engineering and Physical Sciences Research Council’s Global Research Project, which is looking into ways to lessen the impact of global warming in Latin America.

The study has led the University of Surrey to file a patent for a family of new ‘supercatalysts’ for chemical CO 2 recycling. According to the Global Carbon Project, global CO 2 emissions are set to rise in 2017 for the first time in four years – with carbon output growing on average 3% every year since 2006. While carbon capture technology is common, it can be expensive and, in most cases, requires extreme and precise conditions for the process to be successful. It is hoped this new catalyst will help make the technology more widely available across industry, and make extracting carbon dioxide from the atmosphere easier and cheaper. This is an extremely exciting project and we believe we have achieved something here that can make a real impact on CO2 emissions.

Tomas Reina, University of Surrey “This is an extremely exciting project and we believe we have achieved something here that can make a real impact on CO 2 emissions,” said Tomas Reina from the University of Surrey. “The goal we’re all chasing as climate scientists is a way of reversing the impacts of harmful gases on our atmosphere – this technology, which could see those harmful gases not only removed but converted into renewable fuels for use in poorer countries is the Holy Grail of climate science.” “Utilizing CO 2 in this way is a viable alternative to traditional carbon capture methods, which could make a sizable impact to the health of our planet,” said Harvey Arellano-Garcia, head of research in the chemical engineering department at the University of Surrey. “We’re now seeking the right partners from industry to take this technology and turn it into a world-changing process.” This story is adapted from material from the, with editorial changes made by Materials Today.

The views expressed in this article do not necessarily represent those of Elsevier.. Scientists at Rice University calculate that the atom-thick film of boron known as borophene could be the first pure 2D material naturally able to emit visible and near-infrared light by activating its plasmons. The Rice team tested models of three polymorphs and found that triangular borophene (left) was capable of emitting visible light, while the other two polymorphs reached near-infrared. Image: Sharmila Shirodkar/Rice University. An atom-thick film of boron could be the first pure two-dimensional (2D) material able to emit visible and near-infrared light by activating its plasmons, according to scientists at Rice University. That would make the material, known as borophene, a candidate for plasmonic and photonic devices like biomolecule sensors, waveguides, nanoscale light harvesters and nanoantennas. Plasmons are collective excitations of electrons that flow across the surface of metals when triggered by an input of energy, like laser light.

Significantly, delivering light to a plasmonic material in one color (determined by the light's frequency) can prompt the emission of light in another color. Models by Rice theoretical physicist Boris Yakobson and his colleagues predict that borophene would be the first known 2D material to do so naturally, without modification.

The lab's simulations are detailed in a paper by Yakobson with lead authors Yuefei Huang, a graduate student, and Sharmila Shirodkar, a postdoctoral researcher, in the. Boron is a semiconductor in three dimensions but a metal in its 2D form. That prompted the lab to have a look at its potential for plasmonic manipulation. 'This was kind of anticipated, but we had to do careful work to prove and quantify it,' said Yakobson, whose lab often predicts possible materials that experimentalists later make, like borophene or the boron buckyball. With colleagues Evgeni Penev, an assistant research professor at Rice, and alumnus Zhuhua Zhang, Yakobson recently published an extensive review of the state of boron research.

In this new study, the researchers used a computational modeling technique called density functional theory to test plasmonic behavior in three types of free-standing borophene. The material's baseline crystal structure is a grid of triangles – think graphene but with an extra atom in the middle of each hexagon. The lab studied models of plain borophene and two of its polymorphs, solids incorporating more than one crystalline structure that are formed when some of those middle atoms are removed. Their calculations showed triangular borophene had the widest emission frequencies, including visible light, while the other two reached near-infrared. 'We don't have enough experimental data to determine which mechanisms contribute how much to the losses in these polymorphs, but we anticipate and include scattering of plasmons against defects and excitation of electrons and holes that lead to their damping,' Shirodkar said.

Display Drivers For Windows 10 32 Bit here. The researchers said their results raise the interesting possibility of manipulating data at sub-diffraction wavelengths. 'If you have an optical signal with a wavelength that's larger than an electronic circuit of a few nanometers, there's a mismatch,' said Shirodkar. 'Now we can use the signal to excite plasmons in the material that pack the same information (carried by the light) into a much smaller space. It gives us a way to squeeze the signal so that it can go into the electronic circuit.' 'It turns out that's important because, roughly speaking, it can improve the resolution by 100 times, in some cases,' Yakobson explained.

'Resolution is limited by wavelength. By using plasmons, you can store information or write into a material at a much higher resolution because of the shrinkage of the wavelength. This could have great benefits for data storage.'

Experimentalists have made borophene only in very small amounts so far and lack methods to transfer the material from the surfaces on which it’s grown, Yakobson said. Still, there's plenty for theoretical scientists to study and plenty of progress in the labs. 'One should explore other polymorphs and look for the best one,' Yakobson suggested. 'Here, we didn't. We just considered three, because it's pretty heavy work -- but others need to be screened before we know what is achievable.' This story is adapted from material from, with editorial changes made by Materials Today.

The views expressed in this article do not necessarily represent those of Elsevier.. Topological insulators are new materials with special electronic properties that are of great interest to scientists and have many potential applications. Nevertheless, scientists have also been wrestling with a ten-year-old puzzle caused by the fact that the two best methods for probing the electronic states of topological insulators produce different results. Researchers from the University of Amsterdam (UVA) in the Netherlands, together with collaborators in France, Switzerland and Germany, have now found out exactly why, and they report their findings in a paper in. Topological insulators are strange materials: the bulk is insulating and cannot carry an electrical current, yet the surface is conducting. These new materials are of great fundamental interest but are also very promising for a number of future applications in special types of electronics and in quantum computing, and so are the subject of a substantial research effort. The significance of topological materials was underlined last year with the award of the Nobel Prize for the development of fundamental theories setting out the existence and behaviour of topological matter.

There are two powerful experimental methods for examining the behavior of the electrons at the surface of a topological insulator. The first, known as magnetotransport, involves sending a current through the system in the presence of a very large magnetic field. The second involves using an ultraviolet (UV) light beam to examine the surface of the crystal. In this case, the energy of a light particle can be absorbed by an electron at the surface, giving it sufficient energy to escape from the crystal and be analyzed. Scientists can harness this photo-electric effect, known as photoemission, to gather valuable information on the electronic properties at the surface of a topological insulator.

For more than 10 years, scientists have been baffled as to why these two experiments completely disagree when applied to topological insulators. The reason, according to this new study, is that the very first UV light flash, required to record the photoemission data, alters the electronic structure at the surface. The quantity that describes and explains how electrons in a solid do their stuff is called the band structure. It can be seen as a sort of road network that maps out the allowed combinations of energy and wavelength the electron-waves can have in the crystal.

A slice through such a band structure can be easily displayed as a two-dimensional (2D) image. This kind of snapshot contains valuable information about the electronic structure of a topological insulator, and in particular the energy location of the crossing-point of the two branches visible in the band structure. This special feature is called the Dirac point, named after theoretical physicist Paul Dirac, who first developed the theory that describes electrons. Normally, recording a band structure image takes a minute or more, but the UVA-led research team worked hard to bring this down to just a single second. Their studies showed that, initially, the Dirac point appears at an energy matching that from magnetotransport data. After only 20 seconds of UV exposure, however, they found that the Dirac point, and the rest of the band structure with it, slid way down in energy, far from the value found in the transport experiments. It was already known that molecules that stick to the surface of a topological insulator can cause a downward shift of the Dirac point.

These new experiments were able to disentangle the effect of the molecules at the surface and that of the UV light, so the scientists could demonstrate that the very first flash of light plays the role of the starter’s pistol, triggering a rapid downward slide of the Dirac point. Does this finding imply that photoemission needs to be abandoned as a way for studying topological insulators?

On the contrary, now that the effect of the UV light is properly understood, protocols can be developed for ensuring photoemission is used in the right way in future studies. This story is adapted from material from the, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.. This shows the band structure of a topological insulator measured using photoemission. The dark areas indicate which energies [on the y-axis] go together with which (here inverse) wavelengths [on the x-axis] for the electron waves in a topological insulator.

After 20 seconds of exposure to the UV light required for photoemission experiments (right-hand image), the band structure is very different to that after just one second of exposure (left-hand image). The coloured circles show the position of the Dirac point. MIT postdoc, Grace Han, handles a new chemical composite that could provide an alternative to fuel by functioning as a kind of thermal battery.

Photo: Melanie Gonick/MIT. In large parts of the developing world, people receive abundant heat from the sun during the day, but most cooking takes place later in the evening when the sun is down, using fuel – such as wood, brush or dung – that is collected with significant time and effort. Now, a new chemical composite developed by researchers at Massachusetts Institute of Technology (MIT) could provide an alternative. It could be used to store heat from the sun or any other source during the day, acting as a kind of thermal battery, and it could then release the heat when needed, for example for cooking or heating after dark. A common approach to thermal storage is to use what is known as a phase change material (PCM), where input heat melts the material and this phase change – from solid to liquid – stores energy. When the PCM is cooled back down below its melting point, it turns back into a solid, at which point the stored energy is released as heat. There are many examples of these materials, including waxes or fatty acids used for low-temperature applications and molten salts used at high temperatures.

But all current PCMs require a great deal of insulation, and they pass through the phase change temperature uncontrollably, losing their stored heat relatively rapidly. Instead, the new system uses molecular switches that change shape in response to light. When integrated into the PCM, the phase-change temperature of the hybrid material can be adjusted with light, allowing the thermal energy of the phase change to be maintained even well below the melting point of the original material.

The new findings, by MIT postdocs Grace Han and Huashan Li and MIT professor Jeffrey Grossman, are reported in a paper in. 'The trouble with thermal energy is, it's hard to hold onto it,' Grossman explains. So his team developed what are essentially add-ons for traditional phase change materials, or 'little molecules that undergo a structural change when light shines on them'.

The trick was to find a way to integrate these molecules with conventional PCM materials to release the stored energy as heat, on demand. 'There are so many applications where it would be useful to store thermal energy in a way lets you trigger it when needed,' he says. The researchers accomplished this by combining fatty acids with an organic compound that responds to a pulse of light. With this arrangement, the light-sensitive component alters the thermal properties of the other component, which stores and releases energy. The hybrid material melts when heated, and after being exposed to ultraviolet light, it stays melted even when cooled back down.

Next, when triggered by another pulse of light, the material re-solidifies and gives back the thermal phase-change energy. 'By integrating a light-activated molecule into the traditional picture of latent heat, we add a new kind of control knob for properties such as melting, solidification and supercooling,' says Grossman, who is professor in environmental systems as well as professor of materials science and engineering. The system could make use of any source of heat, not just solar, Han says. 'The availability of waste heat is widespread, from industrial processes, to solar heat, and even the heat coming out of vehicles, and it's usually just wasted.' Harnessing some of that waste could provide a way of recycling the heat for useful applications.

'What we are doing technically,' Han explains, 'is installing a new energy barrier, so the stored heat cannot be released immediately.' In its chemically stored form, the energy can remain for long periods until the optical trigger is activated. In their initial small-scale lab versions, they showed the stored heat can remain stable for at least 10 hours, whereas a device of similar size storing heat directly would dissipate it within a few minutes. And 'there's no fundamental reason why it can't be tuned to go higher,' Han says.

In the initial proof-of-concept system, 'the temperature change or supercooling that we achieve for this thermal storage material can be up to 10°C (18°F), and we hope we can go higher,' Grossman says. Already, in this version, 'the energy density is quite significant, even though we're using a conventional phase-change material,' Han says. The material can store about 200 joules per gram, which she says is 'very good for any organic phase-change material'. And already, 'people have shown interest in using this for cooking in rural India,' she says.

Such systems could also be used for drying agricultural crops or for space heating. 'Our interest in this work was to show a proof of concept,' Grossman says, 'but we believe there is a lot of potential for using light-activated materials to hijack the thermal storage properties of phase change materials.' This story is adapted from material from, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier..

Flexible semiconductor Ge thin film grown on mica by van der Waals epitaxy. The film experiences no degradation in its electrical properties even after repeated bending. Photo: Aaron Littlejohn, Rensselaer Polytechnic Institute. Germanium (Ge), an elemental semiconductor, was the material of choice in the early history of electronic devices, before it was largely replaced by silicon. But due to its high charge carrier mobility – higher than silicon by a factor of three – the semiconductor is making a comeback. Ge is generally grown on expensive single-crystal substrates, adding another challenge to making it sustainably viable for most applications.

To address this aspect, researchers at Rensselaer Polytechnic Institute (RPI) have developed an epitaxy method that incorporates van der Waals’ forces to grow Ge on mica. Applications for this mica-grown Ge could include advanced integrated circuits and high-efficiency solar cells. “This is the first time strain-free van der Waals epitaxy of an elemental semiconductor has been demonstrated on mica,” said Aaron Littlejohn, RPI researcher and co-author of a paper demonstrating the work in the.

Growing crystalline film layers on crystalline substrates (called epitaxy) is ubiquitous in semiconductor fabrication. If the film and substrate materials are the same, then the perfectly matched layers form strong chemical bonds for optimal charge carrier mobility. Layering different materials effectively, however, is a challenge because the crystal lattices typically don’t align. To get around this, the researchers employed van der Waals (vdW) forces, phenomena that are based on the probabilistic nature of electrons, which are not in a fixed position around a nucleus.

Rather, they can be anywhere, and the probability that they will be unevenly distributed exists almost all the time. When this happens, there is an induced dipole: a slight positive charge on one side and a slight negative charge opposite.

This produces weakly attractive interactions between neutral atoms. The researchers chose mica as the substrate on which to grow the Ge film because of its atomically smooth surface, which is free of dangling bonds (unpaired valence electrons). This ensured that no chemical bonding would take place during the vdW epitaxy process. Instead, the materials’ interface is held together via weak vdW forces. This allows for the growth of a relaxed film despite the dramatically different crystal structures of the two materials, which have a 23% difference in atomic spacings.

In addition to alleviating the constraints of lattice matching, vdW epitaxy allows the Ge film to be mechanically exfoliated from the mica surface and to stand alone as a substrate-less film. “Our Ge film could be used as a thin-film nanomembrane, which could be integrated into electronic devices more easily than nanocrystals or nanowires,” Littlejohn said.

“It could also serve as the substrate for the subsequent deposition of additional materials for flexible transistors and solar cells, or even wearable optoelectronics.” Ge films about 80nm thick were grown on millimeter-scale muscovite mica substrates. By varying the substrate temperature during deposition and annealing over 300–500°C, the researchers found that the crystal lattice stabilizes at about 425°C. “Previous research implies that elemental semiconductors cannot be epitaxially grown on mica using vdW forces at any elevated temperature, but we have now shown otherwise,” Littlejohn said.

“With the success of our Ge film grown on mica at a practical temperature, we anticipate that other nonlayered elemental or alloyed materials can be grown on mica via vdW epitaxy.” This story is adapted from material from the, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.. Introducing copper ions into a host material (tantalum (IV) sulfide) with PDII. Hydrogen ions force out sodium ions from phosphate glass; these sodium ions then force out copper ions from CuI, shooting them into nanometer-level gaps in tantalum (IV) sulfide. Excessive copper ions crystalize around the tantalum (IV) sulfide as copper metal (right image). Images: Fujioka M.

Et al., Journal of the American Chemical Society, November 16, 2017. A team of researchers at Hokkaido University in Japan has developed a novel material synthesis method called proton-driven ion introduction (PDII) that utilizes a phenomenon similar to ‘ion billiards’. This new method could pave the way for creating numerous new materials, thus drastically advancing materials science. The novel synthesis method is based on a liquid-free process for inserting guest ions into a host material, known as intercalation, and replacing existing ions in the host material with new ions, known as ion substitution, by driving the ions with protons. This study, led by Masaya Fujioka and Junji Nishii at Hokkaido University’s Research Institute for Electric Science, is described in a paper in the.

Conventionally, intercalation and ion substitution are conducted in an ion solution, but this liquid-based process is regarded as cumbersome and problematic. Solvent molecules can be inserted into the host materials along with the guest ions, degrading the crystal quality, while introducing ions into host materials homogeneously can be difficult and some host materials are simply not suitable for use with liquids. The PDII method, by contrast, involves applying a voltage of several kilovolts to a needle-shaped anode placed in atmospheric hydrogen to generate protons (hydrogen ions) via the electrolytic disassociation of hydrogen. The protons migrate along the electric field and are shot into a source of the desired ions – similar to firing a cue ball at a group of balls in billiards. This drives the ions out of the source material and causes them to be introduced, or intercalated, into a nanometer-level gap in the host material.

With this process, the team succeeded in homogenously introducing lithium ions (Li +), sodium ions (Na +), potassium ions (K +), copper ions (Cu +) and silver ions (Ag +) into nanometer-level gaps in tantalum (IV) sulfide (TaS 2), a layered material, while maintaining its crystallinity. Furthermore, the team successfully substituted sodium ions in Na 3V 2(PO 4) 3 with potassium ions, producing a thermodynamically metastable material that cannot be obtained with conventional solid-state reaction methods. “At present, we have shown that hydrogen ions (H +), Li +, Na +, K +, Cu + and Ag + can be used to introduce ions in our method, and we expect a larger variety of ions will be usable. By combining them with various host materials, our method could enable the production of numerous new materials,” says Fujioka. “In particular, if a method to introduce negatively charged ions and multivalent ions is established, it will spur the development of new functional materials in the solid ion battery and electronics fields.” This story is adapted from material from, with editorial changes made by Materials Today.

The views expressed in this article do not necessarily represent those of Elsevier.. Vials containing blue-luminescent carbon dots. Physicists at Ludwig-Maximilians-University (LMU) in Munich, Germany, have demonstrated that the optical and photocatalytic properties of so-called carbon dots can be precisely tuned by controlling the positions of nitrogen atoms introduced into their structure. Thanks to their unusual optical properties, carbon particles with diameters on the order of a few nanometers – so-called C-dots – show great promise for a wide range of technological applications, from energy conversion to bio-imaging. Moreover, C-dots have several practical advantages over comparable materials in that they are easy to fabricate, stable and contain no toxic heavy metals. Their versatility is largely due to the fact that – depending on their chemical composition and aspects of their complex structure – they can either act as emitters of light, in the form of photoluminescence, or function as photocatalysts by absorbing light energy and triggering chemical reactions, such as water splitting.

However, the factors that determine these disparate capabilities are not well understood. Now, physicists at LMU, led by Jacek Stolarczyk, have taken a closer look at the mechanisms underlying these very different properties. Their study, which appears in a paper in, shows that the physicochemical characteristics of these nanomaterials can be simply and precisely tuned by introducing nitrogen atoms into their complex chemical structure in a controlled manner. “Up until now, C-dots have typically been optimized on the basis of the principle of trial and error,” says Stolarczyk.

“In order to get beyond this stage, it is essential to obtain a detailed understanding of the mechanisms that underlie their diverse optical characteristics.” The study was carried out as part of an interdisciplinary project called ‘Solar Technologies Go Hybrid’ (SolTech), coordinated by LMU’s Jochen Feldmann. SolTech is funded by the State of Bavaria to explore innovative concepts for the transformation of solar radiation into electricity and the use of non-fossil – and preferably non-toxic and abundantly available – fuel sources for the storage of energy. C-dots are in many respects ideally suited for such applications. C-dots are made up of networks of polycyclic aromatic carbon compounds, whose complex interactions determine how they react to light.

In the new study, the researchers synthesized C-dots by combining citric acid as a carbon skeleton with a branched, nitrogen-containing polymer, and then irradiated the mixture with microwaves. In a series of experiments, they systematically varied the concentration of the polymer in the mixture, such that different amounts of nitrogen were incorporated into the carbon networks.

They found that the precise synthesis conditions had a critical impact on the mode of incorporation of nitrogen into the carbon lattices that make up the C-dots. This influenced whether a nitrogen atom replaced one of the carbon atoms that form the interlinked 6-membered carbon rings resembling tiny graphene flakes, or instead replaced one of the carbon atoms in the 5- and 6-membered rings found on the free edges of the aromatic structures. “Our investigation showed that the chemical environment of the nitrogen atoms incorporated has a crucial influence on the properties of the resulting C-dots,” says Santanu Bhattacharyya, the first author of the paper and a fellow in Feldmann’s research group. If nitrogen atoms are incorporated inside the graphene-like structures, which happens at intermediate polymer concentrations, this leads to dots that predominantly emit blue photoluminescence when irradiated with light of a suitable wavelength. On the other hand, if they are incorporated at edge positions, which occurs for either very high or very low amounts of the polymer, this suppresses photoluminescence and results in C-dots that photocatalytically reduce water to hydrogen.

In other words, the optical properties of the C-dots can be modified at will by varying the details of the procedure used to synthesize them. The members of the LMU team believe that these latest insights will stimulate further work on the use of these intriguing nanomaterials, both as photoluminescent light sources and as photocatalysts in energy conversion processes.

This story is adapted from material from, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier..

• NEW - Reflects recent developments in fracture mechanics and computer analysis. • NEW - Adds a review chapter. • NEW - Features new topics: • Symmetry considerations. • Rectangular plates in bending. • Plastic action in plates. • Critical speed of rotating shafts. • NEW - Expands discussions of: • Fatigue.

• The reciprocal theorem. • Semi-inverse problems in elasticity. • Thermal stress. • NEW - Reorganizes content: • Provides later coverage of theory of elasticity, thick-walled cylinders, spinning disks, plate bending, and shells of revolution. • Offers earlier coverage of energy methods, unsymmetric bending, and curved beams.

• NEW - Provides 50% new/revised homework exercises. • NEW - Updates references. • Treats topics by going a step or two beyond elementary mechanics of materials and emphasizes the physical view — mathematical complexity is not used where it is not needed. • Features a simple, unambiguous writing style — with complete (yet not verbose) explanations, well-referenced formulas, and concepts grounded in practical situations where possible. • Provides 75 clearly-labeled, worked example problems, as well as many additional examples, shorter explanations, and calculations.

• Uses notation commonly found in advanced texts and papers about the subject addressed. • Includes an abundance of homework exercises (670 total), varied in type and difficulty — many multi-part.

• Includes a chapter on collapse analysis of beams and frames. • Covers plastic conditions in torsion, thick-walled cylinders, and plates in bending. • Discusses the variety and frequent subtlety of buckling problems to show that buckling may be local or global and that buckling may or may not indicate collapse.

• Uses superposition methods to treat discontinuity problems in shells of revolution, such as stresses where an end cap is joined to a cylindrical pressure vessel. • Introduces sectorial area, and uses it in certain problems of shear center and restraint of warping in torsion.

• Reflects recent developments in fracture mechanics and computer analysis. • Adds a review chapter. • Features new topics: • Symmetry considerations. • Rectangular plates in bending. • Plastic action in plates.

• Critical speed of rotating shafts. • Expands discussions of: • Fatigue. • The reciprocal theorem.

• Semi-inverse problems in elasticity. • Thermal stress. • Reorganizes content: • Provides later coverage of theory of elasticity, thick-walled cylinders, spinning disks, plate bending, and shells of revolution.

• Offers earlier coverage of energy methods, unsymmetric bending, and curved beams. • Provides 50% new/revised homework exercises. • Updates references.

Table of Contents 1. Orientation, Review of Elementary Mechanics of Materials.

Stress, Principal Stresses, Strain Energy. Failure and Failure Criteria. Applications of Energy Methods. Beams on an Elastic Foundation.

Curved Beams. Elements of Theory of Elasticity.

Pressurized Cylinders and Spinning Disks. Unsymmetric Bending and Shear Center. Plasticity in Structural Members. Collapse Analysis. Plate Bending. Shells of Revolution with Axisymmetric Loads. Buckling and Instability.