New “Quasiparticles ” Research Allows Data to be Recorded … with LIGHT!

Russian physicists with their colleagues from Europe through changing the light parameters, learned to generate quasiparticles – excitons, which were fully controllable and also helped to record information at room temperature. 

These particles act as a transitional form between photons and electrons so the researchers believe that with excitons, they will be able to create compact optoelectronic devices for rapid recording and processing an optical signal. The proposed method is based on use of a special class of materials called metal-organic frameworks. The study appeared in Advanced Materials. 

To simplify the description of complex effects in quantum mechanics, scientists have introduced a concept of quasiparticles. One of them which is called exciton is an “electron – hole” pair, which provides energy transfer between photons and electrons. 

According to the scientific community, this mediation of quasiparticles will help to combine optics with electronics to create a fundamentally new class of equipment – more compact and energy efficient. However, all exciton demo devices either operate only at low temperature, or are difficult to manufacture which inhibits their mass adoption.


In the new study, the scientists from ITMO University in Saint Petersburg, Leipzig University in Germany and Eindhoven University of Technology in the Netherlands could generate excitons at room temperature by changing the light parameters. 
The authors also managed to control the quasiparticles with ultra-high sensitivity of about hundreds of femtoseconds (10-13 s). Finally, they developed an easy method for data recording with excitons. This all became possible through the use of an individual class of materials called metal-organic frameworks.


Metal-organic frameworks (MOF) synthesized at ITMO University, have a layered structure. Between the layers, there is a physical attraction called van der Waals force. To prevent the plates from uncontrollably coming together, the interlayer space is filled with an organic liquid, which fixes the framework to be three-dimensional.


In such crystals, the researchers learned to bring two types of excitons individually: intralayer and interlayer. The first arise when a photon absorbed by the crystal turns into an electron-hole pair inside a layer, but the second appear when an electron and a hole belong to neighboring layers. In some time, both kinds of quasiparticles disintegrate, re-radiating the energy as a photon. But excitons can move around the crystal while they exist.


The life time of intralayer excitons is relatively short, but their high density and agility allow one to use these quasiparticles to generate light in LEDs and lasers, for instance. Interlayer excitons are more stable, but slow-moving, so the researchers propose them to be used for the data recording. Both types of excitons fit processing of an optical signal, according to the physicists.


The innovative approach for information recording concerns the changing a distance between crystal layers to switch “on” and “off” the interlayer excitons. 
Valentin Milichko, the first author of the paper, associate professor of Department of Nanophotonics and Metamaterials at ITMO University, comments: “We locally heated the crystal with a laser. In the place of exposure, the layers stuck together and the luminescence of excitons disappeared while the rest of the crystal continued shining. This could mean that we recorded 1 bit of information, and the record, in the form of a dark spot, was kept for many days. 

To delete the data, it was enough to put the MOF into the same organic liquid that supports layers. In this case, the crystal itself is not affected, but the recorded information (the dark spot) disappears.”


The authors believe that in the future the new material will help to bring processing of an optical signal to the usual pattern of zeros and ones: “In fact, we can influence the exciton behavior in the crystal, changing the light intensity. At weak irradiation, excitons are accumulated (in ‘1’ state), but if the laser power increases, the concentration of quasiparticles grows so much that they can instantly disintegrate (in ‘0’ state),” says Valentin Milichko.


Typically, excitons occur in dielectric and semiconductor crystals, but the scientists could create these quasiparticles and get control over them in a completely different class of materials, which never was used for this. 
The MOF crystal combines organic components with inorganic that gives it additional properties not available for materials of a single nature. Thus, the organic term allows one to generate excitons at room temperature, but inorganic provides their efficient transfer around the crystal.


Valentin A. Milichko, Sergey V. Makarov, Alexey V. Yulin, Alexander V. Vinogradov, Andrei A. Krasilin, Elena Ushakova, Vladimir P. Dzyuba, Evamarie Hey-Hawkins, Evgeny A. Pidko, Pavel A. Belov (2017), Van der Waals metal-organic framework as an excitonic material for advanced photonics, Advanced Materials

*** From Nanotechnology World 


Scientists at Harvard & Maryland University create a new form of matter: “Time Crystals”

Time crystals may sound like something from science fiction, having more to do with time travel or Dr. Who. These strange materials — in which atoms and molecules are arranged across space and time — are in fact quite real, and are opening up entirely new ways to think about the nature of matter. They also eventually may help protect information in futuristic devices known as quantum computers.


Two groups of researchers based at Harvard University and the University of Maryland are reporting in the journal Nature March 9 that they have successfully created time crystals using theories developed at Princeton University. The Harvard-based team included scientists from Princeton who played fundamental roles in working out the theoretical understanding that led to the creation of these exotic crystals.


“Our work discovered the essential physics of how time crystals function,” said Shivaji Sondhi, a Princeton professor of physics. “What is more, this discovery builds on a set of developments at Princeton that gets at the issue of how we understand complex systems in and out of equilibrium, which is centrally important to how physicists explain the nature of the everyday world.”


Princeton University researchers provided the theoretical understanding that led to the creation of time crystals being reported in the journal Nature March 9 by two groups of researchers based at Harvard University and the University of Maryland. Time crystals feature atoms and molecules arranged across space and time and are opening up entirely new ways to think about the nature of matter. 

The illustration above explains the difference between ordinary crystals (left) such as diamonds, quartz or ice and time crystals (right). (Image by Emily Edwards, University of Maryland)


In 2015, Sondhi and colleagues including then-graduate student Vedika Khemani, who earned her Ph.D. at Princeton in 2016 and is now a junior fellow at Harvard, as well as collaborators Achilleas Lazarides and Roderich Moessner at the Max Planck Institute for the Physics of Complex Systems in Germany, published the theoretical basis for how time crystals — at first considered impossible — could actually exist. 
Published in the journal Physics Review Letters in June 2016, the paper spurred conversations about how to build such crystals.


Ordinary crystals such as diamonds, quartz or ice are made up of molecules that spontaneously arrange into orderly three-dimensional patterns. The sodium and chlorine atoms in a crystal of salt, for example, are spaced at regular intervals, forming a hexagonal lattice.


In time crystals, however, atoms are arranged in patterns not only in space, but also in time. In addition to containing a pattern that repeats in space, time crystals contain a pattern that repeats over time. One way this could happen is that the atoms in the crystal move at a certain rate. 

Were a time crystal of ice to exist, all of the water molecules would vibrate at an identical frequency. What is more, the molecules would do this without any input from the outside world.


The concept of time crystals originated with physicist Frank Wilczek at the Massachusetts Institute of Technology. In 2012, the Nobel laureate and former Princeton faculty member was thinking about the similarities between space and time. In physics parlance, crystals are said to “break translational symmetry in space” because the atoms assemble into rigid patterns rather than being evenly spread out, as they are in a liquid or gas. 

Shouldn’t there also be crystals that break translational symmetry in time?


“The atoms move in time, but instead of moving in a fluid or continuous way, they move in a periodic way,” Sondhi said. “It was an interesting idea.” It also was an idea that led to hot debates in the physics journals about whether such crystals could exist. The initial conclusion appeared to be that they could not, at least not in the settings Wilczek visualized.


Sondhi and Khemani were thinking about a completely different problem in 2015 when they worked out the theory of how time crystals could exist. They were exploring questions about how atoms and molecules settle down, or come to equilibrium, to form phases of matter such as solids, liquids and gases.

While it was common wisdom among physicists that all systems eventually settle down, work during the last decade or so had challenged that notion, specifically among atoms at very low temperatures where the rules of quantum physics apply. It was realized that there are systems that never go to equilibrium because of a phenomenon called “many-body localization,” which occurs due to the behavior of many atoms in a disordered quantum system that are influencing each other.


Work in this area is a long Princeton tradition. The first and seminal concept of how quantum systems can be localized when they are disordered, called Anderson localization, stemmed from work by Philip Anderson, a Princeton professor and Nobel laureate, in 1958. This work was extended in 2006 to systems of many atoms by then Princeton professor Boris Altshuler, postdoctoral fellow Denis Basko, and Igor Aleiner of Columbia University.

While on sabbatical at the Max Planck Institute for the Physics of Complex Systems in Germany, Sondhi and Khemani realized that these ideas about how to prevent systems from reaching equilibrium would enable the creation of time crystals. A system in equilibrium cannot be a time crystal, but non-equilibrium systems can be created by periodically poking, or “driving,” a crystal by shining a laser on its atoms. 

To the researchers’ surprise, their calculations revealed that periodically prodding atoms that were in non-equilibrium many-body localized phases would cause the atoms to move at a rate that was twice as slow — or twice the period — as the initial rate at which they were prodded.


To explain, Sondhi compared the driving of the quantum system to squeezing periodically on a sponge. “When you release the sponge, you expect it to resume its shape. Imagine now that it only resumes its shape after every second squeeze even though you are applying the same force each time. That is what our system does,” he said.


Princeton postdoctoral researcher Curt von Keyserlingk, who contributed additional theoretical work with Khemani and Sondhi, said, “We explained how the time crystal systems lock into the persistent oscillations that signify a spontaneous breaking of time translation symmetry.” Additional work by researchers at Microsoft’s Station Q and the University of California-Berkeley led to further understanding of time crystals. 

As a result of these theoretical studies, two groups of experimenters began attempting to build time crystals in the laboratory. The Harvard-based team, which included Khemani at Harvard and von Keyserlingk at Princeton, used an experimental setup that involved creating an artificial lattice in a synthetic diamond. A different approach at the University of Maryland used a chain of charged particles called ytterbium ions. Both teams have now published the work this week in Nature.


Both systems show the emergence of time crystalline behavior, said Christopher Monroe, a physicist who led the effort at the University of Maryland. “Although any applications for this work are far in the future, these experiments help us learn something about the inner workings of this very complex quantum state,” he said.


The research may eventually lead to ideas about how to protect information in quantum computers, which can be disrupted by interference by the outside world. Many-body localization can protect quantum information, according to research published in 2013 by the Princeton team of David Huse, the Cyrus Fogg Brackett Professor of Physics, as well as Sondhi and colleagues Rahul Nandkishore, Vadim Oganesyan and Arijeet Pal. 
The research also sheds light on ways to protect topological phases of matter, research for which Princeton’s F. Duncan Haldane, the Eugene Higgins Professor of Physics, shared the 2016 Nobel Prize in Physics.


Sondhi said that the work addresses some of the most fundamental questions about the nature of matter. “It was thought that if a system doesn’t settle down and come to equilibrium, you couldn’t really say that it is in a phase. It is a big deal when you can give a definition of a phase of matter when the matter is not in equilibrium,” he said.


This out-of-equilibrium setting has enabled the realization of new and exciting phases of matter, according to Khemani. “The creation of time crystals has allowed us to add an entry into the catalog of possible orders in space-time, previously thought impossible,” Khemani said.


The research at Princeton and the Max Planck Institute was supported by the National Science Foundation (grant no. 1311781), the John Templeton Foundation, the Alexander von Humboldt Foundation and the German Science Foundation’s Gottfried Wilhelm Leibniz Prize Programme.


The papers “Observation of discrete time-crystalline order in a disordered dipolar many-body system” and “Observation of a discrete time crystal” will be published March 9 by Nature.

Princeton University

ITMO University: New Architecture Supercrystals (Quantum Dots) can Enhance Drug Synthesis

QBits 2 050616 Researchers-Break-Room-Temperature-Quantum-Bit-Storage-RecordScientists from ITMO University and Trinity College have designed an optically active nanosized supercrystal whose novel architecture can separate organic molecules, thus considerably facilitating the technology of drug synthesis. The study was published in Scientific Reports.

The structure of the new supercrystal is similar to a helix staircase. The supercrystal is composed of numerous rod-shaped quantum dots—tiny semiconductor pieces of about several nanometers in size. Importantly, unlike individual quantum dots, the assembly possesses the property of chirality. Thanks to this distinctive feature, such supercrystals can find wide application in pharmacology to identify chiral biomolecules.


Structure of the helical chiral supercrystal. Credit: ITMO University

An object is chiral if it cannot be superimposed on its mirror image. The most common example of chirality is human hands. In the supercrystal model, chirality can be visualized as two spiral staircases with quantum dots as steps: one turns right, while the other turns left. Therefore, the supercrystal is able to absorb left-polarized light and skip right-polarized light or other way round depending on the architecture.

Ivan Rukhlenko, head of the Modeling and Design of Nanostructures Laboratory, notes, “As with any chiral nanostructure, the range of applications of our supercrystals is huge. For example, we can use them in pharmacology to identify chiral drug molecules. Gathering in spirals around them, quantum dots can exhibit collective properties that enhance molecule absorptivity by hundreds of times. Thus, the molecules can be detected within solution with much more accuracy”.

Chirality is inherent in almost all , including proteins, nucleic acids and other substances in the human body. For this reason, two mirror forms (enantiomers) of one drug have different biological activity. While one form may produce a therapeutic effect upon interacting with chiral molecules in the organism, the other form may not have any effect at all or even be toxic. This is why careful separation of enantiomers during is vitally important.

Supercrystals with new architecture can enhance drug synthesis
Absorption of circularly polarized light by supercrystal. Credit: ITMO University

In addition to pharmacology, optical activity of supercrystals can be used in several technical applications where light polarization is required. The rod shape of each quantum dot causes them to interact with light along the longitudinal axis, which is why mutual position of quantum dots has key importance for optical properties of the whole structure. Similarly, optical effects of supercrystals are most strongly manifested when the light is distributed along the central axis. Therefore, by orienting the supercrystals in solution scientists can switch optical activity of the system, similarly to the way it is done with liquid crystals.

Supported by Trinity College, scientists have examined the optical response of the model. In order to study the supercrystal, researchers varied a number of morphological parameters of its structure. They stretched it like a spring and changed the distance between quantum dots and their orientation relative to each other.

“For the first time, we could theoretically identify the parameters of chiral supercrystal that let us achieve maximum optical effect. Thanks to this approach, we avoided the fabrication of many unnecessary copies with unpredictable properties,” says Anvar Baimuratov, lead author of the study, research associate at the Centre of Information Optical Technologies (IOT) at ITMO University. “Knowing the output parameters of optical properties, we can model a supercrystal to solve a specific problem. Conversely, having data on the supercrystal structure, we can accurately predict its optical activity.”

Based on the results obtained by the Russian scientists, their colleagues from Dresden University of Technology plan to bring the model to life and synthesize the supercrystal by means of DNA origami. This method allows assembling a helical structure from quantum dots through mediation of DNA molecules. “Experimental study of our supercrystals should confirm their theoretically predicted properties and identify new ones. But the main advantage of new semiconductor structure is already evident—varying its morphology in the synthesis process, we can change optical response of the supercrystal in a wide frequency range,” adds Ivan Rukhlenko.

A number of current technologies are based on the use of single quantum dots. Now, the researchers propose to gather them in supercrystals. “Assembling in blocks, we get more degrees of freedom to change of supercrystal solutions. The more complex the structure is, the stronger its properties depend on how we have put the elements together. Adding complexity to the structure will lead to the appearance of a number of new optical materials,” concludes Anvar Baimuratov.

Explore further: Success in development of novel chirality sensing technique enabling easy determination of optical purity

More information: Anvar S. Baimuratov et al, Chiral quantum supercrystals with total dissymmetry of optical response, Scientific Reports (2016). DOI: 10.1038/srep23321


St. Mary’s College Maryland: New research puts us closer to DIY Spray-on Solar Cell Technology

St Mary Spray on Solar 150928083119_1_540x360A new study out of St. Mary’s College of Maryland puts us closer to do-it-yourself spray-on solar cell technology — promising third-generation solar cells utilizing a nanocrystal ink deposition that could make traditional expensive silicon-based solar panels a thing of the past.

In a 2014 study, published in the journal Physical Chemistry Chemical Physics, St. Mary’s College of Maryland energy expert Professor Troy Townsend introduced the first fully solution-processed all-inorganic photovoltaic technology.

While progress on organic thin-film photovoltaics is rapidly growing, inorganic devices still hold the record for highest efficiencies which is in part due to their broad spectral absorption and excellent electronic properties. Considering the recorded higher efficiencies and lower cost per watt compared to organic devices, combined with the enhanced thermal and photo stability of bulk-scale inorganic materials, Townsend, in his 2014 study, focused on an all-inorganic based structure for fabrication of a top to bottom fully solution-based solar cell.

A major disadvantage compared to organics, however, is that inorganic materials are difficult to deposit from solution. To overcome this, Townsend synthesized materials on the nanoscale. Inorganic nanocrystals encased in an organic ligand shell are soluble in organic solvents and can be deposited from solution (i.e., spin-, dip-, spray-coat) whereas traditional inorganic materials require a high temperature vacuum chamber. The solar devices are fabricated from nanoscale particle inks of the light absorbing layers, cadmium telluride/cadmium selenide, and metallic inks above and below. This way, the entire electronic device can be built on non-conductive glass substrates using equipment you can find in your kitchen.

The outstanding challenge facing the (3-5 nm) inorganic nanocrystals is that they must be annealed or heated to form larger ‘bulk scale’ grains (100 nm to 1 μm) in order to produce working devices. Townsend recently teamed with Navy researchers to explore this process.

St Mary Spray on Solar 150928083119_1_540x360

A spray-on nanocrystal solar cell array.
Credit: Image courtesy of St. Mary’s College of Maryland

“When you spray on these nanocrystals, you have to heat them to make them work,” explained Townsend, “but you can’t just heat the crystals by themselves, you have to add a sintering agent and that, for the last 40 years, has been cadmium chloride, a toxic salt used in commercial thin-film devices. No one has tested non-toxic alternatives for nanoscale ink devices, and we wanted to explore the mechanism of the sintering process to be able to implement safer salts.”

In his latest study, published this year in the Journal of Materials Chemistry A, Townsend, along with Navy researchers, found that ammonium chloride is a non-toxic, inexpensive viable alternative to cadmium chloride for nanocrystal solar cells. This discovery came after testing several different salts. Devices made using ammonium chloride (which is commonly used in bread making) had comparable device characteristics to those made with cadmium chloride, and the move away from cadmium salt treatments alleviates concerns about the environmental health and safety of current processing methods.

The team also discovered that the role of the salt treatment involves crucial ligand removal reactions. This is unique to inorganic nanocrystals and is not observed for bulk-scale vacuum deposition methods. “A lot of exciting work has been done on nanocrystal ligand exchange, but, for the first time, we elucidated the dual role of the salt as a ligand exchange agent and a simultaneous sintering agent. This is an important distinction for these devices, because nanocrystals are typically synthesized with a native organic ligand shell. This shell needs to be removed before heating in order to improve the electronic properties of the film,” said Townsend about the discovery. Because nanomaterials are at the forefront of emerging new properties compared to their bulk counterpart, the study is important to the future of electronic device fabrication.

The research comes in the wake of the Obama Administration’s announcement in July to put more solar panels on low-income housing and expand access to solar power for renters, and recent pledge to get 20 percent of the U.S. total electricity from renewable sources by the year 2030.

“Right now, solar technology is somewhat unattainable for the average person,” said Townsend. “The dream is to make the assembly and installation process so cheap and simple that you can go to your local home improvement store and buy a kit and then spray it on your own roof. That is why we we’re working on spray-on solar cells.” Townsend plans for further research to increase the efficiency of the all-inorganic nanocrystal solar cells (currently reaching five percent), while building them with completely non-toxic components.

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Story Source:

The above post is reprinted from materials provided by St. Mary’s College of Maryland. Note: Materials may be edited for content and length.

Journal References:

  1. Troy K. Townsend, William B. Heuer, Edward E. Foos, Eric Kowalski, Woojun Yoon, Joseph G. Tischler. Safer salts for CdTe nanocrystal solution processed solar cells: the dual roles of ligand exchange and grain growth. J. Mater. Chem. A, 2015; 3 (24): 13057 DOI: 10.1039/C5TA02488A
  2. Troy K. Townsend, Edward E. Foos. Fully solution processed all inorganic nanocrystal solar cells. Physical Chemistry Chemical Physics, 2014; 16 (31): 16458 DOI: 10.1039/C4CP02403F

MIT: Calling Quantum Dots to Order: Structuring QD’s for Increased Solar Energy Conversion

MIT QD Mork_Weidman_Bench_ICMIT chemical engineering graduate student Mark Weidman and colleagues demonstrate how to synthesize lead sulfide nanocrystals of uniform size.

Lead sulfide nanocrystals suitable for solar cells have a nearly one-to-one ratio of lead to sulfur atoms, but MIT researchers discovered that to make uniformly sized quantum dots, a higher ratio of lead to sulfur precursors – 24 to 1 – is better.

MIT chemical engineering graduate student Mark C. Weidman developed the synthetic recipe in the lab of William A. Tisdale, the Charles and Hilda Roddey Career Development Professor in Chemical Engineering at MIT, with colleagues Ferry Prins, Rachel S. Hoffman and 2013 Summer Scholar Megan Beck. Uniformity of size can promote long exciton diffusion lengths in lead sulfide (PbS) quantum-dot films, Weidman says.

Usually quantum dots are synthesized as a colloid, with particles suspended in a liquid. If the quantum dots are all of the same size, they can self-assemble into an ordered lattice. “If they are mono-disperse enough, it’s the thermodynamically favored state,” Weidman explains.

He confirmed the mono-dispersity of his films with transmission-electron and scanning-electron microscopy. Weidman also traveled to the National Synchrotron Light Source at Brookhaven National Laboratory on Long Island, N.Y., to perform grazing-incidence small-angle X-ray scattering (GISAXS) and wide-angle X-ray scattering (WAXS) studies of his thin films.MIT-Switchable-Graphene-Olivares

“Mark and Megan were able to make extremely mono-disperse, unprecedented mono-dispersity in this particular type of nanocrystal, lead sulfide,” Tisdale says. Weidman unraveled the mechanism for the uniform size and structure.

Weidman, who expects to finish his PhD at MIT in 2016, is interested in lead sulfide because of its uses for solar cells. “In something like a lead sulfide film which is used for photovoltaics, for solar cells, in that case you want your quantum dots to absorb light. But then you don’t want it to re-emit.

You want to take that electron and hole and basically get them out of the film, get them to an external circuit. So, you want to maximize diffusion in your film; you want it to be very easy to withdraw this electron and hole pair and you want a long lifetime of that electron and hole pair so you have a lot of time for it to wander around the film and get extracted,” Weidman says.

“We’re hoping to find ways to better increase the efficiency of solar cells by making your diffusion lengths in films of lead sulfide much longer, and that way it’s easier to extract charge carriers from the film.”

Diffusion length refers to the process of excitons (pairs of oppositely charged electrons and holes) moving, or “hopping,” from quantum dot to quantum dot, or from quantum dots to a neighboring material. Both the distance excitons travel and their lifetime affect potential applications.

Weidman was a co-author of a collaborative study among professors Tisdale, Vladimir Bulovic, and Adam Willard of diffusion in quantum dot solids, which measured exciton lifetimes and modeled exciton diffusion lengths. Fellow graduate student A. Jolene Mork assisted in sample preparation and in transient spectroscopy measurements.

For that study, Weidman performed electron microscopy and analysis using image-processing tools and MATLAB programming to determine the separation, or physical distance, between quantum dots in the film. The cadmium selenide core quantum dots with a cadmium zinc sulfur shell averaged center-to-center distances of about 7.9 nanometers apart. “What we learned is you want to make the center-to-center distance as small as possible to have a longer diffusion length, to maximize your diffusion length,” Weidman says.

3D Printing dots-2Quantum dots are also valued for their property of changing color as they change size, which is tied to their changing bandgap. To have a consistent color, you have to have a consistent size among an ensemble of quantum dots. Tisdale group colleague Elizabeth M.Y. (Liza) Lee did simulated size variations in the quantum-dot film for the study, Weidman notes. “This paper is pretty much showing that you can control how much energetic diffusion occurs in films of quantum dots by tailoring how close they are physically,” he explains. 

“The other big implication in this paper is that from what we saw in some of the simulations, some energetic disorder can be good in these films in order to get the ball rolling on energy diffusion. If you have some size variations and that gives you energy variations, then when you excite this film, and you get this population of excited quantum dots, then some of them are higher energy than others, some of them are lower energies, so naturally the excitons that are on the higher-energy quantum dots will find the lower-energy site, and that’s energy diffusion.

So a little bit of size variation can help to speed up that process,” Weidman says. “If you think about it as a hilly landscape, you have these excitons that are at the top of hill, and they find a way to roll down to the bottom of hill, whereas if you had a completely homogeneous film that is flat in energy, then you don’t start energy diffusion as quickly.”

Weidman is lead author a Chemistry of Materials paper that further investigated and characterized the superlattice formation of lead sulfide nanocrystals. “We can make long-range superlattices in which not only are the quantum dots ordered, but their atomic planes are aligned as well,” Weidman explains. “We also found that we can change the ligand species on the surface of our quantum dots, a great way of modifying the film properties, to more compact and functional species without disturbing the superlattice arrangement.” He currently is investigating transporting energy over long distances in infrared materials, which could be applicable to solar cells.

Weidman, a 26-year-old graduate of the University of Delaware, hails originally from Haddonfield, N.J. After completing his doctorate at MIT, he plans to get a job in industry. “I would like to keep working with nanomaterials,” he says. “I think it’s a very exciting area.”