Quantum entanglement—or what Albert Einstein once referred to as — occurs when two quantum particles are connected to each other, even when millions of miles apart. Any observation of one particle affects the other as if they were communicating with each other. When this entanglement involves photons, interesting possibilities emerge, including entangling the photons’ frequencies, the bandwidth of which can be controlled.

Researchers at the Ģ����ý have taken advantage of this phenomenon to generate an incredibly large bandwidth by using a thin-film nanophotonic device they describe in .

The breakthrough could lead to:

• Enhanced sensitivity and resolution for experiments in metrology and sensing, including spectroscopy, nonlinear microscopy, and quantum optical coherence tomography
• Higher dimensional encoding of information in quantum networks for information processing and communications

“This work represents a major leap forward in producing ultrabroadband quantum entanglement on a nanophotonic chip,” says , professor of . “And it demonstrates the power of nanotechnology for developing future quantum devices for communication, computing, and sensing,”

No more tradeoff between bandwidth and brightness

To date, most devices used to generate broadband entanglement of light have resorted to dividing up a bulk crystal into small sections, each with slightly varying optical properties and each generating different frequencies of the photon pairs. The frequencies  are then added together to give a larger bandwidth.

“This is quite inefficient and comes at a cost of reduced brightness and purity of the photons,” says lead author Usman Javid, a PhD student in Lin’s lab. In those devices, “there will always be a tradeoff between the bandwidth and the brightness of the generated photon pairs, and one has to make a choice between the two. We have completely circumvented this tradeoff with our dispersion engineering technique to get both: a record-high bandwidth at a record-high brightness.”

The thin-film lithium niobate nanophotonic device created by Lin’s lab uses a single waveguide with electrodes on both sides. Whereas a bulk device can be millimeters across, the thin-film device has a thickness of 600 nanometers—more than a million times smaller in its cross-sectional area than a bulk crystal, according to Javid. This makes the propagation of light extremely sensitive to the dimensions of the waveguide.

Indeed, even a variation of a few nanometers can cause significant changes to the phase and group velocity of the light propagating through it. As a result, the researchers’ thin-film device allows precise control over the bandwidth in which the pair-generation process is momentum-matched. “We can then solve a parameter optimization problem to find the geometry that maximizes this bandwidth,” Javid says.

The device is ready to be deployed in experiments, but only in a lab setting, Javid says. In order to be used commercially, a more efficient and cost-effective fabrication process is needed. And although lithium niobate is an important material for light-based technologies, lithium niobate fabrication is “still in its infancy, and it will take some time to mature enough to make financial sense,” he says.

Other collaborators include coauthors Jingwei Ling, Mingxiao Li, and Yang He of the Department of Electrical and Computer Engineering, and Jeremy Staffa of the , all of whom are graduate students. Yang He is a postdoctoral researcher.

The National Science Foundation, the Defense Threat Reduction Agency, and the Defense Advanced Research Projects Agency helped fund the research.

Graphene—a flake of carbon as thin as a single layer of atoms—is a revolutionary nanomaterial due to its ability to easily conduct electricity, as well as its extraordinary mechanical strength and flexibility. However, a major hurdle in adopting it for everyday applications is producing graphene at a large scale, while still retaining its amazing properties.

In a, , an associate professor of at the Ģ����ý, and her colleagues at , describe a way to overcome this barrier. The researchers outline their method to produce graphene materials using a novel technique: mixing oxidized graphite with bacteria. Their method is a more cost-efficient, time-saving, and environmentally friendly way of producing graphene materials versus those produced chemically, and could lead to the creation of innovative computer technologies and medical equipment.

Graphene is extracted from graphite, the material found in an ordinary pencil. At exactly one atom thick, graphene is the thinnest—yet strongest—two-dimensional material known to researchers. Scientists from the University of Manchester in the United Kingdom were awarded the for their discovery of graphene; however, their method of using sticky tape to make graphene yielded only small amounts of the material.

“For real applications you need large amounts,” Meyer says. “Producing these bulk amounts is challenging and typically results in graphene that is thicker and less pure. This is where our work came in.”

In order to produce larger quantities of graphene materials, Meyer and her colleagues started with a vial of graphite. They exfoliated the graphite—shedding the layers of material—to produce graphene oxide (GO), which they then mixed with the bacteria Shewanella. They let the beaker of bacteria and precursor materials sit overnight, during which time the bacteria reduced the GO to a graphene material.

“Graphene oxide is easy to produce, but it is not very conductive due to all of the oxygen groups in it,” Meyer says. “The bacteria remove most of the oxygen groups, which turns it into a conductive material.”

While the bacterially-produced graphene material created in Meyer’s lab is conductive, it is also thinner and more stable than graphene produced chemically. It can additionally be stored for longer periods of time, making it well suited for a variety of applications, including field-effect transistor (FET) biosensors and conducting ink. FET biosensors are devices that detect biological molecules and could be used to perform, for example, real-time glucose monitoring for diabetics.

“When biological molecules bind to the device, they change the conductance of the surface, sending a signal that the molecule is present,” Meyer says. “To make a good FET biosensor you want a material that is highly conductive but can also be modified to bind to specific molecules.” Graphene oxide that has been reduced is an ideal material because it is lightweight and very conductive, but it typically retains a small number of oxygen groups that can be used to bind to the molecules of interest.

The bacterially produced graphene material could also be the basis for conductive inks, which could, in turn, be used to make faster and more efficient computer keyboards, circuit boards, or small wires such as those used to defrost car windshields. Using conductive inks is an “easier, more economical way to produce electrical circuits, compared to traditional techniques,” Meyer says. Conductive inks could also be used to produce electrical circuits on top of nontraditional materials like fabric or paper.

“Our bacterially produced graphene material will lead to far better suitability for product development,” Meyer says. “We were even able to develop a technique of ‘bacterial lithography’ to create graphene materials that were only conductive on one side, which can lead to the development of new, advanced nanocomposite materials.”

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Remarkable things happen.

The glass-like material is transformed ever so briefly into something akin to a metal. And the laser generates a burst of electrical current across this tiny electrical circuit. It does so far faster than any traditional way of producing electricity and in the absence of an applied voltage. Further, the direction and magnitude of the current can be controlled simply by varying the shape of the laser—by changing its phase.

Now a URochester researcher—who predicted laser pulses could generate ultrafast currents along nanoscale junctions like this in theory—believes he can explain exactly how and why scientists succeeded in creating these currents in actual experiments.

“This marks a new frontier in the control of electrons using lasers,” says Ignacio Franco, assistant professor of chemistry and physics. He has collaborated with Liping Chen, a postdoctoral associate in his group, and with Yu Zhang and GuanHua Chen at the University of Hong Kong on a computational model to recreate and clarify what happened in the experiment. This work funded by Franco’s NSF CAREER award is now published in .

“You will not build a car out of this, but you will be able to generate currents faster than ever before,” Franco says. “You will be able to develop electronic circuits a few billionths of a meter long [nanoscale] that operate in a millionth of a billionth of a second [femtosecond] time scale. But, more importantly, this is a wonderful example of how differently matter can behave when driven far from equilibrium. The lasers shake the nanojunction so hard that it completely changes its properties. This implies that we can use light to tune the behavior of matter.”

This is exactly what the US Department of Energy had in mind when it listed the control of matter at the level of electrons — and understanding matter “very far away” from equilibrium—among its key challenges for the nation’s scientists.

From theory to experiment to explanation

The DOE issued those in 2007. That same year, Franco, then a doctoral student at the University of Toronto, was lead author of a paper in Physical Review Letters theorizing that extremely powerful, ultrafast electrical currents could be generated in molecular wires exposed to femtosecond laser pulses.

The molecular wires, made of a linear carbon chain, would be connected to metallic contacts forming a nanoscale junction. The current would be generated because a phenomenon called the Stark effect, in which the energy levels of matter are shifted due to the presence of the external electric field of the laser,��is used to control level alignment between the molecule and the metallic contacts.

But this theoretical proposal remained just that. The challenges of actually building a junction that small, and then being able to document what happened before the wires were destroyed by the lasers, were too daunting to validate the theory with actual experiments.

That is until 2013, when researchers led by Ferenc Krausz at the Max Planck Institute of Quantum Optics were able to generate ultrafast currents by exposing a different nanojunction—glass connecting two gold electrodes—to laser pulses.

The exact dynamics involved remained unclear, Franco says. Various theories were advanced by other researchers. But even though the materials were different, Franco suspected involvement of the same Stark effect mechanisms hypothesized in his 2007 paper.

A four-year simulation effort, involving millions of computing hours of Blue Hive computer processing, have confirmed that, says Franco. “We were able to recover the main experimental observations using state-of-the-art computational methods, and develop a very simple picture of the mechanism behind the experimental observations,” he says.

The research illustrates how theory and experiment are mutually reinforcing in advancing science, Franco says. “Theory led to an experiment that nobody really understood, resulting in better theories that are now leading to better experiments” he says. “This is an area in which we still have a lot of things to understand,” he adds.

Chemists have traditionally studied the relationship of a molecule’s structure to its possible functions when the material is at or near thermodynamic equilibrium, he says.

“This research invites you to think about structure-function relations that apply very, very far away from equilibrium.”

It was frustrating work. The chips weren’t making good contact with each other. Madejski gently poked at the chips, then peered over the top of the microscope.

And exhaled.

The sudden waft of warm air swept over the nanofilter, transferring it to the sensor—right on target. The “accident” led Madejski to an important insight: the water vapor in his breath had��condensed on the device, causing��the nanofilter to adhere ever so neatly to the sensor.

“It was like a really high-tech temporary tattoo that I created by accident; lick and stick!” says the PhD student in the a professor of biomedical engineering at the URochester.

And that’s how water vapor became integral to the development and design of a novel device for detecting DNA biomarkers affiliated with disease. Created by McGrath’s lab in collaboration with Professor Vincent Tabard-Cossa and graduate student Kyle Briggs at the University of Ottawa, the device is described in an . The article, and an image from Madejski’s homemade animation of the device in operation, will be highlighted on the cover of the February 2018 print issue.

‘A remarkable structure’

The device is comprised of three ultrathin layers:

• a nanoporous silicon nitride membrane which serves as a prefilter.
• a biosensor membrane with a single nanopore.
• a spacer layer that separates these by only 200 nm.

The arrangement creates a nanocavity filled with less than a femtoliter of fluid—or about a million times smaller than the smallest raindrops.

During operation, the device uses an electric field to lure a strand of DNA to enter one of the pores of the prefilter and then pass through the nanocavity to reach the pore of the underlying sensor membrane. This triggers changes in the device’s electrical current that can be detected and analyzed. The fact that DNA must elongate itself in a consistent way to pass through the two-membrane combination improves the precision and reproducibility of detection.

“This is a remarkable structure,” says McGrath. “We’ve built an integrated system with a highly porous filter within molecular reach of a sensor. I think there are many sensors, particularly those that hunt for biomarkers in raw biological fluids, that would benefit from filtering away unwanted molecules immediately upstream of the detector.”

The method of fabrication instantly wets the nanocavity, which is often difficult at the nanoscale. The device contains dozens of these nanocavities, which may eventually increase the amount of material that can be screened by enabling parallelized biomarker detection.

Solving problems that others need solved

Tabard-Cossa’s lab uses solid-state nanopore devices to find new ways to manipulate and characterize single molecules. His lab was interested in finding new materials that could be used for biomarker detection. The prefilter in the new device addresses a problem with other silicon nanopore detectors: They are more likely to clog than alternative devices that use that biological pores for sensing. Biological membranes, on the other hand, are less stable than solid state nanopores, McGrath noted.

“We love to apply our membrane technologies to solve problems that others need solved. This is a very nice example.,” McGrath says.

McGrath is co-founder of SiMPore, a University-based startup that develops highly portable, chip-based devices that incorporate silicon membranes for a variety of applications, from biological sensing to dialysis.

“I think we’re going to realize the practical advantages of this technology in the near term,” he says. A second generation of the new device, developed at SiMPore, incorporates the prefilter right on the chips during manufacturing at the wafer scale, “so there’s nobody breathing on it anymore,” he notes. “It’s actually all built as one unit and should make future studies very easy. That’s a credit to the ingenuity at SiMPore and quite a legacy for Greg.”

“This is a rare opportunity to see a variety of daguerreotypes in one exhibition, especially numerous plates created in Western New York,” said Mary Ann Mavrinac, vice provost and Andrew H. and Janet Dayton Neilly Dean of River Campus Libraries. “It is truly remarkable to highlight this research—research that may help develop future non-altering techniques for the preservation of this precious cultural process.”

For over 175 years, surviving daguerreotypes have been carefully preserved in private and public collections and displayed in museums and cultural institutions around the world. While damage to daguerreotype plates is often visible by eye, evidence of further deterioration may only be detected at the nano level, by looking at features that are hundreds or thousands of times smaller than the width of a human hair. From 2010-2014, a National Science Foundation grant supported nanotechnology research conducted by two Ģ����ý scientists—Nicholas Bigelow, Lee A. DuBridge Professor of Physics, and Ralph Wiegandt, visiting research scientist and conservator—who explored how environment impacts the survival of these unique, non-reproducible images. In addition to conservation science and cultural research, Bigelow and Wiegandt are also investigating ways in which the chemical and physical processes used to create daguerreotypes can influence modern nanofabrication and nanotechnology.

“The daguerreotype should be considered one of humankind’s most disruptive technological advances,” Bigelow and Wiegandt said. “Not only was it the first successful imaging medium, it was also the first truly engineered nanotechnology. The daguerreotype was a prescient catalyst to the ensuing cascade of discoveries in physics and chemistry over the latter half of the 19^th��century and into the 20^th.”

Blending the past with the future, the exhibition displays the first known daguerreotype of a Rochester graduating class (1853) alongside a 2015 daguerreotype of current University President Joel Seligman, created by Rochester daguerreotypist Irving Pobboravsky. The exhibition will also include a rare daguerreotype of famed abolitionist Frederick Douglass on loan from the Chester County Historical Society in Pennsylvania. Once owned by Susan B. Anthony, this unique portrait will be examined under electron scanning microscopy and displayed with new research findings into its creation and preservation.

The exhibition is on view through February 29, 2016 in the Friedlander Lobby of Rush Rhees Library. A special presentation about the scientific advances surrounding the daguerreotype and their relationship to cultural preservation will be led by Bigelow, Wiegandt, and Jim Kuhn, assistant dean for Special Collections and Preservation, on December 14 from 7-9 p.m. in the Hawkins-Carlson Room of Rush Rhees Library. For more information visit: or call (585) 275-4477.

Scientists are facing a number of barriers as they try to develop circuits that are microscopic in size, including how to reliably control the current that flows through a circuit that is the width of a single molecule.

Alexander Shestopalov, an assistant professor of chemical engineering at the URochester, has done just that, thereby taking us one step closer to nanoscale circuitry.

“Until now, scientists have been unable to reliably direct a charge from one molecule to another,” said Shestopalov. “But that’s exactly what we need to do when working with electronic circuits that are one or two molecules thin.”

Shestopalov worked with an OLED (organic light-emitting diode) powered by a microscopically small, simple circuit in which he connected a one-molecule thin sheet of organic material between positive and negative electrodes. Recent research publications have shown that it is difficult to control the current traveling through the circuit from one electrode to the other in such a thin circuit. As Shestopalov explains in a paper published in the journal Advanced Material Interfaces, the key was adding a second, inert layer of molecules.

The inert—or non-reactive—layer is made of a straight chain of organic molecules. On top a layer of aromatic—or ring-shaped—molecules acts like a wire conducting the electronic charge. The inert layer, in effect, acts like the plastic casing on electric wires by insulating and separating the live wires from the surrounding environment. Since the bottom layer is not capable of reacting with the overlapping layer, the electronic properties of the component are determined solely within the top layer.

The bi-layer arrangement also gave Shestopalov the ability to fine-tune his control of the charge transfer. By changing the functional groups—units of atoms that replace hydrogen in molecules and determine a molecule’s characteristic chemical reactivity—he could more precisely affect the rate at which the current moved between the electrodes and the upper layer of organic molecules.

In molecular electronic devices, some functional groups accelerate the charge transfer, while others slow it down. By incorporating the inert layer of molecules, Shestopalov was able to reduce any interference with the top layer and, as a result, achieve the precise charge transfer needed in a device by changing the functional group.

For example, an OLED may need a faster charge transfer to maintain a specific luminescence, while a biomedical injection device may require a slower rate for delicate or variable procedures.

While Shestopalov overcame a significant obstacle, there remains a great deal of work to be done before bi-layer molecular electronic devices become practical. The next obstacle is durability.

“The system we developed degrades quickly at high temperatures,” said Shestopalov. “What we need are devices that last for years, and that will take time to accomplish.”

Shestopalov’s research was funded by the National Science Foundation and Ģ����ý ChemE Startup.

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The ability to shrink laboratory-scale processes to automated chip-sized systems would revolutionize biotechnology and medicine. For example, inexpensive and highly portable devices that process blood samples to detect biological agents such as anthrax are needed by the U.S. military and for homeland security efforts. One of the challenges of “lab-on-a-chip” technology is the need for miniaturized pumps to move solutions through micro-channels. Electroosmotic pumps (EOPs), devices in which fluids appear to magically move through porous media in the presence of an electric field, are ideal because they can be readily miniaturized. EOPs however, require bulky, external power sources, which defeats the concept of portability. But a super-thin silicon membrane developed at the URochester could now make it possible to drastically shrink the power source, paving the way for diagnostic devices the size of a credit card.

“Up until now, electroosmotic pumps have had to operate at a very high voltage—about 10 kilovolts,” said James McGrath, associate professor of biomedical engineering. “Our device works in the range of one-quarter of a volt, which means it can be integrated into devices and powered with small batteries.”

McGrath’s research paper is being published this week by the journal��Proceedings of the National Academy of Sciences.

McGrath and his team use porous nanocrystalline silicon (pnc-Si) membranes that are microscopically thin—it takes more than one thousand stacked on top of each other to equal the width of a human hair. And that’s what allows for a low-voltage system.

A porous membrane needs to be placed between two electrodes in order to create what’s known as electroosmotic flow, which occurs when an electric field interacts with ions on a charged surface, causing fluids to move through channels. The membranes previously used in EOPs have resulted in a significant voltage drop between the electrodes, forcing engineers to begin with bulky, high-voltage power sources. The thin pnc Si membranes allow the electrodes to be placed much closer to each other, creating a much stronger electric field with a much smaller drop in voltage. As a result, a smaller power source is needed.

“Up until now, not everything associated with miniature pumps was miniaturized,” said McGrath. “Our device opens the door for a tremendous number of applications.”

Along with medical applications, it’s been suggested that EOPs could be used to cool electronic devices. As electronic devices get smaller, components are packed more tightly, making it easier for the devices to overheat. With miniature power supplies, it may be possible to use EOPs to help cool laptops and other portable electronic devices.

McGrath said there’s one other benefit to the silicon membranes. “Due to scalable fabrication methods, the nanocrystalline silicon membranes are inexpensive to make and can be easily integrated on silicon or silica-based microfluid chips.”

The work was done by graduate students Zhiji Han and Fen Qiu, as part of a collaboration between chemistry professors Richard Eisenberg, Todd Krauss, and Patrick Holland, which is funded by the U.S. Department of Energy. Their paper will be published later this month (Nov. 23) in the journal��Science.

The chemists say their work advances what is sometimes considered the “holy grail” of energy science—efficiently using sunlight to provide clean, carbon-free energy for vehicles and anything that requires electricity.

One disadvantage of current methods of hydrogen production has been the lack of durability in the light-absorbing material, but the Rochester scientists were able to overcome that problem by incorporating nanocrystals. “Organic molecules are typically used to capture light in photocatalytic systems,” said Krauss, who has been working in the field of nanocrystals for over 20 years. “The problem is they only last hours, or, if you’re lucky, a day. These nanocrystals performed without any sign of deterioration for at least two weeks.”

Richard Eisenberg, the Tracy H. Harris Professor of Chemistry, has spent two decades working on solar energy systems. During that time, his systems have typically generated 10,000 instances—called turnovers—of hydrogen atoms being formed without having to replace any components. With the nanocrystals, Eisenberg and his colleagues witnessed turnovers in excess of 600,000.

The researchers managed to overcome other disadvantages of traditional photocatalytic systems. “People have typically used catalysts made from platinum and other expensive metals,” Holland said. “It would be much more sustainable if we used metals that were more easily found on the Earth, more affordable, and lower in toxicity. That would include metals, such as nickel.”

Holland said their work is still in the “basic research stage,” making it impossible to provide cost comparisons with other energy production systems. But he points out that nickel currently sells for about $8 per pound, while the cost of platinum is $24,000 per pound.

While all three researchers say the commercial implementation of their work is years off, Holland points out that an efficient, low-cost system would have uses beyond energy. “Any industry that requires large amounts of hydrogen would benefit, including pharmaceuticals and fertilizers,” said Holland.

The process developed by Holland, Eisenberg, and Krauss is similar to other photocatalytic systems; they needed a chromophore (the light-absorbing material), a catalyst to combine protons and electrons, and a solution, which in this case is water. Krauss, an expert in nanocrystals, provided cadmium selenide (CdSe) quantum dots (nanocrystals) as the chromophore. Holland, whose expertise lies in catalysis and nickel research, supplied a nickel catalyst (nickel nitrate). The nanocrystals were capped with DHLA (dihydrolipoic acid) to make them soluble, and ascorbic acid was added to the water as an electron donor.

Photons from a light source excite electrons in the nanocrystals and transfer them to the nickel catalyst. When two electrons are available, they combine on the catalyst with protons from water, to form a hydrogen molecule (H2).

This system was so robust that it kept producing hydrogen until the source of electrons was removed after two weeks. “Presumably, it could continue even longer, but we ran out of patience!” said Holland.

One of the next steps will be to look at the nature of the nanocrystal. “Some nanocrystals are like M&Ms – they have a core with a shell around it,” said Eisenberg. “Ours is just like the core. So we need to consider if they would they work better if they were enclosed in shells.”