Saving Silver: MSE Professor Ray Phaneuf's research group, in collaboration with conservators at the Walters Art Museum in Baltimore, Md., have developed atoms-thick coatings designed to protect silver artifacts from tarnish and corrosion longer and more effectively than nitrocellulose lacquers.
The Department of Materials Science and Engineering at the University of Maryland is deeply invested in nanotechnology research and initiatives, facilities, and education throughout campus and with collaborators at national research laboratories.
Nanotechnology and Nanoscience Research and Initiatives
MSE faculty, graduate students, and even some undergraduates are engaged in a variety of high-profile nanotechnology-based projects whose discoveries could lead to advances in computer and electronic device manufacturing, biological threat detection, microscopy, and the treatment of disease. Below are only a few examples:
Ferromagnetic and Ferroelectric Nano-Materials
Professor Manfred Wuttig and alumnus Shenqiang Ren are working on the synthesis of ferromagnetic and ferroelectric nano-materials. If properly mixed with polymers and spun into films, these materials configure themselves automatically into distinct patterns that are potentially useful. The pictures display two patterns that evolve by mixing their components at different ratios. Each has distinct magnetic properties: The system of superparamagnetic nano-cylinders embedded in a paraelectric matrix (left, top image) could improve the capacity and reception of telecommunication circuits, and help create "virtual antennas". The ferromagnetic "nano-onion" (left, bottom image) might help configure new forms of memory. The material can make certain electronic devices faster and easier to manufacture, as well as more reliable because they would require fewer parts. Wuttig and Ren's materials are both more finely tunable than those currently available, and more easily tuned. For more information, see S. Ren, R. M. Briber and M. Wuttig, "Diblock Copolymer Based Self-Assembled Nano-Magneto-Electric," Applied Physics Letters 93, 1 (2008).
Nanoparticle Engineering
Oded Rabin, Assistant Professor
The properties of nanoparticles strongly depend on size and shape. A silver ring on one's finger is not very different than a silver coin: They have the same color, they same conductivity, the same rate of oxidation. By contrast, a silver nanoring is different than a silver nanodisk, and both are different from a silver nanosphere and a silver nanocube! Graduate and undergraduate students in the department who participate in the nanomaterials courses and laboratory research programs with Professor Oded Rabin are discovering methods to control the shape of nanoparticles using materials science principles. They have prepared libraries of silver nanoparticles of all the shapes mentioned above in the form of piles of small vials containing brightly colored solutions.
To make useful devices out of the particles, assembly is a key step in the process, and a very challenging one given that the particles cannot by seen or picked individually. Rabin and his students are devising methods for assembly based on a lock-and-key approach: They pattern cavities in a substrate (using electron beam lithography) and "encourage" the particles to self-assemble in those cavities. If the size and shape are correct, the nanoparticles will follow the assembly "instructions" and rest in the desired locations. In the SEM image above, the group's nanocubes took positions in the array of pores only 100nm in diameter.
Their method to drive silver nanocubes to self-assemble into clusters in predetermined locations is key to making sensors that take advantage of the unique properties of the nanoparticles. Prof. Rabin’s group prepared chemical sensors containing dimers, pairs of nanocubes, that are more effective than sensors with individual or randomly-placed nanocubes. The group is investigating the effect of particle shape and particle-particle interactions on the efficiency of their sensors.
For more information, see "Nanocube Pairs Are Key to Improved Sensors"
Nanoparticle Enhanced Fluorescence
Strong resonant coupling between light and plasmons in silver or gold nanoparticles leads to a number of striking and technologically important optical effects, among them the enhancement of fluorescence from nearby molecules. Since fluorescence is the technique of choice for many biological assays, significant enhancement would greatly enhance the sensitivity of these assays to a host of target biomolecules. To date, the maximum enhancement available in fluorescence has not been established. This is largely due both to difficulties in controlling the size and shape of the particles, and to the multiplicity of contributing factors: increased radiative decay rate and enhanced electric fields at resonance, "hot spots", i.e. regions of high field between closely spaced particles. The substrate is known to play a role as well; in particular there have been suggestions that certain substrates might play an active role in light-plasmon coupling rather than merely shifting the resonance frequency. In recent work the Phaneuf Group, including graduate student Shu-Ju (Phoebe) Tsai, observed just such an effect, in which the size dependence of the enhancement of fluorescence from monodisperse silver nanoparticles is profoundly altered by the Si substrate. Comparing fluorescence measurements with calculations of the response of the silver nanoparticles to incident light, they found that unlike what is commonly assumed, the variation of the fluorescence enhancement with nanoparticle diameter does not simply follow that of plasmon excitation as measured by the optical extinction. Instead it is the generation of regions of high electrical field intensity near the particle which dominates the fluorescence enhancement that are observed, and that a silicon substrate plays an active role in this regard: sweeping these regions out from beneath the particles as their size approaches the optimum for fluorescence.
For more information, please see the MSE research spotlight "Nanoparticle-Enhanced Fluorescence."
How is MSE at UMD Working with Nanotechnology?
Saving Silver
Volumes So Small, a Drop of Water is a Lake
Members of the undergraduate Class of 2008 studied the behavior of fluids at the nanoliter level, and proposed a "micro-mixer" design that could enhance the performance of lab technologies used in chemical engineering, biology, bioengineering, DNA analysis, and pharmacology
Tiny, Threat-Detecting Lasers
MSE professor Aris Christou "grows" lasers at the mico- and nano-scale that are used as sensors detect biological threats
How Do You Test a Device You Can't See?
MSE professor John Cumings and his research group have developed a new electron microscopy technique that will allow scientists to test nanoscale devices in real-time while they are observed in a transmission electron microscope.
"Growing" Computer Components
MSE Professor Ray Phaneuf has developed a template nature can follow to produce "self-assembling" structures. The template causes atoms to be arranged in a defined pattern that can serve a variety of purposes—a semiconductor in a laptop, a component in a cell phone or a sensor in a wearable device.
Positioning Nanoparticles Where You Need Them
Professor Oded Rabin and his graduate student have developed techniques to position silver nanocubes in predetermined locations on a substrate (surface). These techniques are needed to study interactions between neighboring particles. In recent work the group succeeded to show that pairs of silver nanocubes, positioned face-to-face or edge-to-face, are very effective as chemical sensors utilizing a phenomena called Raman scattering.
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