Prof. George S. Nolas

will be an invited speaker at the upcoming Wilhelm and Else Heraeus conference in Bad Honnef, Germany, on the topic Nanostructured Thermoelectric Materials. 11/23/09

Professors Hari Srikanth and Lilia Woods

will be invited speakers in focus sessions on magnetic oxides and thermoelectrics, respectively, at the upcoming 2010 APS March Meeting in Portland, Oregon 11/16/09

Matthew Beekman (Major Professor: G. Nolas)

has been awarded 2008-2009 Outstanding Dissertation Award from the Graduate School. (11/9/2009)

Prof. Hari Srikanth

Co-organizing a symposium on functional oxide nanostructures and heterostructures at the 2010 Materials Research Society Spring Meeting to be held in San Francisco from April 5 – 9, 2010. Abstract deadline is November 2, 2009.

Applied Physics graduate student Nicholas Bingham from Prof. Srikanth’s Functional Materials Laboratory has been selected with full financial support by the IEEE Magnetics Society to attend the 2009 Summer School in Magnetics to be held from Sept. 20 – 25, 2009 at Nanjing University in Nanjing, China.(8/18/09)

M. Beekman, M. Baitinger, H. Borrmann, W. Schnelle, K. Meier, G.S. Nolas, and Y. Grin, “Preparation and Crystal Growth of Na24Si136”, J. Am. Chem. Soc. 131, 9642 (2009).

The synthesis and single crystal growth of clathrate-II Na24Si136 is performed in one step applying the spark plasma treatment to the precursor Na4Si4. The reported results demonstrate a new route to intermetallic compounds facilitated by the electric field and current. This technique is revealed to offer significant opportunities as a novel preparatory method for synthesis and crystal growth of new and novel materials.
(8/14/09)

 

Profs. Lilia Woods and George Nolas awarded three-year grant from National Science Foundation

Granular Nanocomposites for Improved Thermoelectric Performance: Theory and Experiment

Waste heat can be directly converted to electrical energy through use of various thermoelectric materials. A need persists to develop predictive models that can be utilized as design tools for development of nanostructured bulk thermoelectric materials, which can be formed quickly and, potentially, inexpensively.

Intellectual Merit: Two-component granular nanocomposites will be investigated from analytical as well as experimental perspectives. A microscopic model will take into account the electronic structure properties of the materials, as well as granular characteristics such as the interface barrier and size. Of particular importance will be the interplay between electronic structure changes due to doping of the individual components, and the scattering from the grain interfaces. The experimental research will involve synthesis and characterization of these materials. Measurements will serve as benchmarks for the proposed theory, and will also guide the research. The systems to be investigated are two-phase granular nanocomposites such as lead telluride/europium telluride, lead telluride/bismuth telluride, lead telluride/metal, and bismuth telluride/metal.

Broader Impact: Development of inexpensive, highly efficient thermoelectric materials is a key to realize large scale conversion of waste heat to high grade electrical energy. Other potential benefits include, for example, displacement of compression air conditioners in automobiles, possibly leading to substantial reductions in leakage and emissions of harmful refrigerants into the atmosphere.
(8/11/09)

 

Prof. Oleynik receives a new three-year grant form the Office of Naval Research

Atomic-scale mechanisms of hypervelocity chemistry and detonation

The main goal of the proposed research is to study atomic-scale mechanisms of detonation in energetic materials (EMs). The focus is to understand and predict complex processes arising from the interaction of a strong shock wave with an EM leading to the formation of a detonation front. Such processes include the initiation of the chemical reactions, mechanisms of chemical energy release, and the dynamics of a self-sustained detonation. In contrast to previous studies, the non-equilibrium stages of chemical initiation by the shock wave will be studied by developing and applying a novel “moving window” simulation technique. The unique feature of this method is in explicit inclusion of the shock wave front into the simulation cell, and the ability to investigate the non-equilibrium processes with fine time and space resolutions. Other methods to simulate the properties of detonating EMs such as equilibrium molecular dynamics (MD) with Hugoniot energy and stress constraints will also be used to investigate the properties of the energetic materials during their transformation from their unreacted initial state towards the fully reacted Chapman-Jouguet (CJ) state at the end of the reaction zone.

(8/7/09)

Michael W. Conroy, Doctoral Candidate in Applied Physics Program was awarded the NRC Post Doctoral Fellowship at the Naval Research Laboratory. (8/7/09)

Prof. W.G. Matthews has been awarded a new three-year grant from the National Science Foundation.

Engineering an In Vitro Assembled Corneal Stroma

Summary: The investigators seek to develop an in vitro assembled corneal stroma for eventual use as a replacement tissue to aid the visually impaired. The work is motivated by the ability to assemble collagen fibrils derived from Cucumaria frondosa into mimics of corneal stroma, a technique which already exists within the team. Extension of this ability to mammalian materials is an overarching goal. The research outcomes expected from the proposed work center around defining the principles by which the collagen scaffolds of extracellular matrices (ECMs) and connective tissues may be assembled for application to tissue engineering. Despite the vast amounts of data available on the mechanical properties of the macroscopic constructs formed by collagen, little is known of the mechanics at the level of the collagen molecule or fibril. These properties will be measured, as well as the interactions between the proteoglycan components of the relevant ECM, providing the information needed to rationally design in vitro equivalents of the tissue. Mechanically matching the materials used in the construction of the stroma to those of the native system will be done at the macromolecular and macroscopic scales. Through this university-industrial collaborative research project with MiMedx, Inc., the team has access to collagens and to a wealth of experience in collagen assembly and applications to tissue engineering. Additionally, the industrial collaboration provides a streamlined mechanism by which the research outcomes will be translated into patient oriented products.
Loss of transparency of the cornea due to disease or degeneration can impair vision or totally blind patients, with correction often requiring corneal replacement. In terms of the worldwide population, 250 million people have compromised vision resulting from corneal disease, including over 6 million who have been blinded (NIH NEI). While corneal transplants would alleviate much of this suffering, there is a severe limitation of donor tissue.
Intellectual Merit: The intellectual merit is threefold. 1. For the first time, the mechanics of and interactions between the constituents of collagenous tissues will be systematically and comprehensively explored on multiple length scales, providing a complete picture of how the mechanical properties of filamentous self-organizing systems, in particular type I collagen, are derived. 2. The results will resolve the important question of how load is supported within collagenous tissues. 3. The results also will resolve how the collagen hierarchal forms are established and maintained.
Broader Impacts: 1. The results themselves will benefit those endeavoring to a. develop biomimetic materials for connective tissues, b. develop materials for use as scaffolds in tissue engineering, and c. rationally design self-organizing, three-dimensional systems constructed from nanoscale building blocks. 2. The work is highly interdisciplinary, and as such draws students with interest in biomedical engineering, material science, physics, biology, and biochemistry. The ability to recruit students from underrepresented groups is enhanced by this breadth. 3. The laboratories consist of graduate, undergraduate, and high school students. These students will have the opportunity to work jointly in an academic and an industrial setting. 4. An outreach project has been established in which the principal investigator provides young students (K-12) within the US and abroad the opportunity to participate in research experiments by remotely accessing the instrumentation from their own classroom. 5. A new interface for the atomic force microscope is being developed which will allow the visually impaired to perform force spectroscopy experiments. 6. Finally, the material under study has tremendous potential for societal benefit in its applications as a cornea replacement.
(7/13/09)

 

Prof. M. Batzill received three-year U.S. Department of Energy research grant for $555K.

Photocatalysis of modified transition metal oxide surfaces

Sun light is the most abundant energy source. In order to tap into this resource, more efficient ways for converting solar energy into other forms of energy that can be stored and transported is needed. Harvesting sun light and converting it into chemical fuels is one promising approach to reach the goal of a sustainable energy source. Photocatalysts absorb light and use the generated electron-hole pairs to perform redox reactions on molecules adsorbed at their surfaces. In this way, for example, hydrogen can be produced from hydrocarbons or even water. Currently used photocatalysts, such as TiO2, lack in their efficiency to be viable for an economic energy production. In order to increase their activity these materials need to be modified and their surfaces need to be engineered in order to possess appropriate functionalities. In this proposal we investigate the fundamental principles, and suggest new approaches to make transition metal oxides more effective photocatalysts. The knowledge gained from the proposed experiments will aid the controlled design of materials with increased photochemical surface reactivity.
We will perform studies primarily on single crystalline materials under ultra high vacuum conditions. This enables us to characterize surfaces and to modify them in a controlled manner. We will use multiple surface science techniques to characterize the surface geometrical and electronic structure. Furthermore, the chemical surface properties and the photocatalytic properties are being measured. This approach enables us to determine physical materials properties and to correlate them with their (photo)chemical activity. With these experimental developments we will address diverse issues in photocatalysis such as;

• Surface defects-- What is the importance of surface defects, in particular monoatomic height step edges, for promoting photocatalytic reactions?
• Loading of photocatalysts with noble metals-- What is the metal-cluster size dependence on the activation of photocatalysts?
• Surface functionalities of intrinsic surfaces -- Do different crystallographic orientations of the same material exhibit different photocatalytic functions and why?
• Modification of the surface properties by grafting a monolayer film in order to increase charge trapping at the surface -- Can we enhance charge separation and trapping by controlled surface engineering?
• Increasing the visible light absorption by bulk doping -- How is the materials chemistry of defect formation in doped materials related to the photochemical surface properties?

The fundamental understanding of these processes is necessary to design next generation photocatalysts where several components with different functionalities will act in accord to achieve high efficiencies. The functions of these components will be largely determined by the surfaces and interfaces that join them together at the nanoscale. Thus this proposal will help to define the design-principles for future photocatalytically active materials.
(7/6/09)

 

Prof. G. Nolas and Nathan Crane (from the Department of Mechanical Engineering) have received a new three-year NSF grant.

High Yield Self Assembly of Functional Thermoelectric Devices

The research objective of this award is increase rate and yield of microscale self-assembly processes. In self-assembly, components are designed to spontaneously bond when brought together as by mixing or agitation. The rate of component assembly and the process yield depend on the characteristics of the interaction processes. The research approach will first validate and refine force and energy models of individual self-assembly bonds. These bond models will provide key inputs into a stochastic process models that relate controllable process parameters to process rate and yield. The models will be experimentally validated through assembly of a function microsystem?a micro thermoelectric cooler. The micro thermoelectric cooler will be assembled from high performance nanostructured thermoelectric materials to validate the predictive capabilities of the models. Deliverables include capillary bond models, general self-assembly process models, experimental model validation, process of generating models of related processes, documentation of results, and educational outreach to K-12 students. If successful, the results of this research will enable large scale integration of components too small to effectively pick up and manipulate using current assembly techniques. This will improve performance of microsystems by enabling integration of new materials and devices. For example, smaller thermoelectric elements can be integrated for more efficient cooling of electronic and photonic equipment and lower cost recovery of waste heat. The models and the methods for building them developed through this project can be adapted to self-assembly using other bond types and at other size scales. Examples from this work will be incorporated into presentations to K-6 students to teach important concepts about energy and to increase students? recognition of the role science and engineering play in their lives. High school demonstrations will be used to recruit students for hands-on lab work on the project during the summers. Advances from this project will also be integrated into graduate and undergraduate courses.
(7/15/09)

Prof. L. Woods receives three-year Federal grant from the United States Department of Energy

The central topic of this investigation is the consequences of long ranged interactions in nanostructured graphitic materials. The origins of these forces, their quantitative characterization and the role they play in the assembly of nanostructures are the central theme of the research effort. The research expands on a foundations established in the previous award where studies were conducted on interactions between carbon nanotubes and the dependence of those interactions on geometry and structural features of the nanotubes. The previous efforts allowed development of a general quantum electrodynamical theory of interactions involving quasi-one dimensional graphitic nanostructured materials. The tools are expanded in this proposal and applications to more complex system are addressed, including graphene nanoribbons, carbon nanotubes and metamaterials. The research includes the investigation of the role of quasi-one dimensionality, geometrical curvature, response properties of the graphitic structures, and the unusual strong magnetic response of the metamaterials in order to describe and discover new and interesting functionalities associated with the long ranged interaction force.

Guided by previous studies showing that curvature has a non-trivial effect on the long ranged interactions, the current effort investigates the cylindrical quasi-one dimensional carbon nanotubes and planar quasi-one dimensional graphene nanoribbons because such systems allow the effects of curvature and geometry to be studied in more robust detail. The dielectric and magnetic response properties of the graphitic structures are calculated and are incorporated in the interaction force theories in order to determine their role. An effort with parallel interest considers metamaterials as similar systems with strong magnetic response properties in a wide frequency range.   The quantum electrodynamical theory of interactions previously developed is applied to characterize interactions with these artificially designed materials and add to the theoretical capability to provide guidelines for tuning the sign and magnitude of the long ranged interactions involving graphitic nanostructures.

The research involves collaboration with experimental programs to design and interpret experiments to measure interactions in graphitic nanostructured materials. The research is ultimately interested in discovering new mechanisms and functionalities governing these interactions. A non-exhaustive list of potential impact areas includes the stability of graphitic nanostructured systems, unusual effects based on their mutual interactions, and a general theory that can be applicable to materials with dielectric and magnetic response properties explicitly included.
(6/26/09)

Prof. Batzill receives NSF-CAREER, the most prestigeous award from NSF for junior faculty

            Metal oxide ceramics play an important role in modern technology. Often these materials are being modified by dopants to improve properties or induce new functionalities. These dopants can also drastically influence the surface properties and thus give rise to new catalytic properties, alter interfaces that control charge transfer processes or ion diffusion, and may even influence the stability of the bulk phase. Despite the importance of doped metal oxides, their surfaces are not widely investigated. The proposed studies address this shortcoming. We will investigate the surface and interface properties of doped oxides with a surface science approach, i.e. well defined single crystal surfaces are prepared and the physical and chemical properties are being investigated by various techniques, most importantly by photoemission, temperature programmed desorption, and scanning tunneling microscopy.
            Intellectual merit: The question that is the foundation of all further studies of doped metal oxides is: Do the dopants segregate to the surface and do they form surface phases that lower the surface energy? In oxides there is an additional twist to this seemingly straightforward question. Since the surface energy of many oxides varies with the oxygen chemical potential, the segregation behavior may also be strongly dependent on this thermodynamic parameter. Our studies will take this into account by preparing surfaces under different oxygen partial pressures. We will characterize the structural, electronic, and chemical properties of these surface phases in order to gain critical information that influence diverse applications of oxides ranging from heterogeneous catalysis, solid oxide fuel cells, to organic/inorganic hybrid materials for photovoltaic applications. In further studies we focus on the atomic scale structure with particular emphasis on how individual dopants influence the defect formation at surfaces and thus the chemical surface properties. 
            For the proposed work material systems are selected on the basis of industrial importance and demonstrated ability to prepare model systems suitable for surface science investigations. The systems we propose to study are Sb:SnO2 (ATO) with applications as gas sensor, oxidation catalyst, and transparent conducting oxide electrodes; Y:ZrO2 (YSZ) with applications in solid oxide fuel cells and as thermal barrier coatings, and Zr:CeO2 with applications as oxygen storage material in three way exhaust catalysts.
Broader impact: Our society’s need for abundant and clean energy requires a better understanding of materials in order to develop new concepts. This project studies key components of materials for energy conversion and thus will directly contribute to increase our knowledge in an area of importance to our society. The proposed studies draw from concepts of materials science, solid state physics, and surface chemistry and thus provide an ideal training ground for our future engineers and scientists who will have to have increasingly interdisciplinary skills. The project will provide research experiences for undergraduate students and research projects for graduate students. A wider audience will be educated in the concepts of surface and interface science by developing and teaching a new two semester graduate level course in surface science at the University of South Florida. The importance of attracting talented high school students into a science career is also recognized. Atomic scale scanning tunneling microscopy, which is a key technique for this project, is an excellent vehicle to bring modern science to high schools. An outreach program will be established that takes the excitement of ‘seeing’ atoms and translates it into a hand-on learning experience for motivated high school students and provides a module for teachers for the class room.
(06/18/2009)

Xiaomei Jiang, "Development of Semitransparent Flexible Power Foil for window technology in building-integrate photovoltaic products," New Energy Technology and Florida Hightech Corridor

In the course of two and half years, the goal of this project is to produce the prototype flexible semi-transparentflexible power foil (1ft by 1ft dimension) based on organic semiconductors for energy-generating window glass in building-integrate photovoltaic products. The technology developed in the prototype device will be ready for large-scale, roll-to-roll, and low-cost industrial manufacturing. The objective is to get rid of the current complicated and costly processing techniques such as vacuum deposition, area-limited spin-coating process, and photolithography, meanwhile maintaining the device performance in field application environments.
(5/20/09)

Tim Luttrell, Wei-Kun Li, Xue-Qing Gong, and Matthias Batzill, "New directions for atomic steps: Step alignment by grazing incident ion beams on TiO2(110)", Physical Review Letters 102, 166103 (2009)

Grazing incidence low energy ion beams preferentially erode steps with directional components normal to the azimuthal direction of the beam, thus generating step edges aligned along the beam direction. With this kinetic method the fabrication of thermodynamically metastable low index step edge orientations is demonstrated on TiO2(110). The <110> step edge is prepared; enabling its atomic structure determination by scanning tunneling microscopy and density functional theory. A reconstructed atom configuration is revealed, which is reminiscent of the structure of the rutile-TiO2(001)-2x1 face. (5/20/09)

George S. Nolas, “A fundamental study of inorganic type II clathrate open-framework materials,” Department of Energy, Basic Energy Sciences

This proposal presents a plan to investigate the fundamental structural, transport and optical properties of a class of novel materials, inorganic type II clathrates, with structural frameworks built up from group 14 atoms. The framework can be thought of as being constructed by connecting two different polyhdra, dodecahedra (E20) and hexakaidecahedra (E28), where E represent Si or Ge, together with shared faces. The hexakaidecahedra are among the largest "cages" that are found in inorganic clathrates and can incorporate large atoms. The concentration of the inclusion species can be varied thus allowing for a unique “tunability” of properties with structure and chemical compostion. The rich variety of compositional variations represents an ideal material system to investigate the fundamental properties of group 14 elements in novel crystal structures and bonding schemes. The intellectual merit of investigating this material system is very closely tied with the novel structure that these materials exhibit and their corresponding physical, electrical, thermal and optical properties. This research will reveal novel properties that can only be uniquely investigated in type II clathrates, as will be described in the proposal.

In this proposed work, a fundamental understanding of the type II clathrate system that elucidates the correlation between the growth parameters and the physical properties of the material will be developed. The proposed work will lead to a clear understanding of the unique structure-property relationships in these materials. These materials can be thought as “designer materials” since they can be tuned through the ability to fill or partially fill the polyhedra resulting in compounds with similar crystal structures but different physical properties. The proposed investigation will also have a broader impact in potential technological applications. It will allow for the development of a knowledge-base into the important research for future applications of electronic materials such as opto-electronic applications (direct, tunable gap semiconductors) and thermoelectrics (solid-state power generation) that directly addresses Department of Energy goals. This will have direct impact to national needs (such as new silicon-based opto-electronic materials and small-scale power generation), for example on needs such as thermoelectric automotive waste-heat recovery and solar energy harvesting. In addition, the extensive training of graduate and undergraduate students will benefit greatly these future research scientists. They will receive training in fundamental condensed matter physics, materials science and solid-state chemistry.

Srikanth Hariharan and George S. Nolas, “Nanocomposite clathrate materials for dual functional thermomagnetic and thermoelectric cooling applications,” Army Research Office

This project brings together two established investigators at the University of South Florida in the fields of magnetism (Dr. Hariharan Srikanth) and thermoelectrics (Dr. George Nolas) to jointly address important materials science issues for improving the efficiency and operational characteristics of coolers for IR detectors. IR detectors are vital components for the Army as they are used in night vision, thermal imaging and threat detection systems. While conventional thermoelectric coolers work well down to 150K, there is a need for cooling further to 80K and below. This underscores the need for considering new materials and strategies for developing efficient solid-state coolers with a broad range in working temperature. In this proposal, the investigators outline a novel approach based on combination of thermomagnetic and thermoelectric properties in engineered nanocomposites of rare-earth doped clathrate materials. The research would focus on synthesis of new bulk and nanocomposite forms of clathrates and evaluating their electrical, thermal and magnetic properties in the context of cooling applications. Specifically, experiments will be designed to critically examine the influence of magnetic fields on the charge carriers through the phenomenon of Nernst effect, as well as the magnetic entropy of the spin system. Magneto-caloric effect (MCE) experiments will be done to explore the latter in nanocomposite clathrates that are mixed with lanthanides and other superparamagnetic nanoparticles. The fundamental idea is to synthesize new phases distinct from the bulk clathrate system and promote multiple, order-disorder or metamagnetic transitions over a broad range in temperature (20K to 300K). This is achieved in the proposed nanocomposite clathrate materials by utilizing mixtures of lanthanide elements with different magnetic transition temperatures in the chosen range and also chemically synthesized, superparamagnetic iron oxide nanoparticles in which the blocking temperature is tuned through particle size and inter-particle interactions. Both the Nernst effect signal and MCE are expected to be significantly larger in these proposed materials and thus would allow for testing the viability of these materials as dual functional thermomagnetic and thermoelectric elements The proposed materials research is radically new and, to our knowledge, has not been attempted before with clathrates or other diluted magnetic semiconductor systems. Thus the proposed research also has the chance of broader impact in fields such as Spintronics Fundamental advancement of materials science and physics of thermomagnetic and thermoelectric phenomena are anticipated as well as training of high quality students in DoDspecific research.

MK Kim, “Digital holography of total internal reflection for quantitative phase microscopy of cell-substrate adhesion,” National Science Foundation, BISH (Biophotonics Advanced Imaging and Sensing for Human Health)

We present a program of research to develop Total Internal Reflection digital Holographic Microscopy (TIRHM) for quantitative phase microscopy of cellular adhesion layers. Cell-substrate interactions including attachment, spreading, morphology changes, and migration require a complex series of events to occur in a regulated and integrated manner. To date, the primary tools for imaging these processes such as TIR fluorescence microscopy or interference reflection microscopy, lack quantitative morphological information of the interface or the ability to isolate the interface by optical sectioning. With TIRHM, we propose to develop and apply techniques of digital holography to generate quantitatively precise images of the cell-substrate interface. TIRHM makes use of the phase shift that accompanies frustrated total internal reflection (fTIR) when an evanescent field of TIR is interrupted by the presence of another interface or inhomogeneity. For example, when a cellular specimen placed on a prism is illuminated from below the prism surface, the phase front of reflected light is modulated by the presence of cellular adhesion, which is recorded and reconstructed through digital holography process. The proposed project builds upon the successes of quantitative phase microscopy by digital holography developed during a previous NSF-funded project, where we have generated high-resolution images of cellular and intracellular structures with few-nanometer optical thickness resolution. These are exciting additions to unique and versatile imaging capabilities demonstrated by recent developments in digital holography. Total internal reflection holographic microscopy (TIRHM) will provide an unambiguous quantitative profile of cellular surfaces and help researchers better understand fundamental aspects of cellular motion, such as adhesion, migration, and traction force.