Our research focuses on the science and technology of nonlinear optical materials.  The work straddles materials science, physics, and optical engineering. We have three areas of current interest:

1. Multiferroics: Multiferroics are an exciting class of materials that have co-existing ferroelectricity and magnetism.   To study the coupled dynamics of electrical and magnetic domains, we are performing real-time nonlinear optical probing with simultaneous measurement of coupled properties such as magnetoelectric effect, electro-optic and magneto-optic effects, hysteresis, and dielectric spectroscopy.  The nanoscale structure of single domain walls is studied using scanning probe techniques such as piezoelectric force-, magnetic force-, nonlinear dielectric-, electric force- , and near-field scanning optical microscopies. Modeling tools include Ginzburg-Landau phenomenology, finite element method, and electromagnetic simulations.
2. Nonlinear optical devices:  We are developing a new class of devices by integrating diverse optical functionalities, such as optical frequency conversion, beam steering, dynamic focusing, beam shaping and high-speed switching, on a single ferroelectric chip by microengineering ferroelectric domains into gratings, lenses, prisms, and other arbitrary shapes.
3. Hybrid semiconductor-metal-oxide nanostructures:  In a recent breakthrough with Badding group (Chemistry), we have demonstrated microstructured silica optical fibers which contain hundreds of extreme aspect ratio (~105) semiconductor and metal-filled nanowires in a highly periodic array.  We are currently characterizing light guiding and nonlinear optical responses of these hybrid fibers. 

 Experimental tools include ultrafast femtosecond lasers, electro-optics and fiber optics, scanning probe microscopies, dielectric and magnetic measurements, clean room, cryogenics, and simulations based on home-written MATLAB as well as commercial codes.

Professor Trolier-McKinstry’s research interests are centered around structure-processing-property relationships in electroceramics. This includes work on dielectric and piezoelectric thin films, texture development in piezoelectric ceramics, and spectroscopic ellipsometry.
In the piezoelectric films area, Prof. Trolier-McKinstry is developing sensors and actuators that are compatible with CMOS electronics (and hence low driving voltages).  Her group has approached this by trying to maximize the figure of merit for the material response through control of composition, crystallographic orientation, grain size, and composite connectivity.  The work includes fundamental studies on the factors that control domain wall contributions to the properties and the role of octahedral tilt in influencing response.  More applied research ranges from damage-free patterning approaches of complex oxides, to fabrication of piezoelectric  microelectromechanical systems, including accelerometers, pumps, switches, adaptive optics components, and ultrasound systems with close-coupled electronics.  They are also working on preparing high strain actuator films at low processing temperatures (< 400oC) via pulsed laser crystallization.
Bulk and thin film dielectrics are of interest for on and off-chip decoupling capacitors, as well as tunable components.  Prof. Trolier-McKinstry’s group emphasizes the development of a wide range of dielectrics covering the permittivity range from 30 to 3000.  Recent work has focused on using Rayleigh and Preisach methods to quantify the properties over a wide range of ac and dc electric fields.  The same tools are also being used to study reliability and the relative roles of various defect types in controlling the properties.
Texture development can be used to improve electromechanical response in bulk piezoelectrics.  Joint programs with Prof. Messing have demonstrated that templated grain growth can be utilized to achieve textured ceramics with properties intermediate between those of randomly axed ceramics and single crystals. 

Professor Chung is interested in the development of new polymer chemistry that can lead to new materials with unique chemical and physical properties for applications. In his recent research activities, he has been focusing on the technologies relative to energy and environmental issues. Several current research projects include (a) functionalization of polyolefins (PE, PP, EP, etc.) via the combination of metallocene catalysts and reactive comonomers and chain transfer agents to prepare polyolefins containing side-chain or chain-end functional groups, (b) synthesis of long chain branched polyolefin, including i-PP and s-PS, and studying their thin film processing, (c) studying control radical polymerization based on new functional borane/oxygen initiators to prepare functional fluoropolymers, (d) developing new energy storage technology on the polymer thin film capacitors with high energy density, high power density, and low loss, (e) studying new polyolefin-based ion conductors that show high ion conductivity, good fuel selectivity, long term stability, and cost effective, (f) investigating new polyolefin-based oil superabsorbent (oil-SAP) for oil spill recovery,  (g) synthesizing boron substituted carbon (B/C) materials and doped derivatives for hydrogen storage. My group at Penn State is recognized as a leading research group in the functionalization of polyolefin and fluoropolymers with more than 180 papers and 50 US and international patents published in the past 20 years.

The Messing group is currently focused on developing processes for producing optically transparent ceramics (e.g. Nd-doped YAG), high performance piezoelectrics, and solid state grown single crystals. The strategy is to control sintering and grain growth processes by first establishing a fundamental understanding of how powder synthesis, ceramic phase formation, and powder shaping influence the achievement of specific microstructure-property objectives. We are expert in powder synthesis by spray pyrolysis and phase formation from solution precursors. It has been shown that phase separation in sol gel and precursor system formation plays a major role on phase formation during heating in the alumina, mullite, and lead magnesium niobate systems. In some cases we have developed successful strategies to induce and control phase development and transformation by solid state seeding. We have also carried out extensive studies on the sintering of alumina, mullite, and PMN-PT. In a series of papers we reported how stresses evolve in co-sintered SOFCs and LTCCs. As a result of these studies cyclic loading dilatometry (CLD) has been established as a reliable tool for measuring the viscosity of sintering systems. In the late 90s we developed a novel templated grain growth (TGG) process to obtain oriented microstructures of unprecedented control. In this process we align or position template particles that act as preferred growth sites. Uniquely textured ceramics have been produced by TGG. The properties of texured PMN-PT approach those of single crystals. We use a similar strategy to grow single crystals of PMN-PT, YAG, and BaTiO3 from a dense ceramics by the solid state conversion process. Some of the materials we have studied include mullite, alumina, barium titanate, lead magnesium niobate, strontium barium niobate, sodium bismuth titanate, and yttrium aluminum garnet.

Dr. Chen’s main research interest is in the fundamental understanding of the thermodynamics and kinetics of phase transformations and mesoscale microstructure evolution in bulk solid and thin films using computer simulations. Essentially all engineering materials contain certain types of microstructures, and our success of designing new materials is largely dependent on our ability to control them. Microstructure is a general term that refers to a spatial distribution of structural features that can be phases of different compositions and/or crystal structures, or grains of different orientations, or domains of different structural variants, or domains of different electrical or magnetic polarization, as well as structural defects such as dislocations. It is the size, shape, and spatial arrangement of the local structural features that determine the physical properties of a material such as mechanical, electrical, magnetic and optical properties. For the last decade, Dr. Chen’s group at Penn State is particularly active in developing phase-field models for microstructure evolution during various materials processes including grain growth, coherent precipitation, ferroelectric domain formation, particle coarsening, domain structure evolution in thin films, phase transformation in the presence of structural defects, and effect of stress on microstructure evolution. Current research focus is on the effect of stress/strain on ferroelectric phase transitions and domain structure evolution in ferroelectric and multiferroic thin films, domain structures in ferromagnetic shape memory alloys, electrode microstructure evolution in solid oxide fuel cells and batteries, precipitate microstructure evolution in Al-, Mg-, Ti- and Ni-alloys, strain-dominated morphological evolution, effect of defects such as dislocations on microstructure evolution. Dr. Chen’s group collaborates extensively with experimentalists and with industry.