Spectroscopy plays an important role in revealing the relationship between the physical properties of materials and their nanoscale structure. Individually or in concert, spectroscopic methods are available to examine inter- and intra-molecular interactions, the organization of molecules, the charge transport properties of materials, chemical composition, oxidation state, molecular structure, local coordination environment and molecular dynamical behavior. Spectroscopic methods of characterization are particularly important for the study of non-crystalline materials that cannot be examined easily by diffraction techniques. Materials of current interest to the Francis group include photo-conducting polymers, inorganic-organic composites, molecular aggregates and nanoparticulates.
The photo-physics of electron-hole transport and recombination are studied by examining the transient photo-response of thin films of p- and n-type polymers to nano-second laser excitation. Photo-induced paramagnetism associated with free and bound electrons and holes in semiconductors can also provide information about carrier dynamical behavior. Charge separation and recombination at the p/n junction between polymer films is of interest because the process is of pivotal importance to the creation of efficient thin film polymer photonic devices.
Composites are materials whose properties arise from the interaction of their several components. Composite materials are of interest because they provide a route to a unique and technologically important combination of properties in a single material. Basic research is conducted to better understand how the properties of individual components are modified by their inclusion in a composite. Some of the material properties that may be manipulated in a composite material are magnetic behavior, charge transport phenomena, photochemical properties and nonlinear optical (NLO) behavior. We are studying composite materials formed by the insertion of guest molecules into microporous silica glasses, zeolites and layered materials, such as silicates and transition metal chalcogenides. The inorganic hosts impose a particular organization of the guest molecules through spatial constraints and chemical interactions. A project of current interest involves the creation of asymmetric centers in solids by intercalation of polar or chiral molecules.
Li Tan, M. David Curtis, A. H. Francis. "Charge Transfer in Ferrocene-bearing Conjugated Polymers and Applications in Organic Bi-Layer Photocells", Macromolecules (2002)
X. Weng, S. J. Clarke, W. Ye, S. Kumar, R. S Goldman, A. Daniel, R. Clarke, J. Holt, J. Sipowska, A. Francis, V. Rotberg. "Evolution of Microstructure and Optical Optical Properties of Ion-Beam Synthesized GaAsN Nanostructures", J. Applied Physics, (2002).
T. Coradin, R. Clement, E. Amoual, J. Holt, A. Francis. "Intercalate Aggregation and NLO Properties of Intercalated Lamellar Chalcogeno Phosphate Lattices", Mat. Res. Soc. Symp. Proc. 458 (1999) 91-97.
T Rudalevige, AH Francis, R Zand. "Spectroscopic Studies of Fullerene Aggregates" J. Phys. Chem. A 1998, 102, 9797.