U of R ME : Faculty-Lambropoulos

John C. Lambropoulos

Professor of Mechanical Engineering and Materials Science
Director, Materials Science Program
Senior Scientist in the Laboratory for Laser Energetics
Hopeman 236
Phone: (585) 275-4070, Fax: (585) 256-2509, jcl@me.rochester.edu

Ph.D., Harvard University (1984), M.S., Harvard University (1981), Sc.B., Brown University (1980)

My research area is micromechanics, which bridges materials science and solid mechanics. I am interested in describing the macroscopic behavior of solids by examining their underlying microstructural features, and how mechanical, electrical, and/or optical fields affect the response of homogeneous or heterogeneous materials.

Mechanics & Materials Issues in Optics Manufacturing

With colleagues in the Department of Mechanical Engineering, Institute of Optics, and the Laboratory for Laser Energetics, we study the optimization of optics manufacturing techniques such as deterministic microgrinding, loose abrasive lapping, magnetorheological finishing, and loose abrasive finishing of optical glasses and ceramics. In our approach, we couple mechanics (length scales at the level of 1 m to 1 mm) and materials science (length scales from 1 mm to 1 nm) using extensive experimentation and numerical modeling techniques. Specific topics include material removal mechanisms, subsurface damage, surface microroughness, processing-induced residual stresses in optical glasses, crystals, and polycrystals.

Defect Generation During Crystal Growth

Thermal stresses, developing during the growth from the melt of crystals such as Si or GaAs, induce the multiplication of dislocations, thus deteriorating the optoelectronic properties of the grown crystals. Our research uses numerical models to correlate design parameters (such as crystal growth rate, crystal size, temperature profile) with the induced stresses and the corresponding dislocation densities in an effort to minimize the density of the defects and maximize the crystal size and growth rate.

Thermomechanical/Laser Damage & Fracture in Bulk Solids, Films & Multilayers

Thin films and multilayers are often exposed to complex thermomechanical loads, so that both the thermal and mechanical material properties affect the critical levels that lead to damage. Specific applications include (i) the laser damage of thin optical films, (ii) the thermally induced fracture of optical materials used in high-average-power solid state lasers, and (iii) the enhancement of the fracture toughness of bulk brittle components via residually stressed thin films. In collaboration with colleagues in the Laboratory for Laser Energetics, we have developed experimental techniques to measure the thermal conductivity of thin films and developed models to correlate the thin film thermal conductivity with the film microstructure. These measurements are used in numerical models of laser damage, either by continuum models or molecular dynamics.

Deformation & Fracture of Brittle Materials

To optimize designs in which optical glasses or structural ceramics are used, we measure the mechanical properties of these brittle materials using bulk, microindentation and nanoindentation techniques, with particular attention to near-surface mechanical properties.

Representative Publications

The Thermal Conductivity of Thin Dielectric Films (with M. R. Jolly, C. A. Amsden, M. Sinicropi, D. Diakomihalis, and S. D. Jacobs), J. Appl. Phys., Vol.66, pp.4230-4242, 1989.
Thermoelastic Analysis of Dislocation Generation During Edge-Defined Film-Fed Growth of Polygonal Shells (with Chien-Hsing Wu) J. Crystal Growth, Vol.155, pp.38-46, 1995.
Constitutive Law for the Densification of Fused Silica, with Applications in Polishing and Microgrinding (with Su Xu and Tong Fang), J. Amer. Ceram. Soc. , Vol.79, pp.1441-1452, 1995.
Surface Microroughness of Optical Glasses Under Deterministic Microgrinding (with T. Fang, P. Funkenbusch, S. Jacobs, M. Cumbo and D. Golini), Applied Optics, Vol.35, pp.4448-4462, 1996.
Edge-defined Film-Fed Growth (EFG) of Silicon for Photovoltaic Applications, Encyclopedia of Advanced Materials Science and Technology, 11 volumes, Elsevier Science, 2001.
Spherical cavity expansion in densifying material (with Kai Xin), J. Appl. Phys., Vol.94, pp. 6437-6441, 2003.
UV-laser-induced densification of fused silica: A molecular dynamics study (with L. Zheng and A. W. Schmid), J. Non-Crystall. Solids, Vol.347, pp.144-152, 2004.
Subsurface damage in some single crystalline materials (with J. Randi and S. D. Jacobs), Applied Optics, Vol. 44, pp. 2241-2249, 2005.
Molecular dynamics study of UV-laser-induced densification of fused silica. II. Effects of laser pulse duration, pressure, and temperature, and comparison with pressure-induced densification (with L. Zheng and A. W. Schmid), J. Non-Crystall. Solids, Vol.351, pp.3271-3278, 2005.