Micromechanics; Mechanics & Materials Issues in Optics Manufacturing; Defect Generation During Crystal Growth
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.
- Lambropoulos JC, Jolly MR, Amsden CA, Sinicropi M, Diakomihalis D, Jacobs SD. (1989). The thermal conductivity of thin dielectric films, J. Appl. Phys. 66, pp. 4230-4242.
- Lambropoulos JC, Fang T, Funkenbusch PD, Jacobs SD, Cumbo M, Golini D. (1996). Surface microroughness of optical glasses under deterministic microgrinding, Applied Optics 35, pp. 4448-4462.
- Lambropoulos JC, Xu S, Fang T. (1996). Constitutive law for the densification of fused silica, with applications in polishing and microgrinding, J. Amer. Ceram. Soc. 79, pp. 1441-1452.
- Zheng L, Lambropoulos JC, Schmid AW. (2004). UV-laser-induced densification of fused silica: A molecular dynamics study. J. Non-Crystall. Solids 347, pp.144-152.
- Cox GP, Marshall KL, Lambropoulos JC, Leitch M, Fromen C, Jacobs SD. (2009). Modeling the effects of microencapsulation on the electro-optic behavior of polymer cholesteric liquid crystal flakes, J. Appl. Phys. 106, Article Number 124911.
- Lambropoulos JC, Chunlin Miao C, Jacobs SD. (2010) Magnetic field effects on shear and normal stresses in magnetorheological finishing, Optics Express 18, 19713-19723.
- Rui Shen R, Shafrir SN, Miao C, Mimi Wang M, Lambropoulos JC, Jacobs SD, Yang H. (2010). Synthesis and corrosion study of zirconia coated carbonyl iron particles, J. Colloids and Interface Science 342, 49-56.
- Lambropoulos JC. 2001-2011. Polysilicon and EDF Silicon (Shaped) for solar applications, Encyclopedia of Materials: Science and Technology (Elsevier Ltd), pp. 7718-7724. Editors-in-Chief: K. H. Jürgen Buschow, Robert W. Cahn, Merton C. Flemings, Bernard Ilschner (print), Edward J. Kramer, Subhash Mahajan, and Patrick Veyssière.
- Mehrotra K, Howard HP, Jacobs SD, Lambropoulos JC. (2011). Nanoindentation of high-aspect ratio pillar structures on optical multilayer dielectric diffraction gratings, AIP Advances 1, 042179.
- Oliver, J B; Kupinski, P; Rigatti, A L; Schmid, A W; Lambropoulos, J C; Papernov, S; Kozlov, A; Smith, C; Hand, R D, Stress compensation in hafnia/silica optical coatings by inclusion of alumina layers, Optics Express, Vol. 20 Issue 15, pp.16596-16610 (2012).