Department of Materials Science and Engineering

After an undergraduate degree in Music and a brief career as a professional musician and music teacher, Shefford P. Baker studied Mechanical Engineering and Materials Science. He received his PhD in Materials Science and Engineering at Stanford University in 1993, was a staff scientist at the Max-Planck-Institut für Metallforschung in Stuttgart from 1993 to 1997 and joined the Cornell faculty in 1998. He was Visiting Professor at the Faculté des Sciences et Techniques de Saint Jérome, Université Paul Cézanne, Marseille, in summer 2006. Baker has received several teaching awards at Cornell.

Baker’s research focuses on the unique mechanical properties of materials having microstructural or dimensional length scales in the nanometer regime. Work in the group can be divided into two broad areas.

Thin Films and Nanopatterned Structures are the basic building blocks of micro- and nano-fabricated devices, but may have mechanical properties that are very different from those of the same materials in bulk form. We want to understand (and utilize) these unique properties. We produce films with good control of interface chemistry and composition using high- and ultra-high vacuum physical vapor deposition techniques; characterize their microstructures using electron backscattered diffraction, transmission electron microscopy, and many other methods; and study their thermomechanical behavior using substrate curvature, x-ray diffraction, and others. We model the microstructure and stress states in detail in order to understand processing-structure-properties relationships. Recent achievements include discovery of a new microstructure in Ta thin films and characterization of the phase transformation that produces it, x-ray studies of stress states and relaxation in different texture components in thin metal films, dislocation dynamics simulations and analytical modeling of dislocation structures in thin layers, and quantitative measurements of bonding at interfaces by time-dependent delamination experiments.

Nanocontact Measurements are a powerful method for interrogating mechanical behavior on an extremely fine scale. Recently, with a team of collaborators, we have been using these methods to investigate structure-property relationships in the lamellar and interlamellar regions in trabecular bone as a function of age and vitamin D deficiency.

• Stresses and Deformation Mechanisms in Thin Metal Films: Combining Modeling with Experiments. In this NSF-funded project, we are studying how the evolution of grain and dislocation structures affects stress states, strength and strain hardening in thin metal films. We use discrete dislocation dynamics to study dislocation structures and compare the results with experimental measurements of microstructure and stresses.

• Microstructure and Mechanical Behavior of Tantalum Thin Films: Ta is an amazingly versatile and useful material in micro- and nano-fabricated devices. In this NSF-funded project, we are analyzing the long-range orientation gradients and discontinuous grain boundary structure in a new microstructure that we discovered in phase-transformed Ta thin films using experimental and computational methods.

• Stresses and Deformation in Different Texture Components in Thin Films: Thin films often form with more than one group of preferred crystallographic orientations, or textures. Since most materials are highly anisotropic at the nanoscale, these differently-oriented components have very different properties. With support from Applied Materials Corp. we study how these texture components behave in-situ using x-ray diffraction at the Cornell High Energy Synchrotron Source.

• A Materials Research Approach to Bone: Nanometer Scale Microstructure and Mechanical Properties: Bone is a complex composite material with structure and organization at many length scales. In this NSF-funded project, we are using nanoindentation to understand the structure-properties in the constituents on the micrometer length scale and their dependence on species, age, and nutrition.

* Heiko Th. Hesemann, Peter Müllner, Oliver Kraft, David Nowak, Shefford P. Baker, Ken Finkelstein, and Eduard Arzt, “Texture Dependence of the martensitic Transformation in Cobalt Thin Films,” Scripta Materialia, 48(8) 1129-1133 (2003)

Shefford P. Baker, Rose-Marie Keller-Flaig, and Jonathan B. Shu, “Bauschinger Effect and Anomalous Deformation Induced by Oxygen in Passivated Thin Cu Films on Substrates” Acta Materialia, 51(10) 3019-3036 (2003)

Prita Pant, K.W. Schwarz, and Shefford P. Baker, “Dislocation Interactions in Thin FCC Metal Films,” Acta Materialia, 51(11) 3243-3258 (2003)

Jonathan B. Shu, Susan B. Clyburn, Thomas E. Mates, and Shefford P. Baker, “Effect of Oxygen on the Thermomechanical Behavior of Passivated Cu Thin Films,’ Journal of Materials Research, 18(9) 2122-2134 (2003)

Mengzhi Pang and Shefford P. Baker, “Quantitative Measurements of Subcritical Debonding of Cu Films from Glass Substrates” Journal of Materials Research, 20(9) 2420-2431 (2005)

Eve Donnnelly, Shefford P. Baker, Adele L. Boskey, and Marjolein C.H. van der Meulen, “Effects of surface roughness and maximum load on the mechanical properties of cancellous bone measured by nanoindentation” Journal of Biomedical Materials Research, 77A 426-435 (2006)

Eve Donnelly, Rebecca M. Williams, Seth A. Downs, Michelle E. Dickinson, Shefford P. Baker, and Marjolein C.H. van der Meulen, “Quasistatic and dynamic nanomechanical properties of cancellous bone tissue relate to collagen content and organization” Journal of Materials Research, 21(8) 2106-2117 (2006)

* D. E. Nowak, D. R. Blasini, A. M. Vodnick, B. Blank, M. W. Tate, A. Deyhim, D.-M. Smilgies, H. Abruña, S. M. Gruner, and S. P. Baker, “A six-circle diffractometer with atmosphere- and temperature-controlled sample stage and area and line detectors for use in the G2 experimental station at CHESS” Review of Scientific Instruments, 77 (11) 113301 (2006)

Robert Knepper, Blake Stevens, and Shefford P. Baker, “Effect of oxygen on the thermomechanical behavior of tantalum thin films during the β-α phase transformation” Journal of Applied Physics 100(12) 123508 (2006)

Cormac J. Byrne, Aaron M. Kueck, Shefford P. Baker, and Paul H. Steen “In-situ manipulation of cooling rates during planar-flow melt-spinning processing” Materials Science and Engineering A 459 172-181 (2007)

Robert Knepper and Shefford P. Baker, “Coefficient of thermal expansion and biaxial elastic modulus of β phase tantalum thin films” Applied Physics Letters, 90, 181908 (2007)

Ray S. Fertig III

Aaron M. Vodnick

Michael D. Lawrence