MSE Seminar Series: Frank DelRio
Friday, February 14, 2014
1:00 p.m.-2:00 p.m.
Room 2110 Chemical and Nuclear Engineering Building
301 405 5240
From Si Microdevices to PEG Nanocoatings: Exploring Advanced Materials via Nanomechanics
Materials Measurement Science Division
Nanomechanical Properties Group
Material Measurement Laboratory
Many advanced materials are intended for use in small scale applications, for example, microelectronics, microelectromechanical systems (MEMS), photonics, biotechnology, and magnetic storage, or may be available only in small volumes, for example, during materials development. Developing or optimizing such materials and their processing methods thus requires measurements of structure and properties at small scales. However, establishing processing-structure-mechanical properties linkages at small scales is difficult: Not only are the involved loads and displacements small, making measurement difficult, but issues of specimen gripping and loading alignment, which are also often problematic at large scales, are made more difficult as well. In this presentation, I will summarize recent work on two projects in the Nanomechanical Properties Group at NIST Gaithersburg aimed at addressing these measurement needs. The first project investigated the deformation and fracture strength of single-crystal silicon via the NIST “theta-like” test specimen, with a particular emphasis on using the specimens to elucidate the effects of sample geometry and fabrication technique. Three sets of MEMS-scale single-crystal silicon theta specimens were fabricated using two deep reactive ion etching recipes and a temperature-controlled cryogenic plasma etching recipe, each set resulting in a different specimen surface quality. Each sample was tested by instrumented indentation and finite element analysis (FEA) was used to determine sample strength. Equations developed via FEA translated load-displacement response at the load-point into stress-strain behavior across the theta web region. Strength values for each set of specimens were examined via Weibull statistics. The resulting surface roughness for each etching recipe was determined by atomic force microscopy (AFM) and sample fragments were examined via field-emission scanning electron microscopy. Surface roughness topography and fracture origins located during fractographic analysis of tested samples were compared with strength-limiting flaw size calculations. The second project explored the nanomechanical properties of polyethylene glycol (PEG) coatings on gold surfaces, with a particular emphasis on the homogeneity of both PEG surface coverage and properties, as these determine the efficacy of PEG-coated nanoparticles as cancer treatments. AFM and atomic force spectroscopy (AFS) were used to study the morphology and mechanical properties of thiol-functionalized PEG coatings on gold substrates in solution and in air. AFM was used to investigate the morphology of PEG coatings as a function of concentration and molecular weight; the commonly-observed coverage was in the form of sparse brush-like islands. AFS was used to study the mechanical properties of PEG coatings in compression and tension as a function of molecular weight. Together, the various models were used to map a number of mechanical properties over individual PEG islands, which enabled a statistical approach for assessing the heterogeneity of PEG properties.
About the speaker:
Frank W. DelRio received a B.S. in Mechanical Engineering from Carnegie Mellon University in 1998, after which he worked as a Product Support Engineer at C&D Zodiac, first in Huntington Beach, CA and later in São José dos Campos, Brazil. In 2001, he returned to academia, ultimately receiving an M.S. in Mechanical Engineering from Boise State University in 2002 and a Ph.D. in Mechanical Engineering from the University of Colorado at Boulder in 2006. After working as a postdoctoral researcher in the Department of Chemical Engineering at the University of California, Berkeley, he joined the Material Measurement Laboratory at the National Institute of Standards and Technology (NIST) in Gaithersburg, MD as a leader for the Nanoscale Strength Measurements and Standards project. At NIST, Frank has been recognized with several awards and honors, most recently the Presidential Early Career Award for Scientists and Engineers in 2011, the Adhesion Society Outstanding Young Adhesion Scientist Award in 2012, and the Maryland Academy of Sciences Allan C. Davis Outstanding Young Engineer Award in 2013.