Emergence of New Mechanical Functionality in Materials via Size Reduction

Abstract

Julia R. Greer received her S.B. in Chemical Engineering from the Massachusetts Institute of Technology (1997) and a Ph.D. in Materials Science from Stanford University, where she worked on the nanoscale plasticity of gold with W. D. Nix (2005). She also worked at Intel Corporation in Mask Operations (2000–03) and was a post‐doctoral fellow at the Palo Alto Research Center (2005–07), where she worked on organic flexible electronics with R. A. Street. Greer is a recipient of TR‐35, Technology Review's Top Young Innovator award (2008), a NSF CAREER Award (2007), a Gold Materials Research Society Graduate Student Award (2004), and an American Association of University Women Fellowship (2003). Julia joined Caltech's Materials Science department in 2007 where she is developing innovative experimental techniques to assess mechanical properties of nanometer‐sized materials. One such approach involves the fabrication of nanopillars with different initial microstructures and diameters between 25 nm and 1 µm by using focused ion beam and electron‐beam lithography microfabrication. The mechanical response of these pillars is subsequently measured in a custom‐built in situ mechanical deformation instrument, SEMentor, comprising a scanning electron microscope and a nanoindenter. Read our interview with Prof. Greer on MaterialsViews.commagnified image

Anisotropic size effect in strength in coherent nanowires with tilted twins

“…Characteristic dimensions of the sample include wire width W, wire thickness h, and twin spacing λ. We note that with current experimental techniques in nanoscale tensile testing, [22][23][24] it should be feasible to fabricate NWs with tilted twins shown in Fig. 1(a).…”

Mechanical annealing model of damage in arrays of nanopillars

“…The materials under investigation are for instance nickel, gold, copper, molybdenum and aluminium. These experiments on nano-sized pillars confirm substantial strength-increase via the size reduction of the sample [3]. In works [4,5] concerning compression tests of nanosized nickel and molybdenum pillars a process called "mechanical annealing" has been observed.…”

“…In recent years many tensile and compressive experiments have been performed on nano-and microscale metallic pillars [1][2][3]. The materials under investigation are for instance nickel, gold, copper, molybdenum and aluminium.…”

“…Studies on arrays of free-standing nanopillars subjected to uniaxial microcompression reveal the potential applicability of nanopillars as components for the fabrication of micro-and nano-electromechanical systems, micro-actuators or optoelectronic devices [3,6]. This work concerns a partial damage process in a set of pillars assembled to a flat and rigid substrate.…”

Heterogeneous dislocation nucleation from surfaces and interfaces as governing plasticity mechanism in nanoscale metals

“…We perform uniaxial compression tests at a constant nominal strain rate in two different instruments: (i) Agilent G200 nanoindenter (Agilent, Santa Clara, CA) with a 7-lm flat punch in the Dynamic Contact Module and (ii) SEMentor, a custom-built in situ nanomechanical deformation instrument fitted with a ;10-lm diamond flat punch. 40 Although both machines are inherently load controlled, in our experiments a custom-written software method utilizing a feedback loop controls the applied load to maintain a constant displacement rate, and therefore a constant nominal strain rate. We conducted the compression tests at a series of strain rates, ranging between ;10 À4 and ;10 0 s…”