Materials Science and Engineering A 538 (2012) 89–97 Contents lists available at SciVerse ScienceDirect Materials Science and Engineering A jo ur n al hom epage: www.elsevier.com/locate/msea Plasticity of indium nanostructures as revealed by synchrotron X-ray microdiffraction Arief Suriadi Budiman a , Gyuhyon Lee b , Michael J. Burek b,1 , Dongchan Jang c , Seung Min J. Han e , Nobumichi Tamura f , Martin Kunz f , Julia R. Greer c , Ting Y. Tsui b,∗ a Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM 87545, USA b Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, ON N2L 3G1, Canada c Division of Engineering and Applied Science, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, USA e Graduate School of Energy Environment Water Sustainability, Korea Advanced Institute of Science and Technology, 373-1 Guseong Dong, Yuseong Gu, Daejeon 305-701, Republic of Korea f Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA a r t i c l e i n f o Article history: Received 10 August 2011 Received in revised form 9 December 2011 Accepted 9 January 2012 Available online 17 January 2012 Keywords: Indium Nanopillar X-ray microdiffraction Microstructure Dislocation a b s t r a c t Indium columnar structures with diameters near 1 m were deformed by uniaxial compression at strain rates of approximately 0.01 and 0.001 s -1 . Defect density evolution in the nanopillars was evaluated by applying synchrotron Laue X-ray microdiffraction (SLXRD) on the same specimens before and after deformation. Results of the SLXRD measurements indicate that the dislocation density increases as a result of mechanical deformation and is a strong function of strain rate. These results suggest that the rate of defect generation during the compression tests exceeds the rate of defect annihilation, implying that plasticity in these indium nanostructures commences via dislocation multiplication rather than nucleation processes. This is in contrast with the behaviors of other materials at the nanoscale, such as, gold, tin, molybdenum, and bismuth. A hypothesis based on the dislocation mean-free-path prior to the multiplication process is proposed to explain this variance. © 2012 Elsevier B.V. All rights reserved. 1. Introduction With the increased insertion of nanoscale electronic and pho- tonic devices into technological applications, understanding the mechanical behavior of small scale structures becomes increasingly important to ensure life-time and reliability of these products. In the context of mechanical properties, one of the important scientific discoveries was the emergent size dependence of yield strength in metals once their dimensions are reduced to the micron and sub-micron scales [1–9]. For example, as the dimensions of the fea- ture size in face-centered cubic metal like Au are reduced to less than 1 m, their yield strengths may increase by ∼80 times [10]. One of the possible explanations for this size dependence deeply in the sub-micron regime is the dislocation starvation effect. The premise of this theory is that as the dimension of single crystals are reduced to nanometer scale, mobile dislocations glide along their slip planes to the free surfaces relatively unimpeded, and ∗ Corresponding author. Tel.: +1 519 888 4567x38404; fax: +1 519 746 4979. E-mail address: tttsui@uwaterloo.ca (T.Y. Tsui). 1 New address: School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, MA 02138, USA. therefore annihilate at the free surface without significant interac- tions with other defects. The result is a net reduction in the mobile dislocation density within the nanostructure during mechanical deformation. As the sample is further deformed, the few remain- ing mobile dislocations cannot accommodate the imposed plastic strain, and therefore new dislocations have to be nucleated, which requires high stresses. As the nanostructures get smaller, the number of available dislocation sources decreases, and their oper- ation strength increases, which leads to the ever higher stresses in smaller samples [1,3,9]. This notion of dislocation starvation, coined by the authors as “mechanical annealing”, has also been demonstrated via in situ compression of single crystalline nickel pillars [6]. Shan et al. [6] used an in situ transmission electron microscope (TEM) nanoindenter to illustrate this size effect and showed that the initial dislocations in a focused ion beam (FIB) -fabricated 160 nm diameter nickel pillar completely disappear upon mechanical deformation. Budiman et al. [11] used a non- destructive synchrotron Laue X-ray microdiffraction technique to perform ex situ characterization of the defect density within gold nanopillars before and after the compression tests. These SLXRD results showed no detectable increase of the Laue spot diffrac- tion peak broadening, which indicates there is no net increase of defect density in the small-scale structures after the mechanical 0921-5093/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2012.01.017