On-chip tensile testing of nanoscale silicon free-standing beams
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Enrique Escobedo-Cousin and Sarah H. Olsen Newcastle University, School of Electrical, Electronic & Computer Engineering, NE1 7RU, Newcastle upon Tyne, United Kingdom
Thomas Pardoen Institute of Mechanics, Materials and Civil Engineering, Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium; and Research Center in Micro and Nanoscopic Materials and Electronic Devices, Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium
Jean-Pierre Raskin Research Center in Micro and Nanoscopic Materials and Electronic Devices, Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium; and Institute of Information and Communication Technologies, Electronics and Applied Mathematics, Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium (Received 28 June 2011; accepted 30 September 2011)
Nanomechanical testing of silicon is primarily motivated toward characterizing scale effects on the mechanical behavior. “Defect-free” nanoscale silicon additionally offers a road to large deformation permitting the investigation of transport characteristics and surface instabilities of a significantly perturbed atomic arrangement. The need for developing simple and generic characterization tools to deform free-standing silicon beams down to the nanometer scale, sufficiently equipped to investigate both the mechanical properties and the carrier transport under large strains, has been met in this research through the design of a versatile lab-on-chip. The original on-chip characterization technique has been applied to monocrystalline Si beams produced from Silicon-on-Insulator wafers. The Young’s modulus was observed to decrease from 160 GPa down to 108 GPa when varying the thickness from 200 down to 50 nm. The fracture strain increases when decreasing the volume of the test specimen to reach 5% in the smallest samples. Additionally, atomic force microscope-based characterizations reveal that the surface roughness decreases by a factor of 5 when deforming by 2% the Si specimen. Proof of concept transport measurements were also performed under deformation up till 3.5% on 40-nm-thick lightly p-doped silicon beams. I. INTRODUCTION
The elastic stiffness, fracture strength, and fracture toughness of a perfect macroscopic crystal are intrinsic material properties characterizing the atomic bonding and crystal symmetry. In general, bulk materials are not perfect crystals, and their characteristic strength and fracture toughness can be much lower than the theoretical value. It could be expected that by decreasing dimensions, the probability of defects is reduced and we approach closer to the theoretical strength of a perfect crystal. However, by scaling the material volume in at least one spatial dimension, the number of atoms involved in the surface region becomes significant compared with the total number of atoms. A surface is essentially an abrupt termination of the translational symmetry of the crystal. The surface atoms are less coordinated a)
Address all correspondence to this author. e-mail: umesh.bhask
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