Strength of silicon containing nanoscale flaws
- PDF / 510,044 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 94 Downloads / 167 Views
Silicon is a principal material in submicrometer-scale devices. Components in such devices are subject to intense local stress concentrations from nanoscale contacts during function. Questions arise as to the fundamental nature and extent of any strength-degrading damage incurred at such contacts on otherwise pristine surfaces. Here, a simple bilayer test procedure is adapted to probe the strengths of selected areas of silicon surfaces after nanoindentation with a Berkovich diamond. Analogous tests on silicate glass surfaces are used as a control. The strengths increase with diminishing contact penetration in both materials, even below thresholds for visible cracking at the impression corners. However, the strength levels in the subthreshold region are much lower in the silicon, indicating exceptionally high brittleness and vulnerability to small-scale damage in this material. The results have important implications in the design of devices with silicon components.
With the ever-increasing miniaturization of micro- and nanoelectromechanical systems (MEMS and NEMS), computer chips, sensors, hard drives, and other smallscale devices, materials reliability is a critical factor.1,2 This is especially true of silicon, the material of choice for a large range of such devices. Characteristic dimensions associated with intercomponent contacts, surface asperities, and so forth, tend to scale down with device size. A key issue is whether basic strength relations at the macroscale extrapolate down below the microscale. Strength studies have been carried out on lithographically fabricated small-scale silicon specimens with nearpristine surfaces representative of MEMS components.3,4 Uncommonly high strengths are typical, in the GPa range, but data interpretation in relation to initiating flaws tends to be speculative—the possibility that flaw characteristics may fundamentally change with diminishing scale is rarely considered. Hence the larger question—what is the nature of strength-governing, nanoscale flaws in silicon and other brittle materials?
a)
On leave from Departamento de Física, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain. b) Undergraduate student, Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015. c) Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 19, No. 2, Feb 2004
http://journals.cambridge.org
Downloaded: 14 Mar 2015
Strength studies on surfaces of newly fabricated specimens are not always pertinent to real applications because lifetime-limiting flaws may develop during subsequent function. History-dependent degradation of initially pristine optical glass fibers is a well-documented example—a single contact of a pristine surface by an errant hard particle or asperity may diminish strength by over an order of magnitude.5 Small-scale devices with moving components are especially susceptible to such contacts. Even low loads can induce inordinately high local stresses, exceeding theoretical cohesive bond
Data Loading...
