Mechanisms of Stress Corrosion Cracking in Si: A Hybrid Quantum-Mechanical/Molecular-Dynamics Simulation
- PDF / 367,373 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 99 Downloads / 198 Views
Y8.40.1
Mechanisms of Stress Corrosion Cracking in Si: A Hybrid Quantum-Mechanical/Molecular-Dynamics Simulation Rachid Belkada,1,2 Shuji Ogata,2 Fuyuki Shimojo,3 Aiichiro Nakano,4,5 Priya Vashishta,4,5 and Rajiv K. Kalia4,5 1 Japan Science and Technology Corporation, Kawaguchi 332-0012, Japan 2 Department of Applied Sciences, Yamaguchi University, Ube 755-8611, Japan 3 Departemnet of Physics, Kumamoto University, Kumamoto 860-8555, Japan 4 CCLMS, Louisiana State University, Baton Rouge, LA70803-4001, U.S.A 5 Departement of Computer Science, University of Southern California, Los Angeles, CA90089-0242, U.S.A.
ABSTRACT We investigate mechanisms of stress corrosion cracking in Si using a hybrid quantummechanical/molecular-dynamics simulation code developed recently for parallel computers. We perform the simulation for a cracked Si-model under tension (mode-I opening) with three H2O molecules around the crack front to investigate possible effects of both saturation of dangling bonds of Si with hydrogen atoms and environment molecules on the fracture initiation. Our results demonstrate existence of a path for an H2O molecule to react with Si-Si bonds at the crack front in contrast to a previous theoretical study based on the molecular orbital theory [W. Wong-Ng et al., Comp. Mater. Sci. 6, 63 (1996)].
INTRODUCTION Recent progresses in fabrication techniques of semiconductors and ceramics make it possible to produce very small (nanometer scale) Si-based electro-mechanical components [1]. Due to their small sizes, these components have relatively large surface-to-volume ratios. Their large fractions of surface make the components sensitive and vulnerable to corrosive environment, and hence may shorten their lifetimes. Environmentally enhanced crack growths have been observed in silicate glasses [2]. Theoretical studies have shown that reactive molecules such as water promote slow crack growth by attacking the strained inter-atomic bonds at the crack tip [2]. Stress corrosion cracking in bulk silicon is not observed in experiments. However, an evidence of corrosion cracking was reported in sub-micron-size Si-systems at high strains [3]. There are no explicit explanations on its mechanisms. Stress fields in materials depend on the size and the overall shape of the system since the fields are long-ranged. Understanding combined effects of tensile stress and environmental molecules in such nano-sized systems requires a dynamic simulation of realistic systems with chemical reactions. Wong-Ng et al. addressed the environment effects of H2O on fracture of Si by using the molecular-orbital (MO) method [4]. Their computation used small hydrogen and OH terminated Si cluster (Si8H17OH) to mimic an atomic structure near the crack tip. Dangling bonds on the crack surfaces of Si were saturated with hydrogen and OH. They found that
Y8.40.2
moisture does not enhance crack-growth via chemical reactions in strained Si. They concluded that a water molecule cannot reach the Si-Si crack tip bonds because of the steric repulsion b
Data Loading...
