Crack Growth In Silicon Research Articles

A three dimensional adaptive multiscale method for crack growth in Silicon

A three dimensional concurrently coupled adaptive multiscale method is introduced here to simulate complex crack growth patterns in Silicon, by combining several numerical techniques across the length scales. The coarse scale material is modeled using the virtual atom cluster approach. The strong kinematic discontinuities in the bulk are simulated based on a three dimensional version of the phantom node method. A molecular statics model placed around the crack tip is concurrently coupled with the phantom-based discontinuous formulation, where the coupling between the fine and coarse scales is realized through the use of ghost atoms, whose positions are interpolated based on the coarse scale solution. The boundary conditions to the fine scale model, at the coupling region, are assigned by enforcing the interpolated displacements of ghost atoms. In order to optimize the computation costs, adaptivity schemes for adjustment of the fine scale region as the crack propagates, and coarse graining of the region behind the crack tip, are proposed. The crack tip location is detected based on an energy criterion. All the molecular simulations in the pure atomistic as well as the multiscale model are carried out using the LAMMPS software, triggered through the system command in MATLAB. The performance of the developed framework in terms of computation cost, robustness and versatility, is assessed through several numerical examples concerning crack growth in Silicon. Therefore, the diamond cubic lattice structure of Silicon is used at the fine scale, where the atom-atom interactions are modeled based on the Tersoff potential function. According to the numerical examples presented in this study, savings in computational time using the present multiscale method are observed to be up to 87%, as compared to the pure atomistic model.

Fatigue crack growth in Silicon solar cells and hysteretic behaviour of busbars

Photovoltaic modules are subject to cyclic deformation during their lifetime as a result of vibration, applied loads, and thermal effects. Vibration and applied loads induce cyclic bending on the modules, while operating temperature excursions during the day lead mostly to cyclic axial deformation. In both cases, the region between two solar cells is severely stressed. For cyclic bending, cracks can nucleate near the points where busbars are soldered onto Silicon and might propagate due to fatigue. For cyclic axial deformation, on the other hand, busbars are stressed above the elastic regime and may experience plasticity and hysteretic energy dissipation. The present study focuses on the experimental characterization of such material degradation phenomena related to the above two types of cyclic deformation. For the former, fatigue crack growth in Silicon and its evolution have been quantified by using two independent nondestructive monitoring techniques based on electroluminescence and thermal infrared imaging. For the latter, plasticity and degradation of the material response of busbars has been assessed in relation to different applied cyclic strain levels. The obtained results shed light onto the cyclic response of materials used in photovoltaics, and pinpoint features that should be taken into account in the development of refined standard qualification tests for photovoltaics including cyclic deformation.

Subcritical Crack Growth in Single-crystal Silicon Using Micromachined Specimens

A micromachined specimen with a test section only 150-μm thick was developed for investigating subcritical crack growth in silicon. Crack growth rates in the range 10−4–10−10m/s were measured as a function of applied stress intensity (v–Kcurves) during tests in humid air and dry nitrogen lasting up to 24 h. The fracture toughness,KIcof {110} silicon was also measured at 1.15 ± 0.08 MPa m1/2. While some evidence MPa-m1/2of subcritical crack growth appeared to occur in the region 0.9KIc<K> 0.98KIc, the extremely high crack growth exponent (n100) and the high ratio of the apparent stress corrosion threshold,KIscc, to the fracture toughness,KIscc/KIc> 0.9, suggests that no clear evidence exists for a stress corrosion process in silicon exposed to humid air.

Calculated potential for water enhanced crack growth in silicon

Ab initio molecular orbital calculations have been performed on the model molecules Si 8H 17OH (taking into consideration of the crack wall species -OH and -H) for the crack-tip strain simulation study of silicon and its reaction with water. The calculated equilibrium structure of silicon using a 6-31G ∗∗ basis set agreed well with experimental data. It was found that, regardless of the manner strain was applied, the values of net charge on the two crack-tip Si atoms are similar and that both become slightly more positive as strain increases. In addition to this absence of polarization of the crack-tip SiSi bond under strain, steric hindrance also inhibited the approach of the water molecule to the SiSi crack tip region. These calculations explain why moisture does not enhance crack-growth via chemical reaction in Si, which is different from that observed in silica.

Micromechanical fatigue testing

This paper describes the design, modeling, and experimental test results of a single crystal silicon micromechanical device developed to evaluate fracture and fatigue of silicon based micromechanical devices. The structure is a cantilever beam, 300 microns long, with a large silicon plate and gold inertial mass at the free end. Torquing and sensing electrodes extend over the plate, and with associated electronics, drive the structure at resonance. Fatigue crack propagation is measured by detecting the shift in the natural frequency caused by the extension of a preexisting crack introduced near the fixed end of the cantilever. Experimental data are presented demonstrating time-dependent crack growth in silicon. Crack extensions of 10 to 300 nm have been measured with a resolution of approximately 2.5 nm, and crack tip velocities as low as 2.1×10−14 m/s. It is postulated that static fatigue of the native surface silica layer is the mechanism for crack growth. The methodology established here is generic in concept, permitting sensitive measurement of crack growth in larger fatigue specimens as well.

ChemInform Abstract: LOW‐TEMPERATURE SUBCRITICAL CRACK GROWTH IN SILICON CARBIDE AND SILICON NITRIDE

Chemischer InformationsdienstVolume 7, Issue 36 Physical Inorganic Chemistry ChemInform Abstract: LOW-TEMPERATURE SUBCRITICAL CRACK GROWTH IN SILICON CARBIDE AND SILICON NITRIDE K. D. MCHENRY, K. D. MCHENRYSearch for more papers by this authorT. YONUSHONIS, T. YONUSHONISSearch for more papers by this authorR. E. TRESSLER, R. E. TRESSLERSearch for more papers by this author K. D. MCHENRY, K. D. MCHENRYSearch for more papers by this authorT. YONUSHONIS, T. YONUSHONISSearch for more papers by this authorR. E. TRESSLER, R. E. TRESSLERSearch for more papers by this author First published: September 7, 1976 https://doi.org/10.1002/chin.197636008AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume7, Issue36September 7, 1976 RelatedInformation