Nanoindentation Method To Study Slip Planes in Molecular Crystals in a Systematic Manner

Abstract

A rotating sample method has been developed to study the slip planes of succinic acid by atomic force microscopy (AFM) nanoindentation. A nonaxisymmetric cube corner indenter was utilized to generate an inhomogeneous stress field, which selectively activates different slip systems simply by rotating the sample. The slip planes identified were repeatable and frequently observed for different indentations of the single crystals using four sample rotations. By applying this rotating sample method to both (001) and (010) crystal faces, the repeatedly observed major slip planes were identified as (010) and (111) planes; these agree with the theoretical prediction. Many higher index operative slip planes were identified that were not reported previously. The rotating sample method presented herein is pragmatic and suggests that the anisotropic slip properties of single pharmaceutical crystals can be studied in a systematic manner.

Crystal Indentation Hardness

“…An inhomogeneous stress field was created on the crystals using a sharp cube corner tip, which helped in activating different slip systems when the specimen was rotated. When indentation was performed on both the (001) and (010) crystal faces, the major slip planes were (010) and (111), and they were in agreement with the attachment energy calculations [109]. Interestingly, along with the predicted slip systems, several unpredicted higher index operative slips planes were also observed at different sample rotations [109].…”

“…When indentation was performed on both the (001) and (010) crystal faces, the major slip planes were (010) and (111), and they were in agreement with the attachment energy calculations [109]. Interestingly, along with the predicted slip systems, several unpredicted higher index operative slips planes were also observed at different sample rotations [109]. The AFM images of residual indents on the (001) face of succinic acid, with the (010) trace being the reference, are shown in Figure 19.…”

“…Bhattacharya et al, International Journal of Solids and Structures; published by Elsevier, 1988. Subsequently, FEM nanoindentation simulation of thin films [107][108][109][110], stress distribution [111][112][113], hardness [114][115][116], friction effects [109,117], brittle cracking behaviour [118][119][120] and coatings [121,122] were extensively developed.…”

“…As the indentation distance becomes large enough, the response becomes similar to that of a single crystalline sample. Accordingly, Zhang and Voyiadjis [108] proposed a material length scale that incorporates the effect of distance between the GB and indenter tip r based on the framework developed by Nix and Gao [13], Abu Al-Rub and Voyiadjis [97], Voyiadjis and Abu Al-Rub [109] and Voyiadjis et al [106] as follows:…”

“…Jing et al [109] studied the slip planes of succinic acid with a rotating sample method using AFM nanoindentation. An inhomogeneous stress field was created on the crystals using a sharp cube corner tip, which helped in activating different slip systems when the specimen was rotated.…”