Microstructure evolution in monocrystalline silicon in cyclic microindentations

Abstract

The study presents evidence of the microstructural evolution during cyclic indentation of monocrystalline silicon with a spherical indenter. Transmission electron microscopy examination of microindentation on cross-section view samples showed that the structure change in the transformation zone features a decomposition of the amorphous phase to R8/BC8 crystals. Outside the zone, cyclic loading gives rise to bending of pristine silicon, slip penetration, and radial cracking. The development of the load–displacement curves during consecutive indentations is justified in terms of the phase transformation events observed.

Phase transformations in (111) Si after spherical indentation

“…Similar to observations following indentation on (100) Si to the same load, [1][2][3][4][5]12 plastic deformation is observed beneath the transformation zone. The slip band, labeled P, which extends to a depth of $450 nm, as well as dislocations, labeled S, are evident in Fig.…”

“…At this lowest load, out of the 10 indentations performed, approximately five indents displayed an elbow, and three of them exhibited an elbow followed by pop-out, whereas the remaining two exhibited a kink pop-out. Elbow events have been reported on indentation of (100) Si with spherical 4,5 as well as Berkovich 9,14 indenters. In (111) Si also, elbow events have been observed at low loads with a Berkovich indenter.…”

“…In other words, they are inclined at an angle of 70 to the surface of the sample. In addition to the penetration depths of the defects being less that in (100) Si, [1][2][3][4][5]12 the dislocation density is also significantly lower in (111) Si. Moreover, the slip bands appear only adjacent to the transformation zone and not directly beneath the indenter tip, unlike that observed in (100) Si.…”

“…It has been well established [1][2][3][4][5][6][7] that during loading, the diamond cubic silicon (Si-I) transforms to the metallic (Si-II) phase, accompanied by a volume reduction, which produces a displacement (or pop-in) in the loading curve. On unloading, depending on the indentation load and unloading rate, either amorphous silicon (a-Si) or a mixture of the high-pressure crystalline Si-III and Si-XII phases form, causing either an elbow or a pop-out, respectively, in the unloading curves.…”

“…On unloading, depending on the indentation load and unloading rate, either amorphous silicon (a-Si) or a mixture of the high-pressure crystalline Si-III and Si-XII phases form, causing either an elbow or a pop-out, respectively, in the unloading curves. These metastable phases have been observed in nanoindented silicon by Raman spectroscopy, 2,[8][9][10][11] plan view, 7 and cross-sectional transmission electron microscopy (XTEM) [1][2][3][4][5][12][13][14][15] as well as electrical measurements. 16,17 In addition, XTEM studies, following indentation on (100) silicon, also show slip bands on {111} planes below the transformation zone.…”