Vickers indentations silicon

Fig. 59. The SEM images of scratches produced in (111) Si by a sharp Vickers indenter. Silicon exhibits (a) ductility on a microscale and (b) brittle fracture at the depth of cut beyond the critical value. Scratching direction from left to right.

The bulk densities of all the materials were determined using Archimedes method (AS 1774.5, 1979). The Vickers indentation technique was used to measure the hardness in each case. The applied load in the Vickers hardness tests was 10 kg for silicon nitrides and sialons. However, using the same load produced severe lateral cracking in silicon carbides around indents, which prevented the accurate measurement of the diagonals of indents. Therefore the load was reduced to 0.3 kg for silicon carbide samples. 

Fig. 11. Scanning electron micrograph (SEM) of a 1-N Vickers indentation in (111) silicon revealing plastically extruded material [64].

When fast unloading rates (> 1 mm/min) were applied, only amorphous silicon was observed within indentations (Fig. 17e) [64]. Note also that in all cases the original line at 520 cm has vanished, indicating that no Si-I remains within the contact area after the microhardness test. Similar results were obtained for Vickers indentations [64]. Thus, in contrast to previous electron microscopy studies, Raman microspectroscopy studies have confirmed the presence of the Si-III and Si-XII phases in silicon indentations, providing additional evidence of a Si-I Si-II transformation under the indenter. 

Figure 12.5c and d show radial cracks and a break-out caused by lateral cracks originating from a Vickers indent in the surface of silicon nitride and silicon carbide ceramics. 

T. Lube, Indentation Crack Profiles in Silicon Nitride, Eur. Ceram. Soc., 21,211-18 (2001). D. B. Marshall, Controlled Flaws in Ceramics A Comparison of Knoop and Vickers Indentation, / Am. Ceram. Soc., 66,127-31 (1983). 

Fig. 7.76 Vickers indentation (9.81 N) in a polished silicon nitride sample [23], With kind permission of Elsevier...

Figure 153. Vickers indentation with crack formation after preparation with (a) diamond disk and (b) silicon carbide disk.

Figure 11. Illustration of the massive uplift on the sides of 98 N and 74 N Vickers indentions in silicon nitride. The specimen is strongly tilted and was photographed by a stereo microscope. The magnification bar is only approximate.

M. Khayyat, G. Banini, D. Hasko, and M. Chaudhri, Raman microscopy investigations of structural phase transformations in crystalline and amorphous silicon due to indentation with a Vickers diamond at room temperature and at 77 K, J. Phys. D—Appl. Phys. 36, 1300-1307 (2003). 

In situ conductivity measurements by Clarke et al. [6] (Vickers and Knoop indenters) and by Pharr et al. [8] (Berkovich indenter) showed a drop in Ge resistance during indentation with sharp tips and thus provided the first experimental support to the notion of indentation-induced metallization in germanium. The TEM analysis of the indented Ge samples by Clarke et al. [6] revealed amor-phized material within the indentations, similar to the results obtained on silicon. 

Scanning electron microscopy revealed the formation of debris around the indentation contact area in diamond [196] (Fig. 41a). This correlates with the behavior of silicon and germanium under contact loading, where the formation of plastic extrusions around indentations is believed to be indicative of the pressure-induced metallization (see Section 2.4). The formation of ductile extrusions was reported along the edges of the Vickers impression in diamond and around the deformed top of the diamond indenter [196] (Fig. 41), suggesting that similar transformations occurred in both the indenter and the crystal. 

The hardness of a material quantifies its resistance to permanent shape changes induced by applied mechanical forces such as fiiction or indentation by a sharp object. Scratch resistance is often measured on the Moh 1-10 scale and indentation hardness on the Vickers scale. Single crystal nonporous silicon has a Moh scale hardness of 6 (for comparison, diamond is 10, quartz is 7, calcium carbonate is 3, talc is 1). It has a Vickers hardness of 11.5 GPa. There have now been a few studies of the indentation hardness of porous silicon, with typical values for different types of porous silicon listed in Table 2. 

A study of Vickers hardness of polycrystalline ceramics revealed that cracking may cause critical transition points in the Vickers ISE trends. The transition point was associated with extensive cracking in and around the indentation and a shift in the energy balance during indentation. Different ratios of the indentation work are expended on volumetric deformation and surface fracture processes above and below the transition point. The transition point was very distinct for brittle materials such as silicon carbide. The Vickers hardness transition point was related to a new index of ceramic brittleness defined as ... 

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