Nanoindentation-induced phase transformations in silicon at elevated temperatures

Abstract

The nanoindentation-induced phase transformation behavior of silicon at elevated temperatures (25-150 degrees C) has been studied. Nucleation of Si-III/Si-XII on unloading is enhanced with increasing temperature and at the highest temperatures in an amorphous Si matrix, occurs in a continuous fashion without a pop-out event. Interestingly, for slow unloading at the highest temperatures, formation of Si-III/Si-XII in a crystalline Si matrix was not observed. Elevated temperatures enhance the nucleation of Si-III and Si-XII during unloading but the final composition of the phase transformed zone is also dependent on the thermal stability of the phases in their respective matrices.

Nanoindentation of Silicon and Germanium

“…Whereas phase transformations occurred over this whole temperature range, they tentatively proposed a tetragonal form of Si on unloading and subsequent annealing for indentation at 135°C and suggested that this originated from a new unidentifiable phase formed at 135°C. Furthermore, Ruffell et al (2009b) performed similar studies in the 25-150°C temperature range on dc-Si and found only the expected r8/bc8 or a-Si end phases. However, the probability of formation of the bc8/r8 end phase (as opposed to an a-Si end phase) was enhanced with increasing temperature during fast unloading.…”

“…5, we plot some very recent results of Kiran et al (2015) who have improved and extended the elevated temperature indentation work of Ruffell et al (2009b). Figure 5 shows that the probability of an r8/bc8 end phase increases up to 150°C.…”

Randomness and Statistical Laws of Indentation-Induced Pop-Out in Single Crystal Silicon

“…Research on single crystal silicon under external loads has been given much attention [1,2,3,4,5]. Nanoindentation as a powerful method to characterize properties of materials in micro/nano scale also has been used to study mechanical response of single crystal silicon under the penetration load [6,7,8,9,10,11,12,13,14,15,16]. …”

“…Unlike general materials which have smooth load-depth curves, discontinuities in the unloading curves named pop-out and elbow were observed during indentation testing of single crystal silicon [7,10,12,13,14,15,16], which responded to phase transformations of silicon beneath the indenter. Results of Raman microspectroscopy analysis of nanoindentations indicate that pop-out corresponds to the formation of Si–XII and Si–III phases [17], and elbow resulted from the amorphization of silicon on pressure release [13,14,16,17].…”

“…Phase transformations of silicon are affected by many factors, such as indenter shapes [7,12], loading/unloading rates [12,18], cyclic loading conditions [2,16,19], maximum penetration loads [12,13,14,17], temperature [15] and so on [20]. Usually, pop-out appears easily when lower loading/unloading rates and higher maximum penetration loads are selected, while elbow may be observed more often when faster rates and lower maximum penetration loads are selected [17].…”