Plastic deformation of silicon between 20 °C and 425 °C

Abstract

Mechanical data have been obtained on silicon single crystal under hydrostatic pressure between room temperature and 450 °C. This temperature domain corresponds to the regime where perfect dislocations control plastic deformation. This was achieved using a D-DIA apparatus in the synchrotron beam of NSLS. Stress strain curves were deduced from X Ray diffraction and sample imaging under 5 GPa and a strain rate of 2.5 10. Yield stresses as a function of temperature exhibit different temperature dependence when deformation is controlled by perfect dislocations.1 Introduction Recent studies of Si single crystals plastic deformation have shown that perfect dislocations are nucleated and control the deformation in very high stress conditions [1,2]. Those deformation microstructures are usually obtained in harsh conditions where the applied stress tensor possesses a hydrostatic component which prevents a brittle behaviour of the material. In these conditions it is usually difficult to derive the applied shear stress during the test. Applied shear stress can be obtained post mortem by TEM investigations. The stress information can then be extracted from the dislocation bends curvature joining rectilinear segments lying in two contiguous Peierls valleys. Those bends are very small which makes difficult measuring the local stress. Nevertheless it was shown that perfect shuffle dislocation configurations are found consistent with local applied shear stresses of the order of 1.5 GPa [3]. In order to get insights in the deformation mechanisms at high stress, it is of importance to be able to get the yield stress as a function of temperature in this range of stress, in deformation conditions which could be comparable to those used in the standard deformation tests performed previously at high temperature. This requires conducting experiments under hydrostatic pressure being able to (i) apply independently the hydrostatic component of the stress tensor and a shear stress, (ii) record during the test the stress tensor and the sample deformation. Getting high stress deformation regime in Si needs to use high hydrostatic pressures of the order of 5 GPa [1,2]. Such pressure range can be only obtained using a solid confining medium whose main drawback is the generation of friction stresses and the impossibility to access stress tensor data by reliable sensors within the confining medium. Such drawbacks can be by-passed by measuring stresses using the shift of X-rays diffraction peaks of the sample or a sensor medium during the deformation experiment. Measuring this way the change in lattice parameter in various crystallographic directions, the stress tensor can be deduced through equation of state and elastic constants of the investigated diffracting medium. Such diffraction data have to be obtained in-situ during deformation under pressure; obviously this requires the use of high intensity X-rays beam as well as an experimental set up providing some transparency to X-rays.

Plasticity of indium antimonide between −176°C and 400°C under hydrostatic pressure. Part II: Microscopic aspects of the deformation

“…-In the VLT regime (T < T tr2 ), the model considers that the crystal is brittle at ambient pressure but the superimposition of hydrostatic pressure prevents fractures: the crystal becomes ductile via the nucleation of perfect dislocations belonging to the shuffle set with low activation energy for propagation. This regime is unambiguously observed here in InSb similarly to Si where perfect non-dissociated screw dislocations were observed after deformation at 20°C in a multi-anvil setup [16][17][18].…”

“…Until now, such glide-toshuffle transition has been suggested to appear in several III-V and elemental SCs but had only been observed for Si [15][16][17][18]: the TEM observations presented here suggest that this transition occurs around or below RT in InSb.…”

Theoretical study of kinks on screw dislocation in silicon

“…These experiments have been done for temperatures ranging between 150 and 700 K. [1][2][3][4] Recently, using two different methods, Rabier et al have determined that local stresses required for displacing these perfect dislocations are larger than 1 GPa at 573 K. 61,62 Then, at lower temperatures ͑i.e., well below the brittleductile transition temperature͒, very large stresses are required in order to move the dislocations.…”

Silicon micropillars: high stress plasticity

“…It is interesting to compare the yield stress measurements as a function of temperature obtained in this paper with those relevant from high pressure tests of [7] under 5 GPa hydrostatic pressure. These two sets of data have been ob-…”

“…There are two main interests for investigating high stress plasticity regimes of silicon through the deformation of micropillars: -These mechanical tests appear to be more flexible that high-pressure tests. Indeed those latter experiments require the control of high-pressure techniques as well as the use of a synchrotron machine: mechanical data are obtained in situ from the analysis of X-ray diffraction data [7]. -The deformation of micro object is controlled by dislocation nucleation [8].…”