Origin of a Nanoindentation Pop-in Event in Silicon Crystal

R. Abram, D. Chrobak, and R. Nowak

Phys. Rev. Lett. 118, 095502 – Published 3 March 2017

Abstract

The Letter concerns surface nanodeformation of Si crystal using atomistic simulation. Our results account for both the occurrence and absence of pop-in events during nanoindentation. We have identified two distinct processes responsible for indentation deformation based on load-depth response, stress-induced evolution of crystalline structure and surface profile. The first, resulting in a pop-in, consists of the extrusion of the crystalline high pressure $Si − III / XII$ phase, while the second, without a pop-in, relies on a flow of amorphized Si to the crystal surface. Of particular interest to silicon technology will be our clarification of the interplay among amorphization, crystal-to-crystal transition, and extrusion of transformed material to the surface.

Received 26 July 2016

DOI:https://doi.org/10.1103/PhysRevLett.118.095502

Physics Subject Headings (PhySH)

Crystal phenomena Defects Mechanical deformation Phase transitions Plasticity Pressure effects Semiconductors

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

R. Abram¹, D. Chrobak^1,2, and R. Nowak^1,3,*

¹Nordic Hysitron Laboratory, Department of Chemistry and Materials Science, School of Chemical Engineering, Aalto University, 00076 Aalto, Finland
²Institute of Materials Science, University of Silesia in Katowice, 75 Pulku Piechoty 1A, 41-500 Chorzow, Poland
³Extreme Energy-Density Research Institute, Nagaoka University of Technology, Kamitomioka 1603-1, Nagaoka, Niigata 940-2188, Japan

^*Roman.Nowak@aalto.fi

Article Text (Subscription Required)

Click to Expand

Supplemental Material (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 118, Iss. 9 — 3 March 2017

Reuse & Permissions

Access Options

Article Available via CHORUS

Download Accepted Manuscript

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
The history of the Si crystal nanodeformation reflected by the load-depth $P − h$ curve (a) derived from MD simulations and the contact pressure-depth $p_{c} − h$ graph (b) that exposes the starting point of the $Si − I \to Si − II$ transformation. The latter occurs at an early stage of nanoindentation (b) without any pop-in (a). The discontinuities ( $A$ and $B$ ) show up in the $P − h$ curve as the indentation process progresses.
Reuse & Permissions
Figure 2
Identification of high-pressure phases formed during nanoindentation in Si crystal. The color of an atom denotes the $N N$ number of its nearest neighbors (black-4, red-5, and yellow-6) and allows us to distinguish between the high-pressure formed crystallites of the BCT5 ( $N N = 5$ ), Si-II ( $N N = 6$ ), and metastable $Si − III / XII$ ( $N N = 4$ ) phases [22, 23, 24, 25, 26]. The area from the indenter profile to the pink borderline defines the location of pressure-amorphized silicon. The atoms of the initial Si-I phase are not displayed for clarity.
Reuse & Permissions
Figure 3
The results of MD-simulated indentation that enable us to define the pop-in events in the $P − h$ curve and distinguish them from non-pop-in effects. The number $N$ of Si atoms displaced above the crystal surface defines the sequence of extrusion in the $A_{1}^{'}$ , $A_{2}^{'}$ , $α^{'}$ , and $B^{'}$ zones. The zoomed $P − h$ graph engulfs the $A_{1}$ , $A_{2}$ , and $B$ pop-ins and exposes extrusion of amorphized Si at the $α$ point (b). The indicated events are linked to the transport of deformed Si that occurs in the specific areas $A_{1}^{'}$ , $A_{2}^{'}$ , $B^{'}$ , and $α^{'}$ . The striking discrepancy in the $E_{pot} (h)$ profiles (discontinuity against smooth growth) recorded for the $A_{1}^{'}$ (c) and $α^{'}$ (d) regions serves the criterion of pop-in detection in silicon.
Reuse & Permissions
Figure 4
Structural changes during nanoindentation viewed along the direction perpendicular to the indentation axis (on the $A_{2}^{'} − A_{1}^{'}$ and $α^{'} − B^{'}$ cross sections) that display the $M 1$ (a) and $M 2$ (b) mechanisms. The i–iv snapshots (a) illustrate the extrusion of a mixture of $Si − III / XII$ phases in the $A_{1}^{'}$ and $A_{2}^{'}$ locations. The extrusion of minute crystallites in the $A_{1}^{'}$ area is responsible for the formation of the pop-in $A_{1}$ —the $M 1$ mechanism. The $α^{'} − B^{'}$ cross section (b) reveals the amorphous Si in the $α^{'}$ area [Fig. 3] transported to the surface in accordance with Bradby et al.[12] (v–viii snapshots), and outlines the $M 2$ mechanism that causes no pop-in. The extrusion of the crystallite in the $B$ area (v–viii snapshots) results in the pop-in $B$ (see Fig. 2).
Reuse & Permissions

Physical Review Letters