Ductile deformation mechanism in semiconductor α-Ag2S

Abstract

Inorganic semiconductor α-Ag2S exhibits a metal-like ductile behavior at room temperature, but the origin of this high ductility has not been fully explored yet. Based on density function theory simulations on the intrinsic mechanical properties of α-Ag2S, its underlying ductile mechanism is attributed to the following three factors: (i) the low ideal shear strength and multiple slip pathways under pressure, (ii) easy movement of Ag–S octagon framework without breaking Ag−S bonds, and (iii) a metallic Ag−Ag bond forms which suppresses the Ag–S frameworks from slipping and holds them together. The easy slip pathways (or easy rearrangement of atoms without breaking bonds) in α-Ag2S provide insight into the understanding of the plastic deformation mechanism of ductile semiconductor materials, which is beneficial for devising and developing flexible semiconductor materials and electronic devices.

Tribo‐Induced Structural Transformation and Lubricant Dissociation at Amorphous Carbon–Alpha Olefin Interface

“…Especially, the friction coefficient at 50 GPa shows lower sensitivity to lubricant variety than that at 5 GPa, which is a typical feature for the boundary lubrication state . Hence, on the one hand, introducing C 5 H 10 , C 8 H 16 , or C 12 H 24 into the a‐C–a‐C sliding interface decreases the friction coefficient, but it works more effectively at the low contact pressure, which is similar to previous study, and the increase of friction coefficient with contact pressure may be related to the strong friction‐induced tribochemical reaction at the interface. On the other hand, the selection of lubricant is essential to optimize the friction property, and a lubricant with high viscosity is suggested for systems working at high contact pressure conditions.…”

“…For each a‐C–AO–a‐C friction system at 5 GPa, the AO molecules are distributed at the center of friction interface with a stable plateau region (Figure and Figure S1, Supporting Information) and make no contribution to the coordination of the a‐C structure (Figure S8a, Supporting Information), implying the intermolecular interactions between the a‐C and AOs. The morphologies with neglected AOs (Figure S8b, Supporting Information) also confirm that the bottom and upper a‐C structures are almost completely separated by the AO lubricants without any direct interaction . In addition, the number of intact AO molecules has no change in any case due to the low shearing stress and flash temperature at the friction‐free layer (about 303 ± 1 K) (see Figure S9, Supporting Information).…”

“…Note that at the same contact pressure, there is no significant difference in the morphologies when the lubricant changes from C 5 H 10 to C 8 H 16 and C 12 H 24 , while there is a strong dependence on the contact pressure. At the contact pressure of 5 GPa, the AO molecules are uniformly distributed at the interface after the sliding process and two a‐C–AO interfaces can be clearly distinguished . With an increase of contact pressure to 50 GPa, compared to the cases before the sliding process, the mixing and interaction between the a‐C and AOs enhance drastically after the sliding process, and some AO molecules even bond with C atoms located at the deeper position of a‐C structures, suggesting the existence of lubricant dissociation and significant reconstruction of sliding interface, as will be discussed later.…”

“…Figure shows the morphologies of a‐C–C 8 H 16 –a‐C friction system before and after the sliding process, while those for C 5 H 10 and C 12 H 24 lubricants can be found in Figure S1, Supporting Information. Note that at the same contact pressure, there is no significant difference in the morphologies when the lubricant changes from C 5 H 10 to C 8 H 16 and C 12 H 24 , while there is a strong dependence on the contact pressure.…”

“…Friction results including average friction force, average load, and friction coefficient in a‐C–AO–a‐C systems with different lubricants at contact pressures of a) 5 and b) 50 GPa, respectively. Those for the pure a‐C–a‐C system without lubricant and with C 5 H 10 are also presented for comparison.…”