Suppression of interdiffusion-induced voiding in oxidation of copper nanowires with twin-modified surface

Abstract

Cavitation and hollow structures can be introduced in nanomaterials via the Kirkendall effect in an alloying or reaction system. By introducing dense nanoscale twins into copper nanowires (CuNWs), we change the surface structure and prohibit void formation in oxidation of the nanowires. The nanotwinned CuNW exhibits faceted surfaces of very few atomic steps as well as a very low vacancy generation rate at copper/oxide interfaces. Together they lower the oxidation rate and eliminate void formation at the copper/oxide interface. We propose that the slow reaction rate together with the highly effective vacancy absorption at interfaces leads to a lattice shift in the oxidation reaction. Our findings suggest that the nanoscale Kirkendall effect can be manipulated by controlling the internal and surface crystal defects of nanomaterials.

Resolving single Cu nanoparticle oxidation and Kirkendall void formation with in situ plasmonic nanospectroscopy and electrodynamic simulations

“…3b). Mechanistically, at a critical estimated vacancy cluster size of 4 vacancies, 7 they will start to coalesce to form a larger void. Globally, this process is nicely captured in our TEM images taken at the later oxidation stage, which show the formation of a large void with a straight boundary towards the shrinking metallic core ( Fig.…”

“…Therefore, we speculate that vacancies either are spread out homogeneously over the entire Cu core or that they are localized at the metal-oxide interface. To this end, there are recent studies on Cu nanowires, 6,7 which indicate that vacancies are formed all along the metal-oxide interface and then accumulate at grain boundaries, where voids start to grow. The latter is a consequence of the importance of vacancy sinks and a high vacancy generation rate to enable void nucleation, since the void nucleation barrier of Cu is low (2 eV).…”

“…These conditions are readily fulfilled at surfaces with high atomic step density and at grain boundaries. 7 Since we cannot identify grain boundaries in our particles, we assume that vacancy generation and accumulation takes place at the metal-oxide interface.…”

“…The nanoscale Kirkendall effect (NKE) 1,2 occurs during Cu nanoparticle oxidation as the consequence of O-ions diffusing more slowly in the oxide compared to the Cu-ions. [3][4][5][6] As the end result, this leads to the conversion of the metal particle into a characteristic hollow oxide shell, with the amount of hollowing depending on the ratio between the diffusion rates of the Cu-and O-ions, as well as on the nanostructure itself and on the abundance of defects 7 (Fig. 1a).…”

Defect-driven Selective Metal Oxidation at Atomic Scale

“…Analogous to the strong twin-size dependence of mechanical behaviour in nanotwinned metals [1][2][3] , it is signi cant to study how the chemical reactivity and oxidation could vary with TB spacing, because smaller twins are frequently observed to reduce the reactivity via surface modi cation 12 . To this end, despite the technical di culties in controlling TB spacing experimentally, DFT calculations are used to quantify the mean oxygen binding energy averaged over multiple O interstitial sites of different defectmodi ed surface con gurations, as shown in Fig.…”