Synergistic effects on thermal growth of CuO nanowires

Understanding the Growth of Copper Oxide Nanowires and Layers by Thermal Oxidation over a Broad Temperature Range at Atmospheric Pressure

“…CuO NWs grow on the top; hence, for NWs to vertically elongate, copper has to be supplied through the NW on the very tip. This can be achieved via diffusion along the surface of the NWs, ,, or by diffusion through the twin boundary in bi-crystalline NWs . The twin boundaries present important pathways for the diffusion of Cu atoms, and the diffusion of Cu through the twin boundary may even be favorable over surface diffusion …”

“…Among other factors, stress gradients are believed to be the main driving force for NW growth; however, gas humidity and external electric field should be taken into account. Nevertheless, there are common conclusions to all investigations: upon annealing, first a Cu 2 O layer forms on top of the Cu substrate, followed by a CuO layer on which CuO NWs grow, forming a three-layered composite: Cu/Cu 2 O/CuO. ,− During thermal oxidation, the Cu ions migrate from the Cu substrate by grain boundary diffusion to the top of the CuO layer or toward the Cu 2 O/CuO boundary by the Kirkendall effect . Combined with lattice-mismatch-induced compressive stress on the Cu 2 O/CuO boundary, this expedites Cu ion diffusion through oxide layers to the top of the CuO layer, facilitating growth.…”

“…29,38−41 During thermal oxidation, the Cu ions migrate from the Cu substrate by grain boundary diffusion to the top of the CuO layer 42 or toward the Cu 2 O/CuO boundary by the Kirkendall effect. 43 Combined with lattice-mismatchinduced compressive stress on the Cu 2 O/CuO boundary, this expedites Cu ion diffusion through oxide layers to the top of the CuO layer, facilitating growth. Such stress-driven grain boundary diffusion 40,43,44 and stress relaxation 45−47 commonly listed as causes for CuO NW growth.…”

“…Combined with lattice-mismatch-induced compressive stress on the Cu 2 O/CuO boundary, this expedites Cu ion diffusion through oxide layers to the top of the CuO layer, facilitating growth. Such stress-driven grain boundary diffusion ,, and stress relaxation − are commonly listed as causes for CuO NW growth. Meanwhile, oxygen gradient-driven diffusion due to oxygen consumption on the CuO NW surface is the cause for CuO crystal elongation .…”

“…43 Combined with lattice-mismatchinduced compressive stress on the Cu 2 O/CuO boundary, this expedites Cu ion diffusion through oxide layers to the top of the CuO layer, facilitating growth. Such stress-driven grain boundary diffusion 40,43,44 and stress relaxation 45−47…”