Phase-equilibrium-dominated vapor-liquid-solid mechanism: further evidence

Abstract

mechanism for the growth of h-AlN nanowires by nitriding Al 69 Ni 31 particles in the liquid-solid (δ) phase region (854-1 133°C) [17]. Specifically, at a certain temperature, the yield of AlN nanowires and the composition of the residual Al-Ni alloy are determined by the Al-Ni binary phase diagram. This specific example reveals the possibility to predict and design nanomaterials according to the corresponding phase diagrams. Herein we report the successful prediction of the growth of AlN nanowires by nitriding Al 69 Ni 31 alloy particles across another liquid-solid (β) phase region (1133-1638°C). By using the rapid quenching and growth tracing approaches, all expectations about the growth of the AlN nanowires, the evolutions of lattice parameters and geometries of the coexisting Al-Ni alloy phases were experimentally confirmed quantitatively. The preconditions for the applicability of the PED-VLS mechanism were also clarified. This study provides the further evidence for the PED-VLS growth mechanism, and also corroborates its validity in designing 1D nanostructures. EXPERIMENTAL SECTIONNitriding Al 69 Ni 31 alloy particles and quenching the products Nitridation of Al 69 Ni 31 alloy particles is similar to that in our previous study [17] but in different temperature range, i.e., in the region II of Fig. 1a. The Al 69 Ni 31 particles were dispersed on an alumina plate, and then mounted at the center of a tube furnace (Supplementary information, Fig. S1). The Al 69 Ni 31 alloy particles consist of two phases of o-Al 3 Ni and h-Al 3 Ni 2 (Fig. S2) with size distribution in the range of 1~100 μm [17]. After being pumped and flushed by Ar for several times to remove oxygen and moisture, the furnace was heated up to a desired temperature under N 2 flow of 100 mL min -1 . After 2 h nitridation, the product was pushed into liquid N 2 cooling zone for rapid quenching to avoid phase separation. For comparison, the products were also obtained by slow cooling, i.e., naturally-cooling ABSTRACT Prediction and design of various nanomaterials is a long-term dream in nanoscience and nanotechnology, which depends on the deep understanding on the growth mechanism. Herein, we report the successful prediction on the growth of AlN nanowires by nitriding Al69Ni31 alloy particles across the liquid-solid (β) phase region (1133-1638°C) based on the phase-equilibrium-dominated vapor-liquid-solid (PED-VLS) mechanism proposed in our previous study. All predictions about the growth of AlN nanowires, the evolutions of lattice parameters and geometries of the coexisting Al-Ni alloy phases are experimentally confirmed quantitatively. The preconditions for the applicability of the PED-VLS mechanism are also clarified. This progress provides the further evidence for the validity of the PED-VLS mechanism and demonstrates a practical guidance for designing and synthesizing different nanomaterials according to corresponding phase diagrams based on the insight into the growth mechanism.