Benkouider A, Ronda A, David T, Favre L, Abbarchi M, Naffouti M, Osmond J, Delobbe A, Sudraud P, Berbezier I
CNRS, Aix-Marseille Uni., IM2NP, 13397 Marseille Cedex 20, France.
Nanotechnology. 2015 Dec 18;26(50):505602. doi: 10.1088/0957-4484/26/50/505602. Epub 2015 Nov 18.
Synthesizing Au0.8Si0.2 nanocatalysts that are homogeneous in size and have controlled position is becoming a challenging and crucial prequisite for the fabrication of ordered semiconductor nanowires. In this study, Au0.8Si0.2 nanocatalysts are synthesized via dewetting of Au layers on Si(111) during thermal annealing in an ultra-high vacuum. In the first part of the paper, the mechanism of homogeneous dewetting is analyzed as a function of the Au-deposited thickness (h Au). We distinguish three different dewetting regimes: (I) for a low thickness ([Formula: see text]), a submonolyer coverage of Au is stabilized and there is no dewetting. (II) For an intermediate thickness ([Formula: see text]), there is both dewetting and Au0.8Si0.2 phase formation. The size and density of the Au0.8Si0.2 clusters are directly related to h Au. When cooling down to room temperature, the clusters decompose and reject the Si at the Au/Si substrate interface. (III) For a large thickness ([Formula: see text]), only dewetting takes place, without forming AuSi clusters. In this regime, the dewetting is kinetically controlled by the self-diffusion of Au (activation energy ∼0.43 eV) without evidence of an Si-alloying effect. As a practical consequence, when relying solely on the homogeneous dewetting of Au/Si(111) to form the Au0.8Si0.2 catalysts (without a supply of Si atoms from vapor), regime II should be used to obtain good size and density control. In the second part of the paper, a process for ordering the catalysts using focused ion beam-(FIB) assisted dewetting (heterogeneous dewetting) is developed. We show that no matter what the FIB milling conditions and the Au nominal thickness are, dewetting is promoted by ion beam irradiation and is accompanied by the formation of Au0.8Si0.2 droplets. The droplets preferentially form on the patterned areas, while in similar annealing conditions, they do not form on the unpatterned areas. This behavior is attributed to the larger Au-Si interdiffusion in the patterned areas, which results from the Si amorphization induced by the FIB. A systematic analysis of the position of the nanodroplets shows their preferential nucleation inside the patterns, while thicker platelets of almost pure Au are observed between the patterns. The evolutions of the size homogeneity and the occupancy rate of the patterns are quantified as a function of the FIB dose and annealing temperature. Nice arrays of perfectly ordered AuSi catalysts are obtained after optimizing the FIB and dewetting conditions.
合成尺寸均匀且位置可控的Au0.8Si0.2纳米催化剂，已成为制备有序半导体纳米线具有挑战性且至关重要的前提条件。在本研究中，通过在超高真空中热退火期间Si(111)上Au层的去湿来合成Au0.8Si0.2纳米催化剂。在论文的第一部分，分析了均匀去湿机制与Au沉积厚度（h Au）的函数关系。我们区分出三种不同的去湿状态：(I)对于低厚度（[公式：见原文]），Au的亚单层覆盖得以稳定，且不存在去湿现象。(II)对于中等厚度（[公式：见原文]），既有去湿又有Au0.8Si0.2相形成。Au0.8Si0.2团簇的尺寸和密度与h Au直接相关。当冷却至室温时，团簇分解并在Au/Si衬底界面处排斥Si。(III)对于大厚度（[公式：见原文]），仅发生去湿，不形成AuSi团簇。在这种状态下，去湿在动力学上由Au的自扩散控制（活化能约为0.43 eV），没有Si合金化效应的证据。实际结果是，当仅依靠Au/Si(111)的均匀去湿来形成Au0.8Si0.2催化剂（没有来自气相的Si原子供应）时，应使用状态II来获得良好的尺寸和密度控制。在论文的第二部分，开发了一种使用聚焦离子束（FIB）辅助去湿（非均匀去湿）来排列催化剂的工艺。我们表明，无论FIB铣削条件和Au标称厚度如何，离子束辐照都会促进去湿，并伴随Au0.8Si0.2液滴的形成。液滴优先在图案化区域形成，而在类似的退火条件下，它们不会在未图案化区域形成。这种行为归因于图案化区域中更大的Au-Si相互扩散，这是由FIB诱导的Si非晶化导致的。对纳米液滴位置的系统分析表明它们在图案内部优先成核，而在图案之间观察到几乎纯Au的较厚薄片。图案的尺寸均匀性和占有率的演变作为FIB剂量和退火温度的函数进行了量化。在优化FIB和去湿条件后，获得了排列完美的AuSi催化剂的良好阵列。
