Allison Steven Jay, Cordova Dmitri Leo Mesoza, Hasib Maham, Aoki Toshihiro, Arguilla Maxx Q
Department of Chemistry, University of California Irvine Irvine California 92697 USA
Irvine Materials Research Institute, University of California Irvine Irvine California 92697 USA.
Chem Sci. 2024 Feb 19;15(13):4811-4823. doi: 10.1039/d3sc06456e. eCollection 2024 Mar 27.
Anisotropy often yields unexpected structures and properties in the solid state. In van der Waals (vdW) solids comprised of 1D or quasi-1D (q-1D) building blocks, anisotropy in both intra- and inter-chain directions results in an abundance of crystalline packing motifs and drastically altered physical states. Among these, structurally and chemically complex 1D/q-1D vdW solids that display topologically protected states, unique optical properties, and enhanced electrical transport properties in 1D are sought after owing to their potential as building blocks for next-generation quantum devices that approach the sub-nanometer regime. Yet, the access to such facet- and edge-specific physical states is still limited by the stochastic nature of micromechanical exfoliation. Here, we demonstrate that the representative BiI phase, an established pnictohalide q-1D vdW topological insulator in the bulk, can be crystallized from the vapor phase either into well-defined nanowires or quasi-2D nanosheets. We find that gold nanoparticles (Au NPs) on the growth substrate, in conjunction with the highly anisotropic structure of BiI common to many q-1D vdW crystals, direct the dimensionality of high-purity BiI nanostructures. Systematic variation of Au NP diameters, Bi : I precursor ratios, and growth-deposition temperatures reveal that Au NPs generally act as nucleation sites for vapor-solid (VS) growth of BiI nanowires. Strikingly, post-synthesis analyses of the elemental composition of 20 nm Au NPs on the substrate surface show an equisotichiometric 1 : 1 ratio of Bi to I within the Au NP that triggers the vapor-liquid-solid (VLS) growth of [001]-oriented quasi-2D nanosheets comprised of laterally-ordered [BiI] chains along the perpendicular [100] direction. We rationalize the observed bimodal growth pathways and the morphologically distinct nanostructures based on crystallization habits and orientations of the nanostructures, Bi : I ratios in the resulting Au NPs post-synthesis, and the orientation of stereochemically active Bi lone pairs between adjacent chains. We anticipate that these growth pathways are adaptable to the synthesis of emergent halide- and chalcogen-based 1D vdW nanocrystals with diverse physical and quantum properties.
各向异性在固态中常常会产生意想不到的结构和性质。在由一维或准一维（q-1D）结构单元组成的范德华（vdW）固体中，链内和链间方向的各向异性导致了丰富的晶体堆积模式和物理状态的急剧变化。其中，结构和化学复杂的一维/准一维范德华固体由于其作为接近亚纳米尺度的下一代量子器件构建单元的潜力，而备受关注，它们表现出拓扑保护态、独特的光学性质以及增强的一维电输运性质。然而，获取这种特定晶面和边缘的物理状态仍然受到微机械剥离随机性的限制。在此，我们证明，具有代表性的BiI相，一种体相已确定的磷卤化物准一维范德华拓扑绝缘体，可以从气相结晶为定义明确的纳米线或准二维纳米片。我们发现，生长衬底上的金纳米颗粒（Au NPs），结合许多准一维范德华晶体共有的BiI高度各向异性结构，能够引导高纯度BiI纳米结构的维度。金纳米颗粒直径、Bi : I前驱体比例以及生长-沉积温度的系统变化表明，金纳米颗粒通常作为BiI纳米线气-固（VS）生长的成核位点。引人注目的是，对衬底表面20 nm金纳米颗粒的元素组成进行合成后分析发现，金纳米颗粒内Bi与I的化学计量比为1 : 1，这触发了由沿垂直[100]方向横向有序排列的[BiI]链组成的[001]取向准二维纳米片的气-液-固（VLS）生长。我们基于纳米结构的结晶习性和取向、合成后金纳米颗粒中的Bi : I比例以及相邻链之间立体化学活性Bi孤对的取向，对观察到的双峰生长途径和形态上不同的纳米结构进行了合理说明。我们预计这些生长途径适用于合成具有各种物理和量子性质的新型卤化物和硫族化物基一维范德华纳米晶体。
