van Kats Carlos M, Johnson Patrick M, van den Meerakker Jan E A M, van Blaaderen Alfons
Soft Condensed Matter, Debye Institute, Ornstein Laboratory, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
Langmuir. 2004 Dec 7;20(25):11201-7. doi: 10.1021/la048817j.
We describe the synthesis and the physical properties of suspensions of colloidal silicon and silica rodlike particles. In addition to pure silicon and pure silica rods, we have also synthesized silicon rods with a silica shell and silica rods with a fluorescent silica layer. Pre-patterned p-type (100) silicon wafers were electrochemically etched in electrolyte solutions containing hydrogen fluoride. By the current density being varied while etching, macropores were etched with controllable modulated pore diameters. These silicon structures were transformed into rods with indentations 5.5 mum apart and with lengths up to 100 mum using iterative oxidation in air and dissolution of the silica by HF. Complete oxidation of these rods was also achieved. Sonication of the modulated rods resulted in monodisperse particles of 5.5 mum length and 300 nm width. A high yield of 10(12) particles, or more, is possible with this method. At high concentrations, these particles show nematic ordering in charge-stabilized suspensions. The oxidized silica outer layer of the silicon rods makes the further growth of silica in solution or on a wafer possible. This allows for control of the particles' interaction potential. Labeling with a fluorescent dye and index matching of the complete silica rods enable the study of concentrated dispersions quantitatively, on a single particle level, with confocal microscopy. Because of their high refractive index in the near-IR, the nematic phases of rods with a silica core are also interesting for photonic applications.
我们描述了胶体硅和二氧化硅棒状颗粒悬浮液的合成及其物理性质。除了纯硅棒和纯二氧化硅棒外，我们还合成了具有二氧化硅壳的硅棒以及带有荧光二氧化硅层的二氧化硅棒。预先图案化的p型（100）硅片在含有氟化氢的电解质溶液中进行电化学蚀刻。通过在蚀刻过程中改变电流密度，可蚀刻出具有可控调制孔径的大孔。利用在空气中的迭代氧化以及用氢氟酸溶解二氧化硅，将这些硅结构转变为间距为5.5微米、长度达100微米的带凹痕的棒。这些棒也实现了完全氧化。对调制后的棒进行超声处理可得到长度为5.5微米、宽度为300纳米的单分散颗粒。用这种方法可实现10¹²个或更多颗粒的高产率。在高浓度下，这些颗粒在电荷稳定的悬浮液中呈现向列相有序排列。硅棒的氧化二氧化硅外层使得二氧化硅在溶液中或在硅片上进一步生长成为可能。这有助于控制颗粒的相互作用势。用荧光染料标记以及对完整的二氧化硅棒进行折射率匹配，使得能够利用共聚焦显微镜在单个颗粒水平上对浓缩分散体进行定量研究。由于其在近红外区域具有高折射率，具有二氧化硅核心的棒的向列相在光子应用中也很有意义。
