Lithographically patterned silicon nanostructure towards optical gas sensing

Silicon offers excellent electronic and mechanical properties and can be easily engineered at the nanometer scale which is useful for a large amount of applications such as in electronic devices, self-cleaning, MEMS and solar... [ view full abstract ]

Silicon offers excellent electronic and mechanical properties and can be easily engineered at the nanometer scale which is useful for a large amount of applications such as in electronic devices, self-cleaning, MEMS and solar cells. Silicon which is an indirect band gap semiconductor cannot be used as an efficient light source. On the other hand large scale, well-ordered, periodically patterned silicon structures with a high aspect ratio such as nanowires (NWs), can be used for optical sensing. Synthesis of silicon NWs using a simple and an inexpensive technique, however, still maintaining the advantages of conventional techniques, is now the major challenge.
The aim of this work is to present a new approach of obtaining NWs and nanostructures from crystalline silicon by using a top-down technique which is a combination of laser interference lithography and reactive-ion etching (RIE). As in the case of conventional dry etching technique, where one uses metal as a mask, in our study we use zinc oxide as a hard mask for etching. The advantage of using ZnO is that it is easy to structure it using acidic solutions. Moreover, we avoid the various lift-off steps which are necessary for metallic mask structuring. The main goal is to obtain photoluminescent silicon structures for optical gas sensing applications. The surface of silicon structures having a high aspect ratio (as shown in figure 1(a) below), is functionalized using lanthanide complexes (fig.1(b)) which are photoluminescent. The future perspective of this study is to detect the gas molecules using these functionalized silicon surfaces. The detection method is based on a selective "quenching of luminescence ", which can be induced in the presence of an analyte (gas molecules).
Fig.1: luminescent silicon nanowires: a) Example of silicon nanostructures, b) Silicon surface modified with the terbium complex, c) Photoluminescence from terbium functionalized silicon structures.