ElectrochemicAl Silicon NANOprocessing for the Fabrication of Functional Surfaces at a Reduced Cost – EASi-NANO

The aim of EASi-NANO is to break new grounds in the development of innovative and ambitious processes for the routine-based and low-cost manufacturing of large Si nanoarrays and to integrate these arrays into functional devices. The project is divided into the fabrication of two different types of arrays, Si nanowires (SiNWs) and nanoporous Si (NPSi). Both research axes combine simple photolithographic steps and electrochemical methods in bottom-up and top-down approaches and will be performed side-by-side. Unlike the majority of reported electrochemical and chemical nanostructuration processes, the EASi-NANO techniques will enable a high spatial control at the nanoand microscale, which is essential to fabricate highly organized arrays. Furthermore, these processes will be perfectly adapted for a routine-based preparation of large Si arrays at ambient conditions and without the need for a clean room. The practical use of both types of surfaces developed in EASi-NANO will be demonstrated by integrating them into functional molecular nanoelectronic and sensing devices. To this goal, the SiNW array fabrication technique will be employed for the manufacturing of NW-based field-effect transistors (FETs). Finally, we aim to use NPSi arrays as photelectrodes for the conversion of solar energy into fuel.

This project allowed to obtain several important results that are described below:
First, we developed a new simple process to fabricate arrays of silicon nanospikes. Then, we have shown that the modification of silicon surfaces with dispersed nickel nanoparticles increases considerably their resistance toward etching and allows to use it as an efficient photoanode for water splitting. Recently, a complete study allowed us to elucidate the mechanism. Finally, using these surfaces we could manufacture a new type of «all silicon » photoelectrochemical cell which allows to split water under solar illumination, without the need for additional electrical energy.

Next, we will develop the manufacturing of silicon nanowire arrays by nanoelectrodeposition and we will functionalize them with receptor molecules to make biosensors. We will also continue our research on water-splitting photoelectrodes by integrating the silicon nanospikes that exhibit remarkable optical properties.

1. G. Loget, B. Fabre, S. Fryars, C. Mériadec, S. Ababou-Girard, Dispersed Ni nanoparticles stabilize silicon photoanodes for efficient and inexpensive sunlight-assisted water oxidation, 2017, ACS Energy Lett., 2, 569-573.
pubs.acs.org/doi/abs/10.1021/acsenergylett.7b00034

2. G. Loget, A. Vacher, B. Fabre, F. Gouttefangeas, L. Joanny, V. Dorcet, Enhancing light trapping of macroporous silicon by alkaline etching: application for the fabrication of black Si nanospike arrays, 2017, Mater. Chem. Front., 1, 1881–1887.
pubs.rsc.org/en/content/articlelanding/2017/qm/c7qm00191f

Silicon (Si) micro- and nanofabrication processes are of crucial importance for microelectronics and solar cells as much as for promising emerging technologies in nanoelectronics, biosensing devices, Li-ion batteries, or water-splitting membranes. These applications render the fabrication of Si nanostructured arrays a very hot topic that has attracted immense attention and research effort by the world’s best-ranked universities and leading companies. Manufacturing of highly organized arrays of Si nanostructures usually applies serial processes where the structures are fabricated successively. These techniques require expensive equipment operating under high vacuum and involving high running costs, which prevents a use in the routine-based manufacturing of large-scale arrays. In this context, parallel processes, which enable the simultaneous fabrication of individual nanostructures at designated spots on a large area, are considerably more attractive for decreasing manufacturing time and cost.
The aim of EASi-NANO is to break new grounds in the development of innovative and ambitious processes for the routine-based and low-cost manufacturing of large Si nanoarrays and to integrate these arrays into functional devices. The project is divided into the fabrication of two different types of arrays, Si nanowires (SiNWs) and nanoporous Si (NPSi). Both research axes combine simple photolithographic steps and electrochemical methods in bottom-up and top-down approaches and will be performed side-by-side. Unlike the majority of reported electrochemical and chemical nanostructuration processes, the EASi-NANO techniques will enable a high spatial control at the nano- and microscale, which is essential to fabricate highly organized arrays. Furthermore, these processes will be perfectly adapted for a routine-based preparation of large Si arrays at ambient conditions and without the need for a clean room.
The practical use of both types of surfaces developed in EASi-NANO will be demonstrated by integrating them into functional molecular nanoelectronic and sensing devices. To this goal, the SiNW array fabrication technique will be employed for the manufacturing of NW-based field-effect transistors (FETs). This application will benefit from the fabrication technique that allows to precisely define the number of aligned SiNWs in a single FET, which is very difficult to achieve using the actual solution-based fabrication methods. As a second application, we plan to use our SiNW FET arrays for detection, after modifying those with well-established surface chemistry techniques. Finally, we aim to use NPSi arrays as ultrahigh-capacity molecular memories. In this case, the NPSi arrays will be functionalized with a monolayer of an electroactive molecule by applying Si-H surface chemistry. The huge surface area of NPSi predicts considerably higher charge densities for the so-fabricated molecular micromemories compared to previously reported ones, which can be highly beneficial for the development of molecular charge storage devices.
EASi-NANO is a 42-months JCJC project coordinated by a thirty-year-old CNRS researcher specialized in nanostructuration. He will lead a team of young (average age: 38 years) and dynamic members, which provide the complementary skills required to successfully accomplish EASi-NANO and have already proven the high breakthrough potential of EASi-NANO with preliminary results. Concluding, EASi-NANO is a challenging project involving original approaches for achieving clear objectives that are: i) the development of low-cost processes for the manufacturing of high-quality Si nanostructure arrays and ii) the improvement of innovative technological applications using these arrays.