One dimensional (1D) nanostructures such as nanotubes (NTs) or nanowires (NWs) have been attracting a large interest in the last decades. These 1D nanomaterials exhibit interesting electrical, optical, mechanical and chemical properties thanks to their high aspect ratio and large surface area. Because of their surface properties, NWs have been developed in many applications such as solar cells, biological and chemical sensors, catalysts or batteries. However, due to time consuming, complex and expensive technological techniques, the industrialization of devices based on a unique NWs is limited. Moreover, due to a large variability between NW properties, there is an obvious lack of reproducibility from one device to another. As a consequence, it is difficult to exploit unique properties of NWs into actual devices.
On the contrary, materials composed of randomly oriented NWs offer a good reproducibility and have been attracting recent interest in many applications. Also called “nanonets”, for NANOstructured NETworks as proposed by G. Grüner, such materials show several interesting properties arising either from the individual components, the NWs or NTs, or from the structural properties of the network itself. These properties include:
When the nanonet thickness is significantly thinner than the length scale of its individual components, the nanonet is considered as two-dimensional (2D) because the percolation properties of such network show typical 2D characteristics. Carbon nanonets (composed of carbon NTs, functionalized or not) and metallic nanonets (composed of silver or copper NWs) have been studied for a decade and are widely described in the literature particularly for the fabrication of transparent and conductive thin films for photovoltaic applications. In contrast, there are currently very few studies on 2D nanonets based on nanomaterials other than carbon or silver, such as, for example, Si, ZnO, and other semiconducting NWs, despite the high potential of such materials.
From Serre et al, Nanotechnology 26 (2015) 015201
Composed of Si nanowires (NWs), Si nanonets are, so far, considered by the scientific community as non-interesting material for electrical applications. For example, Hong wrote in one of his highly cited paper: “One of the major problems in using Si-NWs for large area device applications is that it is very difficult to build long-channel devices based on Si-NW networks because individual Si-NWs do not make a good electrical contact with each other due to the native oxide layer. A possible solution is putting intermediate contact pad structures on long Si-NW network channels.” [Nano Letters 8 4523–7 (2008)].
We demonstrate that using adequate processing, it is possible to build percolating networks that show high and long-term performances.
Composed of carbon nanotubes (CNTs), the carbon nanonets are extensively studied since 2000 as they combine high transparency, good conductivity and flexibility. As a consequence, they are promising material for integration into solar cells, emitting devices or display panels… In collaboration with the groups of R. Martel and P. Desjardins, we demonstrate, a highly versatile and simple process to use them as top contact electrode for nanowires. Carbon nanonets are also an interesting starting point to build arrays of CNT electrodes.
mise à jour le 25 mars 2019