Giant electrochemical actuation in a nanoporous silicon-polypyrrole hybrid material

Abstract

The absence of piezoelectricity in silicon makes direct electromechanical applications of this mainstream semiconductor impossible. Integrated electrical control of the silicon mechanics, however, would open up new perspectives for on-chip actuorics. Here, we combine wafer-scale nanoporosity in single-crystalline silicon with polymerization of an artificial muscle material inside pore space to synthesize a composite that shows macroscopic electrostrain in aqueous electrolyte. The voltage-strain coupling is three orders of magnitude larger than the best-performing ceramics in terms of piezoelectric actuation. We trace this huge electroactuation to the concerted action of 100 billions of nanopores per square centimeter cross section and to potential-dependent pressures of up to 150 atmospheres at the single-pore scale. The exceptionally small operation voltages (0.4 to 0.9 volts), along with the sustainable and biocompatible base materials, make this hybrid promising for bioactuator applications.

Dynamic Kerr and Pockels electro-optics of liquid crystals in nanopores for active photonic metamaterials

“…Thus, similarly, as it has been demonstrated for liquid-infused porous structures with electrochemical actuation 85 and wetting changes, 86 as well as versatile multifunctional material behavior in general, 87 our study indicates that liquid crystal-infused nanoporous solids allow for quite simple fabrication of electro-active functional nanomaterials. The functionalization approach by capillarity-driven spontaneous imbibition of the liquid-crystalline melt in combination with tailorability of anodic aluminum oxide 41,88–90 and the availability of other self-organized, optically transparent mesoporous media 10,66,91,92 demonstrate also the versatile character of the presented material fabrication process.…”

Laser-excited elastic guided waves reveal the complex mechanics of nanoporous silicon

“…This reduction can be traced back to inactive silicon walls as discussed in ref. 19 . In that study, the authors modelled the pSi network based on transmission electron micrographs, therefore taking its irregular microstructure into account, and thus providing a more accurate description of the sensitive influence of the silicon scaffold structure on the mechanics compared to earlier work based on an idealised regular honeycomb structure 18,60 .…”

“…3f). This observation suggests that, although some degree of anisotropy may remain in the x 1 x 2 -plane of the plate, for the considered porosity the presence of the pores prevails over the original crystalline nature of bulk silicon (i.e., cubic anisotropy) 19,53 . For bulk silicon, the measured guided modes are in excellent agreement with the guided modes predicted by the theory (continuous white lines in Fig.…”

“…It provides a monolithic single-crystalline medium with anisotropic pores for the fundamental study of confinement effects on matter [7][8][9][10][11][12][13] . Interesting optical, electrical and thermal properties attract the attention of the applied sciences in fields like optoelectronics 14 , biosensing 15,16 thermoelectronics 17 , mechanical actuation 18,19 and energy storage 3,4 . Applications in microelectromechanical systems (MEMS) are promising due to the great availability and compatibility of pSi: The raw material silicon is one of the most common elements on earth and available in unparalleled qualities.…”

“…Wafer-scale pSi can be integrated into existing electrical circuits with reasonable expense since bulk silicon is the predominant material for semiconductor devices 16,20 . Furthermore, pSi is bio-compatible and can be functionalised, by changing, extending or enhancing its properties by subsequent treatments, by incorporating additional functional materials [2][3][4]7,19,21 or direct laser writing in pore space 22 .…”