For a sufficiently large charge imbalance, the electric field generated by the nanoparticle will be able to engender anodic etching not only at the nanoparticle/Si interface but also deeper into the surrounding Si. Electropolishing will occur at the nanoparticle/Si interface where the potential is highest. Farther away from the metal/Si interface, the electric field is high enough to induce either valence 2 or valence 4 etching and the production of nanocrystalline porous Si. A porous layer
surrounding the metal/Si interface would allow for transport of the etchant solution to the interface, which will facilitate etching and the transport of both reactants to and products away from the reactive PSI-7977 molecular weight interface. The oxidant primarily injects holes at the top of the metal nanoparticle rather than at the metal/Si interface, as illustrated Sapanisertib purchase in Figure 3. Figure 3 The mechanism of metal-assisted etching. Charge accumulation on
the metal nanoparticle generates an electric field. Close to the particle, the effective applied see more voltage is sufficient to push etching into the electropolishing regime, facilitating the formation of an etch track approximately the size of the nanoparticle. Further way, the lower voltage corresponds to the porous silicon formation regime. Conclusions The band structure of the metal/Si interface does not facilitate the diffusion of charge away from a metal after an oxidant has injected a hole into the metal. Therefore, the Bumetanide holes injected into the metal are not directly available to induce etching in Si. It is proposed here that the catalytic injection of holes by an oxidant in solution to a metal (film or nanoparticle) in metal-assisted etching (MAE) leads to a steady state charge imbalance in the metal. This excess charge induces an electric field in the vicinity of the metal and biases the surrounding Si. Close to the metal, the potential is raised sufficiently to induce etching with electropolishing character. Further away from the metal, the potential is sufficient to induce etching that leads to the formation of porous
silicon by either a valence 2 or valence 4 process. The balance between valence 2 etching, valence 4 etching, and electropolishing varies depending on the chemical identity of the metal. Authors’ information KWK is a Professor of Chemistry as well as a Chartered Chemist (Royal Society of Chemistry) with a Ph.D. in Chemical Physics from Stanford University and a B.S. in Chemistry from the University of Pittsburgh. Acknowledgements Experiments concerning the stoichiometry of metal-assisted etching to be reported elsewhere were performed together with William B. Barclay, now at the University of Maine. Electron microscopy in support of these experiments was performed with Yu Sun and Mark Aindow at the University of Connecticut.