Electron transfer during metal-assisted and stain etching of silicon

The etching of silicon in fluoride solutions is limited by the kinetics of charge transfer not thermodynamics. This characteristic is what gives fluoride etching its great versatility in making different types of nanostructures as the result of self-limiting chemistry. This review approaches the kinetics of electron transfer from silicon and metal coated silicon to a solution phase species from a fundamental point of view in order to establish a better understanding of the mechanisms of nanostructure formation during metal assisted and stain etching of silicon. Band bending calculations demonstrate that diffusion of holes away from low work function metals such as Ag is not possible. Similarly diffusion of holes outside of the space charge layer is not possible for high work function metals such as Au, Pd and Pt. While direct hole injection may be important for etch track pore formation in the immediate vicinity of the metal, the charge imbalance on or near the metal causes the metal to act like a nanopower supply that polarizes the surrounding Si. This second mechanism is implicated in nonlocal etching of Si during metal assisted etching

The mechanism of galvanic/metal-assisted etching of silicon

Metal-assisted etching is initiated by hole injection from an oxidant catalyzed by a metal nanoparticle or film on a Si surface. It is shown that the electronic structure of the metal/Si interface, i.e., band bending, is not conducive to diffusion of the injected hole away from the metal in the case of Ag or away from the metal/Si interface in the cases of Au, Pd, and Pt. Since holes do not diffuse away from the metals, the electric field resulting from charging of the metal after hole injection must instead be the cause of metal-assisted etching

Metal-Assisted Catalytic Etching (MACE) for Nanofabrication of Semiconductor Powders

Electroless etching of semiconductors has been elevated to an advanced micromachining process by the addition of a structured metal catalyst. Patterning of the catalyst by lithographic techniques facilitated the patterning of crystalline and polycrystalline wafer substrates. Galvanic deposition of metals on semiconductors has a natural tendency to produce nanoparticles rather than flat uniform films. This characteristic makes possible the etching of wafers and particles with arbitrary shape and size. While it has been widely recognized that spontaneous deposition of metal nanoparticles can be used in connection with etching to porosify wafers, it is also possible to produced nanostructured powders. Metal-assisted catalytic etching (MACE) can be controlled to produce (1) etch track pores with shapes and sizes closely related to the shape and size of the metal nanoparticle, (2) hierarchically porosified substrates exhibiting combinations of large etch track pores and mesopores, and (3) nanowires with either solid or mesoporous cores. This review discussed the mechanisms of porosification, processing advances, and the properties of the etch product with special emphasis on the etching of silicon powders

Bubbles: A review of their relationship to the formation of thin films and porous materials

Abstract Bubbles arise at the intersection of gases with other phases. Their role in the formation and applications of thin films and porous materials is complex. At times they are to be avoided. In other cases they are essential to the desired properties and outcomes. In many cases their function, form and production are misunderstood or disregarded. This review seeks to connect a diverse array of technical and fundamental aspects of bubbles so as to facilitate more control and understanding of their functions and utility</jats:p

Silicon in renewable power generation and storage: Decarbonizing the grid and automobile transport

Professor Kurt Kolasinski, Chemistry - Silicon in renewable power generation and storage: Decarbonizing the grid and automobile transport