Doping density, not valency, influences catalytic metal-assisted plasma etching of silicon.

Metal-assisted plasma etching (MAPE) of silicon (Si) is an etching technique driven by the catalytic activity of metals such as gold in fluorine-based plasma environments. In this work, the role of the Si substrate was investigated by examining the effects of the dopant concentration in both n- and p-type Si and the dopant atom type in n-type Si in SF6/O2 mixed gas plasma. At the highest dopant concentrations, both n- and p-type Si initially exhibit inhibition of the MAPE-enhanced etching. As the etch progresses, MAPE initiates, resulting in catalytic etching of the underlying Si at the metal-Si interface. Interestingly, MAPE-enhanced etching increases with decreasing doping concentrations for both n- and p-type Si substrates, distinct from results for the similar but divergent, metal-assisted chemical etching of silicon in liquid. Our findings show that the metal-Si interface remains essential to MAPE, and surface enrichment of the dopant atoms or other surface chemistries and the size of metal nanoparticles play roles in modulating catalytic activity.

Interfacial Contact is Required for Metal-Assisted Plasma Etching of Silicon.

For decades, fabrication of semiconductor devices has utilized well-established etching techniques to create complex nanostructures in silicon. The most common dry process is reactive ion etching which fabricates nanostructures through the selective removal of unmasked silicon. Generalized enhancements of etching have been reported with mask-enhanced etching with Al, Cr, Cu, and Ag masks, but there is a lack of reports exploring the ability of metallic films to catalytically enhance the local etching of silicon in plasmas. Here, metal-assisted plasma etching (MAPE) is performed using patterned nanometers-thick gold films to catalyze the etching of silicon in an SF6/O2 mixed plasma, selectively increasing the rate of etching by over 1000%. The catalytic enhancement of etching requires direct Si-metal interfacial contact, similar to metal-assisted chemical etching (MACE), but is different in terms of the etching mechanism. The mechanism of MAPE is explored by characterizing the degree of enhancement as a function of Au catalyst configuration and relative oxygen feed concentration, along with the catalytic activities of other common MACE metals including Ag, Pt, and Cu.

Combination Growth Factor Therapy via Electrostatically Assembled Wound Dressings Improves Diabetic Ulcer Healing In Vivo.

Chronic skin ulcerations are a common complication of diabetes mellitus, affecting up to one in four diabetic individuals. Despite the prevalence of these wounds, current pharmacologic options for treating them remain limited. Growth factor-based therapies have displayed a mixed ability to drive successful healing, which may be due to nonoptimal delivery strategies. Here, a method for coating commercially available nylon dressings using the layer-by-layer process is described to enable both sustained release and independent control over the release kinetics of vascular endothelial growth factor 165 and platelet-derived growth factor BB. It is shown that the use of strategically spaced diffusion barriers formed spontaneously by disulfide bonds enables independent control over the release rates of incorporated growth factors, and that in vivo these dressings improve several aspects of wound healing in db/db mice.