Silicon hydride passivated

Hydride surface termination has the capability for ideal surface passivation, with each hydrogen atom bonding to a single surface-dangling bond. On silicon, hydride termination has been well researched and shown to provide many advantages, including aqueous stability and limited air stability [13]. The hydride-terminated surface is also of interest as it can be used as a precursor for wet chemical reactions. 

Fig. 16.5. Synthetic methods employed for the functionalization of hydride-passivated porous silicon with monolayers bound via Si-C bonds. Derivatization has been accomplished through the cleavage of Si-Si surface bonds as well as by the reaction of Si-H groups.

As with solution loading, the surface passivation of the porous silicon is important when loading by melt intrusion - if the active is hydrophilic, for example, then the payload is likely to be small for hydride-passivated porous silieon. Some actives can, during loading, chemically oxidize or etch the porous silicon at elevated temperature, while some actives can degrade when in contact with the internally passivated silicon hydride surface. For the majority of applications, the highly reactive hydride surface will be modified before loading, more often than not by thermal oxidation (with, of course, subsequent reductions in pore volume and payload). 

Chen, B., A. K. Flatt, H. Jian, J. L. Hudson, and J. M. Tour. Molecular grafting to silicon surfaces in air using organic triazenes as stable diazonium sources and HF as a constant hydride-passivation source. Chem. Mater. 17, 2005 4832—4836. 

The passivation of silicon, motivated by the centrality of this semiconductor to the microelectronics industry, has been well studied. In addition to excellent passivation allowed by the silicon oxide, silicon can also be passivated with silicon nitride (Si3N4), other dielectrics, metal layers, and hydrogen. Here we focus only on hydride termination, since in addition to acting as a passivating layer for the underlying silicon, the hydride groups provide a versatile starting point for subsequent attachment chemistry. 

Functionalization studies have been carried out at both clean and hydrogen-passivated surfaces. The vast majority of studies on clean silicon substrates are performed under dry ultra-high vacuum conditions (UHV). On the other hand, reactions at hydride-terminated silicon commonly rely on wet chemical methods performed in solution. Regardless of the different environment and surface structure, common principles of the functionalization at semiconductor surfaces are emerging from these studies. 

Ongoing investigations into the chemistry of porous silicon surfaces seek to develop methods for the preparation of chemically functional interfaces that protect the underlying silicon nanocrystallites from degradation without changing or annihilating their intrinsic behavior. The native, hydride-terminated surface is only metastable under ambient conditions and oxidation of freshly prepared porous silicon commences within minutes when exposed to air. While surface oxide can suitably passivate the nanocrystalline silicon and stabilize its photoluminescence, the electrically insulating and structurally defective character of this oxide layer... 

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