Redox-Active Monolayers in Mesoporous Silicon

Abstract

Herein, redox reactions at chemically derivatized porous silicon (PSi) films are investigated. Passivation of the PSi matrix, by replacing metastable Si−H termini with nonpolar SiCCR linkages, allows the electrochemical PSi device to operate in aqueous environments under oxidizing conditions (i.e., electron hole accumulation regime). Cu(I)-catalyzed alkyne−azide cycloaddition reactions are used to anchor ferrocene derivatives and probe electrochemical reactions at the exceedingly large surface area-to-volume ratio of mesoporous PSi. The forward-biased p-type PSi/electrolyte interface retains a quasi-metallic behavior throughout its entire contour, and it does so for prolonged times even when the electrode is poised at potentials at which a bare silicon electrode would rapidly oxidize. The interfacial capacitance of the PSi matrix is, however, unexpectedly low. An explanation is proposed where PSi morphology and the semiconductor space-charge layer capacitance play a significant role in determining the charging properties of the electrode. These results are important for the application of porous semiconductor electrodes in sensing, electrocatalytic, and energyconversion devices.

Degradation mechanism of hydrogen-terminated porous silicon in the presence and in the absence of light

“…4). For the H-PSi wafers before the reaction, the peak for Si-H vibrations around 2100 cm −1 was obvious, 15,16 but completely and partly disappeared after the experiment for 2.5 h in the absence and presence of light, respectively. These results indicated that both reactions should display different degradation mechanisms.…”

A multimodal optical and electrochemical device for monitoring surface reactions: redox active surfaces in porous silicon Rugate filters

“…We have recently reported the modification of PSi with this same surface chemistry to allow the PSi to be used as a high surface area and low capacitance electrode. 6 As we characterized the surface chemistry using XPS, FTIR spectroscopy and electrochemistry in that previous report, here we will concentrate our discussion on the reflectivity measurements shown in Fig. 2.…”

“…1), 23 and pore diameters were in the range of 5-20 nm. 6 The high-reflection wavelength can vary over a wide range and depends on both the thickness and refraction index contrast of the alternating H and L layers. As is shown in Fig.…”

“…5 Second, the process of fabricating these photonic crystals results in a high surface area mesoporous material. Third, porous silicon can also serve as an electrode material, which we have recently reported can have surprisingly low interfacial charging capacitance, 6 a factor which is important in giving the electrode good analytical performances. 7 Fourth, at lower doping levels PSi is IR transparent which means transmission mode FTIR spectroscopy can be performed.…”

Impermeable Graphene Oxide Protects Silicon from Oxidation

“…This shadows the semiconducting properties of Si and becomes more critical for nanoscale devices whose output will be dominated by the SiO x layer . Conventionally, self-assembled monolayers comprising alkyl chains are used to protect Si from oxidation by blocking oxygen and water from reaching the bulk silicon. ,− This however comes with an expense of the need for complicated fabrication procedures that often require external effects, such as heat, light, or radical initiators, to enable the formation of covalent bonds between the monolayer-forming molecules and the surface. − In addition, the length of the alkyl chain on the molecules in the monolayer should be long enough to enable efficient packing . However, longer-chain molecules also come with the expense of blocking electron transfer. − Packing defects in monolayers, which allows for oxygen and water to reach the Si surface, lead to monolayer degradation over time. ,, Hence, there is a need to find a procedure to protect Si from oxidation while preserving the electron-transferring capability of the protecting layer.…”