X-ray photoelectron spectroscopic studies of interfacial chemistry at n-type silicon/liquid junctions

Abstract

The surface chemistry of n-type Si electrodes that had been etched, exposed to electrolyte, and electrochemically cycled has been probed using high-resolution X-ray photoelectron spectroscopy (XPS). n-Si surfaces etched in hydrofluoric acid-ethanol solutions (in air or N, ambients) displayed spectra in the Si 2p region that were free of detectable substrate oxide signals (15 X lo-" mol cm-, SO,; equivalent to 14% of a monolayer). Exposure of HF-C2H50H etched or of 49% HF(aq) etched n-Si surfaces to an electrolyte solution containing CH30H, dimethylferrocene (Me2Fc), and dimethylferricenium (Me2Fc+) generated very low levels, 1 ( 2 f 1) X mol cm-2 of silicon suboxides. Only sub-monolayer levels of SiO,, (4 f 2) X mol cm-2, were detected after electrochemical cycling of illuminated n-Si anodes in contact with CH30H-Me2Fc+/0 electrolytes. Even n-Si photoanodes maintained at short circuit with the CH30H-Me2Fc+/0 electrolyte for substantial periods (> 1000 C cm-, anodic charge passed) formed less than a single monolayer of strained Si02 at the silicon surface. Deliberate anodization of the Si surface in these electrolyte solutions yielded controlled amounts of thicker (8-10 A) Si02 overlayers; these overlayers provided a useful oxide for the formation of high-performance metal-insulatorsemiconductor device structures. These studies demonstrate that HF-C2H50H-or HF(aq)-etched n-Si surfaces are remarkably resistant to oxide formation during photoelectrochemical cycling in CH30H-based electrolytes, and that the outstanding photoelectrochemical Z-Vproperties of the n-Si/CH30H-Me2Fc+/0 junction are not a result of formation of passivating oxide overlayers on the Si surface.

Photoelectrochemical Generation of Electronically Conducting Polymer-Based Hybrid Junctions on Modified Si(111) Surfaces

“…28,29 The separations between these two peaks (0.6 eV) and their area ratios (∼0.55) are in close agreement with the theoretically expected values. 28,29 Furthermore, the formation of silicon oxides resulting from the reaction of remained silicon hydrides with residual oxygen is not detected (i.e., absence of a peak at binding energy 102-104 eV). However, it is important to note that the shift of the Si 2p peak is not a very sensitive measure of oxidation.…”

Reactions of Persistent Carbenes with Hydrogen-Terminated Silicon Surfaces

“…The silicon region of the XPS spectrum was consistent with the ATR-IR results ( vide supra ) in that, as compared to H– SiNPs , 6 · SiNPs experienced a moderate increase in the silicon suboxide (SiO x ) ,,, component (from 10% in H– SiNPs to 25% in isolated 6 · SiNP s), with an increase in its B.E. to 102.7 eV (Figure B); 7 · SiNP exhibited a SiO x peak at 103.0 eV, which constituted 44% of the observed Si 2p signal.…”

Organometallic chemistry on silicon surfaces: formation of functional monolayers bound through Si–C bonds

“…These surfaces can, however, be handled in air for tens of minutes with little degradation which renders them accessible to chemists and materials scientists wishing to use standard Schlenk and glove box techniques. 14 Silicon-hydride termination of commercial, native oxide capped flat crystal silicon wafers is carried out quickly and efficiently in under 10 min using commercially available fluoride sources. Dilute (1-2%) aqueous HF treatment of a Si(100) wafer yields the (100) dihydride NSiH 2 capped surface, and 40% aqueous NH 4 F of a Si(111) wafer provides the atomically flat (111) monohydride •SiH terminated surface.…”