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To better understand the autoxidation mechanism of Cu-based catalysts, we studied the oxidation of Cu sheet exposed to ultrahigh vacuum and air at ambient temperature using X-ray photoelectron spectroscopy (XPS) and density functional theory. Six main stages of Cu autoxidation are revealed: (1) dissociative adsorption of O 2 , (2) coexistence of nondissociative and dissociative H 2 O adsorption, (3) diffusion of O and OH into Cu bulk, (4) formation of metastable Cu 2 O layer, (5) further oxidation and formation of metastable Cu(OH) 2 and CuO layer, and (6) transformation phase of the metastable Cu(OH) 2 to CuO. The formation of Cu(OH) 2 depends on the relative humidity of air and the concentration of adsorbed OH of the Cu sheet. On the basis of these results, we propose that the preservation time of the Cu-based catalysts should be decreased or the catalysts should be preserved in a high vacuum and at low relative humidity. Considering the time of the sample preparation before ex situ XPS analysis and other surface characterizations, the Cu-based catalysts need to be etched by ∼10 s using an Ar ion gun. These findings serve as a guide for the preservation and preparation of Cu-based catalysts before actual measurement.

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Silicon doped with selenium beyond the solid solubility limit was prepared by picosecond pulsed laser mixing of an evaporation-deposited Se film with the underlying p-Si wafer. Photodiodes fabricated from this material exhibit enhanced spectral response over the range from 400 to 1600 nm. The responsivity strongly depends on reverse bias voltage and pulsed laser fluence. At 5 V bias, a room-temperature responsivity of 16 A W −1 at 1000 nm is obtained. At below-bandgap wavelengths, measurable responsivities of 15 mA W −1 at 1330 nm and 12 mA W −1 at 1550 nm are also observed. Extended Se impurity states might form within Si bandgap and contribute to the prominent photoresponse in these photodiodes.

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