Increasing performance demands on photodetectors and solar cells require the development of entirely new materials and technological approaches. We report on the fabrication and optoelectronic characterization of a photodetector based on optically-thick films of dense, aligned, and macroscopically long single-wall carbon nanotubes. The photodetector exhibits broadband response from the visible to the mid-infrared under global illumination, with a response time less than 32 μs. Scanning photocurrent microscopy indicates that the signal originates at the contact edges, with an amplitude and width that can be tailored by choosing different contact metals. A theoretical model demonstrates the photothermoelectric origin of the photoresponse due to gradients in the nanotube Seebeck coefficient near the contacts. The experimental and theoretical results open a new path for the realization of optoelectronic devices based on three-dimensionally organized nanotubes.

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We report on changes of surface structures induced by hydrogen adsorption on a Jahn-Teller distorted magnetite (Fe3O4)(001) surface and priorities of hydrogen-adsorbed sites by means of in-situ scanning tunneling microscopy. The experiments have revealed that surface Fe cations relax toward the bulk-terminated positions by OH species formed between adsorbed-hydrogen and surface ON anion (The labeled "N"in ON denotes that the O-O distance in the surface is compressed compared with bulk). Moreover, two types of surface ON sites were found to be almost equivalent for hydrogen adsorption.

We report two types of adsorption structures in H/Fe3O4(001) film surfaces and the correlation between OH density and Fe electronic states, which have been studied by scanning tunneling microscopy/spectroscopy (STM/STS). Two types of bright protrusions (BPs), whose lengths along the atomic rows are different, are observed in the STM images. The shorter and longer BPs consist of Fe atoms with one and with two OH groups neighbor, respectively. In addition, STS measurements show the higher local density of states (LDOS) just below the Fermi level of Fe atoms with increasing neighboring OH groups. The variation can be attributed to the difference in the gain of electrons from H atoms, which is due to the difference in the number of neighboring OH groups. These results reveal that surface OH density is a factor for determining the LDOS just below the Fermi level of surface Fe atoms.

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