G. Jones

Ultrathin ordered CeO2 overlayers on Pt(111): interaction with NO2, NO, H2O and CO

Abstract The effect of gas exposure on the electronic valence band structure of ultrathin ordered CeO 2− x overlayers on Pt(111) 1×1 single crystals is reported. Resonant photoemission spectra at 120xa0eV excitation energy show the presence of an occupied Cexa04f bandgap state that is associated with Ce 3+ , the concentration of which depends on the sample preparation. Heating in oxygen ( p O 2 =6×10 −5 xa0mbar, T =1000xa0K) yields a lower Cexa04f intensity than heating in vacuum ( T =800xa0K), while the (1.4×1.4) superstructure of the overlayer remains unchanged. A decrease of the Cexa04f bandgap state occurs upon even small exposures of NO 2 at 300 and 400xa0K. At these temperatures, NO does not affect the Cexa04f state. Reflection-absorption infrared spectroscopy (RAIRS) indicates that NO 2 dissociates into NO and atomic oxygen O (a) at bare Pt surface sites. O (a) atoms remain adsorbed, even at 400xa0K, and oxidize Ce 3+ to Ce 4+ . Surprisingly, H 2 O reduces CeO 2− x /Pt(111) at 300xa0K, increasing the Ce 3+ concentration while significant concentrations of molecularly adsorbed water or hydroxyl groups are not formed. Interestingly, CO only reacts with CeO 2− x /Pt(111) following a particular pretreatment of the sample. A decrease of the Cexa04f intensity upon CO exposure was observed only for a vacuum-annealed and an H 2 O-reduced sample, while an NO 2 pre-exposed surface does not react with CO, as measured by a change of the Ce 3+ /Ce 4+ ratio of CeO 2− x /Pt(111).

Electronic structure of Pt overlayers on (1 × 3) reconstructed TiO2(100) surfaces

Abstract The effect of Pt atoms on the Ti 3d emission of Ti3+ states at (1 × 3) reconstructed TiO2(100) surfaces was studied by means of valence band photoemission spectroscopy using synchrotron radiation with excitation energies between 30 and 120 eV. A clean (1 × 3) reconstructed TiO2(100) surface was prepared by Ar+ sputtering and annealing at T = 870 K as checked with low energy electron diffraction. Subsequently, Pt was evaporated in situ using a resistively heated Pt filament. Evaporation was performed stepwise up to a nominal coverage of 1.8 monolayers (ML) as checked with Auger electron spectroscopy (AES). The Pt 4f core levels are shifted to higher binding energies with respect to Pt metal, indicating the presence of small Pt clusters. Difference spectra show a dublet between the TiO2 valence band maximum and the Fermi energy which is attributed to Pt 5d states. We found that the position and the intensity of the Ti 3d band gap emission were not significantly altered upon evaporation of Pt. In addition, the valence band maximum of TiO2 remains unchanged. These findings indicate the absence of an electronic charge transfer due to the high work function of TiO2(100)-(1 × 3) of 5.4 eV, in line with a simple metal-semiconductor contact theory.

Laser‐based multi‐user 3‐D display

Abstract— The development of a multi-user stereoscopic display that does not require the use of special glasses (autostereoscopic), and that enables a large degree of freedom of viewer movement and requires only the minimum amount of information (a stereo pair) for the displays described. The optics comprise an RGB holographic laser projector that is controlled by the output of a multi-target head-position head tracker, an optical assembly that converts the projector output into steerable exit pupils, and a screen assembly comprising a single liquid-crystal display (LCD) and image multiplexing screen. A stereo image pair is produced on the LCD by simultaneously displaying left and right images on alternate rows of pixels. Novel steering optics that replace the conventional backlight are used to direct viewing regions, referred to as exit pupils, to the appropriate viewers eyes. The results obtained from the first version of the display, where the illumination source consists of several thousand white LEDs, are given and the current status of the latest prototype being constructed on the basis of these results is described. The work indicates that a laser-based head-tracking display can provide the basis for the next generation of 3-D display.

European Research into Head Tracked Autostereoscopic Displays

Stereoscopic displays that do not require the wearing of special glasses (autostereoscopic), enable a large degree of freedom of viewer movement and show the minimum amount of information have been developed within several European Union-funded projects. In the ATTEST and MUTED projects a stereo image pair is produced on a single liquid crystal display (LCD) by simultaneously displaying left and right images on alternate rows or columns of pixels. Novel steering optics is used to direct regions, referred to as exit pupils, to the appropriate viewers eyes. The positions of these are controlled by the output of a head position tracker. In the HELIUM3D project an autostereoscopic image is produced with the use of a light engine and illumination is provided by an RGB laser. Exit pupil locations are determined by a head tracker controlling a spatial light modulator (SLM).

Angle-resolved photoemission studies of the \̄gG Shockley surface state on ordered Cu(111) overlayers on TiO2(110)

Angle-resolved photoemission spectroscopy at hv = 70 eV has been used to investigate the surface electronic structure of a thin metal overlayer [Cu(111)] on an oxide substrate [TiO2(110)]. The Cu-film thickness was about 17 A. The Cu(111) gG Shockley state exhibits a noncircular E versus k‖ dispersion around gG in contrast to the behaviour of the single crystal Cu(111) surface state. In addition the overlayer surface state is broadened and shifted by 0.05 eV to lower BE. The energy shift is interpreted as an effect of the surface step density whilst we tentatively assign the k‖ asymmetry of the state to the nature of the overlayer growth which is only commensurate with the substrate along the gGM Brillouin zone direction.