Evaluation of Greenbug and Yellow Sugarcane Aphid Feeding Behavior on Resistant and Susceptible Switchgrass Cultivars

Switchgrass (Panicum virgatum L.) is an emerging biofuel crop that serves as host for aphids. To discern the effects of plant age and possible resistance mechanisms, the feeding behavior of greenbugs (Schizaphis graminum Rondani.) and the yellow sugarcane aphid (Sipha flava Forbes.) was monitored on three diverse switchgrasses by the electrical penetration graph (EPG) technique. Callose deposition and genes associated with callose metabolism were also analyzed to discern their association with plant resistance. There was a strong host effect on greenbugs feeding on lowland cultivar Kanlow at the V3 stage of development, as compared to the greenbug-susceptible upland cultivar Summer and plants derived from Kanlow (♂) × Summer (♀) (K×S) crosses. These data confirmed that Kanlow at the V3 stage had antibiosis to greenbugs, which was absent in the Summer and K×S plants. In contrast, similar effects were not observed for yellow sugarcane aphids, excluding significant differences in the time to first probe on Kanlow plants at the V1 stage and reduction in time spent on pathway processes on Kanlow plants at the V3 stage. These data demonstrated that Kanlow plants may have multiple sources of resistance to the two aphids, and possibly some were phloem based. Microscopy of leaf sections stained with aniline blue for callose was suggestive of increased callose deposition in the sieve elements in Kanlow plants relative to Summer and K×S plants. RT-qPCR analysis of several genes associated with callose metabolism in infested plants was equivocal. Overall, these studies suggest the presence of multiple defense mechanisms against aphids in Kanlow plants, relative to Summer and K×S plants

Real time STM observation of Ostwald ripening of Pd nanoparticles on TiO2(110) at elevated temperature

A simple procedure was developed for the preparation of palladium nanoclusters on TiO2 with a bimodal distribution of particle sizes. Scanning tunnelling microscopy was used to observe the evolution of size distribution in real time at high temperatures. The observations were found to be consistent with an Ostwald ripening mechanism for cluster growth

Direct observation of behaviour of Au nanoclusters on TiO2 (110) at elevated temperatures

Deposition of Au on TiO2(110) at room temperature leads to nucleation of Au nanoparticles whose initial mean diameter varies between about 20 and 50 Å depending on the surface coverage. The behaviour of these clusters at elevated temperatures has been studied by scanning tunnelling microscopy (STM). Annealing surfaces with sub-monolayer coverages of Au at 750 K leads to growth of the larger clusters, but above 873 K evaporation of gold from the surface competes with this ripening processes. At 750 K the Au coverage remains constant over many hours allowing real-time observation of the behaviour of clusters in an "STM movie". Clusters with dimensions around 50 Å are remarkably static over a 6 h time period, but smaller clusters are observed to diffuse, mostly along the [0 0 1] direction. Events including cluster coalescence and cluster nucleation are also identified in the movie sequence. However the growth of the larger clusters at 750 K appears nonetheless to be dominated by Au atom transport across the terraces. © 2001 Elsevier Science B.V. All rights reserved

Ultra-thin oxide films on SiO2: An STM study of their thermal stability in the presence of Au deposit

The annealing of Au particles deposited onto the ultrathin layers of SiO2 on Si (111) has been studied in real time with a high temperature scanning tunnelling microscopy. Annealing did not create significant changes to the morphology of the surface until the surface was heated up to more than 920 K when the gold particles started to display a preference for the step edge. Further heating caused the decomposition of the oxide layer with the formation of voids on the surface in the surface step edge area. Comparison between the gold assisted oxide decomposition and pure oxide decomposition indicates that the two decomposition routes proceed with different mechanisms

Real time STM observation of Au-assisted decomposition of SiO2 films on Si(111) at elevated temperatures

The decomposition of ultrathin layers of SiO2 on Si(1 1 1) has been studied in real time in a high temperature scanning tunnelling microscope. Deposition of Au onto the SiO2 surface lowers the temperature of decomposition from 1000 to 940 K. Film decomposition takes place initially at step edges. The mechanism is shown to involve nucleation of Au nanoparticles at step edges, "sinking" of the Au particles to the buried SiO2/Si interface and accelerated reaction of substrate Si with SiO2 around Au nuclei. The Au/Si surface left after film decomposition supports a row-like reconstruction with a periodicity six times that of Si(1 1 1). © 2002 Published by Elsevier Science B.V

Initial and final state effects in photoemission from Au nanoclusters on TiO2 (110)

Valence level and shallow core states of Au nanoclusters on TiO 2(1 1 0) have been studied by synchrotron excited photoemission. The shift to high binding energy and broadening of the Au4f peaks with decreasing Au surface coverage can be understood in terms of decreasing cluster size and the associated effects of charge on the cluster in the final state. Shifts in the photoemission onset are much more pronounced than the core level shifts and show a strong dependence on the degree of reduction of the TiO 2(1 1 0) substrate. These observations suggest that the photoemission onset is influenced by an initial state effect involving charge transfer from defect states into cluster states. © 2002 Elsevier Science B.V. All rights reserved

The surface structure of TiO2(210) studied by atomically resolved STM and atomistic simulation

The (210) surface of rutile (TiO2) has been studied by the experimental techniques of scanning tunnelling microscopy (STM), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy and by atomistic simulation. Atomic scale imaging in STM is most easily achieved at positive sample bias, thereby sampling empty electronic states. Images from surfaces prepared by ion bombardment and UHV annealing are dominated by terraces supporting bright rows with a ∼ 10 Å separation along the [120] direction as expected for a (1 × 1) reconstruction. The STM images are interpreted in terms of a structure with a lower energy than found in previous atomistic simulation studies. This is built up from {110} nanofacets of dimension a/√2 and 3a/√2, where a is the tetragonal lattice parameter. Several characteristic defect features on the TiO2(210) (1 × 1) surface are discussed in relation to this model. LEED indicates that superstructures involving periodicities of up to 50 Å along [120] co-exist with the (1 × 1) terraces, particularly after prolonged annealing in UHV. Some of these enlarged nanofacets have also been imaged by STM

Photoemission and STM study of the electronic structure of Nb-doped TiO2

High-resolution core- and valence-level photoemission spectra of Nb-doped TiO2 ceramics (Ti1-xNbxO2 with 0.0

Photoemission and STM study of electronic structure of Nb-doped TiO2

High-resolution core- and valence-level photoemission spectra of Nb-doped TiO2 ceramics (Ti1-xNbxO2 with 0.01<x<0.8) have been measured using monochromatic x-ray excitation. Nb doping produces a well-defined photoemission peak in the bulk band gap of rutile, whose intensity increases with increasing doping level. Core-level spectroscopy shows that the Nb is incorporated within the rutile lattice at low doping levels mainly as Nb(V) and that the gap state is associated with Ti(III) ions. This conclusion is reinforced by variable energy photoemission measurements on Ti0.9Nb0.1O2 in the vicinity of the Ti 3p and Nb 4p core thresholds. The photoemission resonance profile for the gap states reaches half maximum intensity at the same energy as found for oxygen-deficient TiO2-x but is shifted from the resonance profile for the Nb 4d states of NbO2. STM images on Nb-doped TiO2(110) are considered in relation to the spectroscopic measurements. Nb dopant atoms are imaged as “bright spot” clusters, implying delocalization of charge from Nb onto neighboring Ti ions. The experimental x-ray photoelectron spectroscopy data are compared with density-of-states profiles derived from local-density approximation calculations on pure and Nb-doped TiO2 clusters. These calculations show that Nb doping of TiO2 introduces new states of mixed Nb4d–Ti3d character above the O 2p valence band of the host material. In addition, there is increased x-ray photoemission intensity across the O 2p valence band owing to strong Nb4d/O2p hybridization and a cross section for ionization of Nb 4d states that is an order of magnitude larger than that for O 2p or Ti 3d states