Using scanning tunneling microscopy (STM), we investigate the spatial distribution of the bridging hydroxyl (OHb) bound excess electrons on the rutile TiO2(110) surface and its temperature dependence. By performing simultaneously recorded empty and filled state imaging on single OHbs at different temperatures in STM, we determine that the spatial distribution of the OHb bound excess electrons retains a symmetric four-lobe structure around the OHb at both 78 and 7 K. This indicates that OHbs are much weaker charge traps compared to bridging O vacancies (Ob-vac). In addition, by sequentially removing the capping H of each OHb using voltage pulses, we find that the annihilation of each OHb is accompanied by the disappearance of some lobes in the filled state STM, thus verifying the direct correlation between OHbs and their excess electrons.

Nanoscale interconnects are an important component of molecular electronics. Here we use X-ray spectromicroscopy techniques as well as scanning probe methods to explore the self-assembled growth of insulated iron nanowires as a potential means of supplying an earth abundant solution. The intrinsic anisotropy of a TiO2(110) substrate directs the growth of micron length iron wires at elevated temperatures, with a strong metal-support interaction giving rise to ilmenite (FeTiO3) encapsulation. Iron nanoparticles that decorate the nanowires display magnetic properties that suggest other possible applications.

Pronouns used as tags (It's funny, that), comparable in certain respects to their much more widely studied question tag counterparts (It's funny, isn't it?), are a feature of the right periphery of clauses in some dialects of British English. In this paper, we investigate the co-occurrence of ProTags with other pragmatic markers in the right periphery and find evidence to support a general ordering principle subjective > intersubjective, consistent with the model proposed in Shinzato (2007). Our searches of multiple corpora have revealed that ProTags can appear in various combinations with markers such as though and you know, as well as question tags (It's funny that isn't it?). By far the most commonly attested were combinations of ProTags and question tags, with the majority having ProTag > question tag ordering. Our results show that there is a strong tendency for a ProTag to precede other right-periphery pragmatic markers consistent with it having subjective core meaning, that it can combine with an intersubjective pragmatic marker to form a compound pragmatic marker with intersubjective meaning, and that certain combinations of pragmatic markers with subjective meaning can exhibit flexibility of ordering at the right periphery. (C) 2021 Elsevier B.V. All rights reserved.

Understanding the mechanism behind the superior catalytic power of single- or few-atom heterogeneous catalysts has become an important topic in surface chemistry. This is particularly the case for gold, with TiO2 being an efficient support. Here we use scanning tunneling microscopy/spectroscopy with theoretical calculations to investigate the adsorption geometry and local electronic structure of several-atom Au clusters on rutile TiO2(110), with the clusters fabricated by controlled manipulation of single atoms. Our study confirms that Au1 and Au2 clusters prefer adsorption at surface O vacancies. Au3 clusters adsorb at O vacancies in a linear-chain configuration parallel to the surface; in the absence of O vacancies they adsorb at Ti5c sites with a structure of a vertically pointing upright triangle. We find that both the electronic structure and cluster-substrate charge transfer depend critically on the cluster size, bonding configuration, and local environment. This suggests the possibility of engineering cluster selectivity for specific catalytic reactions.

Multiply bonded lanthanide oxo groups are rare in coordination compounds and have not previously been reported for a surface termination of a lanthanide oxide. Here we report the observation of a Ce=O terminated ceria surface in a CeO 2 (111)-( × )R30° reconstruction of ≈3 nm thick ceria islands prepared on Pt(111). This is evidenced by scanning tunnelling microscopy (STM), low energy electron diffraction (LEED) and high-resolution electron energy loss spectroscopy (HREELS) measurements in conjunction with density functional theory (DFT) calculations. A Ce=O stretching frequency of 775 cm −1 is observed in HREELS, compared with 766 cm −1 calculated by DFT. The calculations also predict that the Ce=O bond is weak, with an oxygen vacancy formation energy of 0.85 eV. This could play an important role in the facile removal of lattice oxygen from CeO 2 , accompanied by the reduction of Ce IV to Ce III , which is a key attribute of ceria-based systems in connection with their unique catalytic properties.

The properties of materials can be altered by introducing strain. For instance, the critical temperature of superconductors has been raised as has the Curie temperature of ferroelectric materials. As TiO 2 is the most studied single crystal metal oxide, it is highly desirable to understand how strain might be used to tune its properties. Theoretical calculations indicate that the band gap of anatase TiO 2 may be lowered, which would remove one of the roadblocks to its wider use as a photocatalyst. Surface defects on rutile TiO 2 are responsible for a large part of its reactivity and the nature of these may also be affected by strain according to calculations. In this review, the introduction of strain and its effect on reactivity will be examined. The strain in the most part arises from lattice mismatch in the growth of TiO x films on various substrates although cases where TiO 2 is the substrate are also included as is the implantation of Ar clusters in the subsurface of TiO 2 .

A novel method of measuring the core level binding energies of multiple sized nanoparticles on the same substrate is demonstrated using the early stage of Au nanoparticle growth on reduced r-TiO2(110). This method employed in situ scanning tunneling microscopy (STM) and microfocused X-ray photoemission spectroscopy. An STM tip-shadowing method was used to synthesize patterned areas of Au nanoparticles on the substrate with different coverages and sizes. Patterns were identified and imaged using a UV photoelectron emission microscope. The Au 4f core level binding energies of the nanoparticles were investigated as a function of Au nanoparticle coverage and size. A combination of initial and final state effects modifies the binding energies of the Au 4f core levels as the nanoparticle size changes. When single Au atoms and Au3 clusters are present, the Au 4f7/2 binding energy, 84.42 eV, is similar to that observed at a high coverage (1.8 monolayer equivalent), resulting from a cancellation of initial and final state effects. As the coverage is increased, there is a decrease in binding energy, which then increases at a higher coverage to 84.39 eV. These results are consistent with a Volmer-Weber nucleation-growth model of Au nanoparticles at oxygen vacancies, resulting in electron transfer to the nanoparticles.

Electron stimulated modifications of the rutile TiO2(110) surface have been investigated using scanning tunnelling microscopy tip pulses and electron beam irradiation. Tip pulses on the 'as-prepared' surface induce local surface reconstruction and removal of surface hydroxyls in a region around the reconstruction. A defocused beam from an electron gun as well as tip pulses have been used to generate a number of oxygen deficient surfaces. All tip pulse features display an oval profile, which can be attributed to the anisotropic conductivity of the TiO2(110) surface. A novel oxygen deficient phase with well-ordered defective 'nano-cracks' has been identified, which can be produced by either electron beam irradiation or low flash anneal temperatures (similar to 570 K). Annealing such surfaces to moderate temperatures (similar to 850 K) leads to mixed 1 x 1 and 1 x 2 surfaces, until now only achievable by annealing in oxygen or ageing by repeated sputter/anneal cycles. Heating to normal preparation temperatures (1000 K) reforms the clean, well-ordered 1 x 1 surface termination. Our results demonstrate the potential of electron induced processes to modify the oxygen composition and structure of the TiO2(110) surface in a controllable and reversible way for selective surface patterning and surface reactivity modification.

Time-resolved pump-probe photoemission spectroscopy has been used to study the dynamics of charge carrier recombination and trapping on hydroxylated rutile TiO2(110). Two types of pump excitation were employed, one in the infrared (0.95 eV) and the other in the UV (3.5 eV) region. With IR excitation, electrons associated with defects are excited into the bottom of the conduction band from the polaronic states within the band gap, which are retrapped within 45±10 fs. Under UV excitation, the electrons in these band gap states and valence band electrons are excited into the conduction band. In addition to the fast polaron trapping observed with IR excitation, we also observe a long lifetime (about 1 ps) component to both the depletion of hot electrons at the bottom of the conduction band and the refilling of the band gap states. This points to a band gap state mediated recombination process with a ps lifetime.

Water-oxide surfaces are ubiquitous in nature and of widespread importance to phenomena like corrosion as well as contemporary industrial challenges such as energy production through water splitting. So far, a reasonably robust understanding of the structure of such interfaces under certain conditions has been obtained. Considerably less is known about how overlayer water modifies the inherent reactivity of oxide surfaces. Here we address this issue experimentally for rutile TiO2(110) using scanning tunneling microscopy and photoemission, with complementary density functional theory calculations. Through detailed studies of adsorbed water nanoclusters and continuous water overlayers, we determine that excess electrons in TiO2 are attracted to the top surface layer by water molecules. Measurements on methanol show similar behavior. Our results suggest that adsorbate-induced surface segregation of polarons could be a general phenomenon for technologically relevant oxide materials, with consequences for surface chemistry and the associated catalytic activity.

Au/Pd nanoparticles are important in a number of catalytic processes. Here we investigate the formation of Au–Pd bimetallic nanoparticles on TiO2(110) and their susceptibility to encapsulation using scanning tunneling microscopy, as well as Auger spectroscopy and low energy electron diffraction. Sequentially depositing 5 MLE Pd and 1 MLE Au at 298 K followed by annealing to 573 K results in a bimetallic core and Pd shell, with TiOx encapsulation on annealing to ~ 800 K. Further deposition of Au on the pinwheel type TiOx layer results in a template-assisted nucleation of Au nanoclusters, while on the zigzag type TiOx layer no preferential adsorption site of Au was observed. Increasing the Au:Pd ratio to 3 MLE Pd and 2 MLE Au results in nanoparticles that are enriched in Au at their surface, which exhibit a strong resistance towards encapsulation. Hence the degree of encapsulation of the nanoparticles during sintering can be controlled by tuning the Au:Pd ratio.

Au nanoparticles supported on reducible metal oxide surfaces are known to be active catalysts for a number of reactions including CO oxidation and hydrogen production. The exact choice of a metal oxide support has been shown to have a marked impact on activity, suggesting that interactions between Au and the support play a key role in catalysis. For TiO2, a model substrate for Au catalysis, it had been thought that bridging oxygen vacancies are involved in binding Au atoms to the (110) surface based on indirect evidence. However, a recent scanning transmission electron microscopy study of single Pt atoms on TiO2(110) suggests that subsurface vacancies are more important. To clarify the role of bridging or subsurface vacancies we employ scanning tunneling microscopy to determine the bonding site of single Au atoms on TiO2(110). Using in situ deposition as well as a manipulation method, we provide definitive evidence that the bonding site is atop surface oxygen vacancies.

Titanium dioxide is a promising candidate for photocatalytic H2 fuel production, and understanding water splitting on TiO2 surfaces is vital toward explaining and improving the generation of H2. In this work, we electron irradiate anatase TiO2(101) at room temperature to create metastable surface oxygen vacancies in order to investigate their ability to dissociate H2O. Our scanning tunneling microscopy investigations suggest that the surface oxygen vacancies can dissociate H2O by forming bridging OH species. This claim is supported by theoretical calculations from the literature and our previously published spectroscopic measurements.

Postgraduate year 1 (PGY1) and postgraduate year 2 (PGY2) pharmacy residency programs are critical for providing additional education and advanced training after completion of the doctor of pharmacy degree program. PGY1 programs generally have a broad practice focus, and PGY2 programs have a more specialized focus, such as cardiology, oncology, nuclear, or pediatric pharmacy.1 While the benefits of completing a residency have been previously described,2–6 no published study has specifically elucidated the factors motivating PGY1 residents to pursue a PGY2 residency. To evaluate the motivational factors and barriers influencing current PGY1 and PGY2 pharmacy residents’ decision to pursue a PGY2 residency program, we conducted a Web-based survey directed toward all PGY1 and PGY2 residents attending the May 2014 Western States Conference, an annual conference that features residents presenting their research findings. The 3-point Likert-type scale survey (1 = very important, 2 = somewhat important, and 3 = not important) assessed motivational factors and barriers adapted from Bucci et al.7 and McCarthy and Weber.8 Of the 706 potential resident participants, 249 (35.3%) responded. Fifty-one surveys were deemed incomplete and excluded from the analysis, leaving a final cohort of 198 (28.0%) responses. The majority of respondents were women (71.2%), PGY1 residents (76.3%), and age 20–30 years (80.8%). Among the PGY1 residents surveyed, 85.6% were completing a pharmacy practice residency program, 9.8% were completing a community pharmacy residency, and 4.6% were completing a managed care pharmacy residency.

Interest in resolving the mechanisms behind ceria's activity has been intense due to the numerous industrial applications including those in heterogeneous catalysis. In this work, we study the reduction and reoxidation of ultrathin CeO2(111) nanoislands on Rh(111) and Pt(111) substrates, so-called inverse model catalysts, with a combination of real and reciprocal space techniques based on X-ray photoemission electron microscopy (XPEEM) and low energy electron microscopy. Soft X-ray microfocused illumination was employed to reduce the ceria islands, which we are able to control by varying the oxygen partial pressure within the measurement chamber. Low energy electron diffraction measurements of the irradiated ceria films demonstrate the formation of an ordered array of oxygen vacancies leading to a (/7 x root 7)R19.1 degrees superstructure attributed to the i-phase (Ce7O12)(111). Resonant photoelectron spectroscopy provides the required high sensitivity to detect small changes in Ce3+ concentration. The high spatial resolution of the XPEEM allows us to determine that the reduction of the ceria occurs initially at the interface of the islands with the Rh support. Reoxidation of the CeO2-x(111) to CeO2(111) proceeds via spillover of activated oxygen adsorbed on the Rh(111) surface as a (2 x 2) overlayer. Our results highlight the important role that the noble metal plays in the regeneration of the stoichiometric ceria surface, a vital step in many reactions on ceria. This differs from the commonly proposed Mars van Krevelen model in which reoxidation involves direct reaction of the ceria with O-2.

Polarons in metal oxides are important in processes such as catalysis, high temperature superconductivity, and dielectric breakdown in nanoscale electronics. Here, we study the behavior of electron small polarons associated with oxygen vacancies at rutile TiO_{2}(110), using a combination of low temperature scanning tunneling microscopy (STM), density functional theory, and classical molecular dynamics calculations. We find that the electrons are symmetrically distributed around isolated vacancies at 78 K, but as the temperature is reduced, their distributions become increasingly asymmetric, confirming their polaronic nature. By manipulating isolated vacancies with the STM tip, we show that particular configurations of polarons are preferred for given locations of the vacancies, which we ascribe to small residual electric fields in the surface. We also form a series of vacancy complexes and manipulate the Ti ions surrounding them, both of which change the associated electronic distributions. Thus, we demonstrate that the configurations of polarons can be engineered, paving the way for the construction of conductive pathways relevant to resistive switching devices.

The electronic structure of cross-linked TiO2(110)-(1×2) has been investigated using scanning tunneling spectroscopy (STS) and by monitoring changes in ultraviolet photoelectron spectroscopy (UPS) following exposure of the surface to O2. STS reveals two states located in the bandgap, at 0.7 and 1.5eV below the Fermi level. The population of these two states varies over different parts of the (1×2)-reconstructed surface. An additional state at 1.1eV above the Fermi level is observed at the double link part of the structure. All of the bandgap states are attenuated following exposure to O2, while the workfunction is increased. We attribute this to an electron transfer from the surface to the adsorbed oxygen.