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Electricity in many countries such as the US and China is produced by burning fossil fuels in steam-turbine-driven power plants. The efficiency of these power plants can be improved by increasing the operating temperature of the steam generator. In this work, we adopted a combined surface science and computational thermodynamics approach to the design of high-temperature, corrosion-resistant steels for this application. The result is a low-carbon ferritic steel with nanosized transition metal monocarbide precipitates that are thermally stable, as verified by atom probe tomography. High-temperature Vickers hardness measurements demonstrated that these steels maintain their strength for extended periods at 700 °C. We hypothesize that the improved strength of these steels is derived from the semi-coherent interfaces of these thermally stable, nanosized precipitates exerting drag forces on impinging dislocations, thus maintaining strength at elevated temperatures.

Grazing incidence X-ray diffraction and LEED were used together to determine the locations of surface titanium and oxygen atoms of the near-stoichiometric rutile TiO2(100)1 × 3 reconstructed surface. This surface is found to contain (110) microfacets with significant displacements from the ideally terminated bulk atomic positions. The structural model presented is consistent with the stability of the (110)1 × 1 surface and explains naturally the higher order reconstructions observed for the (100) surface at elevated temperatures.

Au was deposited in situ on β-SiC(001) surfaces at room temperature after the substrates were cleaned by annealing, first in a Si flux and then in vacuum. By adjusting the time and temperature of the vacuum anneal, SiC surfaces of four compositions, ranging from Si-rich to Si-deficient, were obtained. Surfaces were monitored using Auger electron, electron energy loss, X-ray photoelectron, and ultraviolet photoelectron spectroscopies as Au films ranging in thickness from ∼ 1 to 37 A were deposited. For Au on Si-terminated β-SiC surfaces, three distinct regions formed as the Au overlayer grew: interfacial Au-Si alloy, pure Au above the alloy, and a surface layer of Au-Si alloy. Interfacial alloy thickness and surface alloy Si concentration were both proportional to the amount of Si on the initial SiC surface. For Au depositions s 5 A, bands bending change, dependent on the initial β-SiC surface composition, were observed. On Si-deficient β-SiC surfaces, the Au growth mode differed completely. Au clusters formed, similar to Au behavior on C substrates. No band bending changes were observed, consistent with weak film/substrate interaction. For the Au/β-SiC system, overlayer composition and morphology are controlled by composition changes in the top 1–2 monolayers of the SiC substrate.

Cubic β-SiC(001) surfaces were cleaned in ultra-high vacuum by heating within a Si atomic flux, allowing contaminant species to desorb while continuously replenishing volatile surface Si. Using this technique, surface compositions ranging from Si-rich to Si-deficient were prepared. Surfaces were subsequently characterized using Auger electron, electron energy loss. X-ray photoelectron, and ultraviolet photoelectron spectroscopies as well as low energy electron diffraction. Data are presented for a range of surface compositions which result in formation of several reconstructions: (3 × 1), c(4 × 2), (2 × 1), c(2 × 2), and (1 × 1). Results are interpreted based on surface models which include ordered arrays of surface Si dimers for Si-rich and Si-terminated surfaces and graphite formation for Si-deficient surfaces.

Auger electron spectroscopy studies of a clean Ni-1at%Th alloy surface were made in the temperature range of 700–900°C. Results show the segregation of thorium to the surface of the alloy with a heat of segregation of −18.8 ± 4.4 kJ/mole. Calculations based on the existing unified theory of segregation in binary alloys yield a much larger value for the heat of segregation. Possible reasons for this discrepancy are discussed. Oxygen exposure at 250°C resulted in the accelerated segregation of thorium to the alloy surface at exposures less than 20 L, with the thorium surface concentration increasing at a much slower rate beyond 20 L. This segregation may play an important role in the methanation activity of thorium-nickel alloys.

Low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), electron energy loss (ELS) and ultraviolet photoemission spectroscopies (UPS) were used to study the structures, compositions and electron state distributions of clean single crystal faces of titanium dioxide (rutile). LEED showed that both the (110) and (100) surfaces are stable, the latter giving rise to three distinct surface structures, viz. (1 × 3), (1 × 5) and (1 × 7) that were obtained by annealing an argon ion-bombarded (100) surface at ~600,800 and 1200° C respectively. AES showed the decrease of the O(510 eV) Ti(380 eV) peak ratio from ~1.7 to ~1.3 in going from the (1 × 3) to the (1 × 7) surface structure. Electron energy loss spectra obtained from the (110) and (100)−(1 × 3) surfaces are similar, with surface-sensitive transitions at 8.2, 5.2 and 2.4 eV. The energy loss spectrum from an argon or oxygen ion bombarded surface is dominated by the transition at 1.6 eV. UPS indicated that the initial state for this ELS transition is peaked at −0.6 eV (referred to the Fermi level EF in the photoemission spectrum, and that the 2.4 eV surface-sensitive ELS transition probably arises from the band of occupied states between the bulk valence band maximum to the Fermi level. High energy electron beams (1.6 keV 20 μA) used in AES were found to disorder clean and initially well-ordered TiO2 surfaces. Argon ion bombardment of clean ordered TiO2 (110) and (100)−(1 × 3) surfaces caused the work function and surface band bending to decrease by almost 1 eV and such decrease is explained as due to the loss of oxygen from the surface.

Stoichiometric and atomically clean CdTe(110) surfaces have been prepared by suitable chemical etching, followed by argon sputtering, and sample annealing in ultrahigh vacuum. Cubic α-tin was grown on CdTe(110) by tin evaporation from a tungsten filament at a substrate temperature of 30°C. Angle-resolved X-ray photoelectron spectroscopy (ARXPS) was used to determine the composition profile of this semiconductor heterostructure nondestructively. In this technique, the angular variations of photoemitted electrons from the substrate and the overlayer are related to the composition profile within the XPS sampling depth. The actual composition profile is obtained by applying the simplex optimization algorithm on the ARXPS data. From our analyses, we conclude that α-Sn grown at 30°C forms an abrupt junction with CdTe(110).

Ultraviolet photoelectron spectroscopy (UPS), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) have been used to study electronic properties and the surface structure of the TiO2(rutile)(110) surface and the Ni/TiO2(110) interface. A sputter-cleaned TiO2(110) surface shows a (1 × 1) LEED pattern after annealing at 400°C for 15 min and a (1 × 2) pattern after an extended annealing at 615°C. AES showed that the O (510 eV) Ti (380 eV ) peak ratio change was within 5% for these two surfaces. From the binding energy shift of the Ni 2p 3 2 peak and the kinetic energy shift of the Ni L3M2,3M2,3 Auger peak as a function of Ni coverage, we measure a relaxation shift of 0.7 eV and a chemical shift of 0.75 eV of the Ni 2p 3 2 peak for bulk Ni relative to half a monolayer of deposited Ni on the TiO2(110)−(1 × 1) surface. These indicated that Ni atoms at the Ni/TiO2(110)−(1 × 1) interface are negatively charged and the amount of charge transferred is estimated to be 0.13 e − Ni atom. On the TiO2(110)−(1 × 2) surface, the amount of charge transfer is roughly 0.07 e − Ni atom. Such a variation in the charge state of Ni may affect the CO chemisorption and hence its methanation activity. Nickel deposited on the TiO2(110) surface diffuses into bulk TiO2 at 300°C or higher. Annealing at 300°C for 5 min results in a (1 × 2) LEED pattern, indicating long range ordering of the Ni overlay er on the TiO2(110) surface.

Measurements of the activation energy for surface self-diffusion in gold by the method of profile decay using a scanning tunneling microscope (STM) have been done on polycrystalline gold films deposited on glass substrate. The peak-to-peak surface roughness was measured as a function of annealing time after annealing at 125° C, 150° C and 170° C with a special pan-cake furnace in the STM. The resultant gold surface diffusion activation energy is found to be ∼21 kcal mol . These experiments demonstrate the unique ability of STM to study surface diffusion over macroscopic distances in the low temperature regime.

Plastic-deformation-enhanced UV photoemission from oriented single crystal surfaces of aluminum has been studied. Clean single crystals of aluminum oriented in [111] direction were flexurally fatigued under UHV conditions and for the first time photoelectron energy distribution curves were obtained as a function of fatigue life using the Hel (21.2 eV) and the HeII (40.8 eV) photon lines. The integrated photocurrent was measured as a function of fatigue life using the photon lines from helium and argon sources. A progressive decrease in work function was observed as the specimen was subjected to increasing number of fatigue cycles. At a strain amplitude of ±0.2%, a drop of 0.2 eV in the work function occurred after 3000 fatigue cycles. Further, significant changes in aluminum valence band emission as a result of fatigue have been observed along with the formation of slip-steps on the surface of the aluminum specimen as seen under the scanning electron microscope. This alteration in the surface microgeometry caused by fatigue is believed to be responsible for the observed changes in the work function and the electronic band structure. The change in the total integrated photoyield caused by fatigue is thus determined by work function and valence band changes.

Deposition of a monolayer of titanium on the TiO2(100)-( 1 × 3) single crystal surface produces an oxygen deficient surface which has the same chemical composition, electronic structure and chemical reactivity as the Ar ion sputtered TiO2(100) surface. From correlations with studies of oxidation of the Ti(0001) single crystal surface, we provide firm evidence for the existence of Ti+3 species on the clean oxygen deficient TiO2 surface. The chemisorption of O2, H2 and H2O has been studied by ultraviolet photoemission spectroscopy (UPS), electron energy loss spectroscopy (ELS), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and thermal desorption on the stoichiometric and Ti+3-rich TiO2(100) surfaces. The presence of surface Ti+3 species causes distinct differences in the nature of chemical bonding between the adsorbed molecule and the substrate surface. From the combination of these studies, we conclude that water is adsorbed associatively on the stoichiometric TiO2(100)−( 1 × 3) surface while it tends to dissociate into surface hydroxyl groups on the Ti+3 rich surface. UPS and ELS show that while adsorption of H2O changes the Ti+3 to a different oxidation state, illumination by band gap energy photons can regenerate Ti+3 species by the reaction Ti+4 + e− → Ti+3. An attempt has been made to correlate these results on well characterized surfaces with studies using TiO2 as a photoanode in the photo-electrochemical cell.

Acetylene and oxygen adsorption on disordered and ordered silicon crystal surfaces of (111) orientation were studied by low-energy electron loss spectroscopy (ELS). There are marked structure-dependent differences in the ELS spectra in the presence of these adsorbates. A model for the acetylene molecule orientation on the silicon (111) ordered surface is proposed to explain the experimental results. ELS data suggest that the electrons in the silicon-oxygen chemisorption bond are more tightly bound on the disordered than on the silicon (111) surface with a (7 X 7) surface structure.

Clean InP(111) surfaces were prepared in an ultra-high vacuum chamber via sputtering and annealing in a phosphorous ambient. Exposing these surfaces to excited oxygen in the 105 L range resulted in a mixed In and P oxide approximately 2.8 A thick. Oxygen exposure did not alter the position of the Fermi level, measured using ultraviolet photoemission, on sputtered/annealed surfaces. The Fermi level typically remained pinned at 1.1 eV above the valence band maximum throughout the oxygen exposures, but decreased to approximately 0.8 eV after deposition of one monolayer of gold. Similar band bending behavior had previously been observed for gold deposited on sputtered/annealed InP(111) not subjected to the intervening oxygen exposure. In addition, Auger measurements indicated possible increased phosphorus oxidation as gold was deposited on the oxygen-exposed InP.