Jeffry A. Kelber

A consistent method for quantitative XPS peak analysis of thin oxide films on clean polycrystalline iron surfaces

Abstract We report a method for the quantitative analysis of the Fe(2p) and O(1s) core level XPS spectra which allows the determination of the Fe2+/Fe3+ ratio within a thin oxide film. The method involves the determination of the intensity of specific shake-up features within the Fe(2p) spectrum. This analytical method is demonstrated by comparing the Fe(2p) spectra of electrochemically modified Fe2+-rich and Fe3+-rich electrodes in a combined UHV-XPS-electrochemical system. Exposure of clean polycrystalline Fe surfaces to low pressures of O2 gas for different time intervals has also been carried out. Quantitative XPS analyses of the oxide films produced by O2 exposures reveal that the oxide films are predominantly trilayers of FeO, Fe3O4 and FeOOH phases, the latter due to ambient background contamination. The analyses demonstrate that a multiplicity of Fe2+ and/or Fe3+ chemical environments and binding energies is present in such films, and this must be explicitly accounted for during quantitative analyses.

Direct evidence for the amorphous silicon phase in visible photoluminescent porous silicon

We report on micro‐Raman spectroscopy studies of porous silicon which show an amorphous silicon Raman line at 480 R cm−1 from regions that emit visible photoluminescence. A Raman line corresponding to microcrystalline silicon at 510 R cm−1 is also observed. X‐ray photoelectron spectroscopy data is presented which shows a high silicon‐dioxide content in porous silicon consistent with an amorphous silicon phase.

Copper wetting of α-Al2O3(0001): theory and experiment

XPS studies have been carried out on sputter deposited copper on a substantially hydroxylated {alpha}-Al{sub 2}O{sub 3}(0001) (sapphire) surface under ultra-high vacuum (UHV) conditions. XPS-derived Cu uptake curves show a sharp change in slope at a coverage of 0.35 monolayer (on a Cu/O atomic basis), indicative of initial layer-by-layer growth. CU(LMM) lineshape data indicate that, prior to the first break in the curve, Cu is oxidized to Cu(I). At higher coverages, metallic CU(0) is. observed. These data agree with first principles theoretical calculations, indicating that the presence of ad-hydroxyl groups greatly enhances the binding of Cu to bulk sapphire surfaces, stabilizing Cu(I) adatoms over two-dimensional metallic islands. In the absence of hydroxylation, calculations indicate significantly weaker Cu binding to the bulk sapphire substrate and non-wetting. Calculations also predict that at Cu coverages above 1/3 monolayer (ML), Cu-Cu interactions predominate, leading to Cu(0) formation. These results are in excellent agreement with experiment. The ability of surface hydroxyl groups to enhance binding to alumina substrates suggests a reason for contradictory experimental results reported in the literature for Cu wetting of alumina.

Analysis of the Auger spectra of CO and CO2

The electron‐excited gas phase carbon and oxygen Auger spectra of CO and CO2 are compared to the spectra calculated by a one‐electron theory. Calculated Auger transition intensities and energies are generally in good agreement with experiment. The disagreement between certain calculated intensities and experiment, however, illustrates those cases where configuration interaction can be expected to provide significant corrections to the one‐electron theoretical results. In addition, a comparison of calculated to experimental final state binding energies reveals the existence, in covalent molecules, of localized two‐hole final states in which two holes are always on the same site. A simple two‐electron theory predicts where such states will occur in the Auger spectra of homonuclear diatomic molecules.

Oxygen radical and plasma damage of low-k organosilicate glass materials: Diffusion-controlled mechanism for carbon depletion

Fourier transform infrared (FTIR) analyses of low-k materials exposed to either oxygen radicals or to capacitively coupled O2 plasma indicate that carbon depletion from these materials is dominated by O radical diffusion. FTIR measurements of changes in absorbance related to silanol formation (3500 cm−1) and carbon depletion (2980 cm−1, 900–700 cm−1) exhibit a linear dependence on the square root of the exposure time. Diffusion is faster for a sample of higher porosity and interconnectedness (k=2.54) than for a sample with lower porosity (k=3.0). However, a sample with high porosity (k=2.57) but low interconnectedness (as measured by liquid diffusion) exhibits a high initial rate of carbon loss, followed by no further carbon loss at longer times. Further, pretreatment of k=3.0 material by 500 eV noble gas ions results in a sharp decrease in the rate of carbon loss upon subsequent exposure to oxygen radicals. The data indicate that the main mechanism of carbon depletion in organosilicate glass (OSG) materi...

Electronic structure of a graphene/hexagonal-BN heterostructure grown on Ru(0001) by chemical vapor deposition and atomic layer deposition: extrinsically doped graphene.

A significant BN-to-graphene charge donation is evident in the electronic structure of a graphene/h-BN(0001) heterojunction grown by chemical vapor deposition and atomic layer deposition directly on Ru(0001), consistent with density functional theory. This filling of the lowest unoccupied state near the Brillouin zone center has been characterized by combined photoemission/k vector resolved inverse photoemission spectroscopies, and Raman and scanning tunneling microscopy/spectroscopy. The unoccupied σ*(Γ(1) +) band dispersion yields an effective mass of 0.05 m(e) for graphene in the graphene/h-BN(0001) heterostructure, in spite of strong perturbations to the graphene conduction band edge placement.

Effect of surface impurities on the Cu/Ta interface

Abstract Auger electron spectroscopy and temperature programmed desorption studies under ultra-high vacuum conditions demonstrate that even sub-monolayer coverages of oxygen or carbide on polycrystalline Ta significantly degrade the strength of Cu/Ta chemical interactions, and affect the kinetics of Cu diffusion into bulk Ta. On clean Ta, monolayer coverages of Cu will de-wet only above 600 K. A partial monolayer of adsorbed oxygen (3 L O2 at 300 K) results in a lowering of the de-wetting temperature to 500 K, while saturation oxygen coverage (10 L O2, 300 K) results in de-wetting at 300 K. Carbide formation also lowers the de-wetting temperature to 300 K. Diffusion of Cu into the Ta substrate at 1100 K occurs only after a 5-min induction period at this temperature. This induction period increases to 10 min for partially oxidized Ta, 15 min for carbidic Ta and 20 min for fully oxidized Ta.

Fundamental mechanisms of oxygen plasma-induced damage of ultralow-k organosilicate materials: The role of thermal P3 atomic oxygen

Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), and ab initio density functional theory-based molecular dynamics simulations demonstrate fundamental mechanisms for CH3 abstraction from organosilicate films by thermal O(P3). Ex situ FTIR analysis demonstrates that film exposure to thermal O(P3) yields chemical changes similar to O2 plasma exposure. In situ XPS indicates that exposure to thermal O(P3) yields O/OH incorporation in the organosilicate film concurrent with carbon loss from the surface region. These results are consistent with simulations indicating specific low kinetic barrier (<0.1 eV) reactions resulting in concurrent Si–C bond scission and Si–O bond formation.

The Effects of an Iodine Surface Layer on Ru Reactivity in Air and during Cu Electrodeposition

X-ray photoelectron spectroscopy (XPS), low energy electron diffraction, and cyclic voltammetry have been used to study the adsorption of iodine on the Ru(0001), air, and water exposure to both clean and iodine covered Ru(0001) surfaces and the stability of the iodine adlayer during Cu overpotential electrodeposition. A Ru(0001)-(√3 X √3)R30°-1 structure was observed after I 2 vapor exposure of the Ru(0001) surface at room temperature. The Ru(0001)-(√3 X √3)R30°-I structure was found to be stable toward ambient air and water exposure. The I ad-layer passivates the Ru(0001) surface against significant hydroxide, chemisorbed oxygen, or oxide formation during exposure to air. Immersion of I-Ru(0001) results in greater hydroxide and chemisorbed oxygen formation than air exposure. A saturation coverage of I on a Ru(poly) electrode similarly passivated the Ru surface against oxidation upon exposure to water vapor over an electrochemical cell in an ultrahigh vacuum electrochemistry transfer system. Studies with combined electrochemical and XPS techniques show that iodine surface adlayer remained on top of the surface after cycles of overpotential electrodeposition/dissolution of copper on Ru(0001). These results indicate the potential bifunctionality of the iodine layer to both passivate the Ru surface in the microelectronic processing and to act as a surfactant for copper electrodeposition.

Interactions of copper with oxidized TaSiN

Abstract Tantalum rich TaSiN exposed to the ambient results in a homogenous surface composition of a silicon rich Ta x Si y O z mixture. The interaction of sputter deposited copper with oxidized TaSiN (O/TaSiN) is investigated using X-ray photoelectron spectroscopy (XPS). Copper is found to wet (grow conformally on) O/TaSiN at 300 K. For copper coverages of less 0.4 ML (based on the Cu to O atomic ratio), copper is present as Cu(I). At higher coverages, Cu(0) is observed. A change in slope of the copper coverage curve is coincident with the change in copper oxidation state. The data indicate that copper is initially deposited in a conformal ionic layer followed by Cu(0) formation in subsequent depositions. The data also show that although the O/TaSiN surface contains significant amounts of silicon and oxygen, the ability of copper to wet O/TaSiN is superior to that of SiO 2 . Post-deposition annealing experiments performed indicate that although diffusion does not occur for temperatures less than 900 K, copper “de-wetting” occurs for temperatures above 500 K.