Photoelectron Peak Intensities Research Articles

Hydrogen reduction of iron ore pellets: A surface study using ambient pressure X-ray photoelectron spectroscopy

Using Ambient Pressure X-ray Photoelectron Spectroscopy (APXPS), this study investigates the reduction behavior of iron oxides in direct reduction (DRI) and blast furnace (BF) pellets. H2, CO, and a H2–CO mixture are used as reducing agents at 650 °C. The investigation aimed to elucidate variations in the rate of reduction over time and under different conditions. Additionally, contour plots are generated to visualize the X-ray photoelectron peak intensity variations as a function of time. Furthermore, phase stability diagrams based on Fe–O–C and Fe–O–H systems are employed to enhance the understanding of reduction behavior. Results revealed that an increased gas flow rate significantly accelerated the reduction rate due to enhanced gas diffusion, while elevated pressure facilitated the reduction of wüstite to metallic iron. Notably, the DRI pellet achieves around 90% metallization degree reduction with hydrogen, but the introduction of carbon monoxide into the reducing gas prevented the reduction of the DRI pellet. In the case of BF pellet reduction, approximately 20% metallization degree is observed using H2–CO (50:50), yet subsequent reoxidation of the reduced iron to wüstite and magnetite occurred. Further investigation identified a significant increase in the partial pressure of H2O and CO2, particularly within the surface porosities, as the underlying cause of this reoxidation phenomenon.

Effect of femtosecond laser-texturing on the oxygen evolution reaction of the stainless-steel plate

We studied the effect of femtosecond (FS) laser-texturing of 316 L stainless steel (SS) plates on their oxygen evolution reaction (OER). Here, the FS laser texturing is adapted to create oxyhydroxide layers with dimple structures on the pristine SS (denoted as B-SS) electrode. The single-side textured SS electrode is represented as FSSS-SS, and the double-side textured SS electrode is described as FSDS-SS. Upon FS laser texturing, significant elements variations of diffraction and photoelectron peak intensities profoundly influence their OER activity. As a result, the above electrode's OER overpotentials in 6.0 M potassium hydroxide (KOH) follow the order of B-SS (257 mV) > FSSS-SS (254 mV) > FSDS-SS (251 mV). However, the above order is reversed in the case of Tafel slopes viz., FSDS-SS (56 mV dec−1) > FSSS-SS (50 mV dec−1) > B-SS (47 mV dec−1). The FS laser textured electrodes exhibit a favorable OER activity regarding overpotential and current density. Besides, based on the Tafel slope analysis, the B-SS electrode shows accelerated OER kinetics. These adverse results may be due to the dimple morphology, reconfiguration of elemental composition, O/Ni/Fe ratios, and the passive nature of catalyst layers, which define the OER performance of SS electrodes.

XPS quantification with universal inelastic electron scattering cross section including intrinsic excitations

In X‐ray excited photoelectron emission (XPS), the shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface. It is also influenced by intrinsic excitations due to the sudden creation of the static core hole. In order to approximately determine the primary excitation spectrum of the considered transition corrected for both extrinsic and intrinsic excitations, we developed in a previous work [E. Gnacadja, N. Pauly, S. Tougaard, Surf. Interface Anal. 52 (2020) 413] a universal analytical expression for the energy loss cross section including extrinsic and intrinsic excitations. We apply the present universal cross section to test to what extent these primary excitations spectra can be used for XPS quantification based on peak area ratios. The procedure is applied to the study of three sets of polycrystalline alloys (Cu0.75Au0.25, Cu0.50Au0.50, and Cu0.25Au0.75) and to three metal oxides (HfO2, ZrO2, and Cu2O). We show that although the individual peaks are very different from those obtained with the classical universal Tougaard cross section, the determined quantitative compositions are equivalent (but not better). This implies that the relative contribution from intrinsic excitations is roughly the same for all peaks for a given sample and they therefore cancel out when peak area ratios are considered.

Correction to Impact of Nonideal Nanoparticles on X-ray Photoelectron Spectroscopic Quantitation: An Investigation Using Simulation and Modeling of Gold Nanoparticles.

Quantitative X-ray photoelectron spectroscopic (XPS) analysis combined with spectral modeling of photoelectrons can be valuable while investigating the surface chemistry of nanoparticles (NPs) with different morphologies. Herein, with the use of NIST Simulation of Electron Spectra for Surface Analysis (SESSA), a comparative analysis of experimental and simulated photoelectron peak intensities in gold nanoparticles (AuNPs) of different morphologies is presented. Three sets of supported AuNPs with different morphologies were selected from a series of as synthesized Au-TiO2 catalyst samples. Using transmission electron microscopy (TEM) analyzed morphological information on the AuNPs as input model parameters in SESSA, XPS spectra were generated from the respective input NP morphologies. A degree of greater mismatch between SESSA simulated and experimental XPS spectra was observed while using the TEM obtained average diameter of the nanoparticles. The degree of mismatch lowered when the true nonspherical shap...

Quantitative analysis of Yb 4d photoelectron spectrum of metallic Yb

The measured Yb 4d3/2 intensity is larger than the Yb 4d5/2 in X‐ray photoelectron (XPS) emission of metallic Yb, which is unexpected. The shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface (including bulk and surface effects) and to intrinsic excitations due to the sudden creation of the static core hole. To quantitatively extract from experimental XPS the primary excitation spectrum (ie, the initial excitation process) of the considered transition, these effects must be included within the theoretical description. The combined effect of both extrinsic and intrinsic excitations can be described by an effective energy‐differential inelastic electron scattering cross section for XPS evaluated by a dielectric response model with the dielectric function as only input. Then, using this cross section, a direct evaluation of the primary excitation spectrum is performed by standard peak shape analysis for thick homogeneous samples. We use this approach in the present paper to determine the Yb 4d photoemission spectrum for metallic Yb. We show that the unexpected larger intensity of Yb 4d3/2 compared to 4d5/2 can be fully accounted for by our model and that the total spectrum consists of a sum of symmetric primary excitation peaks.

Comparisons of Analytical Approaches for Determining Shell Thicknesses of Core-Shell Nanoparticles by X-ray Photoelectron Spectroscopy.

We assessed two approaches for determining shell thicknesses of core-shell nanoparticles (NPs) by X-ray photoelectron spectroscopy (XPS). These assessments were based on simulations of photoelectron peak intensities for Au-core/C-shell, C-core/Au-shell, Cu-core/Al-shell, and Al-core/Cu-shell NPs with a wide range of core diameters and shell thicknesses. First, we demonstrated the validity of an empirical equation developed by Shard for determinations of shell thicknesses. Values of shell thicknesses from the Shard equation typically agreed with actual shell thicknesses to better than 10 %. Second, we investigated the magnitudes of elastic-scattering effects on photoelectron peak intensities by performing a similar series of simulations with elastic scattering switched off in our simulation software. Our ratios of the C-shell 1s intensity to the Au-core 4f7/2 intensity with elastic scattering switched off were qualitatively similar to those obtained by Torelli et al. from a model that neglected elastic scattering. With elastic scattering switched on, the C 1s/Au 4f7/2 intensity ratios generally changed by less than 10 %, thereby justifying the neglect of elastic scattering in XPS models that are applied to organic ligands on Au-core NPs. Nevertheless, elastic-scattering effects on peak-intensity ratios were generally much stronger for C-core/Au-shell, Al-core/Cu-shell, and Cu-core/Al-shell NPs, and there were second-order dependences on core diameter and shell thickness.

Impact of Nonideal Nanoparticles on X-ray Photoelectron Spectroscopic Quantitation: An Investigation Using Simulation and Modeling of Gold Nanoparticles.

Quantitative X-ray photoelectron spectroscopic (XPS) analysis combined with spectral modeling of photoelectrons can be valuable while investigating the surface chemistry of nanoparticles (NPs) with different morphologies. Herein, with the use of NIST Simulation of Electron Spectra for Surface Analysis (SESSA), a comparative analysis of experimental and simulated photoelectron peak intensities in gold nanoparticles (AuNPs) of different morphologies is presented. Three sets of supported AuNPs with different morphologies were selected from a series of as synthesized Au-TiO2 catalyst samples. Using transmission electron microscopy (TEM) analyzed morphological information on the AuNPs as input model parameters in SESSA, XPS spectra were generated from the respective input NP morphologies. A degree of greater mismatch between SESSA simulated and experimental XPS spectra was observed while using the TEM obtained average diameter of the nanoparticles. The degree of mismatch lowered when the true nonspherical shape of the nanoparticles as obtained from TEM images was taken into account for the simulation. This demonstrates the impact of surface morphology on the XPS peak intensities which needs to be incorporated to obtain precise quantified information from the supported nanoparticles. This work demonstrates the applicability of SESSA in combination with experimental XPS and TEM measurements for precise quantification of XPS spectra from complex, nonideal shaped nanoparticles. This study can be extended to include a broad range of nanoparticles with ideal or nonideal geometries, thus providing a simple method to utilize quantitative XPS analysis to a wide range of nanomaterials.

Light-Induced Surface Reactions at the Bismuth Vanadate/Potassium Phosphate Interface.

Bismuth vanadate has recently drawn significant research attention as a light-absorbing photoanode due to its performance for photoelectrochemical water splitting. In this study, we use in situ ambient pressure X-ray photoelectron spectroscopy with "tender" X-rays (4.0 keV) to investigate a polycrystalline bismuth vanadate (BiVO4) electrode in contact with an aqueous potassium phosphate (KPi) solution at open circuit potential under both dark and light conditions. This is facilitated by the creation of a 25 to 30 nm thick electrolyte layer using the "dip-and-pull" method. We observe that under illumination bismuth phosphate forms on the BiVO4 surface leading to an increase of the surface negative charge. The bismuth phosphate layer may act to passivate surface states observed in photoelectrochemical measurements. The repulsive interaction between the negatively charged surface under illumination and the phosphate ions in solution causes a shift in the distribution of ions in the thin aqueous electrolyte film, which is observed as an increase in their photoelectron signals. Interestingly, we find that such changes at the BiVO4/KPi electrolyte interface are reversible upon returning to dark conditions. By measuring the oxygen 1s photoelectron peak intensities from the phosphate ions and liquid water as a function of time under dark and light conditions, we determine the time scales for the forward and reverse reactions. Our results provide direct evidence for light-induced chemical modification of the BiVO4/KPi electrolyte interface.

Process control model for growth rate of molecular beam epitaxy of MgO (111) nanoscale thin films on 6H-SiC (0001) substrates

Magnesium oxide (MgO) is a good candidate for an interface layer in multifunctional metal-oxide nanoscale thin-film heterostructures due to its high breakdown field and compatibility with complex oxides through O bonding. In this research, molecular beam epitaxy (MBE) is used to deposit 10 nm to 15 nm MgO single-crystal films on silicon carbide with hexagonal polytype 6H (6H-SiC) to serve as an interface layer for effective integration of functional oxides. In this work, the effect of MBE process control variables on the growth rate of the MgO film measured in nanometers per minute is investigated. Experiments are conducted at various process conditions and the resulting MgO film growth rate at each combination of process conditions is measured. The process control variables studied are the substrate temperature (100 °C – 300 °C), magnesium source temperature (328 °C – 350 °C), plasma intensity (0 mV – 550 mV), and percentage oxygen on the starting surface of 6H-SiC substrate (9 % – 13 %) after the substrate is prepared by high-temperature hydrogen etching. The film thickness is computed using the effective attenuation length (EAL) of silicon photoelectron peak intensity as measured by x-ray photoelectron spectroscopy (XPS). The film thickness is converted to growth rate by dividing it with the duration of film growth. Using the experimental data, a neural network model is developed to estimate growth rate for any given process variable combination. From this neural network model, multiple replications of data were generated to conduct a 3-level full factorial design of experiments and response surface-based analysis. The study reveals that the plasma intensity has the most significant influence on growth rate. The results indicate that growth rate is relatively low on high-quality substrates with √3 × √3 R30° reconstructed 6H-SiC (0001) surface with optimum oxygen content (approximately 10 %); in contrast, the growth rate is relatively high on substrates with high surface roughness and excessive oxygen on the starting substrate surface.

Quantitative analysis of Ni 2p photoemission in NiO and Ni diluted in a SiO2 matrix

In X-ray excited photoelectron emission (XPS), besides the initial excitation process, the shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface (including bulk and surface effects) and to intrinsic excitations due to the sudden creation of the static core hole. To make an accurate quantitative interpretation of features observed in XPS, these effects must be included in the theoretical description of the emitted photoelectron spectra. It was previously shown [N. Pauly, S. Tougaard, F. Yubero, Surf. Sci. 620 (2014) 17] that these three effects can be calculated by means of the QUEELS-XPS software (QUantitative analysis of Electron Energy Losses at Surfaces for XPS) in terms of effective energy-differential inelastic electron scattering cross-sections. The only input needed to calculate these cross-sections is the energy loss function of the media which is determined from analysis of Reflection Electron Energy Loss Spectra (REELS). The full XPS spectrum is then modeled by convoluting this energy loss cross-section with the primary excitation spectrum that accounts for all effects which are part of the initial photo-excitation process, i.e. lifetime broadening, spin–orbit coupling, and multiplet splitting. In this paper we apply the previously presented procedure to the study of Ni 2p photoemission in NiO and Ni diluted in a SiO2 matrix (Ni:SiO2), samples being prepared by reactive magnetron sputtering at room temperature. We observe a significant difference between the corresponding Ni 2p primary excitation spectra. The procedure allows quantifying the relative intensity of the c3d9L, c3d10L2, and c3d8 final states contributing to the Ni 2p photoemission spectra of the Ni2+ species in the oxide matrices. Especially, the intensity ratio in NiO between the non-local and local contributions to the 3d9L configuration is determined to be 2.5. Moreover the relative intensity ratio of the c3d9L/c3d10L2/c3d8 configurations is found to be 1.0/0.83/0.11 for both the NiO and Ni:SiO2 samples.

Sample-morphology effects on x-ray photoelectron peak intensities. III. Simulated spectra of model core–shell nanoparticles

The National Institute of Standards and Technology database for the simulation of electron spectra for surface analysis has been used to simulate Cu 2p photoelectron spectra for four types of spherical copper–gold nanoparticles (NPs). These simulations were made to extend the work of Tougaard [J. Vac. Sci. Technol. A 14, 1415 (1996)] and of Powell et al. [J. Vac. Sci. Technol. A 31, 021402 (2013)] who performed similar simulations for four types of planar copper–gold films. The Cu 2p spectra for the NPs were compared and contrasted with analogous results for the planar films and the effects of elastic scattering were investigated. The new simulations were made for a monolayer of three types of Cu/Au core–shell NPs on a Si substrate: (1) an Au shell of variable thickness on a Cu core with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm; (2) a Cu shell of variable thickness on an Au core with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm; and (3) an Au shell of variable thickness on a 1 nm Cu shell on an Au core with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm. For these three morphologies, the outer-shell thickness was varied until the Cu 2p3/2 peak intensity was the same (within 2%) as that found in our previous work with planar Cu/Au morphologies. The authors also performed similar simulations for a monolayer of spherical NPs consisting of a CuAux alloy (also on a Si substrate) with diameters of 0.5, 1.0, 2.0, 5.0, and 10.0 nm. In the latter simulations, the relative Au concentration (x) was varied to give the same Cu 2p3/2 peak intensity (within 2%) as that found previously. For each morphology, the authors performed simulations with elastic scattering switched on and off. The authors found that elastic-scattering effects were generally strong for the Cu-core/Au-shell and weak for the Au-core/Cu-shell NPs; intermediate elastic-scattering effects were found for the Au-core/Cu-shell/Au-shell NPs. The shell thicknesses required to give the selected Cu 2p3/2 peak intensity for the three types of core–shell NPs were less than the corresponding film thicknesses of planar samples since Cu 2p photoelectrons can be detected from the sides and, for the smaller NPs, bottoms of the NPs. Elastic-scattering effects were also observed on the Au atomic fractions found for the CuAux NP alloys with different diameters.

Sample-morphology effects on x-ray photoelectron peak intensities. II. Estimation of detection limits for thin-film materials

The authors show that the National Institute of Standards and Technology database for the simulation of electron spectra for surface analysis (SESSA) can be used to determine detection limits for thin-film materials such as a thin film on a substrate or buried at varying depths in another material for common x-ray photoelectron spectroscopy (XPS) measurement conditions. Illustrative simulations were made for a W film on or in a Ru matrix and for a Ru film on or in a W matrix. In the former case, the thickness of a W film at a given depth in the Ru matrix was varied so that the intensity of the W 4d5/2 peak was essentially the same as that for a homogeneous RuW0.001 alloy. Similarly, the thickness of a Ru film at a selected depth in the W matrix was varied so that the intensity of the Ru 3p3/2 peak matched that from a homogeneous WRu0.01 alloy. These film thicknesses correspond to the detection limits of each minor component for measurement conditions where the detection limits for a homogeneous sample varied between 0.1 at. % (for the RuW0.001 alloy) and 1 at. % (for the WRu0.01 alloy). SESSA can be similarly used to convert estimates of XPS detection limits for a minor species in a homogeneous solid to the corresponding XPS detection limits for that species as a thin film on or buried in the chosen solid.

Modeling of X‐ray photoelectron spectra: surface and core hole effects

The shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface and by intrinsic excitations induced by the sudden creation of the static core hole. Besides, elastic electron scattering may also be important. These effects should be included in the theoretical description of the emitted photoelectron peaks. To investigate the importance of surface and core hole effects relative to elastic scattering effect, we have calculated full XPS spectra for the Cu 2p emissions of Cu and CuO with the simulation of electron spectra for surface analysis (SESSA) software and with a convolution procedure using the differential inelastic electron scattering cross‐section obtained with the quantitative analysis of electron energy loss in XPS (QUEELS‐XPS) software. Surface and core hole effects are included in QUEELS‐XPS but absent in SESSA while elastic electron scattering effects are included in SESSA but absent in QUEELS‐XPS. Our results show that the shape of the XPS spectra are strongly modified because of surface and core hole effects, especially for energy losses smaller than about 20 eV. Copyright © 2014 John Wiley & Sons, Ltd.

Determination of the Cu 2p primary excitation spectra for Cu, Cu2O and CuO

The shape and intensity of photoelectron peaks are strongly affected by extrinsic excitations due to electron transport out of the surface (including bulk and surface effects) and to intrinsic excitations due to the sudden creation of the static core hole. These effects must be included in the theoretical description of the emitted photoelectron spectra. We have calculated the effective energy-differential inelastic electron scattering cross section for XPS, including both surface and core hole effects, within the dielectric response theory by means of the QUEELS-XPS software (QUantitative analysis of Electron Energy Losses at Surfaces for XPS). The full XPS spectrum is then modeled by convoluting this energy loss cross section with the primary excitation spectrum that accounts for all effects which are part of the initial photo-excitation process, i.e. lifetime broadening, spin–orbit coupling, and multiplet splitting. The shape of this primary excitation spectrum is determined by requiring close agreement between the resulting theoretical spectrum and the experimental XPS spectrum. These calculations were performed for Cu 2p peaks of Cu, Cu2O, and CuO. For CuO, we compare the obtained primary excitation spectra with first principle calculations performed with the CTM4XAS software (Charge Transfer Multiplet program for X-ray Absorption Spectroscopy) for the corresponding emissions and we find good quantitative agreement.

Sample-morphology effects on x-ray photoelectron peak intensities

The authors have used the National Institute of Standards and Technology Database for the Simulation of Electron Spectra for Surface Analysis to simulate photoelectron spectra from the four sample morphologies considered by Tougaard [J. Vac. Sci. Technol. A 14, 1415 (1996)]. These simulations were performed for two classes of materials, two instrument configurations, and two conditions, one in which elastic scattering is neglected (corresponding to the Tougaard results) and the other in which it is included. The authors considered the Cu/Au morphologies analyzed by Tougaard and similar SiO2/Si morphologies since elastic-scattering effects are expected to be smaller in the latter materials than the former materials. Film thicknesses in the simulations were adjusted in each case to give essentially the same chosen Cu 2p3/2 or O 1s peak intensity. Film thicknesses with elastic scattering switched on were systematically less than those with elastic scattering switched off by up to about 25% for the Cu/Au morphologies and up to about 14% for the SiO2/Si morphologies. For the two morphologies in which the Cu 2p3/2 or O 1s peak intensity was attenuated by an overlayer, the ratios of film thicknesses with elastic scattering switched on to those with elastic scattering switched off varied approximately linearly with the single-scattering albedo, a convenient measure of the strength of elastic scattering. This variation was similar to that of the ratio of the effective attenuation length to the inelastic mean free path for the photoelectrons in the overlayer film. For the two morphologies in which the Cu 2p3/2 or O 1s photoelectrons originated from an overlayer film, the ratios of film thicknesses with elastic scattering switched on to those with elastic scattering switched off varied more weakly with the single-scattering albedo. This weaker variation was attributed to the weaker effects of elastic scattering for photoelectrons originating predominantly from near-surface atoms than for photoelectrons that travel through an overlayer film.

X-ray photoelectron spectroscopy for nondestructive analysis of buried interfaces

The possibility to use high energy X-ray photoelectron spectroscopy as a nondestructive method of in-depth chemical phase analysis of solids is demonstrated. Theoretical background and optimal experimental conditions of in-depth analysis are considered. Interfaces in 5 nm thick HfO2 films synthesized by molecular layering and deposition of organometallic compounds from the gas phase were studied. It was shown that thickness of the layers in multilayer structures can be determined by measuring the intensity of photoelectron peaks.

Non-Destructive Depth Profiling of the Activated Ti-Zr-V Getter by Means of Excitation Energy Resolved Photoelectron Spectroscopy

Non-evaporable Ti-Zr-V ternary getters (NEGs) were studied by means of excitation energy resolved photoelectron spectroscopy (ERXPS). We attempted a quantitative study of the in-depth redistribution of the NEG components during activation. The samples were prepared ex-situ by DC magnetron sputtering on a stainless-steel substrate. The ERXPS measurements were carried out at two incident photoelectron beam angles at energies of 110, 195, 251, 312, 397 and 641 eV. Besides these photon energies, also standard X-ray photoelectron spectroscopy (XPS) was used at a photon energy of 1254 eV. We accumulated Ti 3s, Ti 3p, Ti 3d, V 3s, V 3p, V 3d, Zr 3p, Zr 3d, Zr 4s, Zr 4p, Zr 4d, C 1s, O 1s and O 2s photoelectron peak intensities as functions of the kinetic energies given to them. Under simplifying assumptions, Monte-Carlo calculations of the activated sample concentration profiles were performed to fit the measured spectra intensities. The results proved an in-depth redistribution of the components during the activation process. This way we also contributed to a further development of non-destructive depth profiling by electron spectroscopy techniques.

Effect of growth temperature on the morphology and bonded states of SnO2 nanobaskets

The nanobaskets of SnO2 were grown on in-house fabricated anodized aluminum oxide pores of 80nm diameter using plasma enhanced chemical vapor deposition at an RF power of 60W. Hydrated stannic chloride was used as a precursor and O2 (20sccm) as a reactant gas. The deposition was carried out from 350 to 500°C at a pressure of 0.2Torr for 15min each. Deposition at 450°C results in highly crystalline film with basket like (nanosized) structure. Further increase in the growth temperature (500°C) results in the deterioration of the basket like structure and collapse of the alumina pores. The grown film is of tetragonal rutile structure grown along the [110] direction. The change in the film composition and bonded states with growth temperature was evident by the changes in the photoelectron peak intensities of the various constituents. In case of the film grown at 450°C, Sn 3d5/2 is found built up of Sn4+ and O–Sn4+ and the peaks corresponding to Sn2+ and O–Sn2+ were not detected.

Chemical and structural transformation of sapphire (Al2O3) surface by plasma source nitridation

The chemical, morphological, and structural characteristics of nitrogen plasma treated c-plane sapphire substrate surfaces were studied by x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The plasma treatment was carried out by exposing sapphire substrates (Ts=700 °C) to a flow of 35 sccm of activated nitrogen species generated by a constricted-plasma source for 5–60 min. The emergence of the N 1s peak in XPS indicates nitrogen incorporation in sapphire as soon as after 5 min of nitridation. AFM images show that the sapphire contained a high density of islands after 1 h of nitridation. A thin polycrystalline AlN layer was observed on the nitridated sapphire surface by TEM. Both the thickness of the AlN layer and the N 1s photoelectron peak intensity increase nonlinearly with respect to nitridation time. The nonlinear relationship between the thickness of the nitridated layer and the reaction time suggests the growth of the AlN layer follows a diffusion limited growth mechanism.

Multiple atom resonant photoemission: a new technique for studying near-neighbor atomic identities and bonding

Abstract A new multi-atom resonant photoemission (MARPE) effect between core levels of neighboring atoms in multi-element samples has been observed. Experimental evidence for the effect and several possible applications are considered. In the metal oxides MnO, Fe 2 O 3 , and La 0.7 Sr 0.3 MnO 3 , we have observed a significant enhancement in the core-level photoelectron peak intensity associated with one element in the sample (e.g. O1s) when the excitation energy is tuned through an energetically deeper absorption edge of a second element (e.g. Mn2p or Fe2p or La3d). The effects observed are up to a 105% increase in peak intensity, and a 29% increase in energy-integrated intensity. A generalization of the theory of single-atom resonant photoemission has also been applied to MARPE, and is found to be in semiquantitative agreement with our experimental results.