Peak Intensity Measurements Research Articles

Improvements in the Reliability of X-ray Photoelectron Spectroscopy for Surface Analysis

An overview is given of improvements in the reliability of X-ray photoelectron spectroscopy (XPS) measurements over the past three decades. Early inter-laboratory comparisons showed wide variations in measurements of peak energies and relative peak intensities for the same material. Procedures now exist for calibration of instrumental energy and intensity scales. It was generally necessary in early work to assume that the surface was homogeneous over the XPS sampling depth. It is now possible to assess the extent of compositional inhomogeneities in depth with angle-resolved XPS measurements or from analyses of the photoelectron energy distributions in the vicinity of major peaks. The surface sensitivity of XPS was assumed in early work to be given by the so-called "universal curve" for effective attenuation lengths (EALs) as a function of electron energy. Calculations of electron inelastic mean free paths (IMFPs), however, show appreciable material dependencies. In addition, elastic scattering of the signal electrons is often significant. As a result, the EAL can be appreciably different from the corresponding IMFP. Brief mention is also made of the development of NIST data resources for XPS: an XPS database, IMFP and EAL databases, and standard test data for XPS. The standard test data for XPS are a useful teaching tool for estimating uncertainties of peak parameters for overlapping peaks in an XPS or other spectrum.

Quantitative study of oxygen enhancement of sputtered ion yields. I. Argon ion bombardment of a silicon surface with O 2 flood

A novel quantification approach is applied to determine in situ the amount of surface oxygen within the sputtered particle escape depth during steady-state sputter depth profiling of silicon under simultaneous oxygenation with an oxygen flood gas or with an oxygen primary ion beam. Quantification is achieved by comparing the secondary ion intensities of 16O that is adsorbed or implanted at the Si surface with the measured peak intensities of a calibrated 18O ion implant used as a reference standard. Sputtered ion yields can thereby be related to surface oxygen levels. In the present work the dependences of the partial silicon sputter yield Y and of the positive and negative secondary ion useful yields UY(X ±) (X = B, O, Al, Si, P) on the oxygen/silicon ratio, O/Si, in the sputtered flux are studied for 40Ar + bombardment of Si with simultaneous O 2 flooding. The silicon sputter yield is found to decrease with increasing flood pressure and O/Si ratio by up to a factor of 3. Both positive and negative secondary ion yields are enhanced by the presence of oxygen at the silicon surface. The useful ion yield of Si + scales non-linearly with the atom fraction of surface oxygen; this behavior is shown to invalidate models that suggest that Si + ion yield enhancement is dominated either by isolated oxygen atoms or by formation of SiO 2 precipitates. In contrast a microscopic statistical model that assumes that local Si + ion formation depends only on the number of oxygen atoms coordinated to the Si atom to be ejected fits the ion yield data quantitatively.

High-throughput quantification of phosphatidylcholine and sphingomyelin by electrospray ionization tandem mass spectrometry coupled with isotope correction algorithm

The choline head group containing phosphatidylcholine (PC) and sphingomyelin (SPM) are major eukaryotic lipid components playing an important role in forming membrane microdomains and serve as precursor of signaling molecules. Both lipids can be monitored by positive ion mode electrospray tandem mass spectrometry using a parent ion scan of m/ z 184. Although PC species appear at even m/ z and SPM species at odd m/ z, there may be a significant overlap of their isotopes. In order to separate PC and SPM species, an isotope correction algorithm was established, which utilizes calculated isotope percentages to correct the measured peak intensities for their isotopic overlap. We could demonstrate that this approach was applicable to correct the isotope overlap resulting from spiked PC and SPM species. Quantification was achieved by addition of different PC and SPM species prior to lipid extraction. The developed assay showed a precision, detection limit and robustness sufficient for routine analysis. Furthermore, an analysis time of only 1.3 min combined with automated data analysis using self-programmed Excel Macros allows high-throughput analysis. In summary, this assay may be a valuable tool for detailed lipid analysis of PC and SPM species in a variety of sample materials.

Surface excitations in electron backscattering from silicon surfaces

Surface excitation effects in surface-sensitive electron spectroscopy (XPS, AES, EPES, EELS) influence substantially the measured peak intensities or peak areas. To obtain reliable quantitative information from the electron spectra, the measured intensities should be corrected for these effects. For this purpose, Chen has suggested a simple procedure based on the knowledge of the surface excitation parameter, SEP. The SEP depends on electron energy, the impact and the emission angle of electrons, and a material studied. The SEP can be calculated from the theory or it can be obtained semi-empirically. In this contribution, we compare both procedures. They are applied on measured electron backscattering probabilities from silicon surface with respect to copper and gold standards. Corrected peak areas are finally used for evaluating of inelastic mean free paths for silicon, and compared with the available literature data. Results show that the semi-empirical approach to the SEPs leads to a better agreement with the predicted behavior.

Reproducibility of intravenous intermittent triggered myocardial contrast echocardiography in healthy subjects.

Few data have been published on the reproducibility of baseline subtracted peak intensity obtained from intravenous intermittent triggered myocardial contrast echocardiography. We investigated the reproducibility of the peak intensity measured from intravenous intermittent triggered myocardial contrast echocardiography in 10 young healthy males. The contrast echocardiography was obtained using the second harmonic mode with an intravenous bolus injection of Levovist (first study). The same myocardial contrast echocardiography was repeated after the first study (second study). The myocardial opacification and peak intensity in the 12 segments of the apical 4 and 2 chamber views were assessed visually and quantitatively. The differences in the peak intensity between the initial and repeated measurements in the first study (intraobserver reproducibility) and between the initial measurements in the first and second studies (interinjection reproducibility) were assessed using the Bland and Altman method. The degree of opacification was good or intermediate in 207/228 (91%) of the segments. The agreement of myocardial opacification between the first and second studies was 87/114 (76%). However, significantly higher peak intensity was obtained in apical septal (8200 +/- 6300 au2) and mid septal (8500 +/- 6000 au2) segments in the 4 chamber view and in the mid inferior (12400 +/- 9300 au2) and apical inferior (10700 +/- 6300 au2) segments in the 2 chamber view compared with other segments. The mean differences of the peak intensities according to the Bland and Altman analysis was -1600 +/- 5000 au2 in the intraobserver reproducibility study, and -1100 +/- 5300 au2 in the interinjection reproducibility study. Thus, the measurement error was determined to range from 8400 au2 to 9500 au2 in both studies. We conclude that the peak intensity obtained from intravenous intermittent triggered myocardial contrast echocardiography using Levovist varies significantly among segments in the left ventricular myocardium. Large intraobserver and interinjection variability exists in the measurement of peak intensity, suggesting that the reproducibility of this technique is limited for quantitative assessment of myocardial perfusion.

Real-time myocardial contrast echocardiography for pharmacologic stress testing: is quantitative estimation of myocardial blood flow reserve necessary?

Background Little is known about the diagnostic accuracy of quantitative real-time myocardial contrast echocardiography (MCE) as an adjunct to stress testing. This study was performed to evaluate the agreement between MCE and technetium 99m–sestamibi single photon emission computed tomography (SPECT) for detection of perfusion defects and to investigate whether quantitative assessment of myocardial perfusion can increase the diagnostic value of MCE. Methods MCE was performed at rest and during peak adenosine stress in 50 unselected patients undergoing SPECT imaging. Concordance between the 2 methods was assessed using κ statistics. MCE images were analyzed quantitatively, measuring peak intensity (A) and maximal rise of signal intensity (β). Myocardial blood flow reserve was estimated by calculating the ratios of A adenosine/A baseline (A reserve), β adenosine/β baseline (β reserve), and A × β adenosine/A × β baseline (A × β reserve). Results Visual analysis of MCE agreed well with SPECT (κ = 0.67) with sensitivity of 64%, specificity of 97%, and overall accuracy of 87%. Quantitative analysis showed that peak signal intensity A significantly increased under adenosine stress in SPECT-normal segments (2.6 ± 1.9 vs 3.0 ± 1.6 dB, P < .0001), tendencially decreased in reversible (3.0 ± 2.0 vs 2.4 ± 1.2 dB, P = .07) and remained unchanged in fixed (0.9 ± 0.9 vs 0.8 ± 0.9 dB) defects. β Increased markedly under adenosine in normal segments (0.4 ± 0.4 vs 1.4 ± 1.3, P < .0001) but not in segments with reversible or fixed defects. Receiver operating characteristic showed that β reserve and A × β reserve, but not A reserve, are sensitive parameters for detecting perfusion defects with areas under the curve of 0.84, 0.85, and 0.61, respectively. Cut-off values of 1.9 and 2.3, respectively, for β and A × β reserve yielded sensitivity rates of 79% and 80%, specificity rates of 75% and 78%, and overall accuracy rates of 76% and 79%, respectively. Conclusion Quantitative estimation of myocardial blood flow reserve by MCE parameters corresponds to the evaluation of myocardial perfusion by nuclear imaging and can increase the sensitivity but not the overall accuracy of contrast echocardiography.

Growth types and surface topography of Co, Cu and Co/Cu multilayers studied by AES and STM/SFM

A thin film of cobalt, copper and Co/Cu multilayers deposited on Si(1 0 0) has been studied by an in situ combination of Auger electron spectroscopy and scanning tunnelling/scanning force microscopy. We show that thickness-dependent Auger peak intensity measurements, taken in situ during deposition of constituents of Co/Cu multilayers, combined with microscopy can bring valuable information about growth type of the system components.

Protein abundance quantification in embryonic stem cells using incomplete metabolic labelling with 15N amino acids, matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry, and analysis of relative isotopologue abundances of peptides.

An isotope dilution method for protein quantification is presented in the context of matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOFMS) and mass fingerprinting experiments, revealing an unappreciated high reproducibility and accuracy of relative peak intensity measurements. Labelled proteins were generated by growing cells in a medium containing (15)N-enriched amino acids, and were mixed with proteins of natural isotopic composition from control cells in ratios of approximately 0:1, 1:7, 1:2, 2:1, 7:1, and 1:0 (labelled/unlabelled). Mixtures were separated by two-dimensional gel electrophoresis and analysed by MALDI-TOFMS using typical experimental conditions. A linear relationship is demonstrated between the relative isotopologue abundances (RIA values) for particular peaks in the isotopic distribution of tryptic peptide fragments of the proteins, and the mole fractions of labelled proteins in the mixture. Analysis of RIA values (ARIA quantification) for peptides of six typical silver-stained protein spots for the various mixtures could reproduce the experimentally contrived ratios with approximate errors between 4% (2:1 mixture) and about 18% (1:7 mixture). A consideration of error and its propagation is discussed. ARIA does not require complete separation of the isotope patterns of labelled and unlabelled peptides, and is therefore advantageous in combination with all kinds of labelling experiments in biological systems, because it is compatible with minimal metabolic incorporation of labelling reagent. Simulations indicate that the minimum required (15)N enrichment of the total amino acid pool sufficient for ARIA is less than 4%. In an accompanying paper in this issue, we apply ARIA to proteins differentially labelled with isotope-coded alkylation reagents.

X-ray diffraction measurements of thec-axis Debye-Waller factors ofYBa2Cu3O7andHgBa2CaCu2O6

We report an application of x rays to the measurement of the temperature-dependent Bragg peak intensities to obtain Debye-Waller factors on high-temperature superconductors. Intensities of $(0,0,l)$ peaks of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ and ${\mathrm{HgBa}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{6}$ thin films are measured to obtain the c-axis Debye-Waller factors. While lattice constant and some Debye-Waller factor measurements on high-${T}_{c}$ superconductors show anomalies at the transition temperature, our measurements by x-ray diffraction show a smooth transition of the c-axis Debye-Waller factors through ${T}_{c}.$ This suggests that the dynamic displacements of the heavy elements along the c-axis direction in these compounds do not have anomalies at ${T}_{c}.$ This method in combination with measurements by other techniques will give more details concerning the dynamics of the lattice.

Measurement and calculation of escape peak intensities in synchrotron radiation X-ray fluorescence analysis

In synchrotron radiation X-ray fluorescence experiments, the escape peaks, generating from the Si(Li) solid detector, can disrupt seriously the quantitative and qualitative analysis. In this paper, 14 specimens, such as metals, compounds and plants, have been chosen as objectives to determine the intensities and positions of escape peaks. In all, the characteristic X-ray fluorescence peaks and their escape peaks of 12 elements have been measured. Comparing the experimental values with the standard values, the escape peaks can be discriminated. To calculate the ratios of intensities of the escape peaks and their corresponding characteristic X-ray fluorescence peaks, a simplified Si Kα emergent spherical distribution has been put forward. It is found that the experimental results are in accordance with that of calculation, i.e. both the experimental and theoretical ratios decrease from 1% to 0.1% with the increasing atomic number from 18 to 33 (from 1 to 9 keV in X-ray range).

Effects of Alkyl Chains on the Formation of Self-assembled Monolayers of Thiophenes.

A comparative study of the growth processes of self-assembled monolayers (SAMs) of thiophene and alkylthiophene on Au(111) was made by Fourier-transform infrared reflection absorption spectroscopy (FTIR-RAS). Measurements of temporal peak intensity and the time-dependent Langmuir adsorption isotherm revealed two phases with different molecular orientations during SAM growth of thiophene. In the primary stage, thiophene in the SAM orients parallel to the gold surface. In the second stage, the molecule reorients to a standing-up configuration with respect to the surface. Introduction of alkyl chain to thiophene ring does not essentially change the growth process, but induces a faster growth rate than that of the thiophene SAM. The intermolecular forces of adsorbate, e.g., van der Waals force, play a role as a rate-limiting factor for the self-assembly of adsorbates on the solid surface.

In situ Raman spectroscopic studies of trimethylindium pyrolysis in an OMVPE reactor

An in situ investigation of thermal decomposition reactions of trimethylindium (TMIn) in a vertical, upflow chemical vapor deposition reactor has been carried out using Raman spectroscopy. Monomethylindium (MMIn) and atomic indium were detected along with the precursor TMIn using N2 as the carrier gas. Atomic indium was identified by the peak at 2215 cm−1, which is equal to the difference between two spin–orbit split levels of atomic indium in the ground electronic state. The multiple peaks corresponding to MMIn, which were enhanced by a resonance Raman effect, consisted of fundamentals(ν2 = 1097 cm−1,ν3 = 430 cm−1,ν5 = 1364 cm−1, ν6 = 696 cm−1) and a high progression of overtones and combination bands. Concentration profiles were obtained from the measurements of peak intensities of TMIn, MMIn, and indium at different distances away from the hot susceptor along the vertical centerline of the reactor.

Cube Texture Development in an Al-Mg-Mn Alloy Sheet Worked by Continuous Cyclic Bending

Changes in texture after the continuous cyclic bending (CCB) and the subsequent annealing in sheets of an Al-4.7 mass%Mg-0.7 mass%Mn alloy have been investigated. The CCB was recently proposed as a straining technique that generates a high strain on the surface and a much lower strain in the central layer of the sheet. The Cube texture in the surface layer is sharpened remarkably during the CCB process and the annealing that follows. The 50 CCB passes lead to a sharper texture in all layers of the sheet. After annealing, marked development of the Cube component is observed in the surface layer. On the other hand, for the 20 pass-CCBent sample, the Cube texture appears only after annealing in a salt bath, while this texture is not observed after annealing both in Ar and in air. The mechanism of texture formation and the effect of processing on the sharpening of Cube texture is discussed based on results obtained from the electron backscatter diffraction pattern (EBSP) analysis and from the in-situ measurement of X-ray peak intensity during heating.

Environmental Measurement Technology Using Multiple Internal Reflection FTIR

Environmental sensor which can detect and identify environmental pollution in real time is needed. It could be made by using Multiple internal reflection FTIR(MIR-FTIR) because of its short measurement time and high sensitivity. We chose GaAs which transmits large band lights which many molecule vibration exist in. It is possible to identify the gas which exists in the atmosphere around the crystal by FTIR spectrums. It is also possible to measure concentration of the gas in the atmosphere by measuring peak intensity of it. The result of reproducibility experiment will be reported finally.

Plasma dynamics from laser ablated solid lithium

Emission plasma plume generated by pulsed laser ablation of a lithium solid target by a ruby laser (694 nm, 20 ns, 3 J) was subjected to optical emission spectroscopy: time and space resolved optical emission was characterised as a function of distance from the target surface. Propagation of the plume was studied through ambient background of argon gas. Spectroscopic observations can, in general, be used to analyse plume structure with respect to an appropriate theoretical plasma model. The plume expansion dynamics in this case could be explained through a shock wave propagation model wherein, the experimental observations made were seen to fit well with the theoretical predictions. Spectral information derived from measurement of peak intensity and line width determined the parameters, electron temperature (Te) and electron number density (ne), typically used to characterise laser produced plasma plume emission. These measurements were also used to validate the assumptions underlying the local thermodynamic equilibrium (LTE) model, invoked for the high density laser plasma under study. Some interesting results pertaining to the analysis of plume structure and spatio-temporal behaviour of Te and ne along the plume length will be presented and discussed.

Powder diffraction beyond the Bragg law: study of palladium nanocrystals

An experimental method of measurement of the subtle changes of structure of metal nanocrystals occurring on chemisorption of oxygen, interaction with inert gas and hydrogen,etc., is proposed. The measured patterns and their evolution are interpretedviaatomistic simulations. Described are quantitative observations of the changes in peak position, intensity and half width of the 111 diffraction peak of a palladium catalyst caused by modifying the gaseous environment. The results of the measurements are in line with an atomistic model proposed earlier and prove that the measured average lattice constant of palladium clusters evolves according to their surface relaxation. The evolution of the measured peak intensity suggests surface ordering effects and was used to propose a detailed structural model of nanocrystalline metal particles. The transition of palladium into β-Pd-H in hydrogen under normal conditions was used as a structure probe and provided evidence for the presence of icosahedral clusters in a highly dispersed catalyst. The icosahedral phase is not significantly modified under hydrogen atmosphere and does not transform into the β hydride.

Electronic scattering from Co/Cu interfaces: In situ measurement, comparison with microstructure, and failure of semiclassical free-electron models

We show that novel thickness-dependent film conductance measurements, taken in situ during deposition of NiO/Co/Cu/Co spin valves and compared with thickness-dependent microstructural characterization, indicate a qualitative failure of widely accepted semiclassical free-electron models of giant magnetoresistance (GMR). Both in situ Auger electron spectroscopy covering experiments and ex situ x-ray diffraction measurements of peak intensity for Co/Cu/Co films indicate that the defect concentration does not vary noticeably as a function of thickness. The microstructural measurements suggest that the bulk scattering parameters ρ and λ should be considered to be constant within each layer, and that the surface scattering parameter p does not change between layers. Under these constraints, it becomes difficult to fit even qualitatively the highly asymmetric scattering behavior measured during the formation of Co/Cu vs Cu/Co interfaces. Calculations incorporating realistic band structure resolve the observed inconsistency between free-electron model calculations and experiment. The asymmetry in scattering is understood here to arise simply from the higher density of unfilled d states in Co compared with Cu.

He-atom diffraction from nanostructure transmission gratings: The role of imperfections

The relative diffraction peak intensities of He atoms with an incident beam energy of 65 meV diffracted from a microfabricated 100 nm-period transmission grating are analyzed using both Fresnel and Fraunhofer diffraction theory. The projected slit width could be varied from 50 nm down to less than 1 nm by inclining the grating at angles up to ${\ensuremath{\Theta}}_{0}=42\ifmmode^\circ\else\textdegree\fi{}$ with respect to the incident beam. Good agreement between calculated and measured peak intensities, up to the sixth order, is obtained by accounting for random deviations in the slit positions, and averaging over the velocity spread of the incident beam as well as the spatial extent of the nozzle beam source. It is demonstrated that He atom beam diffraction together with simple transmission measurements is an excellent means of characterizing such gratings including a detailed determination of the slit width, the bar shape, and random as well as periodic disorder.

A complex modulated magnetic structure in CeNi2Al5 persisting at very low temperatures

The orthorhombic compound CeNi2Al5 is magnetically ordered below 2.6 K. Kondo-type interactions together with strong crystal-electric-field (CEF) effects give rise to a complex magnetic structure: (i) its propagation vector is three dimensional and incommensurate, k = (0.500,0.405,0.083); (ii) the Fourier components of the moment associated with this vector are tilted away from the easy-magnetization axis b. Furthermore, the magnetic structure is double k, as the propagation vectors k = (kx, ky, kz) and k´ = (-kx, ky, kz) associated with different magnetic domains are not independent. New experiments have been undertaken to achieve a more precise determination of the magnetic structure. Magnetic peak intensity measurements with higher resolution and polarization analysis have both led to the conclusion that the Fourier component of the magnetic moment deviates slightly from the b-direction. Considering the coupling of the two propagation vectors, the resulting moment describes very flat ellipses with most of the moments very close to b. Neutron diffraction experiments down to 0.4 K have also been performed to investigate the evolution of the magnetic structure at low temperatures.

Rare-earth element determination in minerals by electron-probe microanalysis: application of spectrum synthesis

AbstractElectron-probe microanalysis (EPMA) is applicable to rare-earth elements (REE) in minerals with relatively high REE concentrations (e.g. hundreds of parts per million). However, given that each of the 14 REE has at least 12 X-ray lines in the L spectrum, finding peak-free regions for background measurement can be problematical. Also, measured peak intensities are liable to require correction for interferences. Hitherto, little attention has been paid to the optimisation of background offsets and the implications of the wide variation in REE distribution patterns in different minerals. The ‘Virtual WDS’ program, which enables complex multi-element spectra to be synthesised, has been used to refine the conditions used for different REE distributions. Choices include whether to use the Lβ1 rather than the Lα1 line, background offsets, and counting times for comparable relative precision. Correction factors for interferences affecting peak and background measurements have also been derived.