X-ray photoelectron spectroscopy of merocyanine dyes: III. Structure of the O1s line in the merocyanine 540 dye

The structure of the 01s spectrum for the MC 540 merocyanine dye is resolved using data obtained from XPS analysis of a series of merocyanine dyes displaying less complex O1s signals.The 01s binding energy (BE) of the carbonyl group in these molecules is unusually low and the photoionization peak is accompanied in most cases by a satellite on the high BE side.The data obtained in this study permit a reconstruction of the 01s profile of the MC 540 molecule. The 01s binding energy thus obtained for the carbonyl groups in MC 540 is 531.2 eV. This BE is low when compared to those usually observed for such groups and indicates that, in the MC 540 molecule, they predominantly exist in the ⩾C-O⁻³ form.     

X-ray photoelectron spectroscopy of merocyanine dyes Part VIII. Partial charge and conjugation of heteroatoms in the electroattractor rings

Partial charges for oxygen and sulfur in the electroattractor rings of a series of merocyanine dyes are determined using binding energy-partial charge correlations. The atomic charges are used to study the conjugation of the heteroatoms in the electroattractor part of the dyes. The carbonyl group is highly conjugated in the C-O⁻ form, especially in the nitro dyes, whereas its conjugation is somewhat hindered when a thioketone group coexists in the attractor part, thus suggesting a competition between both attractor groups.     

X-ray photoelectron spectroscopy of merocyanine dyes: VI. shake up satellites in the nitro N1s spectra of some nitromerocyanine dyes

The binding energies and relative intensities of the two components of the nitro N1s spectra in a series of merocyanine dyes indicate that there are two different kinds of shake up phenomena in these molecules depending on the extent of conjugation. The nitro N1s shake up is probably negative in the highly conjugated azaheterocyclic dyes whereas it appears to be normal in a low conjugated benzodithiolic molecule.     

New method to calibrate binding energy using Au nanocolloids in X-ray photoelectron analysis of diamondlike carbon films with different electrical resistivities

A new method to calibrate the binding energy (E_B) using Au nanocolloids as a calibrant in XPS analysis of diamondlike carbon (DLC) is proposed by considering the DLC films with different electrical resistivities. A few microliters of a dilute aqueous solution containing Au nanocolloids were dropped onto a small local surface area of the DLC film, which became a stain before XPS measurements by gradually drying in vacuo. The observed peak E_B of the C 1s spectrum at another native surface (an area without Au nanocolloids) of the DLC film was calibrated by setting that of the Au 4f_7/2 spectrum of the Au nanocolloids to 84.0 (83.98 ± 0.02) eV. The adequacy of this method was investigated by considering the correlation among the full width at half maximums (FWHMs) of the Au 4f_7/2 spectra of the Au nanocolloids on the DLC surfaces and that of a Au plate as a reference. Consequently, the FWHM of the Au 4f_7/2 spectrum of the Au nanocolloids on the DLC surface is a candidate to investigate the differential charging effect of the DLC surface, and the calibration method is reliable if the FWHM agrees with that of the Au plate.     

Influence of an electrostatic potential at the metal/electrolyte interface on the electron binding energy of adsorbates as probed by X-ray photoelectron spectroscopy

We present a study of the influence of an electrostatic potential across the Au(1 1 1)/4,4′-dithiodipyridine (PySSPy)-SAM/0.01 M NaOH interface on the electron binding energies of the N 1s and S 2p orbitals of the adsorbate, as probed by X-ray photoelectron spectroscopy (XPS). The observed systematic binding energy shift for N(1s) with electrode potential of −0.9 eV/V has been assigned to a so-called electrochemical shift, i.e., an apparent shift of the binding energy due to the potential drop in the electric double layer. No systematical shift was observed for the S(2p) core level of the thiol with electrode potential. The results are contrasted by measurements in 0.1 M H₂SO₄, where no electrochemical shift was found for the protonated nitrogen.     

Application of X-ray photoelectron spectroscopy to characterization of Au nanoparticles formed by ion implantation into SiO2

In X-ray photoelectron spectroscopy (XPS) of Au nanoparticles, the width of 5d valence band changes with Au particle size. This enables us to estimate the size of Au nanoparticles by using XPS. In this work, the 5d-band width has been measured for Au nanoparticles formed by ion implantation into SiO₂. The 5d-band width is found to be correlated strongly with the Au concentration. As the Au concentration increases, the 5d-band width becomes larger, indicating that the Au nanoparticles with the larger size tend to be formed in the vicinity of the projected range of Au ions. This correlation agrees very well with the results from transmission electron microscopy.     

Applications of photoelectron spectroscopy to molecular propertles: XVIII. The vertlcal ionization potentials of diphosphene as calculated by perturbation corrections to koopmans' theorem

The vertlcal ionization potentials (VIP's) of dimethyl diphosphene have been computed using perturbation corrections to Koopmans' theorem. These corrections allow an estimate of the effects of polarization and correlation, and show for this molecule an important contribution of the specific correlation of the ion for the ²A_g and ²B_u states. The results predict for the first three VIP's the ordering ²A_g, ²A_u, ²B_u, in agreement with our previous assignment.     

Investigation of the electronic structure of La1−x(M2+)xCrO3, Cr2O3 and La2O3 by X-ray photoelectron spectroscopy

The electronic structures of lanthanum chromites, pure and doped with magnesium and strontium, have been studied in comparison with Cr₂O₃ and La₂O₃ through the use of X-ray photo-electron spectroscopy. The main peaks and satellites of inner and outer electrons are properly assigned. The band structure of LaCrO₃ is determined by using the XPS data and a calculation based on point charge model. The partially filled Cr(3d) band is localized. The conduction is mainly extrinsic. The measured Fermi-level is close to the valence band indicating a low activation energy in agreement with the results of conductivity measurements.     

Oxygen induced segregation of aluminum to α-Cu-Al(1 0 0) alloy surfaces studied by low energy ion scattering and X-ray photoelectron spectroscopy

The effect of annealing temperature on the surface composition of α-Cu-Al(1 0 0) alloys for aluminum concentrations of 5, 12 and 17 at% was investigated using X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). Two initial states of the sample surfaces were examined: sputter-cleaned and oxidized. The effect of annealing temperature on segregation is different for sputter-cleaned and oxidized samples. Aluminum preferential sputtering and strong oxygen induced aluminum segregation were detected on all examined samples. Whilst for the sputter-cleaned surfaces a small thermal induced segregation was observed, the combination of annealing and oxygen exposure resulted in aluminum enrichment in the 100-300% range relative to the bulk concentration. The segregation rate is proportional to the aluminum concentration for sputter-cleaned surfaces and displays a maximum for the oxidized α-Cu-Al(12 at.%)(1 0 0) surface.     

Particle Sizing by Photon Correlation Spectroscopy. Part IV: Resolution of bimodals and comparison with other particle sizing methods

The practical performances of single and multi-angle photon correlation spectroscopy (PCS) for resolving bimodal distributions of industrial poly (methyl methacrylate) samples was investigated in a comparative study by several users affiliated to academic and industrial groups and by two suppliers of commercial equipment. The results for the harmonic intensity averaged diameters obtained by cumulants analysis reported by the different laboratories are in agreement, in addition to the results for the normalized second cumulants. The uncertainty on the latter quantities is large, however. For the bimodal samples with two populations with average diameters in a ratio of about 2.5 : 1, not all users were able to resolve the distribution in its components by single-angle PCS. Some slight improvement was obtained by multi-angle PCS. Other indirect techniques (polarization intensity differential scattering, static light scattering data and disc photosedimentometer) appeared to be superior for resolving the bimodal distributions.     

Investigation of the surface composition of MgOZnO solid solutions by X-ray photoelectron spectroscopy

The surface composition of well-characterized samples of solid solutions MgOZnO, containing up to 25 mol% ZnO, has been studied by recording the intensity of XPS and AES peaks. The influence on the measured intensifies of factors such as surface carbonation and the energy of the measured peaks has been pointed out. The Zn concentration in the outer layer has been found to be considerably higher than in the bulk. The extent of surface enrichment in Zn is in reasonable agreement with the thermodynamic prediction based on the ideal solution approximation.     

Crystallography by LEED: IV. Application of the iso-intensity map method to the Ni(100)-(11, 11)-S system

In the present study, we illustrate in the case of the $\text{Ni(001) and Ni(001)-(1}\text{1}\text{, 11)-S}$surfaces, the application of a procedure of surface analysis by LEED using iso-intensity maps for the specular beam together with a very fast LEED program based on the RFS method. This procedure has several advantages: first, iso-intensity maps prevent one from leaving out important experimental information. Second, the fast LEED program allows one to study a large number of beams previously selected from the maps for their particular interest, thus avoiding finding a wrong result, as could hapen if one looks only at a few beams. It comes out from this study that the adsorption distance $\text{d = 1.3}\text{A}\text{?}$ of the sulfur atoms is confirmed with the help of a cluster type superposition potential for the sulfur layer. The agreement between experiment and theory is generally excellent, except for a very strong experimental peak which is not well reproduced by calculation, whatever the changes in the physical or structural parameters. This has not been reported previously and is similar to what has been found by the same authors for the aluminium (001) surface.     

Surface studies by crystal current measurement of X-ray induced secondary electron emission: II. Application to molecular adsorption: CO,C2H4, O2 and H2 on Ni(100)

The adsorption of CO, C₂H₄, O₂ and H₂ on Ni(100) has been followed by measurement of the variation in X-ray induced crystal current (XCC). With the exception of CO, the Δ XCC versus exposure plots showed breaks in slope associated with changes in overlayer structure. The direction of Δ XCC was found to be opposite to the reported work function changes.     

Absolute measurement of an atomic cascade rate using a two photon coincidence technique. Application to the 4p21S0 -4s4p 1P1 -4s21S0 cascade of calcium excited by a two photon absorption

The two photon coincidence technique yields an absolute measurement of a cascade decay rate without knowing the detection efficiency of each detector. This method is applied to calcium atoms in an atomic beam excited to the 4p²¹S₀ state, and decaying via the resonant ¹P₁ state; it yields the excitation rate of the upper 4p²¹S₀ level. Since the excitation process (two photon absorption) is controlled, one can compute the excitation rate of the upper level as a function of the transition probabilities in the cascade. The lower transition is well known and we can therefore deduce the transition probability for the 4p²¹S₀ -4s4p ¹P₁, transition which previously had not been accurately determined. The preliminary measurements yield a line strength s = 0.98 ± 0.3 au in good agreement with a recent measurement of the lifetime of the 4p²¹S₀ state.