Differential sample charging in ESCA

An ESCA study of some “intermediate” conductors demonstrates a differential charging effect when the sample block is biased. The variation of the intensity and width of the peak from silver 3d electrons in silver iodide is used to show how the flux of the beam, the conductivity of the sample, the size and polarity of the bias and the grid mounting alter the effect. The results suggest that in unbiased samples differential sample charging contributes significantly to the width of peaks.     

ESCA applied to liquids

The conditions for applying ESCA on liquid samples are discussed. A “liquid beam” technique is developed which meets the various requirements. The first spectrum of a liquid is presented, namely from formamide. It is shown that one can adjust the liquid beam so that a complete separation between the ESCA signals from the liquid and the vapour is achieved. The binding energies of the core levels of the elements in the molecule differ from each other in the liquid and the vapour phase by about 1.6 eV. One can also obtain electron spectra from dissolved chemical species. This is illustrated by potassium iodide dissolved in formamide.     

Chemical shifts in ESCA and NMR

A detailed examination of the relationship between chemical shifts in ESCA and NMR is presented. It is demonstrated that even in series of closely related compounds a linear correlation between ESCA and NMR shifts cannot be expected. Included is a discussion of reorganization effects on electron binding energies. The close relation between chemical shifts of ESCA and NMR and the spin—rotation constants of molecules is pointed out.     

ESCA studies of Cr-Co alloys

ESCA examination of films formed on Cr-Co alloys after immersion in 0.1M NaCl for 24 h has shown that the thickness of passive films decreased with an increase in chromium content. Surface films consisted of chromium and cobalt oxides as Cr₂O₃ and CoO. The amount of CoO in the surface film of the alloy was decreased with an increase in chromium but Cr₂O₃ was found at a greater depth in the passive film at any composition. Cr₂O₃ was a major component of the surface film when the chromium content in the alloy was 10% or higher. Electrochemical techniques according to ASTM G59 and ASTM G5 were used for the determination of the relative corrosion rate. Both Co-10 wt.% Cr and Co-30 wt.% Cr alloys investigated showed a lower corrosion rate than the Co-5 wt.% Cr alloy. Corrosion rate measured could be correlated to the surface film composition and structure as determined by ESCA.     

Recent progress in ESCA studies of gases

The development during the most recent years of ESCA applied to free molecules is reviewed. The advantages of studying, when possible, a substance in t     

ESCA studies of Fe-Ti alloys

Fe-Ti alloys containing 5 to 47% Ti have been studied by ESCA. The alloys were exposed to 0.1 M NaCl for 24 h under open-circuit potential (OCP) during which passive films were formed. The passive film consisted of FeO and TiO₂ in the inner layer while Fe₂O₃, water, and hydroxyl groups were present in the outermost monolayers, irrespective of composition. The thickness of the passive layer was reduced from 4.4 nm to 1.0 nm with increasing Ti content. The amount of iron oxide in the passive layer also decreased with increasing Ti. Electrochemical techniques according to ASTM G59 and ASTM G5 were used for the determination of the relative corrosion rate of the alloys. Alloys with 5–28% Ti showed a relatively high corrosion rate but that with 47 wt.% Ti had a much lower corrosion rates.     

ESCA Studies of Supported Catalysts

Abstract

Since ESCA measurement reveals the chemical composition and oxidation states of atoms on the surface of solids [1], it provides a new probe for investigation in the field of catalysis. It has been widely used to investigate directly the surface structure and composition, mechanisms of reaction, poisoning and reactivation; composition activity performance correlationship, etc. ESCA on catalysts has been reviewed by several workers [2–71, but its use in supported catalysts has not received the attention of workers. In this review the potential applications of XPS on several supported catalysts are discussed.     

Quantitative chemical analysis by ESCA

Electron spectroscopy for chemical analysis (ESCA) can be used as a quantitative tool for the determination of the chemical composition of the surface region of a solid if certain parameters are known. The least well known is the electron mean free path. We present values of the electron mean free path for inelastic scattering as a function of energy for all elemental solids (with the exception of the rare earths and the actinides) and we give formulae for the calculation of the mean free paths for compounds. It is shown that this information makes it possible to deduce from ESCA measurements the relative concentration of atoms or molecules distributed homogeneously in the surface region of a material.     

Deconvolution and smoothing: Applications in ESCA

Resolution enhancement by transform techniques has remained suspect because of the knowledge that the results which are obtained are not unique, and the conviction that they are likely to contain spurious features. An understanding of the distribution of signal and noise in the frequency spectrum of the data, and of the effects of combining smoothing with deconvolution makes it possible to define areas where such deconvolution schemes are useful in X-ray photoemission spectroscopy.     

ESCA studies of Ni-Cr alloys

ESCA examination on Ni-Cr alloys has shown that a thin passive film was formed after 24 h immersion in 0.1 M NaCl. The film contained only chromium oxide in the form of Cr₂O₃. Electrochemical techniques according to ASTM G59 and ASTM G5 were used for the determination of the relative corrosion rate of the alloys. Both Ni-10 wt. % Cr and Ni-20 wt. % Cr alloys showed a slightly higher corrosion rate than the Ni-40 wt. % Cr alloy.The present ESCA study of the Ni-Cr system is part of our programme which involves an examination of the four binary alloy systems Fe-Si, Cr-Co, Ni-Cr, and Mo-Ni [1]. The aim is to correlate the structure and composition of the passive films formed in 0.1 M NaCl to the corrosion behaviour in the same solution.     

ESCA studies of Si-Fe alloys

ESCA examination of films formed on Si-Fe alloys after immersion in 0.1 M NaCl for 24 h has hown that the thickness of passive films decreased with an increase in silicon content. A thick passive film containing oxidized silicon and oxidized iron was formed on Fe-20 wt% Si and the oxidized iron was about three times higher than the oxidized silicon in the passive film. However, an obvious reduction in the oxidized iron in the film on Fe-30 wt % Si was observed. Oxidized iron was detected up to a depth of 1.0 nm and at a depth greater than 1.0 nm from the surface, the film was exclusively in oxidized silicon. The film was exclusively silicon oxide when the silicon content was increased to 50 wt %. Electrochemical techniques according to ASTM G59 and ASTM G5 were used for the determination of the relative corrosion rate. Fe-50 wt % Si was found to have a corrosion rate smaller than those lower silicon alloys. This relates to the surface film composition and structure as determined by ESCA.     

Multi-peak ESCA bands of nitroanilines

The ESCA spectra of a series of nitroanilines were obtained. Multi-peak structures were observed in the various energy regions. In the N_1s region this structure was found for the nitro band, but not for the amino band. These effects are interpreted as due to shake up phenomena involving intramolecular charge transfer transitions. A qualitative model for such kind of phenomena is given. It rationalizes the fact that shake up processes are specific to a certain atom or atoms within a molecule. The shake up energies are compared with the ultraviolet absorption ones. The charge density of the atom showing the shake up transition seems to be the main factor in determining the agreement between ESCA and ultraviolet data.     

On the importance of photoconduction in ESCA experiments

With a specially designed experiment it is shown that the absence of charging often observed with materials of low specific conductivity is due to photoconduction. These results lead to a preparation technique which reduces charging to an almost negligible extent.     

ESCA studies of fracture surfaces in welded metals

A fracture device for ESCA studies of internal surfaces in metals is described. By fracturing a specimen under UHV, an uncontaminated surface is obtain The specimen is cooled to produce cleavage or intergranular fracture, depending upon the type of information sought.The technique has been applied to weldments in steels of composition C 0.020, Mn 1.15. In the as-welded state, fracture surfaces yield signals of C, N, and O as well as iron in oxidized state beside metallic iron. Antimony is found on the fracture surface of specimens embrittled by long annealing in ox A strong chemical shift indicates that it is present in the oxidized state.     

ESCA studies of nitrogen-containing stainless steels

ESCA examination of films formed on nitrogen-containing stainless steels after immersion in 0.1 M NaCl revealed that nitrogen was enriched in the outer 0.5 nm of the film at a concentration a few times higher than in the substrate. The N(1s) binding energy varied from 399.6–399.7 eV at the outermost surface of the film to 398.3–398.8 eV in the film at a depth of about 0.5 nm. This indicates a change in the chemical state of nitrogen upon exposure of the nitrogen-containing stainless steels to the solution, and furthermore, that the surface nitrogen enrichment could be of significance in the improved pitting resistance.