Showing papers in "Surface and Interface Analysis in 1979"

Quantitative electron spectroscopy of surfaces: A standard data base for electron inelastic mean free paths in solids

Abstract: A compilation is presented of all published measurements of electron inelastic mean free path lengths in solids for energies in the range 0–10 000 eV above the Fermi level. For analysis, the materials are grouped under one of the headings: element, inorganic compound, organic compound and adsorbed gas, with the path lengths each time expressed in nanometers, monolayers and milligrams per square metre. The path lengths are vary high at low energies, fall to 0.1–0.8 nm for energies in the range 30–100 eV and then rise again as the energy increases further. For elements and inorganic compounds the scatter about a ‘universal curve’ is least when the path lengths are expressed in monolayers, λm. Analysis of the inter-element and inter-compound effects shows that λm is related to atom size and the most accuratae relations are λm = 538E−2+0.41(aE)1/2 for elements and λm=2170E−2+0.72(aE)1/2 for inorganic compounds, where a is the monolayer thickness (nm) and E is the electron energy above the Fermi level in eV. For organic compounds λd=49E−2+0.11E1/2 mgm−2. Published general theoretical predictions for λ, valid above 150 eV, do not show as good correlations with the experimental data as the above relations.

Composition–Depth profiling and interface analysis of surface coatings using ball cratering and the scanning auger microprobe†

Abstract: The provision of accurate composition–depth profiles to depths > 1 μm is important in the characterization and investigation of thick films, surface coatings, surface treatments and many other technologically important applications. At present, such profiles are usually achieved by sequential ion bombardment and surface analysis and hence involve many difficulties in interpretation due to the non-uniform erosion of surfaces under ion bombardment. In this paper a method of obtaining accurate depth profiles is described using a ball-cratering device. The method employs a rotating ball to fashion a well-defined spherical crater in the sample surface, the depth and width of which can be accurately controlled. The specimen is then cleaned in situ using a scanning ion beam for a short period and the composition–depth profile is obtained either by point-by-point analysis down the sloping sides of the crater wall or by using Auger line-scan techniques across the crater. Coating–substrate interface analysis can also be obtained by sputter–depth profiling at a point on the coating close to the exposed substrate. The method is not only considerably faster than ion etching, but the resulting depth profile also has a well-defined depth resolution. Composition–depth profiles through nitrocarburized mild steel surfaces and protective surface coatings are presented to illustrate the usefulness of the technique.

Surface analysis of aromatic polyimide films using ESCA

Abstract: C 1s, N 1s and O 1s core spectra were measured for well-cured polyimide films of poly(N,N′-(p,p′-oxydiphenylene)promellitimide), and of poly(p,p′-oxybis(phenylene)-3,3′,4,4′-benzophenonetetracarboxylimide). Resolvable were: multiple C 1s, two N 1s and two O 1s components. A carbonyl deficiency not due to X-ray-induced decarboxylation was detected. Approximately 45% of the surface carbon matrix was found to be comprised of partially oxidized, non-carbonyl-containing moieties of unknown origin. C 1s chemical shift behavior showed that imide bond formation does occur on curing; the imidization reaction in the surface region is incomplete (or altered) based on the changes in the O 1s and N 1s data with increasing temperature of curing. A surface chemical structure inconsistent with the bulk structural formula is observed.

Backscattering effects in Auger electron spectroscopy: A review

Abstract: Quantitative Auger electron spectroscopy requires knowledge of a factor correcting for backscattering effects. This paper discusses the definition of the backscattering correction and reviews the experimental and theoretical methods for determining this correction. The values of the backscattering factor reported in the literature are compiled, and the dependence of the backscattering factor on the primary beam incidence angle and the solid composition is also briefly discussed.

Secondary ion mass spectrometry at close to single‐atom concentration using DC accelerators

Abstract: Experiments have been conducted which show that secondary ion mass spectrometry (SIMS), together with the addition of a rather low voltage (2 MV) DC accelerator, can become an extremely powerful new technique in many fields of research related to the characterization of surface and bulk solids and with high spatial resolution. The technology is available today to build an instrument that would have high lateral resolution (∼ 1 μm) coupled with a secondary ion transmission coefficient from target to detector >10% with no mass interferences from molecular ions. Molecular ions can be fragmented and analyzed separately. We believe that this combination of secondary ion mass spectrometers and accelerators represents a most significant advance in analytical techniques.

A versatile time-of-flight atom probe for metallurgical applications

Abstract: A computer-controlled atom prove time-of-flight mass spectrometer system is described which permits quantitative microanalysis to be undertaken at the 1–2 nm level. Distinctive features of the system include the use of a Johnston detector, to give low noise, high gain and high detection efficiency; incorporation of a movable channel plate and screen assembly, to provide a variable aperture; and the development of a comprehensive set of computer plate and screen assembly, to provide a variable aperture; and the development of a comprehensive set of computer software, to assist in the processing of data and presentation of analytical results. The system has been used successfully in a number of metallurgical investigations. In this paper, particular attention is given to describing the operating conditions required to achieve optimum performances, and to discussing the questions of background noise reduction and the deconvolution of spectra. The quantitative analysis capability of the instrument is demonstrated by reference to the results obtained from a range of standard materials, including steels. Applications to problems of metallurgical interest are illustrated by the analysis of ultra-fine particles in a Cu/Co alloy, and the analysis of carbides and carbide-matrix interfaces in a 2¼Cr/1Mo steel. The spatial resolution obtainable under different operating conditions is discussed, and the particular problems involved in the study of interfaces by this technique are described in detail.

Thickness measurements on layered materials in powder form by means of XPS and ion sputtering

Abstract: A model for the quantitative analysis of XPS data from coated spherical particles is described. The limitations of the application of flat surface intensity equations to this system are discussed. The predictions are compared with experimentally derived XPS results for SiO2O3 coated TiO2 powder samples. Sputtering profiles for these systems are presented and interpreted.

Modified glow discharge spectroscopy for surface analysis of steels

Abstract: Grimm-type glow discharge spectroscopy (GDS) was installed and evaluated as an emission spectroscopic source for the analysis of steel surfaces and for the determination of in-depth concentration profiles. In order to restrict the abnormal intensity fluctuation at the surface layer, which was observed during analysis of 300 A of the sample surface layer, the third electrode was installed in the light source and a preliminary discharge technique was developed. The purpose of this preliminary discharge is to clean the sample surface and inner wall of the anode pipe, and to produce plasma in the discharge chamber in order to start the main discharge smoothly. By using GDS with this technique (modified GDS) the influence of abnormal fluctuation at the first stage of discharge was completely excluded and the unstable region of the intensity profile at the beginning of discharge was restricted to 10 A or so. This modified GDS was applied to the analysis of the surface of box-annealed steel sheets and the determination of changes in composition with depth below the surface. The results were confirmed by an investigation of the in-depth analysis of the same samples previously conducted with an ion microprobe mass analyzer (IMMA), and this fact revealed the usefulness of modified GDS as a surface analyzer.

Improved depth resolution in Auger depth profiling of multilayered thin films by reactive ion sputtering

Abstract: Reactive ion sputtering (N) is shown to improve depth resolution significantly in conventional Auger electron spectroscopy depth profiling of multilayered metallic thin film samples as compared to standard argon ion bombardment. Layer modulations on the order of the escape depth of the Auger electrons are shown to be discernible by conventional Auger depth profiling in a texturing-prone situation (microscopically modulated thin film samples) when N is used as the sputtering species. Oxygen ion sputtering was observed to give greater improvement in depth resolution than nitrogen, but was also observed to have a deleterious influence on instrument performance. Increasing the N ion energy from 2 to 5 Ke V was found to degrade depth resolution slightly.

Quantitative XPS analysis without reference samples

Abstract: For approximately ten years there has existed a theoretically based concept of fundamental parameters for XRFA (quantitative X-ray fluorescence analysis). From a comparison of the differences specific for XRFA and XPS it can be learned that this concept is also applicable to XPS and allows quantitative analysis without reference samples. Additionally, the influence of an overlayer on analytical XPS results is discussed. The theoretical considerations are confirmed by a series of measurements performed on binary and ternary alloys of Ag/Au/Cu and the results are compared with those of earlier measurements with reference samples. An averaged absolute accuracy of approximately ±2 wt% has been found for both methods, but the advantage of an absolute method needs no further comment.

XPS and Auger LMM analysis of ZnO/Si and ZnO/SiO2 interfaces

Abstract: The interface between ZnO/Si and ZnO/SiO2 was studied by etching through the junction region and analyzing XPS and Auger LMM spectra. By comparing XPS shifts and peak splitting in the Si2p spectra, chemical complexes of the form Si—Ox—Zn (x≃1) were identified at the ZnO/Si interface. The transition from ZnO/SiO2 was characterized by intensity variations in the O1s spectra. Relative to metallic zinc the Auger LMM shifts were −4 eV for ZnO on Si and −3 eV for ZnO on SiO2. Such shifts were attributed mainly to extra-atomic relaxation. Correspondence of levels (zero Auger shifts) was observed in the spectra from the two interface regions suggesting that zinc extra-atomic relaxation was constant throughout a region of varying chemical composition.

Critical assessment by analytical electron microscopy of the significance of XPS measurements of the dispersion of supported catalysts

Abstract: The use of XPS intensity measurements to monitor the dispersion of supported catalysts becomes questionable in the case of an inhomogeneous repartition of the active species. Analytical electron microscopy permits the measurement of such inhomogeneitis. Two particular examples illustrate how misleading interpretations can be avoided by the combined use of these two techniques.

Electron beam effects in Auger electron spectroscopy and scanning electron microscopy

Abstract: Electron beam effects on Si(100) and 5% Fe/Cr alloy samples have been studied by measurements of the secondary electron yield δ, determination of the surface composition by Auger electron spectroscopy and imaging with scanning electron microscopy. Variations of δ as a function of the accelerating voltage Ep (0.5

Interface analysis for the determination of the pH within the boundary layer at a cathode surface

Abstract: The determination of pH value at a cathode surface requires the use of a technique capable of detecting the initial precipitation of a tracer ion. It is shown that XPS fulfils this role and that thicknesses of deposit may be estimated. The results can be correlated well with simple hydrodynamic theory and may be related to deposits formed on power station condenser tubes operating in sea water.

An appraisal of the present position and future potential of inelastic electron tunnelling spectroscopy (IETS)

Abstract: The present position regarding the preparation of junctions suitable for IETS investigation and the various doping procedures is outlined, and a comparison is drawn between IETS and other surface spectroscopies. A survey of the systems already studied of interest in the fields of surface chemistry, heterogeneous catalysis, analytical chemistry and environmental pollution monitoring, adhesion science, radiation damage, biological chemistry and electronic energy level studies is presented. The parameters thought to affect the development of this technique and some potential applications to corrosion inhibitors and metal protection, lubrication studies, solid-state devices and photochemical energy converters are considered.

Auger electron spectroscopy (AES) an appraisal

Abstract: Electron induced Auger electron spectroscopy of solid surfaces has proved a valuable analytical technique over the past ten years. In this paper the state of the technique is reviewed and compared with other methods of Auger spectroscopy, e. g. X-ray induced AES.

XPS–ISS analysis of Al/Ni alloys

Abstract: The change in the surface composition of an Al/Ni alloy (50% by weight Ni) on heating in O2 and treatment in diluted NaOH was investigated by quasi-simultaneous XPS–ISS measurements, using a hemispherical condenser analyser both for ESCA and ISS. The oxidizing experiments were carried out in a valveless, integrated, high pressure, high temperature preparation lock.

The fluorination of the surface of elemental carbon. II—Deposition and stability of florine‐containing species: X‐ray photoelectron spectroscopic studies of flourinated graphite

Abstract: X-ray photoelectron spectroscopy (XPS) has been used to investigate the interaction of fluorine-containing intermediates with the basal plane of freshly cleaved graphite. A polymeric film of polytetrafluoroethylene (PTFE) on the carbon surface was formed on the basal plane by the interaction of microwave discharged hexafluoroethane and tetrafluoroethylene at 0.1 Torr pressure. Photolysis of tetrafluoroethylene near the graphite deposited submonolayer quantities of PTFE on the basal surface. Similar photolysis of hexafluoroacetone produced a reaction of trifluoromethyl radicals with carbon atoms in the graphite surface.

Surface characterization and adhesive bonding of stainless steels: I—the surface characterization of the steels

Abstract: In part I of this study, surfaces of three stainless steels have been characterized by scanning electron microscopy, electron probe microanalysis, Auger electron spectroscopy and X-ray photoelectron spectroscopy. The surface characteristics, which were investigated before and after chemical etching, were found to be strongly dependent upon the method of steel manufacture. The environmental resistance of adhesive joints prepared using the steels depended upon the surface chemistry and roughness induced by the etching treatment. In part II the interface region of the three steels and silane-based primer will be analysed and results correlated with durability studies.

A multichannel electro‐optical detector for rapid acquisition of X‐ray photoelectron spectroscopy data

Abstract: An electro-optical detector easily adaptable to any hemispherical sector photoelectron spectrometer is described. The detector consists of a channel plate electron multiplier array, phosphor screen, silicon intensified target vidicon an optical multichannel analyzer control unit. Data collection rates are improved by more than two orders of magnitude over conventional single channel detectors.

Thermal oxidation of GaOx Ny‐covered GaAs surfaces

Abstract: The thermal oxidation of GaO x N y- covered GaAs surfaces is investigated mainly by means of a combined Auger-sputtering method. It is shown that an oxide layer is formed mainly at the interface between the GaO x N y film and the GaAs on thermal oxidation in O2 gas, but the formation of the interfacial oxide layer is successfully suppressed by oxidizing in an atmosphere of O2 gas diluted with an excess amount of NH3 gas. The effects of oxidation temperature and the oxygen content in the GaO x N y film are further discussed. The properties of the interfacial oxide layer are compared with those of the oxide formed on free GaAs surfaces. Corresponding electrical properties are also examined.

Potassium on the fracture surface of tungsten wires studied by AES

Abstract: Industrial tungsten wires were fractured using Auger equipment. The concentration of potassium on the fracture surface of the variously heat-treated wires was markedly different. The results can be explained assuming that the wires were fractured along the potassium second phases. The spectra, similar to those normally interpreted as indicative of monolayer potassium segregation on the fracture surfaces, are here interpreted as arising from diffusion across the surface after fracture from the potassium inclusions and not from a segregated layer.

Reference levels in electron‐excited and X‐ray‐excited Auger spectra

Abstract: Auger spectroscopy and X-ray photoelectron spectroscopy have evolved using different reference levels for electron energy measurement. Electron-excited Auger spectra are referenced to the vacuum level, and X-ray-excited Auger spectra are referenced to the Fermi level. This can cause confusion, especially when both are recorded in the N(E) mode in the same instrument.

Synchrotrons as sources for low energy Auger spectroscopy

Abstract: Unmonochromatized synchrotron sources are shown to be useful alternatives to electron beams in exciting low energy Auger transitions, and are likely to have applications where small concentrations of impurities in the surface of large samples are being investigated.

Investigation of the initial stages of oxidation of differently prepared aluminium by SIMS

Abstract: The initial stages of oxidation of thin evaporated by SIMS. The highest ratio between the AIO+ ion yield at oxygen coverage ∂=0.13 and zero exposure was observed in the case of the thin film sample; moreover, for the diamond-polished sample this ratio was higher than for the electropolished one. The Al+ ion yield was found to depend on the oxygen uptake and to show a linear function in the range of the oxygen does applied. Calculations were carried out in connection with the sputtering yields of the three differently prepared samples using the ion yield values obtained. The difference between the samples analysed is ascribed to the different oxide content of their surface layers.