Quantitative secondary ion mass spectrometry depth profiling of surface layers of cubic silver halide microcrystals

The present article describes depth-profiling studies on populations of cubic silver halide microcrystals (typical size between 400 and 600 nm). These crystals consist of mixed halides (Cl, Br, I) and are characterized by internal halide distributions such as core-shell structures. Determination of the spatial distribution of the different halides in the microcrystals offers valuable information for the optimization of the crystal design of new photographic materials. The first part describes the calibration of the sputtered depth, which is more complicated than in the one-dimensional case of flat surfaces. In a second part, three different quantification methods [halide intensity ratios, XCs₂⁺ detection (X=halide) and the infinite velocity method] are used to determine the mean composition of the surface layer as a function of sputtered depth in the silver halide crystals. Although particles of submicrometer size are obviously not the ideal samples for depth profiling, a good correlation with values obtained by scanning electron microscopy energy dispersive X-ray microanalysis and wavelength dispersive X-ray fluorescence bulk analysis could be achieved.     

Modeling of the sputtering process of cubic silver halide microcrystals and its relevance in depth profiling by secondary-ion mass spectrometry (SIMS)

Secondary-ion mass spectrometry is frequently used for concentration–depth profiling of macroscopic samples, but it is certainly not a common analytical technique for the analysis of sub-micrometer-size particles. This is because of the additional ion-bombardment-induced artifacts which can occur when a three-dimensional microvolume is sputtered, instead of a flat surface. This paper presents a model of how small cubic photographic Ag(Cl,Br) crystals are eroded under primary-ion bombardment, and the extent to which secondary ions generated at different faces are extracted. The latter is studied by means of the program SIMION, which simulates ion trajectories in complex electrical field systems. It is shown that up to 90% of the secondary ions originating from the side face of a cubic crystal are unable to reach the detector, in contrast with most secondary ions originating from the top face. The angular dependence of the sputtering yield and the elemental ratio of Br/Cl sputtered particles have been calculated by using the well-known computer code TRIM (transport of ions in matter) under some limiting assumptions (possible preferential sputtering is disregarded and a steady-state sputtering process is assumed). The validity of the theoretical model and the calculated results were checked with experimental data. On the basis of the depth profiles presented it is explained why it is still possible to measure an interface inside a cubic volume, even though a group of several hundred crystals is sputtered simultaneously, and even though the orientations of the distinct faces of the cubes relative to the angle of incidence of the primary-ion beam are different.     

Modeling of the sputtering process of cubic silver halide microcrystals and its relevance in depth profiling by secondary-ion mass spectrometry (SIMS)

Secondary-ion mass spectrometry is frequently used for concentration-depth profiling of macroscopic samples, but it is certainly not a common analytical technique for the analysis of sub-micrometer-size particles. This is because of the additional ion-bombardment-induced artifacts which can occur when a three-dimensional microvolume is sputtered, instead of a flat surface. This paper presents a model of how small cubic photographic Ag(Cl,Br) crystals are eroded under primary-ion bombardment, and the extent to which secondary ions generated at different faces are extracted. The latter is studied by means of the program SIMION, which simulates ion trajectories in complex electrical field systems. It is shown that up to 90% of the secondary ions originating from the side face of a cubic crystal are unable to reach the detector, in contrast with most secondary ions originating from the top face. The angular dependence of the sputtering yield and the elemental ratio of Br/Cl sputtered particles have been calculated by using the well-known computer code TRIM (transport of ions in matter) under some limiting assumptions (possible preferential sputtering is disregarded and a steady-state sputtering process is assumed). The validity of the theoretical model and the calculated results were checked with experimental data. On the basis of the depth profiles presented it is explained why it is still possible to measure an interface inside a cubic volume, even though a group of several hundred crystals is sputtered simultaneously, and even though the orientations of the distinct faces of the cubes relative to the angle of incidence of the primary-ion beam are different.     

Quantitative characterization of surface layers on corroded medieval window glass with SIMS

Summary Dark green coloured panes, consisting of lead oxide, potash, lime, magnesia, silica and phosphorus oxide show minor corrosion phenomena compared with other stained glasses used in medieval painted windows. Surface layers and leaching zones on such naturally weathered glass samples can be succesfully characterized by SIMS. This analytical technique enables quantitative depth profiling of the main and trace components of the glass as well as the depth distribution of hydrogen. With the use of relative sensitivity factors of the elements and the different sputtering coefficients of the various layers, a quantification of the depth profiles is possible. According to the results, an ion exchange process leads to incorporation of water and depletion of the glass components potassium, calcium, sodium and lead at the glass surface. The leached elements form precipitations with components of the ambient atmosphere (CO₂, SO₂ etc.). A layer containing compounds of low solubility is built up, which protects the glass surface from further attack by water and moisture.

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Quantitative Charakterisierung von Oberflächenschichten verwitterter mittelalterlicher Fenstergläser mit SIMS

Zusammenfassung Die Sekundärionenmassenspektrometrie (SIMS) wurde zur Charakterisierung von Oberflächenschichten natürlich verwitterter Bleigläser aus mittelalterlichen Glasgemälden verwendet. Diese Gläser enthalten als Hauptkomponenten Kalium-, Calcium-, Silicium- sowie Blei- und Phophoroxid und weisen im Gegensatz zu den übrigen, in Glasgemälden verwendeten gefärbten und ungefärbten Gläsern wesentlich geringere Verwitterungsschäden auf. Mit Hilfe der relativen Empfindlichkeitsfaktoren und unter Berücksichtigung der unterschiedlichen Sputterkoeffizienten in den einzelnen Schichten ist es möglich, die Tiefenprofile zu quantifizieren. Dabei zeigt sich, daß die aufgrund des Verwitterungsprozesses an der Glasoberfläche ausgebildete Gelzone an Blei, Alkalien und Erdalkalien gegenüber dem Bulk verarmt ist. Reaktionen dieser gegen Bestandteile des Wassers ausgetauschten Elemente mit Bestandteilen der Luft (CO₂, SO₂ usw.) führten zur Ausbildung einer weitgehend kompakten Oberflächenzone, die in erster Linie aus wasserunlöslichen Verbindungen besteht und die darunter liegende Glasoberfläche vor einem weiteren Angriff durch Wasser und atmosphärische Schadstoffe schützt.

     

Force constants and bond polarizabilities of thiocyanate ion adsorbed on the silver electrode as interpreted from the surface enhanced Raman scattering

The surface enhanced Raman spectra of the thiocyanate ion is studied in two ways. First, normal mode analysis is employed to determine the force constants of the adsorbed thiocyanate ion. The result shows that the force constant for the CN bond becomes larger while that for the SC bond smaller in the adsorbed state. The adatom model with an effective silver mass of 0.1 m_Ag (m_Ag being the mass of the silver atom) is adequate for the analysis. This implies that the silver adatom is bound to the bulk electrode surface. The adsorption is also shown to be physical. Second, the SER intensifies are analyzed to obtain the molecular polarizability derivatives. The result shows that the polarizability derivative of the CN stretching motion is most responsive to the applied voltage. The polarizability derivative of the SC stretching motion is much smaller than that of the CN bond as compared in the solution. This conclusion is attributed to the adsorption center at the sulfur atom. In general, molecular polarizability derivatives are functions of the frequencies of the exciting lasers and the applied voltages on the electrode.     

Impedance measurements for pressed-pellet electrode membranes based on silver iodide and silver iodide/silver sulfide with solution contacts

Impedance characteristics of pressed pelletm membranes based on silver iodide, mixed $\text{AgI}\text{Ag}{}^2\text{S}$ with molar ratios of 10:1, 1:1 and 1:10, and silver sulfide are investigated by using solution contacts and a computer-controlled automatic measuring system. As membrane bulk impedances were commensurable with those of contacting solutions, special regression methods were necessary for evaluation. Typical resistivities were, in the order indicated above, as follows: 14, 2, 0.3, 0.1 and 0.1 kΩ cm, respectively. Thus, mixing of silver sulfide into the silver iodide matrix decreases dramatically the membrane resistance. These measured bulk membrane resistances are not affected by changes in composition and concentration of bathing solutions, and even the low-frequencies parts of impedance plots were not influenced by different stirring conditions, even in presence of corroding solutions such as thiosulfate or cyanide. Sorption also had no manifest effect on the impedance characteristics, but increasing pressure during membrane preparation or heat treatment significantly increased membrane resistances.     

Catalytic titration of iodide, bromide and thiocyanate by use of the silver catalysed phloxin-persulphate reaction

A method for the catalytic titrimetric determination of iodide, bromide and thiocyanate is described, based on the inhibitory effect of these anions on the silver-catalysed oxidation of phloxin by persulphate in the presence of 2,2'-bipyridyl. The end-point is determined photometrically by measuring the absorbance at 537 nm. Amounts of iodide, bromide and thiocyanate in the 0.01-7.94, 0.11-4.73 and 0.12-3.59mg ranges, respectively, are titrated with a relative error of about 1%.     

Synthesis and spectroscopic studies of phenyllead halide and thiocyanate adducts with hexamethylphosphoramide

Hexamethylphosphoramide (HMPA) adducts of the type Ph₃PbX·HMPA (X=Cl, Br, I, and NCS), Ph₂PbX₂·2HMPA (X=Cl, Br, and I), and Ph₂PbX₂·HMPA (X=Br and I), have been prepared and characterized by infrared, Raman, mass, and ³¹P nmr spectroscopy. Molecular weight and infrared solution data show that Ph₃PbX·HMPA adducts dissociate in benzene, the degree of dissociation being NCS«Cl<Br<I. The thiocyanate adducts Ph₃PbNCS·HMPA and Ph₂Pb(NCS)₂·2HMPA have v(CN) and v(CS) frequencies in the solid state, and v(CN) frequencies and absorptivities in benzene solution consistent with N-bonded thiocyanate in the solid state and in benzene solution. Vibrational frequencies are reported in the range 260 to 80 cm⁻¹ and assignments are made for v(Pb-X), v(Pb-O0, and v(Pb-NCS) modes. The 1:1 adducts Ph₃PbX·HMPA are monomeric and trigonal bipyramidal, whereas the 1:2 adducts Ph₂PbX₂·2HMPA are monomeric and cis-octahedral and the Ph₂PbX₂·HMPA appear to be halogen bridged polymers with lead six-coordinate. Coordination of HMPA causes a small upfield change in ³¹P chemnical shift values, and ²J(Pb-P) values vary with X in the order: NCS>I-Br>Cl for Ph₃PbX·HMPA adducts. Corresponding tin and lead adducts are compared with respect to mode of adduct formation.     

Formation of surface layers on silver nanoparticles in aqueous and water-organic media

Synthetic aspects of silver nanoparticle preparation in one-and two-phase aqueous and water-organic media and the influence of experimental factors on particle size and surface hydrophilicity/hydrophobicity are studied. It is shown that silver nanoparticles with controlled mean size and surface hydrophilic-hydrophobic properties can be obtained through direct synthesis or successive transformations.     

Measurement of the surface dilational viscoelasticity of adsorbed layers with a capillary pressure tensiometer

A capillary pressure tensiometer has been set up to measure the dilational surface viscoelasticity in liquid-air and liquid-liquid surfactant systems, according to the oscillating drop/bubble technique. A specific model which allows the dilational surface viscoelasticity to be inferred from the acquired pressure data is proposed and the critical points concerning the experimental procedure and the data interpretation are discussed. In order to optimize the method, side measurements utilizing the same tensiometer to evaluate equilibrium interfacial tensions and the system compressibility are coupled to this technique. Some nonionic surfactants, polyoxyethylene glycol ethers (C(i)EO(j)) and alkyl dimethyl phosphine oxide (C(12)DMPO), at water-air and water-hexane interfaces have been investigated by this technique. The measured dynamic dilational viscoelasticities are compared with the predictions of theoretical models which consider different adsorption mechanisms.     

Layer-by-layer adsorption of water molecules on the surface of a silver iodide crystal

Computer simulations at the molecular level were used to analyze the mechanism of the nucleation of water condensate from the vapor phase on the surface of a silver iodide crystal at 260 K. The initial stage of the condensation process is the sequential growth of monolayers on the substrate surface without formation of a compact microdroplet. The dependence of the equilibrium work of formation of the condensate film on its thickness exhibits oscillations. The formation of layers close to the substrate surface involves the overcoming of a Gibbs energy barrier.     

Structure and electrochemical behaviour of 4,7-diazaheptyl-trimethoxy-silane and vinyl-trialkoxy-silane adsorbed at silver surface

Novel self-assembled monolayers were obtained on silver using 4,7-diazaheptyl-trimethoxy-silane (SiN) and vinyl-trialkoxy-silane (SiVA, where the alkyl group is 3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60-eicozaoxa- hexaheptaconan). It was shown that thus modified metal surface was protected against electrooxidation. A densely packed monolayer remained stable and did not desorb from the Ag electrode on the potential cycling. The structure of SiN and SiVA as well as their complexes with Li⁺ cations were calculated and visualised by the AM1d and PM5 semi-empirical methods.     

Reversible conversion of nanoparticles of metallic silver and silver oxide in ultrathin TiO2 films: a chemical transformation in nano-space

The in-situ interconversion of silver and silver oxide nanoparticles was achieved in ultrathin TiO2 films using hydrogen and oxygen plasmas as dry redox reagents. Absorption spectroscopy and transmission electron microscopy showed that the chemical transformation gave rise to narrowing of size distributions of both silver and silver oxide nanoparticles upon repeated interconversion.     

Analysis and classification of individual outdoor aerosol particles with SIMS time-of-flight mass spectrometry

Individual aerosol particles sampled in the north of the city Karlsruhe were analysed with a TOF-SIMS instrument. The results confirmed the integral analysis of many particles [1]. In order to employ a signal pattern analysis of the negative secondary ions for the classification of organic compounds an earlier classification scheme for 5 keV Ar⁺ bombardment was found to be generally also applicable for the TOF-SIMS conditions. Two main classes of particles were distinguished, which consist of submicron mainly organic particles of vehicle traffic provenance on one side and coarse particles of geogenic sources on the other side. Additionally, the geogenic class could be devided into a fraction consisting of lime soil and a fraction with alumo-silicate soil. A quantification of the class population was performed by counting the particles of different type.     

Surface-enhanced resonance Raman scattering and density functional calculations of hemicyanine adsorbed on colloidal silver surface

Resonance Raman (RR) and surface-enhanced resonance Raman scattering (SERRS) of 4'-(N,N'-dimethylaminostyryl)-4-propylpyridinium bromide (hemicyanine, HC dye) in acetonitrile solution and on a colloidal silver surface have been investigated. The structure of the dye in the ground (S0) and excited (S1) electronic states was optimized using density functional calculations along with the B3LYP and the configuration interaction with the singlet excitation (CIS) methods, respectively, using the 6-31G basis set. The vibrational frequencies of the molecule were computed at the optimized geometry and compared with the observed Raman bands. A complete normal-mode analysis has been carried out because it is essential for the accurate assignment of the vibrational spectra. From the observed enhancement along various in-plane and out-of-plane vibrations in the SERRS spectrum and from theoretical calculations, it has been inferred that the interaction with the silver surface occurs via the nitrogen lone pair of the pyridyl or the dimethylamino group of the molecule with a tilted orientation. The observed red-shifts in the SERRS spectrum along various vibrations indicate strong interaction (chemisorption) of the HC dye with the silver surface. This is also supported by the presence of a Ag-N stretching vibration at 241 cm(-1). The effect of the dye concentration on the orientation of the molecule is also discussed.     

Interaction of oxygen adsorbed on silver film with hydrogen and ethylene

Kinetic data on hydrogen interaction with adsorbed oxygen testify to the uniformity and constancy of the oxygen bond with the silver surface. The surface reaction of ethylene epoxidation proceeds when the surface coverage by oxygen is higher than a certain threshold value, which is close to 0.4 for silver films at 333 K.     

Mechanism of halide conversion process of colloidal AgCl microcrystals by Br ions : I. Observation of the dynamic changes in shape, structure, and composition

The mechanism of the halide conversion process in suspension of AgCl microcrystals by bromide ions was studied by electron microscopy, X-ray diffractometry, and electron-beam diffractometry. The typical conversion process after the introduction of Br⁻ was found to consist of more than three distinctive steps. The first step was an almost instantaneous reaction within a few seconds for a surface conversion without apparent morphological change of the original particles. The second step was a very rapid epitaxial growth process of virtually pure AgBr crystals on every corner and partly on the edges of the AgCl cubic microcrystals with dissolution of their own {100} faces, which was finished in about 1 min at 25°C. The third step was a much slower process of about 2 h at 25°C (ca. 5 min at 45°C) for the formation of an AgCl_0.5Br_0.5 solid solution developing from the joints of AgBr guest and AgCl host by simultaneous dissolution of the guests and the hosts. After the complete dissolution of the AgBr guests, a further recrystallization process that formed a solid solution richer in chloride content followed. Finally, the conversion virtually stopped midway to yield double-structured particles of Ag(Cl, Br) shell/AgCl core. However, when the initial molar ratio of [Br⁻]₀/[AgCl]₀ was so high as to exceed unity, the original AgCl particles were totally decomposed into about eightfold AgBr particles in number. In this case the steps later than the second one were missing. Also, it was suggested from the subsidiary study on open systems, where bromide ions were added continuously, that the kinetics was basically controlled by the deposition rate of the solute of the AgBr component of the growing parts, though it was switched to being limited by the dissolution rate of the host AgCl crystals when their open surface area for dissolution was extremely diminished.     

Multiple attenuated total internal reflection spectra of ultrathin titanium oxide layers synthesized on a germanium surface

We have realized a vacuum variant for recording the multiple attenuated total internal reflection spectra of ultrathin (2–30 nm) layers of titanium dioxide directly over the course of their synthesis by the molecular lamination method on the surface of germanium single crystals. To a first approximation, there is a linear relationship between the intensity of the bands of the doublet at 890 and 820 cm^–1 (respectivelyv _as andv _s(Ti – O) and the number of molecular lamination cycles (thickness of the synthesized layers); deviations from linearity are due to the effects of the substrate and are expressed in changes in the shape of the contour of the doubletv _as/v _s for thicknesses <10 nm. Redistribution of the intensity in thev _as,v _s bands with an increase in thickness (>20 nm) of the titanium dioxide layer is due to the content of adsorbed H₂O and HCl molecules in the layer, desorption of which when the samples are heated leads to denser packing of the synthesized layers.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 26, No. 2, pp. 251–255, March–April, 1990.