Emission Theory of Amorphous Material Sputtering: the Dependence of the Sputtering Coefficient on the Angle of Primary Ion Beam Incidence

The dependences of the sputtering coefficient on the types of accelerated ions, their energy, and the angle of incidence on a target are calculated. For Ar–Si, Хе–С, and H–W systems, acceptable coincidence between the calculated and experimental data is obtained. Two mechanisms for secondary-particle ejection from solids are established; they determine the dependences of the base sputtering coefficient for the base on the energy and the angle of primary ion incidence on the target.     

SERS from molecules adsorbed on small Ag nanoparticles: A microscopic model

A microscopic approach to surface-enhanced Raman scattering (SERS) from molecules adsorbed on noble-metal nanoparticles is developed. For nanoparticle sizes smaller than 10 nm, the classical electromagnetic enhancement mechanism is modified by quantum-size effects. Using time-dependent local field approximation, we perform systematic analysis of SERS in nanometer-sized Ag nanoparticles. We find that, in small nanoparticles, Raman cross-section enhancement is governed by the interplay between Landau damping of the surface plasmon and interband screening in the nanoparticle surface layer.     

Effect of an axial crystal field on properties of vibronic systems

Taking into account spin-orbit coupling in T-e and T-t₂ systems allows us to explain the linear dependence of the distortion of the system on the strength of the external field (the dependence is linear for fields which are not too strong). An external trigonal field in the T-e system and a tetragonal field in the T-t₂ system leads to the Jahn-Teller minima becoming more shallow and approaching closer to the origin of the coordinate system; i.e., the effect of the external fields in this case in analogous to the effect of spin-orbit coupling.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 333–336, May–June, 1989.     

Fluorescence quenching near small metal nanoparticles

We develop a microscopic model for fluorescence of a molecule (or semiconductor quantum dot) near a small metal nanoparticle. When a molecule is situated close to metal surface, its fluorescence is quenched due to energy transfer to the metal. We perform quantum-mechanical calculations of energy transfer rates for nanometer-sized Au nanoparticles and find that nonlocal and quantum-size effects significantly enhance dissipation in metal as compared to those predicted by semiclassical electromagnetic models. However, the dependence of transfer rates on molecule's distance to metal nanoparticle surface, d, is significantly weaker than the d(-4) behavior for flat metal surface with a sharp boundary predicted by previous calculations within random phase approximation.     

N-(R-Cyclopropyl) Trifluoroacetimidoyl Phosphonates

Abstract

A convenient synthetic approach for previously unknown N-(R-cyclopropyl)trifluoroacetimidoyl phosphonates 5a,b (R?H, CF₃) was developed on the basis of the reaction of respective trifluoroacetimidoyl chlorides with triethyl phosphite. It was shown that imidoyl phosphonates 5a,b exist as equilibrium mixture of Z/E isomers (Z:E ～92:8). Activation parameters of Z–E isomerization were evaluated by ¹⁹F NMR spectroscopy. Catalytic hydrogenation of 5a,b can serve as a convenient method for the synthesis of trifluoroethylaminophosphonates with a rigid N-cyclopropyl group.     

Conductivity and persistent photoconductivity in GaAs epitaxial films containing single and double delta-doped layers

Electrophysical parameters of single and double delta-doped layers in GaAs epitaxial films grown by the metal-organic chemical vapor deposition have been systematically investigated in the temperature range of 4.2 to 300 K. The 2D electron gas density distribution is affected by the overlap of wave functions in neighboring quantum wells, as a result of which the peak on the curve of the Hall mobility in the 2D electron gas versus the separation between the quantum wells shifts. The persistent photoconductivity in delta-doped layers is due to the change in the surface potential caused by the neutralization of the negative charge of surface states by photoexcited holes. A method for comparing delta-doped layers grown under different conditions at different depths from the sample surface has been suggested. Zh. éksp. Teor. Fiz. 113, 693–702 (February 1998)     

Quantifying uncertainty in the measurement of arsenic in suspended particulate matter by Atomic Absorption Spectrometry with hydride generator

Arsenic is the toxic element, which creates several problems in human being specially when inhaled through air. So the accurate and precise measurement of arsenic in suspended particulate matter (SPM) is of prime importance as it gives information about the level of toxicity in the environment, and preventive measures could be taken in the effective areas. Quality assurance is equally important in the measurement of arsenic in SPM samples before making any decision. The quality and reliability of the data of such volatile elements depends upon the measurement of uncertainty of each step involved from sampling to analysis. The analytical results quantifying uncertainty gives a measure of the confidence level of the concerned laboratory. So the main objective of this study was to determine arsenic content in SPM samples with uncertainty budget and to find out various potential sources of uncertainty, which affects the results. Keeping these facts, we have selected seven diverse sites of Delhi (National Capital of India) for quantification of arsenic content in SPM samples with uncertainty budget following sampling by HVS to analysis by Atomic Absorption Spectrometer-Hydride Generator (AAS-HG). In the measurement of arsenic in SPM samples so many steps are involved from sampling to final result and we have considered various potential sources of uncertainties. The calculation of uncertainty is based on ISO/IEC17025: 2005 document and EURACHEM guideline. It has been found that the final results mostly depend on the uncertainty in measurement mainly due to repeatability, final volume prepared for analysis, weighing balance and sampling by HVS. After the analysis of data of seven diverse sites of Delhi, it has been concluded that during the period from 31^st Jan. 2008 to 7^th Feb. 2008 the arsenic concentration varies from 1.44 ± 0.25 to 5.58 ± 0.55 ng/m³ with 95% confidence level (k = 2).     

Volatile probes for spectral research on silicate transformations

A theoretical analysis is presented for the properties of iron-group ions in layer silicates. The most suitable probe for examining AlO₆ AlO₄ transitions is CO²⁺, whose electronic structure makes it capable of reflecting the symmetry of the predominant AlO₆ or AlO₄ elements in layer silicates.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, No. 2, pp. 240–244, March–April, 1989.     

Halogen migration vs. hydrogen halogenide elimination in reactions of 1-chloro-2,2,2-trifluoroethansulfonyl chloride and 1,2,2,2-tetrafluoroethansulfonyl fluoride with amines: theoretical and experimental investigation

A simple and useful method has been proposed for preparing of 1-chloro-2,2,2-trifluoroethan sulfonylchloride. By aminolysis of 1-chloro-2,2,2-trifluoroethansulfonylchloride the chlorine migration proceeds forming the corresponding salts of 1,1-dichloro-2,2,2-trifluoroethansulfinic acid. This process as well as the alternative reaction, elimination of hydrogen halogenide, has been studied using quantum chemistry (DFT and MP2) methods. As the calculation data indicate, an intermediately formed anion undergo intramolecular chlorine migration via a three-membered cyclic transition state. The latter is characterized by the low activation energy (ΔE = 27.0 kcal/mol). The barrier of activation in the case of 1,2,2,2-tetrafluoroethansulfonylfluoride is considerably higher (ΔE = 41.6 kcal/mol). The structures of the 1,1-dichloro-2,2,2-trifluoroethan sulfinic acid and 1,1,2,2,2-pentafluoroethansulfinic acid anions can be considered as donor-acceptor complexes of perhalogenoalkyl anions with SO₂.     

Improvement of reproducibility of trace analysis by spark-source mass-spectrometry

Summary Mechanisms responsible for poor reproducibility of analysis by spark-source mass-spectroscopy are discussed. A new scheme for the output cascade of a radiofrequency generator has been developed. It allows for stabilizing both the charge and impurity mass-spectrum composition at changing the width of the interelectrode gap over a wide range. The causes of transient irreproducibility in mass-spectrometric analysis have been studied and traced to temporal variation in the discharge-circuit parameters. Methods of eliminating this irreproducibility are proposed.

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Verbesserung der Reproduzierbarkeit der funkenmassenspektrometrischen Spurenanalyse

Zusammenfassung Die Ursachen der schlechten Reproduzierbarkeit der mit Hilfe der Fun-kenmassenspektrometrie durchgeführten Spurenanalyse wurden erörtert. Ein neues Schema der Ausgangsstufe des Hochfrequenzgenerators wurde ausgearbeitet. Dies ermöglicht die Konstanthaltung sowohl der Ladung wie der Zusammensetzung des Massenspektrums auch bei weitgehender Veränderung des Elektroden-Zwischenraumes. Die Ursachen der vorübergehenden Nicht-Reproduzierbarkeit massenspektrometrischer Analysen wurden untersucht. Diese wird von der zeitlichen änderung der Ladungsparameter verursacht. Vorschläge für die Behebung dieser Nicht-Reproduzierbarkeit wurden gemacht.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.