Molecular ion implantation in silicon

¹⁵N₂ ⁺ molecular ions were implanted with 10keV (j=10 A/cm²) under high vacuum conditions close to room temperature in 100 silicon (c-Si) to study the¹³N depth distributions, particularly the dependence of peak concentration and dose on the ion fluence. The analysis were performed by the resonant nuclear reaction¹⁵N(p, )¹²C(NRA). A maximum peak concentration of 65 at.% was measured. Thin stoichiometric silicon nitride layers with a thickness of approx. 20 nm (15 at.% nitrogen at the specimen surface) were produced by this low-energy implantation of¹⁵N₂ ⁺ ions with an ion fluence of 1.5·10¹⁷ ions/cm². NRA analysis of 38 keV¹⁵N₂ ⁺ and 19keV¹⁵N⁺ ion implantations were performed to compare the¹⁵N depth distributions. No significant changes in the depth distributions are measured, that means, the molecular¹⁵N₂ ⁺ ions are already disintegrated passing the very first atomic layers of the sample during implantation. Non-Rutherford RBS with⁴He⁺ ions and 3.45 MeV was performed in order to confirm the results obtained by NRA.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Indirect Electroorganic Syntheses—A Modern Chapter of Organic Electrochemistry [New Synthetic Methods (59)]

The electrochemical formation and regeneration of redox agents for organic syntheses (indirect electrolysis) widens the potential of electrochemistry, as higher or totally different selectivities can often be obtained while at the same time the energy input can be lowered significantly. Higher current densities can also be obtained by preventing otherwise often encountered electrode inhibition. New types of redox catalysts can be formed in-situ and can be regenerated after reaction with the substrates. This principle is of increasing importance also for the application of already known redox agents with regard to environmental protection, since large amounts of a product can be generated in a closed circuit using only relatively small amounts of the redox reagent. Consequently the operation of such a process can be greatly simplified, and the release of ecologically objectionable spent reagents into the environment can be prevented. The broad spectrum of redox catalysts currently in use includes, inter alia, metal salts in very low or high oxidation states, halogens in various oxidation states, and, in particular, a wide variety of transition-metal complexes. A great deal of progress has recently been made in the application of organic electron transfer agents, since compounds have been found that are sufficiently stable in both the reduced as well as the oxidized state.     

Synthesis of ferrocenylruthenocene

Summary The dinuclear metallocene, ferrocenylruthenocene, is synthesized by Ullmann coupling of iodoruthenocene with a large excess of iodoferrocene in the melt phase. The compound's ligand-vibrational modes, as reflected in the i.r. spectrum, are virtually identical with those in biferrocene; so is the symmetric ring-metal-ring stretching mode manifested in the low-frequency Raman region. The mass-spectral fragmentation pattern indicates preferential loss of a cyclopentadienyl radical from the ferrocene rather than the ruthenocene unit in conformance with both the lower metal-ring bond strength in, and lower ionization energy of, the iron complex. The¹H n.m.r. patterns of the two metallocene groups, at 90 MHz, are sufficiently well separated from each other to allow their individual evaluation; this finding could have a significant bearing on the characterization of ferrocenylene-ruthenocenylene copolymers of future synthetic programs.     

Octahedral non-heme non-oxo Fe(IV) species stabilized by a redox-innocent N-methylated cyclam-acetate ligand

The ligand 1,4,8-tri-N-methyl-1,4,8,11-tetraazacyclotetradecane-11-acetic acid (Me3cyclam-acetic acid) has been synthesized by Eschweiler-Clarke methylation of cyclam-acetic acid, and the iron(III) complex [(Me3cyclam-acetate)FeN3]PF6, 1, has been synthesized, which has been found to have significantly different properties than its unmethylated analogue, [(cyclam-acetate)FeN3]PF6, 2. Whereas the iron ion in 2 is low spin with S = 1/2, 1 is found to be high spin at temperatures above 100 K, though low-spin species are observed at lower temperatures, indicating a spin crossover phenomenon. The iron(II) species 1red is electrochemically more accessible than 2red since the Fe2+/3+ redox wave in 1 appears approximately 350 mV more positive than the corresponding wave in 2. Also, 1 displays a reversible Fe3+/4+ redox wave, which is irreversible in 2, denoting that the Fe(IV) species 1ox is kinetically stable. 1red and 1ox have been generated electrochemically in solution and studied spectroscopically. M?ssbauer spectroscopy has confirmed that, in both reduction and oxidation, iron is the redox center, that 1red is high spin (S = 2), and that 1ox is low spin (S = 1), in contrast to 2red which is low spin and 2ox which could not be isolated.     

The mono- and bis-(trichloroacetic acid)-solvates of ferricenium trichloroacetate

Summary Inconsistent literature reports on the preparation of the mono- and bis-(trichloroacetic acid)-solvated ferricenium trichloroacetates, (1) and (2) have prompted a comprehensive investigation of the experimental conditions giving rise to the formation of the two ferricenium salts. In agreement with the majority of authors, (2) is reproducibly obtained from trichloroacetic acid and ferrocene in molar ratios of 3 and higher in benzene over a wide range of experimental variables in the presence of air or, preferably, under conditions of oxygen saturation. Treatment of aqueous ferricenium sulfate solutions with trichloroacetic acid in an acid/ferrocene ratio of 3 and above affords the di-solvate, whereas at lower reactant ratios, and under conditions of reduced acidity, formation of the mono-solvate prevails. More efficiently, and in a higher degree of purity, the latter salt is generated from the former by a controlled recrystallization from water. Representative spectroscopic features of the two salts are discussed.     

Schwefeldioxid als Ligand und Synthon. II. Synthese und Reaktionen der Trimethylsilyl-methansulfinsäure und ihrer Derivate

Sulfur Dioxide as Ligand and Synthon. II. Synthesis and Reaction of Trimethylsilyl Methane Sulfinic Acid and its Derivatives Synthesis and reaction of trimethylsilyl methane sulfinic acid and its derivatives, of the type Me₃SiCH₂S(O)? Y (Y = OH, OM, OR, NR₂) synthesized by insertion of SO₂ and R¹NSO, respectively, into Me₃SiCH₂MgCl are described. The compounds obtained are characterized by means of i.r., ¹H, ²⁹Si, and ¹³C n.m.r. spectroscopy.     

Determination of ephedra alkaloids by liquid chromatography/tandem mass spectrometry

In conjunction with an AOAC Task Group on dietary supplements, a liquid chromatography/tandem mass spectrometry (LC-MS/MS) method was validated for measurement of 6 major alkaloids in raw ephedra sinica herb, ephedra extracts, ephedra tablets, complex dietary supplements containing ephedra, and a high-protein drink mix containing ephedra. The amount of ephedrine-type alkaloids present was determined by LC with mass selective detection. Six replicates of each matrix were analyzed on 3 separate occasions. The presence of 6 ephedrine-type alkaloids was detected at a level > 0.5 microg/g based on a 0.5 g sample. The standard curve range for this assay is from 0.02 to 1.0 microg/mL. Appropriate dilutions covered a wide range of specific alkaloid concentrations. The calibration curves for all 6 analytes had correlation coefficients > 0.995.     

OnC *-algebras having linear,polynomial and subexponential growth

Summary Answering a question of Voiculescu [16, Problem 5.9], we show thatC ^*-algebras having filtrations (A _n)_n satisfying the condition lim sup_n ln dimA _n/n=0 (in particular having subexponential growth), are nuclear.For the case of linear growth we obtain the following particular result: letX be a finite dimensional self-adjoint generating system of aC ^*-algebraA such that dim (span (X ⁿ +1))1+dim (span (X ⁿ )), then there exist a finite dimensionalC ^*-algebraC having only irreducible representations of dimension 1 and aC ^*-algebraB, which is generated by a single self-adjoint element, such thatACB.Some other results are given on linear growth and we show that there exist singly generatedC ^*-algebras such that the growth of the filtration (span (X ⁿ ))_n is polynomial, whereX={x,x ^*, 1} is a generating system, and such that in every neighbourhood ofx there exists an invertibley such thatY={1,y,y ^*} is a generating system whose associated filtration (span (Y ⁿ ))_n doesn't satisfy the previous condition of Voiculescu, and in particular does not have subexponential growth.Oblatum 19-X-1991Work partially supported by DFGAllocataire M.R.T., Université Aix-Marseille II (France)     

Simply connected nilpotent Lie groups with quasi-standard -algebras

The problem of when the group -algebra of a locally compact group is quasi-standard is investigated for certain simply connected nilpotent Lie groups. The characterization is in terms of the coadjoint orbit structure in the dual of the Lie algebra.