Carbon precipitation and diffusion in SiGeC alloys under silicon self-interstitial injection

In this work we investigate the diffusion and precipitation of supersaturated substitutional carbon in 200-nm-thick SiGeC layers buried under a silicon cap layer of 40 nm. The samples were annealed in either inert (N₂) or oxidizing (O₂) ambient at 850 °C for times ranging from 2 to 10 h. The silicon self-interstitial (I) flux coming from the surface under oxidation enhances the C diffusion with respect to the N₂-annealed samples. In the early stages of the oxidation process, the loss of C from the SiGeC layer by diffusion across the layer/cap interface dominates. This phenomenon saturates after an initial period (2–4 h), which depends on the C concentration. This saturation is due to the formation and growth of C-containing precipitates that are promoted by the I injection and act as a sink for mobile C atoms. The influence of carbon concentration on the competition between precipitation and diffusion is discussed. Received: 19 October 2001 / Accepted: 19 December 2001 / Published online: 20 March 2002 / Published online: 20 March 2002     

Ueber Fusspunkts-Curven und -Flächen,Normalen und Normalebenen

Ohne Zusammenfassung     

Ueber die reciproke und mit ihr zusammenhängende Verwandtschaften

Ohne Zusammenfassung     

Synthetische und NMR-spektroskopische Untersuchungen der Benzylaminaddition an N-Maleyl-aminosäurederivate

Summary During the addition of amines to maleylamino acids in general -amino derivatives are formed. In order to change the reactivity within the vinylogous maleyl system we introduced the -benzylester group into the starting compound N-(cis--carboxyacryloyl)-phenylalanine methylester1. The obtained benzylester2 is adding benzylamine in -position yielding N-benzyl--aspartyl(-benzyl)-phenylalanine methylester4. The addition reaction was investigated by¹H-NMR-spectroscopy. The structures of the compounds have been confirmed by elemental analysis, IR,¹H-NMR and¹³C-NMR spectroscopy.

     

Reaktion von N-Alkyl-bis(difluorophosphoryl)amiden,RN(POF2)2, mit silylierten Nukleophilen und Et2NSF3

Reaction of N-Alkyl-bis(difluorophosphoryl)amides, RN(POF₂)₂, with Silylated Nucleophiles and Et₂NSF₃ N-Alkyl-bis(difluorophosphoryl)amides, RN(POF₂)₂ (R = Me, Et), react in any case with silylated nucleophiles such as Me₃SiOMe and Me₃SiNEt₂ under cleavage of the PNP bridge forming derivatives of di- and monofluorophosphoric acid. In their reaction with Et₂NSF₃ (RNPF₃)₂ and OPF₃ or PF₅, resp., are obtained. The compounds F₂P(O)? NR? PF₄ and RN(PF₄)₂ postulated as intermediates are not stable.     

CO(2) concentration measurements on air samples by mass spectrometry

A new technique for measuring CO(2) concentration in air samples, based on mass spectrometry, is described as an alternative to the common gas chromatographic method. Using a dual inlet isotope ratio mass spectrometer (IRMS), the ratio of the abundances of the m/z peaks 44 and 28 is determined. The precision of measurements (standard deviation <3 ppmv) is generally as good as the analysis with gas chromatography for small air samples (<1 ml STP of air). A major advantage of this new method is the possibility of parallel elemental and isotopic measurements of many air components. The technique is further improved by new wide mass range mass spectrometers allowing simultaneous intensity measurements of several m/z values between 28 and 44, resulting in an uncertainty of <0.5 ppm. The precision is somewhat limited by the production of N(2)O and NO(2) from N(2) and O(2) in the ion source, which accounts for about half of the signal strength at m/z 44. Copyright 2000 John Wiley & Sons, Ltd.     

Potential reduction method for harmonically convex programming

In this paper, we introduce a potential reduction method for harmonically convex programming. We show that, if the objective function and them constraint functions are allk-harmonically convex in the feasible set, then the number of iterations needed to find an -optimal solution is bounded by a polynomial inm, k, and log(1/). The method requires either the optimal objective value of the problem or an upper bound of the harmonic constantk as a working parameter. Moreover, we discuss the relation between the harmonic convexity condition used in this paper and some other convexity and smoothness conditions used in the literature.The authors like to thank Dr. Hans Nieuwenhuis for carefully reading this paper and the anonymous referees for the worthy suggestions.     

Polarographische Simultanbestimmung von Niob und Zinn in der bin?ren Legierung

Zusammenfassung Die Möglichkeit der gleichzeitigen Bestimmung von Niob und Zinn mit Hilfe der Polarographie wird untersucht. Es wird gefunden, daß die Bestimmung zwar nicht gleichspannungspolarographisch, wohl aber square-wave-polarographisch durchführbar ist. Zur Analyse der binären Nb-Sn-Legierungen (etwa Nb₃Sn) ist 8,0±0,1 m HCl+10 Vol-% Äthylenglykol als Grundelektrolyt geeignet. In diesem Elektrolyten erscheinen die erste Reduktionswelle des Niobs, Nb^VIV, und die zweite Reduktionswelle des Zinns, Sn^IISn, gut getrennt und vermeßbar. Die Differenz der Spitzenpotentiale (E _pNb^V/IV= -0.26V, E _pSn^II/O= -0.46V gegen Quecksilber-Bodenelektrode) beträgt 200 mV.Die beschriebene Methode hat im Vergleich zu den bekannten nichtpolarographischen Analysenvorschriften den Vorzug, eine bis zu 100 mal kleinere Einwaage (bei vergleichbarer Reproduzierbarkeit) und einen verringerten Zeitaufwand zu erfordern.Bei Einwaagen von 2–14 mg beträgt die Genauigkeit der Niobbestimmung 1% rel., die der Zinnbestimmung 2% rel. Eine einzelne Niob-Zinn-Simultanbestimmung dauert 4 Std.

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Summary The possibility of a simultaneous polarographic determination of niob and tin is investigated.It has been found that the determination cannot be carried out by direct current polarography, but square-wave polarography yields good results.8.0±0.1 M HCl+10 vol-% ethylene glycol is suitable as supporting electrolyte for the analysis of the binary Nb-Sn-alloys (Nb₃Sn).In this supporting electrolyte the first reduction-wave of niobium Nb^VNb^IV, and the second reduction wave of tin, Sn^IISn⁰, are well developed and separated. The difference of the peak potential (E _pNb^V/IV= -0.26V, E _pSn^II/O= -0.46V vs. mercury-pool electrode) is 200 mV. Compared with conventional methods the method described has the advantage of requiring smaller amounts of sample (up to 100 times smaller by weight at comparable reproducibility) with a saving of time.With sample amounts of 2 to 14 mg the accuracy of the niobium determination is 1% rel., that of the tin determination is 2% rel. One single simultaneous determination of niobium and tin takes about four hours.

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Herrn Prof. Dr. M. von Stackelberg zum 70. Geburtstag gewidmet.     

1H and 13C NMR signal assignment of cucurbitacin derivatives from Citrullus colocynthis (L.) Schrader and Ecballium elaterium L. (Cucurbitaceae)

2D NMR-derived 1H and 13C NMR signal assignments of six structurally closely related cucurbitacin derivatives are presented. The investigated 2-O-beta-D-glucopyranosylcucurbitacins I, J, K, and L were obtained from Citrullus colocynthis (L.) Schrader whereas the aglyca cucurbitacin E and I were isolated from Ecballium elaterium L.