Cyclische Bis(amino)-arsa-, -stiba-, -bismachloride und ein spezielles Tris-(amino)bismutan

In den Trichloriden von Arsen, Antimon und Bismut lassen sich jeweils zwei Chloratome durch den Liganden -N(tBu)SiMe2N(tBu)- austauschen, wodurch viergliedrige Ringe (SiN2El) entstehen. Sowohl in Lösung (temperatur- und konzentrationsabhängige 1H-NMR-Spektren) als auch im Festkörper (Röntgenstrukturanalysen) besitzen die Verbindungen 3 (El = As), 4 (El = Sb) bzw. 5 (El = Bi) unterschiedliche Assoziationsgrade bzw. Strukturen. Das Arsenderivat 3 kristallisiert monoklin, in der Raumgruppe P21/c mit 4 Formeleinheiten pro Elementarzelle (a = 920,0(6), b = 1 462,9(9), c = 1240,8(7) pm, = 105,8(1)°), das Antimon- und Bismutderivat 4 und 5 sind isotyp und isostrukturell und kristallisieren ortho-rhombisch (Raumgruppe Pnma, Z = 4; Gitterkonstanten für 4: a = 1140,2(8), b = 1095,7(7), c = 1328,7(9) pm; für 5: a = 1105,1(5), b = 1123,3(5), c = 1340,0(8) pm). Während die Kristallstruktur von 3 im wesentlichen aus isolierten Molekülen besteht, die eine schwache Tendenz zu paarweiser Assoziation besitzen (AsClAs Brücken, AsCl = 234,5(1), ClAs = 442,3(1) pm), sind die Moleküle in den Kristallen von 4 und 5 eindimensional verkettet. Die zu den SbN2Si- bzw. BiN2Si-Ringen nahezu senkrecht stehenden Chlorsubstituenten treten mit Nachbarmolekülen derart in Wechselwirkung, daß jedes Sb- und Bi-Atom vierfach koordiniert wird und eine unendliche ElClElCl-Kette entsteht, die an den Chloratomen gewinkelt ist (4): 143,5°, (5): 145,7°. Die verbrückende Rolle des Chloratoms ist bei der Bi-Verbindung stärker ausgeprägt als bei der Sb-Verbindung (SbCl = 247,2(3), ClSb = 352,1(3) pm; BiCl = 274,8(4), ClBi = 304,7(4) pm). Als Nebenprodukt kann bei der Darstellung von 5, eine Verbindung 6 erhalten werden, die nur Stickstoffatome am Bismut gebunden hat: Me2Si(NtBu)2 BiN(tBu)SiMe2(tBu)NBi(NtBu)2SSiMe2. Diese Verbindung 6 kristallisiert monoklin (P21/c, a = 1474,2(3), b = 1477,6(3), c = 1997,7(6) pm, = 94,68(8)°). Die Abweichung von der C2-Symmetrie bei 6 (die zweizählige Achse verläuft durch die mittlere SiMe2-Gruppe) ist nur unbedeutend. Die BiN-Bindungslängen innerhalb der SiN2Bi-Ringe (BiN (Mittel) = 216,5(5) pm) sind kürzer als die außerhalb (BiN (Mittel) = 220,45(5) pm)

Darstellung und Strukturen von Chlorostannaten(II). - II : Neue Chlorostannate(II) von zweiwertigen Kationen

Metall(II)-chloride MCl2 (M Mn, Fe, Co, Ni, Mg) setzen sich mit SnCl2 in Acetonitril im Molverhältnis 1:2 zu Verbindungen [M(CH3CN)6](SnCl3)2 · 2CH3CN (1a-e) bzw. im Molverhältnis 1:3 zu Verbindungen [M(CH3CN)6](SnCl3)(SnCl3) · l/2 CH3CN (2a-e) um. Die Verbindung [Co(CH3CN)6](SnCl3)2 · 2CH3CN (1a) kristallisiert monoklin, Raumgruppe P21/n, Z = 2 (a = 8,401(7), b = 16,30(2), c = 12,90(1) Å, = 107,00(8)°); die Verbindungen 1b-e sind hierzu isotyp. In 1a treten die SnCl3--Ionen zu Paaren zusammen. Die Verbindung [Ni(CH3CN)6](Sn2Cl5)(SnCl3) · 1/2 CH3CN (2a) kristallisiert im triklinen Kristallsystem, Raumgruppe P, Z = 2 (a = 8,69(1), b = 12,91(2), c = 16,81(1)Å, = 71,0(1)°, = 89,9(l)°, = 71,4(1)°); die Verbindungen 2b-e sind zu 2a isotyp. In 2a sind je 2 SnCl3-- und Sn2Cl5--Ionen über schwache SnCl-Kontakte zu anionischen Aggregaten der Form [(Sn2Cl5)2(SnCl3)2]4- verknüpft

Effective passivation of crystalline silicon surfaces by ultrathin atomic-layer-deposited TiOx layers

We characterize the surface passivation properties of ultrathin titanium oxide (TiOx) films deposited by atomic layer deposition (ALD) on crystalline silicon by means of carrier lifetime measurements. We compare different silicon surface treatments prior to TiOx deposition, such as native silicon oxide (SiOy), chemically grown SiOy and thermally grown SiOy. The best passivation quality is achieved with a native SiOy grown over 4 months and a TiOx layer thickness of 5 nm, resulting in an effective lifetime of 1.2 ms on 1.3 Ωcm p-type float-zone silicon. The measured maximum lifetime corresponds to an implied open-circuit voltage (iVoc) of 710 mV. For thinner TiOx layers the passivation quality is reduced, however, samples passivated with only 2 nm of TiOx still show a lifetime of 612 μs and an iVoc of 694 mV. The contact resistivity of the TiOx including the SiOy interlayer between the silicon wafer and the TiOx is below 0.8 Ωcm2. The combination of excellent surface passivation and low contact resistivity has the potential for silicon solar cells with efficiencies exceeding 26%

Growth and Characterization of Ce- Substituted Nd2Fe14B Single Crystals

Single crystals of (Nd1-xCex)2Fe14B are grown out of Fe-(Nd,Ce) flux. Chemical and structural analysis of the crystals indicates that (Nd1-xCex)2Fe14B forms a solid solution until at least x = 0.38 with a Vegard-like variation of the lattice constants with x. Refinements of single crystal neutron diffraction data indicate that Ce has a slight site preference (7:3) for the 4g rare earth site over the 4f site. Magnetization measurements show that for x = 0.38 the saturation magnetization at 400 K, a temperature important to applications, falls from 29.8 for the parent Nd2Fe14B to 27.6 (mu)B/f.u., the anisotropy field decreases from 5.5 T to 4.7 T, and the Curie temperature decreases from 586 to 543 K. First principles calculations carried out within density functional theory are used to explain the decrease in magnetic properties due to Ce substitution. Though the presence of the lower-cost and more abundant Ce slightly affects these important magnetic characteristics, this decrease is not large enough to affect a multitude of applications. Ce-substituted Nd2Fe14B is therefore a potential high-performance permanent magnet material with substantially reduced Nd content.Comment: 11 Pages, 8 figures, 5 table

Generic Fibrational Induction

This paper provides an induction rule that can be used to prove properties of data structures whose types are inductive, i.e., are carriers of initial algebras of functors. Our results are semantic in nature and are inspired by Hermida and Jacobs' elegant algebraic formulation of induction for polynomial data types. Our contribution is to derive, under slightly different assumptions, a sound induction rule that is generic over all inductive types, polynomial or not. Our induction rule is generic over the kinds of properties to be proved as well: like Hermida and Jacobs, we work in a general fibrational setting and so can accommodate very general notions of properties on inductive types rather than just those of a particular syntactic form. We establish the soundness of our generic induction rule by reducing induction to iteration. We then show how our generic induction rule can be instantiated to give induction rules for the data types of rose trees, finite hereditary sets, and hyperfunctions. The first of these lies outside the scope of Hermida and Jacobs' work because it is not polynomial, and as far as we are aware, no induction rules have been known to exist for the second and third in a general fibrational framework. Our instantiation for hyperfunctions underscores the value of working in the general fibrational setting since this data type cannot be interpreted as a set.Comment: For Special Issue from CSL 201

Darstellung und Strukturen von Chlorostannaten(II). - I : Neue Trichlorostannate(II) einwertiger Kationen

KSnCl3 · 1/2 CH3CN wird durch Umkristallisieren von KSnCl3 aus Acetonitril erhalten. Die Verbindung kristallisiert monoklin, Raumgruppe P21/c (a = 4,525(6), b = 20,34(2), c = 8,061(7) Å, = 90,93(9)°). Durch Umsetzung von CuCl mit einer äquimolaren Menge an SnCl2 in Acetonitril erhält man [Cu(CH3CN)3]SnCl3 das in der monoklinen Raumgruppe P21/n kristallisiert (a = 7,984(9), b = 20,77(2), c = 8,34(2) Å = 101,6(1)°). Während in KSnCl3 · 1/2 CH3CN eine dreidimensionale Verknüpfung der SnCl3minus;-lonen vorliegt, an der auch die Kaliumionen beteiligt sind, sind die Trichlorostannationen in [Cu(CH3CN)3]SnCl3 durch SnCl-Brücken zu eindimensionalen Ketten verknüpft

Nanoscale Imaging of Whole Cells Using a Liquid Enclosure and a Scanning Transmission Electron Microscope

Nanoscale imaging techniques are needed to investigate cellular function at the level of individual proteins and to study the interaction of nanomaterials with biological systems. We imaged whole fixed cells in liquid state with a scanning transmission electron microscope (STEM) using a micrometer-sized liquid enclosure with electron transparent windows providing a wet specimen environment. Wet-STEM images were obtained of fixed E. coli bacteria labeled with gold nanoparticles attached to surface membrane proteins. Mammalian cells (COS7) were incubated with gold-tagged epidermal growth factor and fixed. STEM imaging of these cells resulted in a resolution of 3 nm for the gold nanoparticles. The wet-STEM method has several advantages over conventional imaging techniques. Most important is the capability to image whole fixed cells in a wet environment with nanometer resolution, which can be used, e.g., to map individual protein distributions in/on whole cells. The sample preparation is compatible with that used for fluorescent microscopy on fixed cells for experiments involving nanoparticles. Thirdly, the system is rather simple and involves only minimal new equipment in an electron microscopy (EM) laboratory