The surface chemical properties and the electronic properties of vapor grown carbon nanofibers (VGCNFs) have been modified by treatment of the oxidized CNFs with NH(3). The effect of treatment temperature on the types of nitrogen functionalities introduced was evaluated by synchrotron based X-ray photoelectron spectroscopy (XPS), while the impact of the preparation methods on the surface acid-base properties was investigated by potentiometric titration, microcalorimetry, and zeta potential measurements. The impact of the N-functionalization on the electronic properties was measured by THz-Time Domain spectroscopy. The samples functionalized via amination are characterized by the coexistence of acidic and basic O and N sites. The population of O and N species is temperature dependent. In particular, at 873 K nitrogen is stabilized in substitutional positions within the graphitic structure, as heterocyclic-like moieties. The surface presents heterogeneously distributed and energetically different basic sites. A small amount of strong basic sites gives rise to a differential heat of CO(2) adsorption of 150 kJ mol(-1). However, when functionalization is carried out at 473 K, nitrogen moieties with basic character are introduced and the maximum heat of adsorption is significantly lower, at approximately 90 kJ mol(-1). In the latter sample, energetically different basic sites coexist with acidic oxygen groups introduced during the oxidative step. Under these conditions, a bifunctional acidic and basic surface is obtained with high hydrophilic character. N-functionalization carried out at higher temperature changes the electronic properties of the CNFs as evaluated by THz-TDS. The functionalization procedure presented in this work allows high versatility and flexibility in tailoring the surface chemistry of nanocarbon material to specific needs. This work shows the potential of the N-containing nanocarbon materials obtained via amination in catalysis as well as electronic device materials.

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The scalable synthesis of phase-pure crystalline manganese nitride (Mn N ) from a molecular precursor is reported. It acts as a superiorly active and durable electrocatalyst in the oxygen evolution reaction (OER) from water under alkaline conditions. While electrophoretically deposited Mn N on fluorine tin oxide (FTO) requires an overpotential of 390 mV, the latter is substantially decreased to merely 270 mV on nickel foam (NF) at a current density of 10 mA cm with a durability of weeks. The high performance of this material is due to the rapid transformation of manganese sites at the surface of Mn N into an amorphous active MnO overlayer under operation conditions intimately connected with metallic Mn N , which increases the charge transfer from the active catalyst surface to the electrode substrates and thus outperforms the electrocatalytic activity in comparison to solely MnO -based OER catalysts.

Highly concentrated 0.5 M II-VI semiconductor quantum dot solutions for coating applications can be synthesized employing chalcogenolysis and condensation of functionalized cluster-like cadmium and zinc ethoxyacetates. Furthermore, in nucleation studies on CdSe solutions, new magic clusters between 0.42 and 1.7 nm in size were found exhibiting sharp HOMO-LUMO resonances (lowest absorption features) in the optical absorption spectra. High resolution small angle X-ray scattering (SAXS) measurements performed on 1.7 and 3.4 nm CdSe clusters corroborate the size. Information on the intra-cluster structure was hard to derive with respect to the small cluster size. These species could be Koch pyramids with a fractal dimension Df=2 as well as non-fractal zincblende pyramids (additionally checked by XRD and HFtTEM). In any case rather chain-like (Dt= 1) aggregates are formed. It further will be shown that in alcoholic CdSe sols the initially nucleated "seeds" are highly reactive. Their sharp HOMO-LUMO transitions are found to be strongly modified by externally induced chemical reactions. For example, aminosilane capped 1.7 nm clusters decompose rapidly upon exposure to phosphines. After a period of few hours, they begin to re-grow to their original size or they reorganize to give smaller 0.85 nm subunits depending on the P/N ratio. In contrast, 0.85 nm phosphinecapped clusters double their size if exposed to amines. The last process liberates cadmium ions into the solution as found in complementary polarographic measurements. ~ allel to this work and the sol-gel chemistry of metal oxides, addressing metal ethoxy-acetate derived synthesis of II-VI chalcogenide quantum dots, to provide insights into the cluster-cluster aggregate evolution mechanism within the strong exciton confinement regime. We shall demonstrate that chemical surface reactions can change both the cluster optical absorption and fluorescence spectra related to structural changes within cluster-cluster aggregates. This spectroscopic work is supported by SAXS-, XRDand HRTEM investigations addressing a fractal character of highly concentrated semiconductor cluster materials. Experimental GeneralAU manipulations involving silylchalcogenides and phosphines were carried out under argon using the Schlenk technique. Cadmium and zinc acetate dihydrate were purchased from Fluka. Bis(trimethylsily1)selenium (TMS)2Se prepared according to the procedure described elsewhere [15] was stored at 240 K under argon. Bis(trimethylsily1)sulfide (TMS)$3 and bis(trimethylsily1)tellurium (TMS)2Te were purchased from Aldrich and Acros respectively. Anhydrous heptane, pyridjne, tetrahydrofuran (THF) and 2-butoxyethanol in addition to aUcyl amines and tributylphosphine (TBP) were purchased from Aldrich. 3-Aminopropyltriethoxy-silane (AMEO) was purchased from ABCR. All chemicals were used without additional purification.

The structure of mayenite, Ca(12)Al(14)O(33), was investigated by neutron powder diffraction up to 1323 K. It has been described previously as a calcium-aluminate framework, in which 32 of the 33 oxygen anions are tightly bound, containing large cages, 1/6 of them being filled randomly by the remaining 'free' oxygen. At ambient temperature excess oxygen was found, corresponding to the composition Ca(12)Al(14)O(33.5) which was attributed to the presence of hydroxide, peroxide and superoxide radicals in the cages. Above 973 K these are lost under vacuum conditions and the composition becomes stoichiometric. From the refined structural parameters it is concluded that the structure is more adequately described as a relatively stable aluminate framework consisting of eightfold rings of AlO(4) tetrahedra with disordered Ca and 'free' O distributed within. At high temperatures the density of the 'free' oxygen is extremely spread out, with the expansion being related to the high ionic conductivity of this material. Since no continuous density distribution between adjacent cages was found and the 'free' O forms bonds with part of the Ca, the diffusion proceeds via a jump-like process involving exchange of the 'free' oxygen with framework oxygen. The results confirm the recent theoretical predictions of Sushko et al.

Thin semiconductor CuInSe 2 and CuInS 2 films (CIS) with bandgap values (E g ) of around 1.04 eV (for selenide) and 1.5 eV (for sulfide) represent an important class of the currently developed light absorbers for solar energy harvesting. [1,2] Conversion efficiencies of 12±13 % were achieved on large area modules, [1] whereas close to 18 % was achieved with laboratory cells, [3] indicating a large potential for CIS-derived photovoltaic materials. For their preparation, a broad range of physical [1±3] and electrochemical deposition routes [4] are available. Typically, CIS films are created via a rapid thermal sintering of elemental Cu, In and Se layers evaporated on Mo-coated glass substrates. The photovoltaic cell is then completed by overcoating the CIS-macrograins with a thin CdS buffer layer and a metal± organic chemical vapor deposition derived, transparent Al/ ZnO window electrode. In this contribution, we address a low cost colloidal route to nanocrystalline ZnO/CIS bilayers on indium tin oxide (ITO) glass. For the film deposition, concentrated coating colloids, with size-quantized CuInS 2 particles were developed. It is well-established that size quantization in semiconductors (i.e. increasing bandgap energy with decreasing semiconductor dimension) takes place at particle dimensions smaller than the Wannier±Mott (WM) exciton of the corresponding macroscopic bulk phase.[5] By knowledge of the high frequency dielectric constant, e ¥ , and the reduced effective exciton mass, m = 1/(m ±1 e + m ±1 h ), one can calculate the WM-exciton Bohr radius according to R B = (e ¥ /m)´a B , with a B being the Bohr radius of the hydrogen atom. Taking the CIS bulk values [6] of e ¥ = 11, m e = 0.16 and m h = 1.3, we calculated the WM-exciton size to be 8.1 nm, which predicts a blue shift in the optical absorption threshold (below 826 nm = 1240/1.5 eV) for CIS-particle sizes below 8 nm. Figure 1 shows changes in the optical absorption spectrum during the CIS condensation. Condensation was induced on addition of bis(trimethylsilyl)sulfide to a mixture of Cu(I)±P(OPh) 3 and In(III)±P(OPh) 3 complexes (Cu/ In = 1) in Ar saturated acetonitrile (for details see Experimental).At sulfide concentrations~25 % (with respect to the present metals), the absorption spectrum exhibits a shoulder located at 370 nm that is strongly blue-shifted with respect to the bulk crystals (a gap energy difference of more than 2 eV). On further addition of the sulfide source (50 %), the absorption shoulder shifts from 370 nm to 400 nm, and the optical density rises due to increasing particle concentration. Under stoichiometric conditions (100 % S corresponds to the Cu:In:S stoichiometry of 1:1:2), a steep tail is observed with the absorption onset located near 580 nm.A remarkable dynamic color change accompanies this condensation process which can be seen with the naked eye. On each dropwise addition of the sulfide source, the color of the reacting solution rapidly changes from colorless to yellow to orange to red and becomes colorless or yellow agai...

The development of all-solid-state electrochemical energy storage systems, such as lithiumion batteries with solid electrolytes, requires stable, electronically insulating compounds with exceptionally high ionic conductivities. Considering oxides, garnet-type Li7La3Zr2O12 and derivatives, see Zr-exchanged Li6La3ZrTaO12 (LLZTO), have attracted great attention because of its high Li + ionic conductivity of up to 1 mS · cm −1 . Despite numerous studies focusing on conductivities of powder samples, only a few use time-domain NMR methods to probe Li ion diffusion parameters in single crystals. Here we report, for the first time, on temperature-variable 7 Li NMR relaxometry measurements using both laboratory and spin-lock techniques to probe Li jump rates in monocrystalline Li-bearing garnets. Timedomain NMR offers the possibility to study Li ion dynamics on both the short-range and long-range length scale. The techniques applied yield a fully consistent picture of correlated Li ion jump diffusion in LLZTO; the data perfectly mirror a modified BPP-type relaxation response being based on a Lorentzian-shaped relaxation function. The rates measured could be parameterized with a single set of diffusion parameters. Dynamic information about the elementary jump processes, such as jump rates and activation energies, were extracted from complete diffusion-induced rate peaks that are obtained when the relaxation rate is plotted vs inverse temperature. Results from NMR are completely in line with ion transport parameters derived from conductivity spectroscopy. Acknowledgement. We thank our colleagues at the University of Hannover and the TU Graz for valuable discussions. Financial support by the Deutsche Forschungsgemeinschaft