Acidimetrie

Ohne Zusammenfassung     

Coverage-dependent adsorption geometry of octithiophene on Au(111)

The adsorption behavior of α-octithiophene (8T) on the Au(111) surface as a function of 8T coverage has been studied with low-temperature scanning tunneling microscopy, high resolution electron energy loss spectroscopy as well as with angle-resolved two-photon photoemission and ultraviolet photoemission spectroscopy. In the sub-monolayer regime 8T adopts a flat-lying adsorption geometry. Upon reaching the monolayer coverage the orientation of 8T molecules changes towards a tilted configuration, with the long molecular axis parallel to the surface plane, facilitating attractive intermolecular π-π-interactions. The photoemission intensity from the highest occupied molecular orbitals (HOMO and HOMO - 1) possesses a strong dependence on the adsorption geometry due to the direction of the involved transition dipole moment for the respective photoemission process. The change in molecular orientation as a function of coverage in the first molecular layer mirrors the delicate balance between intermolecular and molecule/substrate interactions. Fine tuning of these interactions opens up the possibility to control the molecular structure and accordingly the desirable functionality.     

The Gallides SrRh2Ga2, SrIr2Ga2, and Sr3Ir4Ga4

The gallides SrRh₂Ga₂, SrIr₂Ga₂, and Sr₃Rh₄Ga₄ were obtained from the elements by induction melting and subsequent annealing. They were investigated by powder and single‐crystal X‐ray diffraction: CaRh₂B₂ type, Fddd, a = 573.2(1), b = 1051.3(1), c = 1343.7(2) pm, wR₂ = 0.0218, 398 F² values, 15 variables for SrRh₂Ga₂; a = 576.0(1), b = 1045.5(1), c = 1350.6(3) pm for SrIr₂Ga₂, and Na₃Pt₄Ge₄ type, I$\bar{4}$ 3m, a = 777.4(2) pm, wR₂ = 0.0234, 190 F² values, 11 variables for Sr₃Ir₄Ga₄. The gallides SrRh₂Ga₂ and Sr₃Ir₄Ga₄ exhibit complex, covalently bonded three‐dimensional [Rh₂Ga₂] and [Ir₄Ga₄] networks with short Rh–Ga (241–246 pm) and Ir–Ga (243–259 pm) distances. The strontium atoms fill large cages within these networks. They are coordinated by 8 Rh + 10 Ga in SrRh₂Ga₂ and by 4 Ir + 8 Ga in Sr₃Ir₄Ga₄. The structure of SrRh₂Ga₂ is discussed along with the monoclinic distortion variants HoNi₂B₂ and BaPt₂Ga₂ on the basis of a group‐subgroup scheme.     

On the negative magnetoresistance puzzle at variable range hopping at low temperatures

In this work, we report the results of magnetoresistance studies of variable range hopping down to 30 mK in isotopically engineered Ge with low compensation, and in n-CdTe crystals. Experimentally we find a decrease and disappearance of the negative magnetoresistance with decreasing temperature down to 200 mK, in weak magnetic fields. Such behaviour is in disagreement with the quantum interference theory of Nguen, Spivak and Shklovskii.     

Analysis of diethylstilbestrol and its impurities in tablets using reversed-phase high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method is described which is capable of resolving cis- and trans-diethylstilbestrol (DES), DES mono- and dimethyl ethers and 4,4'-dihydroxystilbene. The mobile phase and internal standard used stabilise the cis-trans DES isomer ratio, and the method is capable of quantitating both isomers in dosage forms without derivatisation. Recovery of DES from tablets is quantitative. Results of tablet analyses using this method are compared with those obtained with the official spectrophotometric procedure.     

Preparation of samples for surface analysis

Analysis of single atomic layers at surfaces and interfaces is now possible routinely, using such techniques as Auger electron spectroscopy, X-ray photoelectron spectroscopy and secondary ion mass-spectroscopy. The handling of specimen surfaces before analysis is therefore critical to ensure a valid measurement of composition.     

Enhanced convergence and robust performance of randomized dynamical decoupling

We demonstrate the advantages of randomization in coherent quantum dynamical control. For systems which are either time-varying or require decoupling cycles involving a large number of operations, we find that simple randomized protocols offer superior convergence and stability as compared to deterministic counterparts. In addition, we show how randomization may allow us to outperform purely deterministic schemes at long times, including combinatorial and concatenated methods. General criteria for optimally interpolating between deterministic and stochastic design are proposed and illustrated in explicit decoupling scenarios relevant to quantum information storage.