Diferrocenophosphaborin: A Planar‐Chiral,Redox‐Active and Anion‐Responsive Ambiphilic Ligand

A new class of Janus‐like ambiphilic ligands is introduced. The rigid diferrocene backbone in heterocycles 4‐SnP and 4‐BP creates an unprecedented chiral environment as demonstrated by multinuclear NMR and single‐crystal X‐ray studies. In addition, the ligands are redox‐responsive and the Lewis acidic borane moiety in 4‐BP can be exploited to further tune the properties: a clear decrease in the CO stretching frequency of a Vaska‐type Rh^I complex 5‐BP is observed upon addition of fluoride ions. Thus, the Lewis acid and Lewis base sites influence each other and their strength can be modulated by redox chemistry and anion binding.     

Alteration of micromilled carbonate δ18O during Kiel Device analysis

Isotopic analysis of carbonate material has been greatly facilitated by the development of autosampling devices such as the Kiel III Carbonate Device, allowing rapid automated analysis of small sample sizes. This analysis is facilitated by holding samples and acid at temperatures around 70 °C prior to reaction. In most situations this has no measurable effect on sample powders on practical timeframes, but, when analyzing exceptionally fine-grained material produced by micromilling, the δ(18)O of both aragonite and calcite is altered by -0.1 ‰/day. Laboratories that use this technique should thoroughly test and correct for this phenomenon and avoid storing pre-weighed materials within the Kiel Device or similar drying oven prior to analysis.     

Capillary Stokes drift: a new driving mechanism for mixing in AC-electrowetting

We studied the flow fields generated inside sessile drops that oscillate periodically between states of high and low contact angle under the influence of alternating electric fields of variable frequency and amplitude. Following the motion of dye patches, we show that the number of oscillation cycles required to achieve mixing scales logarithmically with the Péclet number as expected for chaotic mixing. High speed movies reveal an asymmetry of the drop shape between the spreading and receding phase of the oscillations. This results in net internal flow fields that we characterize by tracing the motion of colloidal seed particles. The strength and frequency dependence of the flow are explained in terms of Stokes drift driven by capillary waves that emanate from the oscillating contact line.     

UV degradability of polysilanes for nanoresists examined by electron spectroscopies and photoluminescence

The aim of this study was to elucidate the degradation mechanisms in polysilanes, especially one-dimensional polysilylenes, with respect to the search for suitable resists for silicon industrial nanotechnologies. To this end we used the combined methods of photoelectron spectroscopies — PES (UPS and XPS) and photoluminescence — PL. Films of aryl-methyl-substituted polysilane chain, poly[methyl(phenyl)silylene] (PMPSi), prepared by casting from benzene solution, were analysed by X-ray and UV-induced photoelectron spectroscopy. Photoelectron spectra were recorded from the pristine PMPSi surface and after the UV photodegradation. Pronounced changes were found in the HeI induced photoelectron spectra indicating redistribution of filled Si 3s-like and Si 3p-like states. The photodegradation by UV radiation for two different degradation wavelengths λ = 266 and 355 nm was examined also by PL. We concentrated on the PL study in the region of the σ*-σ excitonic deexcitation after major degradations, studying the disorder and dangling bonds (DB) created by the degradation process. The results of both complementary methods are interpreted in accordance with our recent paper [1], with the degradation process explained by two competing phenomena, i.e. the energy dependent exciton transport by diffusion process and Si-Si bond scission. Presented at the X-th Symposium on Suface Physics, Prague, Czech Republic, July 11–15, 2005.