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Photoluminescent porous layers were formed on highly resistive p-type silicon by metal-assisted chemical etching using Na2S2O8 as an oxidizing agent. A thin layer of Ag was deposited on the (100) Si surface prior to immersion in a solution of HF and Na2S2O8. The morphology of the porous silicon (PS) layer formed by this method as a function of etching time was investigated by scanning electron microscopy (SEM). It shows that the surface is porous and the thickness of PS layer increases with etching time and is not limited as observed with the electrochemical method. Energy-dispersive X-ray (EDX) was used to analyse the chemical composition of PS layers. The EDX spectra show that the metal is not present on the PS surface after etching. Photoluminescence (PL) from metal-assisted chemically etched layers was measured using a He-Cd laser ...
The application of atomic force microscopy (AFM) tip-mediated molecular transfer (dip-pen nanolithography or DPN) to fabricate nanopatterned (bio)reactive platforms based on dendrimers on reactive self-assembled monolayer (SAM) and polymer thin films is discussed. The transfer of high-molar-mass polyamidoamine (PAMAM) dendrimers (generation 5) and the rapid in situ covalent attachment of the deposited adsorbates onto reactive N-hydroxysuccinimide (NHS) terminated SAMs on gold and NHS-activated polystyrene-block-poly(tert-butyl acrylate) (PS690-b-PtBA1210) block copolymer thin films were investigated as strategies to suppress line broadening by surface diffusion in DPN. By exploiting carefully controlled environmental conditions (such as temperature and relative humidity), scan rates, and in particular the covalent attachment of the den...
Be specific: A supramolecular adsorbate consisting of an adamantyl group (red) and an oligo(ethylene glycol) chain has been designed to prevent nonspecific protein adsorption at cyclodextrin molecular printboards. The adamantyl group allows specific and reversible interactions. Specific immobilization of proteins (gray) is possible through multivalent orthogonal linkers by effective replacement of the monovalent adsorbate (Ni2+ ions (green) may be needed; see picture).
Leaching of palladium species from Pd nanoparticles under C - C coupling conditions was observed for both Heck and Suzuki reactions by using a special membrane reactor. The membrane allows the passage of palladium atoms and ions, but not of species larger than 5 nm. Three possible mechanistic scenarios for palladium leaching were investigated with the aim of identifying the true catalytic species. Firstly, we examined whether or not palladium(0) atoms could leach from clusters under non-oxidising conditions. By using our membrane reactor, we proved that this indeed happens. We then investigated whether or not small palladium(0) clusters could in fact be the active catalytic species by analysing the reaction composition and the palladium species that diffused through the membrane. Neither TEM nor ICP analysis supported this scenario. Fi...
Expect the unexpected: The interaction between cyanuric acid (CA) and melamine (M) molecules is a key structural motif in supramolecular chemistry. The adsorption and coadsorption of M and CA on a Au(111) surface under ultrahigh vacuum (UHV) is investigated using STM with submolecular resolution. In addition to the expected structure with a 1:1 CA/M ratio, a novel phase with a 1:3 CA/M forms upon sequential deposition.
Perovskite powders of La0.3Sr0.7CoO3–were prepared by the thermal decomposition of precursor complexes derived from nitrate solutions using ethylenediaminetetraacetic acid (EDTA) as a complexing agent. The calcination temperature is 920 °C. Powders thus obtained have a low carbon contamination. Dense ceramics with a relative density of about 96% have been prepared after sintering at 1150 °C.
Highly localized, selective deprotection chemistry and efficient grafting reactions in microcontacts between elastomeric stamps and reactive polystyrene-block-poly(tert-butyl acrylate) (PS690-b-PtBA1210) diblock copolymer films are developed. The procedure yields well-defined protein-poly(ethylene glycol) (PEG) nanopatterns (see figure), which may find applications in, for example, cancer-cell-surface interaction studies.
Side effects: A systematic study of surface assemblies of three compounds that form strong H bonds reveals that a slight variation of a submolecular alkyl group, not directly involved in the H bonding itself, has a pronounced influence on the overall self-assembled surface nanostructure.
The Lie-Backlund symmetry algebra for the equation ur=f(x,u, . . ., ur-1, nu ,. . ., nu k) is established.
Cation-templated self-assembly of the lipophilic isoguanosine (isoG 1) with different monovalent cations (M+=Li+, Na+, K+, NH4+, and Cs+) was studied in solvents of different polarity by using diffusion NMR spectroscopy. Previous studies that did not use diffusion NMR techniques concluded that isoG 1 forms both pentamers (isoG 1)5M+ and decamers (isoG 1)10M+ in the presence of alkali-metal cations. The present diffusion NMR studies demonstrate, however, that isoG 1 does not form (isoG 1)5M+ pentamers. In fact, the diffusion NMR data indicates that both doubly charged decamers of formula (isoG 1)102 M+ and singly charged decamers, (isoG 1)10M+, are formed with lithium, sodium, potassium, and ammonium tetraphenylborate salts (LiB(Ph)4, KB(Ph)4, NaB(Ph)4 and NH4B(Ph)4), depending on the isoG 1:salt stoichiometry of the solution. In the pr...
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