Search results for "substrate"
showing 10 items of 1018 documents
Die oligomerisierung endständiger hydroxyacetylene mit rhodiumkomplexkatalysatoren
1982
The substrate and ligand influence on oligomerisation of terminal hydroxyacetylenes catalysed by rhodium complexes has been studied. In this reaction α- and β-hydroxyacetylenes were compared with each other and with an unsubstituted terminal alkyne. The concentration dependant ligand control with Ph3As and Ph3P has been compared and different ligand association behaviour is found, because only with Ph3As as ligand at intermediate concentrations cyclic trimers are selectively formed. Some brief experiments with different p- and o-substituted triphenylarsines show electronic and marked steric influences on the oligomerisation of 3-methylbutyne-1-ol-3.
Lanthanide Discrimination with Hydroxyl-Decorated Flexible Metal–Organic Frameworks
2018
We report two new highly crystalline metal-organic frameworks (MOFs), derived from the natural amino acids serine (1) and threonine (2), featuring hexagonal channels densely decorated with hydroxyl groups belonging to the amino acid residues. Both 1 and 2 are capable of discriminating, via solid-phase extraction, a mixture of selected chloride salts of lanthanides on the basis of their size, chemical affinity, and/or the flexibility of the network. In addition, this discrimination follows a completely different trend for 1 and 2 because of the different locations of the hydroxyl groups in each compound, which is evocative of steric complementarity between the substrate and receptor. Last bu…
Exceedingly Fast Oxygen Atom Transfer to Olefins via a Catalytically Competent Nonheme Iron Species
2016
El mateix article està publicat en alemany a l'edició alemanya d' 'Angewandte Chemie' (ISSN 0044-8249, EISSN 1521-3757), 2016, vol. 128, núm. 21, p.6418–6422. DOI http://dx.doi.org/10.1002/ange.201601396 The reaction of [Fe(CF3SO3)2(PyNMe3)] with excess peracetic acid at −40 °C leads to the accumulation of a metastable compound that exists as a pair of electromeric species, [FeIII(OOAc)(PyNMe3)]2+ and [FeV(O)(OAc)(PyNMe3)]2+, in fast equilibrium. Stopped-flow UV/Vis analysis confirmed that oxygen atom transfer (OAT) from these electromeric species to olefinic substrates is exceedingly fast, forming epoxides with stereoretention. The impact of the electronic and steric properties of the subs…
Crystallization of SrCO3 on a self-assembled monolayer substrate: an in-situ synchrotron X-ray study
2001
Self-assembled monolayers (SAMs) of alkanethiols on gold surfaces show great promise in controlling the nucleation and growth of inorganic minerals from solution. In doing so, they mimic the role of some biogenic macromolecules in natural biomineralisation processes. Crystallization on SAM surfaces is usually monitored ex-situ; by allowing the process to commence and to evolve for some time, removing the substrate from the mother solution, and then examining it using microscopy, diffraction etc. We present here for the first time, the use of high energy monochromatic synchrotron X-radiation in conjunction with a two dimensional detector to monitor in situ, in a time resolved fashion, the gr…
Fluorescence microscopy studies of layer/substrate interaction during the Langmuir-Blodgett transfer: Fractional condensation and local layer modific…
1991
Transfer fluorescence microscopy reveals the substrate-mediated fractional condensation and phase-selective deposition of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylethanolamine (DMPE) monolayers during the LB-transfer. Preferentially the higher ordered liquid-condensed (LC) state is transferred onto the substrate during the transfer of a monolayer in the LC/LE (liquid/expanded) coexistence state on the water subphase. This is manifested in the directly observable attraction of LC-domains towards the three-phase line and observation of a domain-free gap as consequence of the segregation of the fluorescent probe into the floating monolayer adjacent to the three-phase li…
Effect of film thickness on the transport properties of MgB2 synthesized by spray pyrolysis
2011
Abstract Polycrystalline MgB2 films of different thickness have been prepared by employing spray pyrolysis technique on MgO (1 0 0) substrate. The MgB2 and other phases have been confirmed using X-ray diffraction technique and no trace of impurities phases have been found. The resistivity behavior shows that the superconducting transition temperature lies in the range of 37–39 K with narrow transition width. The transport critical current density vary with films thickness and achieved highest value ∼1.2 × 106 A/cm2 at 20 K for 2.0 μm thick film and its values increase as thickness increases.
Proximity Effects on the Charge Density Wave Order and Superconductivity in Single-Layer NbSe2
2021
Collective electronic states such as the charge density wave (CDW) order and superconductivity (SC) respond sensitively to external perturbations. Such sensitivity is dramatically enhanced in two dimensions (2D), where 2D materials hosting such electronic states are largely exposed to the environment. In this regard, the ineludible presence of supporting substrates triggers various proximity effects on 2D materials that may ultimately compromise the stability and properties of the electronic ground state. In this work, we investigate the impact of proximity effects on the CDW and superconducting states in single-layer (SL) NbSe2 on four substrates of diverse nature, namely, bilayer graphene…
Suspended single-electron transistors: Fabrication and measurement
2005
We have fabricated aluminum single-electron transistors in which the island is not in contact with the substrate. This new type of device, which can be called suspended single-electron transistor (SUSET), displayed well-defined I-V and dI/dV-V features typical for high-quality standard SET's.
Macroscopic persistent currents in laser deposited YBa2Cu3O7 films
1989
We have investigated persistent currents in a superconducting YBa2Cu3O7 ring of about 1 cm diameter, which was deposited as c-axis textured film on a SrTiO3 substrate by laser ablation. The currents were registered, via their magnetic field distribution, with a small vibrating pick-up coil. At 77 K persistent currents with negligible decay over 103 s have been observed below a critical current density jc=0.9×105 A/cm2, both for a field-cooled and a zero-field-cooled sample. This demonstrates that it is possible to fabricate dissipationless devices of such films on a relatively large scale.
Response time of a thermometer based on normal metal–insulator–superconductor (NIS) tunnel junctions
2003
Abstract We have measured the thermal response of a superconductor–normal metal–superconductor (SINIS) tunnel junction structure at substrate temperature ∼60 mK by directly heating the electron system in the normal metal island. In our structure, we find the response time is determined by the electron–phonon coupling in the electron temperature range 300– 600 mK . By using AC heating, the cut-off frequency caused by this response time has been measured, showing that SINIS structures operate as a thermometer up to a few MHz in this temperature range.