Search results for " films"
showing 10 items of 2599 documents
Ray optics behavior of flux avalanche propagation in superconducting films
2015
Experimental evidence of wave properties of dendritic flux avalanches in superconducting films is reported. Using magneto-optical imaging the propagation of dendrites across boundaries between a bare NbN film and areas coated by a Cu layer was visualized, and it was found that the propagation is refracted in full quantitative agreement with Snell’s law. For the studied film of 170 nm thickness and a 0.9 μm thick metal layer, the refractive index was close to n = 1.4. The origin of the refraction is believed to be caused by the dendrites propagating as an electromagnetic shock wave, similar to damped modes considered previously for normal metals. The analogy is justified by the large dissipa…
Thermoelectric radiation detector based on a superconductor-ferromagnet junction : Calorimetric regime
2018
We study the use of a thermoelectric junction as a thermal radiation detector in the calorimetric regime, where single radiation bursts can be separated in time domain. We focus especially on the case of a large thermoelectric figure of merit ZT affecting significantly, for example, the relevant thermal time scales. This work is motivated by the use of hybrid superconductor/ferromagnet systems in creating an unprecedentedly high low-temperature ZT even exceeding unity. Besides constructing a very general noise model which takes into account cross correlations between charge and heat noise, we show how the detector signal can be efficiently multiplexed by the use of resonant LC circuits givi…
Development of niobium-based superconducting junctions
2012
This thesis presents a review of publications which mainly focuses on the fabrication and performance of Nb-based normal metal-insulator-superconductor (NIS) tunnel junctions and superconductor-normal metal-superconductor (SNS) Josephson junctions at low temperatures. The Cu/AlOx-Al/Nb based NIS double tunnel junctions were successfully fabricated using conventional electron beam lithography combined with multi-angle thermal evaporation of metals in ultra high vacuum. The subgap characteristics of these junctions showed expected temperature dependence from 0.2 K to 5 K with a good thermometry sensitivity 0.2-0.3 mV/K. Signatures of small electronic cooling effects were observed near the Nb …
Towards Controlled Synthesis of Water-Soluble Gold Nanoclusters : Synthesis and Analysis
2019
Water-soluble gold nanoclusters with well-defined molecular structures and stability possess particular biophysical properties making them excellent candidates for biological applications as well as for fundamental spectroscopic studies. The currently existing synthetic protocols for atomically monodisperse thiolate-protected gold nanoclusters (AuMPCs) have been widely expanded with organothiolates, yet the direct synthesis reports for water-soluble AuMPCs are still deficient. Here, we demonstrate a wet-chemistry pH-controlled synthesis of two large water-soluble nanoclusters utilizing p-mercaptobenzoic acid (pMBA), affording different sizes of plasmonic AuMPCs on the preparative scale (∼7 …
An Easy Route Towards Regioselectively Difunctionalized Cyclens and New Cryptands.
2006
Reductive amination of various aldehydes with cyclen represents a very convenient method for the synthesis of a wide range of 1,7-difunctionalized cyclens, as well as new cryptands.
Isophorone on Au/MgO/Ag(001) : Physisorption with Electrostatic Site Selection
2017
We report a computational study of isophorone C9H14O adsorption on a Ag(001)-supported ultrathin MgO film with Au adatoms and clusters employing density functional theory calculations. The calculations show that the keto form of isophorone is more stable than the enol tautomers both in gas phase and on the MgO/Ag(001) surface. The interaction between the keto isophorone and step and terrace sites of MgO/Ag(001) displays long interaction distances, relatively weakly exothermic adsorption energies, lack of charge transfer, and minor changes in the density of states, all of which indicate that the molecule merely physisorbs on the surface. The step sites are energetically preferred adsorption …
Theoretical Analysis of the M12Ag32(SR)404– and X@M12Ag32(SR)304– Nanoclusters (M = Au, Ag; X = H, Mn)
2014
We analyze the electronic structure and optical properties of the recently reported, structurally known M12Ag32(SR)304– clusters (M = Au, Ag) by using density functional theory and time-dependent density functional perturbation theory. Effects of the chemical changes in the metal core, charge of the cluster, and nature of the thiolate ligand on the electronic structure and optical absorption are reported. In addition, doping the metal core with a magnetic transition metal atom (Mn) or hydrogen (protons) is discussed. Although all these clusters can be considered as 18-electron superatoms with a shell configuration 1S2 1P6 1D10, we find that the optical spectrum is sensitive to the charge st…
Ultrafast electronic relaxation and vibrational cooling dynamics of Au 144(SC2H4Ph)60 nanocluster probed by transient mid-IR spectroscopy
2014
Energy relaxation dynamics of a gold nanocluster with atomically precise composition, Au144(SC2H4Ph)60, is studied by transient mid-IR spectroscopy. The experiment is designed to simultaneously pro...
TDDFT Analysis of Optical Properties of Thiol Monolayer-Protected Gold and Intermetallic Silver–Gold Au144(SR)60 and Au84Ag60(SR)60 Clusters
2014
The optical absorption spectra of atomistic model structures for experimentally isolated all-gold Au144(SR)60 and intermetallic Au84Ag60(SR)60 clusters are systematically analyzed from linear-response time-dependent density functional theory (LR-TDDFT) and time-dependent density functional perturbation theory (TD-DFPT) calculations. The computed spectra, utilizing the atomistic model for Au144(SR)60 published by us in 2009, reproduce closely the experimental observations for corresponding isolated compounds, reported previously by Kumara and Dass in 2011. A collective dipole oscillation within the metal cores of the all-gold and intermetallic clusters is formed as response to light in the v…
Optical Properties of Monolayer-Protected Aluminum Clusters: Time-Dependent Density Functional Theory Study
2015
We examine the electronic and optical properties of experimentally known monolayer-protected aluminum clusters Al4(C5H5)4, Al50(C5Me5)12, and Al69(N(SiMe3)2)183– using time-dependent density functional theory. By comparing Al4(C5H5)4 and the theoretical Al4(N(SiMe3)2)4 cluster, we observe significant changes in the optical absorption spectra caused by different hybridization between metal core and ligands. Using these initial observations, we explain the calculated spectra of Al50(C5Me5)12 and Al69(N(SiMe3)2)183–. Al50(C5Me5)12 shows a structured spectrum with clear regions of low-intensity core-to-core transitions followed by high-intensity ligand-to-core transitions due to its high symmet…