A cryogenic testbed for the characterisation of large detector arrays for astronomical and Earth-observing applications in the near to very-long-wavelength infrared

In this paper we describe a cryogenic testbed designed to offer complete characterisation-via a minimal number of experimental configurations— of mercury cadmium telluride (MCT) detector arrays for low-photon background applications, including exoplanet science and solar system exploration. Specifically, the testbed offers a platform to measure the dark current of detector arrays at various temperatures, whilst also characterising their optical response in numerous spectral bands. The average modulation transfer function (MTF) can be found in both dimensions of the array along with the overall quantum efficiency. Working from a liquid-helium bath allows for measurement of arrays from 4.2 K and active-temperature control of the surface to which the array is mounted allows for characterisation of arrays at temperatures up to 80 K, with the temperature of the array holder known to an accuracy of at least 1 mK, with the same level of long-term stability

Negatively Charged In-Plane and Out-Of-Plane Domain Walls with Oxygen-Vacancy Agglomerations in a Ca-Doped Bismuth-Ferrite Thin Film.

The interaction of oxygen vacancies and ferroelectric domain walls is of great scientific interest because it leads to different domain-structure behaviors. Here, we use high-resolution scanning transmission electron microscopy to study the ferroelectric domain structure and oxygen-vacancy ordering in a compressively strained Bi0.9Ca0.1FeO3-δ thin film. It was found that atomic plates, in which agglomerated oxygen vacancies are ordered, appear without any periodicity between the plates in out-of-plane and in-plane orientation. The oxygen non-stoichiometry with δ ≈ 1 in FeO2-δ planes is identical in both orientations and shows no preference. Within the plates, the oxygen vacancies form 1D channels in a pseudocubic [010] direction with a high number of vacancies that alternate with oxygen columns with few vacancies. These plates of oxygen vacancies always coincide with charged domain walls in a tail-to-tail configuration. Defects such as ordered oxygen vacancies are thereby known to lead to a pinning effect of the ferroelectric domain walls (causing application-critical aspects, such as fatigue mechanisms and countering of retention failure) and to have a critical influence on the domain-wall conductivity. Thus, intentional oxygen vacancy defect engineering could be useful for the design of multiferroic devices with advanced functionality

Negatively Charged In-Plane and Out-Of-Plane Domain Walls with Oxygen-Vacancy Agglomerations in a Ca-Doped Bismuth-Ferrite Thin Film.

The interaction of oxygen vacancies and ferroelectric domain walls is of great scientific interest because it leads to different domain-structure behaviors. Here, we use high-resolution scanning transmission electron microscopy to study the ferroelectric domain structure and oxygen-vacancy ordering in a compressively strained Bi0.9Ca0.1FeO3-δ thin film. It was found that atomic plates, in which agglomerated oxygen vacancies are ordered, appear without any periodicity between the plates in out-of-plane and in-plane orientation. The oxygen non-stoichiometry with δ ≈ 1 in FeO2-δ planes is identical in both orientations and shows no preference. Within the plates, the oxygen vacancies form 1D channels in a pseudocubic [010] direction with a high number of vacancies that alternate with oxygen columns with few vacancies. These plates of oxygen vacancies always coincide with charged domain walls in a tail-to-tail configuration. Defects such as ordered oxygen vacancies are thereby known to lead to a pinning effect of the ferroelectric domain walls (causing application-critical aspects, such as fatigue mechanisms and countering of retention failure) and to have a critical influence on the domain-wall conductivity. Thus, intentional oxygen vacancy defect engineering could be useful for the design of multiferroic devices with advanced functionality

Combined Spectroscopy and Electrical Characterization of La:BaSnO3_\text{3} Thin Films and Heterostructures

For La-doped BaSnO$_\text{3}$ thin films grown by pulsed laser deposition, we combine chemical surface characterization and electronic transport studies to probe the evolution of electronic states in the band structure for different La-doping content. Systematic analyses of spectroscopic data based on fitting the core electron line shapes help to unravel the composition of the surface as well as the dynamics associated with increasing doping. This dynamics is observed with a more pronounced signature in the Sn 3d core level, which exhibits an increasing asymmetry to the high binding energy side of the peak with increasing electron density. The present results expand the current understanding of the interplay between the doping concentration, electronic band structure and transport properties of epitaxial La:BaSnO$_\text{3}$ films.Comment: 7 Figures, 4 Tables in manuscript; and 6 Figures and 1 Table in the Supplementary Informatio

Charge separation and transport in La0.6Sr0.4Co0.2Fe0.8O3-δ and ion-doping ceria heterostructure material for new generation fuel cell

Functionalities in heterostructure oxide material interfaces are an emerging subject resulting in extraordinary material properties such as great enhancement in the ionic conductivity in a heterostructure between a semiconductor SrTiO3 and an ionic conductor YSZ (yttrium stabilized zirconia), which can be expected to have a profound effect in oxygen ion conductors and solid oxide fuel cells [1–4]. Hereby we report a semiconductor-ionic heterostructure La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and Sm-Ca co-doped ceria (SCDC) material possessing unique properties for new generation fuel cells using semiconductor-ionic heterostructure composite materials. The LSCF-SCDC system contains both ionic and electronic conductivities, above 0.1 S/cm, but used as the electrolyte for the fuel cell it has displayed promising performance in terms of OCV (above 1.0 V) and enhanced power density (ca. 1000 mW/cm2 at 550 °C). Such high electronic conduction in the electrolyte membrane does not cause any short-circuiting problem in the device, instead delivering enhanced power output. Thus, the study of the charge separation/transport and electron blocking mechanism is crucial and can play a vital role in understanding the resulting physical properties and physics of the materials and device. With atomic level resolution ARM 200CF microscope equipped with the electron energy-loss spectroscopy (EELS) analysis, we can characterize more accurately the buried interface between the LSCF and SCDC further reveal the properties and distribution of charge carriers in the heterostructures. This phenomenon constrains the carrier mobility and determines the charge separation and devices’ fundamental working mechanism; continued exploration of this frontier can fulfill a next generation fuel cell based on the new concept of semiconductor-ionic fuel cells (SIFCs)

Breaking the Mode Degeneracy of Surface-Plasmon Resonances in a Triangular System

In this paper, we present a systematic investigation of symmetry-breaking in the plasmonic modes of triangular gold nanoprisms. Their geometrical C3 symmetry is one of the simplest possible that allows degeneracy in the particle's mode spectrum. It is reduced to the non-degenerate symmetries Cv or E by positioning additional, smaller gold nanoprisms in close proximity, either in a lateral or a vertical configuration. Corresponding to the lower symmetry of the system, its eigenmodes also feature lower symmetries (Cv), or preserve only the identity (E) as symmetry. We discuss how breaking the symmetry of the plasmonic system not only breaks the degeneracy of some lower order modes, but also how it alters the damping and eigenenergies of the observed Fano-type resonances

Synthesis, Characterization, and Electronic Properties of ZnO/ZnS Core/Shell Nanostructures Investigated Using a Multidisciplinary Approach

ZnO/ZnS core/shell nanostructures, which are studied for diverse possible applications, ranging from semiconductors, photovoltaics, and light-emitting diodes (LED), to solar cells, infrared detectors, and thermoelectrics, were synthesized and characterized by XRD, HR-(S)TEM, and analytical TEM (EDX and EELS). Moreover, band-gap measurements of the ZnO/ZnS core/shell nanostructures have been performed using UV/Vis DRS. The experimental results were combined with theoretical modeling of ZnO/ZnS (hetero)structures and band structure calculations for ZnO/ZnS systems, yielding more insights into the properties of the nanoparticles. The ab initio calculations were performed using hybrid PBE0 and HSE06 functionals. The synthesized and characterized ZnO/ZnS core/shell materials show a unique three-phase composition, where the ZnO phase is dominant in the core region and, interestingly, the auxiliary ZnS compound occurs in two phases as wurtzite and sphalerite in the shell region. Moreover, theoretical ab initio calculations show advanced semiconducting properties and possible band-gap tuning in such ZnO/ZnS structures