Characterization of Aerosol Deposited Cesium Lead Tribromide Perovskite Films on Interdigited ITO Electrodes

Aerosol deposition (AD) is a promising additive manufacturing method to fabricate low-cost, scalable films at room temperature, but has not been considered for semiconductor processing, so far. The successful preparation of cesium lead tribromide (CsPbBr) perovskite films on interdigitated indium tin oxide (ITO) electrodes by means of AD is reported here. The – µm thick layers are dense and have good adhesion to the substrate. The orthorhombic Pnma crystal structure of the precursor powder was retained during the deposition process with no signs of defect formation. The formation of electronic defects by photoluminescence spectroscopy is investigated and found slightly increased carrier recombination from defect sites for AD films compared to the powder. A nonuniform defect distribution across the layer, presumably induced by the impact of the semiconducting grains on the hard substrate surface, is revealed. The opto-electronic properties of AD processed semiconducting films is further tested by electrical measurements and confirmed good semiconducting properties and high responsivity for the films. These results demonstrate that AD processing of metal halide perovskites is possible for opto-electronic device manufacturing on D surfaces. It is believed that this work paves the way for the fabrication of previously unimaginable opto-electronic devices by additive manufacturing

Primary staging and follow-up in melanoma patients – monocenter evaluation of methods, costs and patient survival

In a German cohort of 661 melanoma patients the performance, costs and survival benefits of staging methods (history and physical examination; chest X-ray; ultrasonography of the abdomen; high resolution sonography of the peripheral lymph nodes) were assessed at initial staging and during follow-up of stage I/II+III disease. At initial staging, 74% (23 out of 31) of synchronous metastases were first detected by physical examination followed by sonography of the lymph nodes revealing 16% (5 out of 31). Other imaging methods were less efficient (Chest X-ray: one out of 31; sonography of abdomen: two out of 31). Nearly 24% of all 127 first recurrences and 18% of 73 second recurrences developed in patients not participating in the follow-up programme. In follow-up patients detection of first or second recurrence were attributed to history and physical examination on a routine visit in 47 and 52% recurrences, respectively, and to routine imaging procedures in 21 and 17% of cases, respectively. Lymph node sonography was the most successful technical staging procedure indicating 13% of first relapses, but comprised 24% of total costs of follow-up in stage I/II. Routine imaging comprised nearly 50% of total costs for follow-up in stage I/II and in stage III. The mode of detecting a relapse (‘patient vs. doctor-diagnosed’ or ‘symptomatic vs asymptomatic’) did not significantly influence patients overall survival. Taken together, imaging procedures for routine follow-up in stage I/II and stage III melanoma patients were inefficient and not cost-efficient

Computed tomography in staging of patients with melanoma metastatic to the regional nodes

Background: This study addresses the yield and clinical impact of computed tomography (CT) imaging in otherwise asymptomatic patients with stage III melanoma metastatic to the regional nodes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41414/1/10434_2006_Article_BF02305552.pd

Electric-Field-Induced Domain Switching and Domain Texture Relaxations in Bulk Bismuth Ferrite

Bismuth ferrite, BiFeO3, is an important multiferroic material that has attracted remarkable attention for potential applications in functional devices. While thin films of BiFeO3 are attractive for applications in nanoelectronics, bulk polycrystalline BiFeO3 has great potential as a lead-free and/or high-temperature actuator material. However, the actuation mechanisms in bulk BiFeO3 are still to be resolved. Here we report the microscopic origin of electric-field-induced strain in bulk BiFeO3 ceramic by means of in situ high-energy X-ray diffraction. Quantification of intrinsic lattice strain and extrinsic domain switching strain from diffraction data showed that the strain response in rhombohedral bulk BiFeO3 is primarily due to non-180 ferroelectric domain switching, with no observable change in the phase symmetry, up to the maximum field used in the study. The origin of strain thus differs from the strain mechanism previously shown in thin film BiFeO3, which gives a similar strain/field ratio as rhombohedral bulk BiFeO3. A strong post-poling relaxation of switched non-180 ferroelectric domains has been observed and hypothesized to be due to intergranular residual stresses with a possible contribution from the conductive nature of the domain walls in BiFeO3 ceramics

Stress-dependent crystal structure of lanthanum strontium cobalt ferrite by in situ synchrotron X-ray diffraction

Lanthanum strontium cobalt ferrite La$_{1-x}$Sr$_x$Co$_{1-y}$FeyO$_{3-δ}$ (LSCF) is one of the most studied mixed ionic-electronic conductor materials due to electrical and transport properties, which are attractive for intermediate temperature solid oxide fuel cells (SOFCs), oxygen permeation membranes, and catalysis. The integration of such materials, however, depends on the thermal as well as mechanical behavior. LSCF exhibits nonlinear hysteresis during compressive stress-strain measurements, marked by a remanent strain and coercive stress, i.e., ferroelasticity. However, the origin of ferroelastic behavior has not been investigated under high compressive stress. This study, therefore, investigates the microscopic origin of stress-induced mechanical behavior in polycrystalline (La$_{0.6}$Sr$_{0.4}$)$_{0.95}$Co$_{0.2}$Fe$_{0.8}$O$_{3-δ}$ using in situ synchrotron x-ray diffraction. The data presented here reveals that the strain response originates from the intrinsic lattice strain as well as the extrinsic domain switching strain without any apparent change in crystallographic symmetry. A comparison of the calculated microscopic strain contribution with that of a macroscopic measurement indicates a significant change in the relative contributions of intrinsic and extrinsic strain depending on the applied stress state, i.e., under maximum stress and after unloading. Direct evidence of the microscopic origin of stress-strain response outlined in this paper may assist in guiding materials design with the improved mechanical reliability of SOFCs

Influence of the annealing conditions on temperature-dependent ferroelastic behavior of LSCF

The macroscopic ferroelastic behavior of polycrystalline (La 0.6 Sr 0.4)0.95Co0.2Fe0.8O3−d and its dependence on an- nealing conditions was investigated over a temperature range from − 150°C to 150°C. A temperature- and defect concentration-dependent variation of the ferroelastic behavior was attributed to internal stresses, oxygen defi- ciency, and a corresponding change of the crystal structure. In particular, there was an observed decrease in remanent strain and the formation of a closed ferroelastic hysteresis loop at temperatures below approximately 0 °C for samples annealed in air, which was suppressed through the reduction in oxygen vacancies by annealing the samples in oxygen. The macroscopic mechanical behavior as a function of annealing conditions is discussed with respect to the crystal structure and oxygen deficiency determined by means of x-ray and neutron diffraction

Nonlinear mechanical behaviour of Ba0.5Sr0.5Co0.8Fe0.2O3−δ and in situ stress dependent synchrotron X-ray diffraction study

Perovskite type Ba0.5Sr0.5Co0.8Fe0.2O3 − δ ceramics display nonlinear stress-strain behaviour upon uniaxial compression at room temperature. Step functional loading experiments show that the nonlinear strain response of the material is time dependent, partially reversible and depends on the oxygen vacancy concentration. In situ compressive stress-dependent synchrotron X-ray diffraction reveals that the nonlinearity is not related to ferroelasticity or a stress-induced phase transformation. The oxygen vacancy concentration and average spin state were determined from Rietveld analysis of the magnetic scattering found in the neutron powder diffraction data, indicating their role during mechanical loading. An oxygen vacancy migration model and a spin-state transition are proposed as possible mechanisms of nonlinear mechanical response