Revealing Nanomechanical Domains and Their Transient Behavior in Mixed-Halide Perovskite Films

Halide perovskites are a versatile class of semiconductors employed for high performance emerging optoelectronic devices, including flexoelectric systems, yet the influence of their ionic nature on their mechanical behavior is still to be understood. Here, a combination of atomic-force, optical, and compositional X-ray microscopy techniques is employed to shed light on the mechanical properties of halide perovskite films at the nanoscale. Mechanical domains within and between morphological grains, enclosed by mechanical boundaries of higher Young's Modulus (YM) than the bulk parent material, are revealed. These mechanical boundaries are associated with the presence of bromide-rich clusters as visualized by nano-X-ray fluorescence mapping. Stiffer regions are specifically selectively modified upon light soaking the sample, resulting in an overall homogenization of the mechanical properties toward the bulk YM. This behavior is attributed to light-induced ion migration processes that homogenize the local chemical distribution, which is accompanied by photobrightening of the photoluminescence within the same region. This work highlights critical links between mechanical, chemical, and optoelectronic characteristics in this family of perovskites, and demonstrates the potential of combinational imaging studies to understand and design halide perovskite films for emerging applications such as photoflexoelectricity.     

Sol-Gel Glass-Encapsulated Crown Ethers for the Separation and Preconcentration of Strontium from Acidic Media

Extraction chromatography employing an inert polymeric support impregnated with a crown ether (typically, 4,4’,(5’)-di-(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6)), either neat (i.e., undiluted) or as a solution in 1-octanol, has previously been shown to provide an effective means for the isolation of radiostrontium from a variety of sample types for subsequent determination. In this study, sol-gel chemistry has been employed to prepare sorbents in which DtBuCH18C6 is encapsulated in a silica matrix. The resultant materials have been evaluated for their ability to retain strontium ion and compared to a commercially available extraction chromatographic (EXC) resin. Certain of the new materials are shown to provide uptake efficiencies comparable to those obtained with the commercial resins, although unless a porogen is employed, the kinetics of strontium uptake are significantly slower. In contrast to conventional EXC materials, however, strontium uptake by DtBuCH18C6-loaded glasses does not increase in proportion to the amount of extractant present, indicating that not all of the crown ether present is available for interaction with the metal ion.     

On Stochastic Modeling of Interface Defects in Composite Materials

The article presents mathematical and computational research dealing with the problem of stochastic interface defects occurring in composite materials between their constituents. A mathematical model of the periodic composite with such defects is presented in detail, as well as probabilistic numerical methods enabling computational experiments which are shown in a further part of the text. The fiber-reinforced and laminated composite has been tested in numerical tests as well as the superconducting coil cable-four-component composite to verify how the structural defects considered, according to the model introduced, influence the static behavior of the composites analyzed. All the results obtained and discussed in the article are summarized in concluding remarks which show the directions of further model development, while numerous references enable the reader to study the problem further.     

Absorbing photonic crystals for silicon thin-film solar cells: Design,fabrication and experimental investigation

In this paper, we present the integration of an absorbing photonic crystal within a thin-film photovoltaic solar cell. Optical simulations performed on a complete solar cell revealed that patterning the hydrogenated amorphous silicon active layer as a 2D photonic crystal membrane enabled to increase its integrated absorption by 28 % between 300 and 720 nm, comparing to a similar but unpatterned stack. In order to fabricate such promising cells, we developed a high throughput process based on holographic lithography and reactive ion etching. The influences of the parameters taking part in those processes on the obtained patterns are discussed. Optical measurements performed on the resulting “photonized” solar cell structures underline the regularity of the 2D pattern and a significant absorption increase above 550 nm, similarly to what is observed on the simulated absorption spectra. Moreover, our patterned cells are found to be robust with regards to the angle of incidence of the light.     

Dynamics of incomplete ionized dopants and their impact on4H/6H-SiC devices

The influence of incomplete ionization of dopants in 4H/6H-SiC on transient device behavior has been investigated numerically based on a self-consistent solution of the coupled system of Poisson's equation, the continuity equations of electrons and holes, and balance equations for each donor or acceptor level. If the rise time of a reverse bias pulse is equal or smaller than the characteristic ionization time constant, a dynamically enlarged extension of depletion regions is obtained which can result in a dynamic punchthrough (PT) within back-to-back junction configurations. The respective time constants of nitrogen (N), aluminum (Al), and boron (B) mere measured as functions of temperature in 4H- and 6H-SiC using thermal admittance spectroscopy (AS) and deep level transient spectroscopy (DLTS). At room temperature, for instance, we obtained 60 ps/2 ps, 300 ps/10 ps, and 100 ns/100 ns for N (cubic site), Al, and B in 4H/6H-SiC, respectively. As the time constants of N and Al are small, transient incomplete ionization turns out to be negligible, at least within today's high-power device operation areas. Boron, on the other hand, influences significantly the dynamic device characteristics. In order to demonstrate the implications of these effects, numerical device simulations of a 6H-SiC double-implanted MOSFET and a 4H-SiC thyristor were performed. These simulations allow a detailed analysis of the transient device behavior and the onset of dynamic PT which strongly depends on temperature, structure parameters, and the external excitation     

Thermo-reversible sol–gel transition of TiO2 nanoparticles with surface modified by p-toluene sulfonic acid

In this paper an unprecedent thermo-reversible sol–gel transition for titania nanoparticles dispersed in a solution of p-toluene sulfonic acid (PTSH) in isopropanol is reported. The sol formed by the thermo-hydrolysis at 60 °C of titanium tetraisopropoxide (Ti(OⁱPr)₄) reversibly changes into a turbid gel upon cooling to room temperature. Turbidimetric measurements performed for samples containing different nominal acidity ratios (A = [PTSH]/[Ti]) have evidenced that the gel transformation temperature increases from 20 to 35 °C as the [PTSH]/[Ti] ratio increases from 0.2 to 2.0. SAXS results indicate that the thermo-reversible gelation is associated to a reversible aggregation of a monodisperse set of titania nanoparticles with average gyration radius of ≈2 nm. From the different PTSH species evidenced by Raman spectroscopy and TG/DTA of dried gels we proposed that the thermo-reversible gelation in this systems is induced by the formation of a supramolecular network, in which the protonated surface of nanoparticles is interconnected through cooperative hydrogen bonds between –SO₃ groups of p-toluene sulfonic acid.     

Mathematical Description of Experimentally Determined Charge Distributions of a Unipolar Diffusion Charger

The charge distributions of an improved opposed flow unipolar diffusion charger were measured using a tandem differential mobility analyzer (DMA) set up in a size range of approximately 20–400 nm. The charger is intended to be used in a portable aerosol sizer to measure particle size distributions. The determined charge distributions were represented by lognormal distributions, and a set of equations and coefficients was developed to calculate the charge distributions. These equations can be easily implemented in software for size distribution measurements. The agreement between the mathematically derived and measured charge distributions is very good, with regression coefficients R ² > 0.96. The investigations showed that approximately 55% of 20-nm particles remain uncharged, while up to 25 elementary charges need to be considered for multiple charge correction of 400-nm particles. Comparison with the Fuchs theory delivered satisfying agreement with the measured average charge levels, but charge distributions cannot be described by the Fuchs theory, likely caused by the charger geometry.

Copyright 2012 American Association for Aerosol Research     

Pulmonary thromboembolism

Pulmonary embolism (PE) is a serious complication of chronic obstructive pulmonary disease (COPD). Retrospective studies on patients with COPD treated in the intensive care unit (ICU) were performed to determine: 1) the frequency of PE; 2) the clinical course of PE in cases of COPD in the ICU; and 3) the frequency of PE as a cause of death in the studied group. The frequency of PE was 10.9% in COPD patients. In the group analysed, clinical presentation of PE was characterized by acute severe, life-threatening complications leading to death in 86.7% of cases. PE was the most frequent cause of death (40.6%) in COPD patients in the ICU. The results of treatment of pulmonary embolism in chronic obstructive pulmonary disease are poor and mortality in this group of patients is very high. We believe that improvement of management can be achieved by antithromboembolic prophylaxis, which should be instituted as soon as possible in all patients with chronic obstructive pulmonary disease in the intensive care unit.     

Intratumoral microdistribution of [131I]MB-1 in patients with B-cell lymphoma following radioimmunotherapy

Leprechaunism is a rare autosomal recessive disorder characterized by marked intrauterine and postnatal growth retardation, severe insulin resistance, and altered glucose homeostasis. This syndrome is related to mutations in the insulin receptor (IR) gene that impair the transmission of the insulin signal by several mechanisms. There is no effective therapy and patients usually die within the first months of life. Here we report the prenatal diagnosis of leprechaunism in two unrelated families in which affected children were compound heterozygotes with two different deficient IR alleles. In family Par-1, the disease IR alleles carried a missense mutation located in exon 18 (Arg1092-->Trp) and exon 20 (Glu1179-->Lys). In family Als, a 3-basepair deletion causing the loss of Asn281 in exon 3 and a major deletion of exons 10-13 were present in the maternal and paternal mutant IR alleles, respectively. Prenatal diagnosis was made in each family by a specific approach combining denaturing gradient gel electrophoresis (DGGE) and Southern blotting. This methodology allowed us to correctly predict the genotype of the two fetuses at the IR locus.