Colloidal CsBr Nanocrystals Triggered Inorganic Cation and Anion Exchange Enables High-Performance Perovskite Solar Cells.

Achieving longitudinal doping of specific ions by surface treatment remains a challenge for perovskite solar cells, which are often limited by dopant and solvent compatibility. Here, with the flowing environment created by CsBr colloidal nanocrystals, ion exchange is induced on the surface of the perovskite film to enable the homogeneous distribution of Cs+ and gradient distribution of Br- simultaneously at whole depth of the film. Meanwhile, assisted by long-chain organic ligands, the excess PbI2 on the surface of perovskite film is converted to a more stable quasi-2D perovskite, which realizes effective passivation of defects on the surface. As a result, the unfavorable n-type doping on the top surface is suppressed, so that the energy level alignment between perovskite and hole transport layer is optimized. On the basis of co-modification of the surface and the bulk, the PCE of champion device reaches 23.22% with enhanced VOC of 1.12 V. Device maintains 97.12% of the initial PCE in dark ambient air at 1% RH after 1056 h without encapsulation, and 91.56% of the initial PCE under light illumination of 1 sun in N2 atmosphere for more than 200 h. The approach demonstrated here provides an effective strategy for the nondestructive introduction of inorganic ions in perovskite film.

Magnetism in undoped ZnS nanotetrapods.

The magnetism of undoped ZnS nanotetrapods, synthesized by a solvothermal method, has been investigated by magnetization measurements and first principle numerical calculations. The background magnetic impurity concentrations of Fe, Co and Ni were determined at ppm level by inductively coupled plasma mass spectrometry (ICP-MS). Hysteresis loops of weak ferromagnetism were observed, attributable to the magnetic impurities. However, the total magnetic moments analyzed from the paramagnetism are far beyond the explanations from the presence of these magnetic impurities, by about two orders of magnitude larger. It implies a different origin of the magnetic moments. Electron microscopy analysis reveals that there are defects in the sample. Numerical simulations indicate that the excessive magnetic moments might arise from the local band structure of polarized electrons associated with the defects of cation deficiency. This study elaborates on the understanding of magnetic properties in the non-magnetic II-VI semiconductor nanomaterials.

Magnetization and electric transport properties of single-crystal MgB2 nanowires.

High quality single-crystal magnesium diboride (MgB(2)) nanowires with lengths exceeding 10 µm were successfully synthesized by hybrid physical chemical vapor deposition. The magnetization and electrical transport properties of single-crystal MgB(2) nanowires (NWs) were measured. The superconducting transition temperature of the NWs was 37 K, as confirmed by magnetization measurements. The disordered behavior of the nanowires was observed by four-terminal current-voltage characteristic measurements of an individual NW from T = 10 to 300 K. The temperature-dependent resistivity curves for seven NWs collapsed into a universal curve described by the variable range hopping model, showing intrinsic nonmetallic transport properties. This implies that the granular superconducting defect states are critical to the superconductivity of the individual MgB(2) NWs.

Magnetization reversal and anisotropy with chains of superparamagnetic Ni nanoparticles.

Chains of superparamagnetic (SPM) Ni nanoparticles of 20 and 33 nm in diameter are synthesized by a facile, template-free, wet chemical method in magnetic field. The blocking temperature for the sample of 20 nm appears at T(B) approximately 255 K, above which the sample exhibits SPM behaviors by a M(H) measurement. At T < T(B), the temperature dependent coercivity, Hc(T), is beyond the description by the simple two-well model proposed by Neel and Brown in the early day. In contrast, for the Ni nanochains of diameter larger than the coherence length, Lcoh approximately 25 nm, the magnetization reversal properties are well described by this model. The magnetization reversal behavior of the SPM Ni nanochains with the diameter much smaller than the coherence length is one of the interesting points to study. Possible transition from the localized magnetization reversal mode in the high temperature end to the coherently rotational mode at low temperature is discussed.

Template-free synthesis and self-assembly of aligned nickel nanochains under magnetic fields.

Well-aligned and uniform Nickel nanochains with diameters ranging from 20 to 110 nm have been synthesized using a simple template-free solution-phase method using environment friendly reagents under diverse temperature and magnetic field. Our results indicate that the size and morphology of as-prepared nanochains can be controlled by adjusting the reaction temperature and the applied magnetic fields, respectively. The formation of the aligned chains can be explained by the interactions of magnetic dipoles in the presence of magnetic field. Systematical magnetic measurements demonstrate that the saturation magnetization of the synthesized samples depends crucially on the particle size. Furthermore, the magnetic anisotropy of the well-aligned nickel nanochains is dominated by the shape anisotropy.

Dosimetry audits in Taiwan radiotherapy departments.

Objectives: This study examines the practice of the regulation of Standards for Medical Exposure Quality Assurance (SMEQA) in Taiwan based on on-site quality audit for radiation therapy systems from 2016 to 2019. Methods: 81 radiation therapy departments, 141 linacs, 9 γ knife systems, 34 high dose rate brachytherapy systems, 20 Tomotherapys, and 6 Cyberknives were audited yearly. Data collection and analysis for each institute's documents including QA procedure, ion chamber and electrometer calibration reports, and a questionnaire relating to machine type and staffing, were requested first and reviewed by auditors. On-site SMEQA core item measurements, including beam output, beam profile and energy constancy for external beam therapy systems, and the source strength, positioning, and timer accuracy for brachytherapy systems were audited second. More than 300 photon beams and more than 400 electron beams were measured each year. Results: There were approximately 8.9 radiotherapy units per million population, and 1.2 medical physicists per unit in Taiwan. For the output measurements, more than 78 and 75% of the photon beams and electron beams, respectively, from linacs were with deviations within ±1.0%. Photon beams have lower beam quality measurement deviations than electron beams. Including in-plane and cross-plane measurements, more than 90 and 85% photon and electron beams, respectively, were with flatness consistency within 1.0%. All audit measurements were within the SMEQA acceptance criteria. Conclusions: According to SMEQA regulations on-site QA audits were successfully carried out from 2016 to 2019 for all Taiwan radiotherapy units. The measurement results showed high quality machine performance in Taiwan. Advances in knowledge: Dosimetry audits with directly acquired measurement readings have lower uncertainties; allow immediate feedback, discussion, and adjustment in a timely manner. In addition to regulation system establishment and education and training implementation, the machine quality is closely related to machine maintenance implementation.

Cu2O hollow spheres: synthesis, characterization and magnetic property.

Cu2O hollow spheres with thin shells were synthesized using poly(vinylpyrrolidone) (PVP) as the template in deionized water. In this process, CuAc2.H2O was reduced by acerbic acid in the presence of PVP and sodium hydroxide. Techniques, including XRD, XPS, TEM and HRTEM were used to characterize the morphology, structure and composition of the as-prepared nanomaterials. The results revealed that the average diameter of polycrystalline Cu2O hollow spheres is about 200 nm, with the shells as thin as approximately 10 nm. The formation mechanism, of these hollow spheres was studied. Magnetic property of the sample demonstrates a paramagnetic behavior at 15 K, and it might be attributed to the hollow-sphere structure of the diamagnetic Cu2O.

Magnetic properties of undoped Cu(2)O fine powders with magnetic impurities and/or cation vacancies.

Fine powders of micron- and submicron-sized particles of undoped Cu(2)O semiconductor, with three different sizes and morphologies, have been synthesized by different chemical processes. These samples include nanospheres 200 nm in diameter, octahedra of size 1 µm and polyhedra of size 800 nm. They exhibit a wide spectrum of magnetic properties. At low temperature, T = 5 K, the octahedron sample is diamagnetic with the magnetic susceptibility χ(OH) = -9.5 × 10(-6) emu g(-1) Oe(-1). The nanosphere is paramagnetic with χ(NS) = 2.2 × 10(-5) emu g(-1) Oe(-1). The other two polyhedron samples synthesized in different runs by the same process are found to show different magnetic properties. One of them exhibits weak ferromagnetism with T(C)∼455 K and saturation magnetization M(S)∼0.19 emu g(-1) at T = 5 K, while the other is paramagnetic with χ = 1.0 × 10(-5) emu g(-1) Oe(-1). The total magnetic moment estimated from the detected impurity concentration of Fe, Co and Ni, is too small to account for the observed magnetism by one to two orders of magnitude. Calculations by density functional theory (DFT) reveal that cation vacancies in the Cu(2)O lattice are one of the possible causes of induced magnetic moments. The results further predict that the defect-induced magnetic moments favour a ferromagnetically coupled ground state if the local concentration of cation vacancies, n(C), exceeds 12.5%. This offers a possible scenario to explain the observed magnetic properties. The limitations of the investigations in the present work, in particular in the theoretical calculations, are discussed and possible areas for further study are suggested.

Chain-like structure created by assembly of cobalt nanoparticles using PVP as soft template.

Using a wet chemical method, we have synthesized chain-like structure with diameters of 200-250 nm and lengths of approximately 10 microm formed by assembly of small cobalt nanoparticles. The chain-like structures were realized via reaction of CoCl2 x 6H2O and N2H4 in the presence of PVP in an ethylene glycol solution. Magnetic measurements show a coercivity of about 122 Oe at 300 K. We also propose a possible mechanism for the formation of the chain-like structures.

Marginal leakage of different temporary restorations in standardized complex endodontic access preparations.

This study compared the marginal leakage of temporary restorations using Cavit, IRM, zinc phosphate cement (ZPC), and copper bands cemented with ZPC. Standardized complex endodontic access preparations were made in 176 extracted human molars. The teeth were divided into six groups, including positive and negative controls. A Universal matrix system was placed over each tooth before restoration, except in the copper band group, in which teeth were restored with ZPC after copper band cementation. Marginal leakage was evaluated with a binocular microscope after the teeth were immersed in artificial saliva, colored with 2% methylene blue and buffered to neutral pH, at 37 degrees C for various time intervals after thermal cycling. In the experimental groups, the differences in the leakage scores of the Cavit group and the other groups were very marked. The Cavit group presented the least marginal leakage, irrespective of time, whereas more than half the specimens from the IRM, ZPC, and copper band groups displayed severe leakage from day 1.

Low-temperature fabrication of Au-Co cluster mixed nanohybrids with high magnetic moment of Co.

In recent years, the synergistic effects of Au-based hybrids have generated enormous scientific interest. The hybrids of Au and Co are expected to exhibit attractive properties. In this paper, we report the successful fabrication of the nanohybrids between bulk-immiscible Au and Co with chain-like structures via a mild solution method. Elemental mapping, XRD and EXAFS data reveal that the as-prepared AuCo nanohybrids might be of cluster mixed configuration. A sequential redox and imperfection-promoted aggregation/diffusion process is proposed to elucidate the formation mechanism of the nanohybrids. The as-prepared products exhibit a temperature-independent saturation magnetization with the magnetic moment of Co as high as ~2.95 µ(B) for each Co atom at 300 K, much higher than the bulk value (~1.7 µ(B) for each Co atom) and approaching the theoretical value of an atomic Co (~3.0 µ(B) for each Co atom).

Surface magnetic states of Ni nanochains modified by using different organic surfactants.

Three powder samples of Ni nanochains formed of polycrystalline Ni nanoparticles with an estimated diameter of about 30 nm have been synthesized by a wet chemical method using different organic surfactants. These samples, having magnetically/structurally core-shell structures, all with a ferromagnetic Ni core, are Ni@Ni(3)C nanochains, Ni@Ni(SG) nanochains with a spin glass (SG) surface layer, and Ni@Ni(NM) nanochains with a nonmagnetic (NM) surface layer. The average thickness of the shell for these three samples is determined as about 2 nm. Magnetic properties tailored by the different surface magnetism are studied. In particular, suppression in the saturation magnetization, usually observed with magnetic nanoparticles, is revealed to arise from the surface magnetic states with the present samples.

Well-aligned Nickel Nanochains Synthesized by a Template-free Route.

Highly uniform and well-aligned one-dimensional Ni nanochains with controllable diameters, including 33, 78, and 120 nm, have been synthesized by applying an external magnetic field without any surface modifying agent. The formation can be explained by the interactions of magnetic dipoles in the presence of applied magnetic field. Magnetic measurements demonstrate that the shape anisotropy dominates the magnetic anisotropy. The demagnetization factor, ∆N, is in the range of 0.23-0.36.

Ni/Ni3C core-shell nanochains and its magnetic properties: one-step synthesis at low temperature.

One-dimensional Ni/Ni3C core-shell nanoball chains with an average diameter by around 30 nm were synthesized by means of a mild chemical solution method using a soft template of trioctylphosphine oxide (TOPO). It was revealed that the uniform Ni nanochains were capped with Ni3C thin shells by about 1-4 nm in thickness and each Ni core consists of polygrains. The coercivity of the core-shell nanochains is much enhanced (600 Oe at 5 K) and comparable with single Ni nanowires due to the one-dimensional shape anisotropy. Deriving from the distinctive structure of Ni core and Ni 3C shell, this architecture may possess a possible bifunctionality. This unique architecture is also useful for the study on the magnetization reversal mechanism of one-dimensional magnetic nanostructure.