Defect Passivation via the Incorporation of Tetrapropylammonium Cation Leading to Stability Enhancement in Lead Halide Perovskite

Improving the performances of photovoltaic (PV) devices by suppressing nonradiative energy losses through surface defect passivation and enhancing the stability to the level of standard PV represents one critical challenge for perovskite solar cells. Here, reported are the advantages of introducing a tetrapropylammonium (TPA⁺) cation that combines two key functionalities, namely surface passivation of CH₃NH₃PbI₃ nanocrystals through strong ionic interaction with the surface and bulk passivation via formation of a type I heterostructure that acts as a recombination barrier. As a result, nonencapsulated perovskite devices with only 2 mol% of TPA⁺ achieve power conversion efficiencies over 18.5% with higher V_OC under air mass 1.5G conditions. The devices fabricated retain more than 85% of their initial performances for over 1500 h under ambient conditions (55% RH ± 5%). Furthermore, devices with TPA⁺ also exhibit excellent operational stability by retaining over 85% of the initial performance after 250 h at maximum power point under 1 sun illumination. The effect of incorporation of TPA⁺ on the structural and optoelectronic properties is studied by X‐ray diffraction, ultraviolet–visible absorption spectroscopy, ultraviolet photon–electron spectroscopy, time‐resolved photoluminescence, and scanning electron microscopy imaging. Atomic‐level passivation upon addition of TPA⁺ is elucidated employing 2D solid‐state NMR spectroscopy.     

Performance Enhancement of Tri‐Cation and Dual‐Anion Mixed Perovskite Solar Cells by Au@SiO2 Nanoparticles

Tri‐cation and dual‐anion mixed perovskites have been widely utilized in perovskite solar cell (PSC) applications due to their novel properties such as high absorption, high stability, and low cost. To commercialize the PSCs, further improving the device performance without detrimentally changing the device configuration is important at present. Herein, Au@SiO₂ nanoparticles (NPs) are introduced to modify the interface between mesoporous TiO₂ (mp‐TiO₂) and mixed perovskite with increased main photovoltaic parameters of the device, resulting in a ≈29% enhancement of power conversion efficiency (PCE) from 15.8% to 20.3%. The origins of the enhancement have been studied by exploring the optical absorption, optical power distribution, and charge carrier behaviors within the system. The small perturbation transient photovoltage measurement exhibits prolonged charge carrier lifetimes after the Au@SiO₂ NPs incorporation, and time of flight photoconductivity measurement shows that charge carrier mobilities of this system are also enhanced. These characteristics make metallic nanostructures a promising functional material in facile tuning of the charge carriers transport and further boosting the PCE of the PSCs.     

Comparison of Direct and Indirect Measurements of the Saturation Magnetization of Barium Hexaferrite Synthesized by Coprecipitation

This paper compares the magnetic properties of barium hexaferrite (BaM) powder synthesized by the coprecipitation method as determined by two- magnon scattering theory (microwave spectroscopy) and a direct method (vibrating-sample magnetometry). The microstructural, structural, loss, and magnetic properties were measured by x-ray diffractometry, field-emission scanning electron spectroscopy, network analysis, and vibrating-sample magnetometry, respectively. By using the two-magnon scattering theory and the reflection loss data, the saturation magnetization was calculated. The results revealed that the saturation magnetization determined by the use of the two-magnon scattering theory is about 54.75 emu/g, which closely conforms to the experimental value of 55.00 emu/g obtained using vibrating-sample magnetometry.     

Strong Photoacoustic Signal Enhancement by Coating Gold Nanoparticles with Melanin for Biomedical Imaging

Photoacoustics is a powerful biomedical imaging and detection technique, because it is a noninvasive, nonionizing, and low‐cost method facilitating deep tissue penetration. However, suitable contrast agents need to be developed to increase the contrast for in vivo imaging. Gold nanoparticles are often discussed as potential sonophores due to their large absorption cross‐section and their tunable plasmon resonance. However, disadvantages such as toxicity and low photoacoustic efficiency in the tissue transparency window prevail, preventing their clinical application. As a result, there remains a strong need to develop colloidal photoacoustic contrast agents which absorb in the tissue transparency window, exhibit high photoacoustic signal, and are biocompatible. Here, a facile synthetic approach is presented to produce melanin shells around various gold nanoparticle geometries, from spheres to stars and rods. These hybrid particles show excellent dispersability, better biocompatibility, and augmented photoacoustic responses over the pure melanin or pristine gold particles, with a rod‐shape geometry leading to the highest performance. These experimental results are corroborated using numerical calculations and explain the improved photoacoustic performance with a thermal confinement effect. The applicability of melanin coated gold nanorods as gastrointestinal imaging probes in mouse intestine is showcased.     

CCVD Synthesis of Carbon‐Encapsulated Cobalt Nanoparticles for Biomedical Applications

Carbon‐encapsulated ferromagnetic Cobalt nanoparticles (Co@C) have been synthesized by catalytic chemical vapour deposition (CCVD). The nanoparticles, mainly ranging between 10 and 15 nm, are tightly encapsulated by 2–3 concentric graphitic carbon shells and protected from oxidation. Because of their magnetic properties (saturation magnetization of 106 emu/g and a coercivity HC of 250 Oe), Co@C nanoparticles have been investigated for hyperthermia application. Although the observed values of the specific absorption rate (28.7 W/gCo@C at 30 kA/m and 215.4 W/gCo@C at 70 kA/m) are slightly lower than required in actual hyperthermia therapies, the observed strong heating effect provides a very promising starting point for future clinical application. It is also demonstrated that these nanoparticles can at the same time be used for magnetic resonance imaging (MRI) with an efficiency comparable to commercially available T2 contrast agents.     

基于特征空间逼近的传声器阵列语音信号增强

对现有的基于自动波束形成的传声器阵列语音信号增强算法提出了改进,将各传声器采集到的信号利用ABF(自适应波束形成)进行延时补偿并求和,消除信号中弱相干和不相干噪声;再利用特征空间逼近的方法进一步去除残留的噪声。将一种定阶方法应用到基于特征空间分解的语音信号增强中,利用其“最大稳定”原理,使得有效信号模型的阶数尽可能不受原始信号信噪比的影响,消除了传统定阶过程中的随意性和不稳定性。仿真结果表明:把自适应波束形成技术和特征空间逼近的方法结合起来,能够取得良好的去噪效果。     

Magnetostatic Surface-Wave Propagation in Ferrite Thin Films with Arbitrary Variations of the Magnetization Through the Film Thickness

A variational formulation for the magnetostatic problem in an anisotropic and inhomogeneous region bounded by perfect conductors is described. The method is applied to the special case of magnetostatic surface-wave (MSSW) modes propagating in a ferrite thin film with arbitrary variations of the saturation magnetization through the film thickness. Methods for calculating dispersion relations, delay characteristics, and magnetostatic potential functions are discussed. The functional that is minimized is interpreted in terms of contributions to the mode energy. Also, concepts pertaining to homogeneous films such as mode bandwidth and dimensional scaling effects are extended to the general inhomogeneous case. Calculations for a two-layer film with a gradual transition region and an ion-implanted film are presented as numerical examples.     

Investigations on Structural,Optical and Multiferroic Properties of Bismuth Ferrite Nanoparticles Synthesized by Sonochemical Method

BiFeO₃ nanoparticles have been synthesized using a sonochemical method. The phase identification of the prepared sample was characterized by x–ray powder diffraction, which confirmed the rhombohedral structure. The diffused reflectance spectra showed bands in the ultraviolet and visible regions and the optical band gap was calculated using the Kulbeka–Munk function. The magnetization measurement revealed a ferromagnetic behavior at room temperature and this has been confirmed through an Arrott–Belov–Kouvel plot. The BiFeO₃ nanoparticles exhibit a ferroelectric nature at room temperature and the leakage current density was measured under the applied electric field of ±?30 kV/cm.     

Novel Approach for Tracking Accuracy Enhancement in Infrared Spot Image

In optical tracking system, the macropixels method in which macropixels are used to estimate initial target region and to accurately localize target by choosing appropriate weight function and ratio function has stronger anti-noise ability than the general center of mass for unsymmetry target with low SNR. It is proved that the method can improve precision and speed efficiently: the centroid error is only 0.38 pixel when SNR is −5dB, and processing speed is 20 frame/s for the unsymmetry target of 4 × 4 pixels in infrared spot image of 128 × 128 pixels.     

Cobalt Boron Imidazolate Framework Derived Cobalt Nanoparticles Encapsulated in B/N Codoped Nanocarbon as Efficient Bifunctional Electrocatalysts for Overall Water Splitting

The development of efficient and low‐cost bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desirable for electrochemical energy conversion. Herein, this study puts forward a new Co decorated N,B‐codoped interconnected graphitic carbon and carbon nanotube materials (Co/NBC) synthesized by direct carbonization of a cobalt‐based boron imidazolate framework. It is demonstrated that the carbonization temperature can tune the surface structure and component of the resultant materials and optimize the electrochemically active surface area to expose more accessible active sites, effectively boosting the electrocatalytic activity. As a result, the optimized Co/NBC shows superior bifunctional catalytic activity and stability toward OER and HER in 1.0 m KOH solution. Furthermore, the catalyst can serve as both the anode and cathode for water splitting to achieve a current density of 10 mA cm^?2 at a cell voltage of 1.68 V. Experimental results and theoretical calculations indicate that the excellent activity of Co/NBC catalyst benefits from the synergistic effect of partial oxidation of metallic cobalt, conductive N,B‐codoped graphitic carbon and carbon nanotube, and the coupled interactions among these components. This work opens a promising avenue toward the exploration of boron imidazolate frameworks as efficient heteroatom‐doped catalysts for electrocatalysis.     

MOSFET迁移率增强技术

随着MOSFET特征尺寸的缩小,载流子的迁移率降低已成为器件性能衰退的主要因素之一,迁移率增强技术因此获得了广泛的研究和应用。衬底诱生应力、工艺诱生应力和采用不同的衬底晶向等三类方法都可以显著提高载流子的迁移率。文章综述了常见的几种迁移率增强技术。     

一种基于二分图最优匹配的镜头检索方法

镜头检索是基于内容的视频检索的重要内容.本文首次尝试将二分图的最优匹配用于镜头检索.与现有方法相比,本文提出的方法强调在一一对应的前提下,全面客观地度量两个镜头的相似度.把两个镜头的相似度度量建模为一个带权的二分图:镜头中的每一帧看成二分图的一个结点,两个镜头之间任意帧的相似值作为边的权值.在一一对应的前提下,利用最优匹配的Kuhn-Munkres算法求出该二分图的最大权,以此作为两个镜头的相似度.考虑到检索速度问题,提出了两个改进算法.实验对比结果证实了本文所提方法在镜头检索中的优异表现.     

Control of the Oxygen and Cobalt Atoms Diffusion through Co Nanoparticles Differing by Their Crystalline Structure and Size

The size‐dependent Kirkendall effect is studied by using Co nanoparticles. The sizes of Co nanoparticles differing by their crystal structures called nanocrystallinity, namely amorphous, polycrystalline fcc, single crystalline hcp, and single crystalline ε phase, are modulated from 4 to 10 nm. The nanoparticles self‐assembled in 2D superlattices and differing by their nanocrystallinities are subjected to oxygen at 200 °C for 10 min. With single‐domain nanocrystals differing by their crystalline structure (ε and hcp phases), marked changes in the final structures are observed: upon increasing the nanocrystal size, the ε phase favors formation of a hollow structure whereas a transition from single‐domain hollow to multidomain core/shell structures takes place with the hcp phase. With polycrystalline fcc Co nanocrystals, a transition from a hollow to a yolk/shell structure is observed, whereas with amorphous cobalt, solid CoO nanoparticles are produced at the smaller size and are converted to the core/shell structure at the larger one. These differences in size effect are attributed to the change in the control of the inward flow of oxygen atoms and the outward flow of Co atoms with the crystalline structure of cobalt nanoparticles. Such a diffusion process described here on the Kirkendall effect can be studied for other metal nanocrystals.     

Enhancement of Phosphorescence by Surface‐Plasmon Resonances in Colloidal Metal Nanoparticles: The Role of Aggregates

The spectroscopic and near‐field scanning optical microscopy (NSOM) studies of phosphorescent films doped with colloidal gold nanoparticles (NPs) are presented. Films with a high concentration of 2,3,7,8,12,13,17,18‐octaethyl‐21H,23H‐porphine platinum(II ) dispersed in a neutral polymer poly[(methyl methacrylate)‐co‐(ethyl acrylate)] demonstrate a twofold increase of the phosphorescence quantum yield after the addition of aggregated NPs. In materials doped with unaggregated particles, a decrease of the emission yield is observed. Theoretical modeling of the phosphorescence transients suggests a minimization of the triplet–triplet quenching owing to the presence of fast processes that decrease the concentration of chromophores in the excited state and may be both of radiative and non‐radiative origin. NSOM examination of the films reveals increased light emission around large NP clusters. This observation demonstrates significant enhancement of the spontaneous emission rates by the large aggregates, although unaggregated NPs introduce mostly phosphorescence quenching sites.