Catálogo de publicaciones - revistas

<jats:p>The methylammonium lead triiodide (CH<jats:sub>3</jats:sub>NH<jats:sub>3</jats:sub>PbI<jats:sub>3</jats:sub>)-based perovskite shows a great alluring prospect in areas of solar cells, lasers, photodetectors, and light emitting diodes owing to their excellent optical and electrical advantages. However, it is very sensitive to the surrounding oxygen and moisture, which limits its development seriously. It is urgent to spare no effort to enhance its optical and electrical stability for further application. In this paper, we synthesize the MAPbI<jats:sub>3</jats:sub> perovskite film on the glass substrate with/without the ionic liquid (IL) of 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIMBF<jats:sub>4</jats:sub>) by a simple two-step sequential solution method. The additive of BMIMBF<jats:sub>4</jats:sub> can improve the quality of crystal structure. Moreover, the photo-luminescence (PL) intensity of MAPbI<jats:sub>3</jats:sub> film with BMIMBF<jats:sub>4</jats:sub> is much stronger than the pure MAPbI<jats:sub>3</jats:sub> film after a week in the air, which is almost ten-fold of the pure one. Meanwhile, under the illumination of 405-nm continuous wave (CW) laser, the fluorescent duration of the MAPbI<jats:sub>3</jats:sub> film with BMIMBF<jats:sub>4</jats:sub> is approximately 2.75 min, while the pure MAPbI<jats:sub>3</jats:sub> film is only about 6 s. In fact, ionic liquid of BMIMBF<jats:sub>4</jats:sub> in the perovskite film plays a role of passivation, which prevents the dissolution of MAPbI<jats:sub>3</jats:sub> into CH<jats:sub>3</jats:sub>NH<jats:sub>3</jats:sub> and PbI<jats:sub>2</jats:sub> and thus enhances the stability of environment. In addition, the ionic liquid of BMIMBF<jats:sub>4</jats:sub> possesses high ionic conductivity, which accelerates the electron transport, so it is beneficial for the perovskite film in the areas of solar cells, photodetectors, and lasers. This interesting experiment provides a promising way to develop the perovskite’s further application.</jats:p>

<jats:p>For potential military applications, a flexible metamaterial absorber (MMA) working on whole K-bands with total-thickness of 3.367 mm, ultra-broadband, polarization-insensitive, and wide-angle stability is presented based on frequency-selective surface (FSS). The absorber is composed of polyvinyl chloride (PVC) layer, polyimide (PI) layer, and poly tetra fluoro ethylene (PTFE) layer, with a sandwich structure of PVC–PI–PTFE–metal plate. Periodic conductive patterns play a crucial role in the absorber, and in traditional, it is designed on the upper surface of PI layer to form <jats:italic>LC</jats:italic> resonance. Different from commonly absorber, all the patterns are located on the lower surface of the PI layer in this work, and hence the impedance matching and absorptivity are improved in this purposed absorber. The flexible absorber with patterns on lower surface of the PI layer is compared with that on upper surface of the PI layer, the difference and the reasons are explained by absorption mechanism based on equivalent circuit model, and surface current density and electric field distribution are used to analyze resonance peaks. Absorptivity is greater than 90% in a frequency range of 10.47 GHz–45.44 GHz with relative bandwidth of 125.1%, covering the whole Ku, K, Ka, and some of X, U bands, especially containing the whole K bands from 12 GHz to 40 GHz. Radar cross section (RCS) is reduced at least 10 dB in 11.48 GHz–43.87 GHz frequency ranges, and absorption remained about 90% when the incident angle changed from 0 ° to 55°. The purposed absorber is fabricated, measured, and experiment results show good agreement with theoretical analysis and numerical simulation. After bonded on outer surface of different cylinders with diameters of 200 mm and 100 mm, the absorption of MMA is approximately reduced 10% and 20% respectively, which shows good conformal character with surface of various curvatures. Due to the attractive performance on strong absorption in the whole K-bands, flexible and easy conformal, our design exhibits broad potential application in radar stealth and sensors.</jats:p>

<jats:p>The measuring of the depth profile and electrical activity of implantation impurity in the top nanometer range of silicon encounters various difficulties and limitations, though it is known to be critical in fabrication of silicon complementary metal–oxide–semiconductor (CMOS) devices. In the present work, SRIM program and photocarrier radiometry (PCR) are employed to monitor the boron implantation in industrial-grade silicon in an ultra-low implantation energy range from 0.5 keV to 5 keV. The differential PCR technique, which is improved by greatly shortening the measurement time through the simplification of reference sample, is used to investigate the effects of implantation energy on the frequency behavior of the PCR signal for ultra-shallow junction. The transport parameters and thickness of shallow junction, extracted via multi-parameter fitting the dependence of differential PCR signal on modulation frequency to the corresponding theoretical model, well explain the energy dependence of PCR signal and further quantitatively characterize the recovery degree of structure damage induced by ion implantation and the electrical activation degree of impurities. The monitoring of nm-level thickness and electronic properties exhibits high sensitivity and apparent monotonicity over the industrially relevant implantation energy range. The depth profiles of implantation boron in silicon with the typical electrical damage threshold (<jats:italic>Y</jats:italic> <jats:sub>ED</jats:sub>) of 5.3 × 10<jats:sup>15</jats:sup> cm<jats:sup>−3</jats:sup> are evaluated by the SRIM program, and the determined thickness values are consistent well with those extracted by the differential PCR. It is demonstrated that the SRIM and the PCR are both effective tools to characterize ultra-low energy ion implantation in silicon.</jats:p>

<jats:p>Gallium nitride (GaN) thin film of the nitrogen polarity (N-polar) was grown on C-plane sapphire and misoriented C-plane sapphire substrates respectively by metal-organic chemical vapor deposition (MOCVD). The misorientation angle is off-axis from C-plane toward M-plane of the substrates, and the angle is 2° and 4° respectively. The nitrogen polarity was confirmed by examining the images of the scanning electron microscope before and after the wet etching in potassium hydroxide (KOH) solution. The morphology was studied by the optical microscope and atomic force microscope. The crystalline quality was characterized by the x-ray diffraction. The lateral coherence length, the tilt angle, the vertical coherence length, and the vertical lattice-strain were acquired using the pseudo-Voigt function to fit the x-ray diffraction curves and then calculating with four empirical formulae. The lateral coherence length increases with the misorientation angle, because higher step density and shorter distance between adjacent steps can lead to larger lateral coherence length. The tilt angle increases with the misorientation angle, which means that the misoriented substrate can degrade the identity of crystal orientation of the N-polar GaN film. The vertical lattice-strain decreases with the misorientation angle. The vertical coherence length does not change a lot as the misorientation angle increases and this value of all samples is close to the nominal thickness of the N-polar GaN layer. This study helps to understand the influence of the misorientation angle of misoriented C-plane sapphire on the morphology, the crystalline quality, and the microstructure of N-polar GaN films.</jats:p>

<jats:p>The fluorescence mechanism of HBT-HBZ is investigated in this work. A fluorescent probe is used to detect HClO content in living cells and tap water, and its structure after oxidation by HClO (HBT-ClO) is discussed based on the density functional theory (DFT) and time-dependent density functional theory (TDDFT). At the same time, the influence of the probe conformation and the proton transfer site within the excited state molecule on the fluorescence mechanism are revealed. Combined with infrared vibrational spectra and atoms-in-molecules theory, the strength of intramolecular hydrogen bonds in HBT-HBZ and HBT-ClO and their isomers are demonstrated qualitatively. The relationship between the strength of intramolecular hydrogen bonds and dipole moments is discussed. The potential energy curves demonstrate the feasibility of intramolecular proton transfer. The weak fluorescence phenomenon of HBT-HBZ in solution is quantitatively explained by analyzing the frontier molecular orbital and hole electron caused by charge separation. Moreover, when strong cyan fluorescence occurs in solution, the corresponding molecular structure should be HBT-ClO(T). The influence of the intramolecular hydrogen bond formation site on the molecule as a whole is also investigated by electrostatic potential analysis.</jats:p>

<jats:p>Based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT), the effects of substituent on the excited-state intramolecular proton transfer (ESIPT) process and photophysical properties of 2-(2′-hydroxyphenyl)-4-chloromethylthiazole (HCT) are studied. The electron-donating group (CH<jats:sub>3</jats:sub>, OH) and electron-withdrawing group (CF<jats:sub>3</jats:sub>, CHO) are introduced to analyze the changes of intramolecular H-bond, the frontier molecular orbitals, the absorption/fluorescence spectra, and the energy barrier of ESIPT process. The calculation results indicate that electron-donating group strengthens the intramolecular H-bond in the S<jats:sub>1</jats:sub> state, and leads to an easier ESIPT process. The electron-withdrawing group weakens the corresponding H-bond and makes ESIPT process a little harder. Different substituents also affect the photophysical properties of HCT. The electron-withdrawing group (CF<jats:sub>3</jats:sub>, CHO) has a little effect on electronic spectra. The electron-donating group (CH<jats:sub>3</jats:sub>, OH) red-shifts both the absorption and fluorescence emission peaks of HCT, respectively, which causes the Stokes shift to increase.</jats:p>

<jats:p>Silver indium cadmium (Ag–In–Cd) control rod is widely used in pressurized water reactor nuclear power plants, and it is continuously consumed in a high neutron flux environment. The mass ratio of <jats:sup>107</jats:sup>Ag in the Ag–In–Cd control rod is 41.44%. To accurately calculate the consumption value of the control rod, a reliable neutron reaction cross section of the <jats:sup>107</jats:sup>Ag is required. Meanwhile, <jats:sup>107</jats:sup>Ag is also an important weak <jats:italic>r</jats:italic> nucleus. Thus, the cross sections for neutron induced interactions with <jats:sup>107</jats:sup>Ag are very important both in nuclear energy and nuclear astrophysics. The (n, <jats:italic>γ</jats:italic>) cross section of <jats:sup>107</jats:sup>Ag has been measured in the energy range of 1–60 eV using a back streaming white neutron beam line at China spallation neutron source. The resonance parameters are extracted by an <jats:italic>R</jats:italic>-matrix code. All the cross section of <jats:sup>107</jats:sup>Ag and resonance parameters are given in this paper as datasets. The datasets are openly available at <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://www.doi.org/10.11922/sciencedb.j00113.00010" xlink:type="simple">http://www.doi.org/10.11922/sciencedb.j00113.00010</jats:ext-link>.</jats:p>

<jats:p>Microwave ablation (MWA) is a cancer treatment method. The tumor tissue absorbs electromagnetic energy, which heats and kills it. A microwave ablation antenna plays a critical role in this process. Its radiation field must completely cover the tumor but not the healthy tissue. At present, the radiation pattern of most invasive ablation antennas is spherical. However, in the clinic, the shape of some tumors may be asymmetrical or the antenna cannot be inserted into the center of the tumor for some other reason. In order to solve these problems, a directional heating antenna for microwave ablation is proposed in this paper. The proposed antenna, operating at 2.45 GHz, consists of a monopole and a reflector. The feed is given by a substrate integrated coaxial line (SICL) and coplanar waveguide (CPW). The omnidirectional radiation field of the monopole is reflected by a reflector that is extended from the outer conductors of the SICL to form a directional radiation field. The impedance matching network is designed on SICL to match the antenna to 50 Ω. The antenna is fabricated using a mature printed circuit board (PCB). The reflection coefficient of the antenna in porcine liver tissue measured by a vector network analyzer shows good agreement with the simulations. Then, an ablation experiment in porcine liver is conducted with power of 10 W for 10 min, and the experimental results confirm the validity of the design.</jats:p>

<jats:p>The emerging perovskite solar cells have been recognized as one of the most promising new-generation photovoltaic technologies owing to their potential of high efficiency and low production cost. However, the current perovskite solar cells suffer from some obstacles such as non-radiative charge recombination, mismatched absorption, light induced degradation for the further improvement of the power conversion efficiency and operational stability towards practical application. The rare-earth elements have been recently employed to effectively overcome these drawbacks according to their unique photophysical properties. Herein, the recent progress of the application of rare-earth ions and their functions in perovskite solar cells were systematically reviewed. As it was revealed that the rare-earth ions can be coupled with both charge transport metal oxides and photosensitive perovskites to regulate the thin film formation, and the rare-earth ions are embedded either substitutionally into the crystal lattices to adjust the optoelectronic properties and phase structure, or interstitially at grain boundaries and surface for effective defect passivation. In addition, the reversible oxidation and reduction potential of rare-earth ions can prevent the reduction and oxidation of the targeted materials. Moreover, owing to the presence of numerous energetic transition orbits, the rare-earth elements can convert low-energy infrared photons or high-energy ultraviolet photons into perovskite responsive visible light, to extend spectral response range and avoid high-energy light damage. Therefore, the incorporation of rare-earth elements into the perovskite solar cells have demonstrated promising potentials to simultaneously boost the device efficiency and stability.</jats:p>

<jats:p>Graphene has high light transmittance of 97.7% and ultrafast carrier mobility, which means it has attracted widespread attention in two-dimensional materials. However, the optical absorptivity of single-layer graphene is only 2.3%, and the corresponding photoresponsivity is difficult to produce at normal light irradiation. And the low on–off ratio resulting from the zero bandgap makes it unsuitable for many electronic devices, hindering potential development. The graphene-based heterojunction composed of graphene and other materials has outstanding optical and electrical properties, which can mutually modify the defects of both the graphene and material making it then suitable for optoelectronic devices. In this review, the advantages of graphene-based heterojunctions in the enhancement of the performance of photodetectors are reviewed. Firstly, we focus on the photocurrent generation mechanism of a graphene-based heterojunction photodetector, especially photovoltaic, photoconduction and photogating effects. Secondly, the classification of graphene-based heterojunctions in different directions is summarized. Meanwhile, the latest research progress of graphene-transition metal dichalcogenide (TMD) heterojunction photodetectors with excellent performance in graphene-based heterostructures is introduced. Finally, the difficulties faced by the existing technologies of graphene-based photodetectors are discussed, and further prospects are proposed.</jats:p>