The multiexciton optical gain that stems from the multiple degeneracies of quantum dot (QD) band-edge states, along with the rapid multiexciton Auger recombination, results in a high lasing threshold for colloidal QD lasers, limiting their practical applications. In this article, we propose an approach to achieving a "zerothreshold" optical gain by controlling doping concentration via the QD size. By using Ag2Se, HgSe, and HgS QDs, zero-threshold optical gain was achieved across most wavelengths in the near-infrared and short-wave infrared regions. We established kinetic equations to describe a coupled QD-light-field system, which consists of QDs with varying doping concentrations. Based on this, we calculated the lasing thresholds for the three types of QDs with specific diameters. The results show that by significantly suppressing Auger recombination with the core/alloy/shell structure, pulsed lasing with an average QD occupancy threshold of approximately 0.17, and continuous-wave lasing with a threshold pump intensity of approximately 0.5 kW cm-2 can be achieved. This work presents an air-stable approach to realize "zero-threshold" optical gain and develops a theoretical model to confirm the feasibility of this approach.

Revealing the surface effect of nanoparticles (NPs) is one of the key prerequisites for understanding their extraordinary properties at the nanometer scale. However, active NPs frequently suffer from surface oxidation and contamination, which hinders the realization of their delicate surface-related properties. Upon this issue, this paper develops an in situ evaporation and deposition (in-E&D) method inside a transmission electron microscope (TEM), by which NPs with ultra-clean surfaces can be controllably fabricated and examined. More than 12 types of materials, including Mg, Al, Cr, Mn, Ni, Cu, Zn, Ge, Ag, Sb, Pb, Bi, etc., have been demonstratively verified, and diverse NPs/nanorods have been obtained with featured structures, shapes, phases, etc. It is found that the electron beam-induced thermal effect and the vapor pressure of the precursor material are two decisive parameters for this in-E&D method. With appropriate settings, NP size, number density, and distribution can be designedly modulated. With alloyed/mixed precursors, the in-E&D method can be extended to fabricate binary and even more complex NPs in demand. It provides an effective chance to uncover the property and behavior of delicate NPs which are sensitive and prone to contamination during sample transfer.

Metal nanoparticles have attracted a great deal of interest due to their unique properties of surface plasmon resonance. Metal nanoparticles can enhance the fluorescence emission intensity of quantum dots (QDs) through the local surface plasmon resonance effect, which is mainly determined by the distance between them. Therefore, it is very important to achieve controllable distance between metal and QDs, and study fluorescence enhancement. In this work, the controllable adjustment of the distance between metal nanoparticles and QDs was successfully realized by controlling the thickness of the SiO2 shell of Ag@SiO2 nanoparticles. Firstly, Ag nanoparticles with uniform size distribution and relatively high concentration were prepared, and then the thickness of the SiO2 shell was controlled by controlling the amount of tetra-ethyl orthosilicate (TEOS) in the hydrolysis of TEOS reaction. (3-aminopropyl) triethoxysilane (APS) was used to connect CdS/ZnS QDs with Ag@SiO2 nanoparticles to form Ag@SiO2@CdS/ZnS QD composite nanoparticles. The fluorescence spectra shows that the fluorescence intensity of the Ag@SiO2@CdS/ZnS QD composite nanoparticles is significantly enhanced. Photoexcitation spectra and fluorescence spectra of CdS/ZnS QD and Ag@SiO2@CdS/ZnS QD composite nanoparticles, measured under different energy excitation conditions, indicate that the existence of Ag nanoparticles can enhance the fluorescence intensity of CdS/ZnS QDs. Finally, a further physical mechanism of fluorescence enhancement is revealed.

The development of colloidal near-infrared quantum dot (QD) lasers has been hindered by the high state degeneracy of lead salt QDs and the difficulty in coupling colloidal QDs to the resonant cavity. In this study, we show that the above challenges can be addressed by the self-assembly laser based on Ag2Se QDs. The Ag2Se QDs with the lowest quantized states 2-fold degeneracy are used to replace lead salt quantum dots to achieve low threshold near-infrared optical gain. We employ the finite element method to in depth analyze the mode field distribution and oscillation mechanism of the coffee-ring microcavity. Our results reveal that the light field oscillates in a zig-zag path along the cross-sectional area, indicating strong coupling between the QDs and the cavity mode. Furthermore, we investigate the relationship of cavity length with free spectrum range and laser emission wavelength. Using this relationship and the gain spectrum characteristics of Ag2Se QDs, we design a single-mode near-infrared laser and conduct a comprehensive analysis. The simulation results are used to fabricate a single-mode near-infrared Ag2Se QD coffee-ring microlaser, which exhibits a linewidth of 0.3 nm and a threshold of 158 μJ/cm2. Currently, it holds the record for the lowest laser threshold among near-infrared colloidal QD lasers. The increasing of the laser cavity length leads the emission wavelength to increase from 1300 nm to 1323 nm. In addition, the toxicity of Ag2Se QD is remarkably negligible. Our work promotes the development of environment-friendly near-infrared lasers toward practical lasers.

Colloidal semiconductor nanocrystals have attracted widespread attention due to their tremendous electrical and optical properties. Nanoparticles exhibit a strong tendency to aggregate and sinter in a short period of time during processing or use due to their large surface area-to-volume ratio, which may lead to significant changes in their required performance. Therefore, it is of great significance to conduct in-depth research on the sintering process and mechanism of nanoparticles to maintain their stability. Here, the sintering process of CdSe/CdS core/shell nanocrystals under continuous electron beam irradiation was studied using in situ transmission electron microscopy (TEM). In the early stages of sintering, CdSe/CdS nanocrystals approached each other at a distance of approximately 1–2 nm. As the exposure time to the electron beam increased, the movement of surface atoms on the nanocrystals led to contact between them. Subsequently, the atoms on the contact surfaces underwent rapid motion, resulting in the rapid formation of the neck between the particles. The neck formation between adjacent particles provides strong evidence of a sintering mechanism dominated by surface atom diffusion rather than Ostwald ripening. Further research in this area could lead to the development of improved methods to prevent sintering and enhance the stability of nanocrystals, ultimately contributing to the advancement of nanomaterial-based devices and materials with long-lasting performance.

Metal nanocrystals have been shown to present two sorts of antithetical mechanical behaviors during mechanical tests, that is, "smaller is stronger" and "smaller is weaker". Dislocation-starvation induced strengthening and surface diffusion induced softening are revealed as two main mechanisms that govern such behaviors. However, the competition between these two mechanisms, as well as their relationship with temperature, is still unclear. To probe into this issue, we here perform an investigation on sub-20-nm Au and Co nanocrystals using an electrical loading-coupled transmission electron microscopy, as the electrical loading can create an adjustable local heating effect, providing variable conditions for testing temperature-related competitions between displacive and diffusional events. It is found that surface diffusion is much more sensitive to temperature than dislocation activities. Apparent transitions of deformation mechanisms are observed when surface diffusion is energetically activated or inhibited. Surface curvature acts as a stimulus or mediator to atom diffusion, generating double-edged impacts on the nucleation of dislocation slip. At elevated temperatures (i.e. high electrical loading), the metal nanocrystals present liquid-like behaviors. Their surfaces can consecutively reshape when surface diffusion dominates; otherwise, shape transformations take place in a collapse-and-reconstruction manner.

To achieve high-sensitivity two-photon absorption (2PA) optical limiters and stabilizers, two-photon active materials need to have large 2PA cross-sections. Phase-pure wurtzite (WZ) CdSe/CdS core/shell quantum dots (QDs) with a shell thickness of 11 CdS monolayers were prepared by a high-temperature pyrolysis method, which possess a large volume and nearly defect-free core/shell interfaces. The 2PA cross-section of QDs is measured to be as large as 1.5 × 105 GM by the nonlinear transmittance method. Due to the large 2PA cross-section of phase-pure thick-shell WZ CdSe/CdS core/shell QDs, we successfully explored their application in the field of optical limiting and stabilization. Finally, we successfully fabricated a high-sensitivity optical stabilizer made of a polymer (polymethylmethacrylate) matrix comprising phase-pure thick-shell WZ CdSe/CdS core/shell QDs, which can reduce the amplitude fluctuation by ∼67%. In addition, the device reduces the input energy by ∼40%, indicating that the device can also be applied as an optical limiter. This work promotes the application of optical limiters and stabilizers based on QDs in practical work to a certain extent.

Efficient Auger recombination (AR) presents a significant challenge for the advancement of colloidal quantum dot (QD)-based devices involving multiexcitons. Here, the AR dynamics of near-infrared Ag2Se QDs were studied through transient absorption experiments. As the QD radius increases from 0.9 to 2.5 nm, the biexciton lifetime (τ2) of Ag2Se QDs increases from 35 to 736 ps, which is approximately 10 times longer than that of comparable-sized CdSe and PbSe QDs. A qualitative analysis based on observables indicates that the slow Auger rate is primarily attributed to the low density of the final states. The biexciton lifetime and triexciton lifetime (τ3) of Ag2Se QDs follow R3 and R2.6 dependence, respectively. Moreover, the ratio of τ2/τ3 is ∼2.3-3.2, which is markedly lower than the value expected from statistical scaling (4.5). These findings suggest that environmentally friendly Ag2Se QDs can serve as excellent candidates for low-threshold lasers and third-generation photovoltaics utilizing carrier multiplication.

Regarding the interpretable techniques in the field of image recognition, Grad-CAM is widely used for feature localization in images to reflect the logical decision-making information behind the neural network due to its high applicability. However, extensive experimentation on a customized dataset revealed that the deep convolutional neural network (CNN) model based on Gradient-weighted Class Activation Mapping (Grad-CAM) technology cannot effectively resist the interference of large-scale noise. In this article, an optimization of the deep CNN model was proposed by incorporating the Dropkey and Dropout (as a comparison) algorithm. Compared with Grad-CAM, the improved Grad-CAM based on Dropkey applies an attention mechanism to the feature map before calculating the gradient, which can introduce randomness and eliminate some areas by applying a mask to the attention score. Experimental results show that the optimized Grad-CAM deep CNN model based on the Dropkey algorithm can effectively resist large-scale noise interference and achieve accurate localization of image features. For instance, under the interference of a noise variance of 0.6, the Dropkey-enhanced ResNet50 model achieves a confidence level of 0.878 in predicting results, while the other two models exhibit confidence levels of 0.766 and 0.481, respectively. Moreover, it exhibits excellent performance in visualizing tasks related to image features such as distortion, low contrast, and small object characteristics. Furthermore, it has promising prospects in practical computer vision applications. For instance, in the field of autonomous driving, it can assist in verifying whether deep learning models accurately understand and process crucial objects, road signs, pedestrians, or other elements in the environment.

Colloidal semiconductor nanocrystals have attracted widespread attention due to their tremendous electrical and optical properties. Nanoparticles exhibit a strong tendency to aggregate and sinter in a short period of time during processing or use due to their large surface area-to-volume ratio, which may lead to significant changes in their required performance. Therefore, it is of great significance to conduct in-depth research on the sintering process and mechanism of nanoparticles to maintain their stability. Here, the sintering process of CdSe/CdS core/shell nanocrystals under continuous electron beam irradiation was studied using in situ transmission electron microscopy (TEM). In the early stages of sintering, CdSe/CdS nanocrystals approached each other at a distance of approximately 1-2 nm. As the exposure time to the electron beam increased, the movement of surface atoms on the nanocrystals led to contact between them. Subsequently, the atoms on the contact surfaces underwent rapid motion, resulting in the rapid formation of the neck between the particles. The neck formation between adjacent particles provides strong evidence of a sintering mechanism dominated by surface atom diffusion rather than Ostwald ripening. Further research in this area could lead to the development of improved methods to prevent sintering and enhance the stability of nanocrystals, ultimately contributing to the advancement of nanomaterial-based devices and materials with long-lasting performance.

针对自整角机伺服系统的控制问题,提出将粒子群优化算法应用于模糊控制当中,以改良伺服系统的控制性能.系统将粒子群优化得到的比例因子与量化因子送入模糊控制中的模糊化与反模糊化环节动态调节控制系统的权重因子,再由控制系统调节自整角机的伺服系统.在Matlab/Simulink环境中进行系统的仿真实验测试,试验结果表明:粒子群模糊PID控制系统的超调量仅有3.4％,调节时间为3.945 s.在针对自整角机伺服系统的实验中粒子群模糊PID控制器展现了良好的动态性能,收敛速度快,控制精度高,适应性更强,抗干扰能力强,且在角度跟踪问题上具有良好的跟踪特性,对实际的自整角机伺服系统设计具有参考意义.

把思想政治教育融入专业课程,贯穿于教育的各个环节,培育时代新人是一项非常重要的工作.由于实践教学开展方式的特殊性,理论课程课程思政教育的方式方法,在实践类课程中并不完全适用.以光学课程设计为例,对实践教学课程思政的教学目标、整体思路、重大举措和推进步骤等进行探索,挖掘凝练思政元素并合理设置课程思政融入点,提升学生的综合素质,真正实现全员、全过程、全方位立体化育人,构建全课程育人格局.

Exploring the temperature-dependent photoluminescence (PL) properties of quantum dots (QDs) is not only important for understanding the carrier recombination processes in QD-based devices but also critical for expanding their special applications at different temperatures. However, there is still no clear understanding of the optical properties of CdS/ZnS core/shell QDs as a function of temperature. Herein, the temperature-dependent PL spectra of CdS/ZnS core/shell QDs were studied in the temperature range of 77–297 K. It was found that the band-edge emission (BEE) intensity decreases continuously with increasing temperature, while the surface-state emission (SSE) intensity first increases and then decreases. For BEE intensity, in the low temperature range, a small activation energy (29.5 meV) in the nonradiative recombination process led to the decrease of PL intensity of CdS/ZnS core/shell QDs; and at high temperature the PL intensity attenuation was caused by the thermal escape process. On the other hand, the temperature-dependent variation trend of the SSE intensity was determined by the competition of the trapping process of the surface trap states and the effect of thermally activated non-radiative defects. As the temperature increased, the PL spectra showed a certain degree of redshift in the peak energies of both band-edge and surface states and the PL spectrum full width at half-maximum (FWHM) increases, which was mainly due to the coupling of exciton and acoustic phonon. Furthermore, the CIE chromaticity coordinates turned from (0.190, 0.102) to (0.302, 0.194), which changed dramatically with temperature. The results indicated that the CdS/ZnS core/shell QDs are expected to be applied in temperature sensors.

Electron beam irradiation has become a powerful tool for designing material structures and studying nanostructure growth down to the individual nanoparticle (NP) level; the method has important fundamental research implications and potential technological applications. However, controlling NP growth under high-energy bombardment is challenging owing to the rapid and unconstrained evolution of NPs during nanofabrication. Herein, a real-time in situ study of epitaxial regrowth of partially sublimated NPs was performed using an FEI Titan 80-300 transmission electron microscope operated at 300 kV. Hybrid NPs containing Ag, Cu, and CuAg with particle sizes of 2-20 nm were obtained via electron beam irradiation of large (35 nm) CuAg NPs at 500 degrees C. NPs sublimed with increased temperature. Interestingly, domain-confined layer-by-layer epitaxial regrowth on the Ag{111} and {100} facets was observed for partially sublimated NPs. The newly grown part was mostly Ag, as determined using energy-dispersive X-ray spectroscopy. Electron beam irradiation was a key activator for epitaxial regrowth. This study provides real-time regrowth dynamics information at an atomic level, providing new insights into nanostructure growth control in gaseous environments, finding promising applications in nanofabrication.

为更好地解决四旋翼飞行器的控制精度问题,提出将粒子群算法与模糊PID相结合的方法应用于四旋翼飞行器控制.首先由粒子群优化算法得到量化因子与比例因子,然后通过模糊化与反模糊处理动态调节权重因子,最后通过在Matlab/Simulink平台中对系统进行飞行控制仿真以及抗扰性测试.仿真结果表明,传统PID控制超调量为6.88％,模糊PID控制超调量为4.16％,而粒子群模糊PID控制可以做到基本无超调且调节时间仅有0.954 s,粒子群模糊PID控制器收敛速度更快、精确度更高、适应性更强、稳定性更高,对实际的四旋翼飞行器控制设计工作具有参考价值.

With the growing demand for developing lasers with high stability and integration, temperature-insensitive gain materials are highly desirable. Here, temperature-insensitive near-infrared (NIR) optical gain from low-toxicity Ag2Se quantum dots (QDs) is reported. Due to the large energy splitting between the band-edge hole state and the following state (∼430 meV), the thermal depopulation of the band-edge hole state in Ag2Se QDs is significantly suppressed. The long biexciton lifetime (245 ps at 300 K) of the QDs is sufficient to support the establishment of amplified spontaneous emission (ASE). Consequently, the characteristic temperature of the ASE threshold for the Ag2Se QD film is as high as 360 K, and efficient NIR ASE is observed up to 340 K. In addition, when the temperature is lower than 200 K, the ASE peak position is temperature insensitive because acoustic phonons cannot be effectively excited. Our findings reveal that Ag2Se QDs can be utilized as an excellent gain material for environmentally friendly temperature-insensitive NIR lasers.

Controlling the shape, morphology, and porosity of hollow nanostructures is a pivotal issue for adjusting the characteristics of tailor-made nanomaterials to expand their application to more fields. Although many hollow metal oxides have been developed, studies on the construction of hollow bimetal oxide heterostructures with controllable nanocavities in different morphologies and high crystallinity through Kirkendall effect is still ascendant. Using this strategy, nickel nanotubes with smooth walls and nickel oxide nanotubes containing periodic copper nanoparticles were acquired through continuous oxidation treatments on CuNi nanowires at 25 °C and 200 °C, respectively. Oxidation treatment at high temperature (300 °C) on CuNi nanowires produced nickel oxide nanotubes with a bamboo-like structure and nanoforests. In addition, thin CuO nanowires with diameters of 5–10 nm grew on nanowires at 400 °C. Finally, the mechanisms of sculpting nanocavities at high and low temperatures were elucidated. An in-depth understanding of the thermally stimulated Kirkendall effect in bimetals has a significant influence on the design and fabrication of new hollow multifunctional hetero-nanostructures with potential applications in energy storage, catalysis, and gas sensing.

Temperature sensors are widely used in important fields such as daily home, medical care, and aerospace as a commonly used device for measuring temperature. Traditional temperature sensors such as thermocouples, thermal resistances, and infrared sensors are technically mature; however, they have limitations in the application environment, temperature measurement range, and temperature measurement accuracy. An eye-resolvable surface plasmon-enhanced fluorescence temperature sensor based on dual-emission Ag@SiO2@CdS/ZnS composite nanoparticle film with multiple-parameter detectable signals and high response sensitivity was proposed in this work. The temperature sensor’s x-chromaticity coordinate varied from 0.299 to 0.358 in the range of 77–297 K, while the y-chromaticity coordinate varied from 0.288 to 0.440, displaying eye-resolvable surface plasmon-enhanced fluorescence. The ratiometric response of two isolated photoluminescence (PL) peak-integrated areas located around 446 and 592 nm was found to be significantly temperature dependent, with a thermal sensitivity of 1.4% K−1, which can be used as an additional parameter to measure the precise temperature. Furthermore, the surface state emission peak intensity was linearly related to temperature, with a correlation index Adj. R-Square of 99.8%. Multiple independent temperature estimates can help with self-calibration and improve the measurement accuracy. Our findings show that the designed sensors can detect low temperatures while maintaining stability and reproducibility.

Bimetallic Janus nanostructures (JNs) have attracted much interest because of their promising potential applications induced by unique interface effects, especially in catalysis. Catalytic stability acts a role as significant as catalytic efficiency in the potential applications of catalysts. However, the response of bi -metallic JNs to high temperature has been poorly investigated due to their complex structure and sub-limation kinetics. Herein, the thermal stability and sublimation mechanisms of CuAg JNs are studied through in situ annealing experiments performed in an aberration-corrected FEI Titan 80-300 transmission electron microscope operated at 300 kV. It is proven that CuAg JNs begin to sublimate until the temperature increases to 800 degrees C, although Ag nanostructures can always begin to sublimate at temperatures as low as 500 degrees C. Interestingly, Cu and Ag atoms sublimate simultaneously with a molar ratio likely to preserve at approximately 1 because Cu partially dissolves into the Ag phase at higher temperatures. Furthermore, a rational atomic motion mechanism is proposed to explain the phase transition in which the solid solution forms and the whole special sublimation process. These in situ observations promise to be helpful for understanding the evolutionary behaviors of bimetallic JNs under high temperatures arising in catalytic processes and other applications. (c) 2021 Published by Elsevier B.V.

Beam-induced heating effect on nanoscale samples is a crucial question as it strongly influences the interpretation of observed unusual behaviors. This question is currently under debate without a convincing conclusion. Here, using silver nitride (Ag 3 N) nanoparticles as temperature labels, we perform an investigation on this heating effect inside a transmission electron microscope (TEM) under normal imaging conditions. Combined with experimental measurements and semi-quantitative calculations, a temperature increase of more than 100 K is estimated and confirmed in the graphite carbon nitride (g-C 3 N 4 ) films. Strong temperature gradients are found to exist in the single-end fixed g-C 3 N 4 films. The influencing factors of heat accumulation are also investigated and discussed. Findings in this paper may shed some light on the understanding of the abnormal behaviors of nano-objects observed inside TEM.