Chiral colloidal semiconductor nanocrystals (NCs) are an emerging type of chiral materials. These chiral NCs exhibit unique quantum confinement-determined optical activity and have aroused much ...interest in the multidisciplinary fields of chemistry, physics and biology. Herein, the state-of-the-art progresses of their rational synthesis, fundamental understanding and potential application are summarized. In addition, a personal view about the future development of chiral semiconductor NCs is offered.
The unique capability of magnetic circular dichroism (MCD) in revealing geometry and electronic information has provided new opportunities in exploring the relationship between structure and ...magneto‐optical properties in nanomaterials with extraordinary optical absorption. Here, the representative studies referring to application of the MCD technique in semiconductor and noble metal nanomaterials are overviewed. MCD is powerful in elucidating the structural information of the excitonic transition in semiconductor nanocrystals, electronic transitions in noble metal nanoclusters, and plasmon resonance in noble metal nanostructures. By virtue of these advantages, the MCD technique shows its unrivalled ability in evaluating the magnetic modulation of excitonic and plasmonic optical activity of nanomaterials with varied chemical composition, geometry, assembly conformation, and coupling effect. Knowledge of the key factors in manipulating magneto‐optical properties at the nanoscale acquired with the MCD technique will largely boost the application of semiconductor and noble nanomaterials in the fields of sensing, spintronic, nanophotonics, etc.
Magnetic circular dichroism shows indispensable capability in elucidating the Zeeman splitting of the excitonic transition in semiconductor nanocrystals, the electronic information of discrete optical transitions in noble metal nanoclusters, and the geometry modulation of plasmon resonance in noble metal nanostructures. Key strategies in designing magneto‐optically active advanced nanomaterials are highlighted for potential applications in fields of sensing, spintronics, and nanophotonics.
Using 20 levels of intensity, we measured children’s thresholds to discriminate the six basic emotional expressions from neutral and their misidentification rates. Combined with the results of a ...previous study using the same method (
Journal of Experimental Child Psychology,
102 (2009) 503–521), the results indicate that by 5
years of age, children are adult-like, or nearly adult-like, for happy expressions on all measures. Children’s sensitivity to other expressions continues to improve between 5 and 10
years of age (e.g., surprise, disgust, fear) or even after 10
years of age (e.g., anger, sad). The results indicate that there is a slow development of sensitivity to the expression of all basic emotions except happy. This slow development may impact children’s social and cognitive development by limiting their sensitivity to subtle expressions of disapproval or disappointment.
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•WOx species existed as monotungstate, polytungstate and crystalline m-WO3 phase.•Addition of WOx to Pt/Al2O3 induced hydrogen spillover.•42.4% 1,3-propanediol yield was achieved over ...Pt–10WOx/Al2O3.•1,3-Propanediol yield was proportional to the concentration of Brønsted acid sites.•1,2-Propanediol yield was proportional to the concentration of Lewis acid sites.
Despite 1,3-propanediol possessing high economic value, its production from glycerol hydrogenolysis is a challenging task. Herein, a series of WOx promoted Pt/Al2O3 catalysts with various WOx contents were prepared and investigated for selective production 1,3-propanediol from glycerol hydrogenolysis. To explore the structure feature, these catalysts were fully characterized by BET, CO chemisorption, HRTEM, XRD (in situ XRD), Raman, NH3–TPD, Py–IR, H2–TPR, and XPS. Among them, Pt–10WOx/Al2O3 achieved the highest 1,3-propanediol yield up to 42.4%, which was ascribed to the large concentration of Brønsted acid sites, strong electronic interaction between Pt with WOx and hydrogen spillover. The strong correlation between 1,3-propanediol yield and Brønsted acid site indicated its essential role for the formation of 1,3-propanediol. Meanwhile the linear correlation between 1,2-propanediol yield and Lewis acid site gave direct evidence that Lewis acid site preferentially generated 1,2-propanediol.
Doping B2O3 to Cu/SiO2 catalyst significantly improved activity and long-term performance for glycerol hydrogenolysis to 1,2-propanediol. The strong correlation between 1,2-propanediol yield and Cu ...surface area gave direct evidence that Cu surface area was a key parameter for developing fundamental mechanistic insight into the performance of glycerol hydrogenolysis over Cu-based catalyst.
•B2O3 can promote the dispersion of copper species and stabilize copper particles.•Addition of B2O3 to Cu/SiO2 greatly enhanced activity and stability.•100% Conversion and 98.0% 1,2-propanediol selectivity were achieved over 3CuB/SiO2.•1,2-Propanediol yield was proportional to Cu specific surface area.•Glycerol hydrogenolysis is a structure-sensitive reaction.
Cu/SiO2 catalyst has been extensively applied in glycerol hydrogenolysis for its high selectivity to 1,2-propanediol, while suffering from severe deactivation easily. B2O3 is frequently used as an additive for stabilizing active species. Thus, a series of Cu/SiO2 catalysts with various B2O3 loadings for glycerol hydrogenolysis were prepared via precipitation-gel method followed by impregnation with boric acid. These catalysts were fully characterized by ICP, BET, XRD (in situ XRD), N2O chemisorption, H2-TPR, NH3-TPD, IR, Raman, XPS, and TEM. Addition of B2O3 to Cu/SiO2 can greatly restrain the growth of copper particles and promote the dispersion of copper species upon calcination, reduction and reaction, which resulted in the enhanced catalytic activity and stability. The optimal 3CuB/SiO2 reached complete conversion with 98.0% 1,2-propanediol selectivity. The strong correlation between 1,2-propanediol yield and Cu surface area gave direct evidence that the active Cu species were the primary active sites for glycerol hydrogenolysis.
Most previous studies investigating children’s ability to recognize facial expressions used only intense exemplars. Here we compared the sensitivity of 5-, 7-, and 10-year-olds with that of adults (
...n
=
24 per age group) for less intense expressions of happiness, sadness, and fear. The developmental patterns differed across expressions. For happiness, by 5 years of age, children were as sensitive as adults even to low intensities. For sadness, by 5 years of age, children were as accurate as adults in judging that the face was expressive (i.e., not neutral), but even at 10 years of age, children were more likely to misjudge it as fearful. For fear, children’s thresholds were not adult-like until 10 years of age, and children often confused it with sadness at 5 years of age. For all expressions, including even happy expressions, 5- and 7-year-olds were less accurate than adults in judging which of two expressions was more intense. Together, the results indicate that there is slow development of accurate decoding of subtle facial expressions.
As an emerging type of optically active materials, chiral molecules-stabilized semiconductor quantum dots (QDs) have achieved extensive attention. Unfortunately, understanding of the optical ...characteristics of chiral QDs observed by circular dichroism (CD) spectroscopy remains a great challenge due to their rather weak signals. Herein, we successfully achieve much enhanced CD responses from l- or d-cysteine-stabilized wurtzite CdSe quantum rods (QRs) thanks to their unique optical anisotropy. Furthermore, the optical activity of CdSe QRs is explored to be improved and subsequently become stable with the geometrical aspect ratio (AR) increasing, and such change matches well with alternation of the polarization factor of CdSe QRs. A non-degenerate coupled-oscillator (NDCO) model is established to elucidate the optical activity of chiral QRs, and the positive and negative natures of the CD peaks appearing at the first exciton band are clearly assigned to different transition polarization along 4p z,Se → 5sCd and 4p(x,y),Se → 5sCd, respectively. This work opens the door toward comprehension and design of optically active semiconductor nanomaterials.
Acquiring events massively from single-molecule force spectroscopy (SMFS) experiments, which is crucial for revealing important biophysical information, is usually not straightforward. A significant ...amount of human labor is usually required to identify events in the measured force spectrum during measuring or before performing further data analysis. This prevents the experiment from being done in a fully-automated manner or scaling with the throughput of the measuring setup. In this work, we attempt to tackle this problem with a deep learning approach. A deep neural network model is developed to infer the occurrence of the events using the data stream from the measuring setup. We demonstrated that the proposed method could achieve high accuracy with force spectrums of a variety of samples from both optical tweezers and AFMs by learning from user-given samples instead of complicated manual algorithm designing or parameter tuning. Furthermore, we found that the trained model can be used to perform event detection on datasets measured from a different optical tweezer setup, showing the potential of being leveraged in more complex deep learning schemes.
•This work proposed a user-friendly approach to massively locate the events of interest from experimental SMFS data streams.•To our best knowledge, this work is the first attempt to adopt deep learning methods to locate events in SMFS experiments.•It is demonstrated that the proposed method could learn to locate events for a variety of samples from different instruments including optical tweezers and AFMs.•This method could help to achieve automated measuring on SMFS high-throughput platforms or other deep-learning based SMFS signal analysis.
Nanocrystals (NCs) with identical components and sizes but different crystal structures could not be distinguished by conventional absorption and emission spectra. Herein, we find that circular ...dichroism (CD) spectroscopy can easily distinguish the CdSe nanoplatelets (NPLs) with different crystal structures of wurtzite (WZ) and zincblende (ZB) with the help of chiral l- or d-cysteine ligands. In particular, the CD signs of the first excitonic transitions in WZ and ZB NPLs capped by the same chiral cysteine are opposite. Theoretic calculation supports the viewpoint of different crystal structures and surfaces arrangements between WZ and ZB NPLs contributing to this significant phenomenon. The CD peaks appearing at the first excitonic transition band of WZ or ZB CdSe NPLs are clearly assigned to the different transition polarizations along 4p(x,y,z),Se → 5sCd or 4p(x,y),Se → 5sCd. This work not only provides a deep insight into the origin of the optical activity inside chiral semiconductor nanomaterials but also proposes the design principle of chiral semiconductor nanocrystals with high optic activity.
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