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<i>In-Situ</i> Measurement and Control of the Fermi Level in Colloidal Nanocrystal Thin Films during Their Fabrication
摘要： In engineering a high-performance semiconductor device, understanding of the Fermi level position is critical. Here, we demonstrate that open-circuit potential (OCP) measurements can be used to quantify the Fermi level in nanocrystal thin films in-situ during their solution-based fabrication. We use this method to study the influence of (1) a metal contact and (2) nanocrystal surface termination on the Fermi level of the nanocrystal film, and find that oxidization or reduction of the nanocrystals as well as surface terminations with dipoles can be used to tune the Fermi level over large energy ranges. Finally, to emphasize the compatibility of the technique with device fabrication, we show that we can use blends of ligands to design the Fermi level landscape in a nanocrystal film. Our work highlights that OCP measurements can be used to gain insights into existing device operation and direct further optimization of optoelectronic devices.
关键词： Fermi level,nanocrystals,quantum dots,electronic structure,In-situ measurement
更新于2025-09-04 15:30:14
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Water-dispersible Copper Sulfide Nanocrystals via Ligand Exchange of 1-dodecanethiol
摘要： In colloidal Cu2-xS nanocrystal synthesis, thiols are often used as organic ligands and sulfur source, as they yield high-quality nanocrystals. However, thiol ligands on Cu2-xS nanocrystals are difficult to exchange, limiting the applications of these nanocrystals in photovoltaics, biomedical sensing and photocatalysis. Here, we present an effective and facile procedure to exchange native 1-dodecanethiol on Cu2-xS nanocrystals by 3-mercaptopropionic acid, 11-mercaptoundecanoic acid, and S2- in formamide under inert atmosphere. The product hydrophilic Cu2-xS nanocrystals have excellent colloidal stability in formamide. Furthermore, the size, shape and optical properties of the nanocrystals are not significantly affected by the ligand exchange. Water-dispersible Cu2-xS nanocrystals are easily obtained by precipitation of the nanocrystals capped by S2-, 3-mercaptopropionate or 11-mercaptoundecanoate from formamide, followed by redispersion in water. Interestingly, the ligand exchange rates for Cu2-xS nanocrystals capped with 1-dodecanethiol are observed to depend on the preparation method, being much slower for Cu2-xS nanocrystals prepared through heating-up than through hot-injection synthesis protocols. XPS studies reveal that the differences in the ligand exchange rates are due to the surface chemistry of the Cu2-xS nanocrystals, where the nanocrystals prepared via hot-injection synthesis have a less dense ligand layer due to the presence of trioctylphosphine oxide during synthesis. A model is proposed that explains the observed differences in the ligand exchange rates. The facile ligand exchange procedures reported here enable the use of high-quality colloidal Cu2-xS nanocrystals prepared in the presence of 1-dodecanethiol in various applications.
关键词： thiol ligands,surface chemistry,ligand exchange,colloidal Cu2-xS nanocrystals,water-dispersible
更新于2025-09-04 15:30:14
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Facile Synthesis and Controllable Emission of Tm <sup>3+</sup> /Er <sup>3+</sup> -Doped and -Co-doped α-NaYbF <sub/>4</sub> Upconversion Nanocrystals
摘要： Tm3+, Er3+-doped and -co-doped α-NaYbF4 nanoparticles were synthesized via a facile hydrothermal route with oleic acid as the capping agent. Experimental results showed that the doped NaYbF4 nanoparticles possessed a cubic phase with the average size of ～13 nm. Upon excitation by a 980 nm laser, the as-synthesized nanoparticles exhibited blue and red upconversion emissions corresponding to the monodoped Tm3+, Er3+ in the cubic-phase NaYbF4, respectively, and intense green and red emissions in the Tm3+/Er3+-co-doped NaYbF4 nanoparticles. Furthermore, the possible energy transfer mechanism among Yb3+/Tm3+/Er3+ in α-NaYbF4 nanoparticles was also proposed. The cell toxicity test revealed that the as-synthesized upconversion nanoparticles possessed remarkably low cytotoxicity. All of the advantageous features including facile synthesis, controllable emission, and low cytotoxicity make the upconversion nanoparticles promising for multicolor bioimaging and anti-counterfeiting applications.
关键词： anti-counterfeiting applications,multicolor bioimaging,upconversion nanocrystals,hydrothermal synthesis,energy transfer mechanism,α-NaYbF4,low cytotoxicity,Tm3+/Er3+-doped
更新于2025-09-04 15:30:14
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In situ TEM Study of the Degradation of PbSe Nanocrystals in Air
摘要： PbSe nanocrystals have attracted widespread attention due to a variety of potential applications. However, the practical utility of these nanocrystals has been hindered by their poor air stability, which induces undesired changes in the optical and electronic properties. An understanding of the degradation of PbSe nanocrystals when they are exposed to air is critical for improving the stability and enhancing their applications. Here, we use in situ transmission electron microscopy (TEM) with an environmental cell connected to air to study PbSe nanocrystal degradation triggered by air exposure. We have also conducted a series of complementary studies, including in situ environmental TEM study of PbSe nanocrystals exposed to pure oxygen, PbSe nanocrystals in H2O using a liquid cell, ex situ experiments, such as O2 plasma treatment and thermal heating of PbSe nanocrystals under different air exposure. Our in situ observations reveal that when PbSe nanocrystals are exposed to air (or oxygen) under electron beam irradiation, they experience a series of changes, including shape evolution of individual nanocrystals with the cuboid intermediates, coalescence between nanocrystals, and formation of PbSe thin films through drastic solid‐state fusion. Further studies show that the PbSe thin films transform into an amorphous Pb rich phase or eventually pure Pb, which suggest that Se reacts with oxygen and can be evaporated under electron beam illumination. These various in situ and ex situ experimental results indicate that PbSe nanocrystal degradation in air is initiated by the dissociation and removal of ligands from the PbSe nanocrystal surface.
关键词： in situ TEM,air stability,ligand removal,degradation,PbSe nanocrystals,oxygen exposure
更新于2025-09-04 15:30:14
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Selective growth of palladium nanocrystals on the (100) facets of truncated octahedral Cu <sub/>2</sub> O for UV plasmonic photocatalysis
摘要： We report Pd-based UV plasmon-enhanced photocatalysis and its hot electron effect. The selective crystalline growth of Pd nanocrystals on the (100) facets of truncated octahedral Cu2O was conducted and proved. The photocatalytic activities of Pd/Cu2O at λ = 254 nm and at λ = 365 nm respectively had ca. 18- and 10-fold enhancements due to the hot electron effect.
关键词： palladium nanocrystals,UV plasmonic photocatalysis,hot electron effect,Cu2O
更新于2025-09-04 15:30:14
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Magnetic Properties of Pure and Doped Gallium Nitride Nanocrystals
摘要： In the present paper, Ga1?xCoxN, Ga1?xNixN and Ga1?xTbxN (0 ≤ x ≤ 0.1) nanocrystals have been synthesized by a facile solvothermal method. Crystallographic characterization of synthesized materials has been done using powder X-ray diffraction technique. Recorded diffraction patterns reveal the formation of wurtzite (hexagonal) structured GaN nanocrystals. Electron microscopic studies have been carried for the detailed topographical and morphological analyses of synthesized nanomaterials. Recorded electron micrographs indicate the formation of nearly mono-disperse nanoparticles, having average size ～4 nm. Magnetic measurements of doped nanocrystals revealed ferromagnetic behavior at room temperature however pure GaN is diamagnetic at room temperature.
关键词： Crystallography,Doping,Gallium Nitride Nanocrystals,Magnetic Properties
更新于2025-09-04 15:30:14
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Electrochromic Switch Devices Mixing Small- and Large-Sized Upconverting Nanocrystals
摘要： The hasty progress in smart, portable, flexible, and transparent integrated electronics and optoelectronics is currently one of the driving forces in nanoscience and nanotechnology. A promising approach is the combination of transparent conducting electrode materials (e.g., silver nanowires, AgNWs) and upconverting nanoparticles (UCNPs). Here, electrochromic devices based on transparent nanocomposite films of poly(methyl methacrylate) and AgNWs covered by UCNPs of different sizes and compositions are developed. By combining the electrical control of the heat dissipation in AgNW networks with size-dependent thermal properties of UCNPs, tunable electrochromic transparent devices covering a broad range of the chromatic diagrams are fabricated. As illustrative examples, devices mixing large-sized (>70 nm) β-NaYF4:Yb,Ln and small-sized (<15 nm) NaGdF4:Yb,Ln@NaYF4 core@shell UCNPs (Ln = Tm, Er, Ce/Ho) are presented, permitting to monitor the temperature-dependent emission of the particles by the intensity ratio of the Er3+ 2H11/2 and 4S3/2 → 4I15/2 emission lines, while externally controlling the current flow in the AgNW network. Moreover, by defining a new thermometric parameter involving the intensity ratio of transitions of large- and small-sized UCNPs, a relative thermal sensitivity of 5.88% K?1 (at 339 K) is obtained, a sixfold improvement over the values reported so far.
关键词： electrochromic materials,upconverting nanocrystals,thermal sensitivity,transparent conducting electrode materials,silver nanowires
更新于2025-09-04 15:30:14
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[SpringerBriefs in Materials] Anisotropic Metal Chalcogenide Nanomaterials (Synthesis, Assembly, and Applications) || Synthesis and Assembly
摘要： The synthetic protocol for anisotropic MC nanocrystals has been developed based on accumulation of a largely empirical recipe, followed by inductive conclusion. Afterwards, the initial parameters are optimized to obtain the targeted nanostructures. The systematic synthetic effort is repeated and devised to inter-relate each parameter with a rational design of novel and complex MC through nanostructures. Normally, thermodynamically-controlled growth reflects the inherent symmetry of the crystal structure, hence 3D nanocrystals are readily obtained. Synthesis of nanocrystals that do not have any preferential growth direction requires purposeful shape-guiding. Reduction of the surface energy of a certain facet is a powerful way to obtain anisotropic MCs, which can be achieved by selectively attaching organic surfactants or using the organic templates as the shape-determining reactor. The MC nanocrystals can then be merged to form 1D or 2D nanostructures. Such oriented attachment can be tailored by engineering the interaction between the nanocrystals. Chemical transformation of pre-existing anisotropic nanocrystals into others has recently received a lot of interest because it allows preparation of nanocrystals that are chemically different but have the same shape and dimensions.
关键词： anisotropic MC nanocrystals,oriented attachment,shape-guiding,chemical transformation,synthetic protocol
更新于2025-09-04 15:30:14
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Controllable synthesis of transparent dispersions of monodisperse anatase-TiO2 nanoparticles and nanorods
摘要： Controllable synthesis of monodisperse nanocrystals is still a great challenge. In this study, the control strategy of alcohol medium was developed to conveniently synthesize monodisperse anatase-TiO2 nanocrystals with controllable size and shape by sol-gel method combined with solvothermal treatment. The effects of the amount of stearic acid and water, and molecular structure of alcohol on the size, the shape and the dispersity of TiO2 nanocrystals were explored. The optimum synthesis conditions were achieved. Monodisperse TiO2 nanoparticles and nanorods were obtained by using linear and branched alcohols, respectively. The size of nanoparticles decreased from 12 to 5 nm with increasing carbon number of linear alcohol. The aspect ratio of nanorods was adjusted from 1 to 5 by selecting alcohols with different locations of branched methyl group. The as-prepared monodisperse TiO2 nanocrystals could be readily dispersed in some commonly-used solvents to form transparent nanodispersions. Furthermore, a possible formation mechanism was also investigated.
关键词： Monodisperse TiO2 nanocrystals,transparent dispersion,nanoparticles,nanorods,tunable preparation
更新于2025-09-04 15:30:14
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Exploration of charge carrier delocalization in the iron oxide/CdS type-II heterojunction band alignment for enhanced solar-driven photocatalytic and antibacterial applications
摘要： Recyclable magnetic photocatalysts of iron oxide (IO)/CdS core/shell nanocrystals (CSNCs) were prepared by a facile sequential one-pot method using 3, 3'-thiobispropanoic acid (TDP) as a bridge. The CSNCs showed redshift in absorption edge, decrease in the optical band gap, reduced exciton decay rates and increment in particle size. Quenching studies have been employed to understand the position of the electron/hole wave-functions at the IO/CdS interface. Antimicrobial tests have also been performed using broth tube dilution and disc diffusion methods against S. aureus. Additionally, photocatalytic properties of IO/CdS CSNCs have been evaluated for the decomposition of xylenol blue. In comparison with CdS quantum dots (QDs) and iron oxide nanoparticles (IONPs), the IO/CdS CSNCs showed improved photocatalytic and bactericidal activities. Finally, levels of oxidative damage to proteins and lipids were evaluated.
关键词： Photocatalysis,Wave-function engineering,Advanced oxidation process,Iron oxide/CdS nanocrystals,Photocatalytic bacterial inactivation
更新于2025-09-04 15:30:14