- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Fragmentation of Magica??Size Cluster Precursor Compounds into Ultrasmall CdS Quantum Dots with Enhanced Particle Yield at Low Temperatures
摘要： Colloidal small-size CdS quantum dots (QDs) are produced usually with low particle yield, together with side products such as the particular precursor compounds (PCs) of magic-size clusters (MSC). Here, we report our synthesis of small-size CdS QDs without the coexistence of the PC and thus with enhanced particle yield. For a conventional reaction of cadmium oleate (Cd(OA)2) and sulfur (S) in 1-octadecene (ODE), we show that after the formation of the PC in the pre-nucleation stage, the addition of tri-n-octylphosphine oxide (TOPO) facilitates the production of small-size QDs. We demonstrate that TOPO fragmentizes the PC that have formed, which enables the nucleation and growth of small-size QDs even at room temperature. Our findings introduce a new approach to making small-size QDs without the coexistence of the PC and with improved particle yield. Providing experimental evidence for the two-pathway model proposed for the pre-nucleation stage of colloidal binary QDs, the present study aids in the advance of non-classical nucleation theory.
关键词： crystal growth,nucleation,cadmium sulfide,magic-size clusters,quantum dots
更新于2025-09-23 15:21:01
-
Fragmentation of Magica??Size Cluster Precursor Compounds into Ultrasmall CdS Quantum Dots with Enhanced Particle Yield at Low Temperatures
摘要： Colloidal small-size CdS quantum dots (QDs) are produced usually with low particle yield, together with side products such as the particular precursor compounds (PCs) of magic-size clusters (MSC). Here, we report our synthesis of small-size CdS QDs without the coexistence of the PC and thus with enhanced particle yield. For a conventional reaction of cadmium oleate (Cd(OA)2) and sulfur (S) in 1-octadecene (ODE), we show that after the formation of the PC in the pre-nucleation stage, the addition of tri-n-octylphosphine oxide (TOPO) facilitates the production of small-size QDs. We demonstrate that TOPO fragmentizes the PC that have formed, which enables the nucleation and growth of small-size QDs even at room temperature. Our findings introduce a new approach to making small-size QDs without the coexistence of the PC and with improved particle yield. Providing experimental evidence for the two-pathway model proposed for the pre-nucleation stage of colloidal binary QDs, the present study aids in the advance of non-classical nucleation theory.
关键词： crystal growth,nucleation,cadmium sulfide,magic-size clusters,quantum dots
更新于2025-09-23 15:21:01
-
Ultrafast Excited-State Dynamics of Hydrogen-Bonded Cytosine Microsolvated Clusters with Protic and Aprotic Polar Solvents
摘要： Microsolvation effects on the ultrafast excited-state deactivation dynamics of cytosine (Cy) were studied in hydrogen-bonded Cy clusters with protic and aprotic solvents using mass-resolved femtosecond pump-probe ionization spectroscopy. Two protic solvents, water (H2O) and methanol (MeOH), and one aprotic solvent, tetrahydrofuran (THF), were investigated, and transients of Cy·(H2O)1-6, Cy·(MeOH)1-3, and Cy·THF microsolvated clusters produced in supersonic expansions were measured. With the aid of electronic structure calculations, we assigned the observed dynamics to the low-energy isomers of various Cy clusters and discussed the microsolvation effect on the excited-state deactivation dynamics. With the protic solvents only the microsolvated clusters of Cy keto tautomer were observed. The observed decay time constants of Cy·(H2O)n are 0.5 ps for n=1 and ~0.2–0.25 ps for n=2–6. For Cy·(MeOH)n clusters, the decay time constant for n=1 cluster is similar to that of the Cy monohydrate, but for n=2 and 3 the decays are about a factor of two slower than the corresponding microhydrates. With the aprotic solvent, THF, hydrogen-bonded complexes of both keto and enol tautomers are present in the beam. The keto-Cy·THF shows a similar decay as the keto-Cy monomer, whereas the enol-Cy·THF exhibits a two-fold slower decay than the enol-Cy monomer, suggesting an increase in the barrier to excited-state deactivation upon binding of one THF molecule to the enol form of Cy.
关键词： Cytosine,Excited-state deactivation,Hydrogen-bonded clusters,Microsolvation,Ultrafast dynamics
更新于2025-09-23 15:21:01
-
A spectroscopic study of the globular cluster M28 (NGC 6626)
摘要： We present the abundance analysis for a sample of 17 red giant branch stars in the metal-poor globular cluster M28 based on high-resolution spectra. This is the ?rst extensive spectroscopic study of this cluster. We derive abundances of O, Na, Mg, Al, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Ba, La, Ce, and Eu. We ?nd a metallicity of [Fe/H] = ?1.29 ± 0.01 and an α-enhancement of +0.34 ± 0.01 (errors on the mean), typical of halo globular clusters in this metallicity regime. A large spread is observed in the abundances of light elements O, Na, and Al. Mg also shows an anti-correlation with Al with a signi?cance of 3σ . The cluster shows a Na–O anti-correlation and a Na–Al correlation. This correlation is not linear but ‘segmented’ and that the stars are not distributed continuously, but form at least three well-separated sub-populations. In this aspect, M28 resembles NGC 2808 that was found to host at least ?ve sub-populations. The presence of a Mg–Al anti-correlation favour massive AGB stars as the main polluters responsible for the multiple-population phenomenon.
关键词： globular clusters: individual: M28 (NGC 6626)
更新于2025-09-23 15:21:01
-
Heterometallic Cluster Coordination Polymers Assembled from Cuprous-Halide Clusters and Organotina??Oxygen Pyridinecarboxylate Clusters
摘要： By using the bifunctional ligands bearing carboxylate and N-donor groups, the precursor of nBu2SnO undergoes a transformation to yield organotin–oxygen carboxylate clusters, namely, [(nBu2Sn)4(μ3-O)2(μ2-OH)2(INA)2] (INA = isonicotinate), [(nBu2Sn)5(μ3-O)3(μ2-OH)2(INA)2] and [(nBu2Sn)4(μ3-O)2(NA)4] (NA = nicotinate), resulting in different geometric building units with two or four extension points. Such organotin–oxygen carboxylate clusters assemble with various CunIn clusters such as Cu2I2 rhomboid dimer, Cu4I4 cubic tetramer, Cu6I6 prismatic hexamer to engender various heterometallic cluster coordination polymers.
关键词： organotin–oxygen pyridinecarboxylate clusters,heterometallic cluster coordination polymers,bifunctional ligands,structural dimensions,cuprous-halide clusters
更新于2025-09-23 15:19:57
-
Controlled deposition of size-selected metal nanoclusters on prepatterned substrate
摘要： An endeavor of organizing Cu nano-particles of controlled size in ordered arrays at room temperature is reported. This involves the guided deposition of size-selected nanoparticles otherwise known as nanoclusters via periodic modulation of the substrate surface. Ultra-high vacuum compatible magnetron-based gas-aggregation type source combined with a quadrupole mass filter has been employed to produce the size-selected nanoclusters whereas the surface modulations (ripples) in the nanoscale are induced by low energy oblique angle ion beam irradiation. Morphological aspects of deposited nanoclusters and the substrates were characterized by high-resolution scanning electron microscopy (HRSEM) and atomic force microscopy (AFM). The chemical composition of the deposited nanoclusters was characterized by x-ray photoelectron spectroscopy. The alignment of size-selected metal nanoclusters along the substrate-patterns is observed. Depending upon deposition conditions quality of the organization varies. The optimum angle of deposition for the improved alignment depends on the pattern parameters of the substrate.
关键词： Ion sputtering,Room-temperature organization,Metal nanocluster,Patterned substrate,Supported clusters,Scanning Electron Microscopy
更新于2025-09-23 15:19:57
-
Inorganic molecule-induced electron transfer complex for highly efficient organic solar cells
摘要： Interfacial engineering of electrode modification has been proved to be an effective approach for improving the power conversion efficiency (PCE) of organic solar cells (OSCs). However, compared to the advance in active layer, the study of interfacial modification is seriously lagging behind and the contribution of electrode modification to the PCE enhancement is marginalized. Herein, we synthesized a series of polynuclear metal-oxo clusters (PMCs) with gradually varied chemical composition and photoelectronic properties, by which an efficient and stable hole extraction layer was developed to enhance OSC efficiencies. The PCE of the OSC modified by PMC-4 was improved from 15.7% to 16.3% as compared to the PEDOT:PSS device. Moreover, PMC-4 can be fabricated through solution processing without any post-treatment, and the corresponding device shows improved long-term stability. As revealed for the first time, the strong oxidizing property of PMC can induce the formation of inorganic-organic electron transfer complex with a barrier-free interface for efficient hole extraction. Furthermore, experimental data and theoretical calculation results reveal that the molecular polarization of mixed-addenda PMCs can enhance the capacitance at the AIL/active layer interfaces. As a result, the mixed-addenda PMCs can be processed by blade-coating to make a large-area OSC of 1 cm2, and a certified PCE of 14.3% was achieved.
关键词： power conversion efficiency,hole extraction layer,polynuclear metal-oxo clusters,organic solar cells,interfacial engineering
更新于2025-09-23 15:19:57
-
Zinc Oxo Clusters Improve the Optoelectronic Properties on Indium Phosphide Quantum Dots
摘要： This study explored the effect of zinc precursors on the optical properties of InP quantum dots (QDs) by controlling the reactivity of zinc carboxylates via a simple thermal treatment. The formation of zinc oxo clusters, Zn4O(oleate)6 and Zn7O2(oleate)10, during the thermal decomposition of zinc oleate was confirmed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. By using the zinc oxo clusters as reaction precursors, high-quality InP QDs with high photoluminescence quantum yield (PLQY) and narrow full width at half maximum (FWHM) were synthesized. (Green QDs: PLQY=95%, FWHM=37 nm. Red QDs: PLQY=84%, FWHM=40 nm) The analysis results showed that the improved optoelectronic properties were achieved by two important functions of the zinc oxo clusters: 1) suppressing the rapid depletion of the highly reactive phosphorus source and inducing size uniformity of the In(Zn)P core, and 2) facilitating the formation of an oxidized buffer layer, which effectively controls defects. Likewise, the use of reactivity-controlled species is an effective strategy for the synthesis of well-designed QDs.
关键词： full width at half maximum,InP quantum dots,optoelectronic properties,photoluminescence quantum yield,zinc oxo clusters
更新于2025-09-23 15:19:57
-
Early Low-mass Galaxies and Star-cluster Candidates at <i>z</i> a?? 6a??9 Identified by the Gravitational-lensing Technique and Deep Optical/Near-infrared Imaging
摘要： We present very faint dropout galaxies at z～6?9 with a stellar mass M? down to that are found in deep optical/near-infrared (NIR) images of the full data sets of the Hubble Frontier Fields (HFF) program in conjunction with deep ground-based and Spitzer images and gravitational-lensing magnification effects. We investigate stellar populations of the HFF dropout galaxies with the optical/NIR photometry and BEAGLE models made of self-consistent stellar population synthesis and photoionization models, carefully including strong nebular emission impacting on the photometry. Our best-estimate M?–MUV function is comparable to a model of star formation duration time of 100 Myr that is assumed in Bouwens et al. We derive the galaxy stellar mass functions (GSMFs) at z～6–9 that agree with those obtained by previous studies at M106. Estimating the stellar mass densities r? with the GSMFs, we find a very slow evolution from z～9 to z～6–7, which is consistent with the one estimated from star formation rate density measurements. In conjunction with the estimates of the galaxy effective radii Re on the source plane, we have pinpointed four objects with low stellar masses (M107) and very compact morphologies (Re?40 pc) that are comparable with those of globular clusters (GCs) in the Milky Way today. These objects are candidates of star clusters, some of which may be related to GCs today.
关键词： High-redshift galaxies,Galaxy formation,Stellar mass functions,Globular star clusters,Strong gravitational lensing
更新于2025-09-23 15:19:57
-
[IEEE 2018 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - Saint Petersburg, Russia (2018.10.22-2018.10.23)] 2018 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - Porous Silicon as a Material for Nanocomposites and the Effect of its Parameters on the Morphology of Silver Clusters
摘要： On the example of the por-Si/Ag composites it is demonstrated the ability to control the morphology of the guest material (Ag) by changing the parameters of the porous media (por-Si). Two groups of key parameters of porous materials important for creating composites based on them are discussed. Porous silicon was obtained by electrochemical anodic etching. The introducing Ag into the pores was performed by the cathodic electrochemical deposition. It is observed the increasing the anodizing time is leads to the noticeably changes of wetting angle of por-Si, and, in turn, significantly affects the morphology of Ag clusters. The growth mechanisms of Ag clusters on the por-Si surface and the fields of its potential application are discussed.
关键词： porous texture,surface properties,porous silicon composites,por-Si/Ag composites,electrochemical deposition,surface functionality,silver clusters
更新于2025-09-23 15:19:57