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Number series of atoms, interatomic bonds and interface bonds defining zinc-blende nanocrystals as function of size, shape and surface orientation: Analytic tools to interpret solid state spectroscopy data
摘要： Semiconductor nanocrystals (NCs) experience stress and charge transfer by embedding materials or ligands and impurity atoms. In return, the environment of NCs experiences a NC stress response which may lead to matrix deformation and propagated strain. Up to now, there is no universal gauge to evaluate the stress impact on NCs and their response as a function of NC size dNC. I deduce geometrical number series as analytical tools to obtain the number of NC atoms NNC(dNC[i]), bonds between NC atoms Nbnd(dNC[i]) and interface bonds NIF(dNC[i]) for seven high symmetry zinc-blende (zb) NCs with low-index faceting: {001} cubes, {111} octahedra, {110} dodecahedra, {001}-{111} pyramids, {111} tetrahedra, {111}-{001} quatrodecahedra and {001}-{111} quadrodecahedra. The fundamental insights into NC structures revealed here allow for major advancements in data interpretation and understanding of zb- and diamond-lattice based nanomaterials. The analytical number series can serve as a standard procedure for stress evaluation in solid state spectroscopy due to their deterministic nature, easy use and general applicability over a wide range of spectroscopy methods as well as NC sizes, forms and materials.
关键词： solid state spectroscopy,analytical number series,semiconductor nanocrystals,zinc-blende nanocrystals,stress evaluation
更新于2025-09-04 15:30:14
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Strong Coupling of Folded Phonons with Plasmons in 6H-SiC Micro/Nanocrystals
摘要： Silicon carbide (SiC) has a large number of polytypes of which 3C-, 4H-, 6H-SiC are most common. Since different polytypes have different energy gaps and electrical properties, it is important to identify and characterize various SiC polytypes. Here, Raman scattering is performed on 6H-SiC micro/nanocrystal (MNC) films to investigate all four folded transverse optic (TO) and longitudinal optic (LO) modes. With increasing film thickness, the four folded TO modes exhibit the same frequency downshift, whereas the four folded LO modes show a gradually-reduced downshift. For the same film thickness, all the folded modes show larger frequency downshifts with decreasing MNC size. Based on plasmons on MNCs, these folded modes can be attributed to strong coupling of the folded phonons with plasmons which show different strengths for the different folded modes while changing the film thickness and MNC size. This work provides a useful technique to identify SiC polytypes from Raman scattering.
关键词： folded phonons,SiC micro/nanocrystals,plasmon–phonon coupling
更新于2025-09-04 15:30:14
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The Quantum Efficiency of Charge Transfer Competing Against Non-Exponential Processes: The Case of Electron Transfer from CdS Nanorods to Hydrogenase
摘要： Photoexcited charge transfer from semiconductor nanocrystals to charge acceptors is a key step for photon energy conversion in semiconductor nanocrystal-based light-harvesting systems. Charge transfer competes against relaxation processes within the nanocrystals, and this competition determines the quantum efficiency of charge transfer. The quantum efficiency is a critical design element in photochemistry, but in nanocrystal–acceptor systems its extraction from experimental data is complicated by sample heterogeneity and intrinsically non-exponential excited-state decay pathways. In this manuscript, we systematically explore these complexities using TA spectroscopy over a broad range of timescales to probe electron transfer from CdS nanorods to the redox enzyme hydrogenase. To analyze the experimental data, we build a model that quantifies the quantum efficiency of charge transfer in the face of competing, potentially non-exponential, relaxation processes. Our approach can be applied to calculate the efficiency of charge or energy transfer in any donor–acceptor system that exhibits non-exponential donor decay and any ensemble distribution in the number of acceptors provided that donor relaxation and charge transfer can be described as independent, parallel decay pathways. We apply this analysis to our experimental system and unveil the connections between particle morphology and quantum efficiency. Our model predicts a finite quantum efficiency even when the mean recombination time diverges, as it does in CdS nanostructures with spatially separated electron–hole pairs that recombine with power-law dynamics. We contrast our approach to the widely-used expressions for the quantum efficiency based on average lifetimes, which for our system overestimate the quantum efficiency. The approach developed here is straightforward to implement and should be applicable to a wide range of systems.
关键词： electron transfer,quantum efficiency,semiconductor nanocrystals,non-exponential processes,charge transfer,hydrogenase,CdS nanorods
更新于2025-09-04 15:30:14
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In-doped As2Se3 thin films studied by Raman and X-ray photoelectron spectroscopies
摘要： Amorphous In-doped As2Se3 films with nominal indium contents x up to 7 at. % were prepared by thermal evaporation. Atomic force microscopy studies confirm the uniform film structure with a surface roughness near 5 nm, noticeably higher than for similarly prepared undoped As2Se3 film. X-ray photoelectron spectroscopy (XPS) studies enabled the chemical composition of the films to be examined. As follows from the XPS data, the In content in the film strongly decreases with the film depth. For films with x ≥ 2 at.%, Raman features attributed to transverse and longitudinal optical phonons of InAs are revealed in the Raman spectra as an evidence for the formation of InAs nanocrystallites in the As2Se3:In film under laser illumination.
关键词： X-ray photoelectron spectroscopy,amorphous,film,Raman scattering,atomic force microscopy,semiconductor nanocrystals
更新于2025-09-04 15:30:14
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Stabilizing RbPbBr3 Perovskite Nanocrystals through Cs+ Substitution
摘要： The ABX3-type halide perovskite nanocrystals (NCs) have been a hot topic recently due to their fascinating optoelectronic properties. It has been demonstrated that A-site ion has an impact on the photophysical and chemical properties, such as optical bandgap and chemical stability. The pursuit of halide perovskite materials with diversified A-site species would deepen the understanding on the structure-property relationship of the perovskite family. Herein, we attempt to synthesis the Rb-based perovskite NCs. We discover that the partial substitution of Rb+ by Cs+ helps to stabilize the orthorhombic RbPbBr3 NCs at low temperature, which otherwise can only be obtained at high temperature. The inclusion of Cs+ into RbPbBr3 lattice results in highly photoluminescent Rb1-xCsxPbBr3 NCs. With the increasing amount of Cs+, the bandgap of Rb1-xCsxPbBr3 NCs decreases, leading to the red shift of photoluminescence peak. The Rb1-xCsxPbBr3 NCs (x=0.4) show good stability in ambient condition. This work demonstrates the high structural flexibility and tunability of halide perovskite materials through A-site cation substitution strategy and sheds light on the optimization of perovskite materials for high-performance optoelectronic devices.
关键词： halide perovskite,phase stabilization,cation substitution,RbPbBr3,nanocrystals
更新于2025-09-04 15:30:14
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Effect of Phosphine-Free Selenium Precursor Reactivity on The Optical and Vibrational properties of Colloidal CdSe Nanocrystals
摘要： Phosphine-free selenium precursor solutions have been prepared by heating at temperatures ranging from 160 °C to 240 °C and studied by means of infrared absorption spectroscopy. The colloidal CdSe nanocrystals (NCs) synthesized from all those solutions by the wet chemical method. The influence of heating temperature on the chemical reactivity of selenium precursor and its role on the optical and vibrational properties of CdSe NCs are discussed in details. Their morphology, particle size, structural, optical and vibrational properties were investigated using transmission electron microscopy, X-ray diffraction, UV-Vis, fluorescence and Raman spectroscopy, respectively.
关键词： vibrational properties,Phosphine-free selenium precursor,CdSe nanocrystals,optical properties
更新于2025-09-04 15:30:14
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Catalyst-Assisted Solution–Liquid–Solid Synthesis of CdS/CuInSe <sub/>2</sub> and CuInTe <sub/>2</sub> /CuInSe <sub/>2</sub> Nanorod Heterostructures
摘要： Axial nanowire heterostructures composed of cadmium sulfide (CdS)/copper indium diselenide (CuInSe2) and copper indium telluride (CuInTe2)/copper indium diselenide (CuInSe2) were synthesized by a solution?liquid?solid (SLS) method with the catalyzer of bismuth nanocrystals. Electron microscopy and diffraction studies show CuInTe2 and CuInSe2 segments growing along the [112] direction with a clear epitaxial interface between them. In CdS/CuInSe2 nanorod heterostructures, CuInSe2 and CdS segments grow along the [112] and [111] direction, respectively, with an obvious epitaxial interface between them. Energy-dispersive X-ray spectrometry demonstrates the alloy-free composition modulation in two nanorod heterostructures. In CuInTe2/CuInSe2 nanorod heterostructures, Te and Se are localized in CuInTe2 and CuInSe2 segments, respectively. Cu/In/Se and Cd/S are localized in the CuInSe2 and CdS sections of the CdS/CuInSe2 nanorod heterostructures. This research confirms that the SLS mechanism provides a general alternate technique to prepare multicomponent axial 1D heterostructures that have been difficult to generate by using either catalyst-free solution-phase synthesis or vapor?liquid?solid growth.
关键词： epitaxial interface,nanowire heterostructures,solution?liquid?solid (SLS) method,bismuth nanocrystals,energy-dispersive X-ray spectrometry
更新于2025-09-04 15:30:14
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Structure-Selective Synthesis of Wurtzite and Zincblende ZnS, CdS, and CuInS <sub/>2</sub> Using Nanoparticle Cation Exchange Reactions
摘要： For polymorphic solid-state systems containing multiple distinct crystal structures of the same composition, identifying rational pathways to selectively target one particular structure is an important synthetic capability. Cation exchange reactions can transform a growing library of metal chalcogenide nanocrystals into different phases by replacing the cation sublattice, often while retaining morphology and crystal structure. However, only a few examples have been demonstrated where multiple distinct phases in a polymorphic system could be selectively accessed using nanocrystal cation exchange reactions. Here, we show that roxbyite (hexagonal) and digenite (cubic) Cu2?xS nanoparticles transform upon cation exchange with Cd2+, Zn2+, and In3+ to wurtzite (hexagonal) and zincblende (cubic) CdS, ZnS, and CuInS2, respectively. These products retain the anion and cation sublattice features programmed into the copper sulfide template, and each phase forms to the exclusion of other known crystal structures. These results significantly expand the scope of structure-selective cation exchange reactions in polymorphic systems.
关键词： zincblende,cation exchange reactions,wurtzite,ZnS,metal chalcogenide nanocrystals,CdS,polymorphic solid-state systems,CuInS2
更新于2025-09-04 15:30:14
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Quantum Cutting Luminescent Solar Concentrators Using Ytterbium Doped Perovskite Nanocrystals
摘要： We introduce and demonstrate the concept of quantum-cutting luminescent solar concentrators (QC-LSCs) using Yb3+-doped perovskite nanocrystals. These NCs feature a photoluminescence quantum yield approaching 200% and virtually zero self-absorption loss of PL photons, defining a new upper limit of 150% for the internal optical efficiency (ηint) of LSCs that is almost independent of LSC sizes. An unoptimized 25 cm2 QC-LSC fabricated from Yb3+-doped CsPbCl3 NCs already displayed an ηint of 118.1±6.7% that is 2-fold higher than previous records using Mn2+-doped quantum dots (QDs). If using CsPbClxBr3-x NCs capable of absorbing ~7.6% of solar photons, the projected external optical efficiency (ηext) of QC-LSCs can exceed 10% for >100 cm2 devices which still remains a big challenge in the field. The advantage of QC-LSCs over conventional QD-LSCs becomes especially obvious with increasing LSC sizes, which is predicted to exhibit more than 4-fold efficiency enhancement in the case of window size (1 m2) devices.
关键词： Luminescent solar concentrators,Solar energy,Doped nanocrystals,Quantum cutting,Ytterbium doping
更新于2025-09-04 15:30:14
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Energy level tuning of InP/ZnS nanocrystals by electronically delocalized dithiocarbamate derivatives
摘要： The nanocrystals have characteristics of varying the energy gap between the valence band and the conduction band depending on the size, and are attracting attention as light emitting materials due to the excellent in light stability. Since the bandgap of nanocrystals is determined by the size, it is very important to control the size of the nanocrystals in order to realize the red, green and blue primary color in a display. However, there are many difficulties in finely adjusting the nanocrystal bandgap to a size. In this study, the monodentate amine ligands coordinated on the surface of InP/ZnS nanocrystals are substituted with bidentate dithiocarbamate ligands having a strong coordination ability and electrically resonant structures, so that the nanocrystal can be finely tuned to control the emission spectrum. NMR analysis showed that some amine ligands on the surface of the nanocrystals were substituted with dithiocarbamate ligands. The PL spectra also show that the emission wavelength of the new nanocrystals is increased by about 20 nm (bathochromic shift), indicating that the active region of the exciton (an electron-hole pair) is extended to the delocalized dithiocarbamate ligands as well as the nanocrystals.
关键词： dithiocarbamate ligands,bathochromic shift,Nanocrystals,InP/ZnS
更新于2025-09-04 15:30:14