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The design of ligand‐free platinum nanoclusters (PtNCs) for the field of renewable energy is still challenging. Herein, we reported a fast synthesis of ligand‐free Pt nanoclusters (NCs) by utilizing the outer defect of a representative type of zeolitic imidazolate framework (ZIF). Structural investigation suggests a homogenous distribution of the PtNCs on the outer layer of the ZIF‐8 structure. The as‐prepared PtNCs@ZIF‐8 exhibits high catalytic activity for the hydrogen evolution reaction (HER). The extremely low overpotential with 1.4 mV, high kinetic current (specific and mass activity at 50 mV), and larger exchange current density were achieved in acidic solution, better than those of the commercial 20% Pt/C catalysts under the same condition. Furthermore, the PtNCs can be extracted from the ZIF‐8 structure to both aqueous and non‐aqueous solvent, which could be further used for other systems. These findings allow for a simple route of template‐guided NC synthesis and their release.

Bovine serum albumin (BSA)-protected AgPt bimetallic nanoparticles have been synthesized through a galvanic replacement reaction, using a silver nanoprism as a template. Synthesis was performed without the use of synthetic chemical surfactants, using proteins as a surface coating. Structural and compositional characterizations were performed using several spectroscopic and microscopic techniques. The protein-protected AgPt nanoparticles show effective pH-switchable enzyme mimicking (“nanozyme”) activity similar to catalase and peroxidase. The platinum content in the AgPt nanoparticles is playing an important role in determining the enzymatic catalysis rate of the nanoparticles. Because of their porous structure, molecular payloads such as calcein also can be incorporated into the AgPt nanoparticles, which can be released on demand by chemical triggers, such as hydrogen peroxide.

The design of perovskite oxides with improved textural properties in combination with tunable composition variations is a forward-looking strategy for the preparation of next generation catalytic converter. In the present work we report the template-free synthesis of mesoporous solid solutions of La 0.3 Sr 0.7 Ti 1-x Fe x O 3± ? (0

Tin(II)sulfide (SnS) is a well-known representative of IV–VI semiconducting materials with a layered crystal structure. SnS is of great interest due to its low toxicity and its optical and electrical properties. Here, we report on the first colloidal synthesis of hexagonally shaped single crystalline SnS nanosheets with tunable dimensions. The SnS nanosheets crystallize in the thermodynamically preferred orthorhombic α-phase. High-resolution transmission electron microscopy and electron diffraction were executed in order to determine the growth direction of these hexagonally formed nanosheets. The simple hot-injection approach comprises the injection of a sulfur-oleylamine complex into a hot solution mixture containing oleylamine, oleic acid, tin(II)chloride, and hexamethyldisilazane (HMDS). HMDS is an essential chemical for many colloidal syntheses of two-dimensional nanosheets, but its function is not well described until now. Here, we elucidate the function of HMDS as an essential additive for the form...

The formation of perovskite oxide nanoparticles supported on ordered mesoporous silica with different pore geometry is here presented. Systematic study was performed varying both pore shape (gyroidal, cylindrical, spherical) and size (7.5, 12, 17nm) of the hosts. LaFeO3, PrFeO3 and LaCoO3 were chosen as target guest structures. The distribution of the oxide nanoparticles on silica was comprehensively assessed using a multi-technique approach. It could be shown that the pore geometry plays a determining role in the conversion of the infiltrated metal nitrates to metal oxide. In particular, slow degradation kinetic was observed in highly curved pores, which fostered nucleation and crystallization of the guest species. In spherical pore systems the enhancement of pore size caused a remarkable delay of the decomposition of the metal salts, but at the same time improved the homogeneous distribution of the oxide particles in the matrix.

Advanced functional materials 2020, 1910503 - (2020). doi:10.1002/adfm.201910503, In the realm of colloidal nanostructures, with their immense capacity for shape and dimensionality control, the form is undoubtedly a driving factor for the tunability of optical and electrical properties in semiconducting or metallic materials. However, influencing the fundamental properties is still challenging and requires sophisticated surface or dimensionality manipulation. Such a modification is presented for the example of colloidal lead‐sulfide nanowires. It is shown that the electrical properties of lead sulfide nanostructures can be altered from semiconducting to metallic with indications of superconductivity, by exploiting the flexibility of the colloidal synthesis to sculpt the crystal and to form different surface facets. A particular morphology of lead sulfide nanowires is prepared through the formation of {111} surface facets, which shows metallic and superconducting properties in contrast to other forms of this semiconducting crystal, which contain other surface facets ({100} and {110}). This effect, which is investigated with several experimental and theoretical approaches, is attributed to the presence of lead‐rich {111} facets. The insights promote new strategies for tuning the properties of crystals and new applications for lead sulfide nanostructures., Published by Wiley-VCH, Weinheim

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The rise of two-dimensional (2D) graphene-cognated crystals with nonzero band gaps like transition metal dichalcogenides has led to a rapidly increasing interest in their dimensionality-dependent anisotropic properties, which bear high potential for ultrathin electronics. 2D crystals of the III–VI metal chalcogenide InSe represent a new kind of material class predestined for the use in optoelectronic applications as highly responsive photodetectors and field-effect transistors. We present a solution-processable method for 2D ultrathin InSe nanosheets (≤5 nm with ligands, lateral sizes up to ∼800 μm) with a detailed characterization of the sheet formation by a lamellar ligand templated growth. Optical and electrical transport properties, as well as in depth analysis of the crystal structure and stoichiometry of the colloidal nanosheets by electron and atomic force microscopy, X-ray photoelectron spectroscopy, and scattering methods complete this comprehensive study on a wet-chemical alternative to produce ...

The fluorescence quantum yield (QY) of CdSe dot/CdS rod (DR) nanoparticle ensembles is dependent on the Shell growth and excitation wavelength. We analyze the origin of this dependency by comparing the optical properties of DR ensembles to the results obtained in single-particle experiments. On the Ensemble level, we find that the QY of DRs with shell lengths shorter than 40 nm exhibits no dependence on the excitation wavelength, whereas for DRs with shell lengths longer than 50 nm, the QY significantly decreases for excitation above the CdS band gap. Upon excitation in the CdSe core, the ensemble QY, the fluorescence wavelength, and the fluorescence blinking behavior of individual particles are only dependent on the radial CdS shell thickness and not on the CDs shell length. If the photogenerated excitons can reach the CdSe core region, the fluorescence properties will be dependent only on the surface passivation in close vicinity to the CdSe core. The change in QY upon excitation above the band gap of CdS for longer DRs cannot be explained by nonradiative particles because the ratio of emitting DRs is found to be independent of the DR length. We propose a model after which the decrease in QY for longer CdS shells is due to an increasing fraction of nonradiative exciton recombination within the elongated shell. This is supported by an effective-mass-approximation-based calculation, which suggests an optimum length of DRs of about 40 nm, to combine the benefit of high CdS absorption cross section with a high fluorescence QY.

Herein, we demonstrate that meticulous and in-depth analysis of the reaction mechanisms of nanoparticle formation is rewarded by full control of the size, shape, and crystal structure of superparamagnetic iron oxide nanocrystals during synthesis. Starting from two iron sources, iron(II) and iron(III) carbonate, a strict separation of oleate formation from the generation of reactive pyrolysis products and concomitant nucleation of iron oxide nanoparticles was achieved. This protocol enabled us to analyze each step of nanoparticle formation independently in depth. The progress of the entire reaction was monitored via matrix-assisted laser desorption ionization time-of-flight mass spectrometry and gas chromatography, thus providing insight into the formation of various iron oleate species prior to nucleation. Interestingly, due to the intrinsic strongly reductive pyrolysis conditions of the oleate intermediates and redox process in early stages of the synthesis, pristine iron oxide nuclei were composed exclusively from wüstite irrespective of the oxidation state of the iron source. Controlling the reaction conditions provided a very broad range of size- and shape-defined monodispersed iron oxide nanoparticles. Curiously, after nucleation, star-shaped nanocrystals were obtained that underwent metamorphism toward cubic-shaped particles. Electron energy loss spectroscopy tomography revealed ex post oxidation of the primary wustite nanocrystal, providing a full 3D image of Fe2+ and Fe3+ distribution within. Overall, we developed a highly flexible synthesis, yielding multi-gram amounts of well-defined iron oxide nanocrystals of different sizes and morphologies.

How can ion-exchange process occur in nanocrystals without the size and shape changing and why is the ion transport much faster than in classical interdiffusion processes in macrocrystalline solids? We have investigated these processes at the molecular level by means of high-resolution and analytical electron microscopy in temperature-dependent kinetic experiments for several model reactions. The results clearly show a diffusion process that proceeds exclusively through the interstitial lattice positions with a subsequent "kick out" to remove individual ions from lattice sites without the formation of vacancies. This mechanism has not been observed in nanocrystalline systems before.

Wieso konnen Ionenaustauschprozesse in Nanokristallen unter Erhaltung von Form und Grose erfolgen, und wieso ist der Ionentransport viel schneller, als man es von klassischen Interdiffusionsprozessen in makrokristallinen Festkorpern erwarten wurde? Wir haben diese Prozesse auf der molekularen Skala anhand einiger Modellreaktionen mittels hochauflosender und analytischer Elektronenmikroskopie in temperaturabhangigen kinetischen Untersuchungen verfolgt. Die Ergebnisse belegen eindeutig einen ausschlieslich uber Zwischengitterplatze erfolgenden Diffusionsprozess, gefolgt von einem “Kick-out” zur Verdrangung einzelner Ionen von Gitterplatzen, das ohne Bildung von Leerstellen auskommt und fur nanokristalline Systeme bisher noch nicht diskutiert wurde.

A preparation strategy is developed for monolithic samples of nanoporous gold with a hierarchical structure comprising two nested networks of solid "ligaments" on distinctly different structural length scales. The electrochemical dealloying protocol achieves a large retention of less noble element in a first corrosion step, thereby allowing an extra corrosion step which forms a separate structural hierarchy level. The beneficial impact of adding Pt to the Ag-Au master alloys that are more conventionally used in dealloying approaches to nanoporous gold is demonstrated. At approximate to 6 nm, the lower hierarchy level ligament size emerges extremely small. Furthermore, Pt favors the retention of Ag during the first dealloying step even when the master alloy has a high Au content. The high Au content reduces the corrosion-induced shrinkage, mitigating crack formation during preparation and favoring the formation of high-quality macroscopic (mm-sized) samples. The corrosion effectively carves out the nanoscale hierarchical ligament structure from the parent crystals tens of micrometers in size. This is revealed by X-ray as well as electron backscatter diffraction, which shows that the porous crystallites inherit the highly ordered, macroscopic crystal lattice structure of the master alloy.

CdSe/CdS-Quantum-dots-quantum-rods (QDQRs) with an aspect ratio of ∼ 6 are prepared via the seeded growth method, encapsulated within a shell of crosslinked poly(isoprene)-block-poly(ethylene glycol) (PI-b-PEG) diblock copolymer, and transferred from the organic phase into aqueous media. Their photoluminescence quantum yield (PLQY) of 78% is not compromised by the phase transfer. Within a period of two months the PLQY of QDQRs in aqueous solution at neutral pH decreases only slightly (to ∼ 65%). The two-photon (TP) action cross sections of QDQRs (∼ 10(5) GM) are two orders of magnitude higher than those of CdSe/CdS/ZnS-core/shell/shell quantum dots (QDs, ∼ 10(3) GM) with comparable diameter (∼ 5 nm). After applying PI-b-PEG encapsulated QDQRs onto the small intestinal mucosa of mice in vivo, their strong red fluorescence can easily be observed by two-photon laser scanning microscopy (TPLSM) and clearly distinguished from autofluorescent background. Our results demonstrate that PI-b-PEG encapsulated CdSe/CdS-QDQRs are excellent probes for studying the uptake and fate of nanoparticles by two-photon imaging techniques in vivo.

We analyze the structure and morphology of mesocrystalline, body-centered tetragonal (bct) superlattices of PbS nanocrystals functionalized with oleic acid. On the basis of combined scattering and real space imaging, we derive a three-dimensional (3D) model of the superlattice and show that the bct structure benefits from a balanced combination of {100}PbS–{100}PbS and {111}PbS–{111}PbS interactions between neighboring layers of nanocrystals, which uniquely stabilizes this structure. These interactions are enabled by the coaxial alignment of the atomic lattices of PbS with the superlattice. In addition, we find that this preferential orientation is already weakly present within isolated monolayers. By adding excess oleic acid to the nanocrystal solution, tetragonal distortion is suppressed, and we observe assembly into a bilayered hexagonal lattice reminiscent of a honeycomb with grain sizes of several micrometers.

We present a simple solution processed synthesis route for GaAs nanocrystals (NCs) with narrow size distribution and high crystallinity using wet chemical methods and commercially available inexpensive precursors with reduced toxicity. The reaction pathway can be described in three steps, starting with a transmetalation reaction between the gallium(III) halide precursor GaCl3 and the reduction agent n-butyllithium. At elevated temperatures elemental gallium is released in this process and enables the formation of GaAs NCs with magnesium arsenide (Mg3As2) as the arsenic source. We obtained a variety of different III–V semiconductor NCs including GaAs, InP, InAs, and GaP using this transmetalation reaction pathway.

We report a novel approach of seeded emulsion polymerization in which nanocrystals are used as seeds. Ultrasmall biocompatible polymer-coated nanocrystal with sizes between 15 and 110 nm could be prepared in a process that avoids any treatment with high shear forces or ultrasonication. The number of nanocrystals per seed, the size of the seeds, and the shell thickness can be independently adjusted. Single encapsulated nanocrystals in ultrasmall nanobeads as well as clusters of nanocrystals can be obtained. Polysorbat-80 was used as surfactant. It consists of poly(ethylene glycol) (PEG) chains, giving the particles outstanding biofunctional characteristics such as a minimization of unspecific interactions.

This paper reports on the application of a thin MgO interlayer as a diffusion barrier between a Ni 2 MnIn Heusler film and the substrate consisting of either (0 0 1)InAs or a high electron mobility transistor structure with an InAs channel layer. The functionality of the MgO interlayers is studied in dependence of their layer thicknesses. Our studies reveal that MgO interlayers are effective diffusion barriers, which in conjunction with post-growth annealing significantly improve the structural and magnetic properties of the Heusler films. For all as-grown samples, a Curie temperature of 170 K was found indicating that the Ni 2 MnIn films are crystallized in the B2 phase. Post-growth annealing for 15 h at 350 °C of samples with MgO layer thicknesses smaller than 3 nm leads to a strong decrease in magnetisation. This film degradation may be attributed to the intermixing of the Heusler films with substrate material through not-completely closed MgO films. For samples with a MgO interlayer thickness of 3 nm, the Curie temperature increases up to 300 K. This Curie temperature is close to the value reported for bulk Ni 2 MnIn films in the desired L2 1 phase. Furthermore, an increase in saturation magnetisation by a factor of 2.4 was observed.

We investigate the photoluminescence behavior of individual CdSe nanocrystals attached to silica-coated Au nanoparticles. These hybrid nanostructures show enhanced photoluminescence intensity, suppressed off-states, as well as shorter lifetimes in comparison with the isolated CdSe nanocrystals. The very same investigated hybrid nanostructures are further relocated by transmission electron microscopy to study the corresponding structures and geometries. Correlating the optical and structural properties of the hybrid nanostructures, we find that the lifetime shortening of the CdSe nanocrystals depends on the distance between the CdSe nanocrystals and the Au nanoparticles. The results are compared with theoretical calculations based on the FDTD method and the Gersten–Nitzan model.

Gold nanostars are multibranched nanoparticles with sharp tips, which display extremely interesting plasmonic properties but require optimization. We present a systematic investigation of the influence of different parameters on the size, morphology, and monodispersity of Au nanostars obtained via seeded growth in concentrated solutions of poly(vinylpyrrolidone) in N,N-dimethylformamide. Controlled prereduction of Au(3+) to Au(+) was found to influence monodispersity (narrower plasmon bands), while the [HAuCl(4)]/[seed] molar ratio significantly affects the morphology and tip plasmon resonance frequency. We also varied the size of the seeds (2-30 nm) and found a clear influence on the final nanostar dimensions as well as on the number of spikes, while synthesis temperature notably affects the morphology of the particles, with more rounded morphologies formed above 60 °C. This rounding effect allowed us to confirm the importance of sharp tips on the optical enhancing behavior of these nanoparticles in surface-enhanced raman scattering (SERS). Additionally, the sensitivity toward changes in the local refractive index was found to increase for larger nanostars, though lower figure of merit (FOM) values were obtained because of the larger polydispersity.

Semiconductor nanowires prepared by wet chemical methods are a relatively new field of 1D electronic systems, where the dimensions can be controlled by changing the reaction parameters using solution chemistry. Here, the solution–liquid–solid approach where the nanowire growth is governed by low-melting-point catalyst particles, such as Bi nanocrystals, is presented. In particular, the focus is on the preparation and characterization of CdSe nanowires, a material which serves a prototype structure for many kinds of low dimensional semiconductor systems. To investigate the influence of different reaction parameters on the structural and optical properties of the nanowires, a comprehensive synthetic study is presented, and the results are compared with those reported in literature. How the interplay between different reaction parameters affects the diameter, length, crystal structure, and the optical properties of the resultant nanowires are demonstrated. The structural properties are mainly determined by competing reaction pathways, such as the growth of Bi nanocatalysts, the formation and catalytic growth of nanowires, and the formation and uncatalytic growth of quantum dots. Systematic variation of the reaction parameters (e.g., molecular precursors, concentration and concentration ratios, organic ligands, or reaction time, and temperature) enables control of the nanowire diameter from 6 to 33 nm, while their length can be adjusted between several tens of nanometers and tens of micrometers. The obtained CdSe nanowires exhibit an admixture of wurtzite (W) and zinc blende (ZB) structure, which is investigated by X-ray diffraction. The diameter-dependent band gaps of these nanowires can be varied between 650 and 700 nm while their fluorescence intensities are mainly governed by the Cd/Se precursor ratio and the ligands used.

This paper reports on the influence of deposition temperature on structure and morphology of uncapped Ni 2 MnIn Heusler films grown by molecular beam epitaxy on InAs(0 0 1). Deposition temperatures between 80 and 360 °C and layer thicknesses between 20 and 100 nm have been used. Our studies reveal that during growth beyond 80 °C an intermixing layer arises at the Heusler/substrate interface that is formed by diffusion of arsenic from the substrate. The intermixing process, which is found to take place via interstitial sites, becomes increasingly severe with increasing growth temperature. Furthermore, we find that the films grown at 80 °C are polycrystalline with crystallites in the B2 phase. At 250 °C the films are found to be single-crystalline and pseudomorphically strained in the B2 phase. The desired L2 1 phase and single-crystalline Heusler films are observed at a growth temperature of 300 °C. Interestingly, Heusler films in L2 1 phase are found to have a (1 1 0) surface orientation in contrast to the InAs(0 0 1) substrate crystal. At temperatures higher than 300 °C, strong intermixing and a morphological degradation of the L2 1 Heusler films is observed.

Knowledge of nucleation and growth mechanisms is an important prerequisite for size control during nanoparticle synthesis. However, for many systems the mechanism is not completely understood. Here, investigation of the formation of NixPt1–x nanoparticles that are synthesized via reduction of platinum (II) acetylacetonate and nickel (II) acetate in the presence of oleic acid, oleylamine, and 1,2-hexadecanediol as the reducing agent is reported. Different reaction conditions are studied to reveal the influence on particle size and composition. The composition of the NixPt1–x nanocrystals is tunable through variation of the Ni:Pt ratio. The particle size depends on the concentration of oleic acid, while oleylamine mainly determines the particle shape. The binding of both stabilizing agents on the nanoparticle surface is investigated by attenuated total reflectance Fourier transform infrared spectroscopy. The growth process of the particles is studied by transmission electron microscopy analysis and UV-vis spectroscopy at different reaction stages. Our results lead to the assumption of a single nucleation event, followed by the growth process in the absence of Ostwald ripening. This type of growth can be extended by continuous injection of the molecular precursors, which allows the possibility of particle size control.

Two-dimensional layers of bimetallic cobalt-platinum nanoparticles were prepared from colloidal suspension to serve as model systems for catalytic surface coatings with well-defined chemistry and geometry. After deposition, the particle surfaces were exposed to mild rf plasmas in order to remove the passivating shell of organic ligands that covered their surfaces after preparation. X-ray photoelectron spectroscopy subsequently carried out without exposing the samples to air revealed that all carbon species can be quantitatively removed due to the treatment and that selective oxidation/reduction of the particles is possible. Grazing-incidence small-angle x-ray scattering was used to study plasma-induced changes in the particle ordering with high precision. The measurements prove that even for closely packed layers with lateral distances of less than 2nm, changes in the mean diameters of the particles can be kept in the order of just 1%–2%.

Networked films, comprising gold nanoparticles (ca. 4 nm core diameter) and 1,9-nonanedithiol, are deposited onto oxidized low-density polyethylene (LDPE) substrates via layer-by-layer self-assembly. Scanning electron microscopy and transmission electron microscopy images reveal a compact coating with a granular, nanoscale morphology. Conductance measurements at variable temperature are consistent with an Arrhenius-type activation of charge transport (activation energy: 52 meV). The excellent mechanical robustness of the coatings allows for studying their potential application as strain gauges. Expanding the films by up to 3% is accompanied by a reversible and approximately linear increase in resistance of up to approximately 50% (gauge factor ca. 17). Analyzing the results with an activated tunneling model suggests that the average increase in interparticle distances is significantly smaller than the geometric expansion at the substrate surface.

Magnetic nanoparticles have been assembled into the bilayer membrane of block copolymer vesicles. The nanoparticles decorate the hydrophobic/hydrophilic interface, which leads to bridging of adjacent bilayers and the formation of oligo-lamellar vesicles. The nanoparticle uptake of the vesicles is sufficiently high to become magnetophoretic in external magnetic fields as shown by video microscopy.

Highly ordered soft materials exhibit Bragg peaks that cannot be indexed assuming homogeneous crystal structures. Their origin has been attributed to changes in the crystal structure that are induced by the ordering process such as by application of external fields. This would restrict the use for the generation of highly ordered nano- and microstructured materials where a homogeneous crystal structure is a key requirement. Here, we demonstrate that these Bragg peaks are an inherent property of homogeneous ordered soft materials related to the finite coherence of their crystalline lattice. Their consideration allows a detailed and quantitative analysis of the diffraction patterns of seemingly unrelated materials such as lyotropic liquid-crystalline phases, mesoporous materials, colloidal dispersions, block copolymers, electrorheological fluids and photonic crystals. It further enables us to develop a concise picture of order, line density, field-induced orientation and epitaxial relations for soft-material lattices.

It is commonly accepted that the combination of the anisotropic shape and nanoscale dimensions of the mineral constituents of natural biological composites underlies their superior mechanical properties when compared to those of their rather weak mineral and organic constituents. Here, we show that the self-assembly of nearly spherical iron oxide nanoparticles in supercrystals linked together by a thermally induced crosslinking reaction of oleic acid molecules leads to a nanocomposite with exceptional bending modulus of 114 GPa, hardness of up to 4 GPa and strength of up to 630 MPa. By using a nanomechanical model, we determined that these exceptional mechanical properties are dominated by the covalent backbone of the linked organic molecules. Because oleic acid has been broadly used as nanoparticle ligand, our crosslinking approach should be applicable to a large variety of nanoparticle systems.

The investigation of ultra-thin self-assembled nanoparticle assemblies is currently receiving an overwhelming interest due to their possible applications in next-generation storage devices. Here, we present a comparative study of the ordering characteristics of monodisperse CoPt 3 arrays deposited on different polymeric surface modifiers employing a spin-coating technique. Using grazing-incidence X-ray scattering, scanning electron microscopy and atomic force microscopy, it is demonstrated that well-ordered nanoparticle films exhibiting correlation lengths in the order of 100 nm may be prepared on bis(3-aminopropyl)-terminated polyethyleneglycol using suitable spin-coating conditions.

A nonhydrolytic route to quantum-sized (d9 nm) ZnO nanocrystals in homogeneous organic solutions is presented. Nearly spherical ZnO nanocrystals were grown in a surfactant mixture of hexadecylamine and oleic acid (OLEA) by means of a two-step chemical process, based on the hot reduction (at 180-250 degrees C) of a zinc halide by superhydride (LiBEt3H) followed by oxidation of the resulting product. The experimental results suggested that the controlled growth of ZnO in the nanosized regime depended both on the OLEA-assisted generation of intermediate metallic nanoparticles and on the adjustment of their oxidation conditions by using a mild oxidant, trimethylamine-N-oxide, rather than molecular oxygen. The present synthetic approach demonstrates to be particularly suitable to prepare organic-soluble ultra-small ZnO nanocrystals of low size dispersion and of stable size, which are appealing for optoelectronic, catalytic, and sensing purposes.

We demonstrate that efficient shape control may be achieved in the shell of colloidally grown semiconductor nanocrystals (independent of the core), allowing the combination of a 0-D spherical CdSe core with a 1-D rodlike CdS shell. Besides exhibiting linearly polarized emission with a room-temperature quantum efficiency above 70%, these mixed-dimensionality colloidal heterostructures display large, length-dependent Stokes shifts as well as giant extinction coefficients approaching 107cm-1 M-1.

We report different approaches to the synthesis of size series of highly luminescent CdSe/CdS core−shell nanocrystals. The mixture of hexadecylamine (HDA)−trioctylphosphine oxide (TOPO)−trioctylphosphine (TOP) as stabilizing solvent was found to be very suitable for one-pot synthesis of nearly monodisperse CdSe nanocrystals followed by growing the CdS shell of a desired thickness. The obtained CdSe/CdS nanocrystals exhibited a narrow PL band (fwhm ∼27−35 nm) with reproducible room-temperature quantum yields as high as 50−85%. The emission color is tunable from green to red with increasing diameter of CdSe cores and/or thickness of the CdS shell. The possibility of preparing high-quality CdSe/CdS core−shell nanocrystals from the precursors cadmium acetate and H2S, which are more environmentally benign than conventional ones (e.g., dimethylcadmium) used in the organometallic synthesis of nanocrystals, was demonstrated. General aspects of the nanocrystal nucleation and growth as well as applicability of “gre...

Advanced colloidal syntheses enable the preparation of monodisperse semiconductors and magnetic alloy nanocrystals. They can be further used as building blocks for the fabrication of ordered assemblies: two-dimensional and three-dimensional arrays and colloidal supercrystals. This article reviews our recent activities in these fields. A theoretical description of the evolution of an ensemble of nanoparticles in a colloidal solution is applied to the problem of control over the nanocrystal monodispersity.

New approaches to synthesize photostable thiol-capped CdTe nanocrystals are reported. Post-preparative size-selective precipitation and selective photochemical etching have been developed as methods providing an increase of photoluminescence quantum efficiency of the nanocrystals of up to 40%. Some advantages of thiol-capping in comparison to conventional organometallic syntheses of quantum dots are discussed.

CdSe, CdTe and InP nanocrystals were prepared by an organometallic synthesis using mixtures of highly boiling primary amines and trioctylphosphine (TOP) as the coordinating solvent, and were characterized by powder XRD, SAXS, HRTEM, absorption and luminescence spectroscopy. The use of amines allowed us to obtain small crystalline nanoparticles for all materials investigated. In all cases, as-prepared colloids show rather narrow particle size distributions which can be further improved by standard size selective precipitation. Amino-capped II–VI nanocrystals show strong size-dependent band edge photoluminescence (PL). CdSe nanocrystals with the mean particle size in the range of 1.2–3.0 nm exhibit emission from blue to green with room temperature quantum yields of 15–20%. CdTe nanocrystals (2.5–5.0 nm size range) show a PL tunable from green to red with quantum yields up to 65% at room temperature. InP nanocrystals (1.5–4.0 nm size range) possess a weak emission (

Positively and negatively charged nanoparticles have been mixed together in order to obtain superlattice formation. The interaction between the particles was controlled by adjusting the ionic strength of the solutions. The self-assembly was studied with absorption spectroscopy, powder X-ray diffraction, and high-resolution transmission electron microscopy.

The wide-bandgap semiconducting material, zinc sulfide, has been coated on indium phosphide nanoclusters to a 1-2-Å thickness. The resulting InP-ZnS core-shell particle (as shown in the TEM image; scale 1 cm=5 nm) exhibits bright luminescence at room temperature with quantum efficiencies as high as 23 %.