Publications

Probing Redox Photocatalysis of Trapped Electrons and Holes on Single Sb-doped Titania Nanorod Surfaces

We used a fluorogenic reaction to study in conjunction the photocatalytic properties for both active sites (trapped photogenerated electrons and holes) on individual Sb-doped TiO(2) nanorods with single-molecule fluorescence microscopy. It was found that active sites around trapped holes show higher activity, stronger binding ability, and a different dissociation mechanism for the same substrate and product molecules in comparison with the active sites around trapped electrons. These differences could be elucidated by a model involving the charged microenvironments around the active sites.

Multilaminate Energy Storage Films from Entropy‐Driven Self‐Assembled Supramolecular Nanocomposites

Composite materials comprising polymers and inorganic nanoparticles (NPs) are promising for energy storage applications, though challenges in controlling NP dispersion often result in performance bottlenecks. Realizing nanocomposites with controlled NP locations and distributions within polymer microdomains is highly desirable for improving energy storage capabilities but is a persistent challenge, impeding the in-depth understanding of the structure-performance relationship. In this study, a facile entropy-driven self-assembly approach is employed to fabricate block copolymer-based supramolecular nanocomposite films with highly ordered lamellar structures, which are then used in electrostatic film capacitors. The oriented interfacial barriers and well-distributed inorganic NPs within the self-assembled multilaminate nanocomposites effectively suppress leakage current and mitigate the risk of breakdown, showing superior dielectric strength compared to their disordered counterparts. Consequently, the lamellar nanocomposite films with optimized composition exhibit high energy efficiency (>90% at 650 MV m^-1), along with remarkable energy density and power density. Moreover, finite element simulations and statistical modeling have provided theoretical insights into the impact of the lamellar structure on electrical conduction, electric field distribution, and electrical tree propagation. This work marks a significant advancement in the design of organic-inorganic hybrids for energy storage, establishing a well-defined correlation between microstructure and performance.

Structural and spectroscopic investigations of CdS/HgS/CdS quantum-dot quantum wells

Epitaxial growth in a CdS/HgS heterostructure of nanometer dimensions, prepared by methods of wet chemistry, is demonstrated. High-resolution transmission-electron microscopy is used to determine the shape and crystallinity of this system consisting of a quantum well in a quantum dot. The homogeneous absorption and fluorescence spectra are investigated by transient hole burning and fluorescence line-narrowing spectroscopy. The photophysical measurements provide evidence for charge-carrier localization within the HgS well.

Semiconductor Nanorod Liquid Crystals

Rodlike molecules form liquid crystalline phases with orientational order and positional disorder. The great majority of materials in which liquid crystalline phases have been observed are comprised of organic molecules or polymers, even though there has been continuing and growing interest in inorganic liquid crystals. Recent advances in the control of the sizes and shapes of inorganic nanocrystals allow for the formation of a broad class of new inorganic liquid crystals. Here we show the formation of liquid crystalline phases of CdSe semiconductor nanorods. These new liquid crystalline phases may have great importance for both application and fundamental study.

Arrested solid-solid phase transition in 4-nm-diameter cadmium sulfide nanocrystals

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTArrested solid-solid phase transition in 4-nm-diameter cadmium sulfide nanocrystalsM. Haase and A. P. AlivisatosCite this: J. Phys. Chem. 1992, 96, 16, 6756–6762Publication Date (Print):August 1, 1992Publication History Published online1 May 2002Published inissue 1 August 1992https://pubs.acs.org/doi/10.1021/j100195a042https://doi.org/10.1021/j100195a042research-articleACS PublicationsRequest reuse permissionsArticle Views601Altmetric-Citations96LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts

Synthesis of Composition Tunable and Highly Luminescent Cesium Lead Halide Nanowires through Anion-Exchange Reactions

Here, we demonstrate the successful synthesis of brightly emitting colloidal cesium lead halide (CsPbX3, X = Cl, Br, I) nanowires (NWs) with uniform diameters and tunable compositions. By using highly monodisperse CsPbBr3 NWs as templates, the NW composition can be independently controlled through anion-exchange reactions. CsPbX3 alloy NWs with a wide range of alloy compositions can be achieved with well-preserved morphology and crystal structure. The NWs are highly luminescent with photoluminescence quantum yields (PLQY) ranging from 20% to 80%. The bright photoluminescence can be tuned over nearly the entire visible spectrum. The high PLQYs together with charge transport measurements exemplify the efficient alloying of the anionic sublattice in a one-dimensional CsPbX3 system. The wires increased functionality in the form of fast photoresponse rates and the low defect density suggest CsPbX3 NWs as prospective materials for optoelectronic applications.

Colloidal nanocrystal heterostructures with linear and branched topology

Dataset of automatically extracted sizes and morphologies of AuNPs from literature-mined SEM/TEM images

This is a dataset of automatically extracted sizes and morphologies of Gold nanoparticles, which have been obtained from the analysis of 4365 literature-mined SEM/TEM images. The dataset contains 4365 records, each of which contains extracted size/morphology information and metadata corresponding to a single microscopy image.

Controlled growth of tetrapod-branched inorganic nanocrystals

Classifying handedness in chiral nanomaterials using label error robust deep learning

Nanocrystal/Polymer Composite Photovoltaic Devices

Unlike conventional solar cells, novel polymeric photovoltaic devices have flexibility, large area processibility and potential low costs. We have constructed devices consisting of a composite of CdSe nanocrystals and poly(3-hexylthiophene). The resulting monochromatic power conversion efficiency is 0.7 %. Since the efficiency in these devices is limited by poor electron transport, we seek to improve the mobility of electrons in the CdSe with nanorods in place of nanocrystals. Devices fabricated with small aspect ratio CdSe nanorods and poly(3-hexythiophene) have enhanced conversion efficiencies up to 2 %. To further increase device efficiencies, soluble nanorods of CdSe were synthesized with aspect ratios reaching 20:1 by controlling the kinetics of nanocrystal growth in lyothermal solutions.

Seeded Growth of Highly Luminescent CdSe/CdS Nanoheterostructures with Rod and Tetrapod Morphologies

We have demonstrated that seeded growth of nanocrystals offers a convenient way to design nanoheterostructures with complex shapes and morphologies by changing the crystalline structure of the seed. By using CdSe nanocrystals with wurtzite and zinc blende structure as seeds for growth of CdS nanorods, we synthesized CdSe/CdS heterostructure nanorods and nanotetrapods, respectively. Both of these structures showed excellent luminescent properties, combining high photoluminescence efficiency (approximately 80 and approximately 50% for nanorods and nanotetrapods, correspondingly), giant extinction coefficients (approximately 2 x 10(7) and approximately 1.5 x 10(8) M(-1) cm(-1) at 350 nm for nanorods and nanotetrapods, correspondingly), and efficient energy transfer from the CdS arms into the emitting CdSe core.

Mechanical and electrical properties of CdTe tetrapods studied by atomic force microscopy

The mechanical and electrical properties of CdTe tetrapod-shaped nanocrystals have been studied with atomic force microscopy. Tapping mode images of tetrapods deposited on silicon wafers revealed that they contact the surface with three of its arms. The length of these arms was found to be 130±10nm. A large fraction of the tetrapods had a shortened vertical arm as a result of fracture during sample preparation. Fracture also occurs when the applied load is a few nanonewtons. Compression experiments with the atomic force microscope tip indicate that tetrapods with the shortened vertical arm deform elastically when the applied force was less than 50nN. Above 90nN additional fracture events occurred that further shortened the vertical arm. Loads above 130nN produced irreversible damage to the other arms as well. Current-voltage characteristics of tetrapods deposited on gold revealed a semiconducting behavior with a current gap of ∼2eV at low loads (<50nN) and a narrowing to about 1eV at loads between 60 and 110nN. Atomistic force field calculations of the deformation suggest that the ends of the tetrapod arms are stuck during compression so that the deformations are due to bending modes. Empirical pseudopotential calculation of the electron states indicates that the reduction of the current gap is due to electrostatic effects, rather than strain deformation effects inside the tetrapod.

The Making and Breaking of Lead-Free Double Perovskite Nanocrystals of Cesium Silver–Bismuth Halide Compositions

Replacing lead in halide perovskites is of great interest due to concerns about stability and toxicity. Recently, lead free double perovskites in which the unit cell is doubled and two divalent lead cations are substituted by a combination of mono- and trivalent cations have been synthesized as bulk single crystals and as thin films. Here, we study stability and optical properties of all-inorganic cesium silver(I) bismuth(III) chloride and bromide nanocrystals with the double perovskite crystal structure. The cube-shaped nanocrystals are monodisperse in size with typical side lengths of 8 to 15 nm. The absorption spectrum of the nanocrystals presents a sharp peak, which we assign to a direct bismuth s-p transition and not to a quantum confined excitonic transition. Using this spectroscopic handle combined with high-resolution transmission electron microscopy (TEM) based elemental analysis, we conduct stoichiometric studies at the single nanocrystal level as well as decomposition assays in solution and observe that Ag⁺ diffusion and coalescence is one of the pathways by which this material degrades. Drying the nanocrystals leads to self-assembly into ordered nanocrystal solids, and these exhibit less degradation than nanocrystals in solution. Our results demonstrate that Cs₂AgBiX₆ (X = Cl, Br) nanocrystals are a useful model system to study structure-function relationships in the search for stable nontoxic halide perovskites.

Soft x-ray imaging and spectroscopy of <i>single</i> nanocrystals

Resonant photoemission electron microscopy (PEEM) at the Fe L3,2 absorption edge was utilized to image single γ-Fe2O3 nanocrystals of 10 nm average diameter (∼20 000 Fe atoms) and to record soft x-ray absorption spectra of individual particles. Within the spectral resolution of the experiment, no damage to the individual nanoparticles occurs during repeated, prolonged exposure to the intense x-ray beam. Furthermore, no differences in the position or shape of the soft x-ray absorption spectrum of a single nanocrystal and the ensemble are observed within the experimental resolution. PEEM contrast images and soft x-ray absorption spectra, however, show strong intensity variations between different particles reflecting the size distribution of the sample. This proof-of-principle experiment successfully demonstrates the applicability of x-ray spectromicroscopy to the study of nanoscale systems on a hitherto unachieved length scale.

Tolerance to structural disorder and tunable mechanical behavior in self-assembled superlattices of polymer-grafted nanocrystals

Significance Polymer nanocomposites containing nanoparticle fillers often have enhanced strength, stiffness, and toughness that are highly dependent on nanoparticle spatial distribution, which can be challenging to control in the limit of high nanoparticle loading. Solid superlattices formed from close-packed, ligand-coated inorganic nanocrystals can have high stiffness and large elastic recovery, although nanocrystals interact solely through van der Waals forces. We use polymer-grafted nanocrystals to make superlattices with versatile structural architecture and dimensions to investigate the effects of structural defects, film thickness, and polymer length on mechanical behavior. We find that the elastic response of the superlattice is large even when the arrangement of nanocrystals within the superlattice is perturbed, and that polymer conformation plays a large role in determining mechanical properties.

Atomic Resolution Imaging of Halide Perovskites

The radiation-sensitive nature of halide perovskites has hindered structural studies at the atomic scale. We overcome this obstacle by applying low dose-rate in-line holography, which combines aberration-corrected high-resolution transmission electron microscopy with exit-wave reconstruction. This technique successfully yields the genuine atomic structure of ultrathin two-dimensional CsPbBr₃ halide perovskites, and a quantitative structure determination was achieved atom column by atom column using the phase information of the reconstructed exit-wave function without causing electron beam-induced sample alterations. An extraordinarily high image quality enables an unambiguous structural analysis of coexisting high-temperature and low-temperature phases of CsPbBr₃ in single particles. On a broader level, our approach offers unprecedented opportunities to better understand halide perovskites at the atomic level as well as other radiation-sensitive materials.

Electrical Transport through a Single Nanoscale Semiconductor Branch Point

Semiconductor tetrapods are three-dimensional (3D) branched nanostructures, representing a new class of materials for electrical conduction. We employ the single-electron transistor approach to investigate how charge carriers migrate through single nanoscale branch points of tetrapods. We find that carriers can delocalize across the branches or localize and hop between arms depending on their coupling strength. In addition, we demonstrate a new single-electron transistor operation scheme enabled by the multiple branched arms of a tetrapod: one arm can be used as a sensitive arm-gate to control the electrical transport through the whole system.