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We investigate the early stages of cesium lead bromide perovskite formation through absorption spectroscopy of stopped flow reactions, high-throughput mapping and direct synthesis and titration of potential precursor species. Calorimetric and spectroscopic measurements of lead bromide complex titrations combined with theoretical calculations suggest that bromide complexes with higher coordination numbers than previously considered for non-polar systems can better explain observed behaviors. Synthesis mapping of binary lead halides reveals multiple lead bromide species with absorption peaks higher than 300 nm, including a previously observed species with a peak at 313 nm and two species with peaks at 345 and 370 nm that also appear as reaction intermediates during formation of lead bromide perovskites. Based on theoretical calculations of excitonic energies that match within 50 meV, we give a preliminary assignment of these species as two dimensional magic sized clusters with side lengths of 2, 3 and 4 unit cells. Kinetic measurements of the conversion of benzoyl bromide precursor are connected to stopped flow measurements of product formation and demonstrate that the formation of complexes and magic sized clusters (i.e. nucleation) is controlled by precursor decomposition, whereas the growth rate of 2D and 3D perovskites is significantly slower.

Germanium telluride (GeTe) exhibits interesting materials properties, including a reversible amorphous-to-crystalline phase transition and a room-temperature ferroelectric distortion, and has demonstrated potential for nonvolatile memory applications. Here, a colloidal approach to the synthesis of GeTe nanocrystals over a wide range of sizes is demonstrated. These nanocrystals have size distributions of 10-20% and exist in the rhombohedral structure characteristic of the low-temperature polar phase. The production of nanocrystals of widely varying sizes is facilitated by the use of Ge(II) precursors with different reactivities. A transition from a monodomain state to a state with multiple polarization domains is observed with increasing size, leading to the formation of richly faceted nanostructures. These results provide a starting point for deeper investigation into the size-scaling and fundamental nature of polar-ordering and phase-change processes in nanoscale systems.

Abstract For Abstract see ChemInform Abstract in Full Text.

For over a decade, much effort has been focused on passivation of the high density of localized electronic trap states in colloidal semiconductor quantum dots (QDs), which lead to reduced performance in solar cell, light-emitting diode, laser, and photoconductor applications. However, here we take advantage of the naturally occurring high density of trap states to demonstrate solution-processed high-speed PbSe quantum dot near-infrared photodetectors. Carrier transport dynamics studies reveal multiple trapping and release transport dynamics in band tail states. A sandwich microstrip transmission line photodetector utilizing these QD films was fabricated to achieve high performance by allowing carriers to be swept to the electrodes before they fall into the band tail states. As a result, this device demonstrates external quantum efficiency, responsivity, and response time (full width at half-maximum) of 54%, 0.36 A/W, and 74 ps, respectively.

Lead halide perovskite nanocrystals have attracted intense interest due to their desirable optical properties, diverse structural features, and size-tunable excitonic structure. Here we show that, under ambient conditions, a non-monotonic trend in radiative lifetime emerges from the interplay of size, lattice symmetry and excitonic structure. Small nanocrystals exhibit long radiative lifetimes due to weakly emissive excitons, but the oscillator strength increases and shortens the lifetime for nanocrystals approaching intermediate confinement. For larger nanocrystals with higher exciton density of states (DOS), the radiative lifetime is lengthened due to depopulation of the bright exciton manifold into thermally accessible dim states. A size-dependent structural symmetry lowering transition from cubic to orthorhombic is observed by XRD and MD simulations, and the non-monotonic radiative lifetime trend emerges only in lower symmetry structures with an increased dim exciton DOS. These findings shed light on the impact of nanocrystal size and structure on radiative lifetime and pave the way for tailored optical materials in various optical applications.

Silicon-based photonic devices dissipate substantially less power and provide a significantly greater information bandwidth than electronic components. Unfortunately, large-scale integration of photonic devices has been limited by their large, wavelength-scale size and the weak optical response of Si. Surface plasmons may overcome these two limitations. Combining the high localization of electronic waves with the propagation properties of optical waves, plasmons can achieve extremely small mode wavelengths and large local electromagnetic field intensities. Si-based plasmonics has the potential to not only reduce the size of photonic components to deeply subwavelength scales, but also to enhance the emission, detection, and manipulation of optical signals in Si. In this paper, we discuss recent advances in Si-based plasmonics, including subwavelength interconnects, modulators, and emission sources. From scales spanning slab waveguides to single nanocrystals, we show that Si-based plasmonics can enable optical functionality competitive in size and speed with contemporary electronic components.
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We propose to develop a true user facility for ultrafast x-ray science at the Advanced Light Source. This facility will be unique in the world, and will fill a critical need for the growing ultrafast x-ray research community. The development of this facility builds upon the expertise from long-standing research efforts in ultrafast x-ray spectroscopy and the development of femtosecond x-ray sources and techniques at both the Lawrence Berkeley National Laboratory and at U.C. Berkeley. In particular, the technical feasibility of a femtosecond x-ray beamline at the ALS has already been demonstrated, and existing ultrafast laser technology will enable such a beamline to operate near the practical limit for femtosecond x-ray flux and brightness from a 3rd generation synchrotron.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Colloidal metal phosphide nanocrystals have been extensively explored for energy conversion, optoelectronic devices, and bioimaging applications. However, colloidal synthesis to achieve precise control over size, morphology, and composition remains extremely challenging for these phosphide nanocrystals. This is partly due to the unbalanced reactivity of the metal and phosphide precursors and a poor understanding of their formation mechanisms. Herein, we have utilized defined prenucleation metal-aminophosphine-alkylamine complexes as precursors for the highly tunable synthesis of colloidal metal phosphide nanomaterials with accurate control over morphology and composition. We show that precise control over morphology and composition can be achieved using a highly customizable prenucleation-complex-based method for metal phosphide nanocrystals. Using 31P-nuclear magnetic resonance spectroscopy and mass spectrometry, we reveal the prenucleation complex formation mechanisms and provide a structural analysis of the M-P (M = Cu, Co, Cd, and Ni) complexes. Moreover, we investigated the morphology and structure of the phosphide nanocrystals using electron microscopy and X-ray diffraction experiments. We have further used first-principles calculations and boundary element method-based simulations to gain insights into the structural evolution of these nanocrystals as well as into the impact of the morphology and composition on their plasmonic response. We anticipate that the generalized prenucleation-based colloidal metal phosphide synthesis with precise control of size, shape, and composition could pave the way to yield high-quality metal phosphide nanocrystals with tailored chemical and optoelectronic properties.

We describe the synthesis and three-dimensional structure of a new single-crystalline "hexameric" nanocrystal composed of six near-spherical PbSe nanocrystals arranged at the vertices of an octahedron. We examine the detailed three-dimensional structure of these nanocrystals using electron tomography and demonstrate single-crystal to single-crystal cation exchange to CdSe. We reveal that the growth of these nanocrystals, which form under conditions similar to other anisotropic PbSe nanocrystals, depends on the initial presence of lead oleate particles with approximate diameters of 1.7–3.1 nm that form upon heating lead(II) acetate hydrate in the presence of oleic acid. These lead oleate particles, which are visible by transmission electron microscopy, constitute the beginning of nearly every synthesis of anisotropic PbSe nanocrystals. We show that the lead oleate particles play a definitive role in determining the morphology of the resultant PbSe nanocrystals. We note that the acetate anion, which was previously identified as the key factor in achieving anisotropic PbSe growth, greatly accelerates the formation of the lead oleate particles, and thus appears to be responsible for the subsequent PbSe morphology. However, we demonstrate that acetate is not required for lead oleate particle formation, nor indeed for anisotropic PbSe growth. The potential role of these new particles in other PbSe synthetic preparations from lead(II) oleate is of high interest for future study.

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionSymmetry of Annealed Wurtzite CdSe Nanocrystals: Assignment to the C3v Point GroupJ. J. Shiang, A. V. Kadavanich, R. K. Grubbs, and A. P. AlivisatosCite this: J. Phys. Chem. 1996, 100, 32, 13886Publication Date (Web):August 8, 1996Publication History Published online8 August 1996Published inissue 1 January 1996https://pubs.acs.org/doi/10.1021/jp963478rhttps://doi.org/10.1021/jp963478rcorrectionACS PublicationsCopyright © 1996 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views482Altmetric-Citations6LEARN 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 PDF (131 KB) Get e-Alerts

First principles electronic structure simulations are used to study the atomistic detail of the interaction between organic surfactant molecules and the surfaces of CdSe semiconductor nanoparticles. These calculations provide insights into the relaxed atomic geometry of organics bound to semiconductor surfaces at the nanoscale as well as the electronic charge transfer between surface atoms and the organics. We calculate the binding energy of phosphine oxide, phosphonic and carboxylic acids, and amine ligands to a range of CdSe nanoparticle facets. The dominant binding interaction is between oxygen atoms in the ligands and cadmium atoms on the nanoparticle surfaces. The most strongly bound ligands are phosphonic acid molecules, which bind preferentially to the facets forming the sides of CdSe nanorods. The calculated relative binding strengths of ligands to different facets support the hypothesis that these binding energies control the relative growth rates of different facets, and therefore the resulting geometry of the nanoparticles.