Three-Dimensional Self-Assembly of Chalcopyrite Copper Indium Diselenide Nanocrystals into Oriented Films

CuInSe₂, which is one of the highest efficiency thin-film solar cell active layer materials, has been an attractive target for nanocrystal synthesis and manipulation. Here, we report unprecedented, simultaneous control of the synthesis and self-assembly behavior of CuInSe₂ nanocrystals. These nanocrystals are solution-processable, monodisperse tetragonal bipyramids that exhibit photoconductivity and self-assemble into crystallographically oriented thin films. Structural characterization indicates that these nanocrystals are tetragonal phase, as is used in high-efficiency, second-generation, thin-film solar cells. Elemental analysis indicates that approximately 1:1:2 Cu/In/Se stoichiometry can be achieved, and that the elemental composition can be adjusted from copper-rich to indium-rich with reaction time

Designing Tripodal and Triangular Gadolinium Oxide Nanoplates and Self-Assembled Nanofibrils as Potential Multimodal Bioimaging Probes

Here, we report the shape-controlled synthesis of tripodal and triangular gadolinium oxide (Gd₂O₃) nanoplates. In the presence of lithium ions, the shape of the nanocrystals is readily controlled by tailoring reaction parameters such as temperature and time. We observe that the morphology transforms from an initial tripodal shape to a triangular shape with increasing reaction time or elevated temperatures. Highly uniform Gd₂O₃ nanoplates are self-assembled into nanofibril-like liquid-crystalline superlattices with long-range orientational and positional order. In addition, shape-directed self-assemblies are investigated by tailoring the aspect ratio of the arms of the Gd₂O₃ nanoplates. Due to a strong paramagnetic response, Gd₂O₃ nanocrystals are excellent candidates for MRI contrast agents and also can be doped with rare-earth ions to form nanophosphors, pointing to their potential in multimodal imaging. In this work, we investigate the MR relaxometry at high magnetic fields (9.4 and 14.1 T) and the optical properties including near-IR to visible upconversion luminescence and X-ray excited optical luminescence of doped Gd₂O₃ nanoplates. The complex shape of Gd₂O₃ nanoplates, coupled with their magnetic properties and their ability to phosphoresce under NIR or X-ray excitation which penetrate deep into tissue, makes these nanoplates a promising platform for multimodal imaging in biomedical applications

Synthesis, Shape Control, and Methanol Electro-oxidation Properties of Pt–Zn Alloy and Pt₃Zn Intermetallic Nanocrystals

We report the first synthesis of highly monodisperse Pt₃Zn nanocrystals (NCs). Shape-controlled synthesis generates cubic and spherical Pt–Zn NCs. Reaction temperature is the key to incorporate Zn into Pt, even in the absence of a strong reducing agent. The Pt–Zn NCs are active toward methanol oxidation, with the spherical NCs exhibiting higher activity than the cubic NCs. The Pt–Zn alloy phase can be transformed into the Pt₃Zn intermetallic phase, upon annealing. The intermetallic Pt₃Zn shows better performance than the alloy phase Pt–Zn. Besides the activity toward methanol oxidation, Pt–Zn NCs show excellent poisoning tolerance. With activities comparable to the commercial Pt catalyst, enhanced poisoning tolerance and lower cost, Pt–Zn and Pt₃Zn NCs are a promising new family of catalysts for direct methanol fuel cells

Solution-Based Stoichiometric Control over Charge Transport in Nanocrystalline CdSe Devices

Using colloidal CdSe nanowire (NW) field-effect transistors (FETs), we demonstrated the dependence of carrier transport on surface stoichiometry by chemically manipulating the atomic composition of the NW surface. A mild, room-temperature, wet-chemical process was devised to introduce cadmium, selenium, or sulfur adatoms at the surface of the NWs in completed devices. Changes in surface composition were tested for by energy dispersive spectroscopy and inductively coupled plasma-atomic emission spectroscopy and through the use of the vibrational reporter thiocyanate. We found that treatment with cadmium acetate enhances electron currents, while treatment with sodium selenide or sodium sulfide suppressed them. The efficacy of doping CdSe NWs through subsequent thermal diffusion of indium was highly dependent on the surface composition. While selenium-enriched CdSe NW FETs were characterized by little to no electron currents, when combined with indium, they yielded semimetallic devices. Sulfur-enriched, indium-doped devices also displayed dramatically enhanced electron currents, but to a lesser extent than selenium and formed FETs with desirable <i>I</i>_ON/<i>I</i>_OFF >10⁶. The atomic specificity of the electronic behavior with different surface chalcogens suggested indium was bound to chalcogens at the NW surface, indicating commonalities with and implications for indium-containing CdSe nanocrystal films. Low temperature measurements of indium-doped CdSe NW FETs showed no evidence of impurity scattering, further supporting the existence of an indium–chalcogen interaction at the surface rather than in the core of the NW

Solution-Processed Phase-Change VO₂ Metamaterials from Colloidal Vanadium Oxide (VO_<i>x</i>) Nanocrystals

We demonstrate thermally switchable VO₂ metamaterials fabricated using solution-processable colloidal nanocrystals (NCs). Vanadium oxide (VO_<i>x</i>) NCs are synthesized through a nonhydrolytic reaction and deposited from stable colloidal dispersions to form NC thin films. Rapid thermal annealing transforms the VO_<i>x</i> NC thin films into monoclinic, nanocrystalline VO₂ thin films that show a sharp, reversible metal–insulator phase transition. Introduction of precise concentrations of tungsten dopings into the colloidal VO_<i>x</i> NCs enables the still sharp phase transition of the VO₂ thin films to be tuned to lower temperatures as the doping level increases. We fabricate “smart”, differentially doped, multilayered VO₂ films to program the phase and therefore the metal–insulator behavior of constituent vertically structured layers with temperature. With increasing temperature, we tailored the optical response of multilayered films in the near-IR and IR regions from that of a strong light absorber, in a metal–insulator structure, to that of a Drude-like reflector, characteristic of a pure metallic structure. We demonstrate that nanocrystal-based nanoimprinting can be employed to pattern multilayered subwavelength nanostructures, such as three-dimensional VO₂ nanopillar arrays, that exhibit plasmonic dipolar responses tunable with a temperature change

Synthesis of N‑Type Plasmonic Oxide Nanocrystals and the Optical and Electrical Characterization of their Transparent Conducting Films

We present a general synthesis for a family of n-type transparent conducting oxide nanocrystals through doping with aliovalent cations. These monodisperse nanocrystals exhibit localized surface plasmon resonances tunable in the mid- and near-infrared with increasing dopant concentration. We employ a battery of electrical measurements to demonstrate that the plasmonic resonance in isolated particles is consistent with the electronic properties of oxide nanocrystal thin films. Hall and Seebeck measurements show that the particles form degenerately doped n-type solids with free electron concentrations in the range of 10¹⁹ to 10²¹ cm^–3. These heavily doped oxide nanocrystals are used as the building blocks of conductive, n-type thin films with high visible light transparency

Electrocatalytic and Photocatalytic Hydrogen Production from Acidic and Neutral-pH Aqueous Solutions Using Iron Phosphide Nanoparticles

Nanostructured transition-metal phosphides have recently emerged as Earth-abundant alternatives to platinum for catalyzing the hydrogen-evolution reaction (HER), which is central to several clean energy technologies because it produces molecular hydrogen through the electrochemical reduction of water. Iron-based catalysts are very attractive targets because iron is the most abundant and least expensive transition metal. We report herein that iron phosphide (FeP), synthesized as nanoparticles having a uniform, hollow morphology, exhibits among the highest HER activities reported to date in both acidic and neutral-pH aqueous solutions. As an electrocatalyst operating at a current density of −10 mA cm^–2, FeP nanoparticles deposited at a mass loading of ∼1 mg cm^–2 on Ti substrates exhibited overpotentials of −50 mV in 0.50 M H₂SO₄ and −102 mV in 1.0 M phosphate buffered saline. The FeP nanoparticles supported sustained hydrogen production with essentially quantitative faradaic yields for extended time periods under galvanostatic control. Under UV illumination in both acidic and neutral-pH solutions, FeP nanoparticles deposited on TiO₂ produced H₂ at rates and amounts that begin to approach those of Pt/TiO₂. FeP therefore is a highly Earth-abundant material for efficiently facilitating the HER both electrocatalytically and photocatalytically

Supplemental Material for Pincot et al., 2018

<div>SUPPLEMENTAL FILES</div><div><br></div><div>Supplemental File 1. Statistics from a mixed model analysis of Fusarium wilt resistance among 565 strawberry germplasm accessions grown in randomized complete blocks experiment designs in 2016 and 2017 in Davis, California. </div><div><br></div><div>Supplemental File 2. Selected SNP genotypes and Fusarium wilt resistance phenotypes among 565 F. x ananassa germplasm accessions. The latter are identified by UCD accession numbers or USDA plant introduction numbers and aliases where appropriate. Genotypes are shown for 14 SNPs on the Affymetrix iStraw35 array in linkage disequilibrium with Fw1, a gene conferring resistance to isolate AMP132 of Fusarium oxysporum f. sp. fragariae. Least square means for Fusarium wilt resistance phenotypes are shown for plants phenotyped nine weeks post-inoculation in 2016 and 36 weeks post-inoculation in 2017 field experiments in Davis, California. Plants phenotyped in the summer of 2016 were spring-planted in 2016, whereas plants phenotyped in the summer of 2017 were fall-planted in 2016. Least square means were estimated from four clonal replicates/entry in each study. Chromosome positions are shown for SNPs mapped against a diploid F. vesca reference genome (Edger et al. 2018), in addition to p-values estimated from 2016 and 2017 genome-wide association studies and Affymetrix probes identifiers.</div><div><br></div><div>Supplemental File 3. QTL mapping statistics in two S1 populations for SNPs tightly linked to Fw1, a gene conferring resistance to isolate AMP132 of Fusarium oxysporum f. sp. fragariae in strawberry. The additive and dominance effects and of individual SNP loci were estimated using linear contrasts (p-values are shown for F-statistics associated with each linear contrast). Coefficients of determination (R2) and degrees of dominance (|d/a|) were estimated for each SNP locus.</div><div><br></div><div>Supplemental File 4. QTL mapping statistics for resistance to Fusarium wilt in two F. x ananassa S1 mapping populations genotyped with the Affymetrix iStraw35 SNP array. Collectively, 5,673 co-dominant SNP markers were genetically mapped in the Fronteras S1 population (n = 93) and assembled into 40 linkage groups, where n = number of S1 progeny. Similarly, 7,345 co-dominant SNP markers were genetically mapped in the Portola S1 population (n = 93) and assembled into 50 linkage groups. Linkage groups were numbered and aligned with 28 linkage groups previously described by van Dijk et al. (2014) and Mangandi et al. (2017) and are hypothesized to correspond to the 28 chromosomes in the haploid genome of F. x ananassa. Likelihood-odds (LOD) statistics and linkage group positions (cM) are shown for QTL interval mapping across linkage groups. Linkage groups that did not align to the reference or had fewer than 10 SNPs are excluded from the figure, but were included in the mapping and did not show significant LOD scores. </div><div><br></div><div>Supplemental File 5. Pedigree database for 1,663 F. x ananassa germplasm accessions. The parents and birth years are shown for each individual (germplasm accession). Throughout the database, unknown ancestors are identified with the pre-fix “Unknown” followed by a unique number. “NA” indicates not ‘available’.</div><div><br></div><div>Supplemental File 6. Genotypes and phenotypes for SNPs in linkage disequilibrium (LD) with a Fusarium wilt resistance gene (Fw1) on chromosome 2C in strawberry. The individual plots show Fusarium wilt phenotypes for 565 germplasm accessions among each of the three genotypic classes for 11 SNPs in LD with Fw1 on chromosome 2C. Plants were artificially inoculated with isolate AMP132 of Fusarium oxysporum f. sp. fragariae and phenotyped nine weeks post-inoculation in (A) 2016 and 36 weeks post-inoculation in (B) 2017 field experiments in Davis, California.</div><div><br></div><div>Supplemental File 7. Physical locations in the F. vesca genome, ontologies, and annotations for genes associated with SNPs in linkage disequilibrium with the Fusarium wilt resistance gene Fw1.</div><div><br></div><div>SUPPLEMENTAL DATA FILES</div><div><br></div><div>Supplemental Data File 1. Raw genotypic data for 565 strawberry germplasm accessions genotyped with the iStraw35 SNP array. Each row corresponds to a SNP marker. </div><div><br></div><div>Supplemental Data File 2. Raw genotypic data for 186 individuals of the mapping populations genotyped with the iStraw35 SNP array. Each row corresponds to a SNP marker. </div><div><br></div><div>Supplemental Data File 3. Affymetrix iStraw35 SNP probe set names, alleles, genomic locations per the diploid reference (Edger et al. 2018), and flanking sequences. Cross-reference information for SNPs shared with the iStraw90 SNP array is also provided (Bassil et al. 2015).</div><div><br></div><div>Supplemental Data File 4. Raw phenotypic data (six time points) for 565 germplasm accessions and the Fronteras and Portola S1 mapping populations (NA = missing data).</div><div><br></div

Photocatalytic Hydrogen Evolution from Substoichiometric Colloidal WO_3–<i>x</i> Nanowires

We report direct photocatalytic hydrogen evolution from substoichiometric highly reduced tungsten oxide (WO_<i>x</i>) nanowires (NWs) using sacrificial alcohol. WO_<i>x</i> NWs are synthesized via nonaqueous colloidal synthesis with a diameter of about 4 nm and an average length of about 250 nm. As-synthesized WO_<i>x</i> NWs exhibit a broad absorption across the visible to infrared regions attributed to the presence of oxygen vacancies. The optical band gap is increased in these WO_<i>x</i> NWs compared to stoichiometric bulk tungsten oxide (WO₃) powders as a result of the Burstein–Moss shift. As a consequence of this increase, we demonstrate direct photocatalytic hydrogen production from WO_<i>x</i> NWs through alcohol photoreforming. The stable H₂ evolution on platinized WO_<i>x</i> NWs is observed under conditions in which platinized bulk WO₃ and bulk WO_2.9 powders either do not show activity or show very low rates, suggesting that increased surface area and specific exposed facets are key for the improved performance of WO_<i>x</i> NWs. This work demonstrates that control of size and composition can lead to unexpected and beneficial changes in the photocatalytic properties of semiconductor materials