A series of high-quality bronze titanium oxide films containing endotaxially embedded Pt-based nanoparticles was fabricated using pulsed laser deposition under various oxygen partial pressures (0 to 50 mTorr). We found that morphological control over the embedded Pt nanoparticles is possible by varying the oxygen partial pressure during growth. We also found that the titanium oxide matrix plays an important role in controlling composition, shape, and distribution of the endotaxially embedded Pt-based nanoparticles over this range of oxygen partial pressure by affecting (1) the formation of a segregated layer of Pt–Ti alloy nanoparticles, in addition to the pure Pt nanoparticles, under vacuum, (2) the generation of crystallographic twinning, steps, and kinks within the Pt nanoparticles, and (3) the localized precipitation of Pt nanoparticles spatially confined and morphologically adapted to the extended defects within the matrix.

Since catalytic performance of platinum–metal (Pt–M) nanoparticles is primarily determined by the chemical and structural configurations of the outermost atomic layers, detailed knowledge of the distribution of Pt and M surface atoms is crucial for the design of Pt–M electrocatalysts with optimum activity. Further, an understanding of how the surface composition and structure of electrocatalysts may be controlled by external means is useful for their efficient production. Here, we report our study of surface composition and the dynamics involved in facet-dependent oxidation of equilibrium-shaped Pt3Co nanoparticles in an initially disordered state via in situ transmission electron microscopy and density functional calculations. In brief, using our advanced in situ gas cell technique, evolution of the surface of the Pt3Co nanoparticles was monitored at the atomic scale during their exposure to an oxygen atmosphere at elevated temperature, and it was found that Co segregation and oxidation take place on {111} surfaces but not on {100} surfaces.Keywords: facet-dependent oxidation; gas cell; in situ TEM; Pt−Co nanoparticles; surface elemental distribution;

AbstractFacile fabrication of advanced catalysts toward oxygen reduction reaction with improving activity and stability is significant for proton-exchange membrane fuel cells. Based on a generic solid-state reaction, this study reports a modified hydrogen-assisted, gas-phase synthesis for facile, scalable production of surfactant-free, thin, platinum-based nanowire-network electrocatalysts. The free-standing platinum and platinum–nickel alloy nanowires show improvements of up to 5.1 times and 10.9 times for mass activity with a minimum 2.6% loss after an accelerated durability test for 10k cycles; 8.5 times and 13.8 times for specific activity, respectively, compared to commercial Pt/C catalyst. In addition, combined with a wet impregnation method, different substrate-materials-supported platinum-based nanowires are obtained, which paves the way to practical application as a next-generation supported catalyst to replace Pt/C. The growth stages and formation mechanism are investigated by an in situ transmission electron microscopy study. It reveals that the free-standing platinum nanowires form in the solid state via metal-surface-diffusion-assisted oriented attachment of individual nanoparticles, and the interaction with gas molecules plays a critical role, which may represent a gas-molecular-adsorbate-modified growth in catalyst preparation.

Understanding the structures of catalysts under realistic conditions with atomic precision is crucial to design better materials for challenging transformations. Under reducing conditions, certain reducible supports migrate onto supported metallic particles and create strong metal–support states that drastically change the reactivity of the systems. The details of this process are still unclear and preclude its thorough exploitation. Here, we report an atomic description of a palladium/titania (Pd/TiO2) system by combining state-of-the-art in situ transmission electron microscopy and density functional theory (DFT) calculations with structurally defined materials, in which we visualize the formation of the overlayers at the atomic scale under atmospheric pressure and high temperature. We show that an amorphous reduced titania layer is formed at low temperatures, and that crystallization of the layer into either mono- or bilayer structures is dictated by the reaction environment and predicted by theory. Furthermore, it occurs in combination with a dramatic reshaping of the metallic surface facets.

•Multiple techniques were performed to characterize the CZTSe solar cell system.•Spatially resolved Raman mapping was used to study the chemistry variation.•Unlike the horizontal ones, the vertical grain boundaries helps carrier collection.•The results predicts the optimized cell structure.We report a novel fabrication and multiple high resolution characterizations of Cu2ZnSnSe4 solar cells. The fabrication is based on nanoparticle precursor production by liquid-phase pulsed laser ablation (LP-PLA), electrophoretic deposition of precursor thin film under ambient condition, and selenization. Columnar grain boundaries are studied using spatially mapped Raman spectroscopy and scanning probe microscopy for their compositional and electrical properties. We observe high electrical conductivity near columnar grain boundaries, and propose poor Cu composition as the cause of the enhancement of the collection of minority carriers. We also study horizontal grain boundaries using cross-sectional scanning transmission electron microscopy (STEM). Combining with the device I-V and quantum efficiency, we suggest that the horizontal grain boundaries act as barriers to the transportation of minority carriers. CZTSe cells with efficiencies of 4.77% and 2.20% are compared.

The bronze polymorph of titanium dioxide, known as TiO2(B), has promising photochemical and electronic properties for potential applications in Li-ion batteries, photocatalysis, chemical sensing, and solar cells. In contrast to previous studies performed with powder samples, which often suffer from impurities and lattice water, here we report Raman spectra from highly crystalline TiO2(B) films epitaxially grown on Si substrates with a thin SrTiO3 buffer layer. The reduced background from the Si substrate significantly benefits acquisition of polarization-dependent Raman spectra collected from the high-quality thin films, which are compared to nanopowder results reported in the literature. The experimental spectra were compared with density functional theory calculations to analyze the atomic displacements associated with each Raman-active vibrational mode. These results provide a standard reference for further investigation of the crystallinity, structure, composition, and properties of TiO2(B) materials with Raman spectroscopy.

We demonstrate, in great detail, a completely waterless synthesis route to produce highly crystalline epitaxial thin films of TiO2-B and its more stable variant CaTi5O11, using pulsed laser deposition (PLD).

The bronze polymorph of titanium dioxide, TiO2-B, characterized by a crystal structure with a relatively open layered geometry, is a material of interest for various energy applications, including photovoltaics, catalysts, and high-rate energy storage devices. The related phase, CaTi5O11, which serves as an effective template layer, when deposited on (100) SrTiO3, for the growth of high quality single crystalline films of TiO2-B, is also of interest for such applications. For both materials, a detailed understanding of the film growth and defect structure is deemed critical to the successful realization of these applications in thin film devices. Thus, using results obtained with aberration-corrected transmission electron microscopy, we present an analysis of the defects and interfacial structure in CaTi5O11 films grown on (100) and (110) SrTiO3 substrates, as well as in the TiO2-B film grown on (001) CaTi5O11.

We demonstrate, in great detail, a completely waterless synthesis route to produce highly crystalline epitaxial thin films of TiO2-B and its more stable variant CaTi5O11, using pulsed laser deposition (PLD).