Nanoparticles of metals are interesting nanomaterials because of the large number of possible uses to which they can be put. An example is the need to find non-platinum-based catalysts for fuel cells. It is clear that at the nano-size level, alloying behavior cannot always be predicted by "bulk" phase diagrams, but phase diagrams of nanoparticle systems are not complete and their determination poses a very complex problem. A focus of the present work is to establish reliable phase diagrams of nanoparticle alloys, including Au-Pd, Au-Ag, Pt-Pd, Au-Co and Pd-Ir alloys, all of which have important potential applications. Major instrumentation for this work is the new STEM aberration-corrected microscope with a resolution of 0.08 nm at the University of Texas at San Antonio; it is equipped with state-of-the-art EDS and EELS accessories. Tomography methods in the STEM and TEM will be used to explore the shapes of the nanoparticles in 3 dimensions. The particles will be prepared by a variety of methods, which have proved to be reliable for the production of nanoparticles with controlled size, shape and structure distribution. It is expected that improved understanding will emerge of the conditions leading to core shell or Janus particles for a given alloy concentration. Experimental results will be compared with theoretical calculations of stability and structure using a first principles approach.
NON-TECHNICAL SUMMARY: One of the most important aspects of modern technology is the use of precious metals such as platinum, rhodium or palladium in industrial process related to the chemical industry. These metals are scarce in nature and their use has to be optimized. Currently, if all of the cars in the United States used fuel cells, the nation would likely consume all of the Pt reserves in the world. New technologies are thus required. In this proposal the team is involved in the use of bimetallic nanoparticles. The aim is to use a core of a less valuable metal such as Cu, Au, or Ag to try to induce an atomically thin surface shell of the more active metal Pt, Pd or Rh, as well as to explore the possibility that the combination of the two metals will expose new properties. This project will complement a PREM-NSF program at the University of Texas at San Antonio and will also contribute to the advancement of underrepresented groups, since several of the Ph.D. students involved in the project are Hispanics. The PIs also have outreach components in the Junior Colleges of the San Antonio Area to induce Hispanic students to enroll in the 2-year program and then to a full 4-year program. The PI and Co-PI have considerable experience in recruiting minority students.
" has been supported by NSF into the period 09/15/2011 - 08/31/2014. The project has been successful and has resulted in almost 40 publications on the scientific literature and four PhD theses. It has also been a cornerstone in International collaboration and outreach in the south of Texas. In the previous stages we obtained important results such as the first demonstration of the onion structure in bimetallic alloys, which is now widely accepted as one on the possible structures on bimetallic alloys. One of the most exciting features of metal nanoparticles and nanoalloys is that their properties depend on size and structure. Chemical composition is another factor that affect the physical and chemical properties of a nanoparticle, and the spectrum of possibilities is quite diverse, since the same set of metals A and B may form different structures, depending on the elements, thermal conditions, and details of the synthesis procedure. During this project we have been concentrated on bimetallic systems, which have many practical applications in areas such as catalysis and health. In addition, we have explored the effect of adding a third metal to the alloys with a high control of the shape and crystalline structure allowing real surface site engineering. In the project we work in both theoretical calculations and experimental synthesis and characterization methods for several advanced techniques. We worked following the philosophy delineated on the materials genome initiative i.e.: A strong interplay of the theoretical calculations to guide synthesis and properties and feedback to the theory from the experimental data. We explored the structure (including internal strain) and a number of properties such as electrical, optical and magnetic. We have carried out our work in state-of-the-art instrumentation at atomic resolution level using very powerful set of techniques such as aberration-corrected scanning transmission electron microscopy, electron holography, electron diffraction, high efficiency EDS and EELS. In addition, special stages were used to measure in situ properties. Our systematic study provided the basis for Nano crystal particle Engineering. That means to advance to the possibility of locate atoms of a metal of interest in the surface of a nanoparticle. Our synthesis methods determined a related "quality control" with the chemical activity used for catalysis and biomedical applications, leading into advanced nanotechnology developments. Intellectual Merit: The advance of Nano technology is now link to a much finer control of the structure of nanostructures. Indeed any real application requires reliable and reproducible fabrication methods and stable structures in which their toxicity must be carefully controlled. Nanoparticles are one of the most common systems used in nanotechnology. This project contributed to the advance of the field. In addition, the project has been pioneer in the study of in situ transmission electron microscopy measurements to extract physical and chemical properties from the nanoparticles synthetized. Broader Impact: This project covered a very strong part in the efforts of the PI and UTSA to increase the number of underrepresented minority students in STEM areas in south Texas, this is even more important because of the demographics change on the region which has had an increase on the Hispanic population and need for inducing them to STEM areas which is crucial for the future of the State. Part of our activities have been the Nano Day, the Annual Core 4 STEM Expo targeting 7th and 8th grade students to encourage STEM areas. We also have participated in the "Latina Day", a convention targeting middle school girls, and in the "College and Parent Day" where both students and parents were able to explore what science and engineering do. The project attracted the recruitment of top minority graduate students whose have been graduated from the PhD program at Physics Department and finally the project has been contributed significantly in the increasing number of undergraduate students by the promotion of our findings and new developments in the San Antonio area.
