TEM sequence of a single grain boundary formation, growth, rotation, sliding and migration between two Au nanoparticles.

1. Measuring the strength of individual metal nanoparticles DMR-0934218 It is well established that matter behaves in a different manner at the nanoscale compared with their bulk counterparts. Mostly, this is due to confinement of electron, increased surface to volume ratio, composition, etc.; therefore, the study of matter at the nanoscale is of crucial relevance to continue the development of nano-devices that surrounds our everyday life. Most of the electronic devices use electrical contacts that (usually gold), if not made properly, can fail due to unknown effects when reducing features at the nanoscale. PREM researchers at UTSA have developed a technique to study single gold contacts (single grain boundary) while directly observing the interface in an electron microscope. The grain boundary presents a liquid-like behavior and is free to rotate as one of the nanoparticles is moved manually. Moreover, surface diffusion coefficient and grain boundary energies can be computed from the experimental observations. This methodology can be used for particles for many other metals, oxides, semiconductors, etc., or a combination of them. With these many possibilities, measurements of physical properties of different systems will be done in the near future. Gilberto Casillas (Ph.D. Student) Miguel Yacaman (Advisor) TEM sequence of a single grain boundary formation, growth, rotation, sliding and migration between two Au nanoparticles. Scale bars are 10 nm. For more details, visit the UTSA PREM website at physics.utsa.edu/PREM

2. Measuring the strength of individual metal nanoparticles DMR-0934218 Mechanical properties of materials have been widely investigated for many years in order to develop stronger materials. This can be achieved by changing the structure of the materials at the nano scale, however, a loss in ductility can render these materials impractical in many cases. Thus, the development of materials with high strength and ductility is of high interest in many research areas, from MEMS fabrications to lubricants. It is well known that the properties of any material changes at the nanoscale. Our PREM researchers have been able to test the mechanical properties of individual gold nanoparticles under 80 nm in size. These nanoparticles presented yield strengths in the order of GPa, however, nanoparticles containing coherent twin boundaries were compressed more than 80% without fracturing. Nanoparticles with twin boundaries can be synthesize from many different materials like Cu, Ag, Pt, Pd, opening many possibilities. One of the projects of our PREM is focused in understanding why these nanoparticles present such properties, and a future work is to test particles made out of cheaper materials, such as cooper, in order to implement them in real applications. Gilberto Cassilas (Ph.D. Student) Dr. Miguel Yacaman (Advisor) 100 nm Transmission electron micrographs of an in-situ compression experiment of an individual gold nanoparticle. 20 nm For more details, visit the UTSA PREM website at physics.utsa.edu/PREM