“Alloys at the Nanoscale: The case of nanoparticles” Miguel Jose Yacaman, University of Texas Austin, DMR 0602587

The understanding of how the phase composition and structure of metal alloys at the nanoscale is a very important subject in nanotechnology. In particular, when the alloy has a few nanometers of size the exact phase distribution in equilibrium might determine many properties such as catalytic activity, optical emission and absorption and many others. In this research, we have started a systematic study of phase diagrams of nanoparticles using advanced TEM techniques in the first year of the work we have studied Au/Pd and Au/Ag alloys.The standard model is that bimetallic nanoparticles will be either in an alloyed state of will segregate forming a core shell structure. This behavior will be determined by the synthesis conditions .

We found a surprising new result for Au/Pd nanoparticles prepared by wet chemistry methods. The structure is more complicated consisting in a three-layer structure, an inner core of Pd, a second layer of gold, and a third layer rich in Pd. This opens a new understanding of the properties of nanoparticles. We use STEM –HAADF images at resolution below 0.1 nm using the ACEM facility at ORNL in collaboration with Dr Larry Allard’s group. Figure 1 shows the STEM images at medium and high resolution. By comparing this structure with the ones obtained at different preparation conditions, we will be able to control the properties of nanoparticles. The project is binational between the University of Texas and the University Of Nuevo Leon

Atomic Resolution at

sub Å Level was achieved

Comparing Experimental Images

With Theoretical Calculations

A new structural model of the alloy particle was

developed

Facets with high Miller

indexes Were

Produced

This Project is part of the CIAM international Collaboration. Includes the University Of Texas and Two Mexican labs The University Of Nuevo Leon and The IPICYT. Students

of every lab travel to the other participants laboratories .Four Hispanic students were involved on the project .

The collaboration has produced 4 joint papers Including a Highlight paper in Journal of materials Chemistry. Results of the research has been included in two UT courses .CHE

350 Materials science and CHE 383 nanotechnology

The participants on the project have been participating in lecturing undergrad students

both In Mexico and USA about graduate research opportunities in the participant

institutions

Miguel Jose Yacaman, The University of Texas Austin, DMR 0602587