This proposal uses time of flight atom-probe field ion microscopy (APFIM) to examine the near-surface composition profiles associated with surface segregation in metal alloys. Composition variations in the near surface layers of platinum-rhodium, platinum-gold, platinum-nickel, and molybdenum-rhenium alloys are measured over a depth of 10 to 15 atomic layers. The specimens are in the form of emitter tips with thin films deposited on the tip surface and interfaces parallel to the tip emitter surface. The pattern of chemical distribution is determined as a function of depth below the surface and correlated with alloy behavior such as chemisorption and order-disorder phase transformations. %%% It is important to understand the elemental segregation at the surface of metal alloys because surface composition can affect potential applications that require properties such as oxidation resistance, chemisorption, catalytic behavior, and wear resistance.
