Surface segregation and diffusion kinetics study of a Pt-Ir alloy using the time-of-flight atom-probe field ion microscope

Abstract

Two absolute composition depth profiles of single atomic layer depth resolution have been obtained for the (001) surface of a Pt-20% Ir alloy. Pt segregates only to the top two surface layers. A feature of a diffusion kinetic effect has also been observed from which diffusion parameters of alloy species in the near surface layers are estimated.

3D atom probe study of gaseous adsorption on alloy catalyst surfaces III: Ternary alloys – NO on Pt–Rh–Ru and Pt–Rh–Ir

“…On platinum-ruthenium alloys, slight platinum surface segregation was noted on heating under vacuum [23,24], while platinum also segregated to the surface in a Pt-20%Ir alloy under vacuum heating and with sulphur contaminated surfaces [25,26]. Similar surface enrichment of platinum has also been observed in Pt-Rh [27], although for this alloy the presence of sulphur causes rhodium enrichment instead [28].…”

Advances in atom probe tomography instrumentation: Implications for materials research

“…Reaction cell development has its roots in the binary Ptalloy surface segregation studies of Tsong et al, 31 who used a 1D atom probe equipped with a heating loop to rapidly heat samples. Heating a sample within the analysis chamber has also been extensively employed to study low pressure ( ∼ 10 -3 mbar or 100 Pa) surface restructuring reactions by a combination of fi eld ion microscopy and a 1D atom probe.…”

An investigation of phase separation in the Ir–Pt binary system

“…The diffusion coefficient of Ir in Pt in the 10 atomic layers of the Pt-20 at.%Ir alloy is reported as 0.17 × 10 −16 cm 2 s −1 at 973 K [12]. The time necessary for atoms to move over an arbitrary diffusion distance is estimated using the following equation:…”

“…It is well known from various other alloy systems, where the spinodal decomposition takes place after aging, that a modulated microstructure produces high mechanical strength [10,11]. Because of this segregating tendency (miscibility gap), it was proposed that the Pt atoms will segregate to the surface, and this was observed using atom-probe field ion microscopy [12] and Auger electron spectroscopy [13,14]. Thus, the Ir-Pt alloys are also expected to find use as catalysts for auto emission gas and in fuel cells [15,16].…”