# In-situ observation of temperature-dependent segregation of Ni adatoms on oriented Pd surfaces

## TL;DR

This study uses PAES to observe how Ni adatoms segregate to the surface of Pd crystals at different temperatures, revealing orientation-dependent activation temperatures for segregation.

## Contribution

It provides the first in-situ, temperature-dependent measurements of Ni surface segregation on oriented Pd surfaces using PAES.

## Key findings

- Pd surface segregation occurs at specific activation temperatures.
- Segregation temperature depends strongly on surface orientation.
- Clear surface segregation behavior was observed for all studied orientations.

## Abstract

We report the direct observation of the in-situ temperature-dependent surface segregation of Ni adatoms on single crystalline Pd surfaces using Positron annihilation induced Auger Electron Spectroscopy (PAES). For this study, a single atomic layer of Ni was grown on Pd with the crystallographic orientations Pd(111), Pd(110) and Pd(100). The sample temperature was increased from room temperature to 350$^\circ$C and the intensity of the Ni and Pd signal was evaluated from the recorded PAES spectra. Due to the outstanding surface sensitivity of PAES a clear tendency for Pd segregation was observed for all samples. Moreover the activation temperature T$_0$ for surface segregation was found to depend strongly on the surface orientation: We determined T$_0$ to 172$\pm$4$^\circ$C, 261$\pm$12$^\circ$C and 326$\pm$11$^\circ$C for Pd(111), Pd(100) and Pd(110), respectively.