In-situ monitoring during pulsed laser deposition using RHEED at high pressure

Abstract

Reflection high energy electron diffraction (RHEED) is, due to its surface sensitivity, often used for the analysis and monitoring of thin film growth in ultra-high vacuum deposition systems. RHEED is usually applied in combination with pulsed laser deposition (PLD) by adjusting the background pressure. However, the pressure during PLD is an important parameter because it influences the shape and size of the plasma. Low deposition pressures during PLD can lead to stress, usually compressive, in the film. Moreover, the oxidation power is much higher at higher pressures, which enables growth at higher temperatures, leading to better crystallinity of the as-deposited films. Therefore, relative high pressures are favourable in PLD. Unfortunately, these high pressures hamper the diagnostics of the growing film surfaces by in-situ RHEED. Here, a RHEED system designed for growth monitoring at high deposition pressures is presented. The main problem that has been solved is the increased scattering loss. The losses are minimised by keeping the travelling path of the electrons in the high-pressure region as short as possible. Using a two-stage differential pumping system, we are able to increase the deposition pressure up to 50 Pa. With this system, we have monitored the growth of SrTiO 3, YBa 2Cu 3O 7− δ and SrCuO x , in a background pressure of 15 Pa of oxygen. The first two systems show clear oscillations of the diffracted intensity, indicating two-dimensional growth, with the possibility to control the thin film growth on an atomic level at standard PLD pressures. Furthermore, the mobility of material deposited with one single laser pulse is represented by an additional modulation of the intensity of the RHEED pattern. This gives excess information about the diffusion and nucleation of the deposited material.