Studying Pulsed Laser Deposition conditions for Ni/C-based multi-layers

TL;DR

This study investigates the optimal pulsed laser deposition conditions for Ni/C multi-layers, crucial for future X-ray and gamma-ray telescopes, focusing on process parameters and their effects on layer quality.

Contribution

It provides detailed analysis of growth conditions and their impact on Ni/C multi-layer quality, highlighting the effects of temperature and pressure on intermixing and surface roughness.

Findings

Surface roughness ≤0.2 nm achieved on treated SiO substrates

Higher temperatures (>300°C) cause intermixing detrimental to reflectivity

Droplets during melting increase surface roughness, cannot be fully avoided

Abstract

Nickel carbon based multi-layers are a viable route towards future hard X-ray and soft $\gamma$-ray focusing telescopes. Here, we study the Pulsed Laser Deposition growth conditions of such bilayers by Reflective High Energy Electron Diffraction, X-ray Reflectivity and Diffraction, Atomic Force Microscopy, X-ray Photoelectron Spectroscopy and cross-sectional Transmission Electron Microscopy analysis, with emphasis on optimization of process pressure and substrate temperature during growth. The thin multi-layers are grown on a treated SiO substrate resulting in Ni and C layers with surface roughnesses (RMS) of $\leq$0.2 nm. Small droplets resulting during melting of the targets surface increase the roughness, however, and can not be avoided. The sequential process at temperatures beyond 300$^\circ$C results into intermixing between the two layers, being destructive for the reflectivity of the multi-layer.