Werner Wessels

Ph.D. thesis

Thesis title:

Growth monitoring during pulsed laser deposition of oxides using atomic force microscopy

[thesis in pdf format]




Prof. dr. ing. A.J.H.M. Rijnders / Prof. dr. ir. G. Koster

Date defense:


Throughout this thesis, an atomic force microscopy (AFM) design, containing a high resonance frequency AFM scanner together with high bandwidth SPM electronics is demonstrated, with focus on growth monitoring during PLD of oxides. Moreover, perovskite oxide growth (related) studies are explored using ex situ AFM and reflection high-energy electron diffraction (RHEED).
The majority of this work is focused on the developed AFM. This AFM contains a
flexure scanner, typically used in the field of high speed AFM, and high bandwidth scanning probe microscope (SPM) electronics. The AFM is capable of operating under PLD conditions ranging from pressures 10-6 - 1 mbar O2 at temperatures ranging from RT up to 700 oC.
A proof of principle is shown by imaging of the growth of BiFeO3 islands on a
SrTiO3 substrate under PLD conditions with (sub)nanometer height resolution.
Furthermore, neck formation is limiting imaging of mixed terminated SrTiO3 using
a Si AFM tip. In order to quasi real-time monitor the oxide growth kinetics, a tip-sample (side)approach method using a faster transfer stage has been demonstrated. This tip-sample approach method, reducing the tip-sample approach time, can be applied when deposition and growth are separated in time. Both transfer stage motion time and reposition repeatability are important for monitoring PLD growth of islands using AFM. The experimental results reveal that the transfer stage motion time between the PLD and AFM position can be reduced from several seconds to (sub)seconds with a reposition repeatability error of ± 60 nm. Moreover, no signatures of loss in AFM spatial resolution are found even after more than hundred repetitive side approaches. Some efforts are recommended increasing the bandwidth of both the cantilever and (optical) detection system in order to increase the maximum achievable AFM acquisition rate under oxide PLD conditions. This is required for enabling AFM monitoring of growing perovskite oxide islands during PLD. Moreover, increasing both the AFM feedback bandwidth and transfer stage speed will result in a faster tip-sample approach time using the side approach method.