  The motion of partly gold (Au)-coated Janus particles under laser irradiation
is caused by self-thermophoresis. Despite numerous studies addressing this
topic, the impact of the preparation method and the degree of coverage of the
particle with Au on the resulting thermophoretic velocity has not yet been
fully understood. A detailed understanding of the most important tuning
parameters during the preparation process is crucial to design Janus particles
that are optimized in Au coverage to receive a high thermophoretic velocity. In
this study, we explore the influence of the fabrication process, which changes
the Au cap size, on the resulting self-propulsion behavior of partly Au-coated
polystyrene particles (Au-PS). Additionally, also the impact of an underlying
adhesion chromium layer is investigated. In addition to the most commonly used
qualitative SEM and EDX measurements, we propose a novel technique utilizing
AFM studies to quantify the cap size. This non-invasive technique can be used
to determine both the size and the maximum thickness of the Au cap. The Au cap
size was systematically varied in a range between about 36 % and 74 % by
different preparation strategies. Nevertheless, we showed that the differing Au
cap size of the Janus particles in this range has no effect on the
thermophoretic velocity. This surprising result is discussed in the paper.
