My first appreciation is for my advisor, Prof. Xianfan Xu. His rich experience, insightful suggestions, and patient guidance always drove me to overcome bottlenecks and help me learn more about technologies. He also provided a nice atmosphere with talented peers, state-of-the-art facilities, and illuminating discussions. The experience of working with him will benefit my professional development in the future. I would also like to thank Prof. Timothy S. Fisher, Prof. Xiulin Ruan for being my advisory committee members. Besides, I appreciate Dr Guo, Liang from UC Berkley and Vasudevan Iyer for setting up the experiment optics and characterize some helpful discussions. Finally, I woud like to say thank you to my girlfriend and families, they have supported a lot when I am studying for this Master degree, and when I felt confused about the life and career.
Gold nanoparticle (AuNP) decoration is a commonly used
method to
enhance the optical responses in many applications such as photocatalysis,
biosensing, solar cells, etc. The morphology and structure of AuNPs
are essential factors determining the functionality of the sample.
However, tailoring the growth mechanism of AuNPs on an identical surface
is not straightforward. In this study, AuNPs were deposited on the
surface of a perovskite thin film, strontium niobate (SNO), using
pulsed laser deposition (PLD). AuNPs exhibited a dramatic variation
in their growth mechanisms, depending on whether they were deposited
on SNO thin films grown on magnesium oxide (SNO/MgO) or strontium
titanate (SNO/STO) substrates. On SNO/MgO, the Au aggregates form
large NPs with an average size of up to 3500 nm2. These
AuNPs are triangular with sharp edges and corners. The out-of-plane
direction of growth is favored, and the surface coverage ratio by
AuNPs is low. When deposited on SNO/STO, the average size of AuNPs
is much smaller, i.e., ∼250 nm2. This reduction
in the average size is accompanied by an increase in the number density
of NPs. AuNPs on SNO/STO have a round shape and high coverage ratio.
Such an impact from the substrate selection on the AuNP structure
is significant when the sandwiched SNO film is below 80 nm thickness
and is weakened for 200 nm of SNO films. X-ray diffraction (XRD) and
scanning electron microscopy (SEM) were used to characterize all samples.
Strain analysis was used to explain the growth mechanism of AuNPs.
The average height of AuNPs was measured by using atomic force microscopy
(AFM). Ellipsometry in the visible–near-infrared (vis–NIR)
region was used to characterize the optical response of all samples.
AuNP-decorated SNO/MgO and SNO/STO thin films exhibit different optical
properties, with only gold-decorated SNO/MgO samples showing a size-dependent
epsilon-near-zero behavior of nanoparticles. These results provide
an additional route to control the structure of AuNPs. They can be
used for various plasmonic applications like the design and development
of strain-engineered gold-nanoparticle-decorated devices for surface-enhanced
Raman spectroscopy (SERS) and photocatalysis.
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