PD Research Report for the 2015 year
Name（Research group）Li Wang
（Tamai Research Group, Graduate School of Science and Technology）
Research Theme

半導体ナノ微粒子系の多励起子素過程の解明と光応答分子システムへの応用

Research Period

September, 20th, 2015 ~ March, 31st, 2016

The semiconductor nanostructures are promising to provide multiexciton generation for thephtoswitchable systems. Metal nanostructures are good candidates as electron acceptors with attachmentof semiconductor nanoparticles. They also represent unique optical properties and localized surface
enhancements of electrical fields. In semiconductor and metal hybrid nanosystems, metal components
may influence exciton dynamics by charge separation or electric near-field enhancement.1,2 My
interesting is simulation of the optical properties of metal nanostructures for designation of new typehybrid nanosystems. For example, Pd and Ag/Pd/Ag sandwich nanoplates represent tunable localized
surface plasmon resonance (LSPR) from near infrared to visible region, which can be alternative
materials of normal Au nanostructures. The ultrafast dynamics of Pd and Ag/Pd/Ag sandwich nanoplates
represent a continuous variation of the coherent acoustic phonon vibration with increasing the contentsof Ag. The origin of the vibration was assigned to phonon oscillation from tip to tip or from edge to edgeof the nanoplates. With numerical simulation of eigenfrequency and LSPR by Comsol multiphysics, theresults of deformation of nanoplates and LSPR shift can be used for the explanation of the process ofcoherent acoustic phonon vibration. For this purpose, I simulated the extinction spectra and the structure
vibration of Pd and Ag/Pd/Ag sandwich nanoplates.
The models of Pd and Ag/Pd/Ag sandwich nanoplates are designed according to TEM results asshown in Figure 1. The length/height of Pd nanoplates are estimated to be (27.0 ± 2.3)/(1.8 ± 0.4) nm.
Random distribution of Ag nanoparticles on the plane of Pd nanoplates (probably on both upper andbottom sides) is observed in the TEM images of Ag/Pd/Ag A (Figure 1b), which are prepared with theleast Ag contents. With increasing Ag contents, the brightness of TEM images is enhanced for Ag/Pd/AgJ (Figure 1c), which are prepared with more Ag contents. The structural schematics for the three typical
species are plotted in Figure 1d, which are used as the geometries in the simulation by Comsol
Multiphysics. The content ratios of Ag and Pd for all the Ag/Pd/Ag sandwich nanoplates are obtained
from inductively coupled plasma mass spectrometry (ICP-MS). Hence, the thickness of Ag shell isFigure 1. TEM images of Pd nanoplates (a) and Ag/Pd/Ag sandwich nanoplate with two different Ag contents (b and cfor the samples labeled with Ag/Pd/Ag A and Ag/Pd/Ag J in the text).Schematics of hexagonal Pd nanoplates, Ag/Pd/AgA (Ag nanoparticle decorated on both upper and bottom planes of Pd nanoplates), and Ag/Pd/Ag J (thick Ag shellcoated on both planes of Pd nanoplates) (d).

estimated to be 1.9, 2.9, 3.6, 4.3, 4.7, 8.0, 10.0, 10.5, 13.5, 21.0, and 25.0 nm, respectively. With
increasing Ag content, the eleven Ag/Pd/Ag sandwich nanoplates are labeled as Ag/Pd/Ag A, B, C, D, E,F, G, H, I, J, and K, correspondingly.
The experimental absorption spectraof Pd and Ag/Pd/Ag nanoplates are shownin Figure 2a. The peak position and fullwidth at half maximum (FWHM) ofplasmon band for all the nanoplates aresummarized in Figure 2c. The simulationof extinction spectra for Pd and Ag/Pd/Ag
nanoplates are plotted in Figure 2b andare summarized in Figure 2d. The
simulation

spectrum

isin

a

good

agreement with experimental data for
uncoated Pd nanoplates dispersed in water.
After AgNO 3 solution was gradually
added for growth of Ag shell, the LSPR
peak is red-shifted to 1143 nm for

Figure 2. Experimental extinction spectra and the corresponding
peak wavelength and full width at half maximum (FWHM) of Pd
and Ag/Pd/Ag nanoplates (a and c). Simulation extinction spectraof Pd and Ag/Pd/Ag nanoplates with 2, 4, 8, 12, 20, and 25 nm
Ag shell thickness (b and d).

Ag/Pd/Ag A owing to the plasmonic
percolation behavior.3 However, the simulated spectrum for the model of Ag/Pd/Ag A is almost no shift
from pure Pd nanoplate (data is not shown here). With further adding Ag contents, the LSPR peak begins
blue shift and finally reaches to 460 nm for Ag/Pd/Ag K. With increasing the thickness of Ag shell from
2 to 25 nm, the simulated spectra are also blue shifted from 654 to 452 nm and FWHM becomesnarrower from 170 to 95 nm, correspondingly.
The shift of LSPR of Pd and Ag/Pd/Ag sandwich nanoplates corresponding to the structure
deformation induced by laser irradiation is still in progress. The data will helpful for understanding thesize variation in the process of coherent acoustic phonon vibration of metal nanostructures.
Publications:
1) L. Wang, Y. Tian, T. Okuhata, and N. Tamai, “Charge Transfer Dynamics and Auger Recombinationof CdTe/CdS Core/Shell Quantum Dots”, J. Phys. Chem. C 2015, 119, 17971−17978
2) L. Wang, T. Sagaguchi, and N. Tamai, “Coherent acoustic phonon vibration of Pd and Ag/Pd/Ag
sandwich nanoplates”, (In draft)
Reference:(1) Okuhata, T.; Kobayashi, Y.; Nonoguchi, Y.; Kawai, T.; Tamai, N. Ultrafast Carrier Transfer and HotCarrier Dynamics in PbS-Au Hybrid Nanostructures. J. Phys. Chem. C 2015, 119, 2113-2120.
(2) Masuo, S.; Kanetaka, K.; Sato, R.; Teranishi, T. Direct Observation of Multiphoton Emission
Enhancement from a Single Quantum Dot Using AFM Manipulation of a Cubic Gold Nanoparticle. Acs
Photonics 2016, 3, 109-116.
(3) Chen, H.; Wang, F.; Li, K.; Woo, K. C.; Wang, J.; Li, Q.; Sun, L.-D.; Zhang, X.; Lin, H.-Q.; Yan, C.-H.
Plasmonic Percolation: Plasmon-Manifested Dielectric-to-Metal Transition. ACS Nano 2012, 6, 7162-7171.