Browsing by Author "Chen, Hsiang-An"

Now showing 1 - 3 of 3

Measurement of Interlayer Screening Length of Layered Graphene by Plasmonic Nanostructure Resonances
(2013-10-31)
Chen, Hsiang-An
;
Hsin, Cheng-Lun
;
Huang, Yu-Ting
;
Tang, Ming Lee
;
Dhuey, Scott
The variation in localized surface plasmon resonances of single Au nanodisks (diameter 100 nm and height 25 nm) on 0-13 graphene layers is investigated using dark-field scattering spectroscopy to obtain the graphene electric field screening length. For nanodisks (NDs) with and without underlying graphene layers on a SiO2 (300 nm)/Si substrate, the plasmon resonance red shifts from 604 to 620 nm with increasing graphene layers. The spectra of the plasmonic nanostructures obey an exponential saturation function versus increasing number of layers of graphene from 0 to 13. As a conducting film, the graphene layers screen the electric field generated by the plasmonic resonance of the Au NDs in the vicinity of the interface, and the red shifts of the resonance wavelength are explained in the framework of the electromagnetic field coupling between in-plane antiparallel image dipoles in the graphene layers and the ND dipole. A screening length of 1.2 +/- 0.2 nm, equivalent to 3-4 graphene layers, is experimentally obtained, in good agreement with the measurement by field-effect transistors and theoretical calculation in doped graphene. The resonance shift of plasmonic nanostructures on a layered graphene system provides an alternative and convenient method for screening length measurement of graphene films.
Near-Field Optical Imaging of a Porous Au Film: Influences of Topographic Artifacts and Surface Plasmons
(2013-06-01)
Lin, Yu-Hsuan
;
Haendel, Benjamin
;
Huang, Hung Ji
;
Chen, Hsiang-An
;
Chen, Yung-Fu
In this work, near-field scanning optical microscopy is employed to study a porous Au film and the direct observation of topographic artifacts and surface plasmon influences is revealed. Under tip illumination, topographic artifacts are found to be present in a reflection mode optical image but not in a transmission mode image. A simple algorithm is used for filtering the topographic artifacts and extracting a correct near-field optical image approximately. On the other hand, surface plasmon influences are present in both modes. By using three exciting wavelengths of 488, 647.1, and 520.8 nm, it is confirmed that a suitable wavelength should be chosen for avoiding the surface plasmon interference in a near-field optical investigation of morphological or material dielectric contrast. Finally, plasmonic or nonplasmonic regions on the porous Au film can be identified from the observed optical intensity variation in the optical images obtained at incident polarizations of 0 degrees, 90 degrees, and 45 degrees.
Sodium niobate nanowire and its piezoelectricity
(2008-06-19)
Ke, Tsung-Ying
;
Chen, Hsiang-An
;
Sheu, Hwo-Shuenn
;
Yeh, Jien-Wei
;
Lin, Heh-Nan
Nanowires of crystalline orthorhombic sodium niobate (NaNbO3) with diameters of approximately 100 nm and lengths of several to hundreds of microns, as well as cubes with edges of lengths of hundreds of nanometers were obtained by reacting niobium oxide (Nb2O5) with 10 and 12.5 M NaOH solutions, respectively. The microstructures of the synthesized wiry and cubic piezoelectric materials were investigated, and the details of the reactions were elucidated as well. The piezoelectricity of individual NaNbO3 (Pbma) nanowires was confirmed by piezoresponse force microscopy, and an effective piezoelectric coefficient along the vertical direction of around a few pm/V was obtained. To our knowledge, the present work is the first report of the preparation of NaNbO3 nanowires as well as the determination of piezoelectricity.