arXiv subjects

Yurui Fang

Publications and source records attributed to Yurui Fang.

24 records · Page 2Linked to original sources

arXiv2015

Quantitatively analyzing the mechanism of giant circular dichroism in extrinsic plasmonic chiral nanostructures by the interplay of electric and magnetic dipoles

The plasmonic chirality has drawn a lot of attention because of the tunable circular dichroism (CD) and the enhancement for the signal of chiral molecules. Different mechanisms have been proposed for explaining the plasmonic CD, however, a quantitative one like ab initio mechanism in chiral molecules is still unavailable. In this work, a mechanism similar to the chiral molecules is analyzed. The giant extrinsic circular dichroism of plasmonic splitting rectangle ring is quantitatively investigated theoretically. The interplay of electric and magnetic modes of the meta-structure is proposed to explain the giant CD. The interplay is analyzed both in an analytical coupled electric-magnetic dipoles model and finite element method model. The surface charge distributions show that the circular current yielded in the splitting rectangle ring makes it behave like a magneton at some resonant modes, which interact with electric modes and results in a mixing of the two kinds of modes. The strong interplay of the two kinds of modes is mainly responsible for the giant CD.The analysis of the chiral near field of the structure shows potential applications in chiral molecule sensing.

cond-mat.mes-hall↗

arXiv2015

Formation of Enhanced Uniform Chiral Fields in Symmetric Dimer Nanostructures

Chiral fields with large optical chirality are very important in chiral molecules analysis, sensing and other measurements. Plasmonic nanostructures have been proposed to realize such super chiral fields for enhancing weak chiral signals. However, most of them cannot provide uniform chiral near-fields close to the structures, which makes these nanostructures not so efficient for applications. Plasmonic helical nanostructures and blocked squares have been proved to provide uniform chiral near-fields, but structure fabrication is a challenge. In this paper, we show that very simple plasmonic dimer structures can provide uniform chiral fields in the gaps with large enhancement of both near electric fields and chiral fields under linearly polarized light illumination with polarization off the dimer axis at dipole resonance. An analytical dipole model is utilized to explain this behavior theoretically. 30 times of volume averaged chiral field enhancement is gotten in the whole gap. Chiral fields with opposite handedness can be obtained simply by changing the polarization to the other side of the dimer axis. It is especially useful in Raman optical activity measurement and chiral sensing of small quantity of chiral molecule.

physics.optics↗

arXiv2015

Fano resonance assisting plasmonic circular dichroism from nanorice heterodimers for extrinsic chirality

In this work, the circular dichroisms (CD) of nanorice heterodimers consisting of two parallel arranged nanorices with the same size but different materials are investigated theoretically. Symmetry-breaking is introduced by using different materials and oblique incidence to achieve strong CD at the vicinity of Fano resonance peaks. We demonstrate that all Au-Ag heterodimers exhibit multipolar Fano resonances and strong CD effect. A simple quantitative analysis shows that the structure with larger Fano asymmetry factor has stronger CD. The intensity and peak positions of the CD effect can be flexibly tuned in a large range by changing particle size, shape, the inter-particle distance and surroundings. Furthermore, CD spectra exhibit high sensitivity to ambient medium in visible and near infrared regions. Our results here are beneficial for the design and application of high sensitive CD sensors and other related fields.

physics.optics↗

arXiv2015

Schottky barrier formation and band bending revealed by first principles calculations

An atomistic insight into potential barrier formation and band bending at the interface between a metal and an n-type semiconductor is achieved by ab initio simulations and model analysis of a prototype Schottky diode, i.e., niobium doped rutile titania in contact with gold (Au/Nb:TiO$_2$). The local Schottky barrier height is found to vary between 0 and 1.26 eV depending on the position of the dopant. The band bending is caused by a dopant induced dipole field between the interface and the dopant site, whereas the pristine Au/TiO$_2$ interface does not show any band bending. These findings open the possibility for atomic scale optimization of the Schottky barrier and light harvesting in metal-semiconductor nanostructures.

cond-mat.mes-hall↗

arXiv2014

Resonant surface plasmons of a metal nanosphere can be considered in the way of propagating surface plasmons

Assuming that the resonant surface plasmons on a spherical nanoparticle is formed by standing waves of two counter-propagating surface plasmon waves along the surface, by using Mie theory simulation, we find that the dispersions of surface plasmon resonant modes supported by silver nanospheres match that of the surface plasmons on a semi-infinite medium-silver interface very well. This suggests that the resonant surface plasmons of a metal nanosphere can be treated as a propagating surface plasmon wave.

physics.optics↗

arXiv2011

Activated Vibrational Modes and Fermi Resonance in Tip-Enhanced Raman Spectroscopy

Using p-aminothiophenol (PATP) molecules on a gold substrate as prototypical examples and high vacuum tip-enhanced Raman spectroscopy (HV-TERS), we show that the vibrational spectra of those molecules are distinctly different from those in typical surface-enhanced Raman spectroscopy. Detailed first-principles calculations help to assign the Raman peaks in the TERS measurements as Raman active and infrared (IR) active vibrational modes of dimercaptoazobenzene (DMAB), thus providing strong spectroscopic evidence for the conversion of PATP dimerization to DMAB. The activation of the IR active modes is due to enhanced electromagnetic field gradient effects within the gap region of the highly asymmetric tip-surface geometry. Our TERS measurements also realize splitting of certain vibrational modes due to Fermi resonance between a fundamental mode and the overtone of a different mode or a combinational mode. These findings help to broaden the versatility of TERS as a promising technique for ultrasensitive molecular spectroscopy.

physics.atm-clus↗