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1.
Mitsuhiro Terakawa Yuto Tanaka Go Obara Tatsunori Sakano Minoru Obara 《Applied Physics A: Materials Science & Processing》2011,102(3):661-665
We investigate the dependence of the size parameter in the Mie scattering theory on the near-field enhanced Raman scattering
properties for high dielectric constant ZnO nanorods grown randomly by PLD (pulsed laser deposition). High Raman signals of
Rhodamine 6G (R6G) at 532 nm excitation wavelength were observed with nanorods of 400 nm average diameter. This experimental
result was explained theoretically by the size parameter described in the Mie scattering theory, not by surface plasmon polaritons.
This was also confirmed by the near-field distribution calculated by the FDTD (Finite-Difference Time Domain) method. The
ZnO nanorods with 400 nm average diameter can detect as low as 1 μM of R6G. This near-field enhancement factor is equivalent
to that with 10-nm-thick gold-coated ZnO nanorods (nanoshells) with an average core diameter of 100 nm. Controlling the diameter
of bare ZnO nanorods is effective for obtaining large enhancement factors without an additional process of gold thin film
coating on them. 相似文献
2.
Akira Zenidaka Toshiyuki Honda Mitsuhiro Terakawa 《Applied Physics A: Materials Science & Processing》2011,105(2):393-398
We describe the physics of the SERS based on the optical near-field intensity enhancement on the metallic (plasmonic) and
the nonmetallic (Mie scattering) nanostructured substrates with two-dimensional (2D) periodic nanohole arrays. The calculation
by the Finite-Difference Time-Domain (FDTD) method revealed that the optical intensity enhancement increases with the increase
of the thickness of a gold film coating on the nonmetallic (dielectric) nanostructured Si, GaAs, and SiC substrates. The resonance
spectrum shifts with the changes in the geometrical structure of the void diameter and inter-void distance. It was clarified
that the optical intensity enhancement obtained with the gold-coated substrate is equivalent to that with a gold substrate
at 70-nm thick gold coating on the dielectric substrates in this structure. The resonance spectral bandwidth for Mie scattering
and plasmonic near-fields is different. Therefore, if the Stokes line of the Raman scattering is located within the resonance
bandwidth, the SERS signal is enhanced proportionally to the fourth power of the electric near-field. However, if the Stokes
shift is located out of the resonance bandwidth, the SERS signal enhancement is only proportional to the square of the scattered
near-field. 相似文献
3.
We report strong enhancement (approximately 10(3)) of the spontaneous Raman scattering from individual silicon nanowires and nanocones as compared with bulk Si. The observed enhancement is diameter (d), excitation wavelength (lambda(laser)), and incident polarization state dependent, and is explained in terms of a resonant behavior involving incident electromagnetic radiation and the structural dielectric cross section. The variation of the Raman enhancement with d, lambda(laser), and polarization is shown to be in good agreement with model calculations of scattering from an infinite dielectric cylinder. 相似文献
4.
C. L. Du J. Kasim Y. M. You D. N. Shi Z. X. Shen 《Journal of Raman spectroscopy : JRS》2011,42(2):145-148
Enhanced Raman scattering (ERS) from bulk Si and surface brilliant cresyl blue (Bcb) molecules was investigated by individual polystyrene (PS) microspheres placed on top of the samples. It is revealed that the Raman signal depends both on the microsphere size and the numerical aperture (NA) of the collection lens, and a maximum signal enhancement of ∼11‐ and 40‐fold for Si and Bcb is observed, respectively, showing strong ERS effect. The different ERS behavior was elucidated by electromagnetic simulations using the finite element method. The present work also provides information on individual dielectric sphere for applications in microscopy, spectroscopic imaging and improvement, etc. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
5.
为了研究吸收双层球形微粒的横向光俘获,基于几何光学模型提出了双层带吸收球形微粒的光俘获模型,对TEM00模式高斯光束照射下外层有光吸收的双层电介质球形微粒受到的横向光俘获力进行了数值模拟,取得了光俘获力特性的一系列结果.结果显示,双层球形微粒的外层吸收系数对包括稳态俘获位置,峰值强度,稳态俘获的刚度等光俘获特性有很大影响.此外,内外径的比率对吸收双层球形微粒的光俘获特性也有调制性的影响.在一定条件下,带吸收的双层球形微粒可以被俘获在光轴上,也可能被俘获在中心在光轴上的圆环上.
关键词:
光俘获
几何光学模型
高斯光束
吸收双层球 相似文献
6.
Yuan Zhong-cai Shi Jia-ming 《International Journal of Infrared and Millimeter Waves》2007,28(11):987-992
In a collisional plasma, the collision frequency between electrons and neutrals may be equal to or greater than incident electromagnetic
wave frequency. The complex permittivity can not represent the dielectric property of the plasma perfectly used in the finite
difference in time domain (FDTD). Drude model is adopted to characterize a collisional plasma. Using a commercial FDTD package,
XFDTD 6.0, the electromagnetic scattering of plasma sphere is calculated. By comparison with Mie method, Drude mode is proven
to be suitable. Radar cross-section (RCS) of nonuniform plasma spheres and conductor spheres coated by plasma layer are calculated. 相似文献
7.
Shenghuang LinZhiming Chen Lianbi LiYintu Ba Sujuan LiuMingchao Yang 《Physica B: Condensed Matter》2012,407(4):670-673
The spectra of 6H-SiC crystals including micropipes have been examined for the Si face using Raman scattering. The first-order Raman features reveal that the intensity of the transverse optical phonon band centered at ∼796 cm−1 is sensitive to the micropipes. And the second-order Raman features of the micropipes in bulk 6H-SiC are well-defined using the selection rules for second-order scattering in wurtzite structure. It is found that there are some second-order peaks missing for the micropipe-including sample, which may be induced by the reduction of the incident laser intensity at around the micropipe, especially the uneven surface in the inner wall of the micropipe. These features might also be employed to characterize other structural defects such as screw-dislocations and threading edge dislocations. 相似文献
8.
A novel read-only super-resolution optical disc structure (substrate/mask layer/dielectric layer) is proposed in this paper. By using a Si thin film as the mask layer, the recording pits with a diameter 380nm and a depth 50nm are read out on the dynamic measuring equipment; the laser wavelength α is 632.8nm and the numerical aperture is 0.40. In the course of reproduction, the laser power is 5mW and the rotation velocity of the disc is 4m·s-1. The optimum thickness of the Si thin film is 18nm and the signal-to-noise ratio is 32dB. 相似文献
9.
Raman spectra of microcrystalline silicon layers have been recorded in‐situ during growth. The spectra have been collected under realistic conditions for solar cell deposition. To enable these measurements an electrode with an optical feed through has been developed. By using a metallic grid to shield the feed through it is possible to achieve homogeneous deposition of µc‐Si:H at a sufficient optical transmission. In‐situ Raman measurements were carried out during the deposition of a layer with an intentionally introduced gradient in crystallinity that was seen in‐situ as well in reference measurements performed on the same layer ex‐situ. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
10.
J. Woźniak A. Adamczak G.A. Beer V.M. Bystritsky M. Filipowicz M.C. Fujiwara T.M. Huber R. Jacot-Guillarmod P. Kammel S.K. Kim P.E. Knowles A.R. Kunselman M. Maier V.E. Markushin G.M. Marshall F. Mulhauser A. Olin C. Petitjean T.A. Porcelli V.A. Stolupin J. Zmeskal 《Hyperfine Interactions》1999,119(1-4):63-69
Strong solid state effects in low energy scattering of pμ atoms in solid hydrogen are reported and analyzed. Such effects have been observed in TRIUMF experiment E742 where muons
are stopped in thin frozen (3 K) layers of hydrogen. Emission of low energy pμ atoms from the hydrogen layer into adjacent vacuum was much higher than expected, based on calculations which ignored the
solid nature of hydrogen. Monte Carlo simulations, performed using the scattering cross-sections with solid state effects
taken into account, show the important role of the coherent elastic Bragg scattering in the diffusion of pμ atoms. For pμ energies lower than the Bragg cut-off limit (∼2 meV) the total scattering cross-section falls by several orders of magnitude,
the hydrogen target becomes transparent and the emission of cold pμ atoms takes place.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
Barbara M. Liszka Aufried T. M. Lenferink Geert‐Jan Witkamp Cees Otto 《Journal of Raman spectroscopy : JRS》2015,46(12):1230-1234
The sensitivity of far‐field Raman micro‐spectroscopy was investigated to determine quantitatively the actual thickness of organic thin films. It is shown that the thickness of organic films can be quantitatively determined down to 3 nm with an error margin of 20% and down to 1.5 nm with an error margin of 100%. Raman imaging of thin‐film surfaces with a far‐field optical microscope establishes the distribution of a polymer with a lateral resolution of ~400 nm and the homogeneity of the film. Raman images are presented for spin‐coated thin films of polysulfone (PSU) with average thicknesses between 3 and 50 nm. In films with an average thickness of 43 nm, the variation in thickness was around 5% for PSU. In films with an average thickness of 3 nm for PSU, the detected thickness variation was 100%. Raman imaging was performed in minutes for a surface area of 900 µm2. The results illustrate the ability of far‐field Raman microscopy as a sensitive method to quantitatively determine the thickness of thin films down to the nanometer range. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
12.
13.
We point out in this paper that a TEM101 mode laser beam is convenient to stably levitate either solid or hollow dielectric spheres or metallic ones. Except a sufficient incident flux, there is no stability condition required to levitate solid transparent spheres having a refractive index larger than the one of the surrounding medium. According to the beam and sphere diameters, the equilibrium position will be centered on the beam axis or off-axis. In the case of hollow dielectric or metallic spheres, the lateral stability requires specific conditions on sphere and beam diameters. These conditions are discussed and then experimentally shown by performing optical levitation of these various kinds of spheres either in vertical or in horizontal beams. 相似文献
14.
The amorphous silicon nanoparticles (Si NPs) embedded in silicon nitride (SiNx) films prepared by helicon wave plasma-enhanced chemical vapor deposition (HWP-CVD) technique are studied. From Raman scattering investigation, we determine that the deposited film has the structure of silicon nanocrystals embedded in silicon nitride (nc-Si/SiNx) thin film at a certain hydrogen dilution amount. The analysis of optical absorption spectra implies that the Si NPs is affected by quantum size effects and has the nature of an indirect-band-gap semiconductor. Further, considering the effects of the mean Si NP size and their dispersion on oscillator strength, and quantum-confinement, we obtain an analytical expression for the spectral absorbance of ensemble samples. Gaussian as well as lognormal size-distributions of the Si NPs are considered for optical absorption coefficient calculations. The influence of the particlesize-distribution on the optical absorption spectra was systematically studied. We present the fitting of the optical absorption experimental data with our model and discuss the results. 相似文献
15.
Single layer of dielectric spheres is a recognized model for the basic understanding of some aspects of photonic crystals.
Here we present a systematic study of the effect of compacting in the electromagnetic transmission of dielectric spheres monolayers.
Experiments were performed in the microwave domain (from 10 GHz to 30 GHz) with glass spheres of high dielectric permittivity
ε = 7. Time Domain Finite Integration (TDFI) calculations were also accomplished. Experimental data and TDFI calculations agreement
provides a double check on the lack of experimental artefacts and the correctness of simulation settings. Following the evolution
of the lower frequency spectral peak with layer compacting ratio, we established three different electromagnetic regimes.
For the higher and lower compacting ratio regimes, the peak frequency matches isolated sphere pure resonances, while for intermediate
values of compacting, some transition between these two modes takes place. Extending the study to the complete frequency range,
we find that sphere single layers transmission spectra become closer to isolated sphere scattering calculations as the compacting
ratio is decreased. However as the agreement remains imperfect even for our lowest compacting measurable layer, we conclude
that some structure contribution cannot be neglected even for low compact layers. 相似文献
16.
F.S. Manciu R.E. Tallman B.D. McCombe B.A. Weinstein D.W. Lucey Y. Sahoo P.N. Prasad 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):14
We use infrared (IR) and Raman spectroscopies to investigate the optically active phonon modes in InP nanoparticles and InP/II–VI core-shell nanoparticles fabricated by similar colloidal chemistry methods. The IR transmission spectra of several InP nanoparticle samples exhibit a common absorption feature, which we assign to the Fröhlich mode. The Raman results for the same samples show transverse and longitudinal optical phonon peaks, and scattering strength in between due to surface optical (SO) modes. Infrared spectra of the InP/ZnSe core-shell nanoparticles () exhibit three absorption features, one due to the InP core, and the others associated with the ZnSe shell layer. Raman measurements (12–292 K) also show three phonon-related peaks, whose intensities vary sharply with temperature. The frequencies of the IR and Raman lines are in approximate accord with dielectric continuum theory. 相似文献
17.
In this paper, we report a photonic integrated circuit (PIC), which consisting of a photonic crystal (PC) coupled by a dielectric waveguide to an optical fibre. The PC consists of a sequence of dielectric rods based on a silicon (Si) strip on a silicon dioxide (SiO2) layer. The finite-difference time-domain (FDTD) method is reviewed and then used to model and predict the optical and the geometrical parameters used to design the fundamental elements of the PIC. The air gap width and the etching depth of the grooves are characterised. The coupling between the PC, and traditional dielectric waveguides is studied and coupling efficiency is evaluated. Diffractive losses are shown to affect strongly the performances of the proposed PIC. In addition, the effect of the air gap width on the diffractive losses and the coupling efficiency between successive neighbouring silicon sections is analysed. The field profile distribution in the structure is calculated and performed. The effects of an incorporated defect are studied, showing a high quality factor. 相似文献
18.
Tensile-strained germanium films in Ge/GeSn/Si/GeSnSi multilayer heterostructures grown by molecularbeam epitaxy on Si(001) substrates are investigated by Raman spectroscopy. Biaxial tensile strains in the films reach 1.5%, which exceeds values previously obtained for this system. Splitting of frequencies of long-wavelength optical phonons is experimentally observed; i.e., the shift of the frequency of the singlet induced by biaxial tensile strains is larger than the shift of the frequency of the doublet in agreement with calculations. The strain-induced shift of Raman scattering peaks from two-phonon scattering in germanium is also detected. 相似文献
19.
Prashant Kumar 《Applied Physics A: Materials Science & Processing》2010,98(2):473-479
DC electric-field mediated nanocrystallization of thermally evaporated silicon thin films with nickel as seed/cap layer has
been attempted in complete absence of any external heat input. When 60 nm Si thin film coated onto 5 nm Ni thin film was treated
by a direct current (DC) electric field (up to 3.3 kV/cm up to 5 minutes) after the deposition, amorphous silicon thin films
became nanocrystalline (6–10 nm). Silicon nanograins (average diameter 90 nm) grow to larger sizes (average diameter 240 nm)
with sharpening of grain size distribution. Huge grain growth (4-fold increase) has been observed when nickel was used as
cap layer (5 nm Ni/60 nm Si). XRD data show the signature of nickel silicide formation on the surface in nickel cap layer
case. Field treatment has changed the optical absorption edge (shifts left in nm units) and the refractive index of silicon
thin film when nickel was used as under layer, and an almost negligible effect on the optical properties has been observed
when nickel was used as cap layer. 相似文献
20.
ABSTRACTSemimetal bismuth (Bi) is known to possess a wide range of peculiar properties, owing to its unique electronic band structure. Its electronic band can easily be distorted by structural changes, and thereby undergo transitions between semimetal to either semiconductor or metal states. Utilising a focused laser beam, one can easily introduce structural defects, along with phase changes, oxidation, and morphological modifications. Confocal Raman microscopy indicated that the as-fabricated Bi droplets inhibit the Raman signal from the underlying silicon (Si) substrate. After a laser flash heating step, the intensity of Si optical phonons was strongly enhanced at the positions of Bi droplets, and exceeding the intensity from the bare Si substrate. Thus, such laser irradiating step on the Bi droplets induces an optical phase change. The optical phase change was detected as going from inhibition to strong enhancement of the underlying Si substrate Raman signal. From the observed Bi optical phonon modes (Eg and A1g), alterations in the Raman peaks due to laser exposure indicated that the ordered crystallinity in pristine Bi droplets became deteriorated. The effects of atomic displacements and loss of structural order in Bi droplets impacts its dielectric response. The observed Si Raman signal enhancement is similar to the surface-enhanced Raman scattering effect typically known for noble metals. 相似文献