| 1. |
- Anttu, Nicklas, et al.
(författare)
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Drastically increased absorption in vertical semiconductor nanowire arrays: A non-absorbing dielectric shell makes the difference
- 2012
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Ingår i: Nano Reseach. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 5:12, s. 863-874
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Tidskriftsartikel (refereegranskat)abstract
- Enhanced absorption of especially long wavelength light is needed to enable the full potential of semiconductor nanowire (NW) arrays for optoelectronic applications. We show both experimentally and theoretically that a transparent dielectric shell (Al2O3 coating) can drastically improve the absorption of light in InAs NW arrays. With an appropriate thickness of the Al2O3 shell, we achieve four times stronger absorption in the NWs compared to uncoated NWs and twice as good absorption as when the dielectric completely fills the space between the NWs. We provide detailed theoretical analysis from a combination of full electrodynamic modeling and intuitive electrostatic approximations. This reveals how the incident light penetrates better into the absorbing NW core with increasing thickness of the dielectric shell until a resonant shell thickness is reached. We provide a simple description of how to reach this strongly absorbing resonance condition, making our results easy to apply for a broad wavelength range and a multifold of semiconductor and dielectric coating material combinations.
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| 2. |
- Anttu, Nicklas, et al.
(författare)
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Excitations of surface plasmon polaritons in double layer metal grating structures
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 100:9
-
Tidskriftsartikel (refereegranskat)abstract
- We study the light scattering properties of double layer gratings (DLGs) made from Au on SiO2 substrates. It is found that surface plasmon polaritons (SPPs) can be excited in the DLGs for a separation of up to 150 nm between the two Au grating layers and the collective reflectance spectra exhibit a strong resonant peak and a closely lying dip as a result of the surface plasmon polariton excitations. It is also found that the angle-resolved specular reflectance spectra show a dip-peak pair structure, while the angle-resolved reflectance spectra of higher diffracted orders show a complementary peak-dip pair structure. Finally, operation of the DLGs for efficient wavelength demultiplexing is proposed and discussed in light of these results. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3690947]
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| 3. |
- Chen, Jianing, et al.
(författare)
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Probing Strain in Bent Semiconductor Nanowires with Raman Spectroscopy.
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:4, s. 1280-1286
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Tidskriftsartikel (refereegranskat)abstract
- We present a noninvasive optical method to determine the local strain in individual semiconductor nanowires. InP nanowires were intentionally bent with an atomic force microscope and variations in the optical phonon frequency along the wires were mapped using Raman spectroscopy. Sections of the nanowires with a high curvature showed significantly broadened phonon lines. These observations together with deformation potential theory show that compressive and tensile strain inside the nanowires is the physical origin of the observed phonon energy variations.
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| 4. |
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| 5. |
- Chen, Jianing, et al.
(författare)
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Surface-enhanced Raman scattering of rhodamine 6G on nanowire arrays decorated with gold nanoparticles
- 2008
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Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 19:27, s. 5-275712
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the surface-enhanced Raman scattering (SERS) of rhodamine 6G (R6G) adsorbed on Au nanoparticles attached to InP nanowires. We find that nanowire arrays act as frameworks for effective SERS substrates with a significantly higher Raman signal sensitivity than a planar framework of Au nanoparticles adsorbed two-dimensionally on a flat surface. The SERS signal displays a clear polarization-dependent effect when the nanowires are arranged in a row. We also find that the SERS signal increases with time during continuous laser illumination. The plasmon-enhanced optical forces between Au nanoparticles may either move pairs of nanoparticles closer together or attract adsorbed molecules by moving them to the junctions of Au nanoparticle aggregates. Such effects by plasmon optical forces may cause the observed increase of the SERS signal with continuous laser illumination.
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| 6. |
- Chen, Jianing, et al.
(författare)
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Tip-enhanced Raman scattering of p-thiocresol molecules on individual gold nanoparticles
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:9
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of tip-enhanced Raman scattering on Au aerosol nanoparticles deposited on gold films. Under the tunneling current state, the Au tip and the Au aerosol nanoparticle form a narrow cavity, where large electromagnetic field enhancements are created to enhance Raman scattering enormously. Colorless p-thiocresol molecules are used as probe molecules. The estimated Raman enhancement is about nine orders of magnitude for the tip/particle configuration.
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| 7. |
- Liao, Guangdong, et al.
(författare)
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Multi-Infection Patterns and Co-infection Preference of 27 Human Papillomavirus Types Among 137,943 Gynecological Outpatients Across China
- 2020
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Ingår i: Frontiers in Oncology. - : Frontiers Media SA. - 2234-943X. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Background: The epidemiological feature of human papillomavirus (HPV) infection is distinctive in China. We aimed to investigate the multi-infection patterns and co-infection preference of 27 HPV types among gynecological outpatients across China. Methods: Overall 137,943 gynecological outpatients were recruited from eight tertiary hospitals located in seven regions of China, between July 1st, 2014 and December 31st, 2016. The overall, region-specific, age-specific and type-specific prevalence of HPV infection were calculated, respectively. The pattern of HPV infection was also evaluated. Furthermore, rate ratio was calculated to evaluate the co-infection preference of any two HPV genotypes. Results: The overall prevalence of 27 HPVs' [17 high-risk (hr)/10 low-risk (lr)] infection was 23.5%. The age-specific HPV prevalence showed a "U-shaped" pattern. The most prevalent hrHPV genotypes were 16, 52, and 58. Multiple infections were detected in 25.8% of the HPV-positive women, in which dual infection was more prevalent. HPV 16/18 were likely to co-infected with HPV 31 but unlikely with HPV 52/58, i.e., the co-infection of HPV 16 with HPV 31 was high (3.5-fold), but low for HPV 58 (1.8-fold), and 52 (1.2-fold), while the co-infection of HPV 18 with HPV 31 was high (4.3-fold), but low for HPV 52 (1.9-fold), and 58 (1.7-fold). Conclusions: We found age-specific prevalence of HPV infection showed a "U-shaped" pattern for high and low risk HPV, suggesting the importance of screening among younger women and the necessary of detection among older women. We found a novel co-infection preference of HPV 16/18 with 31, 52, and 58, suggesting a need of developing and marketing prophylactic HPV vaccines that protect against more genotypes in China.
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| 8. |
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| 9. |
- Xu, Hongxing, et al.
(författare)
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Unified treatment of fluorescence and Raman scattering processes near metal surfaces
- 2004
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Ingår i: Physical Review Letters. - 1079-7114. ; 93:24
-
Tidskriftsartikel (refereegranskat)abstract
- We present a general model study of surface-enhanced resonant Raman scattering and fluorescence focusing on the interplay between electromagnetic effects and the molecular dynamics. Our model molecule is placed close to two Ag nanoparticles and has two electronic levels. A Franck-Condon mechanism provides electron-vibration coupling. Using realistic parameter values for the molecule we find that an electromagnetic enhancement by 10 orders of magnitude can yield Raman cross sections sigma(R) of the order 10(-14) cm(2). We also discuss the dependence of sigma(R) on incident laser intensity.
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| 10. |
- ZhiQiang, Guan, et al.
(författare)
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Surface-enhanced Raman scattering on dual-layer metallic grating structures
- 2010
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Ingår i: Chinese Science Bulletin. - : Springer Science and Business Media LLC. - 1001-6538 .- 1861-9541. ; 55:24, s. 2643-2648
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Tidskriftsartikel (refereegranskat)abstract
- Dual-layer Metallic grating (DMG) structures as surface-enhanced Raman scattering (SERS) substrates are studied using benzenethiol as the probe analyte. The DMG structure consists of a SiO2 grating and 100-nm-thick gold coating layers. An enhancement factor of 10(5) is achieved by optimizing the SiO2 grating height within the range from 165 to 550 nm. The enhancement factor dependence on the SiO2 grating height is due to the surface plasmon excitation, which is dependent on the polarization of the incident light, and confirmed by finite difference time domain simulations. This study demonstrates the advantages of high uniformity, reproducibility and sensitivity in the DMG structures for SERS applications.
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| 11. |
- Balmes, Olivier, et al.
(författare)
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Homogeneous surface-enhanced Raman scattering observed from self-assembled gold nanoparticle films deposited from the liquid-liquid interface
- 2005
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Ingår i: Vibrational Spectroscopy. - : Elsevier BV. - 0924-2031. ; 37:2, s. 189-193
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Tidskriftsartikel (refereegranskat)abstract
- The self-assembled gold nanoparticle film deposited from the liquid-liquid interface has been fabricated, and homogeneous surfaceenhanced Raman scattering (SERS) of R6G molecules on the film has been observed. The SERS enhancement factor of the film is estimated to be in the range 10(8)-10(10). Occasionally, there are some sudden jumps in the Raman signal, where the signal is increased a few times. Such jumps are probably caused by single-molecule SERS in some extremely "hot" sites. (c) 2004 Elsevier B.V. All rights reserved.
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| 12. |
- Bian, F., et al.
(författare)
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Ultrasmall Silver Nanopores Fabricated by Femtosecond Laser Pulses
- 2011
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 11:8, s. 3251-3257
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Tidskriftsartikel (refereegranskat)abstract
- Ultrasmall nanopores in silver thin films with a diameter of about 2 nm have been fabricated using femtosecond laser ablation in liquid. Ultrafast laser pulse ablation generates highly nonequilibrium excitated states, from which silver thin films emerge and progressively grow with the assistance of capping agent molecules. During this growth process, capping agent molecules are enclaved within the film, leaving individual ultrasmall pores in the thin film. Our first-principles calculations show that the pore size is critically determined by the dimension of the confined molecules. Our approach advances the capability of optical methods in making nanoscale structures with potential applications in areas such as near-field aperture probes, imaging masks, magnetic plasmonic resonances, and biosensing with individual nanopores.
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| 13. |
- Cong, Feng-Zi, et al.
(författare)
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A facile synthesis of branched silver nanowire structures and its applications in surface-enhanced Raman scattering
- 2012
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Ingår i: Frontiers of Physics. - : Springer Science and Business Media LLC. - 2095-0462 .- 2095-0470. ; 7:5, s. 521-526
-
Tidskriftsartikel (refereegranskat)abstract
- We report a facile method of preparing novel branched silver nanowire structures such as Y-shaped, K-shaped and other multi-branched nanowires. These branched nanostructures are synthesized by reducing silver nitrate (AgNO3) in polyethylene glycol (PEG) with polyvinglpyrrolidone (PVP) as capping agent. Statistical data indicate that for the "y" typed branched nanowire, the branches grow out from the side of the trunk nanowire in a preferential orientation with an angle of 55A degrees between the branch and the trunk. Transmission electron microscopy (TEM) studies indicate that the defects on silver nanowires could support the growth of branched nanowires. Conditions such as the molar ratio of PVP/AgNO3, the reaction temperature, and the degree of polymerization of reducing agent and PVP play important roles in determining the yield of the silver branches. Due to the rough surface, these branched nanostructures can be used as efficient substrates for surface-enhanced Raman scattering applications.
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| 14. |
- Dong, Bin, et al.
(författare)
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Experimental and theoretical evidence for the chemical mechanism in SERRS of rhodamine 6G adsorbed on colloidal silver excited at 1064 nm
- 2010
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 41:7, s. 719-720
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Tidskriftsartikel (refereegranskat)abstract
- The evidence for the existence of a chemical mechanism in surface-enhanced resonance Raman scattering (SERRS) of rhodamine 6G (R6G) adsorbed on colloidal silver excited at 1064 nm is reported on the basis of experimental and theoretical analyses. A weak absorption peak at around 1060 nm for R6G-functionalized silver nanoparticles was observed, which is not present in the individual spectra of R6G or silver nanoparticles. Theoretically, the charge difference density reveals that this weak absorption is a metal-to-molecule charge transfer excited state. Copyright (C) 2010 John Wiley & Sons, Ltd.
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| 15. |
- Dong, Bin, et al.
(författare)
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Is 4-nitrobenzenethiol converted to p,p '-dimercaptoazobenzene or 4-aminothiophenol by surface photochemistry reaction?
- 2011
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 42:6, s. 1205-1206
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Tidskriftsartikel (refereegranskat)abstract
- For the first time, the experimental and theoretical evidence for the conversion of 4-nitrobenzenethiol (4-NBT) to p,p'-dimercaptoazobenzene (DMAB) in Ag and Cu sols by surface photochemistry reaction is obtained with surface-enhanced Raman scattering (SERS) spectroscopy. The SERS spectrum of 4-NBT in Cu sol is identical to that of DMAB produced from 4-aminothiophenol in Ag sol as reported in recent literature, thereby providing direct spectral evidence. Copyright (C) 2011 John Wiley & Sons, Ltd.
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| 16. |
- Dong, Bin, et al.
(författare)
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Local and Remote Charge-Transfer-Enhanced Raman Scattering on One-Dimensional Transition-Metal Oxides
- 2010
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Ingår i: Chemistry - An Asian Journal. - : Wiley. - 1861-4728. ; 5:8, s. 1824-1829
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Tidskriftsartikel (refereegranskat)abstract
- The one-dimensional (1D) transition-metal oxide MoO3 belt is synthesized and characterized with Xray diffraction, scanning electron microscopy, and Raman spectroscopy. Charge-transfer-(CT) enhanced Raman scattering of 4-mercaptobenzoic acid (4-MBA) on a 1D MoO3 belt was investigated experimentally and theoretically. The chemical enhancement of surface-enhanced Raman scattering (SERS) of 4-MBA on the MoO3 belt by CT is in the order of 10(3). The SERS of 4-MBA was investigated theoretically by using a quantum chemical method. The remote SERS of 4-MBA along the 1D MoO3 belt (the light excitation to one side of the MoO3 belt, and the SERS spectrum is collected on the other side of the MoO3 belt) is also shown experimentally, which provides potential applications of SERS. The incident polarization dependence of remote SERS spectra has also been investigated experimentally.
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| 17. |
- Dong, Bin, et al.
(författare)
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Substrate-, Wavelength-, and Time-Dependent Plasmon-Assisted Surface Catalysis Reaction of 4-Nitrobenzenethiol Dimerizing to p,p '-Dimercaptoazobenzene on Au, Ag, and Cu Films
- 2011
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:17, s. 10677-10682
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we experimentally investigate the substrate, wavelength, and time dependence of the plasmon-assisted surface-catalyzed dimerization of 4-nitrobenzenethiol to form p,p'-dimercaptoazobenzene on Au, Ag, and Cu films. We provide direct experimental evidence that surface plasmon resonance plays the most important role in these surface-catalyzed reactions. It is found that the reaction is strongly dependent on the substrate, the wavelength of the laser, and the reaction timescales. Our experimental results revealed that optimal experimental conditions can be rationally chosen to control (accelerate or restrain) this reaction. The experimental results are also confirmed by theoretical calculations.
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| 18. |
- Fang, Yurui, et al.
(författare)
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Ascertaining p,p '-Dimercaptoazobenzene Produced from p-Aminothiophenol by Selective Catalytic Coupling Reaction on Silver Nanoparticles
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:11, s. 7737-7746
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Tidskriftsartikel (refereegranskat)abstract
- Combining experiment and theory, evidence from surface-enhanced Raman scattering (SERS) were obtained for p,p'-dimercaptoazobenzene (DMAB) produced from p-aminothiophenol (PATP) by selective catalytic coupling reaction on silver nanoparticles. The time-dependent SERS spectra of PATE are consistent with the calculated SERS spectra of DMAB), which is the direct evidence or the production of DMAB from PATE by selective catalytic coupling reaction on silver nanoparticles. The so-called "b(2) modes" of PATP is the -N=N- related vibrational modes of DMAB. The silver nanoparticles could be assembled together to form different size of aggregates with different concentration of PATE solution. When the concentration of Ag nanoparticle (the radius 40 nm) in colloid is 35 pM, the time-dependent SERS of DMA B reveals that the better experimental conditions for observing SERS signals of DMA B are (1) concentration of PATE is around 5 x 0(-6) M in which condition the aggregates consist with about 3-5 silver nanoparticles. which are not too big and suitable for SERS measurement, and (2) the Raman signal will be strongest at the thne delay about 27 min for this concentration. By analyzing the symmetry of strong enhanced vibrational modes, it is derived that all ask strong vibrational modes are mostly enhanced by surface plasmons (electromagnetic field). The SERS enhancement calculated with finite-difference time-domain method is on the order of |M|(4) = 9.0 x 10(8) in junctions of AgNPs at 632.8 nm, where |M|(4) = E-loc/E-in and E-loc and E-in are local and incident electric fields, respectively. The total chemical enhancements, including static chemical and resonant enhancements, are on the order of 10(3).
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| 19. |
- Fang, Yurui, et al.
(författare)
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Branched Silver Nanowires as Controllable Plasmon Routers
- 2010
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:5, s. 1950-1954
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Tidskriftsartikel (refereegranskat)abstract
- Using polarization dependent scattering spectroscopy, we investigate plasmon propagation on branched silver nanowires. By controlling the polarization of the incident laser light, the wire plasmons can be routed into different wire branches and result in light emission from the corresponding wire ends. This routing behavior is found to be strongly dependent on the wavelength of light. Thus for certain incident polarizations, light of different wavelength will be routed into different branches. The branched nanowire can thus serve as a controllable router and multiplexer in integrated plasmonic circuits.
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| 20. |
- Fang, Yurui, et al.
(författare)
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Remote-Excitation Surface-Enhanced Raman Scattering Using Propagating Ag Nanowire Plasmons.
- 2009
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 9:5, s. 2049-2053
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Tidskriftsartikel (refereegranskat)abstract
- Using propagating plasmons on silver nanowires as an excitation source we perform surface-enhanced Raman scattering (SERS) at a nanoparticle/wire junction located remotely from the laser illumination spot with sensitivities in a few molecules range. Simultaneous multisite remote-excitation SERS sensing can also be achieved.
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| 21. |
- Frimmer, Martin, et al.
(författare)
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Transport properties of three-terminal ballistic junctions realized by focused ion beam enhanced etching in InGaAs/InP
- 2008
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 93:13
-
Tidskriftsartikel (refereegranskat)abstract
- Three-terminal junction devices are realized in an InGaAs/InP quantum well by focused ion beam (FIB) implantation and selective wet etching. Room temperature electrical measurements show that the fabricated devices exhibit strong nonlinear electrical properties. The results are discussed in terms of ballistic electron transport. It is demonstrated that FIB-enhanced etching processing can be exploited as a maskless, resist-free technique for fabrication of high-quality and functional nanoelectronic devices. (C) 2008 American Institute of Physics.
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| 22. |
- Guan, Zhi-Qiang, et al.
(författare)
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Electromechanical Behavior of Interdigitated SiO2 Cantilever Arrays
- 2010
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Ingår i: Chinese Physics Letters. - 1741-3540. ; 27:2
-
Tidskriftsartikel (refereegranskat)abstract
- Bending and first flexural mode vibration behavior of electrostatic actuated nanometer-sized interdigitated cantilever arrays are characterized under vacuum conditions. The "pull-in" effect in dc driving and the "hard spring effect" in ac driving are observed. A mass sensitivity of 20 fg is expected for our devices due to the ultra-small mass of the arm and relative high.. factor. The mass-spring lump model combined with Green's function method is used to fit the dc driving behaviors including the pull-in voltage. For the ac driving case, the polynomial expansion of the capacitive force is used in the model. The successfully fittings of the pull-in voltage and the hard spring effect prove that our simulation method could be used for guiding the geometrical design of cantilever-based sensors.
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| 23. |
- Han, Huifeng, et al.
(författare)
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Tunable surface plasma resonance frequency in Ag core/Au shell nanoparticles system prepared by laser ablation
- 2008
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 92:2
-
Tidskriftsartikel (refereegranskat)abstract
- A method for preparation of Ag core/Au shell nanoparticles with tunable surface plasma resonance (SPR) band was presented and studied. It was found that the tunable SPR band could be significantly conducted and achieved by laser ablation to Au plate in Ag colloidal solution, leading to the formation of Ag core/Au shell structure by the deposition of Au atoms on the surface of Ag nanoparticles. Dependence of the tunable shift of SPR bands on Ag core/Au shell structure was further illustrated by simulation of absorption spectra based on Mie theory, and consistent with the experimental results.
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| 24. |
- Huang, Yingzhou, et al.
(författare)
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Surfactant-Promoted Reductive Synthesis of Shape-Controlled Gold Nanostructures
- 2009
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 9:2, s. 858-862
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Tidskriftsartikel (refereegranskat)abstract
- We describe a surfactant-promoted reductive route for the shape-controlled synthesis of gold nanostructures by hydrothermal treatment of chloroauric acid in the presence of the surfactant hexadecyltrimethylammonium bromide (CTAB) without using reducing agent. The results show that the cationic surfactant CTAB provides the dual function of promoting Au-III reduction to Au-0 and size- and shape-controlled synthesis of the gold nanocrystals. More importantly, the benefit of the present work stems from the first report on the controlled synthesis of gold nanostructures by hydrothermal treatment of chloroauric acid in the presence of the surfactant CTAB without using reducing agent. The kinetics of the reduction could be manipulated through changes in the CTAB concentration to produce gold nanostructures with shapes ranging from three-dimensional (313) octahedra, triangles, to two-dimensional (213) hexagonal nanoplates in high yields. Growth of gold nanostructures in the CTAB solution with concentration was monitored by microscopic and spectroscopic techniques.
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| 25. |
- Johansson, Peter, 1961, et al.
(författare)
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Surface-enhanced Raman scattering and fluorescence near metal nanoparticles
- 2005
-
Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72, s. 035427-
-
Tidskriftsartikel (refereegranskat)abstract
- We present a general model study of surface-enhanced resonant Raman scattering and fluorescence, focusing on the interplay between electromagnetic (EM) effects and the molecular dynamics as treated by a density matrix calculation. The model molecule has two electronic levels, is affected by radiative and nonradiative damping mechanisms, and a Franck-Condon mechanism yields electron-vibration coupling. The coupling between the molecule and the electromagnetic field is enhanced by placing it between two Ag nanoparticles. The results show that the Raman scattering cross section can, for realistic parameter values, increase by some 10 orders of magnitude (to similar to 10(-14) cm(2)) compared with the free-space case. Also the fluorescence cross section grows with increasing EM enhancement, however, at a slower rate, and this increase eventually stalls when nonradiative decay processes become important. Finally, we find that anti-Stokes Raman scattering is possible with strong incident laser intensities similar to 1 mW/mu m(2).
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| 26. |
- Käll, Mikael, 1963, et al.
(författare)
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Field enhancement and molecular response in surface-enhanced Raman scattering and fluorescence spectroscopy
- 2005
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 1097-4555 .- 0377-0486. ; 36, s. 510-514
-
Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical analysis of surface-enhanced Raman scattering and fluorescence emission from chromophoric molecules located at electromagnetic 'hot spots' in nanoparticle aggregates. The model combines classical electrodynamic enhancement effects with molecular quantum dynamics and allows us to quantify various molecular cross-sections and spectral properties. For a model molecule that simulates rhodamine 6G, we find that an electromagnetic Raman enhancement of the order of loll results in an effective Raman cross-section of the order of 10(-14) cm(2), in agreement with single-molecule Raman measurements.
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| 27. |
- Li, Pan, et al.
(författare)
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Silver nano-needles : Focused optical field induced solution synthesis and application in remote-excitation nanofocusing SERS
- 2019
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 11:5, s. 2153-2161
-
Tidskriftsartikel (refereegranskat)abstract
- Tapered metallic nanostructures that harbor surface plasmons are highly interesting for nanophotonic applications because of their waveguiding and field-focusing properties. Here, we developed a focused optical field induced solution synthesis for unique crystallized silver nano-needles. Under the focused laser spot, inhomogeneous Ag monomer concentration is created, which triggers the uniaxial growth of silver nanostructures along the radial direction with decreasing rate, forming nano-needle structures. These nano-needles are several micrometers long, with diameter attenuating from hundreds to tens of nanometers, and terminated by a sharp apex only a few nanometers in diameter. Moreover, nano-needles with atomically smooth surfaces show excellent performance for plasmonic waveguiding and unique near-field compression abilities. This nano-needle structure can be used for effective remote-excitation detection/sensing. We also demonstrate the assembling and picking up of nano-needles, which indicate potential applications in intracellular endoscopy, high resolution scanning tips, on-chip nanophotonic devices, etc.
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| 28. |
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| 29. |
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| 30. |
- Li, Zhipeng, et al.
(författare)
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Correlation between Incident and Emission Polarization in Nanowire Surface Plasmon Waveguides
- 2010
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 10:5, s. 1831-1835
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Tidskriftsartikel (refereegranskat)abstract
- Nanowire plasmons can be launched by illumination at one terminus of the nanowire and emission can be detected at the other end of the wire. Using polarization dependent dark-held scattering spectroscopy, we measure how the polarization of the emitted light depends on the polarization of the incident light. We observe that the shape of the nanowire termination plays an important role in determining this polarization change. Depending on termination shape, a nanowire can serve as either a polarization-maintaining waveguide, or as a polarization-rotating, nanoscale half-wave plate. The understanding of how plasmonic waveguiding influence the polarization of the guided light is important for optimizing the structure of integrated plasmonic devices
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| 31. |
- Li, Zhipeng, et al.
(författare)
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Directional Light Emission from Propagating Surface Plasmons of Silver Nanowires.
- 2009
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 9:Online September 21, 2009, s. 4383-4386
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Tidskriftsartikel (refereegranskat)abstract
- Thin metallic nanowires are highly promising candidates for plasmonic waveguides in photonic and electronic devices. We have observed that light from the end of a silver nanowire, following excitation of plasmons at the other end of the wire, is emitted in a cone of angles peaking at nominally 45-60 degrees from the nanowire axis, with virtually no light emitted along the direction of the nanowire. This surprising characteristic can be explained in a simple picture invoking Fabry-Perot resonances of the forward- and back-propagating plasmons on the nanowire. This strongly angular-dependent emission is a critical property that must be considered when designing coupled nanowire-based photonic devices and systems.
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| 32. |
- Li, Zhipeng, et al.
(författare)
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Effect of a proximal substrate on plasmon propagation in silver nanowires
- 2010
-
Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 82:24
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate how the properties of a nearby substrate modify the excitation and propagation of plasmons in subwavelength silver wires. With decreasing nanowire-substrate separation, the in-coupling efficiency shows strongly oscillatory behavior due to coherent interference. The plasmon damping increases with decreasing separation due to an increased coupling of the nanowire plasmons to the photonic modes of the substrate.
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| 33. |
- Li, Zhipeng, et al.
(författare)
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Electromagnetic energy flow near metal nanoparticles - II: Algorithms for the calculation of the light scattering of multi-spheres and photon energy transport via linear chains of Ag nanoparticles
- 2007
-
Ingår i: Journal of Quantitative Spectroscopy & Radiative Transfer. - : Elsevier BV. - 0022-4073. ; 103:2, s. 394-401
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Tidskriftsartikel (refereegranskat)abstract
- We present a new algorithm to calculate the near-field distribution of scattered light of multiple nanospheres based on recursive order-of-scattering (OS) and the matrix inversion approaches, which avoids the divergent problem encountered in origin OS method at the resonance condition. Using this method, we investigate the light-transport properties of linear chains of Ag nanospheres. We found a maximum 3 dB damping length of 1.4 mu m of the light propagation when the first sphere of the linear Ag spheres with the radius R = 25 nm was illuminated. The optimal configurations that favor the photon energy transport are investigated as well. (c) 2006 Elsevier Ltd. All rights reserved.
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| 34. |
- Li, Zhipeng, et al.
(författare)
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Multiple-Particle Nanoantennas for Enormous Enhancement and Polarization Control of Light Emission.
- 2009
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 3:3, s. 637-642
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the light emission from dipolar emitters located within nanoparticle antennas. It is found that the enormous emission enhancement can reach nearly a million fold. For multinanoparticle antennas, the polarization of the emissions strongly depends on the geometry of the antennas, the emitted wavelengths, and the dielectric functions of surrounding media. It is shown that a polarization nanorotator, which modulates the emission polarization on the nanometer scale, can be readily realized by varying either the geometry or surrounding media of nanoparticle antennas.
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| 35. |
- Li, Zhipeng, et al.
(författare)
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Nanoantenna effect of surface-enhanced Raman scattering : managing light with plasmons at the nanometer scale
- 2016
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Ingår i: Advances in Physics: X. - : Informa UK Limited. - 2374-6149. ; 1:3, s. 492-521
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Forskningsöversikt (refereegranskat)abstract
- Manipulating light on the nanometer scale is a challenging topic not only from a fundamental point of view, but also for applications aiming toward the design of miniature optical devices. Nanoplasmonics is a rapidly emerging branch of photonics, which offers variable means to manipulate light using surface plasmon excitations on metal nanostructures. As a spectroscopic phenomenon discovered nearly 40 years ago, surface-enhanced Raman scattering (SERS) has been an active topic of fundamental and applied researches. The dominating electromagnetic enhancement in SERS is caused by surface plasmon resonances. This is a typical example of manipulating light intensity with plasmons. Here, we will review the recent SERS studies related to nanoantenna effects on different metal nanostructures based on electromagnetic enhancement. Three aspects will be the focus in this paper: (1) the coupled nanostructures which act as receiving and emitting antenna that can generate enormous SERS enhancement ~E4 even enough for single molecule SERS. (2) The polarization of SERS at the single molecule limit, including the linear and circular polarizations can be manipulated using designed asymmetric antennas. Such an effect can make the traditional 1/2 and 1/4 wave plates miniaturized to the nanometer scale. (3) Combining nanoantenna and waveguiding effects, remote excitation of SERS can be realized, which may open a new area of single molecule SERS on nanophotonic circuits.
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| 36. |
- Li, Z. P., et al.
(författare)
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Optical forces on interacting plasmonic nanoparticles in a focused Gaussian beam
- 2008
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969 .- 1098-0121. ; 77:8, s. 6-
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Tidskriftsartikel (refereegranskat)abstract
- We theoretically analyze optical forces on aggregates of metal nanoparticles in a focused Gaussian beam by extending the generalized Mie theory, which includes higher order multipoles and retardation effects. For two interacting metallic particles, an attractive gradient force, mainly caused by multipole plasmon excitation, exists at short interparticle distances, while induced dipolar fields dominate for separations of the order of the particle radius R or larger. The long-range force component can be either attractive or repulsive depending on the phase of the induced dipoles, as determined by the illumination wavelength and the collective dipolar plasmon resonance. In particular, the repulsive force that occurs for illumination near the plasmon resonance wavelength can be so large that it overcomes the optical trapping effect of the Gaussian beam.
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| 37. |
- Liang, Hongyan, et al.
(författare)
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Controlled Synthesis of Uniform Silver Nanospheres
- 2010
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 114:16, s. 7427-7431
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Tidskriftsartikel (refereegranskat)abstract
- We describe a new route, in which the polyethylene glycol (PEG) is used both as a solvent and reducing reagent and the polymer polyvinglpyrrolidone (PVP) is used as capping agent, for the synthesis of monodisperse silver nanoparticles. Uniform nanospheres with an average diameter of 54 nm can be routinely synthesized in high yield through this approach by using a PVP/AgNO3 molar ratio of 8 at 260 degrees C. Both the reaction temperature and the PVP/AgNO3 molar ratio are crucial for the diameters and size distributions of the nanospheres.
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| 38. |
- Liang, Hongyan, et al.
(författare)
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High-Yield Uniform Synthesis and Microstructure-Determination of Rice-Shaped Silver Nanocrystals
- 2009
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 131:17, s. 6068-6068
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Tidskriftsartikel (refereegranskat)abstract
- High-yield uniform silver nanorices were synthesized by a facile polyol process without the introduction of shape-selected seeds. Nanorices exhibit two plasmon resonance peaks in the visible and near-infrared regions respectively due to their anisotropy. XRD patterns demonstrated the HCP phase coexists with the FCC phase in nanorices. The novel structure of nanorices was characterized by TEM study which shows that the intergrowth of FCC and a small amount of HCP phase, nanoscale FCC (111) twinning structure, and multimodulated structures formed by a complicated stacking sequence along the long axis direction. The correlation between morphology and microstructure is discussed.
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| 39. |
- Liang, Hongyan, et al.
(författare)
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Silver Nanorice Structures: Oriented Attachment-Dominated Growth, High Environmental Sensitivity, and Real-Space Visualization of Multipolar Resonances
- 2012
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 24:12, s. 2339-2346
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Tidskriftsartikel (refereegranskat)abstract
- We have synthesized and investigated the anisotropic growth of interesting silver nanorice. Its growth is kinetically controlled at 100 degrees C, and both oriented attachment and Ostwald ripening are involved, with the former growth mode dominating the anisotropic growth of the nanorice along the < 111 > direction. This one-directional growth is initiated by an indispensable seed-selection process, in which oxygen plays a critical role in oxidatively etching twinned silver crystals. The inhibition of this process by removing oxygen essentially blocks the nanorice growth. Although increasing reaction temperature to 120 degrees C accelerates the one-dimensional growth along the < 111 > direction, further temperature increase to 160 degrees C makes the oriented attachment dominated one-directional growth disappear; instead, the diffusion-controlled two-dimensional growth leads to the emergence of highly faceted truncated triangular and hexagonal plates mainly bound by low energy faces of {111}. Interestingly, we also found that the longitudinal surface plasmon resonance of the nanorice structures is highly sensitive to the refractive index of surrounding dielectric media, which predicts their promising applications as chemical or biological sensors. Moreover, the multipolar plasmonic resonances in these individual nanorice structures are visualized in real space, using high-resolution electron energy-loss spectroscopy.
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| 40. |
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| 41. |
- Mårsell, Erik, et al.
(författare)
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Direct subwavelength imaging and control of near-field localization in individual silver nanocubes
- 2015
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 107:20
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the control of near-field localization within individual silver nanocubes through photoemission electron microscopy combined with broadband, few-cycle laser pulses. We find that the near-field is concentrated at the corners of the cubes, and that it can be efficiently localized to different individual corners depending on the polarization of the incoming light. The experimental results are confirmed by finite-difference time-domain simulations, which also provide an intuitive picture of polarization dependent near-field localization in nanocubes. (C) 2015 AIP Publishing LLC.
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| 42. |
- Mårsell, Erik, et al.
(författare)
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Nanoscale imaging of local few-femtosecond near-field dynamics within a single plasmonic nanoantenna.
- 2015
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 15:10, s. 6601-6608
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Tidskriftsartikel (refereegranskat)abstract
- The local enhancement of few-cycle laser pulses by plasmonic nanostructures opens up for spatiotemporal control of optical interactions on a nanometer and few-femtosecond scale. However, spatially resolved characterization of few-cycle plasmon dynamics poses a major challenge due to the extreme length and time scales involved. In this letter, we experimentally demonstrate local variations in the dynamics during the few strongest cycles of plasmon-enhanced fields within individual rice-shaped silver nanoparticles. This was done using 5.5 fs laser pulses in an interferometric time-resolved photoemission electron microscopy setup. The experiments are supported by finite-difference time-domain simulations of similar silver structures. The observed differences in the field dynamics across a single particle do not reflect differences in plasmon resonance frequency or dephasing time. They instead arise from a combination of retardation effects and the coherent superposition between multiple plasmon modes of the particle, inherent to a few-cycle pulse excitation. The ability to detect and predict local variations in the few-femtosecond time evolution of multi-mode coherent plasmon excitations in rationally synthesized nanoparticles can be used in the tailoring of nanostructures for ultrafast and nonlinear plasmonics.
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| 43. |
- Mårsell, Erik, et al.
(författare)
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Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths
- 2015
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 117:8
-
Tidskriftsartikel (refereegranskat)abstract
- We image the field enhancement at Ag nanostructures using femtosecond laser pulses with a center wavelength of 1.55 mu m. Imaging is based on non-linear photoemission observed in a photoemission electron microscope (PEEM). The images are directly compared to ultra violet PEEM and scanning electron microscopy (SEM) imaging of the same structures. Further, we have carried out atomic scale scanning tunneling microscopy on the same type of Ag nanostructures and on the Au substrate. Measuring the photoelectron spectrum from individual Ag particles shows a larger contribution from higher order photoemission processes above the work function threshold than would be predicted by a fully perturbative model, consistent with recent results using shorter wavelengths. Investigating a wide selection of both Ag nanoparticles and nanowires, field enhancement is observed from 30% of the Ag nanoparticles and from none of the nanowires. No laser-induced damage is observed of the nanostructures neither during the PEEM experiments nor in subsequent SEM analysis. By direct comparison of SEM and PEEM images of the same nanostructures, we can conclude that the field enhancement is independent of the average nanostructure size and shape. Instead, we propose that the variations in observed field enhancement could originate from the wedge interface between the substrate and particles electrically connected to the substrate. (C) 2015 AIP Publishing LLC.
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| 44. |
- Mårsell, Erik, et al.
(författare)
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Secondary electron imaging of nanostructures using Extreme Ultra-Violet attosecond pulse trains and Infra-Red femtosecond pulses
- 2013
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Ingår i: Annalen der Physik. - : Wiley. - 0003-3804. ; 525:1-2, s. 162-170
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Tidskriftsartikel (refereegranskat)abstract
- Surface electron dynamics unfold at time and length scales down to attoseconds and nanometres, making direct imaging with extreme spatiotemporal resolution highly desirable. However, this has turned out to be a major challenge even with the advent of reliable attosecond light sources. In this paper, photoelectrons from Ag nanowires and nanoparticles excited by extreme ultraviolet (XUV) attosecond pulse trains and infrared femtosecond pulses using a PhotoEmission Electron Microscope (PEEM) are imaged. In addition, the samples were investigated using Scanning Electron Microscopy (SEM) and synchrotron based X-ray photoelectron spectroscopy (XPS). To achieve contrast between the nanostructures and the substrate in the XUV images, three different substrate materials were investigated: Cr, ITO and Au. While plasmonic field enhancement can be observed on all three substrates, only on Au substrates do the Ag nanowires appear significantly brighter than the substrate in XUV-PEEM imaging. 3-photon photoemission imaging of plasmonic hot-spots was performed where the autocorrelation trace is observed in the interference signal between two femtosecond Infra-Red (IR) beams with sub-cycle precision. Finally, using Monte Carlo simulations, it is shown how the secondary electrons imaged in the XUV PEEM can potentially reveal information on the attosecond time scale from the near surface region of the nanostructures.
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| 45. |
- Pan, Deng, et al.
(författare)
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Optical interferometric logic gates based on metal slot waveguide network realizing whole fundamental logic operations
- 2013
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Ingår i: Optics Express. - 1094-4087. ; 21:8, s. 9556-9562
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Tidskriftsartikel (refereegranskat)abstract
- Optical interferometric logic gates in metal slot waveguide network are designed and investigated by electromagnetic simulations. The designed logic gates can realize all fundamental logic operations. A single Y-shaped junction can work as logic gate for four logic functions: AND, NOT, OR and XOR. By cascading two Y-shaped junctions, NAND, NOR and XNOR can be realized. The working principle is analyzed in detail. In the simulations, these gates show large intensity contrast for the Boolean logic states of the output. These results can be useful for future integrated optical computing. (C) 2013 Optical Society of America
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| 46. |
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| 47. |
- Shegai, Timur, et al.
(författare)
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Managing light polarization via plasmon-molecule interactions within an asymmetric metal nanoparticle trimer
- 2008
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Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 105:43, s. 16448-16453
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of light with metal nanoparticles leads to novel phenomena mediated by surface plasmon excitations. In this article we use single molecules to characterize the interaction of surface plasmons with light, and show that such interaction can strongly modulate the polarization of the emitted light. The simplest nanostructures that enable such polarization modulation are asymmetric silver nanocrystal trimers, where individual Raman scattering molecules are located in the gap between two of the nanoparticles. The third particle breaks the dipolar symmetry of the two-particle junction, generating a wavelength-dependent polarization pattern. Indeed, the scattered light becomes elliptically polarized and its intensity pattern is rotated in the presence of the third particle. We use a combination of spectroscopic observations on single molecules, scanning electron microscope imaging, and generalized Mie theory calculations to provide a full picture of the effect of particles on the polarization of the emitted light. Furthermore, our theoretical analysis allows us to show that the observed phenomenon is very sensitive to the size of the trimer particles and their relative position, suggesting future means for precise control of light polarization on the nanoscale.
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| 48. |
- Sun, Mengtao, et al.
(författare)
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A Novel Application of Plasmonics: Plasmon-Driven Surface-Catalyzed Reactions
- 2012
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Ingår i: Small. - : Wiley. - 1613-6829 .- 1613-6810. ; 8:18, s. 2777-2786
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Forskningsöversikt (refereegranskat)abstract
- The first experimental and theoretical evidence of the surface-catalyzed reaction of p,p'-dimercaptoazobenzene (DMAB) produced from para-aminothiophenol (PATP) by local surface plasmons was reported in 2010, and since that time a series of investigations have supported these findings using different experimental and theoretical methods. Recent work has also found that local plasmons can drive a surface-catalyzed reaction of DMAB converted from 4-nitrobenzenethiol (4NBT), assisted by local surface plasmons. There are at least three important discoveries in these investigations: 1) in the field of surface-enhanced Raman scattering (SERS) the widely accepted misinterpretation (since 1994) that the chemical mechanism resulting in three additional Raman peaks of PATP in Ag or Au solutions has been corrected with a new mechanism; 2) it is confirmed that SERS is not always a noninvasive technique, and under certain conditions cannot always obtain the vibrational fingerprint information of the original surface species; 3) a novel method to synthesize new molecules, induced by local surface plasmons or plasmon waveguides on the nanoscale, has been found. This Review considers recent novel applications of plasmonics to chemical reactions, especially to plasmon-driven surface-catalyzed reactions.
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| 49. |
- Sun, Mengtao, et al.
(författare)
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Activated vibrational modes and Fermi resonance in tip-enhanced Raman spectroscopy
- 2013
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Ingår i: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics). - 1539-3755. ; 87:2
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Tidskriftsartikel (refereegranskat)abstract
- Using p-aminothiophenol (PATP) molecules on a gold substrate and high-vacuum tip-enhanced Raman spectroscopy (HV-TERS), we show that the vibrational spectra of these 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 IR-active vibrational modes of dimercaptoazobenzene (DMAB), providing strong spectroscopic evidence for the dimerization of PATP molecules to DMAB under the TERS setup. 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. Fermi resonances are also observed in HV-TERS. These findings help to broaden the versatility of TERS as a promising technique for ultrasensitive molecular spectroscopy. DOI:10.1103/PhysRevE.87.020401
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| 50. |
- Sun, Mengtao, et al.
(författare)
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Can information of chemical reaction propagate with plasmonic waveguide and be detected at remote terminal of nanowire?
- 2011
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 3:10, s. 4114-4116
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Tidskriftsartikel (refereegranskat)abstract
- We attempt to provide experimental and theoretical evidence that information of chemical reaction can propagate with plasmonic waveguide along the nanowire and be detected at the remote terminal of nanowire, where the chemical reaction is the surface catalyzed reaction of DMAB produced from PATP assisted by surface plasmon polaritons.
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