共查询到20条相似文献,搜索用时 31 毫秒
1.
C. Kennerknecht H. Hövel M. Merschdorf S. Voll W. Pfeiffer 《Applied physics. B, Lasers and optics》2001,73(4):425-429
The resonant multiple excitation of collective modes in metallic nanoparticles using ultrashort laser pulses leads to an enhanced
multiphoton photoemission from the particles. This effect is here demonstrated for the surface-plasmon resonance of Au nanoparticles
on graphite. The shape of the photoemission spectra is explained by multiphoton photo-assisted thermionic emission from the
nanoparticles and resonant emission via the image-potential state on graphite. Tuning the photon energy between 1.7 eV and
3.2 eV allows the identification of an enhancement of the photoemission yield at 2.1±0.1-eV photon energy that is attributed
to the resonant excitation of the surface plasmon in the Au nanoparticles. This identification of the surface-plasmon excitation
in this energy range is also supported by electron energy loss spectroscopy.
Received: 8 August 2001 / Revised version: 13 September 2001 / Published online: 10 October 2001 相似文献
2.
Lehmann J Merschdorf M Pfeiffer W Thon A Voll S Gerber G 《Physical review letters》2000,85(14):2921-2924
Multiphoton photoelectron spectroscopy reveals the multiple excitation of the surface plasmon in silver nanoparticles on graphite. Resonant excitation of the surface plasmon with 400 nm femtosecond radiation allows one to distinguish between photoemission from the nanoparticles and the substrate. Two different previously unobserved decay channels of the collective excitation have been identified, namely, decay into one or several single-particle excitations. 相似文献
3.
M. Weinelt 《Applied Physics A: Materials Science & Processing》2000,71(5):493-502
Quantum-phase and population decay of image-potential states have been investigated by two-photon photoemission with femtosecond
time resolution. The influence of steps and defects on quasielastic and inelastic scattering processes is illustrated for
a vicinal Cu(119) surface and diluted adsorbate layers of CO and Cu on Cu(001).
Received: 19 April 2000 / Accepted: 2 September 2000 / Published online: 12 October 2000 相似文献
4.
G. Seifert M. Kaempfe K.-J. Berg H. Graener 《Applied physics. B, Lasers and optics》2000,71(6):795-800
Single-color femtosecond pump-probe experiments were performed to investigate the time dependence of laser-induced ultrafast
desorption and deformation processes of silver nanoparticles in glass. After laser excitation at wavelengths close to the
surface plasmon resonance, transient extinction changes were found to exhibit dynamics on quite different time scales ranging
from sub-picoseconds to some hundred ps. The slowest observed decay component is identified as characteristic for the deformation/desorption
processes. Possible mechanisms for these processes are discussed.
Received: 3 April 2000 / Revised version: 3 July 2000 / Published online: 20 September 2000 相似文献
5.
Resonant excitation of the plasmon polariton in supported nanoparticles leads to a strong enhancement of the multiphoton photoemission yield and consequently, the total yield is dominated by the emission from the nanoparticles although they cover only a minor fraction of the surface. This allows investigation of the electron dynamics in supported nanoparticles, directly in the time domain. Here, Ag nanoparticles grown on graphite are used to demonstrate that the transient shape of the photoemission spectrum in time-resolved two-color multiphoton photoemission spectroscopy, reveals the electron relaxation within the nanoparticle, and the dynamic charge transfer between substrate and nanoparticle. The photoemission spectra map the transient electron energy distribution and exhibit a transient shift that is attributed to a dynamic charging of the nanoparticle. The comparison with model calculations comprising the full relaxation cascade in the nanoparticle and substrate, shows that the dynamic charge transfer accounts for almost half of the total deposited energy in the nanoparticle. PACS 78.67.Bf; 73.22.-f; 67.40.Fd; 78.47.+p 相似文献
6.
F.-J. Meyer zu Heringdorf L.I. Chelaru S. Möllenbeck D. Thien M. Horn-von Hoegen 《Surface science》2007,601(20):4700-4705
We developed a novel experiment for time-resolved photoemission microscopy by combining a commercial photoemission electron microscope (PEEM) with a pulsed Ti:sapphire laser oscillator. The laser system, the setup of the delay stage for pump-probe experiments, and the interface between the PEEM and the laser system are discussed. We use self-organization of Ag islands and nanowires on Si(1 1 1) and 4° vicinal Si(0 0 1) to generate structures with a plasmon resonance that matches the photon energy of our laser (?ω = 3.1 eV after frequency doubling). In two-photon photoemission (2PPE) the photoemission yield then directly visualizes the plasmons in the nanostructures. Accordingly, the photoemission yield depends on the size and shape of the nanostructures, and on the polarization of the laser pulses as well. In Ag nanowires, we observe surface plasmon polariton (SPP) waves by a beating that is formed by interference of the SPP wave and the incident laser light. In a pump-probe experiment, we can directly visualize the propagation of the SPP on a femtosecond time scale. 相似文献
7.
M.E. Garcia 《Applied Physics A: Materials Science & Processing》2001,72(3):261-271
A theoretical study of different ultrafast nonequilibrium processes taking place during and after ultrashort excitation of
clusters is presented. We discuss similarities and differences for several processes involving nonequilibrium ultrafast motion
of atoms and electrons. We study ultrashort relaxation of clusters in response to excitations produced by femtosecond laser
pulses of different intensities. We show how different relaxation processes, such as bond breaking, melting, fragmentation,
emission of atoms, or Coulomb explosion, can be induced, depending on the laser intensity and laser pulse duration. We also
discuss processes involving nonequilibrium electron dynamics, such as intraband Auger decay in clusters and ultrafast electronic
motion during collisions between clusters and surfaces. We show that this electron dynamics leads to Stückelberg-like oscillations
of measurable quantities, such as the electron emission yield.
Received: 4 April 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001 相似文献
8.
The damping processes of electronic collective excitations of Ag/Ni(1 1 1) were studied by high-resolution electron energy spectroscopy. The FMHM of the Ag surface plasmon was reported as a function of Ag thickness, primary electron beam energy, Ag surface plasmon energy, and parallel momentum transfer. The broadening of the Ag surface plasmon was found to be related to 5sp–5sp transitions, for which a critical wave vector of 0.2 Å−1 exists. Moreover, we provide a direct evidence of the occurrence of chemical interface damping in thin films, upon doping the Ag/Ni(1 1 1) system with K adatoms. The enhanced plasmon broadening in K/Ag/Ni(1 1 1) was ascribed to the existence of additional electron–hole decay channels at the K/Ag interface. 相似文献
9.
采用新型的热化学还原法,制备了银纳米颗粒掺杂的铋酸盐复合玻璃材料。利用紫外-可见吸收光谱观察到了银纳米颗粒表面等离子谐振(SPR)吸收的峰值位移特性,用拉曼光谱表征了引入银纳米颗粒后玻璃的结构变化。借助飞秒激光脉冲激发下的Z扫描与光克尔闸技术,在近红外波段下研究了材料的三阶非线性光学特性。研究结果表明银纳米颗粒铋酸盐复合材料有着亚皮秒级的非线性响应时间,并且其非线性折射率γ在纳米颗粒的热电子效应以及局部场效应的影响下,较基质玻璃最高可以提升29倍。 相似文献
10.
C. Giannetti G. Ferrini S. Pagliara G. Galimberti F. Banfi E. Pedersoli F. Parmigiani 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):121-125
The non-linear photoelectron spectra obtained by short
laser pulses from a Ag(100) surface show a high-energy electron
emission due to an athermal electron distribution created by the
laser pulse. By comparing the photoemission at normal and
non-normal emission geometry it is possible to evidence the
independence of the hot electron photoemission on the parallel
momentum and on different final-state configurations. A
photoemission correlation measurement evidences that
non-photoelectric effects, as tunneling or thermally assisted
photoemission, do not contribute to the electron yield. Various
theoretical models are discussed on the basis of the present
data. 相似文献
11.
A.V. Aiboushev Yu.E. Lozovik S.P. Merkulova O.M. Sarkisov 《Physics letters. A》2008,372(31):5193-5197
Luminescence of silver nanoparticles photodeposited on titan dioxide nanoparticles of mesoporous film is studied. Luminescence was registered under the two-photon excitation by femtosecond laser pulses of Ti:sapphire laser. It occurs that Ag/TiO2 mesoporous films have high concentration of bright luminescence spots which reveal stability to degradation under long illumination. Various configurations of silver nanoparticles are analyzed to explain the physics of bright luminescence spots (“hot spots”). Luminescence intensity reveals “hot spots” dependence on excitation laser pulse polarization. Properties of Ag/TiO2 system show its promising usage for single molecule spectroscopy and biological objects visualization. 相似文献
12.
Thin films of silver nanoparticles deposited in vacuum by pulsed laser ablation using a YAG:Nd laser
J.C. Alonso R. Diamant P. Castillo M.C. Acosta-García N. Batina E. Haro-Poniatowski 《Applied Surface Science》2009,255(9):4933-4937
We report the deposition of thin films of silver (Ag) nanoparticles by pulsed laser ablation in vacuum using the third line (355 nm) of a YAG:Nd laser. The nanostructure and/or morphology of the films was investigated as a function of the number of ablation pulses, by means of transmission electron microscopy and atomic force microscopy. Our results show that films deposited with a small number of ablation pulses (500 or less), are not continuous, but formed of isolated nearly spherical Ag nanoparticles with diameters in the range from 1 nm to 8 nm. The effect of increasing the number of pulses by one order of magnitude (5000) is to increase the mean diameter of the globular nanoparticles and also the Ag areal density. Further increase of the number of pulses, up to 10,000, produces the formation of larger and anisotropic nanoparticles, and for 15,000 pulses, quasi-percolated Ag films are obtained. The presence of Ag nanoparticles in the films was also evidenced from the appearance of a strong optical absorption band associated with surface plasmon resonance. This band was widened and its peak shifted from 425 nm to 700 nm as the number of laser pulses was increased from 500 to 15,000. 相似文献
13.
T. Vartanyan J. Bosbach F. Stietz F. Träger 《Applied physics. B, Lasers and optics》2001,73(4):391-399
In order to study the ultrafast relaxation dynamics of surface plasmon excitation in metal nanoparticles in the presence of
inhomogeneous line broadening and investigate the influence of the reduced dimensions on the dephasing time T2 in the size regime below about 10 nm, we have recently demonstrated a novel technique based on persistent spectral hole burning
[1]. Here, we describe a theoretical model that has been developed for evaluation of the experimental data and precise determination
of T2 for particles of different size and shape. Comparison of the model to experimental data for Ag nanoparticles on sapphire
shows that the theoretical treatment does not only reproduce the shape of the generated holes but also the dependence of their
widths on the applied laser fluence. As a result, we have a reliable and versatile tool at hand making possible systematic
studies of the ultrafast electron dynamics in small metal particles, and the dependence of the femtosecond dephasing time
on their size, shape and surrounding dielectric.
Received: 12 September 2001 / Published online: 15 October 2001 相似文献
14.
A. Glass T. Rozgonyi T. Feurer R. Sauerbrey G. Szabó 《Applied physics. B, Lasers and optics》2000,71(3):267-276
A femtosecond UV laser pulse is used to resonantly excite CsCl molecules from the ionically bound ground state to the first
excited repulsive state. The excitation leads to the dissociation of CsCl. After a certain time delay a visible (VIS) femtosecond
laser pulse interrupts the dissociation process by resonantly de-exciting the molecule back to the ground state. According
to the Tannor–Rice control scheme, the fraction of dissociated CsCl molecules is controlled by changing the delay time between
the two fs laser pulses. The processes involved are investigated theoretically and experimentally. Based on the results, a
self-learning system has been realized, which is able to control the dissociation without any a priori knowledge of the molecule.
Received: 2 December 1999 / Published online: 24 July 2000 相似文献
15.
Decay times of surface plasmon excitation in metal nanoparticles by persistent spectral hole burning
Stietz F Bosbach J Wenzel T Vartanyan T Goldmann A Trager F 《Physical review letters》2000,84(24):5644-5647
We describe a new technique to determine the homogeneous linewidths of surface plasmon resonances of metal nanoparticles and thus measure the decay time of this collective electron excitation. The method is based on spectral hole burning and has been applied to supported oblate Ag particles with radii of 7.5 nm. From the experimental results and a theoretical model of hole burning the linewidth of 260 meV corresponding to a decay time of 4.8 fs was extracted. This value is shorter than expected for damping by bulk electron scattering. We conclude that additional damping mechanisms have been observed and reflect confinement of the electrons in nanoparticles with sizes below 10 nm. 相似文献
16.
17.
W. Pfeiffer F. Sattler S. Vogler G. Gerber J.-Y. Grand R. Möller 《Applied physics. B, Lasers and optics》1997,64(2):265-268
Direct illumination of the tunneling gap in an ultrahigh vacuum scanning tunneling microscope with ultrashort pump-probe laser
pulses may offer ultimate spatial and temporal resolution in surface experiments. The electronic bandwidth of the tunneling
gap ( 1 THz) does not limit the time resolution. Our experiments show that multiphoton photoelectron emission from the sample limits
the application of this detection scheme at high laser fluence. However, a substrate specific pump-probe effect in the photoelectron
yield with femtosecond transients is observed on Tantalum and on GaAs(110) surfaces.
Received: 5 November 1996 相似文献
18.
M. Bauer C. Wiemann J. Lange D. Bayer M. Rohmer M. Aeschlimann 《Applied Physics A: Materials Science & Processing》2007,88(3):473-480
In combining time-resolved two-photon photoemission (TR-2PPE) and photoemission electron microscopy (PEEM) the ultra-fast
dynamics of collective electron excitations in silver nanoparticles (localized surface plasmons – LSPs) is probed at fs and
nm resolution. Here we demonstrate that the sampling of the LSP dynamics by means of time-resolved PEEM enables detailed insight
into the propagation processes associated with these excitations. In phase-integrated as well as phase-resolved measurements
we observe spatio-temporal modulations in the photoemission yield from a single nanoparticle. These modulations are assigned
to local variations in the electric near field as a result of the phase propagation of a plasmonic excitation through the
particle. Furthermore, the control of the phase between the fs pump and probe laser pulses used for these experiments can
be utilized for an external manipulation of the nanoscale electric near-field distribution at these particles.
PACS 78.47.+p; 78.67.Bf; 79.60.-i; 73.20.Mf 相似文献
19.
Haifeng Yang Haidong He Enlan Zhao Jiguo Qian Jingbin Hao Wei Tang Hua Zhu 《Journal of Russian Laser Research》2013,34(4):362-368
We report on the fabrication of surface nanoparticles and micro/nanograting structures on bulk pure aluminum in air using a 150 fs, 775 nm femtosecond laser. We investigate the size of the generated surface nanoparticles under irradiation with different femtosecond laser pulses. Smaller nanoparticles can be induced by a larger number of laser pulses and a lower laser fluence. In addition, we observe the formation of micro/nanogratings when the laser focus is scanned across a pure aluminum surface in air. We obtain micro- and nano-grating composite structures on a pure aluminum surface by adjusting the laser fluence and scan velocity. Femtosecond laser surface ablation of bulk pure aluminum in air is potentially a promising technique for efficient fabrication of surface nanostructures. 相似文献
20.
M.J. Weida S. Ogawa H. Nagano H. Petek 《Applied Physics A: Materials Science & Processing》2000,71(5):553-559
Hot electron (E-EFermi=0.75 to 1.55 eV) lifetimes for cesiated Cu(100) and Cu(111) surfaces are measured via interferometric time-resolved two-photon
photoemission with a 19-fs intensity FWHM mode locked Ti:sapphire laser at 1.55 eV. The data are analyzed using the optical
Bloch equations and a laser pulse characterized in situ via surface second-harmonic generation interferometric autocorrelation.
It is found that the retrieved hot-electron lifetimes are unphysically fast, and have a strong dependence on the temperature
of the sample and the polarization of the laser. A simple explanation for the data is that the measured signal consists of
contributions from transitions through both virtual and real intermediate states.
Received: 26 July 2000 / Accepted: 8 September 2000 / Published online: 12 October 2000 相似文献