共查询到20条相似文献,搜索用时 31 毫秒
1.
Chi Li Xu Zhou Feng Zhai Zhenjun Li Fengrui Yao Ruixi Qiao Ke Chen Matthew Thomas Cole Dapeng Yu Zhipei Sun Kaihui Liu Qing Dai 《Advanced materials (Deerfield Beach, Fla.)》2017,29(30)
Ultrafast electron pulses, combined with laser‐pump and electron‐probe technologies, allow ultrafast dynamics to be characterized in materials. However, the pursuit of simultaneous ultimate spatial and temporal resolution of microscopy and spectroscopy is largely subdued by the low monochromaticity of the electron pulses and their poor phase synchronization to the optical excitation pulses. Field‐driven photoemission from metal tips provides high light‐phase synchronization, but suffers large electron energy spreads (3–100 eV) as driven by a long wavelength laser (>800 nm). Here, ultrafast electron emission from carbon nanotubes (≈1 nm radius) excited by a 410 nm femtosecond laser is realized in the field‐driven regime. In addition, the emitted electrons have great monochromaticity with energy spread as low as 0.25 eV. This great performance benefits from the extraordinarily high field enhancement and great stability of carbon nanotubes, superior to metal tips. The new nanotube‐based ultrafast electron source opens exciting prospects for extending current characterization to sub‐femtosecond temporal resolution as well as sub‐nanometer spatial resolution. 相似文献
2.
The SnO2 cubes with the rutile structure have been successfully synthesized without using any catalyst. Their morphology and microstructure were studied by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), and elected area electron diffraction (SAED). It is revealed that the SnO2 nanocubes exhibit high crystalline quality. The size of the nanocubes ranges from 100 nm to 300 nm. The side surfaces of nanocubes are {110} planes, while their cube axes are [001] direction. The growth mechanism of SnO2 nanocubes was discussed and we suggested vapor-solid process should dominate the growth. These SnO2 nanostructures represent an important example of spontaneous organization. 相似文献
3.
Lu Han Yu-Xia Zhao Cheng-Mei Liu Lu-Hai Li Xing-Jie Liang Yen Wei 《Journal of Materials Science: Materials in Electronics》2014,25(9):3870-3877
Silver nanomaterials have a wide application in printed electronics due to their excellent electrical conductivity. However, less studies were done to investigate the effects of nanoparticle shape on conductance. In this work, silver nanocubes with edge length of 45 nm and silver nanospheres with the same diameter of 45 nm were successfully prepared via polyol synthesis, and then characterized by scan electron microscopy, transmission electron microscopy, ultraviolet–visible spectrophotometry and dynamic light scattering. Subsequently, the electric conductivities of pastes filled with Ag nanocubes and Ag nanospheres were measured using four point probe resistance measurement by coating on glasses, the result of which showed that, the conductance of Ag nanospheres paste was much superior to that of Ag nanocubes paste with the same silver content and with or without the same mass ratio of m(Ag)/m(PVP). The possible underlying mechanism was further deeply analyzed. 相似文献
4.
Mimura K Dang F Kato K Imai H Wada S Haneda H Kuwabara M 《Journal of nanoscience and nanotechnology》2012,12(5):3853-3861
Ordered structures of barium titanate (BT) nanocubes, strontium titanate (ST) nanocubes and BT/ST nanocubes mixture were directly fabricated on Si and Pt-coated Si substrates using a capillary force assisted assembly method. The morphology of self-assembled structures was observed using field emission scanning electron microscopy (FE-SEM) and scanning probe microscopy (SPM). It was revealed that nanocubes were arranged with various degrees of ordering to develop multilayer and monolayer regions at the surface of substrates. The elemental mapping of the structure consisting of the nanocubes mixture was also investigated by transmission electron microscopy (TEM) with an energy dispersive X-ray spectroscopy (EDX). It was revealed that BT and ST nanocubes coexisted homogeneously in the structure and had possibility to be arranged in order to each other. The piezoresponse properties obtained by scanning probe microscopy (SPM) indicated that the hetero-interface between BT and ST nanocubes would introduce anomaly in piezoelectric properties. 相似文献
5.
Zao Yi Shanjun ChenYan Chen Jiangshan LuoWeidong Wu Yougen Yi Yongjian Tang 《Thin solid films》2012,520(7):2701-2707
Dendritic Ag/Au bimetallic nanostructures have been synthesized via a multi-stage galvanic replacement reaction of Ag dendrites in a chlorauric acid (HAuCl4) solution at room temperature. After five stages of replacement reaction, one obtains structures with protruding nanocubes; these will mature into many porous structures with a few Ag atoms that are left over dendrites. The morphological and compositional changes which evolved with reaction stages were analyzed by using scanning electron microscopy, transmission electron microscopy, UV-visible spectroscopy, selected area electron diffraction and energy-dispersive X-ray spectrometry. The replacement of Ag with Au was confirmed. A formation mechanism involving the original development of Ag dendrites into porous structures with the growth of Au nanocubes on this underlying structure as the number of reaction stages is proposed. This was confirmed by surface-enhanced Raman scattering (SERS). The dendritic Ag/Au bimetallic nanostructures could be used as efficient SERS active substrates. It was found that the SERS enhancement ability was dependent on the stage of galvanic replacement reaction. 相似文献
6.
In this work, PbS nanocubes and nanorods were fabricated via a facile hydrothermal method without using any template and surfactant. The structure and morphology of as-prepared PbS nanocrystals were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). It was found that the anisotropic structure of PbS nanorods were composed of numerous assembled nanocubes, which had an uniform morphology with the mean diameters of about 100-200 nm and lengths of 0.5-7 μm. Furthermore, a possible growth mechanism was proposed to explain the formation of the nanorods on the basis of the time-dependent experimental results. 相似文献
7.
Wei Jia Dexiang Zhang Xun Li Lu Chai Zhigang Zang Chingyue Wang 《Thin solid films》2008,516(8):2260-2263
The purpose of this study was to observe directly the morphology change and grain structure of FeCuNbSiB alloy when it is ablated with femtosecond laser pulses. The morphology and grain microstructure of amorphous FeCuNbSiB alloy was studied using scanning electron microscopy and field emission transmission electron microscopy. The results indicate that partial crystallization occurs at the rim of the laser-ablated hole, where the grain orientations are identical, and there is an amorphous layer outside the grains. This demonstrates that the liquid phase created by the femtosecond laser pulses has led to re-crystallized and partially crystallized zones. 相似文献
8.
Xiuqi Shi Wenfei Li Xinhui Lan Qianqian Guo Guangpeng Zhu Wei Du Tao Wang 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(43):2301949
Transition metal dichalcogenide (TMD)-based 2D monolayer semiconductors, with the direct bandgap and the large exciton binding energy, are widely studied to develop miniaturized optoelectronic devices, e.g., nanoscale light-emitting diodes (LEDs). However, in terms of polarization control, it is still quite challenging to realize polarized electroluminescence (EL) from TMD monolayers, especially at room temperature. Here, by using Ag nanowire top electrode, polarized LEDs are demonstrated based on 2D monolayer semiconductors (WSe2, MoSe2, and WS2) at room temperature with a degree of polarization (DoP) ranging from 50% to 63%. The highly anisotropic EL emission comes from the 2D/Ag interface via the electron/hole injection and recombination process, where the EL emission is also enhanced by the polarization-dependent plasmonic resonance of the Ag nanowire. These findings introduce new insights into the design of polarized 2D LED devices at room temperature and may promote the development of miniaturized 2D optoelectronic devices. 相似文献
9.
Silver nanocubes with sharp or truncated corners were synthesized, deposited on silicon substrates, and functionalized with Raman-active thiols for surface-enhanced Raman scattering (SERS) studies. The use of substrates with registration marks allowed us to correlate the SERS spectra from individual nanocubes to their physical parameters revealed by high-resolution SEM imaging. We observed dramatic variations in SERS intensity when the nanocubes were oriented at different angles relative to the polarization of excitation laser. This angular dependence was less significant when the nanocubes were truncated and became nearly spherical in profile. Numerical calculations were employed to confirm our observations, and to attribute the source of variation to the difference in near-field distribution between different laser polarizations. 相似文献
10.
In this paper, we developed a facile low-temperature solution route to prepare radical-shaped ZnO microprisms and to deposit metal silver on the surface of ZnO to form Ag/ZnO microstructures. The samples were characterized using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. Experimental results show that the deposition of metal Ag nanospecies can be achieved successfully by simply aging the solution at 75 °C, and the radical-shaped microstructures of ZnO are well maintained. The Ag/ZnO microstructures exhibit much lower PL emission intensity and much higher photocatalytic activity than those of radical-shaped ZnO microprisms. 相似文献
11.
We present an experimental investigation of the energy statistics of the linear polarization components of pulses from a Nd:YAG laser that is repetitively Q-switched with an acousto-optic modulator. Varying the modulator-induced diffraction losses leads to changes in the pulse polarization state and the energy statistics of the polarization components. For conventional Q-switching there is no laser oscillation during the low-Q intervals, and we find that the orthogonal components of the pulses can display large relative energy fluctuations even though the total pulse energy is quite stable. In the prelase mode, a weak continuous-wave background seeds the Q-switched pulses and results in the emission of highly linearly polarized, single-longitudinal-mode pulses with small relative energy fluctuations. 相似文献
12.
Laser-induced backside wet etching (LIBWE) is performed using ultrashort 248?nm laser pulses with a pulse duration of 600?fs to obtain sub-wavelength laser-induced periodic surface structures (LIPSS) on the back surface of fused silica which is in contact with a 0.5?mol?l(-1) solution of pyrene in toluene. The LIPSS are strictly one-dimensional patterns, oriented parallel to the polarization of the laser radiation, and have a constant period of about 140?nm at all applied laser fluences (0.33-0.84?J?cm(-2)) and pulse numbers (50-1000 pulses). The LIPSS amplitude varies due to the inhomogeneous fluence in the laser spot. The LIPSS are examined with scanning electron microscopy (SEM) and atomic force microscopy (AFM). Their power spectral density (PSD) distribution is analysed at a measured area of 10?μm × 10?μm. The good agreement of the measured and calculated LIPSS periods strongly supports a mechanism based on the interference of surface-scattered and incident waves. 相似文献
13.
Smaller cuprous oxides (Cu2O) nanocubes were synthesized by solution-phase method at 160 °C, using ethylene glycol reducing Cu(NO3)2·3H2O with poly(vinylypyrrolidone) (pvp) as capping agent. The Cu2O nanocubes were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and X-ray powder diffraction (XRD). SEM showed that most of Cu2O nanocubes were uniform and monodisperse, with the average edge length about 130 nm. The TEM results were consistent with the SEM results. Selected area electron diffraction (SAED) suggested that as-prepared Cu2O nanocubes were single crystalline. The geometric shape and size of Cu2O nanoparticles were greatly affected by the presence of PVP and its molar ratio (in repeating unit) relative to copper nitrate, temperature and the concentration of Cu(NO3)2·3H2O. The mechanism of Cu2O nanocubes formation was also discussed. 相似文献
14.
An aqueous seed-mediated growth method is adapted to explore the shape transformation of quasi-spherical Au seeds to nanocubes in a direct and continuous manner. Quenching the growth process at varied reaction-duration times and exploring the intermediate products by high-resolution transmission electron microscopy and UV/vis spectroscopy shows an abrupt cuboctahedral-to-nanocube transition at 25-27 nm without any change in the nanoparticle size. The size of the obtained nanocubes remains constant (25-27 nm) until most (>90%) of the cuboctahedral nanoparticles are transformed to nanocubes. At this point, the (25-27 nm) nanocubes initiate further continuous and homogeneous growth until they reach 50-nm Au cubes. These observations are ascribed to a scenario in which the kinetically controlled growth mode of the nanoparticle is significantly affected by the surface self-diffusion of metal adatoms, especially when the adatom's self-diffusion distance is comparable with the nanoparticle's size. 相似文献
15.
Ag and Cu nanowires were separately fabricated in a direct current electric field using a solid-state ionic method, and characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Their optical nonlinearities induced by 8 ns laser pulses from a frequency-doubled, Nd:YAG laser at 532 nm, were investigated using the Z-scan technique. Experimental results indicate the metal nanowires have obvious positive refractive nonlinearities and reverse saturated absorption behaviors. The self-focusing behaviors of Ag and Cu nanowires can be attributed to Kerr-induced self-focusing of laser radiation, the nonlinear refractive indexes of Ag and Cu nanowires are n2 = 1.7 × 10− 11 esu and n2 = 2.4 × 10− 11 esu respectively, and the two-photon process of Ag and the one-photon process of Cu are responsible for the difference between Ag and Cu nanowires suspended in de-ionized water in nanosecond nonlinear absorptions. 相似文献
16.
V. S. Dang P. Mikheenko A. Sarkar M. M. Awang?Kechik J. S. Abell P. Paturi H. Huhtinen A. Crisan 《Journal of Superconductivity and Novel Magnetism》2011,24(1-2):505-509
The combination of two methods: Ag substrate decoration and introduction of BZO nano-inclusions has been used in a pulsed laser deposition (PLD) method to increase the critical density (J c ) of YBCO films. The films were deposited on single crystal SrTiO3 (STO) substrates decorated with various architecture of Ag nano-dots. We have studied the diameter and density of Ag nano-dots and their influence on J c of BZO-added YBCO films. We found that 15 laser pulses on the Ag target gives an optimum result in increasing J c in comparison with BZO-doped YBCO films of the same thickness in self-field and low applied magnetic fields. A higher number of laser pulses on the Ag target led to increasing critical current density in high applied magnetic fields only (above 2 T). We have studied films of the thickness from 0.4 ??m to 3.8 ??m and found that the highest J c at all applied fields investigated is achieved for a 1.2 ??m thick film. The transmission electron microscopy clearly shows BZO nano-rods that provide strong c-axis pinning centres in the films. 相似文献
17.
Using the method of laser probing, the laws governing the formation of the liquid-droplet phase of a number of metals (Ni,
Zn, Pb, Ag, and Cu) on exposure of metal targets to intense submicrosecond pulses have been determined. It has been established
that condensation from the vapor of the erosive laser jet is the main mechanism of formation of the liquid-droplet phase of
a metal under given conditions. 相似文献
18.
With a classical ensemble model, we investigated non-sequential double ionization (NSDI) of argon by elliptically polarized laser pulses. The results show that the correlation behaviors of two electrons depend strongly on the laser intensity. At relatively high laser intensity, the momentum spectra of two electrons along the long axis of the laser polarization plane are mainly distributed in the first and third quadrants and display V-like structures. However, at relatively low laser intensity, the momentum spectra of two electrons are mainly distributed in the second and fourth quadrants. By back analyzing the classical trajectories of NSDI, we find that all of the successful NSDI events still come from recollision in the cases of elliptically polarized laser pulses, and the final-state electron repulsion plays a decisive role for the V-like structure along the long axis of the laser polarization plane. In addition, we find that the initial velocity of the first electron at ionization along the short axis of the laser polarization plane are essential for the recollision, and the time delay between the first ionization and recollision depends on the ellipticity strongly. 相似文献
19.