共查询到20条相似文献,搜索用时 44 毫秒
1.
S.D. Sartale 《Surface science》2006,600(22):4978-4985
The growth of Pt nanoclusters on thin film Al2O3 grown on NiAl(1 0 0) was studied by using scanning tunneling microscopy (STM). The samples were prepared by vapor depositing various amounts of Pt onto the Al2O3/NiAl(1 0 0) at different substrate temperatures in ultra high vacuum (UHV). The STM images show that sizeable Pt nanoclusters grow solely on crystalline Al2O3 surface. These Pt clusters appear to be randomly distributed and only a few form evident alignment patterns, contrasting with Co clusters that are highly aligned on the crystalline Al2O3. The size distributions of these Pt clusters are rather broader than those of the Co clusters on the same surface and the sizes are evidently smaller. With increasing coverage or deposition temperature, the number of larger clusters is enhanced, while the size of the majority number of the clusters remains around the same (0.4 nm as height and 2.25 nm as diameter), which differs drastically from the Pt clusters on γ-Al2O3/NiAl(1 1 0) observed earlier. These Pt cluster growth features are mostly attributed to smaller diffusion length and ease to form stable nucleus, arising from strong Pt-Pt and Pt-oxide interactions and the peculiar protrusion structures on the ordered Al2O3/NiAl(1 0 0). The thermal stability of Pt nanoclusters was also examined. The cluster density decreased monotonically with annealing temperature up to 1000 K at the expense of smaller clusters but coalescence is not observed. 相似文献
2.
F. Kokai K. Takahashi D. Kasuya M. Yudasaka S. Iijima 《Applied Physics A: Materials Science & Processing》2001,73(4):401-407
Single-wall carbon nanotubes (SWNTs) were synthesized by the irradiation of 20-ms CO2 laser pulses onto a graphite–Co/Ni target at room temperature. We investigated the effect of laser power density (10–150 kW/cm2) and ambient Ar gas pressure (150–760 Torr) on the abundance of SWNTs with lengths of up to about 200 nm in soot-like carbonaceous
deposits. For a constant power density (30 kW/cm2), depending on the Ar gas pressure, SWNTs with diameters of 1.2–1.4 nm were synthesized. Expansion behavior and temperature-fall
rates of clusters and/or particles in laser plumes were also analyzed by high-speed video imaging and temporally and spatially
resolved emission spectroscopy. The temperature-fall rates were estimated to be 171–427 K/ms. The SWNT growth on the time
scale of a few milliseconds appeared to be related to some features of condensing clusters and/or particles, including resident
densities, collision frequencies and temperatures.
Received: 16 July 2001 / Accepted: 23 July 2001 / Published online: 30 August 2001 相似文献
3.
Enhanced performance of a mutually pumped phase-conjugation setup using two photorefractive crystals 总被引:1,自引:0,他引:1
F. Wang A. Hermerschmidt P. Pogany S.X. Dou H.J. Eichler 《Applied physics. B, Lasers and optics》2001,72(6):755-759
A mutually pumped phase-conjugator (MPPC) consisting of two photorefractive crystals is investigated experimentally at a wavelength
of about 807 nm. In addition to a Rh:BaTiO3 crystal, which is used in a modified bridge configuration for phase-conjugation, a Co:BaTiO3 crystal is used to amplify the phase-conjugate beam by wave-mixing. The phase-conjugate power is at least doubled compared
to that using only one crystal, and the beam quality of the phase-conjugate beam is distinctly improved. Moreover, the temporal
stability of the phase-conjugate output using two crystals is much higher than that using only one crystal.
Received: 7 December 2000 / Revised version: 12 January 2001 / Published online: 27 April 2001 相似文献
4.
S. Rubin M. Holdenried H. Micklitz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):23-28
Well-defined granular Co/Ag films have been prepared by the co-deposition of in-beam prepared Co clusters and Ag atoms. In
this way we were able to study the giant magnetoresistance (GMR) as a function of mean Co cluster size for a fixed Co cluster volume fraction vcl as well as a function of vcl for a fixed . Mean Co cluster size has been varied between and 6.9 nm, Co cluster volume fraction between 5 and 43%. The GMR was measured in-situ at T=4.2 K in magnetic fields 1.2 T. The analysis of the GMR data obtained from these studies clearly shows that spin-dependent scattering at the Co-cluster/Ag-matrix
interface is the only relevant scattering mechanism causing the GMR in our well-defined samples.
Received: 21 April 1998 / Received in final form: 17 May 1998 /
Accepted: 18 May 1998 相似文献
5.
M.F. Luo W.H. Wen C.S. Lin C.I. Chiang S.D. Sartale M.S. Zei 《Surface science》2007,601(10):2139-2146
With reflection high-energy electron diffraction (RHEED) and scanning-tunnelling microscopy (STM), we made measurements on Co and Pt nanoclusters grown by vapour deposition on a thin film of Al2O3/NiAl(1 0 0). The results show that the annealed Co nanoclusters (with mean diameters 2.5, 3.4, 5.8 nm and heights 0.7, 1.5, 1.5 nm, respectively) and Pt nanoclusters (with mean diameter 2.25 nm and height 0.4 nm) are highly crystalline and that their structures are significantly affected by the oxide substrate. Structural analysis based on the RHEED patterns indicates that both Co and Pt clusters have a fcc phase and grow with their (0 0 1) facets parallel to the θ-Al2O3(1 0 0) surfaces, and with their [1 1 0] and [−1 1 0] axes along the [0 1 0] and [0 0 1] directions of the oxide surface, respectively, so (Co(0 0 1)[1 1 0]∥Al2O3(1 0 0)[0 1 0] and Pt(0 0 1)[1 1 0]∥Al2O3(1 0 0)[0 1 0]). This growth is optimal as the Co and Pt fcc (0 0 1) facets match well with the oxygen mesh. To minimize the lattice mismatch, the lattice parameter of the Co clusters expands 4-5% relative to fcc Co bulk, whereas the lattice parameter of the Pt clusters remains near the bulk value, as the Pt fcc (0 0 1) plane has a close lattice match with the oxide surface. 相似文献
6.
Absorptance losses in MgF2, CaF2 and BaF2 during 193-nm (DUV) and 157-nm (VUV) irradiation are investigated by employing a high-resolution laser calorimetric technique
which allows the determination of both single- and two-photon absorptance at energy densities up to 110 mJ/cm2. A strong wavelength dependence of the DUV and VUV absorption characteristics is observed: while effective two-photon absorption
takes place at 193 nm, either no similar effect at all (in the case of BaF2) or only a very minor effect (CaF2) is observed at 157 nm. A first explanation for this absorption behaviour is given, implying the energetic band structure
of CaF2. In addition it is shown that, due to the strong nonlinear dependency, above a critical energy density the absorptance at
193 nm can exceed the absorptance at 157 nm. Furthermore, different single- and two-photon absorption coefficients are determined
for different CaF2 samples at 193 nm, indicating a two-step absorption mechanism. In addition, laser-induced aging is found in a MgF2 sample at 193 nm, but not at 157 nm.
Received: 21 June 2001 / Revised version: 2 November 2001 / Published online: 7 February 2002 相似文献
7.
C. Binns S.H. Baker M.J. Maher S.C. Thornton S. Louch S.S. Dhesi N.B. Brookes 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):189-192
A portable UHV-compatible gas aggregation cluster source, capable of depositing clean mass-selected nanoclusters in situ, has been used at synchrotron radiation facilities to study the magnetic behaviour of exposed and Co-coated Fe clusters in
the size range 250 to 540 atoms. X-ray magnetic circular dichroism (XMCD) studies of isolated and exposed 250-atom clusters
show a 10% enhancement in the spin magnetic moment and a 75% enhancement in the orbital magnetic moment relative to bulk Fe.
The spin moment monotonically approaches the bulk value with increasing cluster size but the orbital moment does not measurably
decay till the cluster size is above ∼ 400 atoms. The total magnetic moments for the supported particles though higher than
the bulk value are less than those measured in free clusters. Coating the deposited particles with Co in situ increases the spin moment by a further 10% producing a total moment per atom close to the free cluster value. At low coverages
the deposited clusters are super-paramagnetic at temperatures above 10 K but a magnetic remanence at higher temperature emerges
as the cluster density increases and for cluster films with a thickness greater than 50 ?(i.e. 2-3 layers of clusters) the remanence becomes greater than that of an Fe film of the same thickness produced by a conventional
deposition source. Thick cluster-assembled film show a strong in-plane anisotropy.
Received 14 December 2000 相似文献
8.
The authors’ endeavors over the last few years with respect to boron nitride (BN) nanotube metal filling are reviewed. Mo
clusters of 1–2 nm in size and FeNi Invar alloy (Fe ∼60 at. %; Ni ∼40 at. %) or Co nanorods of 20–70 nm in diameter were embedded
into BN nanotube channels via a newly developed two-stage process, in which multi-walled C nanotubes served as templates for
the BN multi-walled nanotube synthesis. During cluster filling, low-surface-tension and melting-point Mo oxide first filled
a C nanotube through the open tube ends, followed by fragmentation of this filling into discrete clusters via O2 outflow and C→BN conversion within tubular shells at high temperature. During nanorod filling, C nanotubes containing FeNi
or Co nanoparticles at the tube tips were first synthesized by plasma-assisted chemical vapor deposition on FeNi Invar alloy
or Co substrates, respectively, and, then, the nanomaterial was heated to the melting points of the corresponding metals in
a flow of B2O3 and N2 gases. During this second stage, simultaneous filling of nanotubes with a FeNi or Co melt through capillarity and chemical
modification of C tubular shells to form BN nanotubes occurred. The synthesized nanocomposites were analyzed by scanning and
high-resolution transmission electron microscopy, electron diffraction, electron-energy-loss spectroscopy and energy-dispersive
X-ray spectroscopy. The nanostructures are presumed to function as ‘nanocables’ having conducting metallic cores (FeNi, Co,
Mo) and insulating nanotubular shields (BN) with the additional benefit of excellent environmental stability.
Received: 10 October 2002 / Accepted: 25 October 2002 / Published online: 10 March 2003
RID="*"
ID="*"Corresponding author. Fax: +81-298/51-6280, E-mail: golberg.dmitri@nims.go.jp 相似文献
9.
The growth of Co on thin Al2O3 layers on Ni3Al(1 0 0) was investigated by Auger electron spectroscopy, high resolution electron energy loss spectroscopy (EELS), and scanning tunneling microscopy. At 300 K, Co grows in three-dimensional clusters on top of the Al2O3 layer. A defect structure of the alumina layer plays a crucial role during the early stage of Co growth. After deposition of 10 Å of Co, a complete screening of the dipoles of the Al2O3 layer due to the Co film is found in the EELS measurements. Annealing the Co film reveals a process of coalescence of Co clusters and, above 700 K, diffusion of the Co atoms through the oxide film into the substrate takes place. 相似文献
10.
D. Le Roy R. MorelA. Brenac L. Notin 《Journal of magnetism and magnetic materials》2011,323(1):127-129
We report on a method to orient the easy axes of ferromagnetic nanoclusters during their deposition, with the use of a magnetic field supplied by a set of permanent magnets. This field is applied close to the substrate where the preformed clusters are deposited. The efficiency is demonstrated on an assembly of 4 nm Co clusters produced by a sputtering and gas-condensation technique. The magnetization of the deposited clusters measured at 6 K exhibits an overall in-plane alignment of the easy axes in the direction of the field applied during deposition, HD. Using a Stoner-Wohlfarth model, it is estimated that half of the clusters easy axes lie within 35° from HD. 相似文献
11.
O.A. Yeshchenko I.M. Dmitruk S.V. Koryakov M.P. Galak 《Physica E: Low-dimensional Systems and Nanostructures》2005,30(1-2):25-30
CdP2 nanoclusters were fabricated by incorporation into pores of zeolite Na–X and by laser ablation. Absorption and photoluminescence (PL) spectra of CdP2 nanoclusters in zeolite were measured at the temperatures of 4.2, 77 and 293 K. Both absorption and PL spectra consist of two bands blue shifted with respect to bulk crystal. We performed the calculations aimed to find the most stable clusters in the size region up to size of the zeolite Na–X supercage. The most stable clusters are (CdP2)6 and (CdP2)8 with binding energies of 9.30 and 10.10 eV per (CdP2)1 formula unit, respectively. Therefore, we attributed two bands observed in absorption and PL spectra to these stable clusters. The Raman spectrum of CdP2 clusters in zeolite was explained to be originated from (CdP2)6 and (CdP2)8 clusters as well. The PL spectrum of CdP2 clusters produced by laser ablation consists of the asymmetric band with low-energy tail that has been attributed to emission of both (CdP2)8 cluster and CdP2 microcrystals. 相似文献
12.
Y. Wang C. Zhang Y. Song K. Yang G. Fang X. Xin 《Applied physics. B, Lasers and optics》2002,74(1):43-46
The nonlinear absorption and refraction of the clusters [MoS4Cu4Br2(py)6] and [Et4N]2[MoS4Cu4(SCN)4(2-pic)4] have been investigated using the z-scan technique with a ns laser at 532 nm wavelength. They have the same planar ‘open’
structures and the same skeleton metal atoms; the only difference is that the former has halogen ligands while the latter
possesses pseudo-halogen groups – SCN – as ligands. Alteration of nonlinear refractive index and enhancement of nonlinear
absorption were found in these two clusters. A steady state model of excited state nonlinear refraction was proposed to explain
this phenomenon.
Received: 12 June 2001 / Revised version: 4 September 2001 / Published online: 29 November 2001 相似文献
13.
You Qiang Jiji Antony Amit Sharma Joseph Nutting Daniel Sikes Daniel Meyer 《Journal of nanoparticle research》2006,8(3-4):489-496
Biocompatible magnetic nanoparticles have been found promising in several biomedical applications for tagging, imaging, sensing and separation in recent years. Most magnetic particles or beads currently used in biomedical applications are based on ferromagnetic iron oxides with very low specific magnetic moments of about 20–30 emu/g. Here we report a new approach to synthesize monodispersed core-shell nanostructured clusters with high specific magnetic moments above 200 emu/g. Iron nanoclusters with monodispersive size of diameters from 2 nm to 100 nm are produced by our newly developed nanocluster source and go to a deposition chamber, where a chemical reaction starts, and the nanoclusters are coated with iron oxides. HRTEM Images show the coatings are very uniform and stable. The core-shell nanoclusters are superparamagnetic at room temperature for sizes less than 15 nm, and then become ferromagnetic when the cluster size increases. The specific magnetic moment of core-shell nanoclusters is size dependent, and increases rapidly from about 80 emu/g at the cluster size of around 3 nm to over 200 emu/g up to the size of 100 nm. The use of high magnetic moment nanoclusters for biomedical applications could dramatically enhance the contrast for MRI, reduce the concentration of magnetic particle needs for cell separation, or make drug delivery possible with much lower magnetic field gradients 相似文献
14.
T. Mangen 《Journal of magnetism and magnetic materials》2010,322(13):1863-23808
The formation of Co films on polycrystalline copper in diluted sulphuric acid was investigated by employing cyclic voltammetry (CV), atomic force microscopy, and in-situ magneto-optic Kerr effect (MOKE) techniques. By comparing CV measurements in the pure supporting electrolyte (11 mM K2SO4/1 mM H2SO4) and the cobalt sulphate solution (10 mM K2SO4/1 mM H2SO4/1 mM CoSO4), peaks from voltammetric cycling for copper dissolution, readsorption of dissolved copper ions, cobalt bulk dissolution and oxidation of hydrogen could be resolved. As the electroplating time increases, the size of the Co clusters increases and the deposition of Co corresponds to island growth. The first hysteresis loop occurs at a Co thickness of 0.33 nm in the longitudinal configuration. For films thinner than 7 nm, the Kerr intensity increases linearly because the Curie temperature of the film is well above 300 K. 相似文献
15.
M. A. Pushkin P. V. Borisyuk V. I. Troyan V. N. Tronin I. V. Tronin V. D. Borman 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(7):878-883
The evolution of the electronic structure of pulsed-laser-deposited nanoclusters of noble and transition metals (Au, Cu, Ni, Co, Cr) on a graphite surface with a decrease in their size from 10 to 1 nm has been investigated by scanning tunnel spectroscopy, X-ray photoelectron spectroscopy, and Auger electron spectroscopy. The data obtained suggest that the properties of nanoclusters differ from metallic when the lateral cluster size reaches ~2–3 nm and the height reaches ~1 nm and that the shape of clusters (transition from three-dimensional to two-dimensional ones) significantly affects their transition to the nonmetallic state. 相似文献
16.
Single-frequency Ti:Er:LiNbO3 distributed Bragg reflector waveguide laser with thermally fixed photorefractive cavity 总被引:1,自引:0,他引:1
The first single-frequency Ti:Er:LiNbO3 distributed Bragg reflector waveguide laser with two thermally fixed photorefractive gratings as resonator mirrors is reported.
The optically pumped (λp=1480 nm,120-mW incident power) laser emits up to 1.1 mW at λs=1561.1 nm. The threshold pump power is 70 mW.
Received: 7 June 2001 / Published online: 30 October 2001 相似文献
17.
Bai-Ru Zhao Xiao-Li Dong Peng-Shun Luo Min Gao Zhong-Xian Zhao Lian-Mao Peng Yong-Ming Ni Xiang-Gang Qiu Satoshi Awaji Kazuo Watanabe Fei Wu Bo Xu Li-Hua Zhao F.C. Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):19-23
We have measured the zero field and field cooled magnetization of the lightly oxygen doped Cu-rich La2CuO 4 + δ in a wide temperature range (5 K to 350 K). The data together with the evolution of the magnetic hysteresis loop suggest
that the ferromagnetism with Curie temperature of 280 K coexists with superconductivity below the transition temperature ∼
34 K. The coexistence occurs in the hole-rich clusters of size ? 150 nm, which are electronic phase separated from the hole-poor
antiferromagnetic background.
Received 17 October 2001 相似文献
18.
Pulse-parameter dependence of the configuration characteristics of a micro-structure in fused SiO2 induced by femtosecond laser pulses 总被引:1,自引:0,他引:1
L. Luo C. Li D. Wang H. Yang H. Jiang Q. Gong 《Applied Physics A: Materials Science & Processing》2002,74(4):497-501
The fabrication of a micro-structures in fused SiO2 by femtosecond laser pulses was studied in the range of pulse duration 150∼500 fs, pulse energy 60 nJ to ∼7 μJ and wavelengths
400 nm and 800 nm. The characteristics of the cross section of the micro-structure were explained with the multiphoton-ionization
and avalanche-ionization processes in the femtosecond laser-induced breakdown. The characteristics of the longitudinal length
of the micro-structure relating to the direct-focusing and self-action effects are also discussed.
Received: 10 January 2001 / Accepted: 7 April 2001 / Published online: 23 May 2001 相似文献
19.
F. Sánchez M.V. García-Cuenca C. Ferrater M. Varela 《Applied Physics A: Materials Science & Processing》2002,75(3):381-385
We report on the epitaxial growth of yttria-stabilised zirconia (YSZ) buffer layers on X-cut LiNbO3 (LNO) single crystals by pulsed laser deposition. Despite the low chemical stability of the substrates at high temperature,
high quality fully reproducible films were obtained over a relatively broad range of processing conditions. The films were
(00h) out-of-plane single oriented and the in-plane edge of the YSZ unit cell was aligned with the polar axis of the LNO.
However, the YSZ deposition also promoted the formation of the compound LiNb3O8. This compound is epitaxial and located at the interface. The homogeneous YSZ film presents a uniform surface, free of outgrowths
and with a low roughness. These characteristics are suitable for the epitaxial growth of other oxides, as has been demonstrated
with the preparation of YBa2Cu3O7/CeO2/YSZ/LNO heterostructures. The superconducting YBa2Cu3O7 films were epitaxial, with the c axis perpendicular to the surface and single in-plane orientation, and presented good transport
properties (critical temperatures around 86 K and critical current densities close to 106 A/cm2 at 77 K).
Received: 5 April 2001 / Accepted: 30 July 2001 / Published online: 30 October 2001 相似文献
20.
H. Mendis A. Mitchell I. Belski M. Austin O.A. Peverini 《Applied physics. B, Lasers and optics》2001,73(5-6):489-493
The design and realisation of a SiO2 film-loaded Ti:LiNbO3 integrated acousto-optic tunable filter are presented. An optimised Hamming apodisation is achieved through introducing an
angular offset between the acoustic and optical waveguides along with carefully placed acoustic absorbers. The realised device
has a 20-mm acoustic interaction length and achieves a 3-dB linewidth of 1.8 nm with 19-dB sidelobe suppression. The realised
device is highly efficient, requiring a RF drive power of only 10 mW to achieve complete polarisation conversion. The enhanced
drive efficiency of the device is analysed using both acoustic and optical mode analysis. Based on this analysis, possible
explanations for the improved behaviour are presented and directions that may lead to further enhancements are discussed.
Received: 18 May 2001 / Revised version: 7 August 2001 / Published online: 23 October 2001 相似文献