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1.
Thin films of fullerenes (C60) were deposited onto silicon using matrix-assisted pulsed laser evaporation (MAPLE). The deposition was carried out from a frozen homogeneous dilute solution of C60 in anisole (0.67 wt%), and over a broad range of laser fluences, from 0.15 J/cm2 up to 3.9 J/cm2. MAPLE has been applied for deposition of fullerenes for the first time and we have studied the growth of thin films of solid C60. The fragmentation of C60 fullerene molecules induced by ns ablation in vacuum of a frozen anisole target with C60 was investigated by matrix-assisted laser desorption/ionization (MALDI). Our findings show that intact fullerene films can be produced with laser fluences ranging from 0.15 J/cm2 up to 1.5 J/cm2.  相似文献   

2.
Raman spectra from the first Ti fullerene complex Cp 2Ti(η2-C60) · C6H5CH3 are presented. Compared to spectra of pure C60, the spectra of the Ti complex exhibit a number of new peaks due to the symmetry lowering for C60. The A g(2) mode is downshifted by 12 cm−1 compared to C60, which corresponds to a charge transfer of one electron per Ti-C60 bond. This value (6 cm−1 for one transferred electron) is identical to the downshift of the A g(2) mode in alkali metal fullerides with ionic bonding. The spectra of Cp 2Ti(η2-C60) · C6H5CH3 were compared to the spectra of evaporated TixC60 films. The A g(2) mode in Ti4C60 showed a downshift of about 25 cm−1 compared to pure C60, which corresponds to a charge transfer of one electron per Ti atom; this is similar to the ionic alkali metal fullerides and different from η2-C60-type bonding. From Fizika Tverdogo Tela, Vol. 44, No. 3, 2002, pp. 483–485. Original English Text Copyright ? 2002 by Talyzin, Jansson, Usatov, Burlakov, Shur, Novikov. This article was submitted by the authors in English.  相似文献   

3.
Isotope separation of tritium by CO2 laser-induced multiphoton dissociation (MPD) of C2TF5 is reported for the first time. The MPD spectrum obtained for C2TF5 comprised a broad peak at about 940 cm–1 where C2HF5 was nearly transparent. The unimolecular dissociation of C2TF5 was induced with much lower laser fluence than that for CTF3, another working molecule we proposed for laser isotope separation of tritium. The mechanisms and kinetics of the dissociation of C2TF5 and C2HF5 were investigated under various experimental conditions: laser frequency, pulse energy, pulse duration, tritium concentration, sample pressure, buffer gas pressure and irradiation geometry. Single-step separation factors exceeding 500 were achieved with the most efficientP(20) line in 00o–10o0 transition at 944.2 cm–1.  相似文献   

4.
Diffusion of lithium cations in C60 single crystals driven by electric field has been detected and studied. A novel technique for fullerene crystal doping based on injection of ions through a “superionic crystal/C60 single crystal” heterojunction has been suggested. It has been found that lithium doping of C60 single crystals brings about an ESR signal, and this signal as a function of time has been investigated. The electronic conductivity in LixC60 crystals has a nonmetallic nature. Reflection spectra measured in the IR band have shown that the reflectivity due to free electrons gradually decreases with time, which correlates with the evolution of signals due to ESR and microwave conductivity. Lithium doping of crystals increases the oscillator strength of the T 1u (4) vibrational mode and shifts it to lower frequencies (from 1429 cm−1 to 1413 cm−1), which indicates that one electron is present at the C60 molecule, and this fact may be treated as evidence that the LiC60 phase is generated in a C60 crystal. Zh. éksp. Teor. Fiz. 116, 1706–1722 (November 1999)  相似文献   

5.
Laser-ionization time-of-flight mass spectrometry has been used to probe laser-ablation products from a nitrogen-rich polymer at a wavelength of 308 nm. The ablation products at a laser fluence of 150 mJ/cm2 showed, similar to 532 nm ablation studied previously [18], two strong peaks due to neutral species that were assigned to C+ and CN+, as well as several weak peaks that were assigned to CH+, HCN+, HCNH+, HnN–CN+ (n=1–3), and H2N–C=N–CN+ or H2N–C=N–CN+. The ablation products at 870 mJ/cm2 revealed, in addition to a broad signal due to ionic products generated directly by the ablation laser, several peaks due to neutral products that were assigned to C+, C 2 + , C 3 + , CN+, HCN+, HCNH+, and NCCN+. The most probable flight velocities for major neutral products are 5.7×104 cm/s at 150 mJ/cm2 and 2.3–2.7×104 cm/s at 870 mJ/cm2. The results at a laser fluence of 150 mJ/cm2 support the finding that the translational energy of the tragments has importance for the collision-induced product generation in the laser plume, as suggested earlier [18]. Furthermore, the product generation at 870 mJ/cm2 is interpreted by the ejection of small neutral and ionic fragments, and subsequent reactions among the fragments.  相似文献   

6.
A modified liquid–liquid interface precipitation synthesis of C60 nanorods, effects and opportunities following an in situ photochemical transformation in the liquid state, and an electronic characterization using a field‐effect transistor (FET) geometry are reported. The nanorods feature a high aspect ratio of ≈103 and a notably small average diameter of 172 nm. Interestingly, it is found that a decreased nanorod diameter appears to correlate with distinctly improved electronic properties, and an average electron mobility of 0.30 cm2 V?1 s?1, as measured in a FET geometry, is reported for as‐grown nanorods, with the peak value being an impressive 1.0 cm2 V?1 s?1. A photoexposure using green laser light (λ = 532 nm) is demonstrated to result in the formation of a polymer‐C60 shell encapsulating a monomer‐C60 bulk; such photo‐transformed nanorods exhibit an electron mobility of 4.7 × 10?3 cm2 V?1 s?1. It is notable that the utilized FET geometry only probes the polymer‐C60 nanorod surface shell, and that the monomer‐C60 bulk is anticipated to exhibit a higher mobility. Importantly, photoexposed nanorods can be conveniently processed as a stabile dispersion in common hydrophobic solvents, and this finding is attributed to the insoluble character of the polymer‐C60 shell.  相似文献   

7.
A photoacoustic intracavity configuration is presented; a resonant photoacoustic cell excited in its first longitudinal mode is placed inside the cavity of a CO2 waveguide laser. Due to the high laser power and the sharp intracavity focus, saturation effects occur in the excitation and relaxation process of absorbing C2H4 molecules. A more optimal configuration is applied to measure the C2H4 emission of several Rumex species. A detection sensitivity of 6 ppt (parts per trillion) C2H4 is reached, equivalent to a minimal detectable absorption of 1.8×10–10 cm–1.  相似文献   

8.
The opto-mechanical characteristics, such as the specific mechanical recoil momentum, the specific impulse, and the energy efficiency, of the laser ablation of flat polymer targets ((C2F4) n , (CH2O) n ) have been determined experimentally for the first time for the case of excitation with femtosecond pulses (τ ∼ 45–70 fs) of UV-IR (λ ∼ 266, 400, 800 nm) laser radiation (I 0 up to 1015 W/cm2) under normal atmospheric and vacuum (p ∼ 10−4 mbar) conditions. The efficiency of mechanical recoil momentum generation is analyzed for various regimes of the laser irradiation.  相似文献   

9.
采用飞行时间质谱计测量了纳秒激光诱导C60分子碎裂中轻碎片离子C+n(n≤11)的初始平均动能,结果显示轻碎片离子具有相同的初始平均动能(约为0.34eV),并且该动能在一定范围内不随激光通量的变化而明显改变.结合前人的实验结果,对纳秒激光诱导C60分子碎裂中轻碎片离子C+n(n<30)的主要产生模式作了新的阐述,即C< 关键词: 飞行时间质谱计 轻碎片离子 笼形结构塌陷 初始动能  相似文献   

10.
We present a theoretical study of the short-time relaxation of clusters in response to ultrafast excitations using femtosecond laser pulses. We analyze the excitation of different types of clusters (Hgn, Agn, Sin, C60 and Xen) and classify the relaxation dynamics in three different regimes, depending on the intensity of the exciting laser pulse. For low-intensity pulses (I<1012 W/cm2) we determine the time-dependent structural changes of clusters upon ultrashort ionization and photodetachment. We also study the laser-induced non-equilibrium fragmentation and melting of Sin and C60 clusters, which occurs for moderate laser intensities, as a function of the pulse duration and energy. As an example for the case of high intensities (I>1015 W/cm2), the explosion of clusters under the action of very intense ultrashort laser fields is described. Received: 26 November 1999 / Published online: 2 August 2000  相似文献   

11.
Optical emission from a laser-induced plasma plume is recorded during KrF excimer laser ablation of graphite in a gas mixture of Ar and H2 (3%) for deposition of diamond-like thin films. At sub-GW/cm2 laser intensities the spectrum is dominated by the bands of C2 and CN. From the band intensities, the vibrational temperatures of both radicals are calculated to be 12–15×103 K, and their concentrations are estimated to be 5×1014 cm–3 and 2×1014 cm–3, respectively.  相似文献   

12.
The results are reported of the CO-laser optothermal (OT) detection of impurity gases when their absorption spectra overlap with those of an interfering gas. The influence of the latter was avoided using low gas pressures corresponding to a maximum of the OT sensitivity. Frequency tuned in the 5.2–6.3 m wavelength range, 12C16O and 13C16O waveguide lasers were used. The fine frequency tuning at 490 MHz was achieved for 150 laser transitions of both molecules. The OT sensitivity was estimated by NO2 detection in the presence of water vapor. The minimal detectable concentration proved to be 60 ppb at P 19–18(14) transition of a 12C16O laser for NO2 and 75 ppb on P 12–11(13) transition of a 13C16O laser for H2O.  相似文献   

13.
Absolute cross sections for electron-impact single ionization, dissociative excitation and dissociative ionization of the ethynyl radical ion (C2D+)^+) have been measured for electron energies ranging from the corresponding reaction thresholds to 2.5 keV. The animated crossed electron-ion beam experiment is used and results have been obtained for the production of C2D2+, C2+, C2+_2^+ , CD+, C+ and D+. The maximum of the cross section for single ionization is found to be (2.01 ± 0.02) × 10-17 cm2, at the incident electron energy of 105 eV. Absolute total cross sections for the various singly charged fragments production are observed to decrease by a factor of almost three, from the largest cross-section measured for C+, over C2+_2^+ and CD+ down to that of D+. The maxima of the cross sections are obtained to be (14.5 ± 0.5) × 10-17 cm2 for C2+_2^+, (12.1 ± 0.1) × 10-17 cm2 for CD+, (27.7 ± 0.2) × 10-17 cm2 for C+ and (11.1 ± 0.8) × 10-17 cm2 for D+. The smallest cross section is measured to be (1.50 ± 0.04) × 10-18 cm2 for the production of the doubly charged ion C2+. Individual contributions for dissociative excitation and dissociative ionization are determined for each singly-charged product. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. Kinetic energy release distributions of dissociation fragments are seen to extend from 0 to 6 eV for the heaviest fragment C2+_2^+, up to 11.0 eV for CD+, 14.2 eV for C+ and 11.2 eV for D+ products.  相似文献   

14.
A tunable microwave frequency was added to, or subtracted from fixed frequency13C16O2 and12C18O2 laser lines using the nonlinearity of molecular absorptions. In this way the frequency of 30 transitions of the ν2-band of ammonia were measured with an accuracy of ±0.0005 cm−1. A further four transitions were measured with an accuracy of ±0.0001 cm−1 by saturating the two-photon transition and observing the Lamb dip. For laser lines up to 11 GHz off-resonant with in frared transitions Doppler-limited signals were observed with microwave power densities of only 10 mW/cm2 using a wide-band intracavity cell.  相似文献   

15.
Transient optical Kerr effect of liquids C2H4Cl2 and C2H4Br2 is investigated, for the first time to our knowledge, with a femtosecond (fs) probe laser delayed with respect to a coherent fs pump laser. Coherent coupling and electronic Kerr signals are observed around zero delay when pump and probe overlap. Persisting after the pump-probe overlap are Kerr signals arising from the torsional and other intramolecular vibrations of the trans and gauche conformations; Kerr signals arising from the intermolecular motion are also observed. Vibrational quantum interference is only observed in liquid C2H4Br2 and the related beats data are fitted with the torsional vibrations, 91 cm−1 (gauche) and 132 cm−1 (trans), and the CCBr angle-bending vibrations, 231 cm−1 (gauche) and 190 cm−1 (trans), with dephasing times, 0.45 ps, 0.45 ps, 2 ps, and 1.5 ps, respectively. These vibrational frequencies agree with those obtained in the frequency-domain. That no vibrational mode is observed for C2H4Cl2 might be attributed to ineffective Raman-pumping. Kerr signals observed after the pump-probe overlap are Fourier transformed to give the spectra of the intermolecular motion and the vibrational spectrum, which agrees with the one observed in the infrared absorption and/or Raman scattering heretofore.  相似文献   

16.
The donor-donor (D-D) energy migration interaction parameter CDD in high-concentration Nd3+-doped YAG laser crystal is estimated, for the first time, by using the Yokota-Tanimoto (Y-T) model and the spectral overlap model (SOM) of Kushida. Firstly, the experimental luminescence decay curves of 4F3/2 state of Nd3+ ions in YAG laser crystal at room temperature for 2.0 and 3.0 at% Nd3+ concentrations reported by Mao are fitted successfully by using the Y-T model and the parameter CDD is obtained to be 1.50×10−39 cm6/s. Secondly, the parameter CDD is also directly calculated by using the SOM of Kushida: CDD is calculated to be 2.73×10−39 cm6/s. By comparing the energy migration interaction parameter CDD and the donor-acceptor (D-A) energy transfer interaction parameter CDA (1.794×10−40 cm6/s), it is concluded that energy migration rate between Nd3+ ions in YAG laser crystal was about 11 times larger than energy transfer rate, and that energy migration would play a very important role in high-concentration Nd3+ -doped YAG laser crystal.  相似文献   

17.
The Fourier transform infrared (FTIR) spectrum of the ν8 fundamental band of ethylene-d3 (C2HD3) was recorded with a unapodized resolution of 0.0063 cm−1 in the wavenumber region of 840–980 cm−1. By assigning and fitting a total of 738 infrared transitions using a Watson’s A-reduced Hamiltonian in the Ir representation, rovibrational constants for the upper state (ν8 = 1) up to all five quartic centrifugal distortion terms were derived for the first time. The root-mean-square (rms) deviation of the fit was 0.00076 cm−1. The ground state rovibrational constants of C2HD3 were also determined for the first time by a fit of 450 combination-differences from the present infrared measurements, with rms deviation of 0.00075 cm−1. Local frequency perturbations were not detected in the C-type ν8 band of C2HD3 which is centred at 918.73199 ± 0.00007 cm−1.  相似文献   

18.
A femtosecond pulse laser in the visible spectral region shows promise as a potentially new powerful corneal sculpting tool. It combines the clinical and technical advantages of visible wavelengths with the high ablation quality observed with nanosecond-pulse excimer lasers at 193 nm. A femtosecond and a nanosecond dye laser with pulse durations of 300 fs and 7 ns, and centre wavelengths at 615 nm and 600 nm, respectively, both focused to an area of the order of 10–5 cm2, have been applied to human corneal ablation. Nanosecond laser pulses caused substantial tissue disruption within a 30–100 m range from the excision edge at all fluences above the ablation threshold of F th60 J cm–2 (I th9 GW cm–2). Completely different excisions are produced by the femtosecond-pulse laser: high quality ablations of the Bowman membrane and the stroma tissue characterised by damage zones of less than 0.5 m were observed at all fluences above ablation threshold of F th1 J cm–2 or I th3 TW cm–2 (3×1012 W cm–2). The transparent cornea material can be forced to absorb ultrashort pulses of extremely high intensity. The fs laser generates its own absorption by a multiphoton absorption process.  相似文献   

19.
A stable and convenient optical system to realize the forward phase-matching geometry for degenerate four-wave mixing (DFWM) is demonstrated in the mid-infrared spectral region by measuring DFWM signals generated in acetylene (C2H2) and hydrogen chloride (HCl) molecules by probing the fundamental ro-vibrational transitions. IR laser pulses tunable from 2900 cm?1 to 3350 cm?1 with a 0.025 cm?1 linewidth were obtained using a laser system composed of an injection seeded Nd:YAG laser, a dye laser, and a frequency mixing unit. At room temperature and atmospheric pressure, a detection limit of 35 ppm (~ 9.5×1014 molecules/cm3) for C2H2 was achieved in a gas flow of a C2H2/N2 mixture by scanning the P(11) line of the (010(11)0)–(0000000) band. The detection limit of the HCl molecule was measured to be 25 ppm (~6.8×1014 molecules/cm3) in the same environment by probing the R(4) line. The dependences of signal intensities on molecular concentrations and laser pulse energies were demonstrated using C2H2 as the target species. The variations of the signal line shapes with changes in the buffer gas pressures and laser intensities were recorded and analyzed. The experimental setup demonstrated in this work facilitates the practical implementation of in situ, sensitive molecular species sensing with species-specific, spatial and temporal resolution in the spectral region of 2.7–3.3 μm (3000–3700 in cm?1), where various molecular species important in combustion have absorption bands.  相似文献   

20.
A comparative experimental study of the X-ray emission in the water-window spectral region has been performed using carbon nanofibers (CNFs) of different sizes and graphite plate targets, irradiated with ultra-short (Ti:sapphire) laser pulses. More than an order of magnitude enhancement in the X-ray yield is observed from CNFs of 60-nm diameter with respect to graphite targets. The X-ray emission from CNFs of 160-nm diameter was also high. The integrated X-ray yield of these carbon-based targets scales with the laser intensity (I L) as IL ~ 1.3-1.4I_{\mathrm{L}}^{\sim 1.3-1.4} in the intensity range of 4×1016–4×1017 W/cm2. The effect of the laser pulse duration on the X-ray emission from the CNFs was also studied by varying the pulse duration from 45 fs up to 3 ps at a constant fluence of 2×104 J/cm2. The optimum laser pulse duration for maximum X-ray emission increases with the diameter of the CNFs used. The results are explained from physical considerations of heating and hydrodynamic expansion of the CNF plasma in which resonance field enhancement takes place while passing through two times the critical density. The results add to the efforts towards achieving an efficient low-cost water-window X-ray source for microscopy.  相似文献   

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