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1.
In the present study, the basic issues in C60n+ sputtering are studied using silicon, gold and platinum samples. Sputtering yields are measured for energies in the range of 5-30 keV, by sputtering micrometre sized craters on the surface of flat clean samples and measuring their volumes using atomic force microscopy (AFM). Net deposition of carbon occurs for all three materials at 5 keV, and is not specific to silicon which forms a carbide. The threshold energy for net sputtering is dependent on the sputtering yield and the stopping power of the substrate. Away from the threshold, the sputtering yields agree well with Sigmund and Claussen's thermal spike model after allowance for the sputtering of the deposited carbon atoms. AFM images show the formation of unusual surface topography around the transition region between sputtering and deposition. Analysis of the bottom of a crater using imaging SIMS shows a significant enhancement of carbon clusters as well as various silicon-carbon groups, indicating the importance of carbon deposition and implantation in a gradual mixed layer formed from sputtering. The thickness of this interface layer is shown to be approximately 5 nm.  相似文献   

2.
In the process of investigating the interaction of fullerene projectiles with adsorbed organic layers, we measured the kinetic energy distributions (KEDs) of fragment and parent ions sputtered from an overlayer of polystyrene (PS) oligomers cast on silver under 15 keV C60+ bombardment. These measurements have been conducted using our TRIFT™ spectrometer, recently equipped with the C60+ source developed by Ionoptika, Ltd. For atomic ions, the intensity corresponding to the high energy tail decreases in the following order: C+(E−0.4) > H+(E−1.5) > Ag+(E−3.5). In particular, the distribution of Ag+ is not broader than those of Ag2+ and Ag3+ clusters, in sharp contrast with 15 keV Ga+ bombardment. On the other hand, molecular ions (fragments and parent-like species) exhibit a significantly wider distribution using C60+ instead of Ga+ as primary ions. For instance, the KED of Ag-cationized PS oligomers resembles that of Ag+ and Agn+ clusters. A specific feature of fullerene projectiles is that they induce the direct desorption of positively charged oligomers, without the need of a cationizing metal atom. The energy spectrum of these PS+ ions is significantly narrower then that of Ag-cationized oligomers. For characteristic fragments of PS, such as C7H7+ and C15H13+ and polycyclic fragments, such as C9H7+ and C14H10+, the high energy decay is steep (E−4 − E−8). In addition, reorganized ions generally show more pronounced high energy tails than characteristic ions, similar to the case of monoatomic ion bombardment. This observation is consistent with the higher excitation energy needed for their formation. Finally, the fraction of hydrocarbon ions formed in the gas phase via unimolecular dissociation of larger species is slightly larger with gallium than with fullerene projectiles.  相似文献   

3.
Molecular dynamics simulations were performed to study the behavior of cluster SIMS. Two predominant cluster ion beam sources, C60 and Au3, were chosen for comparison. An amorphous water ice substrate was bombarded with incident energy of 5 keV. The C60 cluster was observed to shatter upon impact creating a crater of damage approximately 8 nm deep. Although Au3 was also found to both break apart and form a damage crater, it continued along its initial trajectory causing damage roughly 10 nm deep into the sample and becoming completely imbedded. It is suggested that this difference in behavior is due to the large mass of Au relative to the substrate water molecule.  相似文献   

4.
The secondary ion mass spectrum of silicon sputtered by high energy C60+ ions in sputter equilibrium is found to be dominated by Si clusters and we report the relative yields of Sim+ (1 ≤ m ≤ 15) and various SimCn+ clusters (1 ≤ m ≤ 11 for n = 1; 1 ≤ m ≤ 6 for n = 2; 1 ≤ m ≤ 4 for n = 3). The yields of Sim+ clusters up to Si7+ are significant (between 0.1 and 0.6 of the Si+ yield) with even numbered clusters Si4+ and Si6+ having the highest probability of formation. The abundances of cluster ions between Si8+ and Si11+ are still significant (>1% relative to Si+) but drop by a factor of ∼100 between Si11+ and Si13+. The probability of formation of clusters Si13+-Si15+ is approximately constant at ∼5 × 10−4 relative to Si+ and rising a little for Si15+, but clusters beyond Si15 are not detected (Sim≥16+/Si+ < 1 × 10−4). The probability of formation of Sim+ and SimCn+ clusters depends only very weakly on the C60+ primary ion energy between 13.5 keV and 37.5 keV. The behaviour of Sim+ and SimCn+ cluster ions was also investigated for impacts onto a fresh Si surface to study the effects that saturation of the surface with C60+ in reaching sputter equilibrium may have had on the measured abundances. By comparison, there are very minor amounts of pure Sim+ clusters produced during C60+ sputtering of silica (SiO2) and various silicate minerals. The abundances for clusters heavier than Si2+ are very small compared to the case where Si is the target.The data reported here suggest that Sim+ and SimCn+ cluster abundances may be consistent in a qualitative way with theoretical modelling by others which predicts each carbon atom to bind with 3-4 Si atoms in the sample. This experimental data may now be used to improve theoretical modelling.  相似文献   

5.
The effect of incident angle on the quality of SIMS molecular depth profiling using C60+ was investigated. Cholesterol films of ∼300 nm thickness on Si were employed as a model and were eroded using 40 keV C60+ at an incident angle of 40° and 73° with respect to the surface normal. The erosion process was characterized by determining at each angle the relative amount of chemical damage, the total sputtering yield of cholesterol molecules, and the interface width between the film and the Si substrate. The results show that there is less molecule damage at an angle of incidence of 73° and that the total sputtering yield is largest at an angle of incidence of 40°. The measurements suggest reduced damage is not necessarily dependent upon enhanced yields and that depositing the incident energy nearer the surface by using glancing angles is most important. The interface width parameter supports this idea by indicating that at the 73° incident angle, C60+ produces a smaller altered layer depth. Overall, the results show that 73° incidence is the better angle for molecular depth profiling using 40 keV C60+.  相似文献   

6.
Optical limiting measurements on C60 in toluene-ethylenepropylenediene polymethylene (EPDM) polymer blends and in EPDM polymer films at three different concentrations have been carried out. The measurements were undertaken using 532 nm wavelength, 10 ns pulses from a frequency-doubled Nd-YAG Laser. The results show that the optical limiting efficiency is concentration dependent and that the limiting efficiency for C60 in toluene-EPDM polymer blends is better than in EPDM polymer film samples.  相似文献   

7.
The profile of the energy deposition footprint is controlled during the C60+ erosion of Si surfaces by varying the incident energy and/or incident angle geometry. Sputter yield, surface topography, and chemical composition of the eroded surfaces were characterized using atomic force microscopy (AFM) and secondary ion mass spectrometry (SIMS). The experiments show that the 10 keV, 40° incident C60+ erosion of Si results in the formation of a C containing, mound-like structure on the solid surface. We find that the occurrence of this C feature can be avoided by increasing the incident energy of the C60+ projectile or by increasing the incident angle of the C60+ projectile. While both strategies allow for the Si samples to be eroded, the occurrence of topographical roughening limits the usefulness of C60+ in ultra-high resolution semiconductor depth profiling. Moreover, we find that the relative effect of changing the incident angle geometry of the C60+ projectile on the profile of the energy deposition footprint, and thus the sputter yield, changes according to the kinetic energy of the projectile and the material of the bombarded surface, a behavior that is quite different than what is observed for an atomic counterpart.  相似文献   

8.
Molecular dynamics simulations of the sputtering of Si by C60 keV bombardment are performed in order to understand the importance of chemical reactions between C atoms from the projectile and Si atoms in the target crystal. The simulations predict the formation of strong covalent bonds between the C and Si atoms, which result in nearly all of the C atoms remaining embedded in the surface after bombardment. At low incident kinetic energies, little sputtering of Si atoms is observed and there is a net deposition of solid material. As the incident kinetic energy is increased, the sputtering yield of Si atoms increases. At 15 keV, the yield of sputtered Si atoms is more than twice the number of C atoms deposited, and there is a net erosion of the solid material.  相似文献   

9.
Different C60 aggregates, i.e. nanoparticles, clusters of nanoparticles and microcrystals in room-temperature solutions, are reported to account for the colors of fluorescence emissions centered at 440, 575 and 700 nm, respectively. And the configurations of C60 aggregation created in solutions are revealed to be closely associated with the characteristic interactions between C60 and solvent molecules. On this basis, aggregation behaviors and thus induced optical properties of C60 have been tentatively controlled through adopting solvent mixtures.  相似文献   

10.
A quartz crystal microbalance (QCM) has been used to determine total-mass sputtering yields of PMMA films by 1-16 keV C60+,2+ ion beams. Quantitative sputtering yields for PMMA are presented as mass loss per incident ion Ym. Mass-lost rate QCM data show that a 13 keV C60 cluster leads to emission equivalent to 800 PMMA molecules per ion. The power law obtained for the increase in sputtering yield with primary ion energy is in good agreement those predicted by “thermal spike” regime and MD models, when crater sizes are used to estimate sputtering.  相似文献   

11.
In this letter, dispersion properties of low-frequency electrostatic waves in a C60 molecule are investigated. It is assumed that C60 molecule is charged due to the field emission, and hence the C60 molecule can be regarded as charged dust spheres surrounded by degenerate electrons and ions. We obtain the dispersion relation for the low-frequency electrostatic oscillations in the C60 molecule by using the quantum hydrodynamic model in conjunction with the Poisson equation.  相似文献   

12.
周建林  牛巧利 《中国物理 B》2010,19(7):77305-077305
This paper reports that the n-type organic thin-film transistors have been fabricated by using C60 as the active layer and polystyrene as the dielectric.The properties of insulator and the growth characteristic of C60 film were carefully investigated.By choosing different source/drain electrodes,a device with good performance can be obtained.The highest electron field effect mobility about 1.15 cm 2 /(V·s) could reach when Barium was introduced as electrodes.Moreover,the C60 transistor shows a negligible 'hysteresis effect' contributed to the hydroxyl-free of insulator.The result suggests that polymer dielectrics are promising in applications among n-type organic transistors.  相似文献   

13.
The optical limiting action of poly(dimethylacetylendicarboxylate) polymer doped with fullerene C60 has been investigated under irradiation with 10 ns laser pulses at 532 nm. The optical limiting measurements were performed at four different dopant concentrations. The threshold limiting fluence at 0.3 J/cm2 was observed at high doping concentrations, with transmission of about 55%. An explanation based on the combination of two-photon absorption and reverse saturable absorption was proposed for its nonlinear optical absorption behavior.  相似文献   

14.
By applying non-equilibrium Green's functions in combination with density-functional theory, we investigate electronic transport properties of C60 coupled to carbon nanotubes and Li electrodes. The results show that electronic transport properties of CNT-C60-CNT and Li-C60-Li systems are completely different. Nonlinear I-V characteristic, varistor-type behavior and negative differential resistance (NDR) phenomenon are observed when electrodes are carbon nanotubes. We discuss the mechanism of I-V characteristics of CNT-C60-CNT systems in details. Our results suggest conductance, energy level of Frontier molecular orbitals, energy gap between HOMO and LUMO, the coupling between molecular orbitals and electrodes are all playing critical roles in electronic transport properties.  相似文献   

15.
李宏年 《物理学报》2004,53(1):248-253
在C60单晶超高真空解理面上制备C60的Rb填隙化合物薄膜.用同步辐射光电子能谱研究了相衍变过程.观察到对应于固溶相、Rb1C60和Rb3C60的电子态密度分布.当数纳米厚Rb3C60薄膜在C60单晶(111)解理面形成后,室温条件下进一步沉积Rb至样品表面不产生fcc到bct或bcc结构相变.C60 关键词: 4C60和Rb5C60吸附相')" href="#">金属性Rb4C60和Rb5C60吸附相 60单晶')" href="#">C60单晶 相衍变 同步辐射光电子能谱  相似文献   

16.
Effects of platinum silicon, graphite and PET substrates on the secondary ion yield of sub-monolayer and multilayer samples of Cyclosporin A following 20 keV Au+, Au3+and C60+ impacts have been investigated. The obtained results of sub-monolayer samples show that platinum enhances the yield of the pseudo-molecular ion following Au+ and Au3+ impacts due to the high density of the substrate that enables the energy of the primary ions to be deposited near the surface. C60+ impacts on sub-monolayer samples are less effective, but there is an enhancement on PET substrates. Impacts of 20 keV Au+ and Au3+ are not very efficient on multilayer samples. 20 keV C60+ impacts enhance the yields significantly, especially for the relatively high molecular weight [M+H]+ ion.  相似文献   

17.
The desorption of NO molecules from a thick C60 film is reported. A thermal desorption spectrum indicates two adsorption sites with binding energies of Eb = 0.30 eV and 0.55 eV. For laser desorption the fullerene surface is exposed to NO and excited by 7 ns UV laser pulses. Desorbing NO molecules are recorded state selectively as well as time resolved. The time-of-flight measurement indicates three different desorption pathways. A fast channel shows rovibronic temperatures of Trot(v″ = 0) = 370 K, Trot(v″ = 1) = 390 K and Tvib = 610 K as well as strong rotational-translational coupling. The desorption yield for the fast channel increases linearly with pulse energy with a desorption cross section of σ = (5.1 ± 0.9) × 10−17 cm2. Dominating the signal for small J″ values is a slow channel with low rotational and translational temperatures of about 110 K. We assign this peak to a laser-induced thermal desorption. For large pump-probe delays the data deviate from the Maxwellian flux distribution and a third channel appears with extremely late arrival times.  相似文献   

18.
Low temperature transport in C60 thin film field-effect transistors has been studied using several samples with various gate voltages. Nearest neighbor hopping and variable range hopping transport have been observed in the low temperature transport measurements. Analyzing the temperature dependence of the transport types, it was found that the electrical properties of the film can be improved by thermally agitated evaporation of C60.  相似文献   

19.
The harmonics of a free electron laser (FEL) were irradiated in vacuum to surfaces of compressed C60 and a mixture of C60 and I2. The power and frequency of the fundamental FEL macro-pulse were ca. 0.5 mJ/pulse and 2 Hz, respectively. The irradiation time was 120-180 min. After irradiation of FEL with a typical wavelength of 450 or 345 nm, the Raman peak of Ag(2)-derived vibration mode of C60 shifted to the lower-energy side. The Raman peak shift of the mixture powder sample was greater than that of pure C60. Furthermore, changes of the crystalline structure indicated that various intermolecular combinations occurred by irradiation. These results strongly suggest that three-dimensional polymerization of C60 was promoted by laser irradiation and the effect of photon-assisted hole-doping from iodine atoms to C60 molecules.  相似文献   

20.
Fullerene C60 thin films on glass substrate (around 2000 ? thickness) were prepared by thermal evaporation technique. The structural, surface morphology and optical properties of the films were studied. The optical properties of fullerene C60 were investigated in the spectral range 200 nm to 900 nm using a UV-Vis spectrophotometer at room temperature as well as at liquid nitrogen temperature (77 K). The optical band gap at room temperature is found to be 2.30 eV, which gradually decreases with lowering the temperature and reaches to 2.27 at 77 K. The thickness and refractive index of fullerene C60 film were calculated by ellipsometry. From the X-ray analysis, we have calculated the grain size, dislocation density, number of crystallite per unit area, and strain of the film at room temperature. The surface morphology of film was analyzed by scanning electron microscope (SEM). The present result show that the fullerene C60 film becomes more conducting at low temperature.  相似文献   

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