Laser desorption of NO from a thick C60 film

The desorption of NO molecules from a thick C₆₀ film is reported. A thermal desorption spectrum indicates two adsorption sites with binding energies of E_b = 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 T_rot(v″ = 0) = 370 K, T_rot(v″ = 1) = 390 K and T_vib = 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.     

Optical limiting behavior of C60 doped ethylenepropylenediene polymethylene polymer

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.     

Sputtering of amorphous ice induced by C60 and Au3 clusters

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.     

Dust acoustic wave oscillations in C60 molecule

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.     

Solvent-induced optical properties of C60

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.     

Rb掺杂C60单晶的相衍变和电子态

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.C_{60 关键词： 4}C₆₀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     

Transport properties and mechanism of C60 coupled to carbon nanotube electrode

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.     

Properties of C60 thin film transistor based on polystyrene

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.     

Optical limiting action of C60 doped poly(dimethylacetylendicarboxylate)

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.     

Artifacts in the sputtering of inorganics by C60

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.     

Experimental observation of negative group velocity in C60 PMMA

The authors experimentally observed the superluminal propagation at negative group velocity in C₆₀ polymethyl methacrylate (PMMA) firstly. The largest time advancement of 7.61 ms was obtained at 1 mg/cm³ of sample concentration, the corresponding group velocity was −0.657 m/s. Fast light in C₆₀ PMMA offers several advantages over liquids or vapors for a variety of possible applications: (i) easy for experimental measurement and practical applications (ii) easy for manufacture, (iii) sample concentration is another convenient parameter to vary the signal delay.     

Stretching the limits of static SIMS with C60

Pristine and Au-covered molecular films have been analyzed by ToF-SIMS (TRIFT™), using 15 keV Ga⁺ (FEI) and 15 keV C₆₀⁺ (Ionoptika) primary ion sources. The use of C₆₀⁺ leads to an enormous yield enhancement for gold clusters, especially when the amount of gold is low (2 nmol/cm²), i.e. a situation of relatively small nanoparticles well separated in space. It also allows us to extend significantly the traditional mass range of static SIMS. Under 15 keV C₆₀⁺ ion bombardment, a series of clusters up to a mass of about 20,000 Da (Au₁₀₀⁻: 19,700 Da) is detected. This large yield increase is attributed to the hydrocarbon matrix (low-atomic mass), because the yield increase observed for thick metallic films (Ag, Au) is much lower. The additional yield enhancement factors provided by the Au metallization procedure for organic ions (MetA-SIMS) have been measured under C₆₀⁺ bombardment. They reach a factor of 2 for the molecular ion and almost an order of magnitude for Irganox fragments such as C₄H₉⁺, C₁₅H₂₃O⁺ and C₁₆H₂₃O⁻.     

FePc与TiO2(110)及C60界面电子结构研究

基于C₆₀受体和有机分子给体的太阳能电池是目前非常重要的一个研究热点, 利用同步辐射真空紫外光电子能谱(SRUPS) 技术研究了酞菁铁(FePc)与TiO₂(110)及C₆₀的界面电子结构, 以及FePc与C₆₀分子混合薄膜的电子结构. SRUPS价带谱显示, FePc沉积在化学计量比与还原态两种不同的TiO₂(110)表面时, FePc分子的HOMO能级均随FePc厚度的变化发生了移动, 而在化学计量比的TiO₂(110)表面位移较大, 同时发生界面能带弯曲, 说明存在从有机层向衬底的电子转移. 在FePc/C₆₀和C₆₀/FePc界面形成过程中, FePc与C₆₀分子的最高占据分子轨道(HOMO)位移大小基本相同. 由界面能级排列发现, 在FePc与C₆₀的混合薄膜中, FePc分子的HOMO与C₆₀分子的最高占据分子轨道能级差较大, 这有利于提高器件开路电压, 改善器件性能.     

Low temperature transport study of C60 thin film FETs

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.     

Formation of Sim and SimCn clusters by C60 sputtering of Si

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 Si_m⁺ (1 ≤ m ≤ 15) and various Si_mC_n⁺ clusters (1 ≤ m ≤ 11 for n = 1; 1 ≤ m ≤ 6 for n = 2; 1 ≤ m ≤ 4 for n = 3). The yields of Si_m⁺ 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 (Si_m≥16⁺/Si⁺ < 1 × 10⁻⁴). The probability of formation of Si_m⁺ and Si_mC_n⁺ clusters depends only very weakly on the C₆₀⁺ primary ion energy between 13.5 keV and 37.5 keV. The behaviour of Si_m⁺ and Si_mC_n⁺ 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 Si_m⁺ 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 Si_m⁺ and Si_mC_n⁺ 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.     

Photon-assisted synthesis of C60 polymers by laser irradiation

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.     

Comparative study of optical parameters of fullerene C60 film at different temperatures

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.     

Energy distributions of atomic and molecular ions sputtered by C60 projectiles

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 Ag_n⁺ 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.     

Bombardment induced surface chemistry on Si under keV C60 impact

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.     

Simulations of C60 bombardment of Si, SiC, diamond and graphite

Molecular dynamics simulations of the 20-keV C₆₀ bombardment at normal incidence of Si, SiC, diamond and graphite targets were performed. The unique feature of these targets is that strong covalent bonds can be formed between carbon atoms from the C₆₀ projectile and atoms in the solid material. The mesoscale energy deposition footprint (MEDF) model is used to gain physical insight into how the sputtering yields depend on the substrate characteristics. A large proportion of the carbon atoms from the C₆₀ projectile are implanted into the lattice structure of the target. The sputtering yield from SiC is ∼twice that from either diamond or Si and this can be explained by both the region of the energized cylindrical tract created by the impact and the number density. On graphite, the yield of sputtered atoms is negligible because the open lattice allows the cluster to deposit its energy deep within the solid. The simulations suggest that build up of carbon with a graphite-like structure would reduce any sputtering from a solid with C₆₀⁺ bombardment.