Fullerene Thin Films Research Articles

Second-harmonic generation spectroscopy and hyper-Rayleigh scattering in Langmuir-Blodgett films of fullerenes

Optical second-harmonic generation (SHG) spectroscopy and hyper-Rayleigh scattering (HRS) were studied in thin Langmuir-Blodgett films of fullerenes. For films above five monolayers a coherent SHG signal was observed, whereas a one-monolayer film only produced HRS. The HRS indicatrices were measured, and a correlation length of the non-linear polarization of about 100 nm was obtained. The increase in SHG intensity for C 60-CN films in comparison with that of C 60 films is well pronounced, particularly at the blue end of the SHG spectra, and is attributed to a resonant surface electric-dipole contribution.

Electronic Tuning of Dynamical Charge Transfer at an Interface: K Doping ofC60/Ag(111)

High-resolution vibrational spectroscopy of fullerene thin films is achieved by sum-frequency generation and infrared absorption. The ${A}_{g}(2)$ mode of ${\mathrm{C}}_{60}$ gains strong infrared activity when the molecule is adsorbed on Ag(111). K doping allows us to demonstrate the process of adsorbate/substrate dynamical charge transfer, by showing, for the first time, the quenching of the mode softening and infrared activity upon tuning of the admolecule electronic properties. These observations enable the quantitative evaluation of the coupling strength of the ${A}_{g}(2)$ vibration to the ${t}_{1u}$ orbital of ${\mathrm{C}}_{60}$.

Adsorption of C 60 on Si(111)√3 × √3R(30°)-Ag

With the aim of using fullerene thin films as potential encapsulating material in surface reconstructions, we have studied the monolayer room temperature adsorption of C 60 on Si(111)∈3 × √3 R(30°)-Ag surfaces using Auger electron spectroscopy as well as high resolution synchrotron radiation core-level spectroscopy. The thermal stability of the encapsulating layers has also been studied: upon heating, a replacement reaction takes place between silver and C 60. Silver desorbs completely around 550°C and a strongly bound C 60 monolayer remains on top of the silicon surface.

In Situ Characterization of Morphology of Organic Thin Films by Total Reflection X-Ray Analysis

In situ characterization of the morphology of organic thin films was newly attempted by using total reflection X-ray analysis (TRXA). Due to cover a substrate with organic molecules during deposition, the intensity of total reflection fluorescence X-rays from a substrate surface decreases. It is expected that the decrement depends on the morphology of thin films. Fullerene (C60) thin films on the silver (Ag) substrates were formed at the substrate temperatures of 17, 50 and 100°C. From a result of in situ observation for the fluorescence X-rays of Ag substrates by TRXA, the intensity steeply decreased at 17°C and was saturated at 50 and 100°C. It was confirmed that the decay curve indicates the ratio of the coverage of C60 and the growth mode of island or layer-by-layer.

In situ Characterization of Functional Organic Thin Films by Energy Dispersive Grazing Incidence X-ray Diffraction

ABSTRACTWe are investigating well-ordered highly crystalline thin films made using organic molecular beam deposition (OMBD) since it is important to control the formation mechanism at the initial growth process. Then, we developed a new in situ technique of energy dispersive grazing incidence X-ray diffraction utilized within an ultrahigh vacuum system. This technique (in situ ED-GID) makes it possible to examine the crystal structure, orientation and morphology of organic thin films during deposition without any damage to the film. In the present review, we examined the growth process of thin films of functional organic dyes, fullerene (C60) and p-sexiphenyl (6P) by using this in situ ED-GID. The crystal strucutre and molecular orientation in epitaxially-grown thin films were confirmed during the initial stages of growth. Also, the morphology of C60 thin films was examined during the deposition. As a result, it was confirmed that the decay curves of X-ray fluorescence indicate different island growth in C60 thin films.

Fullerene doped glasses as solid state optical limiters

We discuss the optical limiting behavior of sol-gel glasses doped with fullerene derivatives. Comparisons to fullerene solutions and thin films are made.

Friction Properties and Film Strength of C<sub>60</sub> Fullerene Thin Films Deposited by Ion Plating Method

C60-based thin films were prepared on Si(111) and quartz substrates as well as on a stainless steel rod (frictional specimen) by vacuum evaporation and rf ion plating methods. Their structures and friction properties were elucidated by Rraman and UV-VIS absorption spectra and by a pendulum type friction machine, respectively. The ion-plated films were composed of C60 and its decomposition product (amorphous carbon: a-C) and the C60/a-C ratio could be controlled by the rf power applied to generate the plasma. An ion-plated film containing C60 was especially useful for preserving a low friction for a long time.

In situ observation of the in-plane structure of C60 thin films on metal substrates prepared by molecular beam deposition

Recently, it has been reported that fullerene (C60) thin films deposited on Ag ( 111 ) surfaces by molecular beam deposition (MBD) have a high degree of crystallinity and are oriented to the substrate surface. However, because there exists only a few characterization methods to directly examine the in-plane structure of the ultrathin film, such as STM, the details were not understood sufficiently. We employed a new system of an energy-dispersive type total-reflection X-ray diffraction (TRXD) method combined with organic molecular beam deposition (OMBD). The TRXD method is developed for the high-sensitivity measurement of the in-plane structure in organic thin films. By using this in situ and real-time observation, the growth process of C60 ultrathin films on Ag (111) surface was observed at the range of a few nanometers. As a result, we confirmed the in-plane structure and the epitaxy on the substrate surface.

An EELS study of the effect of 2 keV Ar + ion irradiation on thin C 60 films

The ion beam (2 keV Ar) induced amorphization of thin fullerene films has been studied by in situ electron energy loss spectroscopy. The diminution of the intensity of characteristic peaks in the EELS spectrum was used to deduce a cross section for the destruction of the C 60 molecules of (0.82 ± 0.2) × 10 −14 cm 2. The cross section is somewhat smaller than that expected using scaling arguments from the results of more energetic ion bombardment (100–300 keV). The differences are interpreted in terms the secondary processes which occur within the collision cascade surrounding the ion as it slows down in the solid.

Coalescence reactions in laser-induced fullerene desorption: the role of fragments

Coalescence reactions of C60 molecules during the laser desorption from fullerene thin films have been investigated using nanosecond and picosecond laser pulses in order to directly identify the primary reaction steps. Reflectron time-of-flight (RETOF) mass spectroscopy was used to obtain the mass and velocity distributions of the desorbed ions. The coalescence products are seen to be formed predominantly in collisions between fragment ions and C60.

Fullerenes and carbon nanotubes

The discovery of fullerenes, carbon nanotubes and other carbon forms has added a new dimension to materials science. Recent research has led to advances in our knowledge of phase transitions of fullerenes, their magnetic, optical and superconducting properties, and fullerene thin films, and has broadened the repertoire of types of manipulations of nanotubes.

Ion-beam-induced modification of fullerene films as studied by electron-energy-loss spectroscopy.

The ion-beam (2 keV Ar) -induced amorphization of thin fullerene films has been studied by in situ electron-energy-loss spectroscopy (EELS). With due care to the electron-beam current, the EELS spectrum may be measured without degradation during the electron bombardment to provide an EELS fingerprint of ${\mathrm{C}}_{60}$ films. The diminution of the intensity of characteristic peaks in the EELS spectrum upon ion impact was used to deduce a cross section for the destruction of the ${\mathrm{C}}_{60}$ molecules of (0.85\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{2}$. This value corresponds closely to the geometric size of one ${\mathrm{C}}_{60}$ molecule, suggesting that each incident Ar ion destroys one ${\mathrm{C}}_{60}$ molecule upon ion impact. This cross section is somewhat smaller than that expected using scaling arguments from the results of more energetic ion bombardment (100-300 keV). The difference may be due to surface processes, which become important for low-energy ion-beam irradiation.

Ion beam radiation damage of thin fullerene films

Previous work on the radiation damage of fullerene by energetic ions does not unambiguously reveal whether fullerene destruction is dominantly due to the transfer of nuclear, or electronic energy. New data is presented, using new systems of analysis, which show that in general it is collisionally induced destruction, due to nuclear transfers, which dominates. This even remains the case when the absolute amount of energy transferred by means of electronic excitation of he fullerene exceeds that from nuclear transfers by more than a hundredfold. Only in the specific case of high energy, heavy ion bombardments can major bulk destruction of fullerence be assigned to energy transfers which are specifically electronic in origin in addition, however, there are quite minor destructive influences due to electronic energy transfer during irradiations of thin film fullerene targets with low energy proton beams.

炭素系薄膜の最近の話題 フラーレンＣ６０薄膜の合成と応用

炭素系薄膜の最近の話題 フラーレンＣ６０薄膜の合成と応用

Ion-beam modification of fullerene.

The response of thin films of fullerene (C60) to energetic ion impact is investigated. The diagnostics employed include Fourier-transform infrared and Raman spectroscopies, cross-sectional transmission electron microscopy, and atomic force microscopy. By combining the information obtained from these diagnostics with that from the dependence of the conductivity on ion dose, it is concluded that each C60 molecule completely disintegrates when hit by an energetic ion. The cross section for the destruction is about 6×10-13 cm2 for irradiation with 620-keV Xe ions. The disintegration occurs when C atoms are knocked out of the molecule either directly by the impinging ion or by an energetic knock-on C atom within the damage cascade. This process is quite different from the Coulomb-explosion mechanism previously proposed in the literature. For very low ion doses (<1×1011 Xe/cm2) most of the C60 molecules remain intact; however this dose is sufficient to completely disrupt the ordering of the C60 molecules in the van der Waals bonded C60 solid. Disruption of the lattice ordering at such low doses is considered to be attributable to the weakness of the van der Waals forces which bind the C60 clusters together into the molecular solid.

Recent Advances in Nanostructural Investigations and Modifications of Solid Surfaces by Scanning Probe Methods

We have studied the nanometer-scale structure of bare substrates as well as of thin films by a variety of scanning probe methods and have correlated their nanostructural and nanophysical properties. Nanomechanical properties, e.g. of thin fullerene films, have been probed by scanning and lateral force microscopy. In particular, we have addressed the question of whether the spherically shaped C60 molecules can act as molecular-scale ball bearings, thereby exhibiting exceptional lubricating behavior. Nanomagnetic properties, e.g. of magnetite, have been studied by magnetic force microscopy (MFM) and spin-polarized scanning tunneling microscopy (SPSTM) from the micrometer scale down to the atomic level. The complementary nature of the information from MFM and SPSTM data is discussed. Nanoelectronic properties, e.g. of nitride-oxide-silicon (NOS) heterostructures, have been probed by scanning capacitance microscopy (SCM). Charge storage on a submicrometer scale in NOS heterostructures has been achieved by applying voltage pulses to the SCM tip. Finally, mechanical nanofabrication based on scanning force methods has been combined with conventional photolithography to obtain superconducting micro- and nanobridges with potential applications for superconducting nanoelectronic devices.

Examination of Vapor Sorption by Fullerene, Fullerene-Coated Surface Acoustic Wave Sensors, Graphite, and Low-Polarity Polymers Using Linear Solvation Energy Relationships

The sorption of vapors by fullerene is compared with the sorption of vapors by an assembled fullerene thin film on a surface acoustic wave vapor sensor. A linear solvation energy relationship derived for solid fullerene at 298 K was used to calculate gas/solid partition coefficients for the same vapors as those examined using the vapor sensor. This relationship correctly predicted the relative vapor sensitivities observed with the vapor sensor. A new linear solvation energy relationship for vapor adsorption by graphite at 298 K has been determined, and solid fullerene and solid graphite are found to be quite similar in their vapor sorption properties. Comparisons have also been made with linear organic and inorganic polymers, including poly(isobutylene), poly(epichorophydrin), OV25, and OV202. In all cases, sorption is driven primarily by dispersion interactions. The assembled fullerene material is generally similar in vapor selectivity to the other nonpolar sorbent materials considered but yields less sensitive vapor sensors than linear organic polymers. 39 refs., 2 figs., 2 tabs.

Spectral and photocarrier dynamics in thin films of pristine and alkali-doped C 60

This article summarizes our contribution to three distinct areas of research on thin films of fullerenes. In the first part we present results of an in-situ optical absorption study on K-doped thin films of C 60 from which an unambiguous assignment of certain low energy electronic transitions in C 60 and K x C 60 was deduced. The second part of the article concerns transient and steady-state photoconductivity (PC) of pristine and oxygen-exposed thin films of C 60 examined as a function of temperature and photon energy. We find that the presence of oxygen is responsible for the creation of deep traps which reduce the steady-state and transient PC by several orders of magnitude, particularly in the 1.6–2.3 eV excitation region. The thermally activated transport in an oxygen-free C 60 sample is quenched upon exposure to oxygen so that both steady-state and transient PC become nearly temperature independent. In the last part we present two examples of utilizing C 60 thin films for application in opto-electronics. The mechanism of light-induced charge transfer at the conducting polymer-C 60 interface is described and the current versus voltage rectifying characteristics (> 10 4) of the MEH-PPV C 60 thin film heterojunction is presented. In addition, a non-linear transient photovoltaic response in a AlC 60 Au sandwich-type device featuring control of polarity with optical bias is described.

Crystal growth and structure of fullerene thin films

The growth and structure of C 60 and C 70 thin film crystals on alkali halide and layered material substrates are described. It is demonstrated that fairly large grains can be grown with the specific orientation to the substrate lattice, especially on layered substrates. The defects in the films fabricated on alkali halides are studied by transmission electron microscopy in detail. The growth mechanism of C 60 and C 70 thin films on these substrates is discussed on a basis of reflection high-energy electron diffraction and atomic force microscopy observation and compared with that on other substrates. The unusual growth characteristics of C 60 and C 70 are discussed and compared with those encountered in thin films of conventional van der Waals crystals.

Reversible Electrochromic Effect in Fullerene Thin Films Utilizing Alkali and Transition Metals

AbstractA simple apparatus is described to rapidly assess the Electrochromic effect of Alkali and Transition Metal species of intercalated Fullerene thin films. Optical transmission loss during the Coloring phase is monitored at 880, 635, 583 and 565 nm while electrochemical intercalation proceeds. The process is repeated during the reverse polarity Bleaching phase. Results are presented for electrolyte systems based on Butyrolactone or water for Ag, Cr, Cu, Mg and Ba species.