Organic thin film devices are of interest for a variety of forthcoming ubiquitous electronics applications. In order to build ubiquitous high-performance devices, it is necessary to fabricate crystalline thin films of various organic materials onto “ubiquitous substrates” that are dictated by applications. However, many organic thin films crystallize only on a limited selection of substrates. Unfortunately, promising organic molecules, which have a large overlap of pi-orbitals between molecules, cannot migrate freely on a substrate because of stronger cohesion between molecules than interaction between the molecule and the substrate. Therefore, enhancement of the molecule-substrate interaction, i.e. ‘molecular wettability’ should promote crystallization. We found that an ultrasmooth monolayer of pentacene (C22H14), which can be grown on many general dielectric substrates, changes the molecular wettability of a substrate for other poorly wettable organic materials. We also demonstrate that a field effect transistor (FET) using a crystalline C60 thin film on a pentacene-buffered substrate can have a mobility of 4.9 cm2/Vs, which is 5-fold higher than that of C60 FETs without the buffer. Molecular wetting-controlled substrates can thus offer a general solution to the fabrication of high-performance crystalline plastic and molecular electronics.

We have fabricated C60 thin films on various substrates (mica, MoS2, HOPG, LiF, NaCl, KBr, KCl and CaF2) by using continuous-wave laser molecular beam epitaxy (CWL-MBE), which is very suitable technique to grow epitaxial organic thin films because of good controllability of evaporation as compared with Knudsen-cell method. The films were evaluated by reflection high-energy electron diffraction with micro channel imaging plate (MCP-RHEED) and atomic force microscopy (AFM). AFM images of the C60 films on mica, MoS2 and HOPG substrates show flat and homogeneous, morphology, and epitaxial growth of the films on mica and MoS2 substrates were observed by RHEED. This result shows mica, MoS2, HOPG substrates are good candidates for epitaxial growth of C60 thin films.

Nanocrystalline diamonds with several hundred nm in diameter have been prepared in a 13.56 MHz low pressure inductively coupled CH4/H2 or CH4/CO/H2 plasma. The bonding structures were investigated by Raman spectroscopy and electron energy loss spectroscopy (EELS). Visible (514 nm) and UV (325, 244 nm) excited Raman spectra with CO additive exhibit peaks at ∼1150 cm-1 assigned to sp3 bonding and at 1332 cm-1 due to zone center optical phonon mode of diamond, respectively. It indicates that the UV excitations are possibly sufficient to excite the σ state of both sp2- and sp3-bonded carbon. The high resolution EELS (HREELS) spectra with CO additive show peaks at ∼1100 cm-1 assigned to C-C stretching vibration of sp3 bonding and at ∼700 cm corresponding to the bending vibration of sp3 bonding. It is qualitatively agreement with the Raman spectra. Furthermore the EELS spectrum without CO additive exhibits two peaks at 284 eV and at 292 eV corresponding to π* states and σ* states, respectively, and is similar to that of graphite rather than that of sp2-rich amorphous carbon. The EELS spectrum with CO additive, on the other hand, shows a peak at 292 eV due to σ * states and is similar to that of diamond. A slight peak appears at ∼285 eV corresponding to π* states. It consequently implies that the particles almost consist of sp3 bondings and that the small amount of sp2 bondings are considered to exist in grain boundaries. The EESL spectra are consistent with the results of Raman scattering and HREELS.

A 13.56 MHz low pressure inductively coupled plasma (ICP) has been applied to prepare diamond films. The Faraday shield drastically suppressed the electrostatic coupling, which frequently causes contamination due to the etching of the quartz tube. The characterizations of the obtained deposits by scanning electron microscopy (SEM), transmission electron diffraction (TED), and reflection high energy electron diffraction (RHEED) revealed that the deposits are composed of microcrystalline diamond and disordered microcrystalline graphite. The CO additive to a CH4/H2 plasma brought about the morphological change from a scale-like deposit to a particle one. Besides, the number of encountered particles was increased with an increase of CO additive. The TED and RHEED observations showed that non-diamond carbon was effectively removed with an increase of CO additive. These results indicate that oxygen-contained radicals produced by the addition of CO play an effective role in the removal of non-diamond carbon in the diamond growth conditions and that the CO additive makes the supersaturation degree of carbon large.

Microcrystalline diamond films have been prepared in a 13.56 MHz low pressure inductively coupled plasma, in which the pressure of CH4/H2and CH4/CO/H2 plasmas was varied from 45 to 50 mTorr. The bonded structures of the obtained deposits were studied by Raman spectroscopy with 514, 325, and 244 nm excitation wavelength. 514 nm excited Raman spectra exhibit two peaks at ∼1355 cm−1 and ∼1580 cm−1 corresponding to sp2 bonding without CO additive (CH4/H2, plasma). New peaks at ∼1150 cm−1 assigned to sp3-bonded carbon network and at ∼1480 cm−1 appear with CO additive (CH4/CO/H2, plasma). 325 nm excited Raman spectra show a shoulder at ∼1150 cm−1, a clear 1332 cm−1 diamond peak, and the peak at ∼1580 cm−1 is remarkably enhanced. In 244 nm excited Raman scattering, the 1332 cm−1 diamond peak is only enhanced whereas the peak at ∼1580 cm−1 is correspondingly diminished. These features of the Raman spectra imply that the vibrational modes of sp2 sites are resonantly enhanced with 514 nm excitation because the 514 nm (2.4 eV) corresponds to the π-π* transition in sp2-bonded carbon, while the 325 nm (3.8 eV) and 244 nm (5.1 eV) excitations are possibly sufficient to excite the σ state of both sp2- and sp3-bonded carbon

A 13.56 MHz inductively coupled plasma(ICP) system has been applied to fabricate diamond and diamond-like carbon from a CH4/H2/Ar plasma. The characterizations of the obtained deposits by transmission electron diffraction, reflection high energy electron diffraction, and Raman scattering revealed that the deposits are diamond crystallites, with crystal sizes ∼1μm, and that they partially include disordered microcrystalline graphite. Although contamination due to etching of the quartz tube exists, this was drastically suppressed by the electrostatic shield(Faraday shield).