Growth Of C60 Research Articles

Solid C 60 layer growth on AlN (0001) surface for C 60 FET structure by MBE

One of the most important problems is how to form an excellent interface between the insulator and the C60 layers in the C60 field-effect doping technique. In this paper, we propose a new structure of the C60 field-effect transistor which consists of an epitaxial AlN layer as the insulator and a C60 epitaxial layer grown on an AlN (0001) surface. We have mainly investigated solid C60 growth on the AlN (0001) surface by the MBE technique in the present work. C60 grains with face centred cubic structure have been obtained on a smooth AlN surface. Four types of the C60 grains were obtained, that is, the 0° orientation and its twin grains and the 30° orientation and its twin grains. We have found that the 0° orientation grains only can be obtained by controlling the growth temperature. The results strongly indicate that an excellent interface between the AlN insulator and the C60 layer can be formed for device applications. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ordering and stabilization of C60 films on the ([formula omitted])R30° Sn/Pt(111) surface alloy

The deposition and growth of C60 on the (3×3)R30° Sn/Pt(111) surface alloy is compared with that on the Pt(111) surface at submonolayer, monolayer and multilayer coverages. We find that alloying Pt(111) with Sn arrests the charge transfer from Pt to adsorbed C60, as seen from the absence of a shift in the T1u(1) vibrational levels of C60 probed by high resolution electron energy loss spectroscopy (HREELS). From low energy electron diffraction (LEED) observations it is determined that whereas ordering and graphitization of C60 on Pt(111) take place at 900K, graphitization of C60 is inhibited by Sn alloyed into Pt(111). The rotated hexagonal LEED pattern of the ordered C60 monolayer is stabilized by the presence of Sn on Pt(111) until 1100K, which is close to the fragmentation temperature of solid C60. Upon heating C60 films on the (3×3)R30° Sn/Pt(111) surface alloy, Sn is dealloyed at about 500K, and this dealloyed Sn reacts with C60 at 450–700K, possibly resulting in polymerization. Auger electron spectroscopy annealing studies and the rise in intensity of the unpolarized Raman-active Ag(2) mode at 1467cm−1 support this conclusion. High temperature fragmentation of C60 in the presence of Sn leads to HREELS peaks at 250 and 740cm−1, prior to the formation of graphite.

Extraordinary growth of C60 on a GaAs(001) As-rich 2×4 surface

We have systematically investigated, by using scanning tunneling microscopy, the adsorption and film growth of C60 on the various GaAs(001) surface phases prepared by molecular-beam epitaxy. For most phases, the C60 overlayer exhibits the usual close-packed fcc(111) configuration with its lattice constant close to that of the bulk C60 crystal. However, in the case of C60 on the As-rich 2×4 substrate, the epitaxial growth is found to be quite different and unique; C60 film takes its (110) crystalline axis; the C60 overlayer is highly strained with a lattice expansion of ∼13%, and this structure is very stable at least up to 10 ML. We will address the underlying formation mechanism of this new structure in terms of a charge transfer from the As-dangling bonds to C60s and a site-specific C60-substrate interaction, as confirmed by molecular dynamic simulations. The present system provides a unique opportunity to study fullerene and/or noble-gas related two-dimensional phenomena, and demonstrates a potential for fabrication of novel fullerene-based devices, such as strained superlattice structures.

Energetic Analysis of Pentagon Road Intermediates of C60-Buckminsterfullerene Formation

We report an energetic analysis of the principal intermediates of the pentagon road (PR) scheme for formation of C60-buckminsterfullerene. All calculations were initially performed using the tight-binding semiempirical method. For selected cases, more rigorous 3-21G/HF and 3-21G/B3LYP calculations were carried out. The first part of this study includes an energetic comparison between the 30-, 40-, and 50-atom PR intermediates and a representative group of 30-, 40-, and 50-atom carbon clusters. While C30 PR is higher in energy than a large variety of graphene sheets and fullerenes, C40 PR and C50 PR are considerably lower in energy than many other isomers; only fullerenes are more stable. Additionally, we examine a plausible mechanism by which C50 PR rearranges to form a C50 cage with D5h symmetry. Because of its large energy barrier, this process is unlikely to affect the C60 growth mechanism.

Surface growth modes analysed with modern microscopic and computing techniques

It is demonstrated how new microscopes with atomic resolution in combination with modern fast computers and computational techniques can be used in a complementary way in the analysis and explanation of crystal growth on surfaces. Examples are given of spiral formation, fractal growth, fullerene formation and the growth of C60 films.Zusammenfassung. Es wird gezeigt, wie neue Mikroskopiertechniken mit atomarer Auflösung in Kombination mit modernen schnellen Computern und neuen Computertechniken genutzt werden können, um auf Oberflächen Kristallwachstum zu analysieren und erklären. Beispiele für Spiralformationen, Fraktalwachstum, Fullerenebildung und Wachstum von C60 Filmen werden diskutiert.

Epitaxial growth of C60 crystals vapor-deposited on a KI (001) surface

Epitaxial growth of C60 was found in vapor-deposited crystals on the KI (001) cleavage surface. C60 molecules deposited on the KI surface, which was preheated at 400 °C, then kept at 195 °C during deposition, crystallized in the face-centered cubic form with two types of morphologies. Truncated pyramidal crystals epitaxially grew along the KI 〈110〉 directions, taking its C60 (001) face parallel to the KI (001) surface. This epitaxial nucleation occurred at a corner of the crossing steps along the KI 〈100〉 directions which were caused by thermal etching of the KI surface. Molecular mechanics and dynamics calculations revealed that a three-dimensional (2×2) commensurate lattice matching between the C60 {100} planes and the KI {100} faces at the step corner attributed to the epitaxial nucleation of the pyramidal crystal, in spite of the lower stability of the monolayer interaction of the C60 (001) face with the KI (001) surface. On the other hand, platelike crystals grew, with the C60 (111) face parallel to the KI (001) surface. A stable monolayer nucleation of the close-packed C60 (111) face made this two-dimensional growth of the platelike crystals possible to occur on the (001) terrace of the etched KI surface.

Effect of Molecular Rotation on Vapor Phase Nucleation: Fullerenes C60and C70

Abstract The effect of rotational free energy of fullerenes C60 and C70 on homogeneous nucleation of crystals from vapor phase have been studied. Classical nucleation parameters have been estimated for the case of nucleation and crystal growth of C60 and C70 by Physical Vapor Transport (PVT) method under different supercooling in the range of 20–150 K, keeping the source temperatures constant. The result shows that the growth of large size single crystals is more feasible in the lower supercooling range. The effect of change in interfacial tension on the critical free energy of formation of the nuclei is also studied.

Adsorption and film growth of C60 on the GaAs(001) 2 x 6 surface by molecular-beam epitaxy.

Adsorption and film growth of C60 on the GaAs(001) 2 x 6 surface by molecular-beam epitaxy.

X-ray pole-figure study of the epitaxial growth of C60 thin films on mica (001)

The growth of epitaxial C60 thin films on mica(001) by thermal evaporation has been studied in detail by X-ray pole-figure measurements. The influence of the deposition rate, the substrate temperature and the film thickness on the in-plane epitaxial arrangements and the formation of twins has been investigated. It has been demonstrated that the C60 growth is determined by two independent and equivalent C60-crystal grain alignments (type-A and type-B). The nearly six-fold symmetry of the mica(001)-substrate surface offers the three-fold fcc-(111)-oriented C60-crystal grains two equivalent crystal alignments. A high deposition rate of 0.5 A/s is responsible for the formation of twins at a substrate temperature of 150°C, which diminishes by a higher substrate temperature of 200°C. By a decrease of the deposition rate down to 0.08 A/s the twins vanish at a film thickness of 200 nm and at the substrate temperature of 150°C. Under the same sublimation conditions, in addition to the type-A and type-B crystal orientations, the growth of the thin C60 films starts with a slight fibre texture which does not appear at a larger film thickness.

X-ray pole-figure study of the epitaxial growth of C60 thin films on mica (001)

X-ray pole-figure study of the epitaxial growth of C60 thin films on mica (001)

Structure and growth phenomena of C60 and C70 single crystals

C60 and C70 single crystals free from solvent contamination grew from their vapour. Large C60 crystals up to a size of about 5 mm×3 mm×3 mm and C70 crystals about 1 mm×1 mm×1 mm were obtained. C60 crystals with fcc structure showed two types of morphological faces, namely {111} and {100}, frequently with twinning on {111} face. C70 crystals obtained have a hcp structure witha=10.1 A andc=16.7 A. DSC and X-ray diffraction analysis indicated that C70 crystal underwent phase transition below 100 C. Morphological observation suggests that the growth of C60 and C70 single crystals is based on layer-spreading mechanism.

Epitaxial growth of C60 and KI(001) surface

Epitaxial growth of C60 is observed for vacuum-deposited crystals on the KI(001) cleavage surface. When the KI surface is kept at 240 °C and the deposition rate is controlled to be less than a monolayer min−1 (∼0.5 nm min−1), rectangular platelike crystals of C60 grow epitaxially. Transmission electron micrographs and electron diffraction patterns of the crystals exhibit that the (002) planes of the face-centered cubic C60 crystal orient in parallel to the KI(001) surface. This epitaxial orientation is explained in terms of thec(2×2) commensurate lattice matching.

Epitaxial growth of C60 on Ag(110) studied by scanning tunneling microscopy and tunneling spectroscopy.

Using a scanning tunneling microscope, the growth of ${\mathrm{C}}_{60}$ on Ag(110) is explored. The substrate influences the natural tendency of the fullerene molecules to pack closely and an overlayer system with twofold rotational symmetry is formed: Ag(110)c(4\ifmmode\times\else\texttimes\fi{}4)${\mathrm{C}}_{60}$. This represents a distorted close-packed configuration for the ${\mathrm{C}}_{60}$ molecules, where the nearest-neighbor distance observed in bulk ${\mathrm{C}}_{60}$ is maintained. Initial island growth occurs on terrace sites away from substrate step edges, which bunch with increasing fullerene coverage. Above monolayer coverage, ${\mathrm{C}}_{60}$ grows epitaxially, maintaining twofold rotational symmetry. Tunneling spectroscopy is used to explore differences between the electronic structure in the monolayer and multilayer regimes.

Scanning tunneling microscopy of ordered C60 and C70 layers on Au(111), Cu(111), Ag(110), and Au(110) surfaces

We have conducted a study of the growth of C60 and C70 on a variety of reconstructed and unreconstructed noble metal surfaces using a UHV scanning tunneling microscope. For reconstructed Au(110) and Au(111) surfaces we observe changes in the superstructure of the metal upon (sub)monolayer adsorption at the fullerene–metal interface. In all the metals studied, formation of a well-ordered hexagonal C60 overlayer is observed after annealing. (110) and (111) substrates show preferred nucleation and growth at terrace and steps, respectively. Time-lapsed images illustrate mobility of C60 arrays and clusters. The role of tip–C60 interactions is elucidated by sequences of images and the prospects for manipulation is discussed.

C60 adsorption on the Si(100)2×1 and Cu(111)1×1 surfaces

The adsorption of C60 molecules on the Si(100)2×1 and Cu(111)1×1 surfaces has been investigated by field ion-scanning tunneling microscopy/spectroscopy. The C60 molecules are stable on the Si(100)2×1 surfaces without rotation at room temperature because of the strong bonding with Si dangling bonds. On the Cu(111)1×1 surface, segregation of individual C60 molecules to the terrace edges and two-dimensional island growth of C60 toward the upper terrace are observed. Bias voltage-dependent scanning tunneling microscopy images of the individual C60 of the monolayer film show unique intramolecular structures, which are interpreted as the local density of the states of C60 interacting with the substrate.

Spiral growth of C60

We have observed the spiral growth of C60 grown on cleaved graphite using atomic force microscopy. Triangular terraces in the spirals consist of a monolayer of C60 having a 10 Å step height which agrees well with (111) lattice constant of fcc-C60. One of the characteristic features of the C60 spiral is the presence of a line defect running from the spiral core and crossing the spiral terraces. As a result, the original helicoid plane transforms into a stack of terraces. We think the C60 spiral growth is terminated by the introduction of a line defect at the early stages of the film growth, resulting from the weak van der Waals forces.