Growth Of C60 Thin Films Research Articles

Organic Semiconductors: Charge‐Transfer‐Controlled Growth of Organic Semiconductor Crystals on Graphene (Adv. Sci. 6/2020)

In article number 1902315, Kilwon Cho and co-workers investigate the growth of C60 thin films on graphene. The crystallinity of C60 thin film is significantly improved when it is grown on p-doped graphene where electron transfer from graphene to C60 is suppressed.

Growth of C60 thin films on Al2O3/NiAl(100) at early stages

The growth of thin films of C60 on Al2O3/NiAl(100) at the earliest stage was studied with scanning tunneling microscopy and synchrotron-based photoelectron spectroscopy under ultrahigh-vacuum conditions. C60 molecules, deposited from the vapor onto an ordered thin film of Al2O3/NiAl(100) at 300K, nucleated into nanoscale rectangular islands, with their longer sides parallel to direction either [010] or [001] of NiAl. The particular island shape resulted because C60 diffused rapidly, and adsorbed and nucleated preferentially on the protrusion stripes of the crystalline Al2O3 surface. The monolayer C60 film exhibited linear protrusions of height 1–3Å, due to either the structure of the underlying Al2O3 or the lattice mismatch at the boundaries of the coalescing C60 islands; such protrusions governed also the growth of the second layer. The second layer of the C60 film grew only for a C60 coverage >0.60ML, implying a layer-by-layer growth mode, and also ripened in rectangular shapes. The thin film of C60 was thermally stable up to 400K; above 500K, the C60 islands dissociated and most C60 desorbed.

A detailed Auger electron spectroscopy study of the first stages of the growth of C60 thin films

In this work we take advantage of the large sensitivity and in-depth resolution of Auger electron spectroscopy (AES) to study in a detailed way the growth of C60 over different substrates, namely Cu(1 1 1), Si(1 0 0) and graphene. The ability of AES, as compared to more local probes like STM or AFM, to follow the process in a dynamic way, allows us to study the growth of C60 below and over one ML, including the change of C60 over either Si or Cu to the growth of C60 over a C60 film. We found that the growth always proceeds layer by layer. This result shows that differences in diffusion barriers are not as important as one may think following the idea of diffusion by a jumping mechanism. We propose that the sticking coefficient, governed by the adsorption energy, is responsible for the differences observed between Cu and Si. Our results also point to a different charge transfer among fullerene molecules and these surfaces. The same result is suggested in the case of C60 over graphene, but in this case our conclusion comes from the variable temperature experiments.

Heteroepitaxial growth of C60 on tetracene single crystal

ABSTRACTWe have developed a method for epitaxial growth of C60 thin films on tetracene single crystals. The crystal orientation of the C60 film was examined by reflection high energy electron diffraction (RHEED) and X-ray diffraction (XRD). In-situ observation by RHEED revealed that the C60 crystallizes from the very initial stage of the deposition (0.1 nm). A 6-fold symmetric pattern, which was observed in a XRD polar scan, can be taken as direct evidence for the epitaxial growth of C60 commensurate with the tetracene (001) surface lattice.

Epitaxial growth of C60 thin films on the Bi(0001)/Si(111) surface

The morphology and atomic structure of C60 fullerene films on the Bi(0001)/Si(111)−7 × 7 surface with different coverages have been studied by scanning tunneling microscopy and spectroscopy and low-energy electron microscopy in high vacuum. It is shown that the most favorable sites for nucleation of C60 islands are double steps and domain boundaries on the surface of epitaxial Bi film.

Epitaxial Growth of C60 Thin Films using Continuous-wave Laser Molecular Beam Epitaxy

ABSTRACTWe 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.

Deposition and structural characterization of high quality textured C60 thin films

We present some features of the growth of C60 thin films on different substrates at temperatures up to 573 K. The crystalline structure of the films was studied by X-ray diffraction, atomic force microscopy and scanning tunneling microscopy. An effect of selective C60 deposition on an Ag/glass substrate held at 523–573 K is demonstrated. C60 was found to be deposited only on the glass part of the substrate but not on the part of the same substrate which had been predeposited with an Ag or Au layer. The potential use of such selective deposition for micro- and nanoscopic C60 pattering and fabrication of C60-based devices is suggested. We report, for the first time, on the possibility of extremely rapid (10–20 Å/s) growth of high quality 〈111〉-textured C60 films onto Ag and Au substrates held at 523–573 K using a simple vacuum deposition technique. Temperature-resolved XRD experiments revealed that textured C60 films undergo a first order phase transition at 250 K.

Initial Stage of C60 Thin-Film Growth on YB66(001) Surfaces

Exposed B156 supericosahedra on a YB66(001) surface were found align periodically in a two-dimensional square lattice. On the YB66(001) surface, C60 molecules were deposited at room temperature. The initial stages of C60 thin-film growth on the YB66(001) surface were studied using a scanning tunneling microscope (STM). In the submonolayer regime, the C60 molecule adsorbed strongly on the surface to show the stripe pattern due to the inner molecule C=C bonds. The adsorbed layer had no long-range ordering. The C60 molecules did not favor the on-top site of the B156 supericosahedron. We propose a model that the C60 molecule adsorbs on triangular sites made up of the B12 icosahedra on each B156 supericosahedron on the surface. Due to size frustration, the C60 molecule occupies only one of two equivalent triangular sites. The model explains the characteristics of the adsorption site and the arrangement of the C60 molecules in the submonolayer regime. In the multilayer regime, the dangling bonds of the surface were passivated by the first layer, and overlayer growth was governed by van der Waals interaction between C60 molecules. An island, the top of which showed a hexagonal lattice, grew on the first layer. The hexagonal lattice was rotated by 10° with respect to the underlying square lattice of the YB66(001) surface.

Sb mediated C60 thin film growth on mica

We studied the growth of C60 thin films on a layer of surfactant Sb which was predeposited on mica substrates with vacuum vapor deposition method. It was found that the growth behaviors of C60 films are significantly affected by the surfactant Sb and the substrate temperature. (112)- and (111)-oriented C60 single-crystal films with large C60 single crystals were obtained when the substrate temperatures were 200 and 215 °C, respectively. The growth mechanisms of the Sb mediated C60 films were attributed to the reduced surface diffusion rate of adsorbed C60 molecules and the lowered boundary potential energy of C60 islands by surfactant Sb.

C60 single crystal films on GaAs/InAs(001) surfaces

In this paper, we report a scanning tunnelling microscopy study of C60 thin film growth on the GaAs(001) As-rich 2 × 6 and InAs(001) In-rich 4 × 2 surfaces prepared by molecular beam epitaxy. On the 2 × 6-As surface, the corrugated potential of the 2 × 6 substrate forces the first monolayer structure to be strongly modified resulting in formation of a ‘double-chain’ commensurate structure. C60-substrate interaction, however, is limited to 2–3 monolayers at the interface and the competing intermolecular interaction governs the 3-dimensional growth of multiple-layer C60 FCC crystalline film on the InAs(001). In 4 × 2 surface, the C60 molecule is very mobile even at room temperature. The intermolecular interaction is significant and overcomes the substrate corrugated potential, and 2-dimensional islands with quasi-hexagonal close-packing form even at submonolayer coverage.

Hot Wall epitaxy of C60Thin Films on Mica and Their Characterization

Abstract The growth of C60 thin films on mica by Hot Wall Epitaxy was studied using high resolution X - ray diffraction. The influence of the Hot Wall source-, wall- and substrate temperature on the crystalline quality of the C60 films was investigated by determining the full width at half maximum (FWHM) Δω of the C60 - (111) reflex in ω - direction (i. e. rocking curve). With the optimal parameters of growth (substrate temperature = 140 C, growth rate = 0.5 Å/s) it is possible to grow 150 nm thick C60 films with an ω - scan FWHM Δω of about 200 arcsec, the best value reported so far, indicating the growth of a perfect monocrystalline C60 layer. Rocking curves of thicker films exhibit a complex shape, which is interpreted as a result of a change in the growth mode of C60 films exceeding a critical thickness. In addition surface cracks appearing on the C60 film surface are investigated using digital image processing. Atomic force microscopy- and photoluminescence measurements performed on the thin films complete this study.

Growth of C60 thin films on GeS(001) studied by scanning force microscopy.

The epitaxial growth of ${\mathrm{C}}_{60}$ thin films sublimed onto GeS(001) substrates under ultrahigh-vacuum conditions was investigated in the range of 0.7--11 monolayers coverage by scanning force microscopy in air. The growth process follows basically a layer-by-layer mechanism if evaporated in the narrow temperature range from 180 to 200 \ifmmode^\circ\else\textdegree\fi{}C, but was found to be very sensitive to even small changes in temperature. At substrate temperatures above 200 \ifmmode^\circ\else\textdegree\fi{}C, the second and higher layers are not stable. For temperatures close to 200 \ifmmode^\circ\else\textdegree\fi{}C, our studies indicate pure layer-by-layer-type growth. Somewhat lower substrate temperatures lead to the formation of two different types of triangular-shaped islands which originate from a different stacking of the molecules, beginning with the second layer. Triangular islands belonging to the same type tend to coalesce, whereas islands of different types are separated by grooves. At substrate temperatures close to 180 \ifmmode^\circ\else\textdegree\fi{}C during evaporation, dendritic islands are formed due to the limited mobility of the ${\mathrm{C}}_{60}$ molecules at this temperature. Furthermore, the growth mode changes to a nonideal layer-by-layer growth where the second and even higher layers start to grow before the first layer has been completed. This behavior can well be explained by a two-dimensional diffusion-limited growth mechanism. Finally, substrate temperatures significantly lower than 180 \ifmmode^\circ\else\textdegree\fi{}C result in films without long-range order.

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)

Response to ‘‘Comment on ‘Crystal growth of C60 thin films on layered substrates’ ’’ [Appl. Phys. Lett. 65, 378 (1994)

Response to ‘‘Comment on ‘Crystal growth of C60 thin films on layered substrates’ ’’ [Appl. Phys. Lett. <b>65</b>, 378 (1994)

Crystal growth of C60 thin films on layered substrates

The process of the C60 thin film crystal growth on layered materials such as MoS2 and mica is studied in detail with a combination of atomic force microscopy (AFM) and reflection high-energy electron diffractometry, and is compared to that on alkali-halide (NaCl) substrates. AFM shows that a single crystal containing triangle-shaped grains of 1–2 μm size with a (111) surface terrace is grown on the MoS2 substrate over a large area through a layer-by-layer process, while the grains on mica are 200–400 nm in size and distribute with some disorder in the orientation. The epitaxial characteristics of the C60 crystal growth on these layered substrates are discussed in comparison with that on alkali-halides.

High-resolution TEM of C60 thin films

The ability to fabricate buckminsterfullerenes, C60 molecules, in reasonably large quantities has made possible studies of the structural properties of this form of carbon when it is in a crystalline state. At room temperature, x-ray diffraction from three-dimensional bulk C60 crystals shows that the molecules are centered on sites of a face-centered-cubic Bravais lattice, A∘ = 14.2Å. Somewhat earlier in time, a study of C60/C70 bulk material using electron diffraction and high resolution electron microscopy has revealed a hexagonal phase. It is now believed that this phase is a simple cubic structure rather than a hexagonal structure. Since it is reasonable to expect that highly ordered C60 thin films will have superior properties to bulk material, several studies have been undertaken to understand the early stages of C60 thin film growth. Monolayer growth on GaAs has been studied by scanning tunneling microscopy., and on mica at room temperature using helium scattering. Along similar lines we have grown thin films of C60 molecules on mica and NaCl and characterized the crystallinity and local structural arrangements. Here we present some of our results of the electron microscope examination of these materials.