Optimizing picene molecular assembling by supersonic molecular beam deposition

Here we report an investigation of the growth of picene by supersonic molecular beam deposition on thermal silicon oxide and on a self-assembled monolayer of hexamethyldisiloxane (HMDS). In both cases film morphology shows a structure with very sharp island edges and well-separated islands which size and height depend on the deposition conditions. Picene films growth on bare silicon covered with hydrophobic HDMS shows islands characterized by large regular crystallites of several micrometers; on the other hand, films growth on silicon oxide shows smaller and thicker islands. We analyzed the details of the growth model and describe it as a balancing mechanism involving the weak interaction between molecules and surface and the strong picene-picene interaction that leads to a different Schwoebel-Ehrlich barrier in the first layer with respect to the successive one. Finally, we study the charge transport properties of these films by fabricating field-effect transistors devices in both top and bottom contact configuration. We notice that substrate influences the electrical properties of the device and we obtained a maximum mobility value of 1.2 cm2 V-1 s-1 measured on top contact devices in air. © 2012 American Chemical Society

Optimizing Nozzle Geometry for Controlling Properties of Molecular Beam with Heavy Organic Molecules

Abstract. The flow in conical supersonic micronozzles and behind them by deposition of pentacene accelerated by helium was studied with the use of direct simulation Monte-Carlo method. The Knudsen number in critical cross-section of nozzles is 0.0043. A directedness of resulting accelerated pentacene flow was studied as a function of cone angle and geometrical Mach number of the nozzle. The intensity of heavy gas flow in the hypersonic region can be elevated by one order using supersonic nozzles

SiC growth on Si(111) from a C-60 precursor: a new experimental approach based on a hyperthermal supersonic beam

Silicon carbide (SiC) films are grown on Si(111) using as a precursor fullerene seeded in helium supersonic beams. The regime of energy and flux distributions, achievable by changing the beam parameters, is well suited to synthesizing SiC films under well ordered conditions, because of better control of the synthesis process and of the C-60 dissociative absorption. This is confirmed by the first experimental results and by morphological and structural characterization of the films produced. Further developments are briefly discussed

Highly ordered growth of alpha-quaterthiophene films by seeded supersonic molecular beam deposition : a morphological study

It is shown that morphology and structure of films of oligothiophenes can be controlled well via supersonic molecular beam epitaxy (SuMBE). The supersonic expansion of oligomers seeded in inert gases makes it possible to tune beam parameters such as kinetic and internal energy, momentum and flux in a range that is shown to play a critical role in the morphology of the surface of the films. By simply varying the seeding in the source, we change the initial state of the oligomers in the beam. In this way, very different morphologies are obtained, ranging from a dendritic-like, typical of a disordered growth, to ordered layered structures. In. this case the terraces observed were characterized by widths on a micron scale and height equal to the molecular length. This last morphology, studied by Atomic Force Microscopy in the tapping mode, is consistent with X-ray diffraction data and the optical response of the same films. These properties are maintained up to unprecedented film thicknesses (greater than or equal to 500 nm)

Supersonic seeded beams of thiophene based oligomers for preparing films of controlled quality

A hyperthermal seedable supersonic beam, specifically designed for the deposition of thiophene based oligomers, is presented. The beam's properties are characterized by time-of-flight mass spectrometry and photoionization spectroscopy. Several quaterthiophene (T4) films under different beam conditions have been prepared and characterized by optical absorption, fluorescence spectroscopy and scanning electron microscopy. Centreline heavier species segregation in the beam is exploited to grow T4 films efficiently from impurities present in raw terthiophene (T3) powders. The morphology and structure of the films can be controlled by the beam's parameters that in turn allow variation in flux density, energy and orientation of molecules in the beam

Role of kinetic energy of impinging molecules in the alpha-sexithiophene growth

We report on the alpha-sexithiophene sub-monolayer growth with supersonic molecular beam deposition by investigating how the kinetic energy of the impinging molecules influences the growth on substrates with different surface wettabilities and temperatures. The results show that the energy of the impinging molecules affects the morphology of the molecular film increasing the coverage and the island size, and reducing the fractality of the sub-monolayer islands. The possibility of directing growth of more ordered islands could improve the performances of electronic devices, which are greatly affected by the structure of the first monolayers. (C) 2011 Elsevier B.V. All rights reserved