Recent activities of the eight divisions (Applied Surface Science, Electronic Materials & Processing, Nanometer Structures, Plasma Science & Technique, Surface Engineering, Surface Science, Thin Film, and Vacuum Science and Technology) of the International Union for Vacuum Science, Technique and Applications (IUVSTA) are reported.
Interface formation process of pentacene thin films on semiconductor surfaces has been studied using low energy electron microscopy (LEEM) and scanning tunneling microscopy. Interface interaction between clean Si surface and pentacene film is optimized by inserting bismuth thin film at the interface, resulting in the formation of monolayer islands larger than 0.2 mm in diameter. Systematic surface reactivity control on Si substrate reveals that the surface states nearby the Fermi level are the origin of the interface interaction between pentacene molecules and semiconductor surfaces. Effect of kinetic growth process on the pentacene film growth is also examined by detailed LEEM observations. The anisotropic growth speed originating from the anisotropic structure of pentacene accompanied with the kinetic growth condition could result in the formation of textured structure inside the single grain grown from a single nucleus.
Organic field effect transistors (OFETs) have attracted much attention as key devices to realize plastic electronics. Low mobility of OFETs is one of the major problems for practical use. To improve the mobility, fabrication technique of high quality organic semiconductor thin films is important. Surfaces of gate insulators are amorphous in many cases, so that a novel technique to control in-plane orientation on such amorphous substrates is urgently required. In this report, application of “graphoepitaxy” to control the in-plane orientation is proposed. The authors discovered that organic semiconductor α-sexithiophene grows with in-plane preferred orientation on artificial periodic grooves fabricated on thermally-oxidized silicon substrates. Using this technique, the test devices of OFETs with oriented 6T thin films were prepared. The mobility has not yet been improved owing to morphological problems of the thin films. A guide to the next step of research is presented based on current imaging by conductive atomic force microscopy.
This review paper describes the present status of passivation films with organic/Inorganic multilayer structure on flexible organic film substrate designed for electronic devices such as organic light emitting diode (OLED). Passivation film of SiNx/CN:H multilayer showed an excellent barrier properties for water and oxygen and strongly suppressed an appearance of dark spots on OLED surface during operation. The luminous efficiency of flexible OLED thus formed with passivation films revealed to be equivalent to that on glass substrate encapsulated by can. substrate.
Evaluations of mechanical properties of organic polymer thin films are important for enhancement of their functions. Measuring and evaluation methods of these properties, i.e., internal stress, shearing stress, tensile modulus, breaking strength, are presented in this paper. In addition, adhesion of these thin films to metal substrates is one of the important properties for enhancement of their functions as well as the mechanical properties. Measuring and evaluation methods of adhesion properties are also presented in this paper.
Bio-components from living body are very attractive nano-materials, because they have already achieved ultra-high and ultimate performance as the result of many cycles of natural selection and mutation. We first succeeded in obtaining the electron from the electron relay system in the inside of PSI by use of molecular wire as a connector, which was designed for facile electron transfer, and also demonstrated FET-operation using the electrons from PSI via. the molecular wire. This study has confirmed the validity of the novel approach and strategy to utilize bio-components as the core parts in an artificial system, which can be applied to many kinds of bio-functions.
It is known that the hold-off voltages of vacuum gaps can be improved by the spark conditioning with repetitive electrical breakdowns. At the initial stage of spark conditioning process, small pulse currents (not breakdowns) were observed, and in turn hold-off voltages were improved. To clarify the generating mechanism of the pulse current and the reason of the improvement in hold-off voltages, repetitive pulse current was generated, and chemical compositions of the electrodes were analyzed before and after experiments. The analysis of chemical compositions was carried out by a X-ray photoelectron spectroscopy (XPS). The XPS analysis revealed that only the anode surface was cleaned by repetitive pulse current flowing. This result suggests that cleaning the anode surface by repetitive pulse current flowing would be one of causes of the improvement in hold-off voltages of a vacuum gap at the initial stage of conditioning process.
The surfaces of the polystyrene films spin-coated on glass were modified by carbon negative-ion implantation with various ion doses from 1×1014 to 3×1016 ions/cm2 at 5 and 10 keV. The implantation conditions with and without a pattering mask were for investigation of the cell-attachment properties and for evaluation of surface physical properties of contact angle, respectively. The contact angles of modified surface were investigated by pure water drop and air bubble method. The lowest angle value of the implanted films at 5 and 10 keV were approximately 72° at 3×1015 ions/cm2 after dipping in the de-ionized water for 2 hours. The lowering of contact angles on C-implanted surfaces when increase the ion dose is due to formation of the OH and C-O bonds. Nerve-cell-attachment properties of modified surface were investigated by the nerve-like cell of rat adrenal pheochromocytoma (PC12h) in vitro. After 2 days culture of the PC12h cells, no cells attached on the polystyrene films implanted with low ion dose from 1×1014 to 3×1014 ions/cm2. On the polystyrene films implanted with the dose order of 1015 ions/cm2, the cells selectively attached only on the implanted region. Whereas on the surfaces implanted with high dose such as 1×1016 and 3×1016 ions/cm2 mostly cells attached on the implanted region, and some attached on the unimplanted region, as well as cells were abnormal in shape and large size. Therefore, the suitable dose implantation for the selective-attachment of nerve-cells on the polystyrene films implanted at 5 and 10 keV were obtained around the dose order of 1015 ions/cm2, and the best condition for the selective attachment properties was at 3×1015 ions/cm2 corresponding to the lowest contact angle.