Crystallization of diamond-like carbon to graphene under low energy ion beam modification

Low-energy ion beam modification was proposed to create graphene on the top of the insulated diamond-like carbon films. In such low-temperature fabrication process the surface of the amorphous carbon could crystallize to graphene as a result of point defect creation and enhanced diffusion caused by the ion bombardment. In the experiment 130 eV argon ion irradiation was used. After the modification the resistivity of the sample surface drops. Raman spectra of the samples measured at 633 nm showed partial crystallization and were similar to the spectra of defected graphene. This result is very encouraging and we hope that by improving this technology it will be possible to fabricate defect-free graphene, which can be used in electronics without transfer to other substrate

Enhanced superconductivity of YBCO interfaces: origin of high critical temperature in layered superconductors

Superconducting transition temperatures Tc of the YBCO film surface and of the YBCO film/substrate interface were measured inductively. It was observed that the interface- Tc is always higher then the surface - Tc. However deposition of silver over-layer enhances the superconducting transition temperatures. This observation was confirmed by four-point resistance measurements. In the annealed YBCO/Ag bilayers magnetic properties of the interface were observed. We believe that such phenomena are a common feature of layered systems. This two dimensional structure reminds the layered microstructure of the high-temperature superconductors and one can suppose that covering of the superconducting layer by non-superconducting layer is a condition for obtaining high critical temperatures in general.Comment: 13 pages, 9 figures, submited to Natur

Supraleitende Bauelemente aus Hochtemperatursupraleitern Abschlussbericht

Results will be presented which were worked out during development of electronic components from high temperature superconductors (YBCO). Due to the complicated structure and the worse performance of the superconductor BiSrCaCuO an examination of this material was resigned. Electronic components from polycrystalline superconductors suffer from instability against environmental influence. Therefore, examinations were concentrated on planar resonators and filters and planar RF-SQUIDs from epitaxial YBCO films. Fabrication of the YBCO films was made by laser deposition. No difficulties occured concerning fabrication and reproduction of YBCO films. During the examinations UHF resonators with a quality factor of up to 60,000 have been developed. Filters made from these resonators have had low insertion loss and high selectivity. The volume of these filters is very small compared to cavity filters with similar performance. Applications in radio engineering are possible. This will lead to a more efficient use of the frequency spectrum for cellular radio, satellite radio, or other communication servies. A fabrication process with high yield for low noise RF-SQUIDs has been developed. The process makes use of well established processes known from semiconductor technology. The SQUID magnetometers are already one order of magnitude more sensitive than non superconducting magnetometers. With suitable flux transformers the sensitivity can be increased significantly. An easy-to-apply cryocooler has been developed for cooling of high-T_c electronic components. (orig./MM)Es werden die Ergebnisse dargestellt, die mit der Entwicklung von elektronischen Bauelementen aus dem Hochtemperatursupraleiter (YBCO) erarbeitet wurden. Aufgrund der komplizierten Struktur und der deutlich schlechteren Eigenschaften des Supraleiters BiSrCaCuO wurde auf eine eingehende Untersuchung dieses Supraleiters verzichtet. Da elektronische Bauelemente aus polykristallinem Material ungenuegende Stabilitaet gegenueber Umwelteinfluessen aufwiesen, wurden die Aktivitaeten auf die Untersuchung von planaren Resonatoren und Filtern und planaren HF-SQUIDs aus epitaktischen Filmen aus YBCO konzentriert. Die Herstellung der supraleitenden Schichten erfolgte mit einer Laser-Depositionsanlage. Es ergaben sich keine Schwierigkeiten bei der reproduzierbaren Herstellung von YBCO-Filmen. Im Verlauf der Untersuchungen konnten planare Resonatoren im UHF-Bereich mit einer Leerlaufguete bis zu 60.000 hergestellt werden. Filter, die aus solchen Resonatoren hergestellt wurden, zeichneten sich durch geringe Einfuegungsdaempfung und hohe Selektivitaet aus. Es wurden planare HT_c-Filter entwickelt, die daempfungsarm sind, eine hohe Selektivitaet aufweisen und kleine Abmessungen haben. Im Bereich der SQUID-Magnetometer konnte ein Herstellungsverfahren fuer RF-SQUIDs entwickelt werden, das sich durch hohe Ausbeute und sehr gute Rauscheigenschaften auszeichnet. Es ist gelungen, das Verfahren so zu entwickeln, dass ausschliesslich etablierte Prozesse der Halbleiterelektronik verwendet werden muessen. Weiterhin wurde ein anwenderfreundliches Kuehlverfahren fuer Komponenten der HT_c-Elektronik entwickelt. (orig./MM)SIGLEAvailable from TIB Hannover: F93B808+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman