5 results on '"Bannani, A."'
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2. Charge transport in thin metallic films
- Author
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Bannani, Amin and Möller, Rolf
- Subjects
ddc:53 ,BEEM ,fullerene ,transport ,bismuth ,Potentiometry ,silicon ,ddc:530 ,Fakultät für Physik » Experimentalphysik ,silver ,dissipation ,Physik (inkl. Astronomie) ,PTCDA - Abstract
In dieser Arbeit wurden die verschiedenen mikroskopischen Beiträge des elektrischen Widerstands zum makroskopischen Widerstand in einem elektrischen Leiter auf Nanometerskala untersucht. Dabei wurde der Transport der Elektronen parallel und senkrecht zur Oberfläche betrachtet. Um den elektronischen Transport parallel zur Oberfläche zu analysieren, wurde die Rastertunnel-Potentiometrie verwendet. Mit ihr lassen sich die mikroskopischen Widerstandsbeiträge lokal auflösen und vom elektrischen Gesamtwiderstand isoliert untersuchen. Als elektrische Leiter wurden Wismut- und Silberfilme verwendet, die mit einer Dicke von bis zu 20 Monolagen auf einem Silizium-Substrat epitaktisch gewachsen sind. In den epitaktischen Bereichen der Wismut- und Silberfilme ist ein mikroskopischer Beitrag zum elektrischen Widerstand durch Stöße der Elektronen mit Phononen gegeben. Weitere wichtige Beiträge zum elektrischen Widerstand ergeben sich durch Streuung der Elektronen an Stufen des Silizium-Substrats und an Korngrenzen im Metallfilm. Aus der Analyse wurde ein spez. Stufen- und Korngrenzenwiderstand bestimmt. In einem weiteren System, der leitfähigen Si(111)- -Ag rekonstruierten Oberfläche, wird der elektrische Widerstand durch Streuung der Elektronen an atomaren Substratstufen und an Domänengrenzen dominiert. Für die Analyse des elektronischen Transports senkrecht zur Oberfläche wurde die Ballistische Elektronen Emissions Mikroskopie (BEEM) verwendet. Es wurde gezeigt, dass das System Wismut auf Si(100) für BEEM Experimente sehr gut geeignet ist. Mit dieser Methode konnte der ballistische Transport durch die beiden organischen Moleküle C60 und PTCDA untersucht werden, die auf dem Wismutfilm aufgebracht wurden. Hierdurch konnten die spezifischen Pfade der ballistischen Elektronen durch die Moleküle erstmalig identifiziert werden. Eine Signatur im BEEM Strom konnte für beide Moleküle auf den LUMO + 1 Zustand zurückgeführt werden. Es wurden einzelne C60 Moleküle identifiziert, bei denen die Transmission der ballistischen Elektronen genauso groß ist wie auf den unbedeckten Wismutbereichen. In this work, the different microscopic contributions to the macroscopic resistivity in an electric conductor were analysed on the nanometer scale. It was distinguished whether the transport of electrons occurs parallel or perpendicular to the surface. To analyse the electronic transport parallel to the surface, Scanning Tunneling Potentiometry was performed. This method allows to resolve the local microscopic contributions to the resistivity and to isolate their contribution from the global electric resistivity. As electric conductor, thin epitaxial bismuth and silver films with a thickness of up to 20 monolayers grown on a silicon single crystal were analysed. The microscopic contributions to the electric resistivity in the epitaxial regions of the film were dominated by electron-phonon scattering. It turned out that scattering of the electrons at substrate steps and at grain boundaries within the metal film contribute to the resistivity as well. A specific step and grain boundary resistivity was determined. For an additional system, the conducting Si(111)- -Ag surface reconstruction, the electric resistivity was dominated by scattering of the electrons at atomic substrate steps and domain boundaries. For the analysis of the electronic transport perpendicular to the surface, Ballistic Electron Emission Microscopy (BEEM) was applied. It could be shown that bismuth on a (100) oriented silicon single crystal substrate is a well suited system for BEEM experiments. This method was used to study the ballistic transport of electrons through the organic molecules C60 and PTCDA, deposited onto the bismuth film. Specific pathways for the ballistic transport of electrons could be identified. The contribution in the BEEM current could be attributed to the LUMO + 1 state for both molecules. Individual C60 molecules could be identified; they exhibit a transmission for the ballistic electrons which is almost as high as for the bare bismuth surface.
- Published
- 2007
3. Ballistic electron and hole transport through individual molecules
- Author
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A. Bernhart, B. Weyers, R Moeller, C. A. Bobisch, A Bannani, and E. Zubkov
- Subjects
History ,Materials science ,Silicon ,business.industry ,Resolution (electron density) ,chemistry.chemical_element ,Schottky diode ,Electron ,Physik (inkl. Astronomie) ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Molecular physics ,Computer Science Applications ,Education ,Bismuth ,Condensed Matter::Materials Science ,Optics ,chemistry ,Ballistic conduction ,Ballistic conduction in single-walled carbon nanotubes ,business ,Ballistic electron emission microscopy - Abstract
Recently the ballistic transport through organic molecules could be analyzed with submolecular resolution by an extension of ballistic electron emission microscopy. In this work we compare the results of ballistic transport of electrons and holes through C₆₀ molecules deposited onto a Bismuth/Silicon Schottky diode. The study of hole transmission also exhibits molecular a resolved pattern in the transmission images showing the molecular periodicity of the C₆₀ layer. © 2008 IOP Publishing Ltd. CA Bobisch
- Published
- 2008
4. Ultrathin Bi films on Si(100)
- Author
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Rolf Möller, M Matena, A Bannani, and C. A. Bobisch
- Subjects
Materials science ,Silicon ,Annealing (metallurgy) ,Mechanical Engineering ,chemistry.chemical_element ,Bioengineering ,Nanotechnology ,General Chemistry ,Epitaxy ,Layer thickness ,Grain size ,Bismuth ,chemistry ,Mechanics of Materials ,Surface roughness ,General Materials Science ,Electrical and Electronic Engineering ,Composite material - Abstract
In this work we report on the growth of high quality bismuth films with a layer thickness of 3–4 nm on a (100)-oriented silicon surface. We present a combined STM and LEED study to determine the best possible growth conditions regarding, for example, film flatness, grain size and low surface roughness. The deposition of bismuth was performed at a low temperature of about 130 K followed by moderate annealing to an ambient temperature or to temperatures slightly above. The result is an epitaxial Bi film with low surface roughness.
- Published
- 2007
5. Ultrathin Bi films on Si(100).
- Author
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C Bobisch, A Bannani, M Matena, and R M
- Subjects
- *
BISMUTH , *THIN films , *SURFACE roughness , *SILICON - Abstract
In this work we report on the growth of high quality bismuth films with a layer thickness of 3-4 nm on a (100)-oriented silicon surface. We present a combined STM and LEED study to determine the best possible growth conditions regarding, for example, film flatness, grain size and low surface roughness. The deposition of bismuth was performed at a low temperature of about 130 K followed by moderate annealing to an ambient temperature or to temperatures slightly above. The result is an epitaxial Bi film with low surface roughness. [ABSTRACT FROM AUTHOR]
- Published
- 2007
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