Ladungstransportuntersuchungen an nanofunktionalen Bauelementen mit Diodencharakteristik basierend auf funktionalisierten Nanopartikeln (2014)

The success of silicon-based information technology is mainly based on its cost effectiveness and on its efficient information storage in semiconductor memory cells. The miniaturization of electronic components is a key element in semiconductor technology that drives operating speed and energy efficiency. However, further shrinking of device structures will face huge technological challenges, so that alternative technologies have to be considered. So called hybrid concepts combine the existing silicon-based electronics with new technologies such as molecular electronics in which molecules or functionalized nanoparticles are studied as electronic components. In this work, different electrode-molecule/nanoparticle/molecule-electrode devices were investigated for their suitability as a diode device in a CMOS compatible system. These arrangements were systematically varied and the transport properties of different mono- or bifunctionalized gold nanoparticles (AuNPs) were characterized between homo- or heterometallic nanoelectrodes (HoNE or HeNe). Mixed functionalized AuNPs and Janus AuNPs (d = 14 ± 1 nm), with different molecules on opposite hemispheres, were used as bifunctionalized AuNP. The first step for understanding the electron transport through these electrode-molecule/AuNP/molecule-electrode devices was the optimization and characterization of the individual components of the devices. Investigations of the AuNPs and AuNP adsorption on the different metals showed that the binding of single-Janus-AuNPs can be controlled by the pH buffer solution. Furthermore, surface-sensitive methods (XPS) confirmed the functionality of the molecules after the immobilization and drying and demonstrated the directed orientation of the Janus-AuNPs. Optimizations in the process of fabrication of HeNE, which involves electron-beam lithography in combination with a hard mask, allowed to produce HeNE, with a distance of d = 13 ± 2 nm, and a yield of about 50%. The AuNPs were immobilized between the nano-electrodes by dielectrophoretic trapping. The electrical characterization of the devices included the analysis of the transport mechanisms, such as Arrhenius, superexchange or tunneling transport. The tunnelling transport was additionally analyzed by the Simmonsmodel, Landauer formula and by „Transition Voltage Spectroscopy“. The charge transport studies of mixed functionalized AuNPs between the HeNe showed diode characteristic due to the different HOMO/LUMO energies of the twomolecules. However, mixed AuNPs showed an uncontrolled orientation between the nanoelectrodes and thus, random asymmetrical contacts are expected. Alsomonofunctionalized AuNP were immobilized in order to obtain diode characteristics. In this case the resulting asymmetric contacts between the different metals and the ligands should cause a rectifying behavior. However, the diode characteristics remained unobserved due to water molecules adsorbed to the ligand shell, which have an approximately equal binding energy at both metal-molecule contacts. Whereas for Janus AuNPs the targeted, directed asymmetric I/U-characteristic can be proved due to the different transmission coefficients of both molecule-metal-contacts and the significantly different HOMO/LUMO levels of themolecules on both hemispheres. In addition to the tunneling process for the Janus-AuNP devices, thermally activated transport processes were observed under heliumor vacuum atmosphere.