TY  - THES
AB  - In this work two new methods for the electrical characterization of nanowires were developed. While imaged in a Low Energy Electron Point Source microscope (LEEPS), individual freestanding nanowires were contacted with a fine metal tip as a movable electrode. By performing systematically length dependent transport measurements the contact contributions were separated from the intrinsic wire resistance, which allows the calculation of the specific resistivity. Besides various metallic and semiconducting materials (Cu, Co, Bi and CdS) special interest was focused towards zinc oxide (ZnO) nanowires, where a strong diameter dependency of the specific resistivity was found. A geometric model was developed to describe this size effect.
In addition to the transport measurements the unique imaging properties of the LEEPS microscope were deployed in order to determine the specific resistivity of a nanowire directly from its LEEPS image. In principle the LEEPS is an electron projection microscope using electrons with energies below 200 eV. Due to their low energy the electrons are very sensitive to weak electrostatic fields. When they pass a charged object they are deflected by a small angle, which makes the detector image differ from a pure geometric projection. This deflection angle includes the information about the local charge density of the imaged object and can be extracted from the LEEPS image.
In the case of conductive nanowires an always present positive charging was observed in the LEEPS microscope. By comparing the LEEPS images with scanning electron microscope (SEM) pictures of the same wire the origin of this positive charging was figured out as a secondary electron yield greater than one. Moreover it was found that the spatial distribution of the charge density along the wire depends on its electrical resistance. Based on these observations a quantitative model was developed, which enables the extraction of the specific wire resistivity directly from a single LEEPS image. Thus the LEEPS microscope affords a fast and simple way for the "contactless" electrical characterization of individual and freestanding nanowires.
DA  - 2008
KW  - Nanodraht
KW  - Elektrische Leitfähigkeit
KW  - Elektronenmikroskop
KW  - Zinkoxid
KW  - Cadmiumsulfid
KW  - Feldemission
KW  - Nanowire
KW  - Electrical conductivity
KW  - LEEPS (Low Energy Electron Point Source)
KW  - Electron microscope
KW  - Zinc oxide
KW  - Cadmium sulfide
KW  - Field emission
LA  - ger
PY  - 2008
TI  - Elektrische Charakterisierung freistehender Nanodrähte mit dem Low Energy Electron Point Source Mikroskop
UR  - https://nbn-resolving.org/urn:nbn:de:hbz:361-13337
Y2  - 2024-11-21T23:22:17
ER  -