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000172850 005__ 20210308142534.0
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000172850 0247_ $$2ISSN$$a1866-1807
000172850 020__ $$a978-3-89336-990-4
000172850 037__ $$aFZJ-2014-06284
000172850 041__ $$aGerman
000172850 1001_ $$0P:(DE-Juel1)138943$$aKorte, Stefan$$b0$$eCorresponding Author$$gmale$$ufzj
000172850 245__ $$aLadungstransport durch Graphenschichtenund GaAs-Nanodrähte untersucht mit einem Multispitzen-Rastertunnelmikroskop$$f2011-01-01 - 2014-12-31
000172850 260__ $$aJülich$$bForschungszentrum Jülich GmbH Zentralbibliothek, Verlag$$c2014
000172850 300__ $$a96 S.
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000172850 3367_ $$02$$2EndNote$$aThesis
000172850 3367_ $$0PUB:(DE-HGF)11$$2PUB:(DE-HGF)$$aDissertation / PhD Thesis$$bphd$$mphd$$s1615196722_4749
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000172850 4900_ $$aSchriften des Forschungszentrums Jülich. Reihe Schlüsseltechnologien/ Key Technologies$$v90
000172850 502__ $$aDissertation, RWTH Aachen University, 2014$$bDissertation$$cRWTH Aachen University$$d2014
000172850 520__ $$aThis work describes the use of the combination of a scanning electron microscope (SEM) and a multitip scanning tunneling microscope (STM) with four tips as a nanoprober. Electrical measurements on graphene layers and freestanding gallium arsenide (GaAs) nanowires were conducted. Four-probe-measurements are necessary to measure the resisitvity of such one- and two-dimensional conductors. Due to unknown voltage drops at contacts that carry currents, additional contacts have to be employed for current-free potential measurements. Therefore, the multitip scanning tunneling microscope with its four individually controllable tips has been upgraded with extended electronics, enabling us to use it as a flexible nanoprober. Graphene layers on insulating SiO$_{2}$ and hexagonal boron nitride (h-BN), prepared by mechanical exfoliation, were contacted with the multitip STM. Tunneling current could not be used as feedback when approaching the first tip. Therefore, a contrast change in the SEM image upon contacting a graphene flake with a tip was used. Once contacted, flakes were scanned by RTM and electrical measurements were conducted. Graphene transferred to h-BN showed bubbles, wrinkles and contaminations. Still, STM images of clean areas revealed a moiré pattern, proving that the atomically thin graphene lay flat on the atomically flat h-BN surface. Four point measurements of these samples showed a poor conductivity of 1/$\sigma$ = 16$^{k \Omega} /box$ and a low field effect mobility of $\mu$ = 300$^{cm^{2}}$/Vs. The reason for this might be the contaminations from the transfer process, as well as effects from prolonged irradiation with electrons from the SEM. Freestanding p-doped GaAs nanowires, grown by metal-organic vapor-phase-epitaxy in the vapor-liquid-solid-growth mode, in a process with two temperature steps, were contacted with the multitip STM. Using three tips as well as the substrate as contacts, four point measurements were performed. It showed that elastic deformation of these flexible nanowires has no significant influence on their conductivity. The high spatial resolution of the combination of a SEM with a multitip STM made it possible to record resistance profiles of freestanding nanowires by performing four point measurements along a nanowire. The main segment of the nanowires, grown at 400$^{\circ}$C for better crystal quality exhibits a resisitivity of a few $^{k\Omega}$/$_{\mu m}$, in agreement with literature values. The nanowire base, grown at 450$^{\circ}$C to facilitate better nucleation, shows an increased resisitvity of several $^{M\Omega}$/$_{\mu m}$. The resistance of the nanowire base is relevant especially for future opto-electronical components based on freestanding nanowires and thus has to be understood. Comparing profiles of nanowires grown by an identical process on different substrates showed that the substrate is not the cause of the increased resistance. From the measured resistivities the dopant concentrations, as well as the thickness of the space charge layer at the surface of the GaAs nanowires were calculated. The nanowire segments grown at 400$^{\circ}$C have a dopant concentration of roughly 10$^{19}$cm$^{-3}$, those grown at 450$^{\circ}$C about 2 $\cdot$10$^{17}$ cm$^{-3}$. In the base the space charge layer poses a considerable constriction to the conduction. A qualitative explanation for the temperature dependence of the dopant concentration is given.
000172850 536__ $$0G:(DE-HGF)POF3-141$$a141 - Controlling Electron Charge-Based Phenomena (POF3-141)$$cPOF3-141$$fPOF III$$x0
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000172850 773__ $$y2014
000172850 8564_ $$uhttps://juser.fz-juelich.de/record/172850/files/FZJ-2014-06284.pdf$$yOpenAccess
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000172850 9141_ $$y2016
000172850 9101_ $$0I:(DE-588b)5008462-8$$6P:(DE-Juel1)138943$$aForschungszentrum Jülich GmbH$$b0$$kFZJ
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000172850 9201_ $$0I:(DE-Juel1)PGI-3-20110106$$kPGI-3$$lFunktionale Nanostrukturen an Oberflächen$$x0
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