% IMPORTANT: The following is UTF-8 encoded.  This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.

@PHDTHESIS{Junker:829125,
      author       = {Junker, Hubertus Hartmut Robert},
      title        = {{L}adungstransportmessung an {G}a{A}s-{N}anodrähten und
                      {E}ntwicklung eines
                      {T}ieftemperatur-{V}ierspitzen-{R}astertunnelmikroskops{C}harge
                      transport measurements at {G}a{A}s-nanowires and development
                      of a low-temperature four-tip scanning tunneling
                      microscope-3},
      school       = {RWTH Aachen University},
      type         = {Dr.},
      address      = {Aachen},
      publisher    = {RWTH Aachen University},
      reportid     = {FZJ-2017-02932},
      pages        = {179pp; XXIII Seiten},
      year         = {2016},
      note         = {RWTH Aachen University, Diss., 2016},
      abstract     = {In order to perform charge transport measurements on
                      freestanding as-grown GaAs nanowires, a room-temperature
                      multi-tip scanning tunneling microscope was utilized as a
                      nanoprober. Four-point resistance measurements along
                      individual nanowires were performed with high spatial
                      resolution. Subsequently, three different samples, grown
                      with different temperature patterns, were investigated.
                      Detailed resistance profiles along several nanowires on each
                      sample were recorded. Three different regions were
                      identified in the resistance profiles: A high resistance
                      region at the nanowire bases (resulting from a suppressed
                      dopant incorporation), a transition region in the middle
                      with higher resistance and a low resistance region at the
                      nanowire tops, with a desired amount of dopant
                      incorporation.A calculation of the size of the depleted zone
                      revealed that nanowires were completely depleted in the high
                      resistance segments. Only in the low resistance region, the
                      current could ow through the conduction channel in the
                      nanowire core. In the high resistance region, the current
                      was owing through surface states. In the transition region,
                      the measured four-point IVs showed a non-linear
                      characteristic. At high biases, the current could transfer
                      from the surface to the better conducting core, while for
                      low biases, the current had to ow via the surface. During
                      the resistance profling, electron beam induced currents were
                      present in the transition region as well as around the
                      nanowire base on the substrate. A new customized
                      low-temperature ultra-high vacuum four-tip scanning
                      tunneling microscope capable of charge and magneto transport
                      measurements has been realized to carry out charge transport
                      measurements on semiconductor nanowires at liquid helium
                      temperature. In order to navigate the four STM tips to
                      desired positions, an SEM was used. SEM images of a test
                      sample were used to optimize the vibration isolation of the
                      experiment. A new nanopositioner (KoalaDrive) was developed
                      to approach the tips to the sample. It could be shown that
                      the KoalaDrive is capable of performing at low temperature
                      (5 K), in ultra-high vacuum with high precision. In images
                      taken with this STM, atomic steps on graphite as well as the
                      525 reconstruction of the Pt(100) surface could be resolved.
                      The low-temperature multi-tip scanning tunneling microscope
                      was used to contact single as-grown GaAs nanowires with one
                      tip. Charging of a part of the tip holders prevented SEM
                      images and conduction measurements with more tips.},
      cin          = {PGI-3},
      cid          = {I:(DE-Juel1)PGI-3-20110106},
      pnm          = {141 - Controlling Electron Charge-Based Phenomena
                      (POF3-141)},
      pid          = {G:(DE-HGF)POF3-141},
      typ          = {PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:hbz:82-rwth-2016-119506},
      doi          = {10.18154/RWTH-2016-11950},
      url          = {https://juser.fz-juelich.de/record/829125},
}