35 research outputs found
Detecting swift heavy ion irradiation effects with graphene
In this paper we show how single layer graphene can be utilized to study
swift heavy ion (SHI) modifications on various substrates. The samples were
prepared by mechanical exfoliation of bulk graphite onto SrTiO, NaCl and
Si(111), respectively. SHI irradiations were performed under glancing angles of
incidence and the samples were analysed by means of atomic force microscopy in
ambient conditions. We show that graphene can be used to check whether the
irradiation was successful or not, to determine the nominal ion fluence and to
locally mark SHI impacts. In case of samples prepared in situ, graphene is
shown to be able to catch material which would otherwise escape from the
surface.Comment: 10 pages, 3 figure
Manipulation of the graphene surface potential by ion irradiation
We show that the work function of exfoliated single layer graphene can be
modified by irradiation with swift (E_{kin}=92 MeV) heavy ions under glancing
angles of incidence. Upon ion impact individual surface tracks are created in
graphene on SiC. Due to the very localized energy deposition characteristic for
ions in this energy range, the surface area which is structurally altered is
limited to ~ 0.01 mum^2 per track. Kelvin probe force microscopy reveals that
those surface tracks consist of electronically modified material and that a few
tracks suffice to shift the surface potential of the whole single layer flake
by ~ 400 meV. Thus, the irradiation turns the initially n-doped graphene into
p-doped graphene with a hole density of 8.5 x 10^{12} holes/cm^2. This doping
effect persists even after heating the irradiated samples to 500{\deg}C.
Therefore, this charge transfer is not due to adsorbates but must instead be
attributed to implanted atoms. The method presented here opens up a new way to
efficiently manipulate the charge carrier concentration of graphene.Comment: 6 pages, 4 figure
Nanostructuring Graphene by Dense Electronic Excitation
The ability to manufacture tailored graphene nanostructures is a key factor
to fully exploit its enormous technological potential. We have investigated
nanostructures created in graphene by swift heavy ion induced folding. For our
experiments, single layers of graphene exfoliated on various substrates and
freestanding graphene have been irradiated and analyzed by atomic force and
high resolution transmission electron microscopy as well as Raman spectroscopy.
We show that the dense electronic excitation in the wake of the traversing ion
yields characteristic nanostructures each of which may be fabricated by
choosing the proper irradiation conditions. These nanostructures include unique
morphologies such as closed bilayer edges with a given chirality or nanopores
within supported as well as freestanding graphene. The length and orientation
of the nanopore, and thus of the associated closed bilayer edge, may be simply
controlled by the direction of the incoming ion beam. In freestanding graphene,
swift heavy ion irradiation induces extremely small openings, offering the
possibility to perforate graphene membranes in a controlled way.Comment: 16 pages, 5 figures, submitted to Nanotechnolog
Graphene on Si(111)7x7
We demonstrate that it is possible to mechanically exfoliate graphene under
ultra high vacuum conditions on the atomically well defined surface of single
crystalline silicon. The flakes are several hundred nanometers in lateral size
and their optical contrast is very faint in agreement with calculated data.
Single layer graphene is investigated by Raman mapping. The G and 2D peaks are
shifted and narrowed compared to undoped graphene. With spatially resolved
Kelvin probe measurements we show that this is due to p-type doping with hole
densities of n_h \simeq 6x10^{12} cm^{-2}. The in vacuo preparation technique
presented here should open up new possibilities to influence the properties of
graphene by introducing adsorbates in a controlled way.Comment: 8 pages, 7 figure
Graphene on Si(111)7×7
We demonstrate that it is possible to mechanically exfoliate graphene under ultrahigh vacuum conditions on the atomically well defined surface of single crystalline silicon. The flakes are several hundred nanometers in lateral size and their optical contrast is very faint, in agreement with calculated data. Single-layer graphene is investigated by Raman mapping. The graphene and 2D peaks are shifted and narrowed compared to undoped graphene. With spatially resolved Kelvin probe measurements we show that this is due to p-type doping with hole densities of nh ≃ 6 × 1012 cm−2. The in vacuo preparation technique presented here should open up new possibilities to influence the properties of graphene by introducing adsorbates in a controlled way.DFG, 130170629, SPP 1459: Graphen
Creating nanoporous graphene with swift heavy ions
This article has an erratum: DOI 10.1016/j.carbon.2017.03.065We examine swift heavy ion-induced defect production in suspended single layer graphene using Raman spectroscopy and a two temperature molecular dynamics model that couples the ionic and electronic subsystems. We show that an increase in the electronic stopping power of the ion results in an increase in the size of the pore-type defects, with a defect formation threshold at 1.22–1.48 keV/layer. We also report calculations of the specific electronic heat capacity of graphene with different chemical potentials and discuss the electronic thermal conductivity of graphene at high electronic temperatures, suggesting a value in the range of 1 Wm−1 K−1. These results indicate that swift heavy ions can create nanopores in graphene, and that their size can be tuned between 1 and 4 nm diameter by choosing a suitable stopping power.Peer reviewe
Phonon-assisted carrier transport through a lattice-mismatched interface
We showed the distinctive unconventional junction effect of MoS2 junctions: a lattice mismatched MoS2. It is unique to observe the difference originated from the atomic interrelation at the interface. The results revealed the dominant scattering source at the conventional naturally stepwise junction, while the misorientationally stacked layer exhibited effectively decoupled behavior and a significantly smaller junction resistance via phonon assist carrier. Therefore, our finding in this paper clearly shows the different mechanisms in carrier transport at both junction interface of MoS2