109 research outputs found
Efficient Auger scattering in Landau-quantized graphene
We present an analytical expression for the differential transmission of a delta-shaped light field in Landauquantized graphene. This enables a direct comparison of experimental spectra to theoretical calculations reflecting the carrier dynamics including all relevant scattering channels. In particular, the relation is used to provide evidence for strong Auger scattering in Landau-quantized graphene
The added value of autobiographical reflexivity with persuasive technology for professional identities of Social Work students: a randomized controlled trial
Ultra-large polymer-free suspended graphene films
Due to its extraordinary properties, suspended graphene is a critical element
in a wide range of applications. Preparation methods that preserve the unique
properties of graphene are therefore in high demand. To date, all protocols for
the production of large graphene films have relied on the application of a
polymer film to stabilize graphene during the transfer process. However, this
inevitably introduces contaminations that have proven to be extremely
difficult, if not impossible, to remove entirely. Here we report the
polymer-free fabrication of suspended films consisting of three graphene layers
spanning circular holes of 150 m diameter. We find a high fabrication
yield, very uniform properties of the freestanding graphene across all holes as
well across individual holes. A detailed analysis by confocal Raman and THz
spectroscopy reveals that the triple-layer samples exhibit structural and
electronic properties similar to those of monolayer graphene. We demonstrate
their usability as ion-electron converters in time-of-flight mass spectrometry
and related applications. They are two orders of magnitude thinner than
previous carbon foils typically used in these types of experiments, while still
being robust and exhibiting a sufficiently high electron yield. These results
are an important step towards replacing free-standing ultra-thin carbon films
or graphene from polymer-based transfers with much better defined and clean
graphene.Comment: 9 pagers, 5 figure
Slow Noncollinear Coulomb Scattering in the Vicinity of the Dirac Point in Graphene
The Coulomb scattering dynamics in graphene in energetic proximity to the Dirac point is investigated by polarization resolved pump-probe spectroscopy and microscopic theory. Collinear Coulomb scattering rapidly thermalizes the carrier distribution in k directions pointing radially away from the Dirac point. Our study reveals, however, that, in almost intrinsic graphene, full thermalization in all directions relying on noncollinear scattering is much slower. For low photon energies, carrier-optical-phonon processes are strongly suppressed and Coulomb mediated noncollinear scattering is remarkably slow, namely on a ps time scale. This effect is very promising for infrared and THz devices based on hot carrier effects
Strong transient magnetic fields induced by THz-driven plasmons in graphene disks
Strong circularly polarized excitation opens up the possibility to generate
and control effective magnetic fields in solid state systems, e.g., via the
optical inverse Faraday effect or the phonon inverse Faraday effect. While
these effects rely on material properties that can be tailored only to a
limited degree, plasmonic resonances can be fully controlled by choosing proper
dimensions and carrier concentrations. Plasmon resonances provide new degrees
of freedom that can be used to tune or enhance the light-induced magnetic field
in engineered metamaterials. Here we employ graphene disks to demonstrate
light-induced transient magnetic fields from a plasmonic circular current with
extremely high efficiency. The effective magnetic field at the plasmon
resonance frequency of the graphene disks (3.5 THz) is evidenced by a strong
(~1{\deg}) ultrafast Faraday rotation (~ 20 ps). In accordance with reference
measurements and simulations, we estimated the strength of the induced magnetic
field to be on the order of 0.7 T under a moderate pump fluence of about 440 nJ
cm-2
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