1,159 research outputs found
LARCMACS: A TEX macro set for typesetting NASA reports
This LARCMACS user's manual describes the February 1988 version of LARCMACS, the TEX macro set used by the Technical Editing Branch (TEB) at NASA Langley Research Center. These macros were developed by the authors to facilitate the typesetting of NASA formal reports. They are also useful, however, for informal NASA reports and other technical documents such as meeting papers. LARCMACS are distributed by TEB for the convenience of the Langley TEX user community. LARCMACS contain macros for obtaining the standard double-column format for NASA reports, for typesetting tables in the ruled format traditional in NASA reports, and for typesetting difficult mathematical expressions. Each macro is described and numerous examples are included. Definitions of the LARCMACS macros are also included
CRIMINAL LAW—THE CRUCIBLE OF ADVERSARIAL TESTING: INEFFECTIVE ASSISTANCE OF COUNSEL AND UNAUTHORIZED CONCESSIONS OF CLIENT\u27S GUILT
Plasmon losses due to electron-phonon scattering: the case of graphene encapsulated in hexagonal Boron Nitride
Graphene sheets encapsulated between hexagonal Boron Nitride (hBN) slabs
display superb electronic properties due to very limited scattering from
extrinsic disorder sources such as Coulomb impurities and corrugations. Such
samples are therefore expected to be ideal platforms for highly-tunable
low-loss plasmonics in a wide spectral range. In this Article we present a
theory of collective electron density oscillations in a graphene sheet
encapsulated between two hBN semi-infinite slabs (hBN/G/hBN). Graphene plasmons
hybridize with hBN optical phonons forming hybrid plasmon-phonon (HPP) modes.
We focus on scattering of these modes against graphene's acoustic phonons and
hBN optical phonons, two sources of scattering that are expected to play a key
role in hBN/G/hBN stacks. We find that at room temperature the scattering
against graphene's acoustic phonons is the dominant limiting factor for
hBN/G/hBN stacks, yielding theoretical inverse damping ratios of hybrid
plasmon-phonon modes of the order of -, with a weak dependence on
carrier density and a strong dependence on illumination frequency. We confirm
that the plasmon lifetime is not directly correlated with the mobility: in
fact, it can be anti-correlated.Comment: 14 pages, 4 figure
Highly confined low-loss plasmons in graphene-boron nitride heterostructures
Graphene plasmons were predicted to possess ultra-strong field confinement
and very low damping at the same time, enabling new classes of devices for deep
subwavelength metamaterials, single-photon nonlinearities, extraordinarily
strong light-matter interactions and nano-optoelectronic switches. While all of
these great prospects require low damping, thus far strong plasmon damping was
observed, with both impurity scattering and many-body effects in graphene
proposed as possible explanations. With the advent of van der Waals
heterostructures, new methods have been developed to integrate graphene with
other atomically flat materials. In this letter we exploit near-field
microscopy to image propagating plasmons in high quality graphene encapsulated
between two films of hexagonal boron nitride (h-BN). We determine dispersion
and particularly plasmon damping in real space. We find unprecedented low
plasmon damping combined with strong field confinement, and identify the main
damping channels as intrinsic thermal phonons in the graphene and dielectric
losses in the h-BN. The observation and in-depth understanding of low plasmon
damping is the key for the development of graphene nano-photonic and
nano-optoelectronic devices
Tuning quantum non-local effects in graphene plasmonics
The response of an electron system to electromagnetic fields with sharp
spatial variations is strongly dependent on quantum electronic properties, even
in ambient conditions, but difficult to access experimentally. We use
propagating graphene plasmons, together with an engineered dielectric-metallic
environment, to probe the graphene electron liquid and unveil its detailed
electronic response at short wavelengths.The near-field imaging experiments
reveal a parameter-free match with the full theoretical quantum description of
the massless Dirac electron gas, in which we identify three types of quantum
effects as keys to understanding the experimental response of graphene to
short-ranged terahertz electric fields. The first type is of single-particle
nature and is related to shape deformations of the Fermi surface during a
plasmon oscillations. The second and third types are a many-body effect
controlled by the inertia and compressibility of the interacting electron
liquid in graphene. We demonstrate how, in principle, our experimental approach
can determine the full spatiotemporal response of an electron system.Comment: 8 pages, 4 figure
Electrical detection of hyperbolic phonon-polaritons in heterostructures of graphene and boron nitride
Light properties in the mid-infrared can be controlled at a deep
subwavelength scale using hyperbolic phonons-polaritons (HPPs) of hexagonal
boron nitride (h-BN). While propagating as waveguided modes HPPs can
concentrate the electric field in a chosen nano-volume. Such a behavior is at
the heart of many applications including subdiffraction imaging and sensing.
Here, we employ HPPs in heterostructures of h-BN and graphene as new
nano-optoelectronic platform by uniting the benefits of efficient hot-carrier
photoconversion in graphene and the hyperbolic nature of h-BN. We demonstrate
electrical detection of HPPs by guiding them towards a graphene pn-junction. We
shine a laser beam onto a gap in metal gates underneath the heterostructure,
where the light is converted into HPPs. The HPPs then propagate as confined
rays heating up the graphene leading to a strong photocurrent. This concept is
exploited to boost the external responsivity of mid-infrared photodetectors,
overcoming the limitation of graphene pn-junction detectors due to their small
active area and weak absorption. Moreover this type of detector exhibits
tunable frequency selectivity due to the HPPs, which combined with its high
responsivity paves the way for efficient high-resolution mid-infrared imaging
Near-field photocurrent nanoscopy on bare and encapsulated graphene
Opto-electronic devices utilizing graphene have already demonstrated unique
capabilities, which are much more difficult to realize with conventional
technologies. However, the requirements in terms of material quality and
uniformity are very demanding. A major roadblock towards high-performance
devices are the nanoscale variations of graphene properties, which strongly
impact the macroscopic device behaviour. Here, we present and apply
opto-electronic nanoscopy to measure locally both the optical and electronic
properties of graphene devices. This is achieved by combining scanning
near-field infrared nanoscopy with electrical device read-out, allowing
infrared photocurrent mapping at length scales of tens of nanometers. We apply
this technique to study the impact of edges and grain boundaries on spatial
carrier density profiles and local thermoelectric properties. Moreover, we show
that the technique can also be applied to encapsulated graphene/hexagonal boron
nitride (h-BN) devices, where we observe strong charge build-up near the edges,
and also address a device solution to this problem. The technique enables
nanoscale characterization for a broad range of common graphene devices without
the need of special device architectures or invasive graphene treatment
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