3 research outputs found
Photoresponse of an Electrically Tunable Ambipolar Graphene Infrared Thermocouple
We explore the photoresponse of an
ambipolar graphene infrared
thermocouple at photon energies close to or below monolayer grapheneās
optical phonon energy and electrostatically accessible Fermi energy
levels. The ambipolar graphene infrared thermocouple consists of monolayer
graphene supported by an infrared absorbing material, controlled by
two independent electrostatic gates embedded below the absorber. Using
a scanning infrared laser microscope, we characterize these devices
as a function of carrier type and carrier density difference controlled
at the junction between the two electrostatic gates. On the basis
of these measurements, conducted at both mid- and near-infrared wavelengths,
the primary detection mechanism can be modeled as a thermoelectric
response. By studying the effect of different infrared absorbers,
we determine that the optical absorption and thermal conduction of
the substrate play the dominant role in the measured photoresponse
of our devices. These experiments indicate a path toward hybrid graphene
thermal detectors for sensing applications such as thermography and
chemical spectroscopy
Asymmetric Growth of Bilayer Graphene on Copper Enclosures Using Low-Pressure Chemical Vapor Deposition
In this work, we investigated the growth mechanisms of bilayer graphene on the outside surface of Cu enclosures at low pressures. We observed that the asymmetric growth environment of a Cu enclosure can yield a much higher (up to 100%) bilayer coverage on the outside surface as compared to the bilayer growth on a flat Cu foil, where both sides are exposed to the same growth environment. By simultaneously examining the graphene films grown on both the outside and inside surfaces of the Cu enclosure, we find that carbon can diffuse from the inside surface to the outside <i>via</i> exposed copper regions on the inside surface. The kinetics of this process are examined by coupling the asymmetric growth between the two surfaces through a carbon diffusion model. Finally, using these results, we show that the coverage of bilayer graphene can be tuned simply by changing the thickness of the Cu foil, further confirming our model of carbon delivery through the Cu foil
Graphene-Based Thermopile for Thermal Imaging Applications
In
this work, we leverage grapheneās unique tunable Seebeck coefficient
for the demonstration of a graphene-based thermal imaging system.
By integrating graphene based photothermo-electric detectors with
micromachined silicon nitride membranes, we are able to achieve room
temperature responsivities on the order of ā¼7ā9 V/W
(at Ī» = 10.6 Ī¼m), with a time constant of ā¼23 ms.
The large responsivities, due to the combination of thermal isolation
and broadband infrared absorption from the underlying SiN membrane,
have enabled detection as well as stand-off imaging of an incoherent
blackbody target (300ā500 K). By comparing the fundamental
achievable performance of these graphene-based thermopiles with standard
thermocouple materials, we extrapolate that grapheneās high
carrier mobility can enable improved performances with respect to
two main figures of merit for infrared detectors: detectivity (>8
Ć 10<sup>8</sup> cm Hz<sup>1/2</sup> W<sup>ā1</sup>) and
noise equivalent temperature difference (<100 mK). Furthermore,
even average graphene carrier mobility (<1000 cm<sup>2</sup> V<sup>ā1</sup> s<sup>ā1</sup>) is still sufficient to detect
the emitted thermal radiation from a human target