7 research outputs found
Ripple Texturing of Suspended Graphene Atomic Membranes
Graphene is the nature's thinnest elastic membrane, with exceptional
mechanical and electrical properties. We report the direct observation and
creation of one-dimensional (1D) and 2D periodic ripples in suspended graphene
sheets, using spontaneously and thermally induced longitudinal strains on
patterned substrates, with control over their orientations and wavelengths. We
also provide the first measurement of graphene's thermal expansion coefficient,
which is anomalously large and negative, ~ -7x10^-6 K^-1 at 300K. Our work
enables novel strain-based engineering of graphene devices.Comment: 15 pages, 4 figure
A photon thermal diode.
A thermal diode is a two-terminal nonlinear device that rectifies energy carriers (for example, photons, phonons and electrons) in the thermal domain, the heat transfer analogue to the familiar electrical diode. Effective thermal rectifiers could have an impact on diverse applications ranging from heat engines to refrigeration, thermal regulation of buildings and thermal logic. However, experimental demonstrations have lagged far behind theoretical proposals. Here we present the first experimental results for a photon thermal diode. The device is based on asymmetric scattering of ballistic energy carriers by pyramidal reflectors. Recent theoretical work has predicted that this ballistic mechanism also requires a nonlinearity in order to yield asymmetric thermal transport, a requirement of all thermal diodes arising from the second Law of Thermodynamics, and realized here using an 'inelastic thermal collimator' element. Experiments confirm both effects: with pyramids and collimator the thermal rectification is 10.9 Ā± 0.8%, while without the collimator no rectification is detectable (<0.3%)
Retraction: A photon thermal diode.
This corrects the article DOI: 10.1038/ncomms6446
In Situ Observation of Electrostatic and Thermal Manipulation of Suspended Graphene Membranes
Graphene is natureās thinnest elastic membrane,
and its
morphology has important impacts on its electrical, mechanical, and
electromechanical properties. Here we report manipulation of the morphology
of suspended graphene via electrostatic and thermal control. By measuring
the out-of-plane deflection as a function of applied gate voltage
and number of layers, we show that graphene adopts a parabolic profile
at large gate voltages with inhomogeneous distribution of charge density
and strain. Unclamped graphene sheets slide into the trench under
tension; for doubly clamped devices, the results are well-accounted
for by membrane deflection with effective Youngās modulus <i><i>E</i> = </i>1.1 TPa. Upon cooling to 100 K, we
observe buckling-induced ripples in the central portion and large
upward buckling of the free edges, which arises from grapheneās
large negative thermal expansion coefficient