5 research outputs found
Electronic Hybridization of Large-Area Stacked Graphene Films
Direct, tunable coupling between individually assembled graphene layers is a next step toward designer two-dimensional (2D) crystal systems, with relevance for fundamental studies and technological applications. Here we describe the fabrication and characterization of large-area (>cm<sup>2</sup>), coupled bilayer graphene on SiO<sub>2</sub>/Si substrates. Stacking two graphene films leads to direct electronic interactions between layers, where the resulting film properties are determined by the local twist angle. Polycrystalline bilayer films have a “stained-glass window” appearance explained by the emergence of a narrow absorption band in the visible spectrum that depends on twist angle. Direct measurement of layer orientation <i>via</i> electron diffraction, together with Raman and optical spectroscopy, confirms the persistence of clean interfaces over large areas. Finally, we demonstrate that interlayer coupling can be reversibly turned off through chemical modification, enabling optical-based chemical detection schemes. Together, these results suggest that 2D crystals can be individually assembled to form electronically coupled systems suitable for large-scale applications
Room-Temperature Spin Filtering in Metallic Ferromagnet–Multilayer Graphene–Ferromagnet Junctions
We
report room-temperature negative magnetoresistance in ferromagnet–graphene–ferromagnet
(FM|Gr|FM) junctions with minority spin polarization exceeding 80%,
consistent with predictions of strong minority spin filtering. We
fabricated arrays of such junctions <i>via</i> chemical
vapor deposition of multilayer graphene on lattice-matched single-crystal
NiFe(111) films and standard photolithographic patterning and etching
techniques. The junctions exhibit metallic transport behavior, low
resistance, and the negative magnetoresistance characteristic of a
minority spin filter interface throughout the temperature range 10
to 300 K. We develop a device model to incorporate the predicted spin
filtering by explicitly treating a metallic minority spin channel
with spin current conversion and a tunnel barrier majority spin channel
and extract spin polarization of at least 80% in the graphene layer
in our structures. The junctions also show antiferromagnetic coupling,
consistent with several recent predictions. The methods and findings
are relevant to fast-readout low-power magnetic random access memory
technology, spin logic devices, and low-power magnetic field sensors
Engineering Graphene Mechanical Systems
We report a method to introduce direct bonding between
graphene
platelets that enables the transformation of a multilayer chemically
modified graphene (CMG) film from a “paper mache-like”
structure into a stiff, high strength material. On the basis of chemical/defect
manipulation and recrystallization, this technique allows wide-range
engineering of mechanical properties (stiffness, strength, density,
and built-in stress) in ultrathin CMG films. A dramatic increase in
the Young’s modulus (up to 800 GPa) and enhanced strength (sustainable
stress ≥1 GPa) due to cross-linking, in combination with high
tensile stress, produced high-performance (quality factor of 31 000
at room temperature) radio frequency nanomechanical resonators. The
ability to fine-tune intraplatelet mechanical properties through chemical
modification and to locally activate direct carbon–carbon bonding
within carbon-based nanomaterials will transform these systems into
true “materials-by-design” for nanomechanics
Engineering Graphene Mechanical Systems
We report a method to introduce direct bonding between
graphene
platelets that enables the transformation of a multilayer chemically
modified graphene (CMG) film from a “paper mache-like”
structure into a stiff, high strength material. On the basis of chemical/defect
manipulation and recrystallization, this technique allows wide-range
engineering of mechanical properties (stiffness, strength, density,
and built-in stress) in ultrathin CMG films. A dramatic increase in
the Young’s modulus (up to 800 GPa) and enhanced strength (sustainable
stress ≥1 GPa) due to cross-linking, in combination with high
tensile stress, produced high-performance (quality factor of 31 000
at room temperature) radio frequency nanomechanical resonators. The
ability to fine-tune intraplatelet mechanical properties through chemical
modification and to locally activate direct carbon–carbon bonding
within carbon-based nanomaterials will transform these systems into
true “materials-by-design” for nanomechanics
Engineering Graphene Mechanical Systems
We report a method to introduce direct bonding between
graphene
platelets that enables the transformation of a multilayer chemically
modified graphene (CMG) film from a “paper mache-like”
structure into a stiff, high strength material. On the basis of chemical/defect
manipulation and recrystallization, this technique allows wide-range
engineering of mechanical properties (stiffness, strength, density,
and built-in stress) in ultrathin CMG films. A dramatic increase in
the Young’s modulus (up to 800 GPa) and enhanced strength (sustainable
stress ≥1 GPa) due to cross-linking, in combination with high
tensile stress, produced high-performance (quality factor of 31 000
at room temperature) radio frequency nanomechanical resonators. The
ability to fine-tune intraplatelet mechanical properties through chemical
modification and to locally activate direct carbon–carbon bonding
within carbon-based nanomaterials will transform these systems into
true “materials-by-design” for nanomechanics