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 (>cm²), coupled bilayer graphene on SiO₂/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