Graphene-protein bioelectronic devices with wavelength-dependent photoresponse

We implemented a nanoelectronic interface between graphene field effect transistors (FETs) and soluble proteins. This enables production of bioelectronic devices that combine functionalities of the biomolecular and inorganic components. The method serves to link polyhistidine-tagged proteins to graphene FETs using the tag itself. Atomic Force Microscopy and Raman spectroscopy provide structural understanding of the bio/nano hybrid; current-gate voltage measurements are used to elucidate the electronic properties. As an example application, we functionalize graphene FETs with fluorescent proteins to yield hybrids that respond to light at wavelengths defined by the optical absorption spectrum of the proteinComment: 10 pages, 3 figures; To appear in Applied Physics Letter

Correlating atomic structure and transport in single-nanometer scale graphene devices

Graphene nanoribbons (GNRs) are promising candidates for next-generation integrated circuit (IC) components, a fact that motivated the exploration of the relationship between atomic structure and transport in graphene patterned at IC-relevant length scales (\u3c10 nm). We first demonstrated superior low- and high-field transport in heterostructures of chemical vapor deposited graphene and hexagonal boron nitride, presenting a scalable methodology for high-quality graphene device integration. To investigate IC-relevance, we introduced a set of novel patterning techniques used to fabricate freestanding GNR devices to widths as small as 0.7 nm, concurrent with simultaneous high-resolution imaging and electrical transport characterization, all conducted within an aberration-corrected transmission electron microscope. We found that sub-10 nm GNRs were inherently disordered and semi-amorphous immediately after patterning. Current-induced Joule heat motivated the structural recrystallization process, resulting in faceted, highly crystalline GNRs with atomically sharp edges. Intrinsic conductance doubled to roughly 2.7e2/h after the recrystallization process, where e is the electron charge and h is Plank\u27s constant, despite an almost three times reduction in device width, attributed in part to the enhanced carrier transport from the higher structural crystallinity. Current annealing enabled the controlled fabrication of crystalline mono- and few-layer GNR devices. We found that the intrinsic conductance of sub-10 nm ribbons scaled with width as G(w) ≈ 0.75 ( e2/h)w[nm] for few-layer GNRs, where w is the width (measured in nm), while monolayer GNRs were roughly five times less conductive. Few-layer GNRs consistently formed bonded-bilayers and were robust structures that sustained currents in excess of 1.5 μA per carbon bond across a 5 atom-wide ribbon. Nanosculpted, crystalline monolayer GNRs exhibited armchair-terminated edges after current annealing, presenting a pathway for the controlled fabrication of semiconducting GNRs with known edge geometry. A third terminal was introduced to allow for in situ modulation of the chemical potential. An electrically isolated graphene electrode was patterned to be in close proximity to sub-10 nm GNR devices, acting as a local side-gate. We found that gating efficiency increased for narrower channels, attributed to the greater field coupling between the GNR and gate. The methodology presented here offers a unique platform to study the interplay between the atomic structure and three-terminal transport properties of single-nanometer scale GNR devices

Correlating atomic structure and transport in single-nanometer scale graphene devices

Graphene nanoribbons (GNRs) are promising candidates for next-generation integrated circuit (IC) components, a fact that motivated the exploration of the relationship between atomic structure and transport in graphene patterned at IC-relevant length scales (\u3c10 nm). We first demonstrated superior low- and high-field transport in heterostructures of chemical vapor deposited graphene and hexagonal boron nitride, presenting a scalable methodology for high-quality graphene device integration. To investigate IC-relevance, we introduced a set of novel patterning techniques used to fabricate freestanding GNR devices to widths as small as 0.7 nm, concurrent with simultaneous high-resolution imaging and electrical transport characterization, all conducted within an aberration-corrected transmission electron microscope. We found that sub-10 nm GNRs were inherently disordered and semi-amorphous immediately after patterning. Current-induced Joule heat motivated the structural recrystallization process, resulting in faceted, highly crystalline GNRs with atomically sharp edges. Intrinsic conductance doubled to roughly 2.7e2/h after the recrystallization process, where e is the electron charge and h is Plank\u27s constant, despite an almost three times reduction in device width, attributed in part to the enhanced carrier transport from the higher structural crystallinity. Current annealing enabled the controlled fabrication of crystalline mono- and few-layer GNR devices. We found that the intrinsic conductance of sub-10 nm ribbons scaled with width as G(w) ≈ 0.75 ( e2/h)w[nm] for few-layer GNRs, where w is the width (measured in nm), while monolayer GNRs were roughly five times less conductive. Few-layer GNRs consistently formed bonded-bilayers and were robust structures that sustained currents in excess of 1.5 μA per carbon bond across a 5 atom-wide ribbon. Nanosculpted, crystalline monolayer GNRs exhibited armchair-terminated edges after current annealing, presenting a pathway for the controlled fabrication of semiconducting GNRs with known edge geometry. A third terminal was introduced to allow for in situ modulation of the chemical potential. An electrically isolated graphene electrode was patterned to be in close proximity to sub-10 nm GNR devices, acting as a local side-gate. We found that gating efficiency increased for narrower channels, attributed to the greater field coupling between the GNR and gate. The methodology presented here offers a unique platform to study the interplay between the atomic structure and three-terminal transport properties of single-nanometer scale GNR devices

Electronic Transport of Recrystallized Freestanding Graphene Nanoribbons

The use of graphene and other two-dimensional materials in next-generation electronics is hampered by the significant damage caused by conventional lithographic processing techniques employed in device fabrication. To reduce the density of defects and increase mobility, Joule heating is often used since it facilitates lattice reconstruction and promotes self-repair. Despite its importance, an atomistic understanding of the structural and electronic enhancements in graphene devices enabled by current annealing is still lacking. To provide a deeper understanding of these mechanisms, atomic recrystallization and electronic transport in graphene nanoribbon (GNR) devices are investigated using a combination of experimental and theoretical methods. GNR devices with widths below 10 nm are defined and electrically measured <i>in situ</i> within the sample chamber of an aberration-corrected transmission electron microscope. Immediately after patterning, we observe few-layer polycrystalline GNRs with irregular sp²-bonded edges. Continued structural recrystallization toward a sharp, faceted edge is promoted by increasing application of Joule heat. Monte Carlo-based annealing simulations reveal that this is a result of concentrated local currents at lattice defects, which in turn promotes restructuring of unfavorable edge structures toward an atomically sharp state. We establish that intrinsic conductance doubles to 2.7 <i>e</i>²/<i>h</i> during the recrystallization process following an almost 3-fold reduction in device width, which is attributed to improved device crystallinity. In addition to the observation of consistent edge bonding in patterned GNRs, we further motivate the use of bonded bilayer GNRs for future nanoelectronic components by demonstrating how electronic structure can be tailored by an appropriate modification of the relative twist angle of the bonded bilayer

Continuous Growth of Hexagonal Graphene and Boron Nitride In-Plane Heterostructures by Atmospheric Pressure Chemical Vapor Deposition

Graphene–boron nitride monolayer heterostructures contain adjacent electrically active and insulating regions in a continuous, single-atom thick layer. To date structures were grown at low pressure, resulting in irregular shapes and edge direction, so studies of the graphene–boron nitride interface were restricted to the microscopy of nanodomains. Here we report templated growth of single crystalline hexagonal boron nitride directly from the oriented edge of hexagonal graphene flakes by atmospheric pressure chemical vapor deposition, and physical property measurements that inform the design of in-plane hybrid electronics. Ribbons of boron nitride monolayer were grown from the edge of a graphene template and inherited its crystallographic orientation. The relative sharpness of the interface was tuned through control of growth conditions. Frequent tearing at the graphene–boron nitride interface was observed, so density functional theory was used to determine that the nitrogen-terminated interface was prone to instability during cool down. The electronic functionality of monolayer heterostructures was demonstrated through fabrication of field effect transistors with boron nitride as an in-plane gate dielectric

Correlating Atomic Structure and Transport in Suspended Graphene Nanoribbons

Graphene nanoribbons (GNRs) are promising candidates for next generation integrated circuit (IC) components; this fact motivates exploration of the relationship between crystallographic structure and transport of graphene patterned at IC-relevant length scales (<10 nm). We report on the controlled fabrication of pristine, freestanding GNRs with widths as small as 0.7 nm, paired with simultaneous lattice-resolution imaging and electrical transport characterization, all conducted within an aberration-corrected transmission electron microscope. Few-layer GNRs very frequently formed bonded-bilayers and were remarkably robust, sustaining currents in excess of 1.5 μA per carbon bond across a 5 atom-wide ribbon. We found that the intrinsic conductance of a sub-10 nm bonded bilayer GNR scaled with width as <i>G</i>_BL(<i>w</i>) ≈ 3/4­(<i>e</i>²<i>/h</i>)<i>w</i>, where <i>w</i> is the width in nanometers, while a monolayer GNR was roughly five times less conductive. Nanosculpted, crystalline monolayer GNRs exhibited armchair-terminated edges after current annealing, presenting a pathway for the controlled fabrication of semiconducting GNRs with known edge geometry. Finally, we report on simulations of quantum transport in GNRs that are in qualitative agreement with the observations