Graphene Origami Research Articles

Position effects of the graphene-origami actuators on the rotation of a CNT nanomotor.

This study designs a carbon nanotube (CNT)-based rotary nanomotor actuated by four graphene origami (G-ori) drivers with adjustable positions. When the drivers' tips have different contact states with the CNT rotor at a finite temperature, the rotor has different rotational states due to different interaction strength between the rotor and the tips. Using the molecular dynamics simulation approach, we study the effects of the drivers' position, such as the gaps between the rotor and the drivers' tips and their layout angles. Numerical results indicate that both the stable rotational frequency (SRF) and the rotational direction change with the layout angles. In an interval from -40° to -25°, the SRF increases monotonously. There also exists an angle interval in which the G-ori drivers fail to actuate the rotor's rotation. The gap offset leads to different SRF of the same rotor. Hence, one can design a rotary nanomotor with controllable rotation, which is critical for its applications in a nanomachine.

Graphene origami structures with superflexibility and highly tunable auxeticity

The two-dimensional structure of graphene makes it difficult to realize flexibility and auxeticity (negative Poisson's ratio) in graphene-based structures. Using molecular dynamics simulations, we demonstrate for graphene origami structures effective tuning of both the flexibility and Poisson's ratio through the geometry, including the potential to combine superflexibility with a highly tunable negative Poisson's ratio in contrast to any existing graphene-based structure. Auxeticity even can be achieved under large applied strain, both tensile and compressive.

Unusual thermal properties of graphene origami crease: A molecular dynamics study

Graphene is a two-dimensional material that can be folded into diverse and yet interesting nanostructures like macro-scale paper origami. Folding of graphene not only makes different morphological configurations but also modifies their mechanical and thermal properties. Inspired by paper origami, herein we studied systemically the effects of creases, where sp2 to sp3 bond transformation occurs, on the thermal properties of graphene origami using molecular dynamics (MD) simulations. Our MD simulation results show that tensile strain reduces (not increases) the interfacial thermal resistance owing to the presence of the crease. This unusual phenomenon is explained by the micro-heat flux migration and stress distribution. Our findings on the graphene origami enable the design of the next-generation thermal management devices and flexible electronics with tuneable properties.

Graphene Origami with Highly Tunable Coefficient of Thermal Expansion.

The coefficient of thermal expansion, which measures the change in length, area, or volume of a material upon heating, is a fundamental parameter with great relevance for many applications. Although there are various routes to design materials with targeted coefficient of thermal expansion at the macroscale, no approaches exist to achieve a wide range of values in graphene-based structures. Here, we use molecular dynamics simulations to show that graphene origami structures obtained through pattern-based surface functionalization provide tunable coefficients of thermal expansion from large negative to large positive. We show that the mechanisms giving rise to this property are exclusive to graphene origami structures, emerging from a combination of surface functionalization, large out-of-plane thermal fluctuations, and the three-dimensional geometry of origami structures.

Crease-induced targeted cutting and folding of graphene origami

Graphene origami (G-ori) can possess unique mechanical properties and achieve some distinctive functionalization by engineering their configurations. However, it remains a tremendous challenge to modulate its formation and properties at the micro- and nano-scales. Herein, we systemically present the formation of G-ori activated by creased marks via molecular dynamics (MD) simulations. The pre-existing creased mark in graphene is created in a controlled way by transforming sp2 to sp3 bonds at the crease. Our results show that the presence of interlayer sp3 bonds at the crease can direct crack growth and hence pave a new way to tailor graphene sheets into specified pieces. The crease also guides the folding process of graphene into various geometric configurations. Sophisticated G-ori can be constructed by designing rational crease distribution on the graphene surface. Checking against the folding process of paper origami shows that the crease-induced targeted folding can be achieved at both nano- and macro-scales in exactly the same way. Our findings provide a simple and feasible method to construct graphene-based nano-devices by designing rational morphological configurations of G-ori.

Graphene origami at the tip of a microscope

Graphene origami at the tip of a microscope

Atomically precise, custom-design origami graphene nanostructures.

The construction of atomically precise carbon nanostructures holds promise for developing materials for scientific study and nanotechnology applications. Here, we show that graphene origami is an efficient way to convert graphene into atomically precise, complex nanostructures. By scanning tunneling microscope manipulation at low temperature, we repeatedly fold and unfold graphene nanoislands (GNIs) along an arbitrarily chosen direction. A bilayer graphene stack featuring a tunable twist angle and a tubular edge connection between the layers is formed. Folding single-crystal GNIs creates tubular edges with specified chirality and one-dimensional electronic features similar to those of carbon nanotubes, whereas folding bicrystal GNIs creates well-defined intramolecular junctions. Both origami structural models and electronic band structures are computed to complement analysis of the experimental results. The present atomically precise graphene origami provides a platform for constructing carbon nanostructures with engineered quantum properties and, ultimately, quantum machines.

Nanomechanical Unfolding of Self-Folded Graphene on Flat Substrate

We report the nanomechanical unfolding of individual self-folded graphene flakes on a flat substrate by using atomic force microscopy techniques. The nanomechanical measurements and molecular dynamics simulations reveal the detailed unfolding process that turns a z-shaped self-folded graphene segment into a flat membrane. A reversible sliding phenomenon in the adhered graphene region during the unfolding process is observed. The findings are useful to better understand the reversible folding properties of graphene and in pursuit of reversible and morphing graphene origami.

Nanomechanical z-shape folding of graphene on flat substrate

Graphene folding is an essential process in the design and manufacturing of graphene origami. Here we report the nanomechanical z-shape (accordion) folding of single graphene sheets on flat substrates by using atomic force microscopy techniques. The quantitative nanomechanical measurements in conjunction with nonlinear mechanics modeling and molecular dynamics simulations reveal that a reversible out-of-plane buckling delamination of graphene occurs in its early-stage folding process, which enables graphene to deform into a stable self-folded z-shape conformation. The research findings are useful to the study of active and controllable folding of graphene and in the pursuit of graphene origami with intricate geometries.

Hydrogenation-Assisted Graphene Origami and Its Application in Programmable Molecular Mass Uptake, Storage, and Release

The malleable nature of atomically thin graphene makes it a potential candidate material for nanoscale origami, a promising bottom-up nanomanufacturing approach to fabricating nanobuilding blocks of desirable shapes. The success of graphene origami hinges upon precise and facile control of graphene morphology, which still remains as a significant challenge. Inspired by recent progresses on functionalization and patterning of graphene, we demonstrate hydrogenation-assisted graphene origami (HAGO), a feasible and robust approach to enabling the formation of unconventional carbon nanostructures, through systematic molecular dynamics simulations. A unique and desirable feature of HAGO-enabled nanostructures is the programmable tunability of their morphology via an external electric field. In particular, we demonstrate reversible opening and closing of a HAGO-enabled graphene nanocage, a mechanism that is crucial to achieve molecular mass uptake, storage, and release. HAGO holds promise to enable an array of carbon nanostructures of desirable functionalities by design. As an example, we demonstrate HAGO-enabled high-density hydrogen storage with a weighted percentage exceeding the ultimate goal of US Department of Energy.