Laser Engineering Nanocarbon Phases within Diamond for Science and Electronics.

Diamond, as the densest allotrope of carbon, displays a range of exemplary material properties that are attractive from a device perspective. Despite diamond displaying high carbon-carbon bond strength, ultrashort (femtosecond) pulse laser radiation can provide sufficient energy for highly localized internal breakdown of the diamond lattice. The less-dense carbon structures generated on lattice breakdown are subject to significant pressure from the surrounding diamond matrix, leading to highly unusual formation conditions. By tailoring the laser dose delivered to the diamond, it is shown that it is possible to create continuously modified internal tracks with varying electrical conduction properties. In addition to the widely reported conducting tracks, conditions leading to semiconducting and insulating written tracks have been identified. High-resolution transmission electron microscopy (HRTEM) is used to visualize the structural transformations taking place and provide insight into the different conduction regimes. The HRTEM reveals a highly diverse range of nanocarbon structures are generated by the laser irradiation, including many signatures for different so-called diaphite complexes, which have been seen in meteorite samples and seem to mediate the laser-induced breakdown of the diamond. This work offers insight into possible formation methods for the diamond and related nanocarbon phases found in meteorites.

Self-Folded Three-Dimensional Graphene with a Tunable Shape and Conductivity.

Three-dimensional (3D) graphene architectures are of great interest as applications in flexible electronics and biointerfaces. In this study, we demonstrate the facile formation of predetermined 3D polymeric microstructures simply by transferring monolayer graphene. The graphene adheres to the surface of polymeric films via noncovalent π-π stacking bonding and induces a sloped internal strain, leading to the self-rolling of 3D microscale architectures. Micropatterns and varied thicknesses of the 2D films prior to the self-rolling allows for control over the resulting 3D geometries. The strain then present on the hexagonal unit cell of the graphene produces a nonlinear electrical conductivity across the device. The driving force behind the self-folding process arises from the reconfiguration of the molecules within the crystalline materials. We believe that this effective and versatile way of realizing a 3D graphene structure is potentially applicable to alternative 2D layered materials as well as other flexible polymeric templates.

Cell Assembly in Self-foldable Multi-layered Soft Micro-rolls.

Multi-layered thin films with heterogeneous mechanical properties can be spontaneously transformed to realise various three-dimensional (3D) geometries. Here, we describe micro-patterned all-polymer films called micro-rolls that we use for encapsulating, manipulating, and observing adherent cells in vitro. The micro-rolls are formed of twin-layered films consisting of two polymers with different levels of mechanical stiffness; therefore they can be fabricated by using the strain engineering and a self-folding rolling process. By controlling the strain of the films geometrically, we can achieve 3D tubular architectures with controllable diameters. Integration with a batch release of sacrificial hydrogel layers provides a high yield and the biocompatibility of the micro-rolls with any length in the release process without cytotoxicity. Thus, the multiple cells can be wrapped in individual micro-rolls and artificially reconstructed into hollow or fibre-shaped cellular 3D constructs that possess the intrinsic morphologies and functions of living tissues. This system can potentially provide 3D bio-interfaces such as those needed for reconstruction and assembly of functional tissues and implantable tissue grafts.