No abstract

Laser-induced graphene (LIG) has received much attention since it enables simple and rapid synthesis of porous graphene. This work presents a robust direct-write LIG-based gas sensor, which senses gases based on thermal conductivity, similar to a katharometer sensor. The gas sensors are fabricated by lasing polyimide substrates with a 10.6 μm CO 2 laser to synthesize LIG. This enables the formation of flexible gas sensors which could be incorporated on a variety of surfaces. High surface area and thermal conductivity of the LIG results in rapid response times for all studied gases. The gas sensors are also embedded in cement to form a refractory composite material. These sensors are used to determine composition of various gas mixtures, such as N 2 and CO 2 , which are the most abundant gaseous species in flue gas. Thus, LIG based embeddable sensors could be incorporated in composites to enable electronically functional construction materials.

Triboelectric nanogenerators (TENGs) show exceptional promise for converting wasted mechanical energy into electrical energy. This study investigates the use of laser-induced graphene (LIG) composites as an exciting class of triboelectric materials in TENGs. Infrared laser irradiation is used to convert the surfaces of the two carbon sources, polyimide (PI) and cork, into LIG. This gives the bilayer composite films the high conductivity associated with LIG and the triboelectric properties of the carbon source. A LIG/PI composite is used to fabricate TENGs based on conductor-to-dielectric and metal-free dielectric-to-dielectric device geometries with open-circuit voltages >3.5 kV and peak power >8 mW. Additionally, a single sheet of PI is converted to a metal-free foldable TENG. The LIG is also embedded within a PDMS matrix to form a single-electrode LIG/PDMS composite TENG. This single-electrode TENG is highly flexible and stretchable and was used to generate power from mechanical contact with skin. The LIG composites present a class of triboelectric materials that can be made from naturally occurring and synthetic carbon sources.

Focused electron beam induced deposition (FEBID) is one of the few techniques that enables direct-write synthesis of free-standing 3D nanostructures. While the fabrication of simple architectures such as vertical or curving nanowires has been achieved by simple trial and error, processing complex 3D structures is not tractable with this approach. In part, this is due to the dynamic interplay between electron-solid interactions and the transient spatial distribution of absorbed precursor molecules on the solid surface. Here, we demonstrate the ability to controllably deposit 3D lattice structures at the micro/nanoscale, which have received recent interest owing to superior mechanical and optical properties. A hybrid Monte Carlo-continuum simulation is briefly overviewed, and subsequently FEBID experiments and simulations are directly compared. Finally, a 3D computer-aided design (CAD) program is introduced, which generates the beam parameters necessary for FEBID by both simulation and experiment. Using this approach, we demonstrate the fabrication of various 3D lattice structures using Pt-, Au-, and W-based precursors.

Laser-induced graphene (LIG) is a multifunctional graphene foam that is commonly direct-written with an infrared laser into a carbon-based precursor material. Here, a visible 405 nm laser is used to directly convert polyimide into LIG. This enabled the formation of LIG with a spatial resolution of ∼12 μm and a thickness of <5 μm. The spatial resolution enabled by the relatively smaller focused spot size of the 405 nm laser represents a >60% reduction in LIG feature sizes reported in prior publications. This process occurs in situ in an SEM chamber, thus allowing direct observation of LIG formation. The reduced size of the LIG features enables the direct-write formation of flexible electronics that are not visible to the unaided eye. A humidity sensor is demonstrated which could detect human breath with a response time of 250 ms. With the growing interest in LIG for flexible electronics and sensors, finer features can greatly expand its utility.