One-Step Laser-Guided Fabrication of 3D Self-Assembled Graphene Micro-Rolls

Abstract

Laser-induced graphene (LIG) has been systematically investigated and employed because of the spartan laser synthesis and functional three dimensional (3D) foam-like structures. However, thermally induced deformation during laser processing is generally undesirable and, therefore, strictly suppressed. This work introduces a novel laser-guided self-assembly approach integrated into the fabrication of LIG to generate multiscale 3D graphene foam structures in a single step. Leveraging the photothermal effects of laser ablation on polyimide films, we achieve concurrent LIG production and self-assembly, enabling the transformation of two dimensional films into 3D micro-rolls. The process is finely tuned through interface modification and optimized laser parameters, allowing precise control over the geometry of the resulting structures. Systematic investigations reveal that varying laser power and line spacing effectively adjust the diameters of the LIG micro-rolls. Characterization indicates that the LIG micro-rolls can be fabricated with very large curvature and limited internal space, enhancing the potential for microscale applications. Furthermore, our laser strategy facilitates the creation of symmetric, asymmetric, and double-tube micro-rolls, underscoring its design flexibility. This work highlights the potential of the laser-guided self-assembly strategy in graphene nanomaterials and miniaturized applications, which has been exemplarily verified through the LIG micro-roll supercapacitors.

Keywords: laser nanofabrication; laser-induced graphene; micro-roll; self-assembly; strain engineering.

Figure 1

Laser fabrication of LIG micro-rolls. (a) The preprocesses include dropping the methylcellulose solution onto the glass substrate, attaching the PI thin film, and squeezing the PI film with a scraper. (b) The laser writing from the backside of the glass, during which the LIG forms and rolls up. (c) Two captures showing a real LIG microroll during laser scribing. Scale bar, 1 mm. (d) A fabricated LIG microroll array. Scale bar, 1 mm. (e) A PI thin film with many LIG micro-rolls. Scale bar, 2 mm.

Figure 2

Nano/microscale structures on LIG micro-rolls. (a) A TEM image of a LIG flake edge (I), and a STEM image of the grain boundaries. Scale bar, 5 nm. (b) A TEM image of the porous structures on a LIG flake, and the corresponding mapping results showing the elements C, Si, and Na. Scale bar, 100 nm. (c) A TEM image of a curved LIG flake and the corresponding mapping results showing the elements C, Si, and Na. Scale bar, 50 nm. (d) A SEM image of a LIG microroll (I) and its amplified area (II). Scale bar, 100 μm. (e) The flake structure on the LIG microroll surface (I) and the corresponding substrate surface (II). Scale bar, 10 μm. (f) The smooth structure on the LIG microroll surface (I), the tilted view of the smooth structure (55°) (II), and the corresponding substrate surface (III). Scale bar, 10 μm. (g) The line structure on the LIG microroll surface (I), the tilted view of the smooth structure (55°) (II), and the corresponding substrate surface. Scale bar, 10 μm. (h) The atomic percentage of elements for all three types of structures. (i) The representative Raman curves for three types of structures. (j) The statistic of I_G/I_D values.

Figure 3

Adjustment of LIG microroll diameters with laser settings. (a–e) The micro- rolls with laser powers of 0.86, 0.96, 1.03, 1.13, and 1.24 W, respectively. (I) is the top view, and (II) is the amplified figure of (I). (III) is the tilted view (55°), and (IV) shows one end for every microroll. (V) is the micro/submicron-structures for LIG micro-rolls. (f) The statistic of LIG microroll diameters under different laser powers. (g) The representative Raman curves for LIG micro-rolls under different laser powers. (h) The statistic of I_G/I_D values under different laser powers. (i–m) The micro-rolls with laser line spacing of 6, 5, 4, 3, and 2 μm, respectively. (I) is the top view, and (II) is the amplified figure of (I). (III) is the tilted view (55°), and (IV) shows one end for every microroll. (V) is the micro/submicron-structures for LIG micro-rolls. (n) The statistic of LIG microroll diameters under different laser line spacings. (o) The representative Raman curves for LIG micro-rolls under different laser line spacings. (p) The statistic of I_G/I_D values under different laser line spacings. Scale bar, 100 μm.

Figure 4

Control of rolling directions with laser scanning pathways. (a, b) The illustration of laser scanning pathways to make a rectangular thin film roll from the long sides and short sides (I) and real LIG micro-rolls (II). (c, d) The illustration of laser scanning pathways to make a semicircular thin film rolling from the two different directions (I) and real LIG micro-rolls (II). (e) The illustration of laser scanning pathways to make two rectangular thin films roll up (I), and real LIG double tube construction (II). (f) The illustration of laser scanning pathways to make two triangular thin films roll up (I), and real LIG double tube construction (II). (g, h) The illustration of laser scanning pathways to make asymmetric thin films roll up (I), and real LIG asymmetric micro-rolls (II). These red lines indicate the laser scanning paths and directions. These white dashed lines and white arrows indicate the boundaries of patterned films and rolling orientations. Scale bar (a–h), 1 mm.

Figure 5

Supercapacitor application benefits from the 3D structures of the proposed LIG micro-rolls. (a) The fabrication process for the 3D LIG-PI-LIG structure based on laser manufacturing. (b) Schematic diagram of LIG-MRSCs. (c–e) SEM images of the overall device, PI gap, and LIG electrode. Scale bar (c), 1 mm. Scale bar (d, e) 200 μm. (f–h) CV curves of LIG-MRSCs with different gaps of 86, 120, and 153 μm across scan rates ranging from 20 to 500 mV s^–1. (i–k) GCD curves of LIG-MRSCs with different gaps of 86, 120, and 153 μm across current densities ranging from 0.2 to 5 mA cm^–2. (l) Areal capacitances of LIG-MRSCs gained from (f–h) in comparison to LIG-PPCs with a gap of 153 μm at the same CV scan rates. (m) Areal capacitances of LIG-MRSCs gained from (i–k) in comparison to LIG-PPCs with a gap of 153 μm at the same GCD current densities. (n) The cycling stability of the LIG-MRSC with a gap of 86 μm at the current density of 1 mA cm^–2 during the 1000 GCD cycles, containing the GCD curves for cycles 1–4, 498–501, 997–1000.