Direct laser writing carbonization based on internal-reflection setup for fabricating shape-tailorable and sealed in-situ carbon features

The recently-developed direct laser writing carbonization method based on an internal-reflection setup (IR-DLWc) reported in our works is a novel and efficient approach that enables a controllable fabrication of carbon features sealed in the interior of polyimide film in-situ, which may lead to the flexible and versatile preparation of carbon-based functional devices and wearable electronics. To fully exploit this useful method, in the present study, we combine the experimental and modeling/simulation studies to elucidate the unique photothermal and thermomechanical processes and to reveal the processing-structure relationship of this novel technique. The processing conditions that allow for the sealing of the carbon dot created by IR-DLWc were identified; and the empirical relation between the size of the carbon dots and the laser processing conditions were established. Moreover, it was found that the thermal–mechanical stress induced by the trapped pyrolysis gas is able to deform the PI matrix surrounding a carbon dot and to cause polymer chain reorientation. This phenomenon was further utilized to tailor the shape of carbon features for readily fabricating highly-sensitive piezoresistive sensors, which has been successfully demonstrated for the underwater use in mapping the ultrasound field.