Direct writing of calcium phosphate/graphite nanocomposite film using laser induced graphitization of polyimides

Abstract

We report the direct writing technique of synthesizing calcium phosphate/graphite nanocomposite using laser-induced polyimide (PI) film graphitization. Two forms of nano calcium phosphate were prepared via a mechanochemical processing technique using eggshells, calcium oxide powders and diammonium hydrogen phosphate (DHP). The processed powders were characterized using fourier transform infrared (FTIR) spectroscopy. FTIR results demonstrates that both CaO and eggshell transitions through a phase change when the material is synthesized with DHP. New C=O peak and ratio change change between Calcium carbonate and phosphate was observed by increasing the mechanochemical processing time. Calcium phosphate/graphite nanocomposites were synthesized by laser irradiation of calcium phosphate-covered polyimide surfaces. The chemical structure of the synthesized nanocomposite surfaces was characterized using Ramam spectroscopy. The surface morphology and chemical composition were imaged using SEM and EDS mapping. Four electrode resistance measurements were used to determine the surface electrical conductivity. Raman spectroscopy reveals that nanocomposite that were irradiated multiple time had a lower ID/IG ratio. Eggshell CaP based laser induced graphite (LIG) had an ID/IG ratio of 0.65 during the first time it was irradiated and 0.38 when the film was irradiated five times. Similarly, CaOCaP LIG also had a higher ID/IG ratio of 0.55 during the first layer and 0.42 on the 5th layer. Furthermore, C-O, C=O stretch modes and various 〖PO〗_4 groups were found on both variant of calcium phosphate/graphite nanocomposite. SEM results exhibited novel nuclei structures on the surface that resemble a hierarchical porous network and EDS mapping was able to illustrate Calicum and Phosphate was well synthesized while the interconnecting tubes were a mixture of Graphite, Calcium and phosphate. Sheet resistance of LIG, CaOCaP LIG, and EggCaP LIG had a sheet resistance of 103Ω∎, 85Ω∎, 54Ω∎ respectively. This technique is advantageous for the manufacturing of biosensors and bioelectronics due to the straightforward one-step direct writing process and the enhanced cell adhesion properties of the rough surface.