Oxide semiconductors are one of the key components for flexible and transparent electronics, but their use has been limited by the work function of contact materials. Carbon-based materials are strong candidates for flexible transparent electrodes, and nitrogen-doped carbon materials have been specifically investigated due to the controllability of their work function. Of the many methods to dop nitrogen, the pyrolysis of biomolecules is a particular focus since it is a simple, inexpensive process that yields a high atomic percent of nitrogen. Polydopamine (pDop), which is inspired by adhesive proteins in mussels, has been suggested for use as a precursor for pyrolysis, and the pyrolyzed pDop–Cu hybrid film shows the lowest resistivity (1.4 × 10−4 Ω cm) in pyrolyzed carbon so far, for which copper chelation is attributed to reduction in resistivity. The pyrolyzed film also shows a transparency of 84%, and it is stable in cyclic bending tests up to 105 cycles. The films are further applied to the source and drain of a field-effect transistor, and the devices achieve a high performance that is comparable to that from molybdenum contacted device, with the work function ranging from 4.51 to 4.31 eV.
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Pyrolysis gives rise to a structural change in the pDop– Cu film, which is supported by Figure 1b showing X-ray photoelectron spectroscopy (XPS) nitrogen 1s spectra. The only NH peak (399.68 eV) is observed in the pristine pDop–Cu film, while pyrrolyic N (400.98 eV) and pyridinic N (398.38 eV) are observed at pyrolyzed films. This means that nitrogen bonding changes into in-plane nitrogen bonding within the carbonaceous film. The atomic percent of nitrogen for the pristine and 600, 700 , and 800 °C pyrolyzed films are 6.6%, 5.5%, 4.4%, and 4.0%, respectively. Copper chelation is proved in the XPS results shown in Figure 1c. Both the pristine film and the pyrolyzed films have high copper (0) (932.58 eV) peaks and weak copper (II) (934.78 eV) peaks. Small ion satellite peaks (944.48 eV) which are proof of copper (II) are also observed. The intensity of the copper (II) shoulder peak decreases after pyrolysis, and this means that copper (II) is mostly reduced to copper (0) after pyrolysis. Conclusively, pyrolyzed pDop–Cu can be understood as a copper-and nitrogen-doped graphitic carbon. This graphitization is supported by the D and G peaks in the Raman spectra (Figure S2, Supporting Information).
This work was supported by Samsung Research Funding Center of Samsung Electronics under Project Number SRFC-MA1401-51.
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All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials