Annealing effect on the chemical structure of diamondlike carbon

The effect of annealing in an ultrahigh vacuum on the chemical structure of diamondlike carbon (DLC) was investigated using photoelectron spectroscopy, thermal desorption spectroscopy, electrical resistivity, and micro-Raman spectroscopy measurements. The line shapes of the $C1s$ photoelectron spectra depended on annealing temperature. The relative intensities of four chemical components in the spectra were quantitatively evaluated: $sp3$ carbon with carbon-carbon bonds (C–C $sp3$ carbon), $sp2$ carbon with carbon-carbon bonds (C–C $sp2$ carbon), $sp2$ carbon with hydrogen-carbon bonds (H–C $sp2$ carbon), and $sp3$ carbon with hydrogen-carbon bonds (H–C $sp3$ carbon). The variation of the ratio of the components demonstrated that hydrogen in DLC is emitted to the outside in between 450 and $600°C$⁠, and the remaining DLC is graphized above $600°C$⁠. The increase in the asymmetry of the $C1s$ spectra and the decrease in the electrical resistivity of the DLC film with annealing temperature agree with the picture that the H–C bonds in DLC produces large free spaces in the structure, which inhibit conductive routes and lead to high electrical resistivity.