Polymeric amorphous carbon films with an extended range of optical gaps

• Hydrogenated amorphous carbon film with extended optical gap range (1 to 4 eV) and low intrinsic stress (0.1 to 0.2 GPa).
• Relative content of CHx carbon–hydrogen groups from high-resolution FTIR and NMR data.
• Location of the samples in the carbon–hydrogen ternary phase diagram.
• Under-investigated areas in the deposition parameter space of amorphous carbon film.

A new type of hydrogenated amorphous carbon (a-C:H) film is prepared under low bias voltage and an extended range of plasma density in a radio-frequency plasma enhanced chemical vapor deposition system (RF-PECVD). The obtained a-C:H samples are grown on electrically floating substrates instead of substrates mounted on the powered or the grounded electrode of RF-PECVD, and have structure and properties that are significantly different from regular a-C:H films. The samples have an optical gap ranging from 1 to 4 eV, while maintaining low intrinsic stress between 0.1 and 0.2 GPa. Fractions of all types of CHx carbon–hydrogen groups of the obtained samples are measured, analyzed, and used to locate these samples in the carbon-hydrogen ternary phase diagram. The obtained samples are located in the same general area as the regular a-C:H films, indicating configurational rather than compositional structural differences. The hydrogenation ratio of sp3 carbons in the obtained samples is found to remain at a very high level, and is used to explain their unique properties.