A single layer of C_(84) molecules is embedded into Si (111) surfaces through a controlled self-assembly process in an ultrahigh vacuum chamber. The topography and optoelectronical characteristics of C_(84) embedded Si (111) surfaces are determined using an UHV scanning probe microscope. The C_(84) embedded silicon surface has a wide band gap of ~3.4eV, high emission efficiency and low turn-on voltage. Those properties are crucial to nano-electronics, optoelectronics, and the fabrication of semiconductor carbide. The photoluminescence emission experiments further confirm the corresponding band gap value obtained from I-V curves. The charactertics of C_(84) embedded silicon surfaces are in good agreement with experimental measurements and theoretical first-principles calculations.