Hydrogenated amorphous carbon films have many unique properties

they have attracted much attention because of their applications in many kinds of optoelectronic devices such as light emitting diodes and field emission devices.It was well known that the film structures and properties were varied in a wide range by changing many factors such as hydrogen content and treatment.In this paper

the influence of hydrogen dilution on the optical properties of a-C:H films was studied.The a-C:H films were prepared in a capacitance coupled plasma enhanced vapor chemical deposition system at 13.56MHz.The gas mixture of CH

4

and H

2

was used as source and the flow rate of the H

2

was changed.The structures and optical properties were investigated by Fourier-transform infrared spectra

photoluminescence spectra and optical absorption spectra.It was concluded that hydrogen dilution can

to some extent

etch the weak bonds in films

decrease the size of sp

2

clusters

and increase the sp

3

C-H

n

con-tent which results in the increase of the optical band gap of a-C:H films.The optical band gap increased from 2.57eV to 2.72eV with increasing hydrogen dilution ratio.Consequently

the PL peak energy has a blue shift from 2.5eV to 2.75eV under the excitation with 3.54eV light.The further increase of the hy-drogen dilution will induce the change of the bonding configurations in the carbon films

which results in the multiple PL bands in the luminescence spectra at room temperature.The a-C:H films include both sp

3

C-C

C-H and sp

2

carbon related clusters.The C=C bonds can exist in the form of olefinic chains

six-fold ring aromatic species et al.Under different hydrogen dilution conditions

the main C=C structure in the sp

2

clusters was different

which induces the different structures and optical properties of a-C:H films.