Preparation And Optical Properties Of The Dlc Films. Study

The microstructure of unhydrogenated diamond-like carbon(DLC) films is considered to be a mixture of sp~2 and sp~3 hybridized carbon atoms that constitute the amorphous structure.The properties of DLC films can be tailored by deposition techniques as well as deposition parameters in a wide range which can approach to diamond or graphite films.Its hardness, modulus of elasticity,band gap,optical transmissivity and electrical resistivity,etc can be tailored according to different conditions.All these properties make DLC attractive for researcher and application department.One of the methods of choice used to deposit unhydrogenated DLC films is pulsed laser deposition(PLD) using KrF excimer laser.By changing the experimental parameters,we investigate the relation between microstructure, optical properties and conditions.There are some points as followed:(a) The DLC films are prepared in different repetition rate of pulse lasers and deposition temperatures and pulse laser intensity,when the repetition rate or deposition temperature increase,the D peaks in Raman spectra become stronger accompanying with the up-shift of G peaks.The experiment results indicate that the sp~2 sites increase and the clusters grow large when the repetition rate or substrate temperatures increase.The model of C atoms ordering and Beeman theory were used to explain the growing mechanism.At the same time,with the increase of laser intensity,the Raman spectra shows that the microstructure of the samples includes more sp~3 bonding structure while as the laser intensity increases furtherly no improvement in the quality of the films can be obtained.(b) The photoluminescence(PL) properties,optical constants,transmitted spectrum were deeply studied.The optical band gap was obtained using the Tauc formula.When the repetition rate or the temperature increase,the PL intensity increase while the transmissivity and resistivity decrease.The experiment results are corresponding well with the I_D/I_G ratio and G peaks position from fits to Raman spectra.The nature of localized states and the carrier recombination mechanism in the material were detail discussed.The PL can be attributed to carder localization within an increasing sp~2 clusters.(c) The DLC films were prepared in in nitrogen gas environment.It was found that when the gas pressure was increased the D peak in the Raman spectra was becoming apparent.And at the same time the AFM shows that there are some small spherical particles on the surface of the films as the increase of nitrogen gas pressure.It can be concluded that the nitrogen gas environment dose not facilitate the formation of high quality DLC films.The effects of ambient gases on the structure and optical properties are detail discussed.We analyze preliminarily the role of nitrogen gas on the process of DLC films growing.