Study On Microstructure And Optical Properties Of Nitrogen-doped Amorphous Carbon And Amorphous Carbon Nanocluster Thin Films

In recent years,carbon-based materials have been a research hotspot both at home and abroad.Among them,the application of amorphous carbon(a-C)thin films is particularly extensive.People have studied amorphous carbon thin films for many years,but the reported results are different,and further research is needed.In this work,we have studied the microstructure and optical properties of amorphous carbon thin film materials in two different ways.One is to dope the amorphous carbon film with nitrogen,and the prepared nitrogen-doped amorphous carbon film(a-CN_x)has a structure change and better light transmission compared to the amorphous carbon film;Another way is to use annealing to generate carbon nanoclusters in the hydrogenated amorphous silicon carbide film,and the structure of the carbon nanoclusters has a great influence on the optical properties of the film,which is discussed in detail in this paper.In this thesis,plasma enhanced chemical vapor deposition(PECVD)technology was used to prepare nitrogen-doped amorphous carbon thin films and carbon-rich hydrogenated amorphous silicon carbide thin films,and annealing treatment was used to generate carbon nanoclusters in a-SiC_x:H thin films.Studies have shown that the structure and optical properties of the film can be adjusted by changing the process parameters of the film.Using various material analysis and testing techniques,the effects of ammonia flow rate and annealing temperature on the microstructure and optical properties of the film were studied.The main research results obtained are as follows:(1)For nitrogen-doped amorphous carbon films.Fourier infrared spectroscopy(FTIR)confirmed that the incorporation of nitrogen produced an nitrogen-doped amorphous carbon film,and characterized the chemical bonds and functional groups contained in the film.X-ray photon spectroscopy(XPS)test results show that the film sp~2C=C increases first and then decreases as the ammonia flow increases;sp~3C-N related to N first increases and then decreases,and the sp~2C=N bond content trend is exactly the opposite.The results show that as the flow rate of ammonia increases,the chemical bonds in the film are converted.Ultraviolet-visible absorption spectroscopy(UV-Vis),as an important means of characterizing the optical properties of nitrogen-doped amorphous carbon thin films,shows that the film has enhanced light transmission performance and increased optical band gap after doping with nitrogen,laying a foundation for its application in solar cells.(2)For carbon-rich a-SiC_x:H thin films.Raman spectroscopy shows that during the annealing process(Ta)greater than 650?,the precipitation,growth and decomposition of carbon nano-dots coexist in the a-SiC_x:H thin film.It can be found by XPS measurement that with the increase of Ta,the formed carbon nanoclusters can be oxidized and removed from the near surface of the annealed a-SiC_x:H film.The reduction of the optical band gap(E_g)of a-SiC_x:H thin films can be attributed to the formation and graphitization of carbon nanoclusters in the thin films.High resolution transmission electron microscopy(HRTEM)test results show that as Ta increases from 650 to 750°C,the size of carbon nanoclusters gradually decreases,and even some carbon nanoclusters smaller than 10 nm can be found.In addition,by increasing Ta,the dispersion of carbon nanoclusters in the a-SiC_x:H film can also be improved.At the same time,the areal density of carbon nanoclusters seems to increase with increasing Ta.However,compared with carbon nanoclusters dispersed in chemical solvents,the dispersibility of carbon nanoclusters embedded in a-SiC_x:H films is still poor.Depending on the change in photoluminescence(PL)signal as Ta increases,it may not be appropriate to attribute PL emission to carbon nanoclusters in the a-SiC_x:H thin film,and the PL peak may originate from related defect states in the thin film.