| In the field of preparing thin films and nanoparticles,Supercritical Fluid Deposition(SCFD)technology can effectively avoid the high temperature trouble caused by chemical vapor deposition.In order to minimize deposition temperature and improve deposition quality.In this paper,MoO2(acac)2 was used as precursor to deposit thin films and nanoparticles on sapphire substrates.The solubility of Mo source precursors in supercritical CO2,the influencing factors of crystallization nucleation and the thermodynamic problems in the preparation process were studied.The main work and results are as follows:(1)The solubility of MoO2(acac)2 in CO2 was 0.809×10-4-4.829×10-4 at the temperature from 40℃ to 60℃,pressure from 7.38 MPa to 20 MPa by using static solubility measurement method.When the pressure increases at a certain temperature,the solubility of MoO2(acac)2 increases.The higher temperature,the more obvious the influence of pressure on the solubility.The Chrastil model,Asachi-Lu model and Gordillo model were used to correlate the measured experimental data of solubility.(2)The MoO2(acac)2-CO2 system was experimented on by selecting the deposition pressure of 10-20MPa,the temperature from 40℃ to 60℃,time is 8h,pressure relief rate from 0.2 MPa/s to 2 MPa/s,and the precursor mass from 200 mg to 250 mg.SEM,EDS and XRD were used to analyze the nanoparticle distribution on the substrate surface.The depositional pressure has an obvious effect on the nucleation rate.With the increase of depositional pressure,the nucleation rate also increases correspondingly.The pressure relief rate has a great influence on the morphology of nanoparticles,and there is an optimal pressure relief rate in a certain range.(3)Analyze the classical nucleation theory,Turk model and Debenedetti model to calculate the critical nucleation radius and nucleation rate.The similarities and differences between supercritical rapid pressure relief nucleation and classical nucleation theory are put forward,and the energy variation provided by rapid pressure relief is included in crystallization nucleation,so as to revise the classical nucleation theory. |
