Influence Of A High Magnetic Field On The Growth Of Film Prepared By Vacuum Evaporation

Currently, the science and technology of film preparation has been becoming a fundamental and dispensable means for the development of new materials. The film deposition, structure and extension during the growth process determine its physical and chemical properties. Magnetic field is a novel way to control the crystal growth since it can induce the crystal to grow along the direction of lower magnetic energy because of the anisotropy of magnetic susceptibility. Appling magnetic field in the process of films can improve the film performance by orientating the crystal growth. Therefore, it has a great significance to study the effect of magnetic field on the film nucleation, growth and quality. In this paper, Zn, Te and Bi films were prepared by the method of vacuum evaporation using resistance heating technology in the magnetic field. X-ray diffraction (XRD), scanning electronic microscope (SEM), transmission electron microscope (TEM), atomic force microscope (AFM) and photoluminescence (PL) spectra were employed to study the grain orientation, surface morphology and roughness of films prepared under the different magnetic field, evaporating time, temperature, substrate type and setting direction. The results effectively explore the film nucleation and growth mechanism under the magnetic field. Thereby a new criterion for oriented growth of thin films in a magnetic field is proposed. This provides a favorable guidance for preparing film in the magnetic field in the industry.Firstly, the effect of magnetic field intensity on the grain size and orientation of Zn film were studied. The magnetic field could result in the smaller grains in the films, which is due to the nucleation promotion and the diffusion inhibition from magnetic field. The magnetic field enhances the c-axis oriented growth of Zn film prepared on the substrate which is set in the direction vertical to the magnetic field. The priority growth orientation of the samples changes from the original (002) to (101), prepared on the substrate set in the direction parallel to the magnetic field. The preliminary theoretical calculation of using magnetic orientation shows that the orientation growth of film in a magnetic field occurs when the orientation growth energy is larger than 62J/m3.Secondly, the ZnO thin films by oxidation in air were prepared under the different orientation of Zn thin films in the magnetic field. The effects of (101)-oriented and (002)-oriented Zn thin films on the grain size and optical properties of ZnO thin film were investigated. XRD and SEM results show that the former has a finer grain size. UV-Vis and photoluminescence (PL) spectroscopy results show that the former has the higher optical intensity. This is attributed to the finer grain and no full oxidization of Zn doping.Thirdly, the effects of magnetic field on the grain orientation of non-metallic bonded Te thin film were investigated. XRD results show that the grain orientation growth in Te thin films prepared in the magnetic field changes from the (011) into (012). But the SEM results show that no significant change in the surface morphology of Te films. FEM analysis shows that the reason is due to the angle of 19°between the (011) and (012) surface, which is not large to see the difference. The substrate temperature can significantly change the growth orientation from the <012> original priority growth direction into the <100> direction for Te films in the 4T magnetic field and at the temperature of 120℃. The temperature is not favorable for the orientation effect of the magnetic field. The earlier deposition of Te films on the different substrates was prepared with and without magnetic field. SEM results show that the magnetic field can promote the nucleation. The theoretical analysis shows that the magnetic field decreases the critical nucleation energy and the critical nucleation radius, but has no certain effect on the nucleation rate during the thin film growth. In addition, a new criterion ((?)B~2V≥σ·ΔS) for oriented growth of thin films in a magnetic field was proposed by investigating the Bi films which have a larger magnetic susceptibility difference among the different crystal orientation. The magnetic susceptibility difference of Bi is larger about ten times than that of Zn. The strongest peak of the Bi films prepared in less than 6T magnetic field is (003) plane, which is same as that of the samples without magnetic field (which have no preferred orientation growth). This phenomena is contradicted to the traditional theory of magnetic orientation ( (?)B~2V≥kT). Therefore, a new criterion ((?)B~2V≥σ·ΔS) for oriented growth of thin films in a magnetic field is proposed, which is evidenced by the experiment of the grain orientation from (003) to (202) of the Bi film applied larger than the 6T magnetic field.Lastly, the atomic force microscope (AFM) was introduced to study the effect of magnetic field on the surface topography of Bi films. The root mean square roughness Sq analysis shows the roughness of Bi films prepared in the 10T magnetic field tends to decrease, compared with that of the samples without magnetic field. The same orderliness is also found for the samples with the different deposition times of 30s, 60s and 120s. This may be induced by the change of the magnetic flux density at the hunch peak of Bi thin films. In the end, the research on the dynamic scaling analysis shows the magnetic field can not modify the random deposition mode of Bi thin films.