AFM And MFM Studies On The Microstructures And Magnetic Properties Of The Metallic Thin Film System On Liquid Substrates

Since the fact that liquid materials can truly employed as thin film substrates was discovered in 1990's, it has attracted increasing interest in studying the formation mechanism, microstructures and physical properties of the metallic and organic crystals thin films on the liquid substrates because of their different behaviors from that on solid surfaces.Nonmagnetic [Silver (Ag), Gold (Au), Copper (Cu)] and magnetic [Iron (Fe)] film systems, deposited on liquid (silicone oil) substrates by thermal evaporation method, have been fabricated successfully and the growth mechanism, microstructures, internal stress patterns as well as magnetic domains in the magnetic films are studied systematically in this dissertation. The major results are summarized as follows:(1) It is found that the growth mechanism of both the nonmagnetic and magnetic thin films on liquid surfaces approximately obey the two-stage growth model. The first stage involves nucleation and growth of atomic compact and ramified clusters; the subsequent stage includes random diffusion of the clusters and formation of the large ramified aggregates on the liquid surfaces. In the continuous copper films, band-shaped ordered patterns with macroscopical length scale and with quasi-periodic characteristics are observed.(2) An obvious edge diffusion phenomenon of the metallic atomic clusters and ramified aggregates is observed in our Ag film system. The experiment shows:the Ag atomic clusters and ramified aggregates diffuse toward the edge of the oil substrate during and after the deposition, therefore, the coverage of the Ag clusters in the central area of the sample is smaller than that on the sample edge. This phenomenon is more obvious with the increase of the substrate temperature; for a fixed film thickness, as the oil temperature increases, the coverage decreases.(3) Further study on the Cu, Ag and Au film systems by atomic force microscopy (AFM) are presented. It is found that the metallic atomic ramified aggregates and continuous films exhibit a granular structure. The size of the granularities exhibits the Gaussian distribution. The size distributions of the granularities in both the aggregates and films depend on the nature of the materials apparently. In the Au films system, we study the morphologies of the down surface and up surface of the film and it shows different morphologies and exhibit different structures.(4) Magnetic domain structures are newly observed in the continuous Fe films while no magnetic signal is detected in the Fe ramified aggregates. MFM studies for the Fe films (10.0 nm≤d≤80.0 nm) show that the domain wall structure is widespread and irregularly shaped and the oscillation phase shift△θ, which records as the magnetic force image, changes from 0.29°to 0.81°with the increase of the film thickness, corresponding to the magnetic force gradient from 1.4×10-3 to 4.0×10-3 N/m, respectively. Finally, we perform MFM measurement on Fe/glass samples and the cross-tie walls of various sizes confined in the Fe film system are observed experimentally.This dissertation is organized as following:In chapterⅠ, firstly, a brief introduction on the fabrication method, formation mechanism, as well as computer simulation of the thin film systems on solid and liquid substrates is given. And then, the magnetic domain theory and the observation methods for the magnetic domain structures are introduced. At last, the principle of the AFM and MFM are also presented.In chapterⅡ, the formation mechanism, microstructures and the band-shaped ordered patterns in the Cu film system on silicone oil surfaces are studied systematically.In chapterⅢ, the influences of the liquid substrate temperature on the formation mechanism of Ag clusters are studied. AFM studies on the microstructures of the Ag and Au ramified aggregates as well as the up and down surfaces of the Au continuous films are presented.In chapterⅣ, we research the characteristic microstructures and magnetic properties of the rough Fe film system deposited on silicone oil and glass surfaces.In chapterⅤ, main conclusions and prospect are presented.