Matrix-assisted Pulsed Laser Evaporation Of Polymer Thin Films And The Research

Pulsed laser deposition (PLD) is the most commonly used technology for the preparation of inorganic thin films, and it has already achieved great success. However, because of the high laser energy, the organic molecules were vulnerable to be damaged in varying degrees during the deposition process of organic thin films, and it severely limited the applications of the pulsed laser deposition technology in the preparation and research of organic thin film. In order to effectively eliminate the decomposition of organic molecules caused by the laser radiation, in the late 1990s, on the basis of pulsed laser deposition technology, the U.S. Navy Research Laboratory (NRL) had developed matrix-assisted pulsed laser evaporation technology. The basic principle of this technology is as following. The matrix molecules which absorbed laser energy prevent organic/polymer materials from direct interacting with laser photon and, thereby avoid the decomposition of organic/polymer materials, so as to promote the development of the study on organic films by laser evaporation technology. A large number of experiments showed that the composition and structure of thin films prepared by matrix-assisted pulsed laser evaporation are similar to that of the starting material.At present, foreign researchers have deposited and studied a series of organic, polymer and biomaterial films by matrix-assisted pulsed laser evaporation, such as polyethylene glycol, polyaniline, functionalized polysiloxane, fibrinogen blood proteins, triacetate-pullulan polysaccharide and glucose and so on, and quite satisfying results have been obtained. Untill now, there was no domestic research in this field was reported. We have built an equipment for matrix-assisted pulsed laser evaporation in National Synchrotron Radiation Laboratory in University of Science and Technology of China to deposit and study organic/polymer thin films. In this paper, we deposited and studied polyimide and polyaniline thin films with different laser beams. A preliminary discussions about deposition and applications of organic/polymer films prepared by matrix-assisted pulsed laser evaporation were presented.This dissertation is composed of three parts.In the first part, we reviewed and summed up the development of pulsed laser deposition, matrix-assisted pulsed laser evaporation, polyimide and polyaniline. The research works on matrix-assisted pulsed laser evaporation abroad show that matrix-assisted pulsed laser evaporation is an effective tool for the preparation of organic/polymer and biomaterials thin films and it's important to built an experimental set-up home for developing new-brand films.In the second part, detailed experimental equipments and related operation steps were given.In the third part, we prepared polyimide and polyaniline films by matrix-assisted pulsed laser evaporation technology, and analyzed these films by AFM, FTIR, Uv-Vis absorption spectroscopy, XPS and XRD.In chapter 3, polyimide thin films were made with KrF excimer laser and polyamic acid solution target. The FTIR spectroscopies showed that the characteristic peaks of films were coincide to that of the target. This fully shows that the advantages of matrix-assisted pulsed laser evaporation technology, that is, the decomposition of organic/polymer or biomaterials were effectively avoided with the protection of matrix. However, the Uv-Vis absorption spectroscopy showed that, although the chemical composition and characteristic structures are well maintained, the molecular weight changes significantly.That can be explained as following. The process of matrix-assisted pulsed laser evaporation is a combination of photochemical effect and photothermal effect,and the photochemical effect which made the structures of materials change is inevitable. AFM images showed that film morphology is stronglydepend on laser energy. With the increasing of laser energy, the film quality becameworse. So, the low-energy laser is conducive to the preparation of high-quality films.From chapter 4 to chapter 6, undoped and doped polyaniline films were madewith different laser wavelength and different laser energy,and analyzed results byAFM, FTIR, Uv-Vis absorption spectroscopy, XPS and XRD are present. The impactof laser energy on the chemical structure of the film was evaluated by the infraredspectral,and the result showed that the higher the laser energy was, the more thechemical changed. The comparison between the films with different wavelength lasershowed, that laser wavelength has an obvious impact on the chemical structure of thefilm. The chemical structures of films with long laser wavelength are more similar tothat of polyaniline target. This is due to that the longer the laser wavelength is, thelower energy the laser photon is of, and photothermal effect dominanted whilephotochemical effect weakened during the process of deposition. The results of XRDshowed that different wavelength of laser are of great on the condensed structures ofpolyaniline films, and film with different wavelength had different crystallinestructure. The comparison between polyanilines of different doping showed that, dueto the different stability of polyanilines of different doping, the influence of laser onthe structure of the film was quite different.In chapter 7, the influence of laser and doping on the structure and surface morphology of polyaniline films were discussed. AFM showed that not only laser energy, but also laser wavelength strongly influenced the surface morphology of the film. The surface morphology of the film made with shorter laser wavelength is superior to that of the film made with longer laser wavelength. In addition, the surface morphology is also depend on the temperature of target, laser frequency and the distance between target and substrate. From the point of view of chemical structure, a longer wavelength and higher laser energy is conducive to make a better film, and the impact of doping on the film is also clear. In the past, researchers agreed that polyaniline powder or film doped with inorganic acid was a little bit crystalline, while those doped with organic acid were of amorphous structures. But in our experiment, the XRD shown that the polyaniline films doped with inorganic acid are of amorphous structures and no diffraction peaks appear, while the films doped with sulfosalicylic acid are of a little bit crystalline and a relative sharp diffraction peak appears on 2θ=32.8°.