Tribological Studies On Nanolubricant Thin Films Prepared With Langmuir-Blodgett And Self-assembly Technique

As an ultrathin lubrication films, LB films are helpful to solve the friction and abrasion of running components of high technologies such as magnetic record, MEMS/NEMS. Two key difficulties which LB films are applied to engineering are the following: one is to enhance the ability of load-carrying or thermal stability; the other is to improve the cohesion strength between film and substrate.Moreover, self-assembly technique is uninfluenced by substrate materials and shapes, fit for assembly in large scale and is a simple and effective method to prepare nanolubricant thin films.The thesis mainly includes two parts:Part One: Preparation and tribological behaviors of ZrO2 thin films combined with Langmuir-Blodgett technique Zirconium oxide thin films on Si (111) substrate with controllable thickness in nanometer scale were prepared by annealing LB films of zirconium salt of arachidate at 500℃for 30 minutes. The microstructure, morphology and wear mechanisms of the film were analyzed based on atomic force microscopic, X-ray photoelectron spectrometric, and scanning electron microscopic observations of the original and worn surfaces of the films. As shown in the topography image, ZrO2 thin film is composed of compact particles whose diameters range from 20nm to 30 nm, and has no obvious cracks. XPS survey spectra of ZrO2 thin film demonstrates that the silicon substrate is covered by ZrO2 completely with little noncrystalline Zr(SO4)2. After sliding 500 cycles under a low load of 0.5N the worn ZrO2 thin film showed a slick surface and shallow and narrow furrows due to mild scratching without cracks and peels corresponding with its lower friction coefficient and longer antiwear life. After sliding 3,000 cycles discontinuous plastic deformation and grits occur attributed to shearing strength, and these debris in wear tracks accelerated wear and obvious furrows formed. With the increasing of sliding cycles, the worn surface is characterized by severe plastic deformation, scuffing and spalling.Part Two: Tribological properties of La2O3 thin films prepared by Langmuir-Blodgett and self-assembly techniqueLa2O3 thin film deposited on Si <111> was successfully prepared by LB and self-assembly technique, respectively. As shown in the topography image, La2O3 thin film by LB technique is composed of nanoparticles whose diameters range from 100nm to 120 nm, and the density of the particals increases with the deposited layers of LB films of lanthanum salt of arachidate. However, the self-assembly thin film is covered by compact and uniform particles with few clusters. From XPS analysis we can conclude both of the films are composed of La2O3. La2O3 thin film by LB technique showed a tribological behavior of brittle thin films, invalidation of the film was characterized by spalling, abrasive dust sloughing and shallow damage depth. And heat treatment in preparation reduced adhesion effects, and the lubricant film also confined damage depth, leading to improved anti-stiction capability. However, the self-assembly film has a strong anti-stiction capability due to its low shear strength, and obvious shear deformation can be observed. Meanwhile, fresh film formed after abrasion leading to polished surface and then weak plowing effects, corresponding to its quite low friction coefficient. So the self-assembly film was acknowledged as a plastic film, invalidation of the film was characterized by plastic deformation, with higher damage depth and larger abrasive dusts.