This research project will focus on the mechanism of matrix assisted pulsed laser deposition of thin polymer and organic films. These thin films are crucial to the advancement of technology in such areas as chemical and biological sensing, antistiction coatings, and flat panel displays, and many others as well. In this technique a polymer or other organic material to be deposited as a thin film is dissolved in a solvent matrix and then the solution is frozen and placed in a vacuum chamber. The volatile solvent is pumped away and the organic material is deposited as a thin film. Our recent research results, as well as others, have shown that the laser wavelength and matrix used can greatly affect the characteristics of the deposited films. Once this wavelength specificity and the role of guest-host interactions are understood, the deposition of high quality films in a reproducible manner will be facilitated.
The broader impacts of this research project begin with the fact that it is intrinsically multidisciplinary. In this fashion, the results obtained from this work will be of interest to researchers in almost every science and engineering discipline. As such, the pool of students who may participate is naturally large. Since Rutgers-Camden is a diverse campus in a developing urban environment, the participation of traditionally underrepresented groups in this project is naturally facilitated. Finally, the training of undergraduate students and the postdoctoral fellow supported by this project will be enhanced by Rutgers-Camden's commitment to both undergraduate participation in research and close faculty mentoring.
This grant was concerned with the deposition and characterization of thin polymer films through the use of a laser-based technique. Thin polymer films are crucial to the advancement of many technologies. They can be used as protective coatings on hard drive platters, antimicrobial surfaces, organic photovoltaics for solar cells, and optical diffusers on glass, just to name several examples. We used a technique that is a variation of pulsed laser deposition (PLD). In PLD, a focused high powered laser is incident upon a target that is placed into a vacuum chamber. The laser creates an atomic vapor which condenses on an appropriately placed substrate. However, this technique will not work well with polymers and other organics because they are primarily composed of carbon, hydrogen, oxygen, and nitrogen. It is much more likely that the organic material would be decomposed into small molecules that do not recreate the complicated structure that was started with. The advantages of PLD are that coatings that are produced with it adhere well to the substrate and the thickness can be controlled precisely. One way to preserve the structure of the polymer is to use a dilute and frozen solution as the target. The laser energy is primarily taken up by the solvent (host) and the polymer (guest) is entrained as it leaves the surface. A substrate that is placed in the path of the ejecta will collect a thin film. This technique is known as matrix-assisted pulsed laser evaporation "MAPLE." It is considered to have all of the advantages of PLD with a minimum of drawbacks. Our work is concerned with the influence of wavelength and solvent-polymer interactions in MAPLE. In particular, we focused on the influence of these parameters on the morphology of the deposited films. Our goal is to understand the conditions under which smooth and uniform thin films may be produced. Our results showed that the laser wavelength strongly influences the features and smoothness of the films. This is most noteworthy when the absorption of laser light by the material is strongly influenced by temperature. In general, we found that so long as the laser wavelength is not one that causes photochemical decomposition of either the solvent or polymer, the stronger the laser light absorption, the better. We also studied the influence of the polymer-solvent interactions on the properties of the thin films. Here, we found that the solubility of the polymer strongly influences the feature size, and hence roughness, of the deposited films. We were able to quantify our results in some cases through the use of Hansen Solubility Parameters. However, not all polymer-solvent combinations can be analyzed in this way. Other work that was performed under this grant included the deposition of silver-polymer nanocomposites for both nonlinear optical and anti-microbial applications. Optical diffusers were fabricated using rough polymer films, and more recently, we have focused on small organic molecules that could be used in memory and photvoltaic applications.
