Film deposition under the microscope

(supervisor: Rudi Winter)

Nature of project: experimental, data analysis

Available to full-time physicists only.

Project description and methodology

Spin coating is a technique used frequently to produce reproducibly well-defined thin films of materials on a small scale, e.g. for research purposes or when producing prototypes of electronic devices[1]. The film is created by applying a drop of a precursor solution to the substrate, which is then spun very rapidly to remove excess material and leave just a smooth thin film. Any solvent will evaporate during the spinning process. As a result, the morphology of the film is governed by a balance of mechanical factors and solvent evaporation.

In this project, we will study the spin coating process and its dependence on parameters such as temperature, spin speed, concentration of precursor solution or solvent vapour pressure using a polymer blend as the system under study.

The ageing of films will be studied using an optical microscope with digital camera to allow monitoring of structures in the micrometre range in real time, starting as soon after deposition as possible.

Photographs taken will be analysed[2] in terms of structures developing in the film depending on the various parameters studied. In addition, colour changes of the film (interference fringes) will be analysed and interpreted in terms of film thickness[3].

A successful project will develop beyond the above in one/some of the following directions:
If structures with lateral dimensions at the limit of the resolving power of the optical microscope are found, some of these samples could be studied by Atomic Force Microscopy (AFM)[4] to extend the data range.

When considering where to take your project, please bear in mind the time available. It is preferable to do fewer things well than to try many and not get conclusive results on any of them. However, sometimes it is useful to have a couple of strands of investigation in parallel to work on in case delays occur.

Additional scope or challenge if taken as a Year-4 project: A Y4 version of this project could extend the film thickness aspect by taking and analysing ellipsometric data (images or point measurements) to corroborate and calibrate the film thickness estimates from the colour changes observed.

Initial literature for students:

  1. K Norrman et al.; Annu Rep Prog Chem C 101 (2005) 174
  2. Micrograph analysis software manual: http://gwyddion.net/
  3. KN Allpress, BJ Cowell, AC Herd; J Chem Ed 58 (1981) 741
  4. J Kumaki; Polymer J 48 (2016) 3

Novelty, degree of difficulty and amount of assistance required

The processes to be studied and methods used are well established but the combination is unusual and will take some experimentation. There is potential to make genuinely new research findings if the parameter space is covered comprehensively and diligently.

Project milestones and deliverables (including timescale)

milestoneto be completed by
Develop experimental protocol that allows real-time monitoring of filmsend of November
Identify polymer system; plan and prioritise parameter space to be studiedChristmas
Identify data analysis protocol; familiarisation with softwareend of February
Comprehensive coverage of parameter spaceEaster

Students taking this project will have to submit a full risk assessment form