Deposition of polymeric thin films by PVD process. Hachet Dorian 09/03/2016

Transcription

1 Deposition of polymeric thin films by PVD process Hachet Dorian 09/03/2016

2 Polymeric Thin Films nowadays

3 The evaporation of polymers

4 Ionization-Assisted Method Vacuum deposition 0,055eV/molecule at 1000 C Ionization-Assisted deposition 1V acceleration corresponds to 1eV/ionized molecule

5 The benefits of a high energy Creation of nucleation centers Activation of polymerization Surface cleaning by sputtering

6 MAPLE (Matrix Assisted Pulsed Laser Evaporation) MAPLE 6,2 ev/pulse (at 200nm) Really homogeneous thin film with a thickness of some tens of nanometres

7 ENDS Student does not talk beyond this point Information slides follow for other students to read If information slides are unclear please contact the author for clarification.

8 Definition of the problem When a polymer is dissolved and then evaporated, the macromolecules break because of their thermal energy. In order to get a thin film of a good quality and with a good adhesion, the polymerization has to happen on the substrate. However, in the vacuum deposition method, this is not happening because the energy of the monomers is low.

9 Information Slide (1) : Ionization-Assisted Method Ionization-Assisted Method is an improvement of the usual evaporation method. An ionizer is added between the evaporator and the substrate in order to ionize a part of the evaporated material. Like a usual evaporation method, it is processed over high vacuum. To get an idea of the importance of the ionization mechanism, one can compare the energies of the particles with or without the ionizer. Without it, a particle gets E=kT/2 from the evaporation. E=0,055eV at 1000 C. With the ionizer polarized with 1V, E=1eV at the same temperature of evaporation which is equivalent to an evaporation at C.

10 Information Slide (2) : The effect of the kinetic energy Like we have seen in the last slide of the presentation, both high kinetic energy and charge of the particle contribute to the higher quality of the polymer layer. The kinetic energy enhances the creation of nucleation site (a), surface migration (b), surface cleaning by sputtering (c) and surface adhesion (d).

11 Information Slide (3) : The effect of the charge The charge acquired by ionization of the particle enhances the nucleation and growth (a), the polymerization (b) and the alignment of the dipoles (c). This last fact can be used to depose effective piezoelectric polymeric layer like with polyurea films.

12 Information Slide (4) : MAPLE MAPLE states for Matrix-Assisted Pulsed Laser Evaporation. The method is base on a consumable frozen target made of the dissolved polymer within a volatile solvent. The target is frozen between -40 and -160 C. A UV light laser pulses on the target which absorbs most of the energy (6,2 ev by pulse at 200nm). This energy is evaporating the target and the rest is then converted to kinetic energy inducing multiple collision within the evaporated particles. This leads to the desorption of the polymer without any damage. The more volatile particle of the solvent are then pumped away while the polymer is deposited directly on the substrate.

13 Information Slide (4) : MAPLE The atmosphere of the chamber must be high vacuum (ultra high vacuum is not needed) or pressurized inert atmosphere with nitrogen for example. Under these conditions, the method is creating really homogeneous films with a thickness from some tens of nanometers according to the number of pulses.

14 References [1] Piqué, A., Auyeung, R., Stepnowski, J., Weir, D., Arnold, C., McGill, R. and Chrisey, D. (2003). Laser processing of polymer thin films for chemical sensor applications. Surface and Coatings Technology, , pp [2] Usui, H. (2000). Polymeric film deposition by ionization-assisted method for optical and optoelectronic applications. Thin Solid Films, 365(1), pp [3] Usui, H. and Tanaka, K. (2016). index. [online] Web.tuat.ac.jp. Available at: [Accessed 19 Feb. 2016].