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LEA LIPES: Laboratoire Interaction Plasma Extrême Surface

A common European Laboratory between Institut Jean Lamour (F) and Centre de Recherche Public Gabriel Lippmann (L)

For more than 10 years, the group ESPRITS from Institut Jean Lamour in Nancy (F) has been developing collaborative research works with the Science and Analysis of Materials (SAM) department from Centre de Recherche Public Gabriel Lippmann in Luxembourg

The ESPRITS group has expertise in plasma physics, chemistry and engineering including plasma diagnostics, plasma kinetic modelling and numerical simulation. The 19 researchers and technical staff develop fundamental and applied research related to the following topics:

  • plasma wall interaction in the framework of the ITER program
  • high pressure plasma
  • thermochemical surface treatment
  • plasma assisted thin film deposition

 

Recently, some works have focused onto the capability of using atmospheric pressure plasma for achieving surface nano-structuration.

 

The Science and Analysis of Materials (SAM) department is a laboratory that is both a fundamental and applied research facility as well as an analytical services laboratory. It provides assistance to more than 100 industrial and academic partners worldwide in their technological research and development, with regard to materials and surfaces R&D. The SAM department has become a reference laboratory in the fields of:

  • characterisation of materials, surfaces and interfaces;
  • innovative surface treatments;
  • design and development of scientific instruments.

 

Resulting from the long term collaboration between the two groups, and based on their complementary expertises, both teams applied successfully to get the label Laboratoire Européen Associé (joint European Laboratory), a wall-less unit of CNRS and CRP-GL named LIPES (Laboratoire Interaction Plasma Extrême Surface).

This new crossborder unit was officially kicked off on January, 19-20 2011.

LEA LIPES works on studying the interactions between a plasma source and the top most surface of various materials. Focus is done onto the « building » of the top surface, from the single species deposited up to the complete single layer. The objective aims at a better understanding of the behaviour of any isolated species as it reaches the surface, using approaches of chemical physics. It will thus be possible to understand and predict the behaviour of reactive species on well characterized surfaces. Consequently this will allows us to orientate the plasma surface processing to functionalize the materials with specific properties.

 

Study of plasma interactions with simple molecules to treat living materials

 

Within the framework of the LIPES wall-less laboratory, we started a collaborative work on the treatment of simple molecules for applications in the field of living materials. Reversible blood coagulation can be performed by atmospheric pressure plasmas, for instance. However, blood, like all living materials, is extremely complex and there is a long way to go to improve our understanding of the interactions undergone by these materials when they are submitted to a non-thermodynamic equilibrium medium like a gas discharge. We chose to simplify this issue by looking at the interaction of plasmas with simple molecules and to establish a reactivity map by the nature of the bonds present in the chosen molecules. In amino acids, the elemental brick of life, one finds acid (-COOH) and amine (-NH2) groups, C-C and CH bonds. We can also find phenyl rings, double bonds, thio-ethers, etc. Until now, we studied the interactions of remote discharges (i.e. where no electrons and ions survive but the neutral species) with C-C and C-H, COOH and phenyl rings by using respectively hexatriacontane (C36H74), stearic acid (CH3-(CH2)16- COOH) and biphenyl (C12H10).

 

The study of stearic acid is given here as an interesting result concerning a specific function: the acid function. There is no species present in Ar-O2, Ar-H2 and Ar-N2 remote plasmas that can attack the acid function. Currently, we are investigating Ar-O2- H2 mixtures to create OH groups that could destabilize this function. Nevertheless, we were able to highlight several interesting mechanisms. First, the deposition of stearic acid occurs in the form of micrometric beads (see figure). During the first moments of the remote plasma treatment under Ar-O2, we observed by LDIToF- SIMS a dewetting of the beads on the surface which then form a quasi-continuous film. Next, the etching of this film takes place, and gives new islands on the carbonaceous surface. We could see that the XPS signal of carbon for instance reaches a maximum during the treatment time. The etching mechanisms of stearic acid are exactly the same as those of long chain alkanes, including hexatriacontane that we studied in detail. On the other hand, used as thick films, the stearic acid cannot be easily etched. We discovered it was due to the mobility of the radical chains which enhance cross-linking reactions. We also understood that oxidizing species in the remote plasma diffuse in the acid over a significant surface, inducing subsurface reactions that are responsible for the synthesis of large bubbles in the core of the material. Finally, by pulsing the plasma and limiting the temperature, we could etch thick films of stearic acid.

 

Tof-SIMS images of the surface of a silicon substrate covered by a layer of stearic acid and treated for one minute in a pulsed Ar-10%O2 remote plasma. Left: image of CxHyOz-like species. Right, image of silicon. We notice that the stearic acid coating is made of beads with a mean diameter close to 15 μm.


Références
E.A. Bernardelli, T Belmonte, D. Duday, et al., Plasma Chem. Plasma Proc., 31 (2011) 189-203 (part I)
E.A. Bernardelli, T Belmonte, D. Duday, et al., Plasma Chem. Plasma Proc., 31 (2011) 205-215 (part II)
T. Belmonte, E. A. Bernardelli, M. Mafra, et al. Surf. Coat. Technol. 205 (2011) S443–S446