Paper TF-WeE4
Depth Profiling Organic Thin Films with Argon Cluster Beam
Wednesday, December 10, 2014, 6:40 pm, Room Makai
| Session: |
Thin Film Synthesis and Characterization III |
| Presenter: |
Jean-Jacques Pireaux, University of Namur, Belgium |
| Authors: |
J.-J. Pireaux, University of Namur, Belgium
Nittler, University of Namur, Belgium
Noël, University of Namur, Belgium
Houssiau, University of Namur, Belgium
|
| Correspondent: |
Click to Email |
Many modern devices are based on multilayers of different materials, combined to reach a specific application. Monoatomic ion beam depth profiling did – and still do- immensely contribute to the learning of such multilayered structures containing metallic and oxide films; but one couldn’t study (in ToF-SIMS, AES or XPS) an organic/other material interface, or an organic multilayered structure because of the damages induced by the ion beam. For the profiling of organic layers, the development and commercial availability of sputtering sources based on poly-atomic ions (SF6, C60, coronene) came as a significant and promising evolution; the still more recent Argon cluster-ion source appears now as a revolution for a true quantitative depth analysis of organic films. Numerous applications of gas cluster ion beams have been presented at international conferences; publications study the influence of cluster size, of cluster energy on sputter rates on series of different polymers, and on depth resolution in sputter depth profiles [1]. The present work aims to study by XPS the sputter yield, and the depth resolution in samples consisting of multilayered amino-acid films while profiling with different Ar cluster ions (Thermo Fisher Scientific Escalab 250Xi spectrometer, MAGSIS source). The materials were chosen for their ease to be reproducibly deposited by sequential thermal evaporation in high vacuum under quartz-crystal balance monitoring ; the method revealed successful for the study of delta layers in dual beam Cs+/Bi3+ profiling in ToF-SIMS [2]. Phenylalanine (Phe) and tyrosine (Tyr) were used for this study. Although both amino acids differ only by an OH- group, their characteristic chemical fingerprints could be differentiated throughout the whole depth profile. Both materials surprisingly present a very different sputter yield: the erosion yield of Phe is larger (almost twice the value, depending on the Ar cluster size and energy) than for Tyr – a trend that is completely reversed in ToF-SIMS using Cs+[2,3] ; this strongly suggests different sputtering mechanisms, that will be reviewed during the presentation. Depth resolution at the interface between two layers is found to be better when sputtering from the high sputter yield material to the low one. It is worth to note in addition that, as suggested by Laser scanning confocal microscopy, the gas cluster ion beam profiling does not increase significantly the sample surface roughness.
[1] P.J. Cumpson et al, J.V.S.T. A31 (2013)020605 ; SIA 45 (2013)601
[2] C. Noël, University of Namur, Master Thesis, 2013
[3]C. Noël, L. Houssiau. SIMS Europe 2014 Conf., Münster.