Jean-Pierre Moliton

Polymer gratings achieved by focused ion beam

Abstract As part of the development of polymer-based devices in the field of lightwave technology, a method for the implementation of gratings etched in PMMA and fluorinated polyimide using focused ion beam (FIB) technology is reported. The interest for these devices results from the fact that diffractive optical elements (DOEs) provide elegant answers to the wave-division-multiplexing (WDM) technique. More precisely surface relief gratings (SRGs) are of high interest at the stage of wavelength demultiplexing. We will present three kinds of gratings, echelon grating, crossed gratings and gratings with circular apertures. The entire processing method is exposed. Ion irradiation parameters and time of exposition are reported. The design parameters are entirely driven by a computer. All these parameters are studied in relation with the polymer nature. The limitations in microfabrication are presented, of course as a function of the polymer, but also as a function of the film coating process.

Optical waveguides etched in 6FDA-ODA by focused ion beam

Here is described a dry process to etch optical waveguides in polymers without geometric defect of the guiding structure. The dimensions are optimized for wavelengths of around 1.5 μm used in telecommunications. The implementation of focused ion beam (FIB) appears as an emerging technology to limit the optical losses resulting from shrinking feature size of patterning with classical wet lithography. The influence of experimental parameters are reported, just as well as the resulting etching rate in a fluorinated polyimide, the 6FDA-ODA. The results are connected with the damaging mechanisms of polymers by ion bombardment. The advantages and the limits of the process are considered in view of the fabrication of a complete device.

Etude des traces d'ions lourds dans des films de triacetate de cellulose preirradies ou non en photons γ

Abstract Cellulose triacetate produced by a method developed in our laboratory is studied as a solid-state track detector. It is bombarded by Ar ions, alpha particles and fission fragments of californium. it is shown that the detector response is affected by the concentration of the plasticizer. The effects of γ preirradiation on v g are correlated with our results from infrared investigations. In the dosage range of 1.9 × 106−11.4 × 106 rads, the ion tracks are not significantly changed, which is explained by a comparison between the energy provided by the bombarding ions and the energy deposited by the γ rays.

Transparent all organic TFT fabrication by low cost process without clean room

Here is studied a process for the fabrication of a transparent all organic field effect transistor (OTFT) in a low cost way, without clean room. A major difficulty lies in the fact that substratum is CR39reg, an organic glass. Pentacene, PMMA, and ITO are implemented as respectively semiconductor, insulator, and materials for source, drain and gate electrodes. In preliminary results, ion beam sputtering (IBS) is used as technique for ITO deposition. Transistors characteristics are discussed. To improve the characteristics and increase the reproducibility, a DC magnetron process is proposed for the ITO deposition on CR39reg.Transparency and conductivity of the ITO layer obtained by this method are presented and discussed

Plasmons as the primary mechanism of ion-induced modifications in polymers

Abstract The phenomena that lead to modifications of polyimide, polycarbonate and polyparaphenylene irradiated by an ion beam in the 100 keV energy range are studied. A model of energy transfer based on plasmon-like collective effects occurring during the physical stage of the ion-polymer interaction, previously implemented for poly(methyl methacrylate) and cellulosic derivatives, is extended to these polymers. In the framework of this model, we carry out quantum-chemical calculations of the valence-band density of electronic states. The resulting theoretical spectrum is then compared with the experimental plasmon line obtained by electron-energy-loss spectrometry. This approach sheds light on the selective bond cleavages induced by the energy transfer at the primary physical step of the ion-polymer interaction.

Relation between plasmons and the valence-band density of states in polymethylmethacrylate: Influence of ion irradiation on damage selectivity

Abstract A physical model is presented that aims at rationalizing the selectivity of bond breakage observed when polymethylmethacrylate is irradiated by ions in the 10–500 Kev energy range. This model, previously proposed by Brandt and Ritchie, is based on electronic collective effects. The coupling between the pure plasma oscillation at ωp and the oscillation of free electrons at (ω2 k0)½ makes the whole electronic population resonant at the frequency ωrp = (ω2 p+ (ω2 k0))½. By computing the valence-band density of states, we are able to calculate (ω2 k0) and then to deduce the theoretical value of ωrp. On the other hand, we provide an experimental measurement of ωrp and study its dependence on ion fluence by electron-energy-loss spectroscopy. The validity of the model of Brandt and Ritchie is then discussed in the light of both theoretical and experimental data.

Contribution to the research on cellulose diacetate as a solid state track detector

Abstract While having a similar composition to Cellulose Triacetate, Cellulose Diacetate is a less sensible heavy ions detector. With a 0.9 N potash etching at 20°C, ions which have higher Z than Carbon are not recorded and the Etch Rate Ratio is about 1 to 2 for Cu and Kr ions. The study of the infrared absorption spectra shows a decrease of the v(O-H) band intensity at 3500 cm−1 for CDA, when it increases for CTA.

The interface structure of polyimide guides etched by ion irradiation

Abstract Ion irradiations in the 100 keV energy range are carried out for polyimide etching in order to achieve wave guiding structures. Three irradiation processes are implemented: A single bombardment and two bombardment sets, one with increasing ion energies, the second with decreasing ion energies. The purpose of this paper is to show how the etching depth can be controlled and to characterize the resulting interface layer, where the refraction occurs.

Enregistrement des traces de protons dans des detecteurs de type cellulosique

Abstract After a brief summary of main papers on cellulose proton track detectors, the results of our experiments on the subject are given: cellulose nitrate CN 85, from Kodak France, seems to be the best for proton track detection. Its efficiency is 100% from 50 keV up to 760 keV, while the angle of the impinging particle on the detector does not exceed 60°; these results were obtained with etching conditions as follows: KOH 4N, 30°C.

Thermal assisted ion shrinkage (TAIS) of fluorinated polyimide for optical telecommunication devices

Abstract In the framework of the development of low cost optical devices for telecommunications, here is studied the shrinkage of 6FDA-ODA polyimide films by ion irradiation as a function of five parameters: the ion fluence, the ion fluence rate, the ion energy, the ion nature and the target temperature. In the 30–350 keV energy range for impinging ions, the shrinkage remains constant whatever the tested fluence rate is. An upper limit appears for fluences above 10 16 ions cm −2 . The etching is linearly dependent on the ion beam energy and reaches a maximum around 1 μm by thermal assisted ion shrinkage (TAIS) with Na + irradiations.