A. Houdayer

Studies of the earliest stages of plasma-enhanced chemical vapor deposition of SiO2 on polymeric substrates

Abstract We have studied the structure of hyper-thin (thickness, d ≤10 nm) SiO 2 coatings deposited by plasma-enhanced chemical vapor deposition (PE-CVD) on various polymers (polypropylene, polyimide, polyethyleneterephthalate). Rutherford backscattering spectroscopy (RBS) has shown that the concentration of silicon atoms per unit area is a linear function of the deposition time, t , for t ≥0.5 s. Using reactive ion etching (RIE) in O 2 plasma, we observe that the coatings are continuous, not island-like, even for d ≈2 nm; this is confirmed by X-ray photoelectron spectroscopy (XPS), at high values of the take-off angle. In conclusion, PE-CVD film growth on polymers occurs in a layer-by-layer (Frank-van der Merwe), not in a Volmer–Weber (island coalescence) mode.

Growth and structure of hyperthin SiO2 coatings on polymers

Transparent inorganic oxide coatings on polymers are playing an increasingly important role in pharmaceutical, food, and beverage packaging, and more recently in encapsulation of organic, light-emitting display devices. Such coatings are being prepared by physical or by chemical vacuum-deposition methods. They possess barrier properties against permeation of gases or vapors when they are thicker than a certain critical thickness, dc; for d<dc, the “oxygen transmission rate” (in standard cm3/m2/day/bar), for example, is roughly the same as that of the uncoated polymer. This fact is commonly attributed in the literature to a “nucleation” phase of the coating’s growth, during which it is thought to present an island-like structure. In order to test this hypothesis, we have deposited hyperthin SiO2 coatings on various flexible polymeric substrates using plasma-enhanced chemical vapor deposition. The film thicknesses investigated here, well below dc (typically in the range 1–10 nm), were determined by Rutherfo...

MeV proton irradiations and atomic oxygen exposure of spacecraft materials with SiO2 protective coatings

Abstract Polymeric materials used for the construction of spacecraft include polymer-matrix composites for structural components, and backface-metallized plastic films such as DuPont Kapton ™ H polyimide, and Teflon ™ FEP fluoropolymer, as thermal control materials. In orbital space-flight, these polymers encounter a very destructive environment comprising ionizing radiation (keV electrons, MeV protons), ultraviolet photons, and hyperthermal atomic oxygen (AO). Therefore, the exposed surfaces of these polymers need to be protected by thin inorganic coatings, such as SiO 2 . We report preliminary research results on possible synergistic effects of exposing SiO 2 -coated polymers, first to MeV proton irradiation, then followed by high fluences of AO. The coatings, ≤ 0.5 μm thick, are applied by dual-frequency (MW/RF) plasma-enhanced CVD (PECVD). Samples of Kapton and Teflon were irradiated with 1-, and 20-year equivalent doses of 1 MeV protons (≈ 6.5, and 130 kGy, respectively), followed by ≥ 10 21 O atoms/cm 2 . Irradiation effects are assessed by comparison with witness samples on the basis of microscopy and mechanical property measurements.

Investigations of SiOx-polymer “interphases” by glancing angle RBS with Li+ and Be+ ions

Abstract In order to better understand the formation of an “interphase”, which is a known feature between SiO 2 coatings deposited by plasma enhanced chemical vapor deposition (PECVD) and polymeric substrates, we have deposited such layers on Kapton® polyimide (PI). Various deposition routes have been used, namely thermal evaporation (physical vapor deposition, PVD), and distributed electron cyclotron resonance (DECR) PECVD, with the substrate placed within the active glow zone and downstream from it. The actual presence and the width of the interphase were investigated using glancing angle Rutherford backscattering spectroscopy (RBS), with a scattering angle of 92°. To maximize the depth resolution, the RBS experiments have been performed using “heavy” (Li + and Be + ) ions.

Characterization by RBS of hyper-thin SiO2 layers on various polymers

Abstract In order to investigate the growth mode of plasma-enhanced chemical vapor deposited (PECVD) SiO 2 gas barrier layers on various polymers (namely polyimide, PI; polyethyleneterephthalate, PET; polycarbonate, PC) we use Rutherford backscattering spectroscopy (RBS) in two different ion beam modification (IBM) geometries, with 1 and 1.5 MeV α particles (He 2+ ions). In the case of Kapton ® PI, a polymer which is damaged very little by the incident ion beam, we have followed the evolution of the surface concentration of silicon atoms versus PECVD growth duration: the relationship was found to be perfectly linear over a film thickness range 5⩽ d ⩽500 A. Using grazing incidence, we found a 7 nm thick “interphase” region between the SiO 2 coating and the substrate. However, for the case of the two other polymers (PET and PC), major artifacts were noted during RBS measurements, even under very mild beam conditions (1 nA, 8.0×10 12 ions/cm 2 ), because of the creation of abundant volatile molecular fragments by the incident particles below the surface of the organic substrate. Scanning electron micrographs confirm the damage caused by these volatile species, as they escape through the sample surface; this greatly limits the use of the RBS technique for most polymers, including PET and PC.

The microbeam facility at the University of Montreal

Abstract The 4.5 MV Dynamitron injector for our 6 MV Tandem is now used to provide a proton beam for a dedicated FIXE, RBS, PIGE microbeam facility. An electrostatic quadrupole triplet lens produces a beam spot of 20 μm diameter. The target chamber, which is a modified 4 in. Dependex cross, houses an electron flood gun, and SB detectors. The targets are mounted on a stepper motor controlled HPT 040 micromanipulator. A 30 mm2 Si(Li) detector (FWHM = 154 eV at 5.9 keV) is used for PIXE measurements. Data on the impurities found in “water trees”, which are associated with breakdown in electrical cables, will be presented.

Trace element and surface analysis at the University of Montreal

The Tandem at the Laboratoire de Physique Nucleaire is now used for: Rutherford backscattering spectroscopy (RBS) and elastic recoil detection (ERD) with time of flight (TOF), channeling-ERD/RBS/PIXE, high energy implantation, and PIXE (proton induced X-ray emission) trace element analysis. A PIXE/RBS microbeam on the 4.5 MV Dynamitron will also be described.

Quantitative PIXE analysis of powdered pottery samples bound in an organic matrix

Abstract We have developed a method for preparing thin samples (about 1 mg/cm 2 ) of pottery powder by the centrifugal precipitation technique, using an organic binder (collodion). We measure accurately the amount of organic material in the samples by the p-p reaction. With this information, a good quantitative determination of the elemental composition of the samples by PIXE analysis is achieved. The sensitivity, accuracy and reproducibility of our method were verified by measuring the composition of several samples prepared with the standard pottery of Permian and Asaro. The abundances of 12 elements (from 1% to about 10 ppm) of Z ⩾ 22 have been determined with 3 MeV incident protons. The reproducibility and accuracy are very satisfactory. We have undertaken a systematic study of a collection of ceramic shards originating from Western Africa. The abundances of 18 elements of Z ⩾ 21 have been determined. The effect of the inhomogeneity of the ceramic composition is reflected in a fluctuation of the elemental composition of our samples.

Micro-PIXE analysis of impurity distributions in “trees” grown in high-voltage cables

Abstract Water treeing and electrical treeing are degradation processes occurring in the polyethylene insulation of underground high-voltage cables that can lead to premature breakdown. In order to determine the nature and content of impurities present in the trees, which typically have dimensions of 50–200 μm, a PIXE (proton-induced X-ray emission) microbeam system with a beam-spot diameter of less than 20 μm has been installed on a 4.5 MV Dynamitron accelerator. The capabilities of this system are illustrated by multi-element radial scans that show the presence of a wide variety of contaminants in the trees.

Radiation-induced degradation of polymeric spacecraft materials under protective oxide coatings

Abstract We report the results of experiments, in which two SiO2-coated polymers (Kapton® polyimide, and Mylar® polyester), and ITO-coated Kapton® are exposed to high-energy radiation. Possible modification or damage of the coating–polymer interface is assessed by adhesive testing, using a CSEM MicroScratch tester, with which we measure the “critical load” (Lc) for coating delamination from the polymer surface, and by microscopy, compared with untreated witness samples. We deposit thin (sub-μm) coatings of SiO2 by plasma-enhanced chemical vapor deposition (PECVD), in order to obtain strong (chemical) bonding at the substrate/coating interface. 100 keV protons and a hydrogen microwave plasma “lamp” with an MgF2 window at a power density of 125 μW cm −2 are used to irradiate the sample surfaces.