Papers

AVS1996 Session AS-ThA: Polymer Surfaces

Thursday, October 17, 1996 1:30 PM in Room 105B

Thursday Afternoon

Start	Invited?	Item
1:30 PM		AS-ThA-1 Surface Modification of Polymers using Plasma Source Ion Implantation Y. Lee, S. Han, J. Lee, J. Yoon (Korea Institute of Science and Technology) Polymer Surface modification to improve wettability, adhesion, and biomedical compatibility has wide industrial applications. Plasma source ion implantation (PSII) technique was used for hydrophilization or hydrophobization of polymer surfaces using various gases. To modify the polymer surfaces, polymer samples are placed on the target stage in the vacuum chamber, plasma is generated, and high negative voltage pulses are applied to the samples. The ions are extracted from the plasma and implanted into the polymer surface with the energy corresponding to the high voltage applied to the sample. The implanted ions form the hydrophilic or hydrophobic functional groups on the polymer surface. Polymer plates were modified with plasmas of different gases and for varying lengths of implantation time. Oxygen, nitrogen, and argon ion implantation increased the hydrophilicity of polymer surfaces significantly. On the other hand, methane and fluorocarbon plasma-implanted polymers showed enhanced hydrophobic property. Characterization of plasma-source-ion-implanted polymers was performed using a contact angle meter and Time-of-Flight Secondary Ion Mass Spectrometry(TOF-SIMS). The permanence of treated surfaces was evaluated with respect to ageing time. The ion-implanted samples were stored under ambient conditions and monitored over time to see the changes in contact angles with the distilled water. After 10 days, the implanted surfaces still showed very low contact angles. The experimental results showed that plasma source ion implantation is a very promising technique for industrial application of polymer surface modification due to its effectiveness, controlability, stability of treated surfaces, uniform treatment of large area, and simplicity of the equipment.
1:50 PM		AS-ThA-2 SIMS of Polymer Films and Modified Polymer Surfaces R. Short (University of Sheffield, United Kingdom, UK); A. Leeson, M. Alexander (University of Sheffield, United Kingdom); D. Briggs, M. Hearn (ICI Wilton, United Kingdom); A. Beck (University of Sheffield, United Kingdom) The application of secondary ion mass spectrometry for the study of polymer surfaces has been the subject of numerous investigations. SIMS has been shown to be a very useful tool in the identification of polymeric materials at surfaces. For a limited number of polymers detailed fragmentation schemes have been proposed. These relate key ions to the original polymer structure. Success has been achieved with the series of alkyl methacrylate polymers. Perhaps the most serious limitation of SIMS has been uncertainity in the reproduciblity of the technique. Investigation of the literature reveals that SIMS spectra from nominally the same material e.g. PMMA can exhibit remarkable differences in the relative intensities of specific key ions. In part, different performances of SIMS instruments may account for this. Lack of standardisation in material also contributes. One PMMA is not the same as another. Important variables include the presence of the additives, molecular weight, polydispersity, thermal history, sample preparation and sample age. This list is not exhaustive. The effects of some of these variables have been studied, but we are not aware of a systematic investigation based on well characterised material. We have, therefore, undertaken a study of how these affect the SIMS spectra of PMMA standards. A quantitative measure of the reproducibility enables the effects of these variables to be made clear. We have also applied SIMS to the investigation of a class of unknown materials, plasma polymerised alkyl methacrylates and are able to start to quantify how the plasma variables, power and monomer flow rate affect molecular structure.
2:30 PM		AS-ThA-4 Analysis by TOF-SIMS of Perfluoro-polyethers with Active Endgroups A. Spool (IBM Storage Systems); P. Kasai (IBM Research Division) The rich and intense negative ion SIMS spectra of Perfluoro-poly(ethers) (PFPEs) are drastically altered when these molecules have active endgroups (-CF\sub2\CH\sub 2\OH, -CF\sub 2\COOH). We compare and contrast TOF-SIMS analyses of demnum-SA, demnum-SH, krytox-OH, krytox-acid, Z-dol, and Z-diac. The demnum and krytox polymers have the active endgroups only at one end, while the PFPEs with the Z backbone are bifunctional. The negative ion spectra are again best rationalized as the result of dissociative electron capture. The spectra of the non-functionalized polymers had been dominated by the single electron capture event at the ether oxygens, R-O-R' + e- followed by fragmentation, R-O- + \super .\R'. For the monofunctionalized polymers, fragments of this type contain only the non-functionalized end of the molecule (perfluoropropyl-). The other half of the major repeat pattern is now absent from the spectra. For the difunctionalized Z type polymers, the negative ion spectra are now dominated by internal fragments resulting from multiple dissociative electron capture events. The positive ion spectra of the alcohol ended polymers show new peaks resulting from cation formation at the -CF\sub 2\CH\sub 2\OH endgroup, showing approximately the MW distribution of the polymer. The positive ion spectra, along with molecular orbital calculations, show that this endgroup has a propensity to cationize. We propose that anions containing the alcohol endgroup are neutralized by the formation of a cation at that end of the molecule. The reactive nature of the acid endgroup can be similarly used to explain the negative ion spectra of PFPEs containing this endgroup.
2:50 PM		AS-ThA-5 Temperature Programmed SIMS: Desorption and Surface Diffusion of Polymer Molecules on Metal Substrates M. Deimel, H. Rulle, V. Liebing (Physikalisches Institut der Universit\um a\t M\um u\nster, Germany); A. Benninghoven (Physikalisches Institut der Universit\um a\t, Germany) Static SIMS analysis of polymer monolayers deposited onto noble metal substrates is a well suited technique for the characterization of polymer materials. Such layers have extensively been investigated concerning the identification of polymers and the determination of secondary ion (SI) yields, damage cross sections, and of transformation probabilities. But so far, most of such investigations have been carried out at room temperature. In order to study the influence of the sample temperature, we equipped a Time-of-Flight (TOF) mass spectrometer with a device for temperature control. In this contribution we report on the investigation of polymer monolayers on metal substrates by temperature programmed SIMS. We selected five model polymers for this investigation, representing five polymer classes of different chemical as well as SIMS behaviour: polystyrene (PS), polydimethylsiloxane (PDMS), polymethylmethacrylate (PMMA), the perfluorinated polyether Krytox, and polyethyleneglycol (PEG). We found an evaporation of intact molecules at well defined target temperatures for all investigated polymers when the samples are heated. From the temperature dependence of the yields of cationized intact oligomers we determined the activation energy for the desorption E\sub A\ as a function of the polymer chain length according to the Polanyi-Wigner-model. For all polymers E\sub A\ increases linearly with the polymer chain length. In addition, we studied the surface diffusion behaviour of these polymers using Imaging TOF-SIMS. For PDMS and Krytox we determined diffusion coefficients in the range of 10\super -7\-10\super -6\ cm\super 2\/s, whereas for all other polymers no surface diffusion occurs at room temperature.
3:10 PM		AS-ThA-6 Surface Characterization of Poly (p- phenylenevinylene) and its Derivatives, MEH-PPV and DMOS-PPV, using XPS and Static SIMS S. Kim (LG Electronics Research Center, Korea); H. Shim (Korea Advanced Institute of Science and Technology); D. Hwang (University of Cambridge); J. Lee, S. Kim, T. Kim (LG Electronics Research Center, Korea) The \phi\-conjugated polymers have received much attention for their use in the field of light emitting diodes (LEDs). Poly (p- phenylene-vinylene) and its derivatives, MEH-PPV and DMOS-PPV, have been used as the active luminescent layer. It is well known that polymer surfaces and metal-on-polymer interfaces play an important role in the stability and reliability of the polymer LEDs. In this work, surface analyses were performed using X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SSIMS) to investigate the polymer surface of PPV and its derivatives. The polymers were spin-casted onto glasses with thickness of about 1000 \Ao\. Besides the photoelectron lines and valence band spectra, X-ray induced Auger electron spectra and energy loss spectra were obtained using monochromatized Al K\alpha\ X-ray source. The changes in the intensity of \phi\ -> \phi\* transition and the amount of the plasmon energy loss among the three polymers could be explained with the structure of the polymers. Similar results were also observed in the fine structure of the X-ray induced Auger electron spectra. Positive and negative ions in the range of m/z = 0 - 255 were measured using SSIMS. A better understanding of the surface chemistry of PPV, MEH-PPV and DMOS-PPV was given from the complementary results of XPS and SSIMS.
3:30 PM		AS-ThA-7 Charge Neutralization Effects in High Resolution Electron Energy Loss Spectra (HREELS) of Polymer Surfaces J. Pireaux, Ch. Gregoire, l. Yu, R. Caudano (Facult\aa e\s Universitaires Notre-Dame de la Paix - LISE, Belgium) When insulating polymer or organic layers cannot be prepared as very thin films either by spin-coating or physical vacuum sublimation onto a metallic substrate, they cannot be studied by HREELS without charge neutralization, i.e. the use of the defocused beam from an auxiliary Auger electron gun (1, 2). For thick polymer surfaces, the influence of charge neutralization upon quantitative HREELS data has been recently addressed, suggesting that surface charging and (over)compensation affect the electron scattering and the near-surface probed depth; this has been attributed to the alteration of the primary beam energy by residual (positive or negative) surface charging (3). In order to more precisely address this question, we shall report on the systematic investigation of the significant vibrational spectra of one industrial polyethylene terephthalate (PET) film : for different experimental parameters (Eo : electron primary energy, varying between 2 and 10 eV; EA : Auger-gun electron energy, varying between 300 and 1 000 eV; IA : Auger gun emission current, varying between 0.1 and 3.5 mA; different scattering, specular and non specular, geometries), both the HREELS fingerprints and total electron loss spectra giving a direct measure of the real E0 were recorded. They do not evidence any significant alteration of the electron primary energy. Thus, alternate explanations for the influence of charge neutralization on HREELS polymer spectra recorded with different spectrometers will be suggested and discussed. 1. M. LIEHR, P.A. THIRY, J.J. PIREAUX and R. CAUDANO, Phys. Rev. B33 (1986) 5682 2. J.J. PIREAUX in "Surface Characterization of Advanced Polymers", Eds. L. Sabbatini and P.G. Zambonin, VCH, Weinheim (1993) p 47-82 3. G. APAI and W.P. MCKENNA, J. Chem. Phys. 98 (1998) 9735.
3:50 PM		AS-ThA-8 HREELS Studies of Vapor Deposited Polyaniline Thin Films R. Plank, J. Vohs (University of Pennsylvania); N J Dinardo (Drexel University) Polyaniline has received much attention due to its interesting electrical properties and technological promise as a conducting polymer. Polyaniline films are generally synthesized by chemical or electrochemical methods, however these 'wet' fabrication techniques are incompatible with many potential applications in the microelectronics industry. Alternatively, polyaniline films can be produced by vapor deposition. In this work, the structure and electronic properties of ultra-thin vapor deposited polyaniline films were characterized using High Resolution Electron Energy Loss Spectroscopy (HREELS). The HREELS results demonstrate that vapor deposition produces highly crystalline films composed of relatively short polymer chains. A plasma frequency indicative of Drude-like behavior was detected in the far-IR for films doped with HCl. This result demonstrates that vapor deposition can be used to produce films with high conductivities. The influence of film thickness and the identity of the substrate on the physical properties of polyaniline films has also been studied.
4:10 PM		AS-ThA-9 Polymer Self-Assembled Thin Films and Their Applications for Chemical Sensing B. Swanson, S. Johnson, J. Shi, D. Li, X. Yang (Los Alamos National Laboratory) Polymer self-assembly has been studied to fabricate a number of multilayer and multifunctional thin films for chemical sensing applications. Polymeric ions and molecular ions were deposited on the substrate surface layer by layer through electostatic interactions or chemical bonding. The films were characterized by ATR-FT-IR, UV-vis, XPS, X-ray reflectivity, ellipsometry and neutron reflectivity. The applications of these thin films for chemical sensing based on surface acoustic wave (SAW) devices will be discussed. It will be demonstrated that the sensing properties of fabricated films towards organic analytes can be controlled at the molecular level by using polymers with different functionality and by changing the surface polymer or thickness of the film.
4:30 PM		AS-ThA-10 Variable Angle Internal Reflection Raman Spectroscopy of Multi-layer Polymer Thin Films N. Fontaine, T. Furtak (Colorado School of Mines) We have developed and perfected a non-destructive Raman spectroscopy method which can be applied to the characterization of single- and multi-layered polymer films. The approach is related to the waveguide technique, but involves the acquisition of data as a continuous function of the angle of the incident excitation beam. It is extremely sensitive to the refractive index profile (to +/- 0.0002) and thickness (to +/- 10 nm) of the film. The unique nature of the Raman signature provides a means of studying the depth distribution of molecular identities and modifications which are a result of processing or aging. We have identified important beam handling requirements and precision limits that must be controlled to generate the necessary well-defined, variable electromagnetic field profiles. Our procedure involves exact optical field calculations using a new transfer matrix formulation which we have developed. In addition to the experimental details, our presentation will also describe the application of the technique to several prototypical structured polymer film systems.