AVS1996 Session AS-TuP: Aspects of Applied Surface Science Poster Session

Tuesday, October 15, 1996 6:30 PM in Ballroom A
Tuesday Evening

Time Period TuP Sessions | Topic AS Sessions | Time Periods | Topics | AVS1996 Schedule

AS-TuP-1 The Influence of pH on Nanofriction: A Possible Route to Nanochemical Imaging
A. Marti, G. H\um a\hner, N. Spencer (ETH Zurich, Switzerland)
Force measurements with an AFM (atomic force microscope) are highly sensitive to both tip and surface properties. Oxide surfaces and also some organic species are electrically charged in aqueous solutions, due to the interaction of surface groups (e.g. -OH) with H\sub 3\O\super +\ or OH\super -\ ions. A large number of these surfaces display an isoelectric point (IEP), corresponding to the pH at which the net surface charge is zero if there is no specific adsorption of ions. Previous work shows that the normal forces between tip and substrate may be attractive or repulsive depending on the surface charges and thus pH. Our data show that the kinetic friction (i.e. lateral force) between a Si\sub 3\N\sub 4\ tip and various surfaces in electrolyte solution is also strongly influenced by pH and sensitive to the IEP of the materials under investigation (when maintaining constant ionic strength). It was found that the friction between the AFM tip and the substrate is greater in the attractive case, i.e. when tip and sample are oppositely charged, compared to the repulsive case where tip and sample are similarly charged [1]. The pH-dependent kinetic friction images measured with the LFM (lateral force microscope) can therefore help to image different surface species according to their surface electrochemical properties and thus show potential for nanochemical imaging.[1] A. Marti, G. H\um a\hner, and N. D. Spencer, Langmuir 11, (1995) 4632
AS-TuP-2 Characterization of Atomic Force Microscopy Cantilevers used As Molecular Probes
G. Lee, N. Turner, L. Chrisey (Naval Research Laboratory); P. Dorsey (SFA Inc.)
By functionalizing silicon oxynitride AFM probes with specific chemical species, it is possible to characterize the chemical and physical properties of single molecules and surfaces on the nanometer scale. Cantilevers generally were modified by a multistep deposition procedure with 1) an organosilane film, 2) a heterobifunctional crosslinker, and 3) the molecule of interest. The surface and bulk composition of the AFM probe may be heterogenous; this can have a significant impact on the success (and reproducibility) of the multistep chemistry and subsequent use of the cantilevers. Analytical techniques such as XPS, AES, EDXA, and confocal laser fluorescence spectroscopy were employed to characterize the AFM probes. Variations from the expected composition of the commercial AFM cantilevers were found that rendered the probes incompatible with the functionalization chemistry. The cantilever surface composition was altered with pulsed laser deposition to provide a suitable substrate, i.e., SiO\sub2\, for the functionalization chemistry and was analyzed subsequently. The cantilever modifications were successful in terms of bioactivity and coating density.
AS-TuP-3 Hard Drive Analysis using Time-of-Flight Secondary Ion Mass Spectrometry
T. Schuerlein, C. Evans, P. Lindley, G. Strossman (Charles Evans and Associates)
Time-of-Flight SIMS (TOF-SIMS) is a surface analysis technique which has proven to be a useful tool in the analysis of hard disk drive components. TOF-SIMS is an extremely surface sensitive technique which is capable of identifying both atomic and molecular materials with detection limits ca. 2 orders of magnitude better than XPS or AES. Identification of molecular contaminants is accomplished using high mass resolution mass spectra. The technique is capable of imaging small features and defects with lateral resolutions of better than 0.2 micrometers.TOF-SIMS can be used to analyze both hard disks and heads. Applications investigating lubricants on hard disks that will be shown include: lube identification, identification of contaminant within the lube, segregation of lube additives, and the extent of lube degradation,. Hard disks also may be analyzed to identify and show localization of trace metal contamination (including cobalt and tin) as well as defect or particle analysis and identification.TOF-SIMS has also been successful in the analysis of read-write heads. Specific capabilities that will be shown include: identification and mapping of many types of pole tip contamination; metal segregation and smearing of the tips; and defects found on the head.
AS-TuP-4 Accurate Depth Profiling of the SiO\sub 2\/Si Interface by Surface SIMS
V. Chia, S. Smith, M. Edgell (Charles Evans & Associates)
The importance of thermal oxide films in IC processing is illustrated by its many applications such as gate oxide in MOSFETs, capacitor oxide in DRAMs, tunnel oxide in EAROMs, and screening oxide to randomize ion implants and reduce junction depths and contamination. The growth rate of high-quality, stable oxide films formed at high temperatures have been successfully predicted by the Deal-Grove model for silicon having surface doping levels below 10\super 19\ atoms/cm\super 3\. However, for thin film regimes (<300 \Ao\) this model is quantitatively inaccurate and requires adjustments to the B (parabolic rate constant) and B/A (linear rate constant) constants. This becomes relevant as VLSI devices continue to reduce in size and gate and tunnel oxide thicknesses in the range of \<=\100 \Ao\ is required. The ability to model the affects of Group III and Group V dopants in Si on oxidation growth rates is therefore of particular interest. SurfaceSIMS is an analytical technique that can accurately depth profile these dopants (B, In P, As, and Sb) from the SiO\sub 2\ surface through the SiO\sub 2\/Si interface into the Si substrate. The detection limits for P and B at \<=\10\super 16\ atoms/cm\super 3\ is sufficient to provide detail information for independent modelling of segregation. This paper presents the capability of SurfaceSIMS to: 1) accurately profile dopant species across oxide interfaces and compares the results with modelling data and: 2) provide dopant and impurity distribution information at the SiO\sub 2\/Si interface before and after oxide removal by HF.
AS-TuP-5 Determination of the Chemical Phase of Surfaces during Film Growth using MSRI
J. Schultz, K. Waters, J. Holecek (Ionwerks); V. Smentkowski, A. Krauss, D. Gruen (Argonne National Laboratory)
The surface analytical method referred to as mass spectroscopy of recoiled ions (MSRI) uses an energetic ion beam to induce a binary collision with species present on a surface. The energy of the binary collision is sufficient to induce complete molecular decomposition. The elemental surface species are ejected from the surface in the forward scattering direction and the ionic species are mass and energy analyzed, providing elemental analysis of the surface being studied. By comparing the positive recoil ion to negative recoil ion yields of various surfaces, we have found that MSRI can be used to characterize the chemical phase of surface species. It will be demonstrated that the positive-to-negative ion ratio of amorphous carbon, graphite, and diamond surfaces are distinct. Similar observations have been noted for hexagonal vs cubic BN, and there is reason to believe that measurements of the positive-to-negative ion ratio using MSRI may provide a general means of identifying various phases present at the surface. MSRI analysis during film growth at pressures of greater than 1 mTorr is possible. By measuring the positive to negative ion ratio during film growth, it will be possible to determine (and modify) the phase of the growing film -- during growth. Work supported by the U.S. Department of Energy, BES-Materials Sciences, under contract W-31-109-ENG-38 and CRADA C9405001The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory ("Argonne") under Contract No. W-31-109-ENG-38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid-up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.
AS-TuP-6 SIMS Characterization of an Amorphized Si Layer for Ultra-Shallow Junctions
I. Ivanov, S. Pramanick, W. Stockwell (AMD)
The paper describes the results of evaluation of SIMS technique to measure thickness of an amorphized Si layer during low-energy ion implantation for ultra-shallow junctions. The variations of Si molecular ion yields through a thick amorphized layer and single-crystal Si are measured, correlated to RBS channeling data and extrapolated to describe a nanometer -range thin amorphized Si layers. The effects of cesium and oxygen primary ions are measured at various ion beam energies and fluences. The measured layer profile distortions caused by energetic primary ions are corrected using a non-linear model. SIMS measurements of possible defect densities at the amorphized/single-crystal silicon interface and the role of atmospheric contaminants at this interface during anneal are discussed.
AS-TuP-7 SIMS Characterization of Na in SiO\sub 2\ Thin Films using Sample Cooling
J. Vajo (Hughes Research Laboratories)
Sample cooling to 95K has been found to suppress ion bombardment-induced migration of Na in SiO\sub 2\ thin films thereby improving the accuracy and reproducibility of SIMS depth profiles. Migration of mobile ions, such as Na, together with loss of secondary ion signal, due to sample charging, are persistent problems in SIMS analysis of SiO\sub 2\ thin films. Both problems can be alleviated by careful charge compensation using electrons. However, while charge compensation conditions that maximize secondary ion intensities are relatively easily achieved, it is much more difficult to achieve conditions that completely eliminate migration of Na to the SiO\sub 2\/Si interface. In addition, elimination of migration is often not reproducible even for nominally identical analysis conditions. The effects of sample cooling are illustrated for samples consisting of 430 nm of deposited SiO\sub 2\ ion implanted with Na at energies from 10 to 140 keV and fluences from 4 x 10\super 12\ to 1 x 10\super 14\ ions/cm\super 2\. SIMS profiles obtained at room temperature, with and without optimized charge compensation, are compared with those obtained at 95K. The profiles are also compared with the results of TRIM simulations. Sample cooling is found to expand the range of analysis parameters including primary ion energy, angle of incidence, sputtering rate and charge compensation conditions that eliminate Na migration. Decreasing the sensitivity to these parameters yields more reproducible profiles.
AS-TuP-8 A Complete Characterization of BPTEOS using SIMS
W. Stockwell, I. Ivanov, J. Manjkow (AMD)
The semi-conductor industry has steadily relied on BPTEOS, as an intermetallic dielectric for more than twenty years. As the complexity of integrated circuits increases it is even more important to properly characterize all the thin films. Tighter geometries require that the properties of the materials to be consistent and reliable. BPTEOS has in the past proved to be a difficult material to characterize. Wet chemistry has been an analytical method of choice in the past for accurate boron and phosphorous quantification but not many IC maufacturers have this capablity. Fourier transform infrared analysis, FTIR calibrated periodically by wet chemistry, is a successful method for measuring test wafers in the fabrication cleanroom but is limited to analyzing planar films on Si. This paper reports a method of using secondary ion mass spectrometry, SIMS, to quantify boron and phosporus on product, as well as test, wafers. A time dependent study of B and P dopant distributions in BPTEOS films with and without a poly cap is measured. The stability of as-deposited films is also compared to densified films. The sputter rates using O2 and Cs ion beams and corresponding chemical mechanical polishing rates are measured for BPTEOS films with different B and P concentrations. The variation of relative sensitivity factors, RSFs, used in SIMS quantification, is evaluated taking into account the standard used. We compare results using a special BPTEOS films and P and B implanted in oxide standards. The paper presents an atomic force microscopy analysis to study the surface topology and surface composition of these films.
AS-TuP-9 Temperature Programmed SIMS: Molecular Overlayers on Si Wafer Surfaces
M. Deimel, D. Rading, G. Egbers, E. G\um o\cke (Physikalisches Institut der Universit\um a\t M\um u\nster, Germany); A. Benninghoven (Physikalisches Institut der Universit\um a\t, Germany)
Heating of adsorbed molecules results in an excitation of all vibrational modes. The thermal energy is distributed rather evenly over the whole molecule so that weakest bonds tend to break first. In the case of physisorbed molecules these are the bonds to the substrate and the molecules desorb intactly. For chemisorbed molecules the binding energy to the substrate is in the same order as the intermolecular binding energy. Therefore, both an intact evaporation as well as a thermal induced degradation may occur, but at distinctly higher temperatures. Due to this differences in the temperature behaviour a distinction between physisorption and chemisorption is possible.We applied Temperature Programmed Secondary Ion Mass Spectrometry (TP-SIMS) to the investigation of molecular overlayers on Si-substrates. The investigated samples include monoreactive silane layers formed by the self assembly process as well as different model substances used in semiconductor processing prepared by spincoating.For the silane layers the yields of all charactristic secondary ions (SI) are not influenced by the sample temperature (T<670K). This indicates a strong bonding to the substrate with binding energies greater than 2 eV (chemisorption). In the case of physisorbed molecules an evaporation of intact molecules at relatively low temperatures is observed and the binding energy to the substrate can be determined. In the case of an intact evaporation all characteristic SI originating from the same molecules show the same temperature behaviour. This allows the assignment of characteristic SI in the spectra even for unknown surface species e.g. on a contaminated wafer surface.
AS-TuP-10 A ToF SIMS Evaluation of the Effectiveness of Sulfuric Acid/Hydrogen Peroxide Rinsing of Si
G. Nelson, P. Clews (Sandia National Laboratories)
Sulfuric acid hydrogen peroxide mixtures (SPM) are widely used in the semiconductor industry for removing organics from wafer surfaces. This viscous mixture is difficult to rinse off of the wafer surface. Light Point Defect (LDP) measurements after rinsing indicated that the residual contamination left on the wafer surface results in micron size particle growth after the wafers have been stored in a clean room environment. Imaging Time-Of-Flight SIMS (TOF SIMS) measurements determined that the particles contained SO\sub x\ and NH\sub 4\. In order to minimize the amount of deionized water required to rinse the SPM cleaned wafers without compromising the wafer cleanliness, a study to understand the particle growth mechanism has been carried out. TOF SIMS was used to monitor the effectiveness of the rinse by measuring the residual S on the surface as a function of rinsing conditions. This paper reports the result of these studies and suggests a particle growth mechanism that involves the interaction of the clean room atmosphere with the S on the surface of the Si wafer. This model is consistent with the experimental data. \super *\This work was performed at Sandia National Laboratories, which is operated for the U.S. Department of Energy under contract no. DE-AC04-94AL85000. This work was funded through a cooperative research and development agreement with SEMATECH.
AS-TuP-11 High Resolution Transmission Electron Microscopy of Electron Beam Induced Transformations in Zirconia-Alumina Nanolaminates
M. Schofield, M. Gajdardziska-Josifovska, C. Aita (University of Wisconsin, Milwaukee)
Nanolaminates consisting of alternating layers of polycrystalline zirconia and amorphous alumina were grown by reactive sputter deposition and studied by high resolution transmission electron microscopy (HRTEM). The high temperature tetragonal phase of zirconia is stabilized at room temperature in these nanolaminates by limiting the zirconia layer thickness to less than about 6 nm. In analogy to zirconia-containing composite systems with micron-sized crystallites, the tetragonal zirconia undergoes a transformation to the stable room temperature monoclinic phase upon application of stress, resulting in a transformation toughening of the material.HRTEM was used to induce the zirconia transformation in situ by locallized electron beam irradiation. For different electron doses, sequences of images were recorded, and phase determination of individual zirconia nanocrystallites was obtained by quantitative analysis of the HRTEM images of the zirconia layers.Under extreme irradiation exposures corresponding to electron doses of 5x108 electrons/=C52, significant changes were observed, and characteristic structures were identified in association with the zirconia transformation. Under moderate electron doses (3x106 electrons/=C52), changes of a continuous nature were observed, but no stable monoclinic phase was found, suggesting that the tetragonal nanocrystallites are resistant to electron beam irradiation. This contention is supported by results of experiments involving continuous irradiation of the sample under normal imaging illumination. This mild irradiation of the sample produced no stable monoclinic phase under observation times of up to an hour.
AS-TuP-12 The Nanometer-scale Structure of Polymer-clay Composites
T. Porter, M. Hagerman, M. Eastman, J. Attuso, E. Bain (Northern Arizona University)
The inclusion of organic guests such as aniline and pyrrole into hectorite thin films has been investigated. The subsequent polymerization of these guests on the clay surface and in the interlayer gallery regions are studied using scanning force microscopy (SFM), electron paramagnetic resonance (EPR) spectroscopy, X-ray diffraction (XRD), and impedance spectroscopy. A high degree of aniline surface polymerization as well as intergallery polymerization with a reduction of Cu(II) centers is observed for Cu(II)-exchanged clay films. The impedance of the aniline-hectorite film also decreases as the polymer forms. The impedance spectra of these systems can be modeled using simple circuits. Investigations of the inner architecture of polymer-clay composites are crucial in the development of nanochemical materials including chemical sensors, photonic thin films, and inorganic-organic conductive polymer assemblies.
AS-TuP-13 Characterization of Chitosan and Rare-earth Metal Doped Chitosan Films using XPS
H. Jiang (Anteon Corporation); W. Su (Wright Laboratory); J. Grant (University of Dayton)
X-ray photoelectron spectroscopy has been used to study the effects of dopant rare-earth metal ions on thin chitosan films fabricated from chitosan - acetic acid solutions. These films are being studied for optical applications as they are transparent over the wavelength range of 300 to 3000 nm and exhibit low optical loss in a waveguiding geometry. For this work, chitosan was dissolved in 2 wt% acetic acid and a doping ratio of 30 wt% to chitosan was used. The rare-earths used for doping were Nd\super +++\ from Nd(NO\sub 3\)\sub 3\ and Er\super +++\ from ErCl\sub 3\. The precursor solutions were filtered and the films were formed by spin-coating the solutions on gold coated coverglass substrates at room temperature. After drying, the films were analyzed with a Surface Science Instruments M-Probe spectrometer using monochromatic Al K\alpha\ radiation. Data were taken at take-off angles (measured relative to the surface plane) of 30 and 90 degrees to check for surface contamination. All films showed clear evidence for multiple chemical states of nitrogen. The main N 1s peak was separated into two components, with the lower binding energy component attributed to nitrogen in the undoped chitosan. The other component is a combination of the weak interaction with acetic acid and complexation with the rare-earth metal ions. The C 1s peak was resolved into three components and the intensities were compared with those expected from chitosan. The agreement was good for the undoped films, but surface contamination affected the results for the doped films. No significant change in the O 1s peak shape was observed, indicating that hydroxyl groups are not involved in the complexation. This work supports a model where complexes of the rare-earth metal ions are formed with amine groups of the chitosan. - ---------- This work was sponsored by the Materials Directorate, Wright Laboratory, Air Force Materiel Command, Unites States Air Force, Wright-Patterson AFB, Ohio 45433-6533, USA.
AS-TuP-14 The Effects of Iron Content on TiN Diffusion in Float Glass
T. Paulson, C. Pantano (Pennsylvania State University)
The bottom surface of float glasses, by the very nature of the float technique, become enriched in tin, generally accepted as primarily SnO, during manufacturing. Upon subsequent annealing in air, the SnO diffuses toward the surface and becomes oxidized. The accumulation of SnO\sub 2\ at the surface, described as the segregation coefficient, decreases sharply as the iron content of the glass is increased. The degree of initial tin penetration depends on numerous factors such as the composition/redox of the glass, the activity of oxygen in the tin bath, metallic contamination of the float bath, oxygen contamination in the atmosphere above the tin and/or the temperature of the glass/tin. In fact, there are such a large number of variables that it would be difficult to isolate, and further investigate, the dominant mechanisms of tin penetration on a commercial float line.In order to study the tin diffusion in float glasses under controlled conditions, a miniature float bath apparatus, which fits into a horizontal tube furnace, has been developed in our lab. The tin used in our experiments was initially heat treated in a graphite boat at 600\super o\C in a H\sub 2\:N\sub 2\ atmosphere to remove any native oxide and reduce the amount of dissolved oxygen in the tin. The float experiments were carried out at temperatures ranging from 700 to 1100\super o\C, and the tin-sides of the glasses were analyzed using SIMS, EPMA, and XPS. As the iron content of the glass increased or the float temperature increased, the degree of tin penetration decreased. The combined effects of glass composition and temperature, both in the tin bath and during annealing, will be discussed in this presentation.
AS-TuP-15 Oxide Thickness and Color Changes on Erbium Dideuteride Films
T. Taylor, C. Maggiore, H. Kung, D. Cooke, F. Steinkruger, D. Powers, Jr. (Los Alamos National Laboratory)
Erbium thin films, grown using electron-beam deposition, have been loaded from the gas phase with deuterium to give a light-blue dideuteride compound. The color is observed to darken a variable amount when exposed to air depending on the processing conditions, which include activation of a native oxide layer by heating above 250 C at pressures below 10\super-7\ Torr. Surface science, microscopy, ion beam, and optical diagnostics have been utilized to understand the processing chemistry and the atmospheric oxidation that occurs after re-exposure to air. X-ray photoelectron spectroscopy has shown that the activation step involves decomposition of hydroxyl and carbon species during reconfiguration of the oxide and growth of surface carbide. The oxide that results from the activation and loading serves as a reactive template with nucleation sites. Higher processing temperatures produce a film that is more prone to color change. These effects will be discussed in terms of oxide thickness and light scattering as they relate to the atomic-level and processing steps found during the deuterium loading.
AS-TuP-16 Surface Composition and Electrical Properties of Treated Carbon Blacks
T. Lenk, M. Wartenberg, L. Smith (Raychem Corporation)
Carbon blacks are intrinsically conductive materials, and carbon filled composites are an important class of conductive polymers. Electrical conductivity varies between carbon blacks, and part of the variation shows a correlation with the surface chemistry. This work explores the relationship between surface chemistry and conductivity in more detail. A commercial carbon black was first cleaned by extraction with water and toluene. A portion of the material was then subjected to heat treatment under nitrogen at temperatures ranging from 450 to 1200C. The heat treatment decreased both the surface oxygen concentration and the electrical resistivity of the powder. Another portion of the material was oxidized by exposure to nitric acid at concentrations ranging from 0.2 to 15.9N. The increasing surface oxygen content in this case correlates with an increase in the powder resistivity. Peak fitting of the oxygen 1s region was used to determine the distribution of surface oxygen species after the various treatments, and correlations with resistivity changes were seen for both the acid and heat treated samples.
AS-TuP-17 Selected Energy Growth of Al Nitride Observed with In Situ Emission Microscopy
M. Kordesch, V. Ballarotto (Ohio University)
Several selected energy nitrogen sources are combined with in situ emission microscopy in order to observe the growth of AlN. Seeded Molecular Pulsed Beam (SMPB) gas sources offer a very narrow energy spread neutral beam for materials growth. Two versions of the SMPB source, the first one, an unskimmed pulsed valve in close proximity (30mm) to the growth surface in a chamber equipped with a photoelectron emission microscope (PEEM) is used for in situ real time observation of pulsed beam deposition. The pulses typically used range from 200 µs to 1.5 ms with stagnation pressure of 20 psig. The second system uses a skimmed pulsed beam. Initial experiments using a 5% Ammonia in Hydrogen beam onto a Al covered Si surface have been performed. The beam was pulsed for approximately 40 minutes for a duration of 300 us at frequency of 0.5 Hz. Two sets of experiments were performed, 300 K deposition of Al and ammonia exposure and 300 K deposition and post-deposition annealing to about 900 K. Ammonia adsorption was observed in both cases; unstable, "flickering" electron emission sites were observed during annealing. The morphology of the films formed by various processes will be discussed. This work is partially supported by BMDO/ONR grant N0014-95-1-0298 and N00014-96-1-0782.
AS-TuP-18 An XPS Study of the Chemical Interaction between Bn and Ti/TiN
S. Seal (University of Wisconsin, Milwaukee); E. Benko (The Institute of Metal Cutting, Poland); N. Sobczak (Foundry Research Institute, Poland); T. Barr (University of Wisconsin, Milwaukee)
Many nitrides, particularly Bn and TiN, have stimulated commercial interest because of their extreme hardness, wear and corrosion resistance, and thermal and electrical properties. All of these features are enhanced by the resulting structures and the large degree of covalency exhibited by the metal nitride bonds. Coatings of select nitrides with film of related materials may particularly influence these properties in critical surface and interfacial regions. Materials of interest include the deposition by PVD of Ti and TiN on BN substrates. Some of these systems were then subjected to varying degrees of physical and thermal alteration. Resulting structural and morphological features have been investigated with electron microscopy and X-ray diffraction (XRD). Critical importance is attributed to the chemical behavior of species deposited and grown at the resulting interfaces. Detailed X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and Secondary ion mass spectrometry (SIMS) have been rendered of these interfaces using cross-sectional display and sputter etching. Movement of nitridation and interference from oxidation and carbide formation are of particular concern.
AS-TuP-19 Surface Structural Study of 1-Cyano-3-Phenyl-Urea Organic Thin Films
H. Gao, L. Ma, Z. Xue, S. Pang (Chinese Academy of Sciences); Y. Song, H. Chen (Peking University, China)
Different types of the surface structure of 1-cyano-3-phenyl-urea (CPU) thin films on highly oriented pyrolitic graphite (HOPG) substrates were observed with scanning Tunneling microscopy (STM). The CPU is a new synthesized organic material, and its metallic composites, such as Ag-CPU, show striking functional properties. The CPU thin films on HOPG were prepared by an ionized-cluster-beam (ICB), physical vacuum deposition and solution dip methods. It was found that the CPU was polymerized during the ICB deposition, and 5 to 8 CPU molecules formed a cuboid-like structure. At a low CUP concentration in the solution, double-CUP units can be arranged periodically on the HOPG substrate. The possible formation mechanism of these structures is discussed in this report.
AS-TuP-20 An Interaction Free Energy Analysis of Solvent Effect on Surface Segregation of Polymer Blends
J. Zhao (State University of New York, Buffalo); J. Gardella, Jr. (AVS)
The free energy of interaction \Delta\G\sub 132\ [1] (1=polymethylmethacrylate-PMMA, 2=polyvinylchloride-PVC, 3=methylethylketone-MEK or tetrahydrofuran-THF), which is defined as the free energy of interaction between two semi-infinite parallel sla bs of phase 1 and phase 2 and separated by a film of 3, was calculated from their surface tension parameters \gamma\\super LW\ (Lifshitz-Van der Waals interaction), \gamma\\super +\ and \gamma\\super -\ (electron acceptor-donor interaction). An analysis o f solvent-3 effect on the surface segregation of polymer blend-1 and 2 was achieved by the calculated \Delta\G\sub 132\ data. The higher the \delta\G\sub 132\ value means the stronger the immiscible tendency of the polymer blend, hence the more extensive the surface segregation is.Our result shows that \Delta\G\sub PMMA|MEK|PVC\=-3.94mJm\super -2\ and \Delta\G\sub PMMA|THF|PVC\=-2.84mJm\super -2\. This is to say, for the same preparing conditions, MEK-cast PMMA-co-PVC blend films show less extent of surface segregation then THF-cas t films. The increase of the \Delta\G\sub 132\ of THF-cast blend is due to the change of \gamma\\super LW\(MEK)=24.6mJm\super -2\ to \gamma\\super LW\(THF)=27.4mJm\super -2\, while the less electron donor property of THF than that of MEK partially balance s this change. This result is in agreement with the experimental observations studied by Schmidt and Gardella using ATR FTIR and XPS in our lab [2].[1] C.J. VanOss, Interfacial Forces in Aqueous Media, New York:M. Dekker, 1994 [2] J. Schmidt and J. Gardella, Macromolecules, 22, 4489 (1989)
AS-TuP-21 Polymer Surface Modification using Hydrazine and Hydrazine Derivatives
C. Lawson, J. Fulghum (Kent State University); D. Surman (Kratos Analytical)
Derivatization of polymer surface groups to improve XPS sensitivity is currently of increasing interest due to the availability of high resolution monochromatic x-ray sources and efficient charge neutralization systems. Gas-phase derivatization methods have a number of advantages over solution methods, including decreased swelling or reorientation of the polymer and increased surface sensitivity of the derivatization. Hydrazine has previously been used to modify surface carbonyl groups in polymers such as poly(vinyl methyl ketone) (PVMK) in the gas phase. We will compare derivatization by hydrazine and several hydrazine derivatives. The sensitivity of valence band spectra to changes in the polymer surface and the use of angle-resolved valence band spectra to evaluate the extent of modification will be presented. This project has been supported by Dow Chemical, the NSF Science and Technology Center for Advanced Liquid Crystalline Optical Materials (ALCOM) under DMR89-20147, and the W.M. Keck Foundation.
AS-TuP-22 XPS and ISS Analysis of Copper Overlayers on COOCH3- Terminated Self-assembled Monolayers
A. Czanderna, G. Herdt (National Renewable Energy Laboratory)
The purpose of our metal/self-assembled monolayer (SAM) studies is to characterize chemical and physical interactions between SAMs terminated by specific organic functional groups (OFGs) and vacuum deposited metals. SAMs are used as model organic surfaces to control experimental variables in these studies. In the present work, x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) were used to characterize methyl 16-mercaptohexadecanoate (MMHD, HS(CH2)15COOCH3) SAMs on gold films before and after vacuum deposition of up to 1.0 nm Cu onto the OFG of the SAM end group. XPS C 1s and Cu 2p spectra give no detectable evidence of chemical interaction between Cu and the OFG at 295 K, but the Cu LMM and, especially, O 1s gave evidence of a weak interaction between Cu and the O in the OCH3 part of the ester. Results from ISS analysis of 1.0 nm deposited Cu on these SAMs show that Cu penetrates MMHD in approximately 440 min. at 295 K. We attribute the slower penetration of Cu through MMHD relative to other non-interacting systems (e.g. Cu, Ag, or Au/CH3) to weak interactions. *This work was supported by NREL under Contract No. DE-AC36-83CH10093 to the U.S. Department of Energy.
AS-TuP-23 Interfacial Chemistry of Accelerated Weathered Metallized Polymer Materials
G. Jorgensen, D. King, H. Kim (National Renewable Energy Laboratory)
Low cost, highly durable, polymer reflectors are critical elements of solar thermal concentrator systems. Correlation between accelerated weathering and real time in-service environmental exposure will allow accurate service lifetime prediction of these materials. An extensive sample matrix of silvered polymethylmethacrylate (PMMA) polymer mirrors was prepared. The samples were optically characterized and introduced into accelerated exposure testing in a XENOTEST 1200 LM environmental chamber. Spectral hemispherical reflectance was measured as a function of exposure time, and selected samples were discontinued at various exposure times to allow surface analysis (XPS) of the silver/polymer interface. Correlations between optical degradation and interfacial chemistry as a function of exposure time is discussed. *Performed under DOE contract DE-AC36-83CH10093
AS-TuP-24 Extracting More Chemical Information from X-ray Photoelectron Spectroscopy by using Monochromatic X-rays
P. Sherwood (Kansas State University)
Monochromatized X-ray sources have been available for use in commercial X-ray Photoelectron spectrometers for more than 20 years. Nevertheless most X-ray photoelectron spectroscopic data is collected using achromatic radiation. This paper will discuss the advantages of using monochromatized XPS combined with high resolution data collection for the study of core and valence band XPS. Examples to be discussed will include studies of oxidation and corrosion and carbon fiber surfaces. Both core and valence band XPS will be covered, and in both cases additional chemical information will be seen to be available when monochromatized XPS is combined with high resolution data collection. Examples will also be provided of how fine details of the valence band data can be understood by comparison of the experimental spectra with spectra calculated from cluster and band structure calculations.
AS-TuP-25 Dependence of Film Morphology on the Preparation of Surface Alignment Layers in Nanometer Scale Polyimide Films by Quantitative Infrared Spectroscopy
G. Hietpas, J. Sands, S. Kumar, D. Allara (Pennsylvania State University)
Thin films of Poly(biphenyl dianhydride-p-phenylene diamine) (BPDA-PDA) in the 5-300nm range were prepared by spin casting of the polyamic acid precursor onto Si[111] substrates, and imidized at 573-673K. The films were characterized by X-ray reflectivity (XRR), ellipsometry, infrared (transmission and reflection) polarization difference spectroscopy (IRPDS). Quantitative determination of film structure was made by detailed analysis of the IRPDS spectra using established 4X4 matrix methods to account for the large dielectric anisotropy. The data show that the film structure consists of the expected layered stacks with backbone planes parallel to the substrate in randomly oriented domains. A greater degree of in-plane order was observed as the film thickness decreased. The response to unidirectional buffing was found to be directly related to the degree of in-plane orientation of the initial film structure.
Time Period TuP Sessions | Topic AS Sessions | Time Periods | Topics | AVS1996 Schedule