AVS2001 Session AS-MoP: Student Poster Competition/Aspects of Applied Surface Analysis I Poster Session
Monday, October 29, 2001 5:30 PM in Room 134/135
Monday Afternoon
Time Period MoP Sessions | Topic AS Sessions | Time Periods | Topics | AVS2001 Schedule
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AS-MoP-1 Vesicle to Supported Bilayer Transformation Kinetics; Influence from Vesicle Size, Temperature and Surface Support
E. Reimhult, K. Dimitrievski, V.P. Zhdanov, F. Höök, B. Kasemo (Chalmers University of Technology, Sweden) Supported phospholipid bilayers (SPB) on solid surfaces are biologically functional components of high current interest, e.g., for biosensors, tissue engineering, and basic science (Sackman, Science 271:43 (1996)). We investigate how the kinetics of vesicle to bilayer transformation on SiO2 depend on vesicle size using small Extruded Unilamellar Vesicles (EUV; diameter~30-200 nm) and Small sonicated Unilamellar Vesicles (SUV; diameter~25 nm)) and temperature (T~5 to 30°C). ). The experimental results are complemented by computer modeling and MC simulations. Our results reveal weak but significant vesicle size-dependent kinetics. The rate and completeness of the vesicle-to-bilayer transformation is strongly dependent on temperature and the vesicle-to-bilayer formation on SiO2 can under certain circumstances be completely inhibited at low temperatures. In addition, the vesicle-surface interaction was investigated for various surfaces, including oxidized Au, Pt and Ti, which all demonstrate adsorption of vesicles in an intact state independent of vesicle size and temperature. The obtained results extend our previous studies at constant vesicle size and temperature (Keller et al, Phys Rev B 61: (3) 2291 (2000)) and constitute a platform that will significantly improve the possibility to control the process on microm-nm fabricated surfaces, from which more complex functional supported bio-membranes are constructed. |
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AS-MoP-2 Thermal and Electron-beam Irradiation Effects on the Surfaces of Niobium1
Q. Ma, R.A. Rosenberg (Argonne National Laboratory) Superconducting radio frequency (SCRF) cavities represent the future for producing high acceleration gradients. Many problems encountered during the course of rf cavity production, such as the field emission of impurity particulate, have largely been solved, and nowadays gradients as high as 25 MV/m are readily achievable. However, new issues are emerging that limit further increases of the accelerating gradient. It has become increasingly apparent that further advances in cavity performance will be linked to scientifically understanding the nature of the surface oxide layer. Preliminary results of a study of the surfaces of Nb samples for SCRF cavities are presented. The samples were prepared by chemical etching or electro-polishing, the processes used in cavity production. The surfaces of such prepared samples are covered typically by a layer of oxides and some hydrocarbons. The study is focused on thermal effect on the surfaces of as-prepared samples and on electron-beam interaction with these surfaces. At temperatures from 200 C to 300 C, the surface oxide reduction occurs. The native Nb2O5 oxide reduces to Nb2Ox (x ≤ 1). Some niobium carbide also forms on the surfaces. As a result, the secondary electron yield (SEY) decreases dramatically. At these temperatures, oxygen migration into Nb is evidenced, for which the diffusion coefficient is estimated. It is also found that the SEYs of as-prepared samples decrease significantly under electron-beam irradiation, which can be accounted for by the electron-beam-induced changes in surface chemistry. These changes will be discussed in terms of the effect of the cross section of electron/matter interaction. |
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AS-MoP-3 Determination of In-Depth Profiles Using Deconvolution of Angle Dependent XPS: Model Systems and Copolymer Surface Compositions
C.M. Mahoney (State University of New York at Buffalo); J. Elman (Eastman Kodak); J.A. Gardella, Jr. (State University of New York at Buffalo) The depth information obtained by angle dependent XPS is not a direct measure of the composition as a function of depth. All atoms within the path of the probing X-ray will contribute to the signal, but the contribution of each will decrease exponentially with distance from the free surface. The spectra obtained are convoluted in a manner which will be more representative of the very surface, rather than deeper into the bulk. Here we test a numerical algorithm with defined boundary conditions based on polymer compositions. Unlike previous algorithms, this method was designed for samples with compositional gradients, as is common with many copolymer systems. Previously we have reported this method in studying copolymer surfaces including poly(amideurethane), Dimethylsiloxane-Urea-Urethane, and Poly(imidesiloxane) block copolymers. However, most of this work has described the relative compositions between various polymers. It is of interest to determine the accuracy of this algorithm in determining overlayer thicknesses and concentration depth profiles. The accuracy was determined through comparison of the calculated values to model systems based on polymer chain configurations. It has been determined that this method is accurate in the approximation of overlayer thicknesses in copolymer systems. The accuracy of this technique will be further examined through measurement of a reference material containing a thin layer (20-30Å) of poly(methylmethacrylate) (PMMA) deposited on Si containing its native oxide. |
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AS-MoP-4 Defect Layer Detection at the Surface of Polycrystalline Cu(In,Ga)Se2 by SIMS Depth Profiling, AES, SEM and TEM
S.E. Asher, F.S. Hasoon, H. Althani, K.M. Jones, C.L. Perkins, M.R. Young (NREL) Polycrystalline thin-film solar cells based on the ternary chalcopyrite semiconductor Cu(In,Ga)Se2 (CIGS) have produced devices with the highest recorded efficiencies for any thin film technology, near 19%.At NREL, absorber films are grown using a three-stage process with co-evaporation of the elements in a Se atmosphere.1 The growth parameters of the final stage are important to obtaining high efficiency devices. Recently, cross-sectional SEM and TEM results have shown that certain third-stage growth conditions result in the formation of a defect layer near the surface of the absorber layer. This layer can be up to 250 nm thick depending on conditions. However, despite the change in microstructure, Auger depth profiles across this interface do not reliably show the presence of a compositional change. We have found that a simple SIMS depth profile following Na correlates well with the existence of the defect layer near the surface of the CIGS layer. We believe this is due to increased Na incorporation along the defects and grain boundaries in this layer. In this study, SIMS results are correlated with AES compositional profiles and SEM and TEM micrographs. SIMS provides a rapid means to access compositional changes occuring in the near surface region of the CIGS absorbers. |
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AS-MoP-5 Charged Layer Calculation for an Effective Surface/Interface Analysis of Insulating Oxides using AES
S. Wannaparhun, S. Seal, V. Desai, K. Scammon, Z. Rahman (University of Central Florida) Auger Electron Spectroscopy (AES) can provide compositional information with excellent spatial resolution. Unfortunately, charging problem has known to be a major obstacle for characterizing insulating materials. Four parameters affect the degree of charging phenomenon; (i) resistivity of materials, (ii) primary electron beam energy, (iii) total electron yield, and (iv) sample thickness. First three parameters have been paid attention for overcoming the problem, however the charging problem still exists. Herein, a proposed model to overcome the charging in all insulating materials has found to be successful in analyzing insulating materials. A negatively charged layer will present at the top surface when the insulating material is analyzed using an e-beam. The negatively charged layer thickness is a function of the e-beam energy and other material constants (such as density, average atomic number, and average atomic mass). The accumulated negative charges will dissipate to the ground when the sample thickness is equal or less than the charged layer. Hence, the sample thickness in this case is defined as an effective thickness. Both capacitor and double charged layer models are applied to calculate the effective thickness of insulating materials for Auger analysis without charging. The effective thickness is used as a criterion for sample preparation. Focused ion beam (FIB) technique is utilized to prepare a specimen with the effective thickness as predicted by the model for minimal or no charging during analysis. An oxide/oxide ceramic matrix composite; Nextel 720 fiber/ aluminum oxide for high temperature applications in gas turbine was selected for this study. A thin specimen including an interface between the fiber and the matrix is imaged and corresponding AES spectra are acquired from selected regions with no charging. The results are compared to a thicker sample, which suffered severe charging during AES analysis. The effective thickness for more than fifty solid oxides are also calculated using our model for future AES analysis without charging and is presented in a periodic table format. |
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AS-MoP-7 Innovative Design of a Temperature Controlled Sample Holder
D. Castro Alves, O.M.N.D. Teodoro, A.M.C. Moutinho (New University of Lisbon, Portugal) To study many surface phenomena, the sample temperature is a fundamental parameter. Adsorption and desorption, as well as diffusion, are examples of experiments where the temperature plays an important role. In this work, we described a sample holder adequate to work in a temperature range of 100K to 1200K with the possibility to achieve fast cooling and heating rates. The central part of the sample holder is similar to a ball bearing. The external piece was built in copper OHFC and is connected to the cold source a liquid nitrogen reservoir. The inner ring was made in molybdenum and holds the sample. Between this ring and the external piece, sapphire balls provide the proper thermal connection good thermal conductivity at low temperatures and poor cond uctivity at high temperatures. The sample may be tight and released via a bolt in the external piece. Since the perimeter of this piece is open, the bolt decreases the perimeter of the groove where the balls are fitted and subsequently the inner ring (als o open) is compressed against the sample. This provides a very good thermal contact without the need of welding, as is the case of many sample holders. In order to control the temperature, heating is provided by electron bombardment from the opposite side of the surface under study. A thermocouple is connected directly the sample and is used to measure the temperature. Control is performed by computer. Further details as well as heating and cooling rates will be presented. |
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AS-MoP-8 TOF-SIMS and XPS Characterisation of Novel Perfluoropolyether-urethane Ionomers from Aqueous Dispersions
R. Canteri, G. Speranza, M. Anderle (ITC-IRST, Italy); S. Turri, S. Radice (Ausimont SpA, Italy) The introduction of perfluoropolyether (PFPE) bifunctional macromers, in polyurethane coatings1,2 has lead to an improvement of the durability characteristics and surface properties of the material, while maintaining the advantage of an easy application technology in a variety of environmental conditions and temperatures.3 In this work we present a surface characterisation by TOF-SIMS and XPS of a new series of polymer thin films containing PFPE macromers, applied in form of PolyUrethane Aqueous Dispersions (PUAD). In fact, environmental issues are forcing the development of waterborne polymer systems (dispersions or emulsions) to reduce the problems of solvent emissions in the atmosphere. The PUAD systems presented in this work can be defined as polyurethane ionomers, since self-dispersion in water is achieved by using co-monomers containing a -NR3 or a -COOH group, which can be salified with acids or bases. A number of experimental parameters like polymer molecular weight, crosslinking, average fluorine content as well as position of fluorinated segments in the macromolecular backbone, are investigated by selective syntheses and molecular characterization of a series of model PFPE containing polyurethane ionomers. The analysis of the outermost layer of the dried waterborne coatings by TOF-SIMS is compared with analyses by XPS obtained at two different take off angles for sampling different thickness. These results are finally compared with those obtained on the solventborne crosslinked coatings4 containing similar PFPE macromers. |
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AS-MoP-9 Experimental vs. Theoretical Studies of Amine Reaction Pathways on Si(100)
A.J. Carman, S.M. Casey (University of Nevada, Reno) Theoretical analysis of methylamine (MA) and dimethylamine (DMA) adsorption on silicon clusters has been undertaken to deduce the mechanism by which small carbon- and nitrogen-containing molecules react with the silicon surface. Possible dissociative adsorption pathways have been examined including calculating transition states from the physisorbed state to the dissociated, chemisorbed products. Three reaction pathways were examined: N-H bond cleavage, N-C bond cleavage, and C-H bond cleavage, followed by adsorption of the resulting fragments. The N-H bond cleavage pathway presents the lowest transition state to dissociative adsorption for both molecules. MA adsorption on the Si(100)-(2x1) surface has also been studied experimentally using Auger electron spectroscopy (AES), low-energy electron diffraction, and thermal desorption spectroscopy (TDS). Experimental evidence shows that at room temperature MA chemisorbs dissociatively on this surface. TDS data show that the chemisorbed adsorbates can decompose via reactions that form gaseous hydrogen, ammonia, and methylimine products. AES results show that MA surface decomposition leads to the slow deposition of carbon- and nitrogen-based films. An analysis of the AES and TDS data will be discussed along with results from the theoretical adsorption studies to examine the predictive power of these computational methods. |
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AS-MoP-10 TOF-SIMS and Laser-SNMS Characterization of Cell Cultures and Tissue Material
M. Fartmann, S. Dambach (Universität Münster, Germany); A. Wittig, W. Sauerwein (Universitätsklinikum Essen, Germany); H.P. Wiesmann (Klinik und Poliklinik für Mund-, Kiefer- und Gesichtschirurgie Münster, Germany); H.F. Arlinghaus (Universität Münster, Germany) In medical and pharmaceutical research, knowledge of the distribution of drugs and intrinsic elements and molecules in tissue sections and even inside individual cells is of great interest. We have applied TOF-SIMS and Laser-SNMS for imaging and quantifying atomic and molecular species in biological samples. Both techniques can simultaneously detect all masses with very high sensitivity and sub-cellular resolution. Since most of the sputtered particles are neutrals, Laser-SNMS has the additional advantage of significantly reducing the matrix effect. To prepare cell cultures for mass-spectrometric analysis, a freeze-fracturing method was used. Hereby the cells are sandwiched between two substrates before being frozen. This sandwich is then pried apart in its frozen state, so that some cells are torn. Subsequently, the samples are freeze-dried. The fractured cells can then be examined with TOF-SIMS and Laser-SNMS. Successful sample preparation is characterized by the distribution of the Na/K ratio. We have used TOF-SIMS and Laser-SNMS to examine freeze-fractured, freeze-dried bone and cancer cell cultures and freeze-dried cryosections of bone tissue. For analysis, a gridless reflectron-type TOF mass spectrometer with a 30 keV Ga LMIG and an excimer laser was used. For nonresonant postionization, the excimer laser beam (wavelength = 193 nm) was focused down in front of the target. With both techniques, high resolution elemental and molecular images and mass spectra were obtained from cell cultures and tissue samples. Ion-induced electron images were obtained to identify individual cells. The measurement of the Na/K ratio clearly showed that the preparation technique preserves the chemical und structural integrity of the cells. It can be concluded that TOF-SIMS and Laser-SNMS are well suited for imaging trace element and molecule concentrations in biological tissues. |
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AS-MoP-12 Evaluation of the Surface Morphology of Chemically Treated Fluorides by AFM
M. Suzuki (Tohoku Institute of Technology, Japan) Alkaline earth fluorides are suitable materials as substrates for the epitaxial growth of several semiconductors, and the (111)surface of cleaved CaF2 or BaF2 and (Ca,Ba)F2 buffer layers on (111)Si have mainly been used. The crystalline quality of epitaxial layers are influenced by the surface morphology and structure of fluoride substrates and it has been known that bombardment of energetic electrons or ultra-violet irradiation makes the surface structure of fluorides change and improve the quality of epitaxial layers on them. In this study, wet chemical treatments were applied to fluoride substrates and their effectiveness was evaluated in improving the surface morphology by atomic force microscopy(AFM) and reflection high energy electron diffraction(RHEED). The polished (111)CaF2 and BaF2 substrates with optical flatness were chemically treated at room temperature by using diluted solutions of HF,HCl, and NH4Cl for the different concentrations and treatment times . The morphological changes of substrates by treatment with different solutions were compared in detail. The best results were obtained for the CaF2 treated with 16.3%HF for 15 minutes and for the BaF2 with 0.3%HCl for 35 seconds. Under this condition, the surface roughness(rms) of both substrates could be obtained to be within a few nanometers, which provides a capability for epitaxial growth of high quality layers . Evaluations with RHEED would be also discussed. |
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AS-MoP-13 Impurity Dopant Profile Measurement and Quantization in sub-100nm Region
E.-S. Kang, H.-J. Hwang (Chung-Ang University, Korea); G.-Y. Lee (Samchok National University, Korea) We have quantitatively extracted 1-dimensional carrier profiles from the scanning capacitance microscope (SCM) dC/dV versus V curves using the SCM inversion modeling. This is based on the spherical capacitor model not the common parallel-plate capacitor model. Since the current SCM system has a poor reproducibility for obtaining the local dC/dV curves in the higher dopant concentration region, this problem will prevent us from acquiring carrier depth information correctly. For the more accurate inverted dopant profile in sub-100nm region, therefore, we have added some factors such as SCM tip/sample interaction and fully-calculated volume charges into previous modeling parameters. Also, we have designed a new capacitance detector operating about 1.8GHz frequency. It consists of a voltage-controlled oscillator with PLL (Phased-Lock Loop), a microstrip resonator, a RF mixer IC for detecting the capacitance variations. This technique will bring a greater enhancement for the current SCM sensitivity and performance. |
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AS-MoP-14 Non-destructive Testing of Mechanical Properties of Thin Films below 100 nm with Laser-acoustic Waves
T. Schuelke, D. Schneider, B. Schultrich (Fraunhofer Institute for Materials and Beam Technology) The non-destructive testing of hard-coatings is highly desirable. The available test methods are permanently confronted with manifold new demands of the surface engineering arising from reducing film thickness, more complicated film composition and extreme mechanical requirements as high hardness, stiffness and adhesion. The laser-acoustic technique based on surface acoustic waves is a relatively new surface test method, but its capability for testing thin and hard coatings has already been demonstrated. The laser-acoustic method yields the Young's modulus revealing the effect of varying bonding structure of the material, porosity and other micro-defects, including insufficient adhesion. The method has been adapted to the requirements of testing ultra-thin films. The special methodical aspects of testing these films are presented, such as the effect of measuring accuracy, bandwidth and sample dimension. |
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AS-MoP-15 Atomic-Scale Modeling of Plasma Enhanced Chemical Vapor Deposition of Hydrogenated Amorphous Silicon Thin Films
S. Sriraman, S. Ramalingam, E.S. Aydil, D. Maroudas (University of California, Santa Barbara) Hydrogenated amorphous silicon (a-Si:H) thin films grown by plasma assisted deposition from silane containing discharges are widely used in photovoltaic and flat-panel display technologies. Despite extensive research, the elementary processes that lead to film deposition, H incorporation, and defect generation are still not well understood. Developing deposition strategies for improving film quality requires a fundamental understanding of the interactions of radicals, such as SiHx (0 |