AVS2004 Session AS-MoP: Poster Session
Monday, November 15, 2004 5:00 PM in Room Exhibit Hall B
Monday Afternoon
Time Period MoP Sessions | Topic AS Sessions | Time Periods | Topics | AVS2004 Schedule
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AS-MoP-1 Producing Substrates for MALDI-MS by Chemomechanically Scribing Silicon and Glass.
R. Blake, G. Jiang, C. Thulin, M.R. Linford (Brigham Young University) Miniaturized matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) sample supports have been developed on silicon and glass for improving analysis sensitivity and reproducibility of biomolecules. Clean silicon and glass were silanized with a fluorinated compound that produces extremely hydrophobic surfaces. After silanization 200 micron diameter hydrophilic anchors were chemomechanically scribed with a diamond tip onto silicon and glass in the presence of water. These hydrophilic areas pin aqueous solutions of matrix and peptide. As the water evaporates the matrix and peptide are pinned to the hydrophilic areas, concentrating and localizing the analyte to a small spot that is fully covered by the ionizing laser beam. Thus, both sensitivity and reproducibility of the analysis are simultaneously improved. MALDI-MS spectra of water soluble peptides, glufibrinopeptide B and angiotensin II, with 2,5-dihydroxy benzoic acid (DHB) as matrix on silicon or glass substrates showed the expected improvements both in sensitivity and reproducibility. Compared to previous reports, this method of making miniaturized MALDI-MS sample supports is rapid, cheap, and could be undertaken in a typical laboratory. |
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AS-MoP-2 TOF-SIMS Investigation of Selected Excipients in Color Coated Placebo Tablets
X. Dong, C.A.J. Kemp (Eli Lilly and Company) Time of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS) was applied to investigate the surface and cross-section of placebo tablets. Eight excipients, including lactose, hydroxypropyl cellulose (HPC), and microcrystalline cellulose (MCC) were examined, as well as color coat mixture and polishing material used in placebo tablets. The investigation of raw materials shows that HPC can be distinguished from other excipients based on its unique peaks present in positive ion TOF-SIMS spectra. Most peaks observed in the spectra of MCC were also detected in the spectra of lactose, which makes it difficult to distinguish MCC from lactose. The comparison between the spectra obtained from tablet surface and cross-section shows that the chemical composition of tablet surface is different from that of bulk. Mg, which comes from a polishing material used on the outside of the tablet, dominates placebo surface spectra, while Na, which is one of constitutes of several excipients, dominates the cross-section spectra. In addition, peaks corresponding to HPC were much more abundant in the surface spectra than in the cross-section spectra, comparing to peaks corresponding to MCC/lactose. The preliminary results suggest that HPC might migrate more easily to sample surface than MCC and lactose during the tablet manufacturing process. The possibility of surface contamination is relatively low, since HPC related peaks were consistently found in surface spectra of all placebo tablets examined, as well as one house drug tablet analyzed in previous work. |
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AS-MoP-3 Cluster Primary Ion Bombardment Facilitates ToF-SIMS Analysis of Biological/Tissue samples
V.S. Smentkowski (General Electric Global Research Center); A. Schnieders (Ion-Tof USA, Inc.); F. Kollmer (Ion-Tof GmbH); R. Kersting (Tascon GmbH, Germany); J.A. Ohlhausen, M.R. Keenan, P.G. Kotula (Sandia National Laboratories) Biological/tissue samples present a number of analytical challenges including the detection of trace quantities of high mass species within large (few mm) areas of samples. Recent advances in both ToF-SIMS instruments (such as stage rastering and liquid metal polyatomic ion sources) and data reduction protocol are facilitating biological/tissue analysis. In this poster, we will compare ToF-SIMS spectra and images collected using both Ga (mono-atomic) and Gold 3 (polyatomic) primary ion sources on treated brain tissue sections. Using polyatomic gold we are able to detect and image high mass (> 1,500 amu) species; these species were not detected in the spectra collected using Ga (even with a higher Ga primary ion fluence). The wealth of information contained in spectral images collected using polyatomic gold is tremendous, and the resulting spectral images can be difficult to interpret. In this poster we will also demonstrate that Multivariate Statistical Analysis (MVSA) tools such as AXSIA (Automated eXpert Spectrum Image Analysis) are useful for deconvoluting the spectral images. Using AXSIA, we are able to separate low yield species from high yield species in the high mass (ca. 760 amu) region of the ToF-SIMS spectra. The AXSIA component of this work was funded in part under CRADA SC00/01609 PTS 1609.02 (GE/Sandia). Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. |
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AS-MoP-4 Using ToF-SIMS as a High Throughput Screening Tool for Lightweight Hydrogen Storage Materials
J.P. Lemmon, J.-C. Zhao, V.S. Smentkowski (General Electric Global Research Center) Combinatorial Chemistry (CC) coupled with High-Throughput Screening (HTS) techniques are being used at the General Electric Global Research Center to generate and characterize multi-component samples in order to accelerate the discovery of new hydrogen storage materials for automotive applications. In order to meet the DoE target of 6 weight percent hydrogen by the year 2010, the hydrogen storage material must contain low Z (low weight) components. Low Z elements can not be detected using techniques that rely on X-ray generation, such as Electron Probe Microanalysis (EPMA) and/or X-Ray Fluorescence (XRF). ToF-SIMS is ideally suited for the rapid screening of low Z materials since it allows for the detection of all elements and can also image large areas (eg. 70mm x 70mm) in less than 2 hours. ToF-SIMS images can be measured while the combinatorial chemistry library is being heated and/or maintained at the desired temperature in the range of 100 to 600° C. Temperature programmed ToF-SIMS experiments will be used to measure the hydrogen desorption processes of combinatorial chemistry libraries. Select examples will be presented. |
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AS-MoP-5 Comparative Analysis of a Pt/Rh Catalyst Sample with TOF-SIMS and Laser-SNMS
A. Schnieders (ION-TOF USA, Inc.); F. Kollmer (ION-TOF GmbH, Germany); M. Fartmann, H.F. Arlinghaus (Universität Münster, Germany); V.S. Smentkowski (General Electric Global Research Center) In the field of catalysis, the analyst often needs to detect and image the distribution of trace quantities of species within the top most surface layer. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) is a well-established technique for such analysis. Unfortunately, quantitative TOF-SIMS analysis is not always easy to accomplish. Laser postionization of sputtered neutrals (Laser-SNMS) provides a higher sensitivity for many elements than TOF-SIMS, and in case of non-resonant multiphoton ionization (NRMPI), Laser-SNMS also provides for more uniform useful yields over the whole elemental range, thus enabling a more straight-forward way of quantification. In this paper, we compare the use of TOF-SIMS and Laser-SNMS with NRMPI for the analysis of a noble-metal treated stainless steal catalyst sample. The main analytical question focused on the determination of the lateral distribution of Pt and Rh on the surface of an actual (dirty) sample. Despite the relative low sensitivity for Pt, TOF-SIMS analysis enabled the determination of the lateral distribution of Pt and Rh on the surface. Quantification of these metals was possible by normalizing the corresponding ion intensities to those of a matrix signal. In comparison to TOF-SIMS, Laser-SNMS provided higher sensitivities for Pt and Rh as well as for other metals detected on the surface. To obtain accurate quantification, relative sensitivity factors for Pt and Rh were established on control samples. The lateral distributions thus measured confirmed those determined with TOF-SIMS. The similar results obtained with both techniques allowed establishing a procedure for quantification of TOF-SIMS results on similar samples. |
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AS-MoP-6 Application of Time Interpolation to SIMS Isotopic Ratio Measurements
D. Simons, K.J. Coakley, A.M. Leifer (National Institute of Standards and Technology) Secondary ion mass spectrometry (SIMS) can be used to perform localized isotopic ratio measurements on a micrometer scale. Such measurements have broad applicability in areas of biology, geology and astronomy. A specific application area of recent interest is nuclear forensics, whereby SIMS has been applied to the search for evidence of uranium enrichment activities through the measurement of the relative abundances of U-235 and U-238 in micrometer-sized particles. In SIMS measurement systems, the count rate of isotopes may vary in time as a limited sample quantity is consumed during the analysis. Since only one isotope at a time is measured in conventional ion counting detection systems, this drift can introduce systematic error into the estimate of the ratio of any two isotopes. Hence, correcting the data for drift is critical to the accurate determination of isotopic ratios and their associated uncertainties. We consider isotopic measurements in a pairwise fashion, with the more abundant isotope of the pair designated as the major isotope and the less abundant one as the minor isotope. We correct the measurements for drift by aligning the major and minor time series of isotopic pairs by use of linear interpolation. We estimate an isotopic ratio for each of two cases. In one case the time series of the more abundant isotope is aligned with respect to the time series of the less abundant isotope. In the second case the less abundant isotope is aligned with respect to the more abundant one. We average both of these estimates to get a drift-corrected estimate. We present an analytical formula for the uncertainty of the isotopic ratio which accounts for correlation introduced by interpolation. We also present an approximate hypothesis test procedure to detect and quantify possible time-dependent drift of the measured isotopic ratio during a single analysis. |
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AS-MoP-7 Carbon Mediation on the Growth of Self-Assembled Ge Quantum Dots on Si (100) by Ultra High Vacuum Chemical Vapor Deposition
P.S. Chen (Electronics Research & Service Organization, Industrial Technology Research Institute, Taiwan); S.W. Lee (Industrial Technology Research Institute, Taiwan); M.-J. Tsai (Electronics Research & Service Organization, Industrial Technology Research Institute, Taiwan); C.W. Liu (Industrial Technology Research Institute, Taiwan) The growth of self-assembled Ge quantum dots (QDs) with carbon mediation on Si (100) by a hot wall ultra-high-vacuum chemical vapor deposition system with different growth temperatures and surfactant gas flow rates was investigated. The ethylene (C2H4) and methylsilane (SiCH6) gas were as surfactants prior to the growth of Ge QDs, respectively. Small dome-like Ge QDs were observed after carbon treatment as compared to the hut shaped Ge cluster without any carbon pre-treatment at 550 °C. Those dome-like Ge QDs have a mean base width and height of about 40 and 5 nm, respectively, and the density is about 6.7 ï,´ 109 cm2 at the growth temperature of 550 °C. Comparison with boron mediation, strong Câ?"H bonds during the epitaxy growth play different roles and lead to this dramatic modification of Ge QDs morphologies. Furthermore, multifold Ge/Si layers were also carried out to enhance the emission intensity with first Ge layer treated by C2H4) and avoid the generation of threading dislocations. |
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AS-MoP-8 Field Emission Analysis and Optimization of Carbon Nanoflake Edge Emitters
X. Zhao, R.A. Outlaw, J.J. Wang, M.Y. Zhu, D.M. Manos, B.C. Holloway (College of William and Mary) Ultra thin carbon nanoflake (CNF) films have been inductively grown by rf chemical vapor deposition on a variety of substrates. The CNF films grow vertically with respect to the substrate and have flake thicknesses of < 2 nm with terminating edges as small as a single atom layer (graphene). The inordinately high field enhancement factor of the flakes represents a high tunneling efficiency and electron emission. In addition, the packing density of the flakes is also extremely high suggesting that CNF films have great potential as field emission cathodes. To optimize the field emission from these films, the growth conditions, deposition temperature, deposition time and chemical composition were varied. The turn-on field, I-V behavior, noise level, robustness, maximum current density and field emission energy spectra for selected deposition condition were observed. The CNF films were also coated with thin layers of Ti, Zr and Hf and heated to form low work function carbide edges. The resulting characteristics were then compared to uncoated CNF. Adsorption effects of H2O and H2 for both the uncoated and coated CNF were also studied. |
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AS-MoP-9 Ti Metal Cluster on the Carbon Nanotube
S. Lee, H. Kim, J. Lee, B.Y. Choi, Y.S. Cho, Y. Kuk (Seoul National University, South Korea) Junctions between metal and carbon nanotube (CNT) have been investigated mainly with transport experiments for the last several years. However, their detailed electronic and geometric structures are not fully revealed. We have created junctions between CNT and Ti metals by depositing the metal on CNT and the electronic and geometric structures have been studied with low temperature scanning tunneling microscopy. Ti metal is preferentially coated near the edges and in the gaps between CNTs. In spatially resolved tunneling spectroscopy, the metallic states are observed on Ti surfaces and the state extended into CNT area, suggesting the existence of mixed states near the junctions1. The origin of the mixed states and observed screening lengths will be discussed. 1) S. Dag, E. Durgun, and S. Ciraci, Phys. Rev. B 69, 121407(R) (2004). |
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AS-MoP-10 Depth Resolution of Inverse Calculation from ADXPS to Depth Profile
A. Tanaka (Physical Electronics, Japan); D.G. Watson (Physical Electronics USA) A practical inverse calculation method is discussed which transforms the data from angle dependent x-ray photoelectron spectra (ADXPS) to depth profile using a maximum entropy method. The depth resolution of the method is evaluated using an 84%-to-16% resolution, which is less than 0.7 nm for natural oxide when optimizing 5 take off angle data. Theoretical comparison is also discussed. |
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AS-MoP-11 Study of the Oxidation Behavior of Aluminum and Aluminum Alloys Using X-Ray Photoelectron Spectroscopy
G.D. Claycomb, P.M.A. Sherwood (Kansas State University) The oxidation behavior of high purity aluminum and two aluminum alloys, after exposure to a variety of aqueous environments, has been studied by using core and valence band X-ray Photoelectron Spectroscopy. Freshly abraded samples were exposed to de-oxygenated, normal and oxygenated quadruply distilled water for one hour at room temperature, 40º, 70º and 100ºC. For pure aluminum, single oxidized aluminum compounds were formed in some instances while mixtures were formed in other cases. For the alloys, the oxidized aluminum compounds were mixed with oxides of the alloying elements in some instances and in other cases where the films had thickened sufficiently, single oxidized aluminum compounds were found on the outermost surface. Identification of the types of oxides being formed was achieved by using valence band photoelectron spectrum. The spectra were analyzed by using a comparison with the valence band spectra of known oxidized aluminum compounds and spectra generated by additions of the spectra from the known oxidized aluminum compounds together with approaches that used difference spectra. This work is based upon work supported by Luxfer Gas Cylinders. |
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AS-MoP-12 Chemical State Analysis Boron and Phosphorus on Si Wafer Surface Measured by TRXPS
Y. Iijima, T. Tazawa (JEOL, Japan) It is well known that x-ray photoelectron spectroscopy (XPS) is a meaningful analytical technique for the chemical characterization of material surface, but the detection limit of XPS is inferior to that of other methods, such as secondary ion mass spectrometry (SIMS) and total reflection x-ray fluorescence (TXRF) analysis. Recently, in developing a new DRAM, the energy of P and B injected into an Si wafer was bound to be lowered. Accordingly, the investigation of the chemical bonding states of these elements on the Si wafer surface has become important. Since B1s and P2p photoelectron peaks overlap with the energy loss peaks of Si2s and Si2p peaks, it is difficult to detect a small amount of B and P injected into the Si wafer by XPS. Therefore, the use of x-ray total reflection has become noteworthy in photoelectron spectroscopy. This is because TRXPS (total reflection x-ray photoelectron spectroscopy) can greatly reduce the number of inelastically scattered electrons contributing to the background of photoelectron spectrum, as the effective analysis depth of TRXPS is nearly equal to the x-ray penetration length in the solid. In addition to this, TRXPS is expected to give a lower detection limit. In this work, we examined the chemical bonding state of B and P on the Si wafer by means of TRXPS. In what follows, the effectiveness TRXPS method to the semiconductor surface analysis will be described. |
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AS-MoP-13 XPS Characterization of Ingaalp/ingap Quantum Well Structures
Y.J. Yoon, L.V. Yashina, B.Y. Kim, V. Kureshov (Samsung Electro-mechanics Co., Ltd, Korea) InGaAlP/InGaP heterostructures are important for light emission in laser diodes. Post growth characterization of InGaAlP solid solution composition is actual problem in the optimization of growth parameters due to compositional dependent mismatch and Eg value. The mismatch is mostly influenced by Ga/In ratio, whereas Eg is governed by Al/Ga ratio. In practice the set of accessible diagnostic procedures is limited by photoluminescence study and XRD. For the quasibinary solid solution composition can be estimated using lattice constant or Eg dependences on mole fraction whereas for the quaternary solid solution this approach can not be applied rigorously. The use of direct analytical techniques is complicated by many factors such as low thickness of layers, restrictions in depth resolution, surface preparation problem. InGaAlP/InGaP multilayered structures with layer thickness ~ 5 nm were studied by XPS. The superlattices were obtained by MOCVD on GaAs(100) substrate. XPS study was carried out using monochromatic Al Ka source in Quantera SXM. Two independent procedures were applied: (1) sputtering depth profiling and (2) Angle dependent photoemission registration for the samples containing well/barrier interface in the layer under analysis. In 3d, Ga 2p, Al 2s, P 2s peak intensities were calibrated using the set of reference alloy samples InGaP, InAlP and pure compounds InP, GaP. Sputtering rate compositional dependence was also taken into account. Sputtering was carried out using Zalar rotation to reach maximal depth resolution. For the depth profiles analysis attenuation length and surface roughness after sputtering, estimated by AFM, were taken into consideration. The obtained results are compared with SIMS data. |
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AS-MoP-14 XPS, AFM, and Confocal Microscopy Data Correlation: Characterization of Polymer Blend Systems to Create a 3D Volume
J.L. Fenton, K. Artyushkova, J. Farrar, J.E. Fulghum (The University of New Mexico) No single non-destructive technique readily provides both surface chemistry and component distribution through the depth of polymer samples. Visualization based upon multiple analytical characterization techniques can be used to create a 3-D map of polymer chemistry. This work combine data from XPS, AFM, and confocal microscopy analysis of polyvinylchloride/polymethylmethacrylate and polystyrene/polybutadiene blends. Confocal microscopy images are used to create a volume that can be correlated with XPS images and spectra in order to semi-quantitatively map the distribution of chemical components within the blends. The correlated data will be combined with AFM images to incorporate surface topography measurements. This work has been partially supported by NSF CHE-0113724 and the NSF IGERT CORE program. |
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AS-MoP-15 Auger Analysis of Corrosion Scale Formed on a Ni-Cr-Fe Alloy by Exposure to Supercritical Water at Elevated Temperature.
S.A. Wight, J.E. Maslar, E.S. Windsor (NIST) A nickel-chromium-iron alloy (Inconel 600) was exposed to water at elevated temperatures and pressures (approaching conditions of the critical point of water). This alloy is used in boiler systems and the mechanisms of corrosion and failure are of interest. The water temperatures and pressures were selected to simulate conditions to which this alloy might be exposed during operation. Two coupons were exposed under slightly difference conditions and differences in degree of corrosion were observed. While the alloy composition is well known, the composition of the corrosion layer depends strongly on exposure conditions. Auger electron spectrometry was applied to help investigate the composition of the corrosion layer. The discontinuous nature of the oxidation layer and the proximity to the unoxidized substrate make this a challenging analysis. Auger analysis is complimented with energy dispersive spectrometry, and focused ion beam techniques to solve this complicated analysis problem. |
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AS-MoP-16 Electronic Structure of Rare-Earth Oxoborates: A Photoemission Investigation
A.J. Nelson, J.J. Adams, K.I. Schaffers (Lawrence Livermore National Laboratory) Calcium's rare-earth (R) oxoborates are nonlinear optical materials with general composition Ca4RO(BO3)3 (R3+ = La, Sm, Gd, Lu) that have potential for high-average power laser frequency conversion and intra-cavity doubling. X-ray photoemission was applied to study the valence band electronic structure and surface chemistry of these novel materials and their rare-earth oxide model compounds. Core-level and valence band results for the rare-earth oxides La2O3, Sm2O3, Gd2O3, and Lu2O3, were applied to the interpretation of the photoemission spectra of select oxoborate crystals. Specifically, high resolution photoemission measurements on the La and Gd 3d and 4d, Ca 2p, B 1s and O 1s core lines and valence band were used to evaluate the surface and near surface chemistry of lanthanum calcium oxoborate (LaCOB) and gadolinium calcium oxoborate (GdCOB). Results for these oxoborate crystals revealed that the occupied states exhibit a high degree of mixing between the p-f bonding-antibonding states. In addition, general treads in the 3d and 4d core-level line shapes and occupied 4f valence band states of the rare-earth oxide model compounds are best understood in terms of final state effects. This work was performed under the auspices of the U.S. Dept. of Energy by the University of California Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48. |
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AS-MoP-17 Photoelectron Spectroscopy Study of the Aging and Plasma Treatments Effects on PECVD a-SiC:H Films for Advanced Interconnects
V. Jousseaume, O. Renault (CEA-DRT-LETI, France); G. Passemard (ST-Microelectronics, France) The ageing of amorphous hydrogenated SiC (a-SiC:H) films grown by PECVD and used as potential low k dielectric barrier materials in advanced interconnects was investigated by x-ray photoelectron spectroscopy. Very thin layers (20-60 nm) and a special sample holder were used in order to minimize detrimental charging effects during analysis. It is shown that ageing on non-treated films proceeds by the introduction of up to 20at.% of oxygen into the film after 15 days of air exposure in the clean room, and that O is present in relatively high concentration at the very early stages of air exposure1. By XPS is evidenced the benefits of both He and H2 plasma treatments in term of drastic limitation of the reoxidation upon ageing, with an atomic percentage of O being stable at around 7at.% after 15 days. At the same time, on untreated samples, the Si/(Si+C) ratio is remaining constant and both Si2p and C1s core-level profiles show up a constant evolution as a function of ageing time, with a decrease of the relative intensity of Si-C bonds and an increase of oxycarbide and C-C, C-H groups. This evolution will be compared with the case of plasma treated samples and possible mechanisms of ageing will be proposed taking into account results from FTIR analysis, stress and dielectric constant measurements2. |
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AS-MoP-18 Thermally Nitrided Stainless Steels for Polymer Electrolyte Membrane Fuel Cell Bipolar Plates: Beneficial Modification of Passive Layer on AISI446
H.M. Meyer III, M.P. Brady, K.L. More, B. Yang (Oak Ridge National Laboratory); H. Wang, J.A. Turner (National Renewable Energy Laboratory) Proton exchange membrane fuel cells (PEMFCs) are of great current interest for power generation due to their high efficiency and environmentally friendly, near-zero emissions. Since cost is critical, metal alloys would be ideal as bipolar plates but suffer from inadequate corrosion behavior due to high electrical resistance by the formation of surface oxides or degrade cell performance by contaminating the membrane with metal ions. Recently, it was discovered that thermally grown Cr nitrides (CrN/Cr2N) on a model Cr-bearing alloy, Ni-50Cr (wt%), show great promise for corrosion resistance and electrical conductivity in PEMFC bipolar plate environments fototnote 1. Work is ongoing to form similar nitride surfaces on less expensive Ni-Cr and Fe-Cr base alloys. This poster describes an effort to use a relatively inexpensive ferritic stainless steel (AISI446 MOD-1) as bipolar plate material and specifically looks at its surface chemistry, corrosion resistance, and interfacial contact resistance. Thermal nitridation for 2 h at 1100ºC resulted in little nitrogen uptake and a tinted surface. Analysis by SEM, XPS, and AES suggests a complex heterogeneous modification of the native passive oxide film by nitrogen, rather than the desired micron range thick exclusive Cr-rich nitride layer. Surprisingly, this modification resulted in both good corrosion resistance under simulated cathodic and anodic conditions and low ICR, well over an order of magnitude lower than the untreated alloy2. Details of the nitrided surface chemistry of this alloy will be presented. |
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AS-MoP-19 Preparation and Lithography of Monolayers on Silicon Surface and Their Molecular Recognition
Y. Takahashi (Waseda University, Japan); N. Shirahata (National Institute for Materials Science, Japan); A. Hozumi (National Institute of Advanced Industrial Science and Technology, Japan); S. Asakura (Waseda University, Japan); T. Yonezawa (University of Tokyo, Japan) Functionalization of hydrated silicon surface is a starting stage in the development of molecular, biomolecular and semiconductor devices. Refluxing of 1-alkene under nitrogen with H-terminated Si gives an uniform Si-C linked monolayer with atomically flatness through thermal hydrosilylation. We have reported that the monolayer can be prepared from a dilute solution of 1-alkene (< 1 wt%) and even from powder of 1-alkene molecules. This basic finding that the monolayer can be prepared from the powder implies that solid materials, including those with exceedingly high melting points or no melting points, have the potential to be transformed into monolayers directly bonded to inorganic substrates, with the only limitation being that the material must be soluble into any kinds of solvents. The carbohydrate monolayer recognizes the specific protein molecules selectively. Lithography of such monolayer can be done by UV-light irradiation. Furthermore, the particle monolayer of alkenethiol-stabilized gold nanoparticles were also be anchored onto silicon by similar reaction. These findings will promise that individual nanoscale materials can be manipulated based on monolayer formation mechansm. |
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AS-MoP-20 Importance of Binding Energy Reference Materials for Understanding the Chemistry of Oxidized-Iron Arsenic-Adsorbing Materials
B.M. Sass (Battelle Columbus); M.H. Engelhard, D.R. Baer (Pacific Northwest National Laboratory) Arsenic as a contaminant in drinking water is a growing problem around the world. Consequently many research and commercial efforts are being made to develop low cost and effective means for producing acceptable quality drinking water. Iron oxide based sorbing minerals are now available commercially. However, the effectiveness, lifetime and ability to recycle these materials are not adequately understood. The extent of arsenic sorption and the chemical nature of the sorbed species are important to understanding the chemistry that take place on the surface and the long term effectiveness. We have used XPS to measure the arsenic coverage on the mineral surfaces and to examine arsenic chemical state. Because of the limited amount of arsenic oxidation state data in general, the variability of binding energies observed in the existing data, and the lack of data for arsenic sorbed onto oxidized iron phases, to interpret our data it was necessary to examine As(III) and As(V) oxides as well as ferric arsenite and ferric arsenate compounds. Based on these references the arsenic sorbed onto the commercial sorbers was found to be mostly As(V) in the conditions examined. |
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AS-MoP-21 Analysis of Leed Images to Obtain Surface Geometries of Amines and Alcohols Adsorbed on the Si(100)-2x1 Surface
J.K. Dogbe, S.M. Casey (University of Nevada, Reno) Image analysis of low-energy electron diffraction (LEED) intensity vs. voltage (IV) curves was used to analyze the surface geometries of amines and alcohols adsorbed on the Si(100)-2x1 surface. Clean silicon and ammonia-covered surfaces were used as calibration systems. The data from these surfaces compare well within experimental uncertainties. Results to be presented include the dimethylamine, trimethylamine and ethanol-covered surfaces. These results will be compared to computational treatments of probable reaction pathways of these adsorbates on silicon using the cluster models of the surface. Also to be presented will be comparisons of results for these reactions from slab models of the surface. |
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AS-MoP-22 Surface Planarization Characteristics of WO3 Thin Film for Gas Sensing
W.S. Lee, P.J. Ko (Chosun University, South Korea); Y.J. Seo (DAEBUL University, Korea) There has been an increasing interest in the material and electrical properties of inorganic compound that are insulators at low temperature, but are good conductors at high temperature. In particular, n-type semiconductors such as SnO2, WO3, TiO2 and ZnO have extensively been used for detecting reduction gases. For the applications of gas sensors, it is necessary to have a microstructure with small grain size yielding large ratio of the surface area to the bulk. Also, the surface roughness deteriorates light reflection, pattern resolution, and device performance because they are dependent on surface morphology or roughness. Therefore, it is important to control the microstructure and surface morphology for the advanced sensor application. Chemical mechanical polishing (CMP) process is a useful guideline for improving the surface roughness. In this paper, we investigated the CMP effects on the surface morphology of WO3 thin films prepared by RF sputtering system. In order to compare the polishing characteristics of WO3 thin film, we discussed CMP removal rate (RR) and within-wafer non-uniformity (WIWNU%), particle size distribution, and the microstructures of surface and cross-sectional layer by atomic force microscopy (AFM) analysis. And the effects of added oxidizer contents on the WO3 CMP characteristics were investigated to obtain the higher removal rate and lower non-uniformity. This work was supported by a Korea Research Foundation grant (KRF-2002-005-D00011). |
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AS-MoP-23 Scanning Capacitance Microscopy Study on the Stability of the Electrical Junctions Formed by Spike Annealing and Rapid Thermal Annealing
M.-N. Chang, C.-Y. Chen (National Nano Device Laboratories, Taiwan) Scanning capacitance microscopy (SCM) has been widely used to profile two-dimensional carrier distribution and examine the electrical junctions of silicon-based devices. Ion implantation combined with proper annealing treatments is indispensable to produce a needed electrical junction. In general, the annealing treatments can be rapid thermal annealing (RTA) or spike annealing (SA) at high temperature. Due to the photoperturbation effects on SCM, there are many difficulties in employing SCM to investigate the temperature influence on electrical junctions. In this work, we have provided a reliable method to control the photoperturbation levels on the studied samples and employed low-photoperturbed SCM, operated under the same photoperturbation levels, to study the stability of the electrical junctions formed by RTA and SA. Studied samples were p+/n junctions formed by BF2+ implantation at low energies. RTA and SA processes were performed at 1050 °C in N2 ambient. The width and pitch of the designed grating pattern are 0.8 and 2 microm, respectively. The differential capacitance images clearly show that post-SA and -RTA furnace annealing at low temperatures can induce the electrical junction narrowing. With secondary ion mass spectroscopy, it is further revealed that the junction narrowing may occur even if atomic diffusion is negligible. The experimental results indicate that point defect generation/recombination associated with dopant deactivation plays an important role of junction width modification during the following low temperature processes. According to this study, the electrical junction formed by high temperature annealing is unstable. The physical mechanism of junction width variation induced by low temperature processes will be discussed in depth. |
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AS-MoP-24 XPS Analysis Under External Stimuli
S. Suzer, U.K. Demirok, G. Ertas (Bilkent University, Turkey) Earlier, we demonstrated that, by applying external voltage bias to the sample rod while recording XPS spectra, it was possible to influence the measured binding energy differences by controlling the partial charging/discharging of different surface layers or domains either by electrons created from a filament, or by stray electrons within the vacuum system stemming form X-ray tube, vacuum gauges, etc.[1, 2]. We had used this to separate otherwise overlapping XPS peaks belonging to different surface features.[3] Later, we expanded it to extract time-dependent information. [4] In this contribution, we will present our extended investigation of different surface structures like Au nanoclusters deposited on SiO2 substrates or thin organic layers of various thickness, etc., using different external voltage stimuli over other external elements like resistors, capacitors for extracting information related with the dielectric properties of surface structures and probing nanocluster-surface interactions. [1] B. Ulgut, and S. Suzer, J. Phys. Chem. B 107, 2939 (2003). [2] F. Karadas, G. Ertas, and S. Suzer, J. Phys. Chem. B 108, 1515 (2004). [3] S. Suzer, Anal. Chem. 75, 7026 (2003). [4] U. K. Demirok, G. Ertas, and S. Suzer, J. Phys. Chem. B 108, 5179 (2004). |