AVS2001 Session NB-SuP: NBS/NIST Centennial
Sunday, October 28, 2001 6:20 PM in Room 121
Sunday Evening
Time Period SuP Sessions | Topic NB Sessions | Time Periods | Topics | AVS2001 Schedule
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NB-SuP-1 Resonance Tunneling: from Field Emission to Molecular Electronics with Intermediate Stops; a Thirty Five Year NBS/NIST Saga
J.W. Gadzuk (National Institute of Standards and Technology) Initiation of the modern era of surface science is generally acknowledged to have occurred in the 1960's, a period marked by the recognition and development of measurement and theoretical techniques for studying surface properties and processes on the (single!) atomic level. Resonance tunneling of field emitted electrons through adsorbates on metal surfaces reported in a 1969 NBS paper was the first-ever work in which the electronic energy level spectra of adsorbed atoms was observed and theoretically interpreted (as "skewed" Fano profiles).1,2 Variants and extensions of the theory have formed the basis for subsequent NBS/NIST studies of resonant tunneling/scattering phenomena involved in desorption,3 basic STM operation,4 quantum wells,5 scanning tunneling spectroscopy of Kondo systems,6 and molecular electronics.7 A useful synergism amongst these studies illustrates the positive consequences of a long-term commitment to the search for varied realizations of a common fundamental process (here resonance tunneling). Fortunately this research strategy has been possible at NBS/NIST throughout much of its first 100 years.8 |
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NB-SuP-2 Scanning Tunneling Microscopy in the Electron Physics Group at NIST1
J.A. Stroscio, E.W. Hudson, R.J. Celotta, D.T. Pierce (National Institute of Standards and Technology) The history of scanning tunneling microscopy in the NIST Electron Physics Group (EPG) spans more than 3 decades. In this poster presentation we will document the development of scanning tunneling microscopy in the EPG group, starting back in the 1960's when Russell Young developed the "Topografiner", and continuing to the present where state-of-the-art measurements are made with a scanning tunneling microscope operating at 2 K and in magnetic fields at 10 T. |
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NB-SuP-3 Spin-Polarized Electrons at NBS/NIST*
D.T. Pierce, R.J. Celotta, J. Unguris (National Institute of Standards and Technology) Over the past 25 years, the NIST Electron Physics Group has pioneered the use of spin-polarized electron measurement techniques in condensed matter and atomic physics. The work began with the development of an electron gun, based on photoemission from negative electron affinity GaAs, which produced an intense beam of electrons with easily reversible spin polarization. This allowed us to make sensitive surface magnetometry measurements such as polarized electron scattering and spin-polarized low-energy electron diffraction (SPLEED) measurements of magnetic surfaces. The spin-polarized electron gun enabled us to demonstrate the first spin-polarized version of inverse photoemission spectroscopy (SPIPES) and allowed others to add spin polarization to several surface measurement techniques including electron energy loss spectroscopy (SPEELS) and low energy electron microscopy (SPLEEM). We also developed a compact, efficient spin analyzer that is particularly well suited to measure the spin polarization of secondary electrons emitted from magnetic samples in a scanning electron microscope. This measurement technique, known as scanning electron microscopy with polarization analysis (SEMPA), provides high-resolution images of surface magnetization. SEMPA measurements have proven powerful for investigating both fundamental problems, such as interlayer exchange coupling of magnetic multilayers, and technological questions, such as the magnetic microstructure of small magnetic device elements. We describe a new SEMPA instrument designed to meet the magnetic imaging challenges of the near future. |
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NB-SuP-4 Investigations of Electron Emission and Scattering Phenomena at Surfaces
C.J. Powell (National Institute of Standards and Technology) An overview will be given of almost four decades of work at NBS/NIST in which different phenomena associated with electron emission from surfaces and electron scattering by surfaces were investigated. These investigations, made with many coworkers, range from analyses of energy-loss spectra from liquid metals to studies of different Auger-electron lineshapes, reviews of electron attenuation lengths and inner-shell ionization cross sections, interlaboratory comparisons of AES and XPS peak energies and intensities, investigations of correlation effects in inner-shell excitations, calculations of electron inelastic mean free paths, investigations of elastic-electron scattering effects in AES and XPS, measurements of electron attenuation lengths, development of improved procedures for the calibration of binding-energy scales of XPS instruments, development of standard test data for XPS, and development of NIST databases for applications in XPS and AES. |
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NB-SuP-5 Application-Tunable Chemical Microsensors: Multicomponent Research for New Measurement Technology
S. Semancik, R.E. Cavicchi, M.C. Wheeler, N.O. Savage, C.J. Taylor (National Institute of Standards and Technology) For more than 15 years, NIST has been involved in fundamental surface science, thin film science, and sensor science studies directed at advancing solid state chemical sensing technology toward new levels of performance and reliability. Adsorption-induced property changes occurring at the surfaces of thin films have been investigated and employed for detecting and quantifying a wide range of gases and vapors with microscale devices. Tunability for varied applications has been realized through the use of multielement arrays with sensing films of differing composition, and individually adjustable operating temperatures. In this presentation we review efforts in our program, with an emphasis on key interfacial phenomena, as well as on vacuum-based materials processing and characterization. Research to be described includes examination of: vacancy defects in oxide semiconductors (which set base conductance levels for conductometric gas sensing films), micromachining of Si (to produce low power device platforms - "microhotplates"), thermally-activated CVD (to incorporate sensing materials into microscale structures), correlations between adsorbed species and interfacial electronic transport, temperature-driven adsorbate transient phenomena, and microscale chemical cross-talk. In addition, we illustrate the utility of the microhotplate array platforms as research tools for combinatorial optimization of the compositions and microstructures of sensing film materials, and investigation of gas-surface interactions. |
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NB-SuP-6 The NIST Synchrotron Ultraviolet Radiation Facility
U. Arp, M.L. Furst, E.W. Hagley, T.B. Lucatorto, C.S. Tarrio, C.W. Clark (National Institute of Standards and Technology) In 1961 NBS established the first dedicated synchrotron radiation source, the Synchrotron Ultraviolet Radiation Facility (SURF). The first experiment performed at SURF, two-electron photoexcitation of He, created significant excitement in the world of atomic physics, and demonstrated the utility of synchrotron radiation for performing experiments in the vacuum ultraviolet and beyond. The SURF synchrotron, designed for nuclear physics experiments, was converted to the SURF II electron storage ring, which is more suitable as a radiation source. A SURF II - SURF III upgrade, accomplished in 1998, involved replacement of the original synchrotron magnet with a new magnet for improved field uniformity and higher energies, and an enhanced radio-frequency system for more stable operation. SURF III plays a key role in synchrotron-based radiometric metrology at NIST, especially in the DUV and EUV regions of the spectrum, for three reasons. First, SURF’s optical output is easily calculable from first principles. This characteristic is related to the fact that it has a perfectly circular orbit. Second, SURF can operate stably over a wide range of electron energies, from below 100 MeV to 380 MeV, which allows one to tune the wavelength of peak output over different regions of the DUV and EUV and thus minimize effect of out-of-bandwidth radiation. The third relates to the stability of the continuous output. Since 1967 SURF has been used to provide calibration services, starting with the calibration of standard detectors in the UV spectral region. Since then several other metrological activities have been implemented at SURF III beamlines. Beamline 2 is home to a spectrometer calibration facility, which allows users to calibrate space-borne photodetector packages in the wavelength region from 1 nm to 400 nm with an accuracy of less than 1 %. Beamline 3 is currently being developed as the U.S. National Standard for the calibration of standard light sources in the air UV from 200 nm to 400 nm. Beamline 4 provides us with the ability to calibrate standard detectors in the region from 120 nm to 320 nm in support of the U.S. National UV scale. Beamline 7 provides characterization of thin-film multilayer EUV mirrors, having the unique capability of handling mirrors as large as 450 mm, which is especially relevant to the developers of EUV lithography. Beamline 9 provides the Nation’s standard for detectors in the region from 5 nm to 50 nm, in continuation of the program started in 1967. |
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NB-SuP-7 Surface and Microanalysis Science Division: From XPS Standards to Near-field Optical Microscopy.
R.R. Cavanagh, S.J. Stranick, C.A. Michaels (National Institute of Standards and Technology) The Surface and Microanalysis Science Division at NIST has worked with the AVS community over the years to develop the measurement science that underlies a range of surface measurements. Key activities have included theoretical and experimental efforts ranging from the modeling of inelastic electron scattering events at surfaces, studies of ion, electron, and photon induced surface reactions, and optical probes of buried interfaces, to energy and state and time-resolved studies of the dynamics of surface processes. Recent efforts have investigated the use of near-field optical methods to combine spectroscopic contrast with the spatial resolution of scanned probe methods. We have developed an infrared near-field scanning optical microscope that incorporates a tabletop femtosecond laser-based infrared source with an illumination mode apertured probe. The application of the near field infrared instrument to thin homopolymer films, to blends of polyethylacrylate and polystyrene, and to titanium dioxide particles with acrylic melamine will serve to illustrate the utility of this method for characterizing chemical nanostructures. |
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NB-SuP-8 Surface Science at the NBS / NIST SURF-II Synchrotron Light Source
R.L. Kurtz (Louisiana State University); T.E. Madey (Rutgers, The State University of New Jersey); R.L. Stockbauer (Louisiana State University) A retrospective of surface science experiments performed at the NIST SURF-II synchrotron for the time period of 1980 to the early 1990's will be presented. The measurements that were performed during that time period included a range of photoemission and stimulated desorption studies of surfaces. Among the standards measurements, a technique was developed to measure quantitative electron mean-free paths in condensed molecular solids. Other studies that were conducted applied photoemission to evaluate the oxidation of metals and the adsorption of simple molecules on metals and oxides. Stimulated desorption was the focus of a number of other experiments from both metals and oxides and a collection of data from a range of these measurements will be presented. |
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NB-SuP-9 Cluster SIMS Research at NIST
J.G. Gillen (National Institute of Standards and Technology) Secondary ion mass spectrometry (SIMS) is a widely used technique for the determination of both the surface and in-depth elemental and molecular composition of a wide variety of solid materials. The National Institute of Standards and Technology has been at the forefront of SIMS research for nearly 30 years. A major recent activity at NIST has been the development and application of Cluster SIMS. In SIMS, the surface to be analyzed is bombarded in ultrahigh vacuum with an energetic ion beam (typically Ar+, O2+, Cs+ or Ga+) with subsequent detection of characteristic sputtered secondary ions by mass spectrometry. In the Cluster SIMS approach, the standard ion beams are replaced with small polyatomic or cluster primary ions such as SF5+ or C10-. When a cluster ion strikes a surface with several keV of energy, it dissociates into its constituent atoms with each constituent retaining a fraction of the initial energy. The reduction in impact energy results in a reduced penetration depth below the surface and the possibility for improved SIMS depth resolution. The dissociation of the cluster ion also leads to a localized deposition of energy in the near-surface region of the sample that may enhance the yield of characteristic molecular ions by several orders of magnitude providing greater sensitivity for organic surface characterization. Research at NIST in Cluster SIMS covers the range from ion source development to demonstration of Cluster SIMS advantages in applications to semiconductors, polymers, and biomolecules. |
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NB-SuP-10 Triply Differential Photoelectron Spectroscopy at SURF-II
R.L. Stockbauer (Louisiana State University); D.L. Ederer (Tulane University); J.B. West (Daresbury Laboratories); K. Codling (Reading University); A.C. Parr (NIST); J. Dehmer (NSF) Starting in 1979, we developed a sophisticated spectrometer that was used to make angularly and vibrationally resolved photoelectron measurements. The studies concentrated on resonance phenomena in gas phase atomic and molecular systems. The initial instrument utilizing a single spectrometer was replaced with a dual spectrometer system in the early 1980s. These instruments were used to obtain detailed vibrationally resolved information on the effects of shape resonances and autoionization on the distribution of the final states of the molecular ion. We were the first to report striking non-Franck-Condon intensity distributions associated with a shape resonance in N2. Subsequent studies uncovered unusual intensity distributions in the vibrationally resolved spectra that could not be directly explained by predictions of traditional calculations of molecular photoionization. The high resolution and sensitivity of the NIST spectrometer enabled the identification of a new Rydberg series in O2. The most comprehensive data set was taken on the CO2 molecule, discovering forbidden interactions between vibrational bending and stretching modes. We will review the highlights of over a decade of work. |
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NB-SuP-11 Future Directions of Vacuum and Low Gas-Flow Metrology at NIST
A. Lee, J.P. Looney, A.P. Miiller, P.J. Abbott (National Institute of Standards and Technology) The vacuum and low-flow metrology project areas at NIST develop and maintain standards to disseminate the highest measurement capability to US industry, advance measurement science, and establish international measurement comparability. In the years to come, we plan to: Introduce New Measurement Standards: - Investigate intrinsic pressure standards based on material fixed points and atomic calculations - Extend spinning rotor gauges ~10-7 Pa, potentially replacing ion gauges entirely as secondary standards - Develop in-situ, non-intrusive flow calibration techniques for reactive gases and vapors in semiconductor fabrication - Offer a leak-into-atmosphere calibration service and extend the range of the leak-into-vacuum service (applications OLED-substrate permeation, refrigeration, nuclear containment, pressure vessels, etc.) - Develop primary oil manometers utilizing a 4-color column-height determination scheme - Create an on-demand SRG calibration service via provision/exchange of calibrated rotors Improve Current Standards and Measurement Capabilities: - Reduce uncertainties in our orifice flow standard by nearly an order of magnitude - Work with industry to make RGAs more reliable and quantitative instruments - Offer on-site proficiency testing of mass flow controllers, and thermophysical data on new electronic gases Ensure Measurement Comparability: - Continued leadership in international, regional and domestic comparisons of measurement standards - Improve the vacuum metrology capability of the SIM region - Develop a real-time capability to remotely operate and observe instruments under calibration or testing |