AVS2001 Session AS-TuM: High Spatial Resolution and Imaging
Tuesday, October 30, 2001 8:20 AM in Room 134
Tuesday Morning
Time Period TuM Sessions | Abstract Timeline | Topic AS Sessions | Time Periods | Topics | AVS2001 Schedule
| Start | Invited? | Item |
|---|---|---|
| 8:20 AM | Invited |
AS-TuM-1 Chemical Specific Imaging and Micro-spectroscopy of Metal/Semiconductor Interfaces
M. Kiskinova (Sincrotrone Trieste, Italy) Schottky barrier inhomogeneity at metal/semiconductor interfaces has been considered an important factor in explaining the non-ideal behaviour of the Schottky diodes. However, qualitative understanding of the factors controlling the Schottky barrier later al variations requires a technique capable of probing both the local chemical and structural speci fics of the metal/semiconductor interface and the corresponding band bending at the surface. This requirement has partly been met by adding submicrometer la teral resolution (≤ 0.1 µm) to the photoelectron spectroscopy, a chemically sensitive method with a probing depth that can be set to be less than 100 Å and the Schottky barriers can be determined from the energy shifts of the photoelectron spectra. The ac cess of photoelectron spectromicroscopy to microscopic interface properties will be illustrated by some recent results for metal/GaN interfaces, obtained using the scanning photoelectron microscope at the ELETTRA light source. The investigations were f ocu sed on development of chemical heterogeneity at related to the defective structure of the GaN epilayers. Using case studies of technologically important Au, Ni, Ti/GaN contacts lateral variations in the microscopic morphology and their effect on the l ocal Schottky barriers will be presented and discussed. The measured negligible lateral band bending fluctuations despite the differences in the film thickness and chemical composition has been identified as a property of the metal/GaN interfaces, not w el l un derstood in the frame of the existing theoretical models. ˙. s∆∆ˇ. |
| 9:00 AM |
AS-TuM-3 The Combination of a Laboratory X-ray Source with an Energy Filtered Bolt-on PEEM Optics: An Innovative Approach Towards Micro-XPS Instrumentation of the Future
M. Merkel, M. Escher, Th. Kammler, J. Settemeyer (FOCUS GmbH, Germany); D. Funnemann, B. Gottschlich (OMICRON GmbH, Germany); M. Klais, A. Oelsner, Ch. Ziethen, G. Schönhense (Johannes Gutenberg Universität, Germany) Due to remarkable advances in micro and nano technology, the need for microscopically resolved spectroscopic information continues to increase. The photoemission electron microscope (PEEM) is capable of delivering, laterally, high-resolution images together with detailed spectroscopic information.1 In combination with laboratory excitation sources in the VUV and X-ray range, it offers a very simple method for chemically analysing sample surfaces. To this end, dispersive filters (e.g. of the hemispherical type) are already being used successfully.2 The use of a retarding field analyser combined with a PEEM is an innovative and versatile attempt to obtain microspectra and/or energy filtered images. We describe the instrumentation and we present results obtained with a bolt-on, state-of-the-art PEEM, combined with a modular imaging, high pass energy filter of the RFA type. The excitation is accomplished using a common monochromatised laboratory bolt-on X-ray source. With this equipment, it is possible to obtain XPS-spectra from sample regions smaller than 1µm with an electron energy range up to more than 1000 eV wide.3 Despite the fact that the PEEM acts as a low-pass filter, one could acquire spectra up to the Fermi cut-off without difficulty. The low intensity of high-energy photoelectrons arising from a low excitation source intensity is crucial for tuning the PEEM optics to the desired kinetic energy. The optimal, electron optical parameters typically deviate strongly from those applying to the threshold regime of the PEEM. We offer a means to optimise the optics regardless of the available intensity of the excitation source. |
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| 9:20 AM |
AS-TuM-4 High Spatial and Spectral Resolution XPS Analysis of Pseudo-Aluminium Alloy Corrosion Sensors
C.J. Blomfield (Kratos Analytical Ltd, UK); S.J. Harris, M.C. Hebbron, C.C. Figgures, L.A. Brimecombe (British Aerospace, UK) Due to increased aircraft lifetimes and a move towards the use of chrome free protective coatings, corrosion sensors will be used to monitor future aircraft structures. These may be based upon pseudo aluminium alloy structures, which will be used to assess the localised corrosion in the airframe. The paper desribes the analysis of a selection of reference materials and actual corrosion sensors (PLR and Galvanic) following corrosion testing. XPS was used to study the distribution of the corrosion products around the sensor and to identify the composition of the surface of the sensors post testing. A combination of both high spatial resolution XPS imaging and small area XPS analysis were used to analyse to sensors fabricated on high resistance silicon and kapton. |
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| 9:40 AM |
AS-TuM-5 Correlation of High Spatial Resolution XPS Imaging with Phase Contrast AFM using Classification Methods
J.E. Fulghum, K. Artyushkova, J. Farrar (Kent State University); D. Surman (Kratos Analytical, Inc.); S. Page (Kratos Analytical, UK) Understanding the surface morphology of heterogeneous organic samples can require the use of several different imaging, as well as spectroscopic, techniques. Even if the techniques have a comparable field of view, correlating data can be difficult since the imaging methods are likely to have different spatial resolutions, sampling depths, sample preparation requirements, damage mechanisms, and data interpretation considerations. Spatial resolution in laboratory-based XPS imaging instruments is now approaching the sub-micron scale. As the XPS spatial resolution improves, correlations with microscopic techniques such as AFM become potentially possible. We will discuss methods for correlating the chemical information in photoelectron images with the phases identified through phase contrast AFM. Image classification methods can be used to identify and compare components in photoelectron and AFM images. Results for both polymer grids and heterogeneous polymer blends will be discussed. This work has been partially supported by NSF ALCOM (DMR89-20147). |
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| 10:00 AM | Invited |
AS-TuM-6 Progress in Scanning Tunneling Microscopy at Solid / Liquid Interfaces
K. Wandelt (Universität Bonn, Germany) A newly designed electrochemical scanning tunneling microscope (EC-STM) enables the combination of STM and electrochemical measurements (e.g. cyclic voltammetry) within a realistic volume of liquid (electrolyte). Furthermore three different detection modes with the STM, namely potentiostatic, potentiodynamic and spectroscopic, open the possibility to monitor surface structures, structural transition as well as absolute adsorption sites with subatomic resolution. In this lecture a description of the fully homemade electrochemical STM will be given, and its high in-situ performance will be demonstrated by some selected examples including the atomic structure of anionic adsorbates, the morphological changes of the respective electrode surface, the deposition of metal layers and the growth of molecular films. |
| 10:40 AM |
AS-TuM-8 Solvent-Assisted Modification of Polymer Surfaces Using Scanning Force Microscopy
F. Stevens, R. Leach, J.T. Dickinson (Washington State University) The response of thin polymer films and bulk surfaces to combined stress and solvent is important for applications such as protective barriers (e.g., various wrappings), in controlled drug release from polymer hemispheres, resists for lithography, and nanometer scale surface modification. Over a wide range of normal forces, when a polymer is scanned by SFM in contact mode in a solvent, material is not worn away, but rather the polymer surface expands forming a nanometer scale "bump" at and surrounding the scanned location. Furthermore, for sub-micron scan areas one often observs a series of parallel ridges (moguls) perpendicular to the fast scan direction. Previous reports of the formation of raised material have nearly all been in air, required long times or very high forces to form; little evidence has been presented for the mechanism of formation. We have engaged in a detailed study of protrusion formation and raised ridges using poly(methyl methacrylate) in alcohol based solvents. In addition to scanning in air, we have scanned the polymer surface in four solvents with dramatic differences in response. We have also observed the effects of varying contact force, and the effect of using cantilevers with different force constants. We present evidence that both plastic deformation and tip induced swelling play major roles in the observed polymer surface modification by SFM. The stresses applied by the tip generate tensile forces around the tip that likely increase the quantity of solvent that can enter the surface. We show that adding Rhodamine 6G dye to the solvent provides us with evidence that indeed solvent is going into the polymer. Using fluorescence microscopy we can monitor the uptake of dye as a function of scanning and solvent parameters. This study also shows the possibility of introducing small quantities of a chemical into the polymer surface in a highly localized (nanometer scale) fashion. |
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| 11:00 AM |
AS-TuM-9 AFM Sample Averaging
M. Hasselblatt (University of California at Davis); E.M. Bradbury (Los Alamos National Laboratory) Soon after its invention,1 Scanning Tunneling Microscopy (STM) developed into a prominent tool for surface analysis in the physical sciences. A rapid expansion of this type of microscopy beyond the physical sciences was achieved by the Atomic Force Microscope (AFM).2 Both types of Scanning Probe Microscopies (SPMs) yield topographic bitmaps of surface properties. Unfortunately, a rigid analysis of these bitmaps is often neglected in light of the ``beautiful'' images obtained. Here, we present a novel approach to enhance the interpretation of data containing repetitive features. It is based on the combination of linear correlation and bilinear bitmap rotation to average over multiple occurrences of the same feature in one SPM micrograph. Essentially, our procedure is similar to sample averaging in any kind of spectroscopy, or adding images acquired by electron microscopy. It can be used successfully to increase the signal to noise ratio of SPM data and to gain more confidence in data analysis of repetitive features.
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| 11:20 AM |
AS-TuM-10 Study on Modification of Hydrogen Trap Site in Nickel and Stainless Steel Using Atom Probe
T. Yoshimura (Hitachi, Ltd., Japan); Y. Ishikawa (Yokohama National University, Japan) Hydrogen is a dominant outgassing species from stainless steel vacuum chambers and components in ultra-and extremely high vacuum. Vacuum firing and oxidation are common practice to attain a low out gassing rate. Only a few studies have been taken so far to measure the hydrogen concentration profiles in ultrahigh vacuum materials, stainless steel,1 copper2 and aluminum.3 These studies utilize high energy (MeV order) ion beams to probe for hydrogen. Unfortunately, because of energy spread of ion beam, the depth resolution is limited to be layers than 7.5nm, which is equivalent to the thickness of the surface oxide layers of stainless steel as well as those of aluminum alloys prepared in the controlled atmospheres. Consequently, means of MeV ion beam technique, it is hardly possible to examine the hydrogen concentration depth profile in the surface oxide layers or the oxide-metal interface. Atom probe - field ion microscopy (AP-FIM) is unique among the family of surface analysis techniques in that it examines only the outermost atomic layer of the surface atom-by-atom and depth profiling is possible by means of layer-by-layer evaporation without disturbing the structure underneath. The atom probe has no mass limitations from hydrogen to heavier elements and is equally sensitive to all elements. The present study employs a position sensitive atom probe (PoSAP),4 which is a recent addition to variants of the atom probe and makes three dimensional chemical analysis with single atom sensitivity possible, to examine the hydrogen concentration depth profiles in the surface layers as well as the oxide-metal interface.5 Nickel and aged stainless steel comprising Cr-rich region and Fe-rich region with nanometer size was chosen as a model system for modification of hydrogen trap site. Annealing and oxidation of nickel and stainless steel are carried out as the method to modify the hydrogen trap site. Deuterium was used for this experiment in order to increase the atom probe detection quantity of trapped hydrogen. The number of deuterium trapped in Nickel decreases after annealing, which is a modification of trap site by annealing. Deuterium trapped in the oxide layer and in the oxide-nickel interface has been observed with sufficient resolution to determine the extent of trapping on an atomic scale, which is a modification of trap site by oxidation. No remarkable segregation of deuterium trap site was recognized in the separated ferritic phase of aged duplex stainless steel, because the modulated structure has a match interface. However, after oxidation, the number of trap site decreases and the trap site tends to move to the interface between Cr-rich region and Fe-rich region and the oxide-metal interface. Furthermore it should be noted that clustered trap sites would be observed with the modification treatment of oxidation. |