Isaacson, M.

Kopf, D.

Langmore, J.

Parker, N. W.

Utlaut, Mark

English

University of Portland

University of PortlandPilot ScholarsPhysics Faculty Publications and Presentations PhysicsWinter 1977Atomic Resolution Observations of Heavy AtomAdsorbates on Low Atomic Number SubstratesMark UtlautUniversity of Portland, utlaut@up.eduM. IsaacsonD. KopfJ. LangmoreN. W. ParkerFollow this and additional works at: https://pilotscholars.up.edu/phy_facpubsPart of the Physics CommonsThis Journal Article is brought to you for free and open access by the Physics at Pilot Scholars. It has been accepted for inclusion in Physics FacultyPublications and Presentations by an authorized administrator of Pilot Scholars. For more information, please contact library@up.edu.Citation: Pilot Scholars Version (Modified MLA Style)Utlaut, Mark; Isaacson, M.; Kopf, D.; Langmore, J.; and Parker, N. W., "Atomic Resolution Observations of Heavy Atom Adsorbates onLow Atomic Number Substrates" (1977). Physics Faculty Publications and Presentations. 62.https://pilotscholars.up.edu/phy_facpubs/62Abstract: Atomic resolution observations of heavy-atom adsorbates on low-atomic-number substrates* M. Isaacson,+ D. Kopf, J. Langmore,i N. W. Parker,§ and M. Utlaut Depariment of Physics a"d the Enrico Fermi Institute, The University of Chicago. Chicago, lllinois 60637 (Received I September 1976) PACS numbers: 82.65.My, 66.30.Jt, 61.16.Di The feasibility of utilizing a high-resolution scanning trans-mission electron microscope (STEM)1 to study the adsorption and diffusion of heavy atoms on low atomic number substrates is being investigated. It is shown that the study of surface phenomena 011 an atomic scale may be possible with the STEM.2 The technique should be complementary to existing methods of studying surfaces at atomic resolution since the STEM is capable of observing substrate-adsorbate systems not easily accessible by other methods. Two types of measurements which can be performed with existing instrumentation have been demonstrated. They are (1) the measurement of the spacing distribution of adatoms deposited onto substrates, and (2) the measurement of the diffusion of individual adatoms on substrates. Initially, our attention has been concentrated on thin evaporated carbon film substrates and solvent evaporated heavy atom-containing molecules as adsorbates, because of the ease of preparation of such samples. However, one should be able to extend the method to any substrate that can be made of small enough mass thickness and any adsorbate that can be visualized.3 We have (1) found that uranium and silver atoms deposited at low concentrations (from 7 X 10- 4 atoms/ A2 to 5 X 10- 3 atoms/ A2) exhibit preferential spacings with respect to one another (the pair-spacing distribution is peaked), and (2) 434 J. Vac. Sci. Technol., Vol. 14, No. 1, Jan./Feb. 1977 measured the thermal hopping of uranium and silver atoms on carbon substrates (deposited from dilute solutions of U02Clz and AgCN, respectively) at room temperature. For the uranium atom samples, we have observed a tendency for· atom pairs to move together as a unit. In addition, we have shown that the effects of electron beam induced motion for the samples observed a re (within our experimental error) negligible. •This work was supported by the U.S. Energy Research and Development Administ ration. This paper will be published in two parts: Pt. I in Ul-tramicroscopy 1 (J976) and Pt. II in the Proceedings of the Natiorud Academy of Sciences (USA). t Alfred P. Sloan Research Fe llow IPresent address: Medical Research Council Laboratory fur Molecular Biology, Hills Road, Cambridge, England CB2 2QH. ~Hertz Foundation for the Advan.:eme nt of Applied Science predoctoral fe llow. 1J. W all, J. Lang more, M. Isaacson. a nd A. V. C rewe, Proc. Nat. Acad. Sci. (USA) 7 1, 1 (1974). 2M. Isaac;on and N . W. Parker, in llTRT/ SEM/ 76 VoU, edited by O. Johari (llTRI, C hicago. 1976), p. 345. 'IA. V. C rewe, J. Langmnre, and M. Isaacson, in Physical Aspects of Electron Microscopy and M icrobeam Analysi~. edited by B. Siegel a nd D. Beaman (Wiley, New York, 1975), p. 47. Copyright © 1977 by the American Vacuum Society 434 

Atomic Resolution Observations of Heavy Atom Adsorbates on Low Atomic Number Substrates

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Atomic Resolution Observations of Heavy Atom Adsorbates on Low Atomic Number Substrates

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