16. DESIGNING NANOSTRUCTURES FOR NEW FUNCTIONAL MATERIALS


B.B. Rath
Naval Research Laboratory
Washington, DC 20375-5341, USA

Abstract

High demands on materials performance, particularly for functional applications in miniaturized systems, have brought revolutionary changes in materials synthesis, processing, and fabrication concepts. Recent advances have demonstrated that materials with nanometer scale structures can be successfully designed at the atomic and molecular levels to exhibit unique properties by using many methods. Improved and unexpected properties of these materials have an impact on a wide spectrum of phenomena including superconduction, magnetism, quantum electronics, non-linear optics, cluster stability, and nucleation and growth. Concurrent with innovative processing and fabrication, new characterization tools such as scanning tunneling microscopy, atomic force microscopy, and magnetic force microscopy have revolutionized our understanding of interatomic interactions and structures of atomic and molecular self-organization. Selected observations of recent studies in this emerging field will be presented with recommendations for future research.

Editor's note: The following materials have been reproduced from the viewgraphs used by B.B. Rath in his presentation.

Materials Research In A New Era

"I am inspired by the biological phenomena in which chemical forces are used in repetitious fashion to produce all kinds of weird effects (one of which is the author)."
                                                                                            — Richard Feynman
                                                                                                  Eng. and Sci. Mag.
                                                                                                  Cal. Tech. Feb. 1960

Materials: Unprecedented Technological Advances


Superconductivity
Electronics & sensors
Ceramics
Biomaterials
Carbons
Polymers
Materials for the environment
Magnetism
Optics and optoelectronics
Composites (smart materials)
Intermetallics
Under-dense materials
Ferrous alloys

Characterization tools ------------STM/AFM, atom-resolved TEM, angle-resolved Auger synchrotron radiation

Synthesis/processing ------------ MBE, MOCVD, PLD, spin casting, spray pyrolysis, E-beam/X-ray, UV lithography

High performance computing --- density functional approach, Car-Parrinello, molecular dynamics, Monte Carlo (see Fig. 16.1)

Industrial pull ------------------- improved system performance, economic competitiveness


Fig. 16.1. Trade-offs in computational materials physics.

Economic Drivers

Proximal Probe

Operating classes with order of magnitude lateral resolution

I. Electron Tunneling

    Scanning Tunneling Microscopy                                                             0.1 nm

    Scanning Tunneling Spectroscopy—electronic, EPR                               0.1 nm

    Laser Assisted Tunneling Spectroscopy—electronic, vibrational ?           0.1 nm

    Spin Polarized Tunneling—magnetic                                                       0.1 nm

    Ballistic Elec Emission Micro-/Spectroscopy—buried interface               1 nm

II. Proximally Focused Field Emission

    Scanning Electron Microscopy                                                               1 nm

    Microfabricated Field Emission Sources                                                 1 nm

    Electron Excited AES, PES, Fluorescence, Luminescence                     10 nm

III. Force (10-7 to 10-14 Newtons)

    "Atomic Force" Microscopy—repulsive, nanomechanics (incl. tribology) 1 nm

    Surface Force—Van der Wall, patch, electrostatic, ...                             0.1 - 10 nm

    Magnetic Force Microscopy—magnetism                                               10 nm

    Surface Potential—single electron                                                           10 nm

    Capacitance—dielectric                                                                         10 nm

IV. Near Field

    Optical—evanescent wave tunneling, nanoaperature, fluorescence           10 nm

    Chemical Potential—thermocouple junction                                             1 nm

    Acoustic—elastic                                                                                   10 nm

    Conductance—membrane transport                                                       10 nm

    Electrochemical—surface reactivity                                                         10 nm


Published: August 1997; WTEC Hyper-Librarian