Directed Energy Interactions with Surfaces

Staff

Principal Investigator

  • Michael J. Pellin
  • Wallis F. Calaway
  • Dieter M. Gruen
  • Michael R. Savina
  • Igor Veryovkin

Visiting Scientist

  • Emil Tripa
  • Bruce V. King

Secretary

  • Barbara Hall

Theme

Using world-class tools, this program seeks to develop a predictive understanding of the effects of directed energy sources (ions, electrons, and photons) on the composition, structure, and material properties of surfaces and other materials whose dimensions are of atomic scale. These tools, based on laser postionization ofatomsandmoleculesdesorbed by directed energy sources have been developed at ANL and provide the program with uniquely sensitive methods for trace analysis of surfaces,nano-materials, and for probing particle-surface and laser-surface interactions.

Accomplishments

  • Fundamentals of Particle Desorption
    • Laser Desorption from Brittle Solids. Our understanding of laser interactions with oxide, aggregate, and composite materials has been significantly improved. Thermal shock was discovered to be the preferred mechanism for surface material removal from these materials and application of appropriate laser pulses can lead to significantly higher removal rates and surfaces free of thermal processing. The effect of nanoabsorptive sites (Au particles in SiO2) in otherwise transparent media has been shown to produce ablation even when sites are isolated deep in the solid, demonstrating the plausibility of a nano-particulate mechanism for optical damage at the National Ignition Facility.
    • Sputtering of Clusters. Building on earlier pioneering work on the ejection of cluster molecules during energetic ion bombardment of surfaces, we have proven that electronic excitation during sputter ejection of molecules (Ca2 from a Ca surface) is minimal. In contrast, rotational, vibrational and translational energies are large.
  • Trace Analysis of Samples with Atomic Dimensions. The unique combination of high useful yield(atoms detected/atoms removed) and high discrimination provided by the Resonant Ionization Mass Spectrometers developed under this FWP, allow for the first time trace analysis of samples containing only a few atoms of the analyte of interest. Extensive modeling of sputtering and ion trajectories has lead to the development of a new instrument (currently being commissioned) which combines useful yields in excess of 0.3 (compared to state of the art large frame SIMS instruments with useful yields ~10-3Ð10-5) with the ability to measure at concentrations down to 1 part per trillion (ppt).
  • Isotopic Analysis. Isotopic analysis of sub-micron SiC grains has been performed for >ppm level impurities. The isotopes form a geminate record of stellar nucleosynthesis and demonstrate for the first time the range of stars that contributed material to our solar system. Moreover, our results reveal that at least some of the material present in the solar system was not formed by s-, r- or p-nucleosynthesis, but rather, are formed by a distinctive neutron-burst mechanism.
  • Molecular Surface Analysis. Building on earlier work demonstrating that one-photon vacuum ultraviolet (VUV) photoionization can provide a fragmentation free method for analysis of large molecules, the highest reported molecular useful yield (0.005) was obtained using an F2 excimer laser with sufficient intensity to saturate the photoionization volume. Currently efforts are underway to combine the high pulse energy, tunable VUV from the 4th generation light source at ANL with a microfocus ion probe mass spectrometer to provide a small spot (100 nm), sensitive, and discriminative probe of the molecular content of a surface or nanometer-scale object.

Impact

This work has resulted in numerous invited talks and publications including articles in Science and Physical Review Letters. The microfocus ion probe mass spectrometer developed under this FWP is the most sensitive in the world, particularly when applied to samples containing limited numbers of atoms or molecules. As the analytical difficulties associated with nanoscience become apparent, the demonstrated ability to detect single impurity atoms (even isotopes) or molecules when they are present only at the ppt level will be extremely useful. Fundamental laser desorption work in this area received the Energy100 Award for the discovering that 308 nm Excimer Laser removes organic material by electronic excitation - one of the Department of EnergyÕs top scientific contributions of the 20th century.

Interactions

Collaborative publications with a wide range of University (including University of Chicago, Washington University St. Louis, California Institute of Technology, University of Newcastle) and National Labs (ANL, SNL, LLNL) have appeared in the last few years. Further, our unique tools are applied in collaborative research on problems of particular importance to DOE. This work includes studies of optical damage with the National Ignition Facility, studies of laser/surface interactions with the Environmental Management Science Program, and studies of surface oxidation and corrosion with both SCLTR and the Office of Industrial TechnologiesÕ Aluminum Vision.