Dr. Richard R. Cavanagh

Deputy Director of the Chemical Science and Technology Laboratory (CSTL). CSTL is one of the nine technical Operational Units within the National Institute of Standards and Technology and has ~325 technical staff of and an annual Budget of approximately $85M. The NIST Mission is to promote U.S innovation and industrial competitiveness by advancing measurement science, standards, and technology in ways that enhance economic security and improve quality of life. CSTL supports NIST’s Mission by addressing customer needs for measurements, standards, and data in the areas broadly encompassed by chemistry, chemical engineering and the biosciences. Areas of growth and/or increased emphasis include bioscience and health, nanometrology, assessment of climate change and renewable energy technologies. The laboratory is organized into five Divisions along disciplinary lines:

• Analytical Chemistry: Chemical measurements research and services in: inorganic, organic and electroanalytical chemistry; atomic, molecular and mass spectrometry; and microanalytical technologies
  

• Biochemical Science: DNA chemistry, sequencing; Protein structure, properties, and modeling; Biomaterials; Biocatalysis and bioprocessing measurements
  

• Chemical and Biochemical Reference Data: Experimental, theoretical, and computational research on the identity and reactivity of chemical species, emphasizing data, information, and protocols for the identification of chemical and biochemical species
  

• Process Measurements: Research, calibration services and provision of primary standards for temperature, pressure, vacuum, humidity, fluid flow, air speed, liquid density and volume, and gaseous leak-rate measurements; Sensor research
  

• Surface and Microanalysis Science: Nanoscale chemical characterization; Particle characterization and standards; Electronic and advanced materials characterization; Surface and interface chemistry; Advanced isotope metrology
  

• Thermophysical Properties: Experiment, theoretical, and simulation research on the properties of gases, liquids, and solids, emphasizing thermophysical properties

Research Activities and Interests:

Over the past twenty-nine years, I have been involved in a broad range of research that applied laser-based methods to the study of molecular processes at surfaces. I have published over 100 papers, with the vast majority focused in the area of surface dynamics. Since joining NBS (NIST) in 1979, my scientific work has been directed toward a more complete understanding of reactions at surfaces through detailed measurements of surfaces and their response under chemical reaction. Since joining NIST, I have been involved with measurement techniques such as infrared absorption spectroscopy, reflection-absorption infrared spectroscopy, Raman spectroscopy, inelastic neutron scattering, quasielastic neutron scattering, laser induced fluorescence, multiphoton ionization, ultrafast pump-probe techniques, near-field optical methods, Auger electron spectroscopy, etc.

I have authored or co-authored 20 papers in the refereed literature in the area of energy partitioning as a result of surface reactions. The research in these papers is centered on laser-based characterization of molecules that have desorbed from surfaces. Through laser-induced fluorescence and multiphoton ionization techniques, the degree of excitation in translational, rotational, vibrational and electronic degrees of freedom was assessed. From the measured distribution of energy, it was possible to gain new insights into the energy transfer events that led to desorption. Extended interactions with theoretical experts led to a model for hot-electron induced surface chemistry that has become the standard in the field. This work also demonstrated surface-state mediated photodesorption and rotational cooling on desorption. Recently, these methods have been combined with femtosecond desorption lasers to probe the newfound regime of femtosecond desorption. This work has provided definitive evidence that transient heating is responsible for the novel desorption phenomena that have been widely reported by many industrial and academic researchers. This groundbreaking work demonstrated that laser pulses can lead to desorption mediated by hot electrons, surface states, and short-lived thermal transients. The reaction pathways that were conclusively demonstrated helped to point the direction to new approaches for exploiting optically stimulated surface chemistries.

I have also been involved in the development of time-resolved infrared laser methods to follow the decay of vibrational excitation in adsorbed layers on metal surfaces. These efforts began using picosecond pulses to probe metal carbonyls in solution and supported on SiO₂. The extensive experiments indicated that multiphonon relaxation was able to account for the decay rates. When these methods were brought to bear on CO bound to metal single crystals, a much faster decay channel was observed and attributed to electron-hole pair channels. The research demonstrated the collective nature of the adsorbate excited states for the CO/Pt(111) system, and provided a detailed evaluation of the role of population decay and dephasing. We have extended the time-resolved pump-probe techniques to assess the effect of visible excitation of metal surfaces, discovering that the energy transfer from the excited electrons of the underlying metal to the adsorbate degrees of freedom is dominated by coupling to the low frequency adsorbate modes. This work has required extensive modeling of transient surface optical effects.

My recent technical interests have moved away from studies of single crystal surfaces, focusing on a novel form of microscopy for characterizing nanostructured surfaces. Near field scanning optical microscopes (NSOMs) have been constructed under my leadership to allow visible, Raman, and infrared imaging at spatial resolutions that cannot be achieved working at the diffraction limit. In the infrared instrument, the approach incorporates a broadband femtosecond laser source, and infrared focal plane array, and a novel NSOM instrument that allows simultaneous collection of transmitted and reflected light. The instrument is able to record spectra across the 150 cm^-1 bandwidth of the laser on each shot, with data acquisition for each specimen resolution element requiring 1 second. These instruments are being used to probe the heterogeneity of chemical materials such as polymer blends, nanostructures, and catalysts. 

Awards:

• NRC/NBS Postdoctoral research associate (1979 - 1980)
• Department of Commerce Silver Medal (1985) with Dr. David S. King for their state-resolved studies of molecular desorption.
• Department of Commerce Gold Medal (1990) for work in laser diagnostics of energy transfer processes at surfaces.
• Samuel Wesley Stratton Award (1992) with Drs. M.P. Casassa, E.J. Heilweil, D.S. King and J.C. Stephenson for outstanding scientific achievements in laser studies of chemical dynamics.

Membership and Professional Activities:

• American Chemical Society
• American Vacuum Society
  - Executive committee of the AVS Surface Science Division (1988-1990)
  - Fellow (2003)
• American Physical Society
  - Fellow (2004)
• Physical Electronics Conference
• General Treasurer 1985-1989 : Local 1990 Conference Co-chair
• Vibrations at Surfaces 1990 - Local Organizing Committee
• Gordon Research Conference - Dynamics of Gas Surface Interactions - Vice Chair ’93; Chair ‘95
• Adriatico Research Conference - Lasers in Surface Science - Co-chair ‘94
• Associate Editor – Journal of Chemical Physics ‘95-‘98
• Council for Chemical Research, Board Member ‘07-present