Office: Ekeley W145B
Lab: Ekeley S166, S166A, S170
Lab Phone: 303-492-8516, 303-492-6992, 303-492-7173
University of California, Berkeley, Calif.; Ph. D. in Chemistry, March 1983.
Yale University, New Haven, Conn.; B.S. in Chemistry, May 1977.
Surface Chemistry, Nanotechnology/Materials, Physical Chemistry, Renewable Energy
Faculty Research Award from College of Engineering and Applied Science, University of Colorado at Boulder, 2006
University of Colorado at Boulder Faculty Assembly Excellence in Research, Scholarly, and Creative Work Award, 2006
American Chemical Society Colorado Section Award, 2004
R&D 100 Award for Particle-ALD, 2004
Inventor of the Year, University of Colorado at Boulder, 2004
National Science Foundation Creativity Award, 2002-2004
Fellow, American Vacuum Society, 2000
Fellow, American Physical Society, 1997
Presidential Young Investigator Award, 1988-1993
Alfred P. Sloan Foundation Fellow, 1988
IBM Faculty Development Award, 1988
Dupont Young Faculty Awardee, 1988
Dreyfus Award for Newly Appointed Faculty in Chemistry, 1985
AT&T New Faculty Award, 1985
Bantrell Post-doctoral Research Fellow, Spring 1983-Fall 1984
Miniaturization to the nanometer scale has been one of the most important trends in science and technology over the past decade. The chemistry to fabricate nanolayers, the engineering for nanocomposite design and the physics of nanostructure properties have created many exciting opportunities for research. These new interdisciplinary areas in nanoscience and nanotechnology supersede the more traditional disciplines and demand new paradigms for collaboration.
Our research is focusing on the fabrication, design and properties of ultrathin films and nanostructures. We are developing new surface chemistries for thin film growth, measuring thin film growth using in situ techniques and characterizing thin film properties. This research is relevant to many technological areas such as semiconductor processing, flexible displays, MEMS/NEMS, Li ion batteries and fuel cells. Our research bridges many disciplines and we have collaborators in the Departments of Chemistry, Chemical Engineering, Mechanical Engineering and Physics on campus and many others at universities, industries and national laboratories off campus.
Many of our surface chemistry and thin film growth investigations utilize atomic layer deposition (ALD) techniques . ALD is based on sequential, self-limiting surface reactions as illustrated in the accompanying figure. This unique growth technique can provide atomic layer control and allow conformal films to be deposited on very high aspect ratio structures. ALD methods and applications have developed rapidly over the last ten years. ALD is on the semiconductor road map for high-k gate oxides and diffusion barriers for backend interconnects. ALD is also employed in magnetic read-write heads and is employed to fabricate capacitors for DRAM.
ALD is based on sequential, self-limiting surface chemical reactions. One of the classic ALD systems is Al2O3ALD. Al2O3 ALD is based on the binary reaction: 2Al(CH3)3 + 3H2O -> Al2O3 + 6CH4 can can be split into the following two surface half-reactions [2,3]:
A) AlOH* + Al(CH3)3 -> AlOAl(CH3)2* + CH4
B) AlCH3* + H2O -> AlOH* + CH4
where the asterisks denote the surface species. In the (A) reaction, Al(CH3)3 reacts with the hydroxyl (OH*) species and deposits aluminum and methylates the surface. The (A) reactions stops after all the hydroxyl species have reacted with Al(CH3)3. In the (B) reaction, H2O reacts with the AlCH3* species and deposits oxygen and rehydroxlates the surface. The (B) reactions stops after all the methyl species have reacted with H2O. Because each reaction is self-limiting, the Al2O3 deposition occurs with atomic layer control.
By applying these surface reactions repetitively in an ABAB... sequence, Al2O3 ALD is achieved with a growth rate of 1.1 Å per AB cycle . This approach is general and can be applied to many important binary materials such as MgO  and TaN . The ALD method can also be extended to deposit single-element metal films. For example, the binary reaction for tungsten deposition: WF6 + Si2H6 -> W + 2SiHF3 + 2H2 can be split into separate WF6 and Si2H6 half reactions to obtain W ALD . Film growth during Al2O3 and W ALD can be recorded using a variety of techniques including the quartz crystal microbalance (QCM) . QCM results for Al2O3 and W ALD are shown in the above figure.
Similar self-limiting surface reactions can be employed for the growth of organic polymer films. This film growth is described as molecular layer deposition (MLD) because a molecular fragment is deposited during each reaction cycle . The precursors for MLD have typically been homobifunctional reactants. A cartoon illustrating the MLD process is shown in the above figure. MLD methods have been developed for the growth of organic polymers such as polyamides .
In addition to organic polymers, the precursors for ALD and MLD can be combined to grow hybrid organic-inorganic polymers . For example, Al(CH3)3 (trimethylaluminum (TMA)) and HO(CH2)2OH (ethylene glycol (EG)) can be reacted to obtain an aluminum alkoxide polymer known as "alucone" . Many other hybrid organic-inorganic polymers are possible by mixing various ALD and MLD reactants. The hybrid organic-inorganic MLD films are very interesting because their chemical and mechanical properties can be tuned by varying the nature of the organic group.
There are many important new applications for ALD and MLD. For example, Al2O3 ALD on polymers produces excellent gas diffusion barriers that are needed for flexible display and thin film solar devices on polymer substrates . ALD coatings on the electrodes of Li ion batteries can also stabilize the capacity versus charge-discharge cycles and improve the lifetime of the battery [12,13]. Metal ALD is also useful for efficiently depositing expensive precious metals for use in catalysis . Semiconductor ALD may also be important in defining a new family of nano-photovoltaic devices .
Our research spans from surface chemistry development to the application of the ALD thin films. We grow our ALD and MLD thin films in various viscous flow hot-wall reactors , rotary reactors for coating particles  and plasma ALD reactors . Our in situ techniques for measuring thin film growth include quartz crystal microbalance (QCM)  and Fourier transform infrared spectroscopy . Our ex situ techniques for studying thin films include x-ray reflectivity (XRR) and x-ray photoelectron spectroscopy. We also have access to a variety of other techniques outside of our laboratory at the Nanofabrication Characteriztion Facility such as field-emission scanning electron microscopy and nanoindentation.
Board of Directors, American Vacuum Society, January 2010-December 2013.
Member, Editorial Board, Coatings-Open Access Journal, November 2010-Present
Member, Conference Committee for American Vacuum Society Topical Conference on Atomic Layer Deposition (ALD 2002-ALD 2010).
Co-Founder, ALD NanoSolutions, Fall 2001. Member of Scientific Advisory Board, 2002-Present. Chair of the Trustees, American Vacuum Society, January-December 2009.
Trustee, American Vacuum Society, January 2007-December 2009.
Member, Board of Editors, Surface Review and Letters, January 1998-Present.
Member, Thin Film Division Program Committee of American Vacuum Society, October 1999-Present.
Member, Thin Film Division Executive Committee, American Vacuum Society, January 2007-December 2008.
Chair, International Symposium of the American Vacuum Society, October 30-November 4, 2005, Boston, Massachusetts Chair, American Vacuum Society Topical Conference on Atomic Layer Deposition (ALD 2001), May 14-15, 2001, Monterey, California.
Chair, Thin Film Division of the American Vacuum Society, January - December 2002. Vice Chair, Thin Film Division of the American Vacuum Society, January - December 2001.
Member, Board of Assessment of NIST Programs, Panel for Chemical Science and Technology, National Research Council, January 1993-December 1998.
Co-Chair, Gordon Research Conference on Electronic Materials: Chemistry, Excitations and Processing, July 6-10, 1997 in New Hampshire.
Member, Executive Committee of Electronic Materials and Processing Division, American Vacuum Society, January 1996-December 1997.
Co-Chair, Symposium on Environmental Heterogeneous Processes, American Chemical Society National Meeting, New Orleans, LA, March 24-28, 1996.
Guest Editor, Thematic Issue on Heterogeneous Catalysis, Chemical Reviews, May 1995. Chair, Microphysics of Surfaces: Nanoscale Processing, Topical Meeting of the Optical Society of America, Sante Fe, NM, Feb. 9-11, 1995.
Associate Editor, Chemical Reviews, July 1992- Dec. 1994. Member, National Materials Advisory Board Committee on New Currency Design: Counterfeit Deterrent Features for the Next Generation, June 1992-May 1994.
Member, Defense Science Study Group, Institute for Defense Analysis, Alexandria, Virginia, Spring 1989- Fall 1991.
Alumni Member, Fall 1991- Present.