Crowell, John
Materials chemistry, surface kinetics of metals/semiconductors, CVD, photo-induced deposition, thin-film spectroscopy.

Contact Information
Professor of Chemistry and Biochemistry

Office: Urey Hall 5230
Phone: 858-534-5441
Group: View group members
1984 Ph.D., University of California, Berkeley
1979 B.S., University of Illinois
1986 Postdoc, University of Pittsburgh
Awards and Academic Honors
Regent's Fellowship, University of California, Berkeley
Merck Award, University of Illinois
Research Interests
Research in my group is focused on exploring the surface chemistry of materials, especially the fundamental processes on surfaces that govern chemical reactions, deposition, and thin film formation. Our experiments are conducted in ultrahigh vacuum using single crystal metal and semiconductor surfaces, porous semiconductor and oxide materials, and supported metal surfaces. These surfaces are investigated using various surface characterization techniques, including Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), atomic force microscopy (AFM), desorption / reaction mass spectrometry (TPD), and vibrational spectroscopy utilizing electron scattering (HREELS) and reflection or transmission infrared spectroscopy (MIRIRS, RAIRS, and TIRS). Our studies examine the structure, bonding and chemical reactivity of species adsorbed on surfaces, the kinetics of chemical reaction processes at surfaces, and the growth and physical / chemical properties of thin films and interfaces. The focus of selected studies of current interest are briefly described below.

Epitaxial Deposition and Photochemistry at Semiconductor Surfaces

We are exploring the chemistry of semiconductor surfaces, especially the Group IV surfaces of Si and Ge. Our focus is the fundamental surface processes that occur during deposition. For example, we have examined both the thermal and photochemical reaction of various hydrided precursors such as disilane and digermane with Si and Ge single crystal surfaces. Through a microscopic understanding of the adsorption and reaction processes taking place during deposition, and their correlation to the atomic film structure, we believe we can enhance one's ability to build devices with desired optical and electrical properties. We are also examining how dopants such as phosphorus or arsenic modify the reactivity and chemical behavior of Group IV surfaces, and how dopant incorporation can be controlled using CVD on an atomic level.

Dielectric Thin Film Growth by Chemical Vapor Deposition

Dielectric films are an ever increasing component of integrated circuit technology and are used to isolate semiconducting layers, interconnects, and devices. As device sizes become reduced to increase speed, the quality and thickness uniformity of these dielectric films become increasingly important. Development of dielectric films sufficient for these needs is one of the major challenges facing the advancement of the semiconductor industry. Our interest is in obtaining a detailed knowledge of the deposition process (i.e. delineation of the reaction mechanism, elucidation of reaction intermediates, and modeling of the deposition chemistry) in order to improve and control film quality and to develop new dielectric films or sources tailored for specific purposes. Our studies involve in-situ analysis of growth by CVD, coupled with surface analysis of the resulting film in UHV. Current studies involve APCVD of SiO2 from tetraethoxysilane (TEOS) and ozone, and CVD of high k materials.

Nucleation Aspects of Deposition using Variable Temperature Scanning Tunneling Microscopy

In order to fabricate nanoscale structures, one must know how nucleation occurs following different processing steps and different deposition chemistries. Through the use of IR spectroscopy coupled with scanning tunneling microscopy, we can delineate the adsorption and reaction species and determine the deposition chemistry, in combination with knowledge of the surface morphology and structure. Our initial studies are examining the step by step nucleation process and the resulting film morphology during Group IV epitaxial growth.

Laser Desorption Mass Spectrometry from Porous Silicon

A new desorption/ionization strategy based on pulsed laser desorption/ionization from a porous silicon surface is being explored for biomolecule analysis. Desorption/ionization on silicon (DIOS) uses porous silicon to trap analytes deposited on the surface and laser irradiation to vaporize and ionize these molecules. DIOS has been demonstrated for a wide range of small molecules as well as biomolecules at the femtomole level with little or no fragmentation. We have demonstrated the application of DIOS-MS to small molecule analysis, quantitation, protein identification, on-chip reaction monitoring, on-chip separation and post-source decay structural analysis. DIOS offers many unique advantages including good sensitivity, low background ion interference, and high salt tolerance, a demonstrated potential for automation, and compatibility with microfluidics and microchip technology on silicon.
Primary Research Area
Physical/Analytical Chemistry
Interdisciplinary interests

Outreach Activities
For every class that I teach I provide 4 hours per week of contact office hours with the students. In addition to discussing the course material, I also often advise students on other aspects of their academic career, especially research opportunities, volunteer work, study habits, learning aids, etc. Many of these students are in underrepresented groups.

I routinely write 10-15 letters of recommendation per year for students applying to medical school, pharmacy school, dental school, and graduate school. I meet with the students on multiple occasions to discuss their goals, to discuss their background, and to advise them on succeeding at the next level prior to writing their letter. A significant portion of these students are in underrepresented groups.
Selected Publications