Brock Research Group

Brief Biography

After receiving his doctoral degree, Brock spent two years as a postdoctoral research associate at the Massachusetts Institute of Technology and then joined the Cornell faculty in 1989.  At Cornell he is affiliated with the Cornell Center for Materials Research and is Director of the G-Line Division of the Cornell High Energy Synchrotron Source.  He is a member of Sigma Xi, the American Physical Society, the American Association for the Advancement of Science, and the Materials Research Society.

Research Interests

For over 100 years, our fundamental understanding of the structure of materials on atomic length scales has been advanced by direct structural measurements using x-rays.  Modern synchrotrons provide over 8 orders of magnitude higher fluxes than laboratory based sources.  This flux enables us to utilize higher resolution: higher angular resolution for diffraction, higher energy resolution for spectroscopies, higher time resolution for dynamics, and higher spatial resolution for imaging.  We employ modern synchrotron-based x-ray techniques to measure the structure directly on length-scales ranging from 1 – 50,000Å on time scales ranging from 10^-6 – 10³ seconds.  We are currently concentrating our studies on pulsed laser deposition (PLD) of complex oxide thin films.

The desire to manufacture devices with characteristic features on (sub)nanometer length scales has driven an enormous effort to create thin films with precisely controlled chemical composition, crystal structure and morphology. Energetic processing techniques offer the enticing prospect of gaining additional control at the nanoscale over thin-film deposition and processing. However, our fundamental understanding of non-thermal growth and surface processing is in an early stage of development. We are studying the fundamental processes governing deposition via Pulsed Laser Deposition (PLD).  Empirically, by tuning the substrate temperature, background gas pressure, laser pulse rate, and energy density of the laser pulse, high quality films of many cubic perovskite (e.g., colossal magnetoresistance (CMR), piezoelectric, and high T_C superconducting materials) can be grown using PLD. Our time-resolved x-ray structural measurements directly test proposed growth models.  This research program is a component of the CCMR’s IRG-3 and is based at CHESS.

I am also working to develop the next generation of x-ray sources. LINAC based x-ray sources such as (pulsed) X-ray Free Electron Lasers (XFELs) and (cw) Energy Recovery LINACs (ERLs) will create diffraction limited and degenerate x-ray beams that will enable coherent and time-resolved techniques previously only possible with optical lasers.  Our long term goal is to generate, manipulate, and utilize coherent x-ray beams for atomic-scale structural measurements on the relevant fundamental time-scales.

Selected Publication

• J.D. Brock, J.D. Ferguson and A.R. Woll. X-ray scattering studies of the surface structure of complex oxide films during layer-by-layer growth via pulsed laser deposition. Metallurgical and Materials Transactions A (2009).
• S. Hong, A. Amassian, A.R. Woll et al. Real time monitoring of pentacene growth on SiO2 from a supersonic source. Applied Physics Letters 92, 253304-1 (2008).
• J.D. Ferguson, A.R. Woll, G. Arikan, D.S. Dale, A. Amassian, M.W. Tate and J.D. Brock. Time Resolved In-Situ Diffuse X-ray Scattering Measurements of the Surface Morphology of Homoepitaxial SrTiO3 Films During Pulsed Laser Deposition. In Mater. Res. Soc. Symp. Proc. (eds. Scott, J.F., Gopalan, V., Okuyama, M. & Bibes, M.) Vol. 1034E, pages 1034-K10-20 (2008).
• D. Dale, Y. Suzuki and J.D. Brock. In situ x-ray reflectivity studies of dynamics and morphology during heteroepitaxial complex oxide thin film growth. Journal of Physics: Condensed Matter 20, 264008 (2008).
• J.D. Brock and M. Sutton. Materials Science and X-ray Techniques. Materials Today 11, 52-55 (2008).
• D. Dale, A. Fleet, A. Woll, Y. Suzuki and J.D. Brock. In-situ Studies of Pulsed Laser Deposition Growth at CHESS. Synchrotron Radiation News 20, 32-37 (2007). 
• J.M. Pomeroy and J.D. Brock. Critical nucleus phase diagram for the Cu(100) surface. Physical Review B (Condensed Matter and Materials Physics) 73, 245405.1-7 (2006).
• Fleet, D. Dale, A.R. Woll, Y. Suzuki and J.D. Brock. Multiple Time Scales in Diffraction Measurements of Diffusive Surface Relaxation. Physical Review Letters 96, 055508.1-4 (2006).
• D. Dale, A. Fleet, Y. Suzuki and J.D. Brock. X-ray scattering from real surfaces: Discrete and continuous components of roughness. Physical Review B (Condensed Matter and Materials Physics) 74, 085419:1-8 (2006).
• Fleet, D. Dale, Y. Suzuki and J.D. Brock. Observed Effects of a Changing Step-Edge Density on Thin-Film Growth Dynamics. Physical Review Letters 94, 036102.1-4 (2005).
• H.-H. Wang, A. Fleet, J.D. Brock, D. Dale and Y. Suzuki. Nearly strain-free heteroepitaxial system for fundamental studies of pulsed laser deposition: EuTiO3 on SrTiO3. Journal of Applied Physics 96, 5324-5328 (2004). 
• D. Dale, A. Fleet, J.D. Brock and Y. Suzuki. Dynamically tuning properties of epitaxial colossal magnetoresistance thin films. Applied Physics Letters 82, 3725-3727 (2003).
• M. Sutton, Y. Li, J.D. Brock and R.E. Thorne. X-ray intensity fluctuation spectroscopy measurements of the charge density wave phases of NbSe3. Journal De Physique IV 12, 3-8 (2002).
• O. Malis, J.D. Brock, R.L. Headrick, M.-S. Yi and J.M. Pomeroy. Ion-induced pattern formation on Co surfaces: An x-ray scattering and Kinetic Monte Carlo study. Physical Review B (Condensed Matter) 66, 035408 (2002).
• Y. Li, D.Y. Noh, J.H. Price et al. Observation of dynamic coupling between the Q(1) and Q(2) charge-density waves in NbSe3. Physical Review B 63, 041103 (2001).
• K.L. Ringland, A.C. Finnefrock, Y. Li, J.D. Brock, S.G. Lemay and R.E. Thorne. Sliding charge-density waves as rough growth fronts. Physical Review B 61, 4405-4408 (2000).
• M.V.R. Murty, A.J. Couture, B.H. Cooper, A.R. Woll, J.D. Brock and R.L. Headrick. Persistent layer-by-layer sputtering of Au(111). Journal of Applied Physics 88, 597-599 (2000).