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X-RAY RUNS: Apply for Beamtime

2017  Nov 1 - Dec 21
2017  Proposal/BTR deadline: 9/1/17

 

Marleen Kamperman

(Contact: E. Fontes - ef11@cornell.edu)

 

Two Cornell graduate students had their posters chosen for prizes at the 2007 Fall Meeting of the Materials Research Society (MRS) held November 26 – 30 in Boston, Massachusetts. Fourteen posters were awarded prizes out of over 2000 presented, each eligible for prizes up to $500. The winning posters were chosen on the basis of excellence in technical content, appearance, graphic design and presentation quality, and were displayed prominently for an audience of over 5100 scientists from the US and beyond.

John Ferguson, a graduate student with advisor Joel Brock in the Applied and Engineering Physics (A&EP) department, presented a poster entitled “Time Resolved In-Situ Diffuse X-ray Scattering Measurements of the Surface Morphology of Homoepitaxial SrTiO3 Films during Pulsed Laser Deposition.” Collaborators from the Cornell Center for Materials Research (CCMR), Materials Science and Engineering (MSE) and Cornell High Energy Synchrotron Source (CHESS) included Gökhan Arikan and Joel Brock (A&EP, CCMR), Arthur Woll and Darren Dale (CHESS), and Aram Amassian (MSE, CCMR). Ferguson is an MSE student and receives research support from CCMR, which boasts about his award and related research thrusts on their web site (www.ccmr.cornell.edu/news).

Ferguson ’s poster highlighted very recent results of an ongoing project to study thin film growth in strontium titanate. Strontium titanate is one of a large class of complex oxide materials that exhibit a wide variety of unexpected physical, electronic and magnetic properties. Surprising, for example, is that two electrically insulating materials such as these can combine to produce a buried interface that is electrically conductive. As promising as these materials are for technological applications, though, detailed experimental information about their growth is still very limited and obtaining such information is an ongoing challenge.


Poster prizewinners John Ferguson (second from right)
and Arthur Woll (second from left) with judges
.

The Pulsed Laser Deposition (PLD) growth system built into the G3 experimental station at CHESS was designed to address these challenging systems. There, the growth of homoepitaxial thin films can be monitored during the deposition process via both x-ray reflectivity and surface diffuse x-ray scattering measurements. Perfecting the diffuse scattering measurements was an innovation Ferguson helped develop over the past year. Using a CCD detector in 1D “streak-camera” mode, with 0.3-second time resolution, data were collected during growths at multiple substrate temperatures (figure 2a). Traditionally, the specular reflectivity oscillations are monitored to count the layer-by-layer growth of the two-dimensional films. The weaker diffuse scattering between Bragg rod positions is evidence of single unit cell high islands on the growing surface (figure 2b), and can be used to extract the density of these islands. The group demonstrated an order of magnitude increase in nucleation density when the substrate temperature was decreased by approximately 300oC.


Figure 2: X-ray scattering geometry using the CCD area detector in a “streak camera mode” (a) and measured diffuse scattering profiles from the small islands on the otherwise flat surface (b). The central peak is a Bragg reflection and the side lobes due to diffuse scattering. Black points are experimental values and the colored lines are lineshape fitting results. [1]

The most compelling (and remarked upon) aspect of Ferguson ’s poster was a visually appealing AFM image of small islands growing atop the wide, flat terraces of the growing thin film (see figure 3). Besides being an almost self-explanatory image of small island growth, the image also provides quantitative agreement with the diffuse x-ray scattering measurements. A Fourier transform of the AFM islands produces a pseudo-scattering pattern that agrees remarkably well with the diffuse x-ray measurements shown in figure 2b.


Figure 3: AFM image of the as-grown strontium titanate thin film showing small island formation on terraces.  The insert shows a larger area scan. [1]

Cornell won two out of three poster prizes Thursday night when graduate student Marleen Kamperman was also awarded a prize for her poster entitled “Porous High Temperature Ceramics Structured on Multiple Length Scales.” Kamperman is a graduate student with Ulrich Wiesner in the department of Materials Science and Engineering and shared the prize with coauthors Robert Weissgraeber and Andrew Burns. She reported on how they fabricated porous high temperature ceramics with hierarchically ordered pore structures and discussed how these structures offer great promise in structural applications because of their excellent thermal stability and mechanical properties in combination with a high surface area and low flow resistance. They developed an easy to control bottoms-up approach towards hierarchically ordered high temperature ceramics structured on multiple length scales, from a few nanometers to tens of microns. They structured the ceramics by combining micromolding, latex sphere templating and cooperative assembly of a polysilazane with an amphiphilic block copolymer. Relatively large micron-sized latex spheres were found to self-assemble into an ordered lattice in the channels of a micromold. Smaller latex nanospheres packed closely in the interstices between the micron-sized spheres. During both the poster session and later at an oral presentation Kamperman discussed implications of these findings for various applications of these model ceramic systems.


Figure 4: Poster prizewinner Marleen Kamperman (center) with judges.

The day before gaining additional notoriety for her poster, Kamperman was one of six graduate students chosen to be honored with a “Graduate Student Gold Award.” On Wednesday evening MRS Society First President Alan Hurd presented awards to graduate students who authored or co-authored symposium papers that exemplified significant and timely research. She earned this honor for her paper on porous high temperature ceramics presented during the special session on Tuesday afternoon.

Kamperman came to Cornell via Utrecht, the Netherlands, where she studied chemistry at the University of Groningen and majored in Polymer Chemistry. In Groningen she performed research on reactive hot-melt adhesives for car windows. She joined the Wiesner group in 2003 and is currently developing ordered mesoporous high temperature ceramics using block copolymers as structure-directing agents. Although conventional laboratory-based analytical methods were sufficient for the work cited for the MRS award, as one of the CHESS G-line graduate students, Marleen routinely uses CHESS for much of her work. Recent work done at CHESS includes studying organic photovoltaics and making nanostructured TiO2 thin films from soft-etch block copolymer templates. She has utilized Grazing Incidence Small Angle X-ray Scattering (GISAXS) to characterize film structure in electrochemically-grown nanostructured TiO2 films.

In retrospect Marleen says of the MRS meeting: “Winning the awards was one thing, but the nice mail from people who found out [about our work] and congratulations are the most rewarding.

CHESS is proud of the excellent work the graduate students were able to accomplish and congratulates them on their outstanding posters and prizes.

[1] Figures 2 and 3 from: John David Ferguson, Gokhan Arikan, Arthur R. Woll, Darren S. Dale, Aram Amassian and Joel Brock; Time Resolved In-Situ Diffuse X-ray Scattering Measurements of the Surface Morphology of Homoepitaxial SrTi03 Films During Pulsed Laser Deposition, in Ferroelectrics, Multiferroics, and Magnetoelectrics, edited by J.F. Scott, V. Gopalan, M. Okuyama, and M. Bibes (Mater. Res. Soc. Symp. Proc. Volume 1034E, Warrendale, PA, 2007).