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Outcome: Researchers at the University of Pennsylvania have demonstrated a new, unique, lab-based environmental X-ray photoelectron spectroscopy (e-XPS) system that allows surfaces of materials to be characterized while exposed to elevated gas pressures (conventional XPS is limited to very low pressures). Funding from this grant enabled the system to be tested for the first time.Impact: This vastly expands the conditions under which one can study the composition and bonding of atoms on surfaces. We are using this tool to study the surfaces of diamond-like carbon (DLC) thin films. DLC films are in demand as coatings for many applications, such as advanced energy systems, manufacturing, aerospace, automotive, nanomechanical devices, and next-generation hard disks.

Our e-XPS allows us to study DLCs at their critical environmental conditions, e.g., in oxidizing conditions at elevated temperatures, to understand the ways in which the surface degrades.

Environmental X-ray Photoelectron Spectroscopy for Materials Characterization

Robert W. Carpick, University of Pennsylvania, DMR 1107642

Courtesy of HGST

e-XPS system at U. Penn

Publication: F. Mangolini, et al. , Review of Scientific Instruments, 2012

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Outcome: Environmental X-ray photoelectron spectroscopy (e-XPS) is one of the most important developments in surface materials analysis in the last decade. The e-XPS system in our lab allows the investigation of the surface chemistry of any material while exposed to gas pressures as high as 0.4 Torr while controlling the temperature from 100 – 800 K. This is one of only the three lab-based instruments in the world with such capabilities, and the only one coupled to scanning probe microscope for additional surface characterization. Funding from this grant enabled the system to be tested for the first time.

Environmental X-ray Photoelectron SpectrometerRobert W. Carpick, University of Pennsylvania, DMR 1107642

Publication: F. Mangolini, J. Ahlund, G. E. Wabiszewski, V. P. Adiga, P. Egberts, F. Streller, K. Backlund, P. G. Karlsson, B. Wannberg, and R. W. Carpick, Review of Scientific Instruments, 2012

Explanation: The data above show the photoemission signal from a silver surface. From high vacuum to 0.001 Torr of N2 gas exposure, the signal is unaffected. At higher pressures, while the signal decreases, it is still clearly resolved up to 0.4 Torr. This shows that surfaces can be studied while exposed to gases at pressures more than 7 orders of magnitude higher than conventional XPS.

We are now applying the e-XPS to study the surface chemistry of diamond-like carbon (DLC) films to understand their thermal stability, oxidation, and wetting behavior.

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Robert W. Carpick, University of Pennsylvania, DMR 1107642

Prof. Carpick’s and his Nanomechanics Laboratory, including the student and postdoc who participate in this NSF project, took part in “Philly Materials Day 2013” (February 2, 2013), a day-long event aimed to raise the scientific awareness of children, teenagers, and adults about materials science.

Members of Rob Carpick’s group explaining concepts to children and teenagers during the Philly Materials Day 2013

http://www.seas.upenn.edu/event-photo-archives/PhilMatDay_2.2.13/

The booth they prepared by was entitled “Nanotribology: the science and application of friction at the nanoscale”. It comprised hands-on activities and informal science education experiences with a special focus on atomic force microscopy and carbon-based materials (diamond, graphite, and diamond-like carbon). Hundreds of members of the public attended the event.