OSTC

Optical Science and
Technology Center

Research Highlights

UIMF Users’ Research Projects

X-Ray gratings for high-resolution spectroscopy

PI: Randall McEntaffer

Ph.D. student: Casey DeRoo

Our project at the UIMF is focused on making the next-generation of X-ray reflection gratings for use in future X-ray astronomical observatories and missions. In order to disperse an X-ray spectrum effectively, a reflection grating must have groove spacings on the order of 100 nm. Furthermore, the groove pattern must be sculpted to match the X-ray telescope used for the spectrometer. Finally, the pattern must be produced over large areas so as make an instrument with enough collecting area to observe faint astronomical sources. These unique challenges can be addressed by the commonly used set of microfabrication processes. Nanoimprinting allows for a pre-produced “master” grating to be replicated over large formats in a time and cost-effective manner. Further chemical processing using plasma etching and several wet etches allow for the grating groove profile to be sculpted on the nanometer scale. Finally, an electron beam evaporation step allows the fabricated grating to be coated with a high X-ray reflectivity material. Using these gratings in an astronomical X-ray spectrometer operating under reasonable future mission conditions would result in 3-10x fold increase in spectral resolution and a significant increase in diffraction efficiency compared with the current operating instruments. In addition, these Iowa-made gratings will be used in the future Off-Plane Grating Rocket Experiment (OGRE), a sounding rocket being fabricated at the University of Iowa for flight in 2017.

UIMF Tools: NX-1006 Nanonex Nanoimprinter

                      Oxford RIE NGP80

                      Angstrom Electron Beam Evaporator

 

Figure 1: An illustration of the process used to produce X-ray reflection gratings using a set of tools at the UIMF

Publication: R. McEntaffer, Casey DeRoo et al., “First results from a next-generation off-plane X-ray diffraction grating”, Experimental Astronomy, vol. 36, pp 389-405 (2013)

http://link.springer.com/article/10.1007%2Fs10686-013-9338-1

Photovoltaic: Plastic Solar Cells

PI: Markus Wohlgenannt

Students: Yifei Wang, Kevser Tiras

Climate change and high oil prices are some of the reasons to develop novel renewable energy sources. Photovoltaic devices, which convert sun light into electricity, are particularly promising. The relatively large cost of current panels based on ultra-high-purity silicon crystals is an impediment to the wide spread utilization of solar energy. The Wohlgenannt group will develop a novel kind of plastic solar cells using nanoimprint lithography (see figure below). These organic photovoltaic (OPV) cells have several advantages over competing technologies: (a) low-cost synthesis, and (b) easy manufacture of devices using solution-casting techniques such as spray painting.

UIMF tools: Nanonex Nanoimprint,

                     Oxford RIE NGP80 for Plasma Etch, Wet etching

                     OAI Optical Lithography

                     Wyko 3D Optical Profiler

Figure: Schematic of the fabrication process for the OPVs: (a) Stamp or mold that will be replicated into the donor conjugated polymer, (b) Topography of donor polymer after nanoimprinting, (c) device after deposition of the acceptor layer, (d) final OPV prototype

 

Effect of hydrogen sulfide gas on silicone films

PI: Scott K Shaw

Student: Radhika S Anaredy

Silicone polymers have a wide range of applications in electronics where they are used as a protective and insulating layer for various components or circuits. Hydrogen sulfide, present in some application environments, has been found to attack silicones thereby causing the device or circuit to fail. This project studies the effect of H2S exposure on model silicone films. We use the Dektak Profiler to support quantitative studies of film degradation by measuring the profile of nanometer-thick silicone films.

UIMF Tools: Dekdak Profilometer, Wyko 3D Optical Profiler

 

Figure: Pressure sensor chips with protective silicon films (Honeywell)

 

Characterization of femoral head damage in medical implants

PI: Dr. Thomas Brown

Co-PI: Dr. Anneliese Heiner

Student: Karen Kruger

In total hip replacements, femoral head damage can lead to accelerated wear of the polyethylene liner, reducing the implant’s lifetime. This damage is difficult to quantitatively access due to the micron-level damage features appearing over relatively large areas. The Wyko 3D optical profilometry allows damage features over large areas of the femoral heads to be analyzed.

Figure: (a) Global level photograph of retrieval femoral head, (b) local optical profiler scan of indicated damage region revealing micron-level damage features

Publication: K. M. Kruger, N. M. Tikekar, A. D. Heiner, J. J. Lannutti, J. J. Callaghan, T. D. Brown, “Modeling Polyethylene Wear Acceleration Due to Femoral Head Dislocation Damage”, Journal of Arthroplasty. Submitted (2013)

 

Semiconductor Nanowires

PI: John Prineas

Student: Jing Bian

Semiconductor nanowires are at the forefront of new methods of epitaxial growth, and are promising materials and applications ranging from transistors to photovoltaics.  The Prineas group is developing new methods for growing nanowires, and is studying defects that limit their performance. 

UIMF tools: Reactive Ion Etcher, Sputterer, EBeam Lithography

Figure: Scanning Electron Micrograph of GaAs nanowires