Center For Microanalysis Of Materials Research Articles

Radiochromic film dosimetry for protons up to 10 MeV with EBT2, EBT3 and unlaminated EBT3 films

Passive dosimetry with radiochromic films is widely used in proton radiotherapy, both in clinical and scientific environments, thanks to its simplicity, high spatial resolution and dose-rate independence. However, film under-response for low-energy protons, the so-called linear-energy transfer (LET) quenching, must be accounted and corrected for. We perform a meta-analysis on existing film under-response data with EBT, EBT2 and EBT3 GAFchromic™ films and provide a common framework to integrate it, based on the calculation of dose-averaged LET in the active layer of the films. We also report on direct measurements with the 10 MeV proton beam at the Center for Microanalysis of Materials (CMAM) for EBT2, EBT3 and unlaminated EBT3 films, focusing on the 20–80 keV μm−1 LET range, where previous data was scarce. Measured film relative efficiency (RE) values are in agreement with previously reported data from the literature. A model on film RE constructed with combined literature and own experimental values in the 5–80 keV μm−1 LET range is presented, supporting the hypothesis of a linear decrease of RE with LET, with no remarkable differences between the three types of films analyzed.

Dual Templating Synthesis of Mesoporous Titanium Nitride Microspheres

We gratefully acknowledge Prof. W. M. Kriven and J. Bell for their generous assistance in TGA/DSC data acquisition. This material is based on work supported by the U.S. Department of Energy, Division of Materials Sciences under Award No. DE-FG02-07ER46418, through the Frederick Seitz Materials Research Laboratory at the University of Illinois at UrbanaChampaign. This research was carried out in part in the Center for Microanalysis of Materials, UIUC, which is partially supported by the U.S. Department of Energy under grant DE-FG02-07ER46418. Supporting Information is available online from Wiley InterScience or from the author.

Optical exposure characterization and comparisons for discharge produced plasma Sn extreme ultraviolet system

A critical issue for EUV lithography EUVL is the minimization of collector degradation from intense plasma erosion, debris deposition, and hydrocarbon/oxide contamination. Collector optics reflectivity and lifetime heavily depend on surface chemistry and interactions between fuels and various mirror materials, such as silicon, in addition to high- energy ion and neutral particle erosion effects. As a continuation of our prior investigations of discharge-produced plasma DPP and laser- produced plasma LPP Xe plasma interactions with collector optics sur- faces, the University of Illinois at Urbana-Champaign UIUC has ana- lyzed collector samples before and after exposure in a Sn-upgraded Xtreme Technologies EUV source. Sn DPP postexposure characteriza- tion includes multiple samples, Si/Mo multilayer film with normal inci- dence, 200-nm-thick Ru film with grazing incidence, as well as a Gibb- sian segregated GS Mo-Au alloy developed on silicon using a dc dual- magnetron cosputtering system at UIUC for enhanced surface roughness properties, erosion resistance, and self-healing characteris- tics to maintain reflectivity over a longer period of mirror lifetime. Surface analysis draws heavily on the expertise of the Center for Microanalysis of Materials at UIUC, and investigates mirror degradation mechanisms by measuring changes in surface roughness and film thickness as well as analysis of deposition of energetic Sn ions, Sn diffusion, and mixing of multilayer. Results from atomic force microscopy AFM and auger elec- tron spectroscopy AES measurements show exposure effects on sur- face roughness and contamination. The best estimates of thickness and the resultant erosion measurements are obtained from scanning electron microscopy SEM. Deposition, diffusion, and mixing effects are ana-

The visigothic treasure of Torredonjimeno (Jaén, Spain): A study with IBA techniques

The visigothic treasure of Torredonjimeno (Jaén, Spain) was found by chance in the year 1926 buried in an olive grove. The finding consisted of some hundreds fragments of gold objects and gems coming from several votive crowns and crosses, some of them belonging to an unidentified visigothic king. The treasure may belong chronologically to the same period as the Guarrazar treasure or, possibly, to a somewhat later time, but the pieces are fragmented and of less technological workmanship than the latter. This is the reason why the Torredonjimeno treasure has not attracted as much attention from archeologists and art historians as that from Guarrazar. On the occasion of an exhibition showing together all the objects of the treasure, it is normally kept in three different museums in Barcelona, Cordoba and Madrid, a number of pieces were analyzed, using PIXE, PIGE and RBS, at the external microbeam facility installed at the Center for Micro-Analysis of Materials.

First measurements with the Madrid 5 MV tandem accelerator

The 5 MV Cockcroft-Walton tandem accelerator from HVEE recently installed at the Center for Micro-Analysis of Materials on the Campus of the University Autonoma of Madrid is in operation since September 2002. The machine is mainly dedicated to ion beam analysis. In this work, we report on the first measurements performed. They include calibration of the terminal voltage using p-γ reactions and elastic α–α resonances on C, O, N, Al and Si. RBS and ERD measurements using He and Si beams are now routinely performed. Samples of different nature including, among others, SiN, SiON, and porous Al 2O 3, were also characterized.

TEM Studies of Shear Bands in a Bulk Metallic Glass Based Composite

In 1980’s the discovery of multicomponent systems with exceptional glass forming ability enabled the synthesis of metallic glasses at relatively low cooling rates, 10−1 — 102 K/s and at a larger thicknesses. Bulk metallic glasses normally have very high yield stress, σy = 0.02 · Y (Y is Young’s modulus), high elastic limit of about 2%, but fail with very little global plasticity, typically along a localized shear band at a 45 degree angle with respect to the applied stress.The material studied in the present work is a two-phase Zr56.3Ti13.8Cu6.9Ni5.6Nb5.0Be12.5 alloy,prepared by in-situ processing. The alloy consists of amorphous and crystalline phases. In-situ TEM straining (tensile) experiments were performed at room temperature in JEOL 4000EX operating at 300kV. The experiments were carried out in the Center for Microanalysis of Materials in the University of Illinois at Urbana-Champaign. The goal of the study was to understand the deformation mechanisms of such composite material.

An environmental cell Transmission Electron Microscope

The ability to observe directly and at high spatial resolution the interactions between environments and materials affords the material scientist new and unique opportunities. This capability is realized in the Environmental Cell Transmission Electron Microscope Facility which has been installed as part of the Center for Microanalysis of Materials at the Materials Research Laboratory of the University of Illinois at Urbana-Champaign.The Facility is based on a JEOL 4000EX equipped with a specially designed pole piece. An aperture limited, differentially pumped, environmental cell has been installed in this pole piece. The system is shown schematically in Figures 1 and 2. Figure 1 is a plan view of a section through the objective lens pole-piece, with the microscope axis perpendicular to the plane of the paper, showing the cell enclosing the sample rod, the gas handling system and the location of the magnetically levitated Turbo-Molecular pumps. Figure 2 shows a cross-sectional view of the environmental cell and the gas handling system. As shown in Figure 2 the electron beam passes through a series of five apertures which allow the column vacuum to be maintained while the cell pressure is increased. The actual cell apertures are located at the apex of cones to minimize the gas path length, allow maximum tilt and still permit high- angle diffraction data to be obtained. Differential pumping of the cell is achieved by the four turbo- molecular pumps, the location of which can be seen in the Figures. With this arrangement the environmental cell is capable of supporting 400 torr of N2 gas which has no noticeable effect on the microscope operation. This allows the microscope to be operated with a LaB6 filament. The gas handling system was designed to handle a variety of environments including corrosive ones.

The Center for Microanalysis of Materials

The main purpose of the Center for Microanalysis of Materials is to serve the 250 or so people, from the materials-science research community on the Urbana campus of the University of Illinois, who use its facilities each year. (This represents about 80% of all researchers in this field on campus.) However, there is also a continuing interest in working with scientists from other institutions via collaborative research programs.The Center houses a large number of state-of-the-art instruments in almost all aspects of microanalysis: electron microscopy, x-ray diffraction, backscattering spectroscopies and several techniques in surface microanalysis. This equipment is operated and maintained by a team of full-time professional staff. Staff members also train users and collaborate in their research.The virtue of having microanalytical resources organized this way is that each research group can call on a very broad range of techniques. It can use Auger spectroscopy this week, EXAFS next and a combination of SIMS and TEM the week after that. This possibility is not available in universities where each instrument is acquired and run by one particular group.

The Center for Microanalysis of Materials

“Excuse me,” said a graduate student that I’ve not seen before, “I’d like to get some time on the Auger.”