Center For Advanced Microstructures And Devices Research Articles

Dose‐response curve of EBT, EBT2, and EBT3 radiochromic films to synchrotron‐produced monochromatic x‐ray beams

This work investigates the dose-response curves of GAFCHROMIC(®) EBT, EBT2, and EBT3 radiochromic films using synchrotron-produced monochromatic x-ray beams. EBT2 film is being utilized for dose verification in photoactivated Auger electron therapy at the Louisiana State University Center for Advanced Microstructures and Devices (CAMD) synchrotron facility. Monochromatic beams of 25, 30, and 35 keV were generated on the tomography beamline at CAMD. Ion chamber depth-dose measurements were used to determine the dose delivered to films irradiated at depths from 0.7 to 8.5 cm in a 10 × 10 × 10-cm(3) polymethylmethacrylate phantom. AAPM TG-61 protocol was applied to convert measured ionization into dose. Films were digitized using an Epson 1680 Professional flatbed scanner and analyzed using the net optical density (NOD) derived from the red channel. A dose-response curve was obtained at 35 keV for EBT film, and at 25, 30, and 35 keV for EBT2 and EBT3 films. Calibrations of films for 4 MV x-rays were obtained for comparison using a radiotherapy accelerator at Mary Bird Perkins Cancer Center. The sensitivity (NOD per unit dose) of EBT film at 35 keV relative to that for 4-MV x-rays was 0.73 and 0.76 for doses 50 and 100 cGy, respectively. The sensitivity of EBT2 film at 25, 30, and 35 keV relative to that for 4-MV x-rays varied from 1.09-1.07, 1.23-1.17, and 1.27-1.19 for doses 50-200 cGy, respectively. For EBT3 film the relative sensitivity was within 3% of unity for all three monochromatic x-ray beams. EBT and EBT2 film sensitivity showed strong energy dependence over an energy range of 25 keV-4 MV, although this dependence becomes weaker for larger doses. EBT3 film shows weak energy dependence, indicating that it would be a better dosimeter for kV x-ray beams where beam hardening effects can result in large changes in the effective energy.

Verification of TG‐61 dose for synchrotron‐produced monochromatic x‐ray beams using fluence‐normalized MCNP5 calculations

Ion chamber dosimetry is being used to calibrate dose for cell irradiations designed to investigate photoactivated Auger electron therapy at the Louisiana State University Center for Advanced Microstructures and Devices (CAMD) synchrotron facility. This study performed a dosimetry intercomparison for synchrotron-produced monochromatic x-ray beams at 25 and 35 keV. Ion chamber depth-dose measurements in a polymethylmethacrylate (PMMA) phantom were compared with the product of MCNP5 Monte Carlo calculations of dose per fluence and measured incident fluence. Monochromatic beams of 25 and 35 keV were generated on the tomography beamline at CAMD. A cylindrical, air-equivalent ion chamber was used to measure the ionization created in a 10 × 10 × 10-cm(3) PMMA phantom for depths from 0.6 to 7.7 cm. The American Association of Physicists in Medicine TG-61 protocol was applied to convert measured ionization into dose. Photon fluence was determined using a NaI detector to make scattering measurements of the beam from a thin polyethylene target at angles 30°-60°. Differential Compton and Rayleigh scattering cross sections obtained from xraylib, an ANSI C library for x-ray-matter interactions, were applied to derive the incident fluence. MCNP5 simulations of the irradiation geometry provided the dose deposition per photon fluence as a function of depth in the phantom. At 25 keV the fluence-normalized MCNP5 dose overestimated the ion-chamber measured dose by an average of 7.2 ± 3.0%-2.1 ± 3.0% for PMMA depths from 0.6 to 7.7 cm, respectively. At 35 keV the fluence-normalized MCNP5 dose underestimated the ion-chamber measured dose by an average of 1.0 ± 3.4%-2.5 ± 3.4%, respectively. These results showed that TG-61 ion chamber dosimetry, used to calibrate dose output for cell irradiations, agreed with fluence-normalized MCNP5 calculations to within approximately 7% and 3% at 25 and 35 keV, respectively.

SU-E-T-155: Dose Response Curve of EBT2 and EBT3 Radiochromic Films to a Synchrotron-Produced Monochromatic X-Ray Beam.

This work investigates the dose-response curves of Gafchromic EBT2 and EBT3 radiochromic films using synchrotron-produced monochromatic x-ray beams. These dosimeters are being utilized for dose verification in photoactivated Auger electron therapy at the LSU Center for Advanced Microstructures and Devices (CAMD) synchrotron facility. Monochromatic beams of 25, 30 and 35 keV were generated on the tomography beamline at CAMD. Ion chamber depth-dose measurements were used to calculate the dose delivered to films irradiated simultaneously at depths from 0.7 - 8.5 cm in a 10×10×10-cms polymethylmethacrylate phantom. AAPM TG-61 protocol was applied to convert measured ionization into dose. Calibrations of films at 4 MV were obtained for comparison using a Clinac 21 EX radiotherapy accelerator at Mary Bird Perkins Cancer Center. Films were digitized using an Epson 1680 Professional flatbed scanner and analyzed using the optical density (OD) derived from the red channel. For EBT2 film the average sensitivity (OD/dose) at 50, 100, and 200 cGy relative to that for 4-MV x- rays was 1.07, 1.20, and 1.23 for 25, 30, and 35 keV, respectively. For EBT3 film the average sensitivity was within 3 % of unity for all three monochromatic beams. EBT2 film sensitivity shows strong energy dependence over an energy range of 25 keV - 4 MV. EBT3 film shows weak energy dependence, indicating that it would be the better dosimeter for Auger electron therapy. This research was supported by contract W81XWH-10-1-0005 awarded by The U.S. Army Research Acquisition Activity, 820 Chandler Street, Fort Detrick, MD 21702-5014. This report does not necessarily reflect the position or policy of the Government, and no official endorsement should be inferred.

SU-E-T-101: Dosimetry Intercomparison for a Synchrotron-Produced Monochromatic X-Ray Beam.

This study performed a dosimetry intercomparison for synchrotron-produced monochromatic x-ray beams. Ion chamber depth-dose measurements in a polymethylmethacrylate (PMMA) phantom were compared with the product of MCNP5 Monte Carlo calculations of dose per fluence and measured incident fluence at 25 and 35 keV. The ion chamber measurements are being used to calibrate dose output for cell irradiations designed to investigate photoactivated Auger electron therapy at the LSU Center for Advanced Microstructures and Devices (CAMD) synchrotron facility. Monochromatic beams of 25 and 35 keV were generated on the tomography beamline at CAMD. A cylindrical, air-equivalent ion chamber was used to measure the ionization created in a 10×10×10-cm3 PMMA phantom at depths of 0.6 - 7.7 cm. AAPM TG-61 protocol was applied to convert measured ionization into dose. MCNP5 simulations of the irradiation geometry were performed to determine the dose deposition per photon fluence in the phantom. Photon fluence was determined using a NaI detector to make scattering measurements of the beam from a polyethylene target at angles 15 - 60 degrees. Differential Compton and Rayleigh scattering cross sections were used to derive the incident fluence. At 35 keV dose measurements for equal exposures determined using the MCNP5-fluence results underestimated those of the ion chamber by 1.8 - 4.8% for PMMA depths from 0.6 - 7.7 cm, respectively. At 25 keV there was an overestimate of 6.6 - 1.9%. These results show that TG-61 ion chamber dosimetry, used to calibrate the dose output for the cell irradiations, is accurate within approximately 7% for beam energies 25-35 keV. This research was supported by contract W81XWH-10-1-0005 awarded by The U.S. Army Research Acquisition Activity, 820 Chandler Street, Fort Detrick, MD 21702-5014. This report does not necessarily reflect the position or policy of the Government, and no official endorsement should be inferred.

Status of the Center for Advanced Microstructures and Devices (CAMD)—2010

The J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices (CAMD) is a 1.3 GeV synchrotron-radiation facility owned and operated by the State of Louisiana. Fifteen beamlines provide radiation for CAMD users and cover the spectral range from the far IR to X-rays of ca. 40 keV. Eleven of them receive radiation from bending magnets and four from a 7 T wavelength shifter. A wide range of basic and applied scientific experiments as well as microfabrication are performed at these beamlines. The nanomaterial synthesis and characterization laboratory at CAMD continues to add new instruments such as SQUID magnetometer (Quantum Deign MPMS XL5) and high precision microfluidic-based nanomaterials synthesis equipment complementing already available facilities. We have recently received NSF MRI funding for a multipole 7.5 T wiggler that will become operational in 2012. Generous equipment donations from the University of California at Riverside (Professor Jory Yarmoff) and the University of Bonn (ELSA facility) will provide users with two additional VUV beamlines in the near future.

X-ray Absorption Spectroscopy Investigation of Different Crystallographic Structures of Cobalt Nanoparticles

ABSTRACTThe ultimate goal of nanotechnology is to design successful syntheses to produce nanomaterials with required properties. The properties of nanoparticles mainly depend on their size, shape and crystal structure, hence control over these factors is a major issue in this field. In this study, Co nanoparticles with four different crystallographic structures (hcp, fcc, bcc and epsilon) have been wet-chemically synthesized by varying precursors and surfactants in the reaction. Co K-edge absorption spectra were collected in transmission mode at the XMP beamline at the Center for Advanced Microstructures and Devices (CAMD). The X-ray Absorption Near Edge Structure (XANES) and Fourier Transformed Extended X-ray Absorption Fine Structure (FT EXAFS) spectra were analyzed using the “fingerprint method”, i.e. by comparing them with either standard compounds or with the simulated spectra that were calculated using the FEFF8 code. EXAFS spectra were also analyzed by fitting them with relevant crystallographic models in r-space including higher coordination shells using the IFEFFIT analysis program. All four crystal structure types were conclusively determined by using this approach.

Synchrotron powder X-ray diffractometer beamline at J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices

The J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices (CAMD) is a synchrotron ring operating at 1.3 GeV, with the ring current typically ranging from 230 to 100 mA. An X-ray powder diffraction beamline was recently commissioned at CAMD at the bending magnet port 7A. The powder diffraction beamline consists of a Brazilian-designed double crystal monochromator, a Huber four-circle diffractometer, and a Canberra germanium solid-state detector. The monochromator is equipped with Si 111 and Ge 220 crystals. The Canberra high purity germanium solid-state detector has a resolution of 130 eV at Mn K α. For typical use, the diffractometer circle is set to 17 cm, and the source and receiving slits have been set to 300 and 200 μm, respectively. A sample spinner is used for improved particle size averaging. Wavelength can be shifted in a matter of minutes. Preliminary runs of NIST standards, for example, lanthanum hexaboride (LaB 6) (SRM 660a), show good performance over a wide two-theta range. Rietveld refinement of novaculite (SiO 2) shows lower residual error for the same mineral compared to that obtained from a run with a conventional X-ray source. At the beamline, the user can use MDI's Jade version 7.5 software. The user also has access to International Center for Diffraction Data's Powder Diffraction File-2 database consisting of more than 163,000 inorganic entries and International Crystal Structure Data's crystal structure database with more than 93,000 entries.

The infrared microspectroscopy beamline at CAMD and its application in plant–pathogen interactions

At the beginning of 2006, the first infrared microspectroscopy beamline at the Louisiana State University, Center for Advanced Microstructures and Devices (CAMD) storage ring came into operation. The infrared microscope has recently been upgraded with a new liquid nitrogen-cooled mercury–cadmium–telluride detector, MCT-A, and a new dipole chamber to improve the signal-to-noise ratio and extend the beamline capability to far-IR region. In this contribution, we report first results, by using the microspectroscopy beamline, in the investigation of plant–pathogen interactions: apple– Venturia inaequalis causing scab. The infrared spectra of the healthy plant leaves were compared to those obtained from the infected ones. These spatially resolved data are used to understand the dynamics of physiological modifications, which occur during pathogenesis.

Status of the Center for Advanced Microstructures and Devices (CAMD)—2007

The J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices (CAMD) is a 1.3 GeV synchrotron-radiation facility owned and operated by the State of Louisiana. Sixteen beamlines provide radiation for CAMD users and cover the spectral range from the far IR to X-rays of ca. 40 keV. Twelve of them receive radiation from bending magnets with the remaining four from a 7-T wavelength shifter. A wide range of scientific experiments related to basic and applied sciences and engineering as well as microfabrication are performed at these beamlines. A nanomaterials synthesis laboratory is present at CAMD which very effectively utilizes the available facilities.

Facility Update: The Center for Advanced Microstructures and Devices: A Status Report

The J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices (CAMD) is a second-generation synchrotron-radiation facility owned and operated by the state of Louisiana through Louis...

Performance of the infrared microspectroscopy beamline at CAMD

The first infrared (IR) beamline at the Center for Advanced Microstructures and Devices (CAMD) at Louisiana State University has been successfully constructed and commissioned. The beamline features a simple optical design with a minimal number of optical components. A pair of mirrors, planar and toroidal, is utilized for extracting synchrotron radiation (50 and 15 mrad, in horizontal and vertical directions, respectively) from the bending magnet port to a diamond window located outside of the shielding wall. Synchrotron radiation is then collimated by an off-axis parabolic mirror and fed into a Thermo Nicolet Continuum microscope through a Thermo Nicolet Nexus 670 FT-IR spectrometer. The microscope’s performances with synchrotron-radiation and conventional-thermal sources were compared in the mid-IR spectral range (11700–400cm−1). Effective beam spot size at sample position of the microscope was measured to be 35×12μm2 (FWHM). It was also determined that synchrotron radiation has substantial advantages over the conventional thermal source: ∼30 times better intensity and ∼100 times better S/N at aperture size of the microscope smaller than 15×15μm2. This performance allows infrared spectroscopy analysis in a small area with a diffraction-limited spatial resolution.

Decomposition Behavior of Ti-doped NaAlH4 Studied using X-ray Absorption Spectroscopy at the Titanium K-edge

ABSTRACTThe local bonding environment of Ti3+-dopant atoms in NaAlH4 after decomposition to release H2 has been studied using x-ray absorption fine structure (XAFS). The titanium K-edge spectra from doped hydride samples and the standard materials TiCl3 and TiO2 were collected in ambient atmosphere at the synchrotron source at the Center for Advanced Microstructures and Devices (CAMD). Titanium valence states present in the spectra collected from Ti-doped NaAlH4 after decomposition in air are Ti3+ and Ti4+. The Ti3+ is attributed to unreacted TiCl3. The Ti4+ present in the sample is attributed to TiO2 occurring after air oxidation. Coupled with studies of the kinetics of hydrogen desorption reactions, examination of dopant ion valence states after entry into the lattice may lead to better understanding of the interrelationship between lattice doping and desorption kinetics.

Swelling behaviour of poly(methylmethacrylate) thick resist layers in deep X-ray lithography.

The understanding and optimization of lithographic conditions are particularly important for irradiation of thick resist layers in deep X-ray lithography. The causes and consequences of radiation-induced formation and accumulation of gaseous species inside the poly(methylmethacrylate) (PMMA) resist matrix are discussed. Thick PMMA layers were exposed to high-energy photons from a bending-magnet beamline at the Center for Advanced Microstructures and Devices (CAMD). The focus of this work was to explore the swelling behaviour of PMMA resist of thickness between 50 micro m and 1.6 mm. The influence of various exposure parameters, such as photon energy, filtering conditions, electron current in the storage ring, scan length and scan speed, exposure atmosphere etc., on the swelling of the resist are discussed. The effect of pre-exposure annealing of the PMMA sheets and of temperature variation during irradiation was also investigated. Exposure with optimized X-ray spectral distribution, incident power density, absorbed dose and rate of energy deposition inside the resist allowed swelling of the resist to be minimized during exposure.

Instrumentation for synchrotron based micromachining at the Center for Advanced Microstructures and Devices (abstract)

The J. Bennett Johnston Sr., Center for Advanced Microstructures and Devices (CAMD) is a synchrotron radiation facility owned by Louisiana State University and operated with financial support from the State of Louisiana (for information how to submit a project proposal go to: http://www.camd.lsu.edu). The centerpiece of CAMD is a 1.3–1.5 GeV electron storage ring. CAMD supports a strong program in x-ray lithography micromachining (XRLM) or LIGA. A total of four beamlines equipped with different scanners is available for exposures. A 2.500 sq. ft class 100 clean room provides basic processing capability for MEMS including optical lithography, thin film deposition, electroplating, and metrology. Three micromachining beamlines are connected to bending magnets. All beamlines are “white light” beamlines, terminated with a beryllium window. The typical source point to scanner distance is 10 m and the horizontal acceptance ranges from 6.5 to 10 mrad. A number of low Z filters can be inserted into the beam adapting the exposure spectrum to the resist thickness. Two beamlines are equipped with commercial scanners from Jenoptik GmbH (for details see Jenoptik’s webpage at www.jo-mikrotechnik.com/) and one beamline with a “vacuum” scanner designed in house. The latest model of Jenoptik’s DEX02 scanner has been installed at CAMD’s XRLM1 beamline in December 2000 and allows advanced exposures using overlay as well as tilt and rotate functions. In addition to these beamlines CAMD has installed a “white light” beamline at its 7 T wiggler source. Preliminary exposure tests in ultrathick samples (1 mm and thicker) have been conducted using an “air scanner.” Currently this beamline is dismantled and will be reinstalled together with a PX beamline. In the article further details of the beamlines and scanners as well as some examples of applications of LIGA microstructures fabricated at CAMD will be discussed.

Status of the Center for Advanced Microstructures and Devices (CAMD)-2001

The current status of the Louisiana State University Center for Advanced Microstructures and Devices electron storage ring, beamlines, and the scientific program are described.

X-ray Spectro-Microscopy and Micro-Spectroscopy in the 2100 eV to 12000 eV Region (Invited)

ABSTRACTAn x-ray microprobe beamline was recently developed and commissioned at the Center for Advanced Microstructures and Devices (CAMD), Louisiana State University. It achieves a moderate horizontal and vertical focal spot size of 18.8 µm × 7.0 µm (σ), respectively. The beamline and end-station are designed and optimized to perform (i) spatially-resolved x-ray fluorescence spectroscopy (spectro-microscopy) using the broad intense spectrum of the white synchrotron radiation, and (ii) spatially-resolved x-ray absorption spectroscopy (micro-spectroscopy) in the energy region of 2100eV to 12000 eV. These dual capabilities enable K-edge measurements and mapping, in non-vacuum conditions, of low-Z elements down to Cl, S, and P that are of both environmental interest and technological importance. In this paper, an application of this novel synchrotron tool to elucidate the elemental distribution (microstructure) and chemical state (speciation) of Mn, Cl, S, and P-containing particulates emitted from automobile engines burning methylcyclopentadienyl manganese tricarbonyl- (MMT-) added fuel will be discussed in detail. Future opportunities of this microbeam technique in materials science and materials characterization will also be outlined.

Proposal of superconducting 7 Tesla wiggler for LSU-CAMD

The superconducting 7 Tesla wiggler is destined for the Center for Advanced Microstructures and Devices (CAMD), Louisiana State University (LSU), USA. The wiggler contract was awarded to the Budker Institute of Nuclear Physics (Budker INP) in the open tender in May 1996 and the wiggler will be installed in the CAMD site in December of 1997. The wiggler is a three pole superconducting magnet with maximum field of 7 T in central pole and the side poles field of 1.65 T. The wiggler is inserted into a special liquid helium cryostat. The main distinction of this wiggler from others is that the horizontal orbit deviation at the maximum field of the wiggler central pole is equal to zero due to the special orbit compensation at any level of wiggler field. Such compensation is realized by two conventional correcting magnet located at the both ends of the wiggler straight section. Characteristics of the magnetic system, helium cryostat and radiation properties of the wiggler are described in this article.

X-Ray Microfabrication at the Center for Advanced Microstructures and Devices (CAMD)

The Center for Advanced Microstructures and Devices (CAMD) has established infrastructure and experience for deep X-ray lithography and functions as a print-shop for high aspect ratio microstructures in the US. A major up-grade of the facility will be completed by the end of 1997. It includes the installation of a wavelength shifter as a hard X-ray source for ultra-deep X-ray lithography and for cost effective, batch fabrication of high aspect ratio micro-components. This paper describes the X-ray micromachining facility and programs at CAMD. The scientific and engineering activities exemplified by results of current studies are reported.

X-ray microfabrication activities at the Center for Advanced Microstructures and Devices (CAMD) (invited)

The x-ray lithography and micromachining facility at CAMD is described. It consists of four dedicated beamlines and exposure stations using the synchrotron radiation delivered by the CAMD storage ring and 230 m2 of fully equipped clean room. The scientific and engineering activities exemplified by results of current studies are reported.

III. X-RAY MICRO-LITHOGRAPHY AND THICK RESIST STUDIES AT CAMD

CAMD (Center for Advanced Microstructures and Devices) utilizes the radiation from a 1.2-1.5GeV electron storage ring with a critical-wavelength range 9.5-4.8Å. The storage ring at CAMD provides suitable radiation for X-ray micro-lithography and microfabrication work. High resolution, thin and thick resist processing techniques, including resist application, exposure and development were explored. New techniques such as transfer mask and equivalent filtration are introduced and demonstrated. Issues of latent image formation in exposed resist are addressed. Examples of structures fabricated using described techniques are presented.