Graph based multilevel algorithms for preconditioning finite element problems (open access)

Graph based multilevel algorithms for preconditioning finite element problems

This paper discusses: (1) A general block-factorization (matrix) form of multilevel preconditioners; algebraic methods; (2) Selecting parameters based on the matrix topology; graph based algorithms; (3) Examples of coarsening; (4) Numerical experiments.
Date: March 24, 2000
Creator: Vassilevski, P S
Object Type: Article
System: The UNT Digital Library
Actinic inspection of multilayer defects on EUV masks (open access)

Actinic inspection of multilayer defects on EUV masks

The production of defect-free mask blanks, and the development of techniques for inspecting and qualifying EUV mask blanks, remains a key challenge for EUV lithography. In order to ensure a reliable supply of defect-free mask blanks, it is necessary to develop techniques to reliably and accurately detect defects on un-patterned mask blanks. These inspection tools must be able to accurately detect all critical defects whilst simultaneously having the minimum possible false-positive detection rate. There continues to be improvement in high-speed non-actinic mask blank inspection tools, and it is anticipated that these tools can and will be used by industry to qualify EUV mask blanks. However, the outstanding question remains one of validating that non-actinic inspection techniques are capable of detecting all printable EUV defects. To qualify the performance of non-actinic inspection tools, a unique dual-mode EUV mask inspection system has been installed at the Advanced Light Source (ALS) synchrotron at Lawrence Berkeley National Laboratory. In high-speed inspection mode, whole mask blanks are scanned for defects using 13.5-nm wavelength light to identify and map all locations on the mask that scatter a significant amount of EUV light. In imaging, or defect review mode, a zone plate is placed in the reflected …
Date: March 24, 2005
Creator: Barty, A.; Liu, Y.; Gullikson, E.; Taylor, J. S. & Wood, O.
Object Type: Article
System: The UNT Digital Library
STELLA-II: DEMONSTRATION OF MONOENERGETIC LASER ACCELERATION. (open access)

STELLA-II: DEMONSTRATION OF MONOENERGETIC LASER ACCELERATION.

Monoenergetic laser acceleration of trapped microbunches has been demonstrated for the first time. An inverse free electron laser (IFEL) is used to create microbunches, which are then accelerated by a second IFEL using a tapered undulatos. An adjustable magnetic field chicane is located between the two IFELs and is used to control the phase of the microbunches with respect to the laser field in the second IFEL. The IFELs are driven by a single lases beam from a high peak power CO{sub 2} laser. During the experiment, the trapped portion of the microbunch electrons had an energy gain of >16% with an energy width of -0.86% (full width at half-maximum).
Date: March 24, 2004
Creator: KIMURA,W. D. BABZIEN,M. BEN-ZVI,I. GALLARDO,J. C. KUSCHE,K. P. POGORELSKY,I. V. SKARITKA,J. YAKIMENKO,V. ET AL.
Object Type: Article
System: The UNT Digital Library
Review of Practice for Deeply Embedded/Buried Npp Structures Subject to Seismic Loadings. (open access)

Review of Practice for Deeply Embedded/Buried Npp Structures Subject to Seismic Loadings.

Motivated by many design considerations, several conceptual designs for advanced reactors have proposed that the entire reactor building and a significant portion of the steam generator building will be either partially or completely embedded below grade. For the analysis of seismic events, the soil-structure interaction (SSI) effect and passive earth pressure for these types of deeply embedded structures will have a significant influence on the predicted seismic response. Sponsored by the US Nuclear Regulatory Commission (NRC), Brookhaven National Laboratory (BNL) is carrying out a research program to assess the significance of these proposed design features for advanced reactors, and to evaluate the existing analytical methods to determine their applicability and adequacy in capturing the seismic behavior of the proposed designs. This paper summarizes a literature review performed by BNL to determine the state of knowledge and practice for seismic analyses of deeply embedded and/or buried (DEB) nuclear containment type structures. Included in the paper is BNL's review of the open literature of existing standards, tests, and practices that have been used in the design and analysis of DEB structures. The paper also provides BNL's evaluation of available codes and guidelines with respect to seismic design practice of DEB structures. Based …
Date: March 24, 2004
Creator: Xu, J.; Hofmayer, C.; Miller, C. & Graves, H.
Object Type: Article
System: The UNT Digital Library
Understanding Particle Defect Transport in an Ultra-Clean Sputter Coating Process (open access)

Understanding Particle Defect Transport in an Ultra-Clean Sputter Coating Process

Low-defect mask blanks remain a key technical challenge to Extreme Ultraviolet Lithography (EUVL). The mask blank is ion-beam sputter-coated with an 81-layer Mo/Si multilayer stack for high reflectance at {lambda} = 13.4nm. The current mask coating process can achieve a median added defect level of 0.05 defects/cm{sup 2} (12 added defects 90nm or larger on a 200mm Si-wafer test substrate), but this must be reduced by about a factor of 10 to meet mask cost requirements for EUVL. To further reduce the particle defect level, we have studied pathways for particle transport, using test particles and particles native to the coating process, and combined the results into a computational model of particle transport in an ion-beam sputter system. At process pressure, gas drag is negligible for particles above 100nm, so particles travel ballistically until they hit a surface. Bounce from chamber walls allows particles to reach all surfaces in the chamber if they have initial velocities above {approx}100m/s. The ion beam has sufficient momentum to entrain slower particles and accelerate them toward the sputter target, where some can bounce to the substrate. The model shows preliminary agreement with experimental defect distributions on witness wafers at various positions within the coating …
Date: March 24, 2003
Creator: Walton, C.; Kearney, P.; Folta, J.; Sweeney, D. & Mirkarimi, P.
Object Type: Article
System: The UNT Digital Library
Characterization of Functionalized Self-Assembled Monolayers and Surface-Attached Interlocking Molecules Using Near-Edge X-ray Absorption Fine Structure Spectroscopy (open access)

Characterization of Functionalized Self-Assembled Monolayers and Surface-Attached Interlocking Molecules Using Near-Edge X-ray Absorption Fine Structure Spectroscopy

Quantitative knowledge of the fundamental structure and substrate binding, as well as the direct measurement of conformational changes, are essential to the development of self-assembled monolayers (SAMs) and surface-attached interlocking molecules, catenanes and rotaxanes. These monolayers are vital to development of nano-mechanical, molecular electronic, and biological/chemical sensor applications. This dissertation investigates properties of functionalized SAMs in sulfur-gold based adsorbed molecular monolayers using quantitative spectroscopic techniques including near-edge x-ray absorption fine structure spectroscopy (NEXAFS) and x-ray photoelectron spectroscopy (XPS). The stability of the gold-thiolate interface is addressed. A simple model SAM consisting of dodecanethiol adsorbed on Au(111) degrades significantly in less than 24 hours under ambient laboratory air. S 2p and O 1s XPS show the gold-bound thiolates oxidize to sulfinates and sulfonates. A reduction of organic material on the surface and a decrease in order are observed as the layer degrades. The effect of the carboxyl vs. carboxylate functionalization on SAM structure is investigated. Carboxyl-terminated layers consisting of long alkyl-chain thiols vs. thioctic acid with short, sterically separated, alkyl groups are compared and contrasted. NEXAFS shows a conformational change, or chemical switchability, with carboxyl groups tilted over and carboxylate endgroups more upright. Surface-attached loops and simple surface-attached rotaxanes are quantitatively …
Date: March 24, 2004
Creator: Willey, T & Willey, T
Object Type: Thesis or Dissertation
System: The UNT Digital Library
CONCEPTS FOR CAPACITIVELY RF-SHIELDED BELLOWS IN CRYOGENIC STRUCTURES. (open access)

CONCEPTS FOR CAPACITIVELY RF-SHIELDED BELLOWS IN CRYOGENIC STRUCTURES.

Bellows are frequently required in accelerators and colliders. Usually RF-shields with spring fingers are employed to screen the bellows. The lack of accessibility in cryogenic systems can be a problem and asks for alternate solutions to eliminate possible overheating, sparking, etc that occurred in intensive beams. This note addresses an alternate kind of RF shield, which uses capacitive contact instead of mechanical contact. The analysis, as well as numerical example of a superconducting cavity structure, shows that the capacitive RF shield satisfies the impedance requirements of both beam and HOMs. The capability of thermal isolation is also analyzed.
Date: March 24, 2004
Creator: ZHAO,Y. HAHN,H.
Object Type: Report
System: The UNT Digital Library
Ancient Glass Studies: Potential Archaeological Sites Relevant to Low-Activity Waste Disposal at Hanford (open access)

Ancient Glass Studies: Potential Archaeological Sites Relevant to Low-Activity Waste Disposal at Hanford

In this document we identify several archaeological sites that may be of use in validating the ILAW performance assessment. Glasses that might be recovered at these sites would be recovered with the surrounding soil. This soil would be analyzed and the distribution of elements released from the glass to the soil would be mapped. Coincidence of the actual migration and the modeled migration would constitute a validation exercise of the current performance assessment model for the Hanford Site.
Date: March 24, 2003
Creator: Strachan, Denis M.
Object Type: Report
System: The UNT Digital Library
Design and Status of the Visa II Experiment. (open access)

Design and Status of the Visa II Experiment.

VISA II is the follow-up project to the successful Visible to Infrared SASE Amplifier (VISA) experiment at the Accelerator Test Facility (ATF) in Brookhaven National Lab (BNL). This paper will report the motivation for and status of the two main experiments associated with the VISA II program. One goal of VISA II is to perform an experimental study of the physics of a chirped beam SASE FEL at the upgraded facilities of the ATF. This requires a linearization of the transport line to preserve energy chirping of the electron beam at injection. The other planned project is a strong bunch compression experiment, where the electron bunch is compressed in the chicane, and the dispersive beamline transport, allowing studies of deep saturation.
Date: March 24, 2004
Creator: Andonian, G.
Object Type: Article
System: The UNT Digital Library
DNA Damage Quantitation by Alkaline Gel Electrophoresis. (open access)

DNA Damage Quantitation by Alkaline Gel Electrophoresis.

Physical and chemical agents in the environment, those used in clinical applications, or encountered during recreational exposures to sunlight, induce damages in DNA. Understanding the biological impact of these agents requires quantitation of the levels of such damages in laboratory test systems as well as in field or clinical samples. Alkaline gel electrophoresis provides a sensitive (down to {approx} a few lesions/5Mb), rapid method of direct quantitation of a wide variety of DNA damages in nanogram quantities of non-radioactive DNAs from laboratory, field, or clinical specimens, including higher plants and animals. This method stems from velocity sedimentation studies of DNA populations, and from the simple methods of agarose gel electrophoresis. Our laboratories have developed quantitative agarose gel methods, analytical descriptions of DNA migration during electrophoresis on agarose gels (1-6), and electronic imaging for accurate determinations of DNA mass (7-9). Although all these components improve sensitivity and throughput of large numbers of samples (7,8,10), a simple version using only standard molecular biology equipment allows routine analysis of DNA damages at moderate frequencies. We present here a description of the methods, as well as a brief description of the underlying principles, required for a simplified approach to quantitation of DNA damages by …
Date: March 24, 2004
Creator: Sutherland, B. M.; Bennett, P. V. & Sutherland, J. C.
Object Type: Book
System: The UNT Digital Library
Radiography and ultrasonic calculation workbooks: installation and use (open access)

Radiography and ultrasonic calculation workbooks: installation and use

The radiography and ultrasonic calculation workbooks are intended to assist Level I, II and III NDE personnel in calculations used in routine job applications. These workbooks are an upgraded version of Microsoft Excel{reg_sign} spreadsheets, which were originally set up in October 1988, using a Macintosh Plus{reg_sign} computer and Microsoft Excel{reg_sign} version 1.5. A description of these was released as ''Computerized Calculations for Radiography and Ultrasonics'', UCRL-JC-105419 in November 1990 and published in Materials Evaluation, Volume 49/Number 4, in April 1991. Over the years as Microsoft improved the capabilities of the Excel program to include the abilities to make sketches and to have multiple tabbed pages in a document called a ''workbook'' we have now modified the calculation spreadsheets to include these enhancements. Following is a short description on how to install and use these workbooks on a Macintosh or PC.
Date: March 24, 2000
Creator: Rikard, D & Dolan, K
Object Type: Text
System: The UNT Digital Library
Defining and Testing the Influence of Servo System Response on Machine Tool Compliance (open access)

Defining and Testing the Influence of Servo System Response on Machine Tool Compliance

Compliance can be defined as the measurement of displacement per unit of force applied e.g. nano-meters per Newton (m/N). Compliance is the reciprocal of stiffness. High stiffness means low compliance and visa versa. It is an important factor in machine tool characteristics because it reflects the ability of the machine axis to maintain a desired position as it encounters a force or torque. Static compliance is a measurement made with a constant force applied e.g. the average depth of cut. Dynamic compliance is a measurement made as a function of frequency, e.g. a fast too servo (FTS) that applies a varying cutting force or load, interrupted cuts and external disturbances such as ground vibrations or air conditioning induced forces on the machine. Compliance can be defined for both a linear and rotary axis of a machine tool. However, to properly define compliance for a rotary axis, the axis must allow a commanded angular position. Note that this excludes velocity only axes. In this paper, several factors are discussed that affect compliance but emphasis is placed on how the machine servo system plays a key role in compliance at low to mid frequency regions. The paper discusses several techniques for measuring …
Date: March 24, 2004
Creator: Hopkins, D J
Object Type: Article
System: The UNT Digital Library
NIKE3D a nonlinear, implicit, three-dimensional finite element code for solid and structural mechanics user's manual update summary (open access)

NIKE3D a nonlinear, implicit, three-dimensional finite element code for solid and structural mechanics user's manual update summary

This report provides the NIKE3D user's manual update summary for changes made from version 3.0.0 April 24, 1995 to version 3.3.6 March 24,2000. The updates are excerpted directly from the code printed output file (hence the Courier font and formatting), are presented in chronological order and delineated by NIKE3D version number. NIKE3D is a fully implicit three-dimensional finite element code for analyzing the finite strain static and dynamic response of inelastic solids, shells, and beams. Spatial discretization is achieved by the use of 8-node solid elements, 2-node truss and beam elements, and 4-node membrane and shell elements. Thirty constitutive models are available for representing a wide range of elastic, plastic, viscous, and thermally dependent material behavior. Contact-impact algorithms permit gaps, frictional sliding, and mesh discontinuities along material interfaces. Several nonlinear solution strategies are available, including Full-, Modified-, and Quasi-Newton methods. The resulting system of simultaneous linear equations is either solved iteratively by an element-by-element method, or directly by a direct factorization method.
Date: March 24, 2000
Creator: Puso, M; Maker, B N; Ferencz, R M & Hallquist, J O
Object Type: Report
System: The UNT Digital Library
Practical SQE on a Large Multi-Disciplinary HPC Development Team (open access)

Practical SQE on a Large Multi-Disciplinary HPC Development Team

In this paper we will discuss several software engineering practices that have proven useful in a large multidisciplinary physics code development project at Lawrence Livermore National Laboratory. In the project discussed here, as with many large scale efforts in HPC scientific computing, we have had to balance the competing demands of being a stable ''production'' code that our user base can rely on with being a platform for research into new physics, models, and software architectures. Much of this has been learned through necessity and experience. Likewise, much of it has been learned through interactions with other similar projects and hearing of their successes, and tailoring their ideas to our own requirements. The ideas presented here are not meant to necessarily transfer to other environments with different needs. It is our belief that projects need to be given large latitude in defining their own software engineering process versus a prescribed a solution. However, the ideas presented here are hopefully high level and general enough that we hope other projects might find some inspiration and adopt similar methods if it is to their benefit, much as we have done through the years.
Date: March 24, 2004
Creator: Neely, J R
Object Type: Article
System: The UNT Digital Library
Environmental Management System Plan (open access)

Environmental Management System Plan

Executive Order 13423, Strengthening Federal Environmental, Energy, and Transportation Management establishes the policy that Federal agencies conduct their environmental, transportation, and energy-related activities in a manner that is environmentally, economically and fiscally sound, integrated, continually improving, efficient, and sustainable. The Department of Energy (DOE) has approved DOE Order 450.1A, Environmental Protection Program and DOE Order 430.2B, Departmental Energy, Renewable Energy and Transportation Management as the means of achieving the provisions of this Executive Order. DOE Order 450.1A mandates the development of Environmental Management Systems (EMS) to implement sustainable environmental stewardship practices that: (1) Protect the air, water, land, and other natural and cultural resources potentially impacted by facility operations; (2) Meet or exceed applicable environmental, public health, and resource protection laws and regulations; and (3) Implement cost-effective business practices. In addition, the DOE Order 450.1A mandates that the EMS must be integrated with a facility's Integrated Safety Management System (ISMS) established pursuant to DOE P 450.4, 'Safety Management System Policy'. DOE Order 430.2B mandates an energy management program that considers energy use and renewable energy, water, new and renovated buildings, and vehicle fleet activities. The Order incorporates the provisions of the Energy Policy Act of 2005 and Energy Independence and …
Date: March 24, 2009
Creator: Fox, Robert; Thorson, Patrick; Horst, Blair; Speros, John; Rothermich, Nancy & Hatayama, Howard
Object Type: Report
System: The UNT Digital Library
Post-Closure Inspection Letter Report for Corrective Action Units on the Nevada Test Site (open access)

Post-Closure Inspection Letter Report for Corrective Action Units on the Nevada Test Site

None
Date: March 24, 2009
Creator: National Security Technologies, LLC
Object Type: Report
System: The UNT Digital Library
A Spatially Resolving X-ray Crystal Spectrometer for Measurement of Ion-temperature and Rotation-velocity Profiles on the AlcatorC-Mod Tokamak (open access)

A Spatially Resolving X-ray Crystal Spectrometer for Measurement of Ion-temperature and Rotation-velocity Profiles on the AlcatorC-Mod Tokamak

A new spatially resolving x-ray crystal spectrometer capable of measuring continuous spatial profiles of high resolution spectra (λ/dλ > 6000) of He-like and H-like Ar Kα lines with good spatial (~1 cm) and temporal (~10 ms) resolutions has been installed on the Alcator C-Mod tokamak. Two spherically bent crystals image the spectra onto four two-dimensional Pilatus II pixel detectors. Tomographic inversion enables inference of local line emissivity, ion temperature (Ti), and toroidal plasma rotation velocity (vφ) from the line Doppler widths and shifts. The data analysis techniqu
Date: March 24, 2009
Creator: Hill, K. W.; Bitter, M. L.; Scott, S. D.; Ince-Cushman, A.; Reinke, M.; Rice, J. E. et al.
Object Type: Report
System: The UNT Digital Library
RAPID MEASUREMENTS OF NEPTUNIUM OXIDATION STATES USING CHROMATOGRAPHIC RESINS (open access)

RAPID MEASUREMENTS OF NEPTUNIUM OXIDATION STATES USING CHROMATOGRAPHIC RESINS

The Savannah River Site's (SRS) H-Canyon facility uses ceric ammonium nitrate (CAN) to separate impure neptunium (Np) from a high sulfate feed stream. The material is processed using a two-pass solvent extraction purification which relies on CAN to oxidize neptunium to Np(VI) during the first pass prior to extraction. Spectrophotometric oxidation-state analyses normally used to validate successful oxidation to Np(VI) prior to extraction were compromised by this feed stream matrix. Therefore, a rapid chromatographic method to validate successful Np oxidation was developed using Eichrom Industries TRU and TEVA{reg_sign} resins. The method was validated and subsequently transferred to existing operations in the process analytical laboratories.
Date: March 24, 2009
Creator: Diprete, D; C Diprete, C; Mira Malek, M & Eddie Kyser, E
Object Type: Article
System: The UNT Digital Library
CZT Virtual Frisch-grid Detector: Principles and Applications (open access)

CZT Virtual Frisch-grid Detector: Principles and Applications

Cadmium Zinc Telluride (CdZnTe or CZT) is a very attractive material for using as room-temperature semiconductor detectors, because it has a wide bandgap and a high atomic number. However, due to the material's poor hole mobility, several special techniques were developed to ensure its suitability for radiation detection. Among them, the virtual Frisch-grid CZT detector is an attractive option, having a simple configuration, yet delivering an outstanding spectral performance. The goal of our group in Brookhaven National Laboratory (BNL) is to improve the performance of Frisch-ring CZT detectors; most recently, that effort focused on the non-contacting Frisch-ring detector, allowing us to build an inexpensive, large-volume detector array with high energy-resolution and a large effective area. In this paper, the principles of virtual Frisch-grid detectors are described, especially BNL's innovative improvements. The potential applications of virtual Frisch-grid detectors are discussed, and as an example, a hand-held gamma-ray spectrometer using a CZT virtual Frischgrid detector array is introduced, which is a self-contained device with a radiation detector, readout circuit, communication circuit, and high-voltage supply. It has good energy resolution of 1.4% (FWHM of 662-keV peak) with a total detection volume of {approx}20 cm{sup 3}. Such a portable inexpensive device can be used …
Date: March 24, 2009
Creator: Cui,Y.; Bolotnikov, A.; Camarda, G.; Hossain, A. & James, R. B.
Object Type: Article
System: The UNT Digital Library
A dedicated superbend x-ray microdiffraction beamline for materials, geo-, and environmental sciences at the advanced light source (open access)

A dedicated superbend x-ray microdiffraction beamline for materials, geo-, and environmental sciences at the advanced light source

A new facility for microdiffraction strain measurements and microfluorescence mapping has been built on beamline 12.3.2 at the advanced light source of the Lawrence Berkeley National Laboratory. This beamline benefits from the hard x-radiation generated by a 6 T superconducting bending magnet (superbend) This provides a hard x-ray spectrum from 5 to 22 keV and a flux within a 1 mu m spot of ~;;5x109 photons/ s (0.1percent bandwidth at 8 keV). The radiation is relayed from the superbend source to a focus in the experimental hutch by a toroidal mirror. The focus spot is tailored bytwo pairs of adjustable slits, which serve as secondary source point. Inside the lead hutch, a pair of Kirkpatrick-Baez (KB) mirrors placed in a vacuum tank refocuses the secondary slit source onto the sample position. A new KB-bending mechanism with active temperature stabilization allows for more reproducible and stable mirror bending and thus mirror focusing. Focus spots around 1 um are routinely achieved and allow a variety of experiments, which have in common the need of spatial resolution. The effective spatial resolution (~;;0.2 mu m) is limited by a convolution of beam size, scan-stage resolution, and stage stability. A four-bounce monochromator consisting of two …
Date: March 24, 2009
Creator: Lawrence Berkeley National Laboratory. Advanced Light Source.
Object Type: Article
System: The UNT Digital Library
DOE A9024 Final Report Functional and Nanoscale Materials Systems: Frontier Programs of Science at the Frederick Seitz Materials Research Laboratory (open access)

DOE A9024 Final Report Functional and Nanoscale Materials Systems: Frontier Programs of Science at the Frederick Seitz Materials Research Laboratory

The scientific programs of the FSMRL supported under the DOE A9024 Grant consisted of four interdisciplinary research clusters, as described. The clusters were led by Professors Tai Chiang (Physics), Jeffrey Moore (Chemistry), Paul Goldbart (Physics), and Steven Granick (Materials Science and Engineering). The completed work followed a dominant theme--Nanoscale Materials Systems--and emphasized studies of complex phenomena involving surfaces, interfaces, complex materials, dynamics, energetics, and structures and their transformations. A summary of our key accomplishments is provided for each cluster.
Date: March 24, 2009
Creator: Lewis, Jennifer A.
Object Type: Report
System: The UNT Digital Library
Overview of Results from the National Spherical Torus Experiment (NSTX) (open access)

Overview of Results from the National Spherical Torus Experiment (NSTX)

None
Date: March 24, 2009
Creator: Gates, D. A.; Ahn, J.; Allain, J.; Andre, R.; Bastasz, R.; Bell, M. et al.
Object Type: Report
System: The UNT Digital Library
Point Defect Characterization in CdZnTe (open access)

Point Defect Characterization in CdZnTe

Measurements of the defect levels and performance testing of CdZnTe detectors were performed by means of Current Deep Level Transient Spectroscopy (I-DLTS), Transient Charge Technique (TCT), Current versus Voltage measurements (I-V), and gamma-ray spectroscopy. CdZnTe crystals were acquired from different commercial vendors and characterized for their point defects. I-DLTS studies included measurements of defect parameters such as energy levels in the band gap, carrier capture cross sections, and defect densities. The induced current due to laser-generated carriers was measured using TCT. The data were used to determine the transport properties of the detectors under study. A good correlation was found between the point defects in the detectors and their performance.
Date: March 24, 2009
Creator: Gul, R.; Li, Z.; Bolotnikov, A.; Keeter, K.; Rodriguez, R. & James, R.
Object Type: Article
System: The UNT Digital Library
Harnessing microbial subsurface metal reduction activities to synthesise nanoscale cobalt ferrite with enhanced magnetic properties (open access)

Harnessing microbial subsurface metal reduction activities to synthesise nanoscale cobalt ferrite with enhanced magnetic properties

Nanoscale ferrimagnetic particles have a diverse range of uses from directed cancer therapy and drug delivery systems to magnetic recording media and transducers. Such applications require the production of monodisperse nanoparticles with well-controlled size, composition, and magnetic properties. To fabricate these materials purely using synthetic methods is costly in both environmental and economical terms. However, metal-reducing microorganisms offer an untapped resource to produce these materials. Here, the Fe(III)-reducing bacterium Geobacter sulfurreducens is used to synthesize magnetic iron oxide nanoparticles. A combination of electron microscopy, soft X-ray spectroscopy, and magnetometry techniques was employed to show that this method of biosynthesis results in high yields of crystalline nanoparticles with a narrow size distribution and magnetic properties equal to the best chemically synthesized materials. In particular, it is demonstrated here that cobalt ferrite (CoFe{sub 2}O{sub 4}) nanoparticles with low temperature coercivity approaching 8 kOe and an effective anisotropy constant of {approx} 10{sup 6} erg cm{sup -3} can be manufactured through this biotechnological route. The dramatic enhancement in the magnetic properties of the nanoparticles by the introduction of high quantities of Co into the spinel structure represents a significant advance over previous biomineralization studies in this area using magnetotactic bacteria. The successful production of …
Date: March 24, 2009
Creator: Coker, Victoria S.; Telling, Neil D.; van der Laan, Gerrit; Pattrick, Richard A.D.; Pearce, Carolyn I.; Arenholz, Elke et al.
Object Type: Article
System: The UNT Digital Library