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Tim Elam

Principal Physicist

Email

wtelam@apl.washington.edu

Phone

206-685-3092

Research Interests

X-ray Spectroscopy

Biosketch

Dr. Elam's main research interest is X-ray spectroscopy. He has worked in the areas of X-ray absorption, emission, fluorescence, and non-resonant inelastic scattering. His present efforts focus on using X-ray fluorescence in difficult environments. He has built an X-ray fluorescence spectrometer (XRFS) to measure heavy metal contaminants in soils and sediments that is directly pushed via cone penetrometery without drilling. His latest project was a borehole XRFS for use in the Mars Subsurface Access Program and it is now being adapted to make in-situ measurements of diffusion of stable isotopes of nuclear waste elements through native rock without radioactivity. Dr. Elam is also the hardware lead for the APL Ice Diver. He is Chair of the Denver X-ray Conference, serves on the Advisory Board for X-ray Spectrometry, and is a member of the International Center for Diffraction Data. He was the American Institute of Physics Congressional Science Fellow for 1991. He has more than 100 publications in refereed scientific journals and holds 5 patents.

Education

B.S. Physics, Mississippi State University, 1973

M.S. Physics, University of Maryland, 1977

Ph.D. Physics, University of Maryland, 1979

Publications

2000-present and while at APL-UW

Comparison of transport theory predictions with measurements of the decrease in shallow water reverberation level as the sea state increases

Thorsos, E., J. Yang, W.T. Elam, F.S. Henyey, F. Li, and J. Liu, "Comparison of transport theory predictions with measurements of the decrease in shallow water reverberation level as the sea state increases," Proc., Meetings on Acoustics, 19, 070024, doi:10.1121/1.4800711, 2013.

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2 Jun 2013

Transport theory has been developed for modeling shallow water propagation and reverberation at mid frequencies (1-10 kHz) where forward scattering from a rough sea surface is taken into account in a computationally efficient manner. The method is based on a decomposition of the field in terms of unperturbed modes, and forward scattering at the sea surface leads to mode coupling that is treated with perturbation theory. Reverberation measurements made during ASIAEX in 2001 provide a useful test of transport theory predictions. Modeling indicates that the measured reverberation was dominated by bottom reverberation, and the reverberation level at 1 and 2 kHz was observed to decrease as the sea surface conditions increased from a low sea state to a higher sea state. This suggests that surface forward scattering was responsible for the change in reverberation level. By modeling the difference in reverberation as the sea state changes, the sensitivity to environmental conditions other than the sea surface roughness is much reduced. Transport theory predictions for the reverberation difference are found to be in good agreement with measurements.

Reverberation modeling with transport theory

Thorsos, E.I., J. Yang, W.T. Elam, and F.S. Henyey, "Reverberation modeling with transport theory," J. Acoust. Soc. Am., 131, 3355, doi:10.1121/1.4708579, 2012.

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1 Apr 2012

Transport theory has been developed for modeling shallow water propagation at mid frequencies (1-10 kHz) where forward scattering from a rough sea surface is taken into account in a computationally efficient manner. The method is based on a decomposition of the field in terms of unperturbed modes, and forward scattering at the sea surface leads to mode coupling that is treated with perturbation theory. Transport theory has recently been extended to model shallow water reverberation, including the effect of forward scattering from the sea surface. Transport theory results will be compared with other solutions for reverberation examples taken from ONR Reverberation Modeling Workshop problems. These comparisons show the importance of properly accounting for multiple forward scattering in shallow water reverberation modeling.

Smart pile-up consideration for evaluation of high count rate EDS spectra

Eggert, F., T. Elam, R. Anderhalt, and J. Nicolosi, "Smart pile-up consideration for evaluation of high count rate EDS spectra," IOP Conf. Ser.: Mater. Sci. Eng., 32, 012008, doi:
10.1088/1757-899X/32/1/012008, 2012.

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7 Mar 2012

This work describes a new pile-up consideration for the very high count rate spectra which are possible to acquire with silicon drift detector (SDD) technology. Pile-up effects are the major and still remaining challenge with the use of SDD for EDS in scanning electron microscopes (SEM) with ultra thin windows for soft X-ray detection. The ability to increase the count rates up to a factor of 100 compared with conventional Si(Li) detectors, comes with the problem that the pile-up recognition (pile-up rejection) in pulse processors is not able to improve by the same order of magnitude, just only with a factor of about 3. Therefore, it is common that spectra will show significant pile-up effects if count rates of more than 10000 counts per second (10 kcps) are used. These false counts affect both automatic qualitative analysis and quantitative evaluation of the spectra. The new idea is to use additional inputs for pile-up calculation to shift the applicability towards very high count rates of up to 200 kcps and more, which can be easily acquired with the SDD. The additional input is the 'known' (estimated) background distribution, calculated iteratively during all automated qualitative or quantitative evaluations. This additional knowledge gives the opportunity for self adjustment of the pile-up calculation parameters and avoids over-corrections which challenge the evaluation as well as the pile-up artefacts themselves. With the proposed method the pile-up correction is no longer a 'correction' but an integral part of all spectra evaluation steps. Examples for the application are given with evaluation of very high count rate spectra.

More Publications

X-ray emission spectroscopy of nitrogen-rich compounds

Villa, F.D.,T. Jach, W.T. Elam, J.J. Rehr, and J.D. Denlinger, "X-ray emission spectroscopy of nitrogen-rich compounds," J. Phys. Chem. A, 115, 3243-3250, doi: 10.1021/jp108539v, 2011.

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31 Mar 2011

Nonresonant X-ray emission spectroscopy was used to compare the nitrogen-rich compounds ammonium nitrate, trinitrotoluene, and cyclotrimethylene-trinitramine. They are representative of crystalline and molecular structures of special importance in industrial and military applications. The spectral signature of each substance was analyzed and correlated with features in the electronic structure of the systems. This analysis was accomplished by means of theoretical simulations of the emission spectra and a detailed examination of the molecular orbitals and densities of states. We find that the two theoretical methods used (frozen-orbital density functional theory and real-space Green's function simulations) account semiquantitatively for the observed spectra and are able to predict features arising from distinct chemical complexes. A comparison of the calculations and the data provides insight into the electronic contributions of specific molecular orbitals, as well as the features due to bandlike behavior. With some additional refinements, these methods could be used as an alternative to reference compounds.

Transport theory for shallow water propagation with rough boundaries

Thorsos, E.I., F.S. Henyey, W.T. Elam, B.T. Hefner, S.A. Reynolds, and J. Yang, "Transport theory for shallow water propagation with rough boundaries," In Proceedings, Second International Shallow-Water Acoustics Conference (SWAC'09), Shanghai, 16-20 September 2009, 99-105 (AIP, 2010).

4 Oct 2010

Transport theory for shallow water propagation with rough boundaries

Thorsos, E.I., F.S. Henyey, W.T. Elam, B.T. Hefner, S.A. Reynolds, and J. Yang, "Transport theory for shallow water propagation with rough boundaries," In Proceedings, Second International Shallow-Water Acoustics Conference, Shanghai, 16-20 September 2009, 99-105 (AIP, 2010).

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6 Sep 2010

At frequencies of about 1 kHz and higher, forward scattering from a rough sea surface (and/or a rough bottom) can strongly affect shallow water propagation and reverberation. The need exists for a fast, yet accurate method for modeling such propagation where multiple forward scattering occurs. A transport theory method based on mode coupling is described that yields the first and second moments of the field. This approach shows promise for accurately treating multiple forward scattering in one-way propagation. The method is presently formulated in two space dimensions, and Monte–Carlo rough surface PE simulations are used for assessing the accuracy of transport theory results.

Predicting the Utility of Non-Resonant Inelastic X-ray Scattering (NRIXS) for Standoff Explosives Detection

Elam, W.T., G. Seidler, T. Fister, K. Nagel, and L. Buck, "Predicting the Utility of Non-Resonant Inelastic X-ray Scattering (NRIXS) for Standoff Explosives Detection," APL-UW TR 0903, November 2009.

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1 Nov 2009

The research reported here was a component of a three-year program at the University of Washington to improve fundamental knowledge that is important for developing new technologies and approaches to counter improvised explosive devices (IEDs). The focus of our component was to develop methods for identifying explosive materials using X-ray spectroscopy.

All chemical explosives store energy in specific, high-energy chemical bonds. Detecting and classifying explosives is a matter of analyzing the structure of these bonds by some method, either direct or indirect. One direct method is to measure the X-ray emission spectrum of the relevant elements involved in the chemical bonds, such as nitrogen or oxygen in a typical explosive. A complementary technique is provided by a particular type of non-resonant inelastic X-ray scattering (NRIXS).

The microcalorimeter X-ray detector: A true paradigm shift in X-ray spectroscopy

Jach, T., J.N. Ullom, and W.T. Elam, "The microcalorimeter X-ray detector: A true paradigm shift in X-ray spectroscopy," Eur. Phys. J. Special Topics, 169, 237-242, 2009.

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1 Jan 2009

The microcalorimeter x-ray detector registers the heat deposited in an absorber from individual x-ray photons by means of a sensitive thermometer. It combines advantages of wavelength-dispersive and energy-dispersive detectors: relatively high energy resolution over a broad energy spectrum. Operating at very low temperatures reduces the noise, making the high energy resolution possible. The absorber can be tailored to any energy range, from soft x-rays to gamma rays. After many years of development, several designs have reached a level of performance and reliability that makes them competitive x-ray detectors for many kinds of experiment. We survey current microcalorimeter detectors using several different thermometers. Their applications already run from chemical analysis to plasma physics and x-ray astronomy. We describe two examples of how the microcalorimeter detector can enable novel determinations in x-ray physics.

Matrix-free laser desorption/ionization of ions landed on plasma-treated metal surfaces

Volny, M. M. Sadilek, K.E. Jackson, M. Diener, W.T. Elam, and F. Turecek, "Matrix-free laser desorption/ionization of ions landed on plasma-treated metal surfaces," J. Mass Spectrom., 43, 1265-1273, doi:10.1002/jms.1402, 2008.

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1 Mar 2008

We report new experiments in which laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF-MS) was applied to detection and characterization of gramicidin S and IgG pentapeptide (DSDPR) that were reactively landed on plasma-treated stainless steel surfaces. The distributions of [M * H]+, [M + Na] and [M + K]+ ion species in LDI-TOF for gramicidin S and IgG pentapeptide (DSDPR) were found to be markedly different from those in conventional MALDI-TOF spectra of the same samples. LDI-TOF mass spectra showed a strong preference for [M + K]+ adducts even in the presence of a large excess of sodium cations, or following surface treatment with trifluoroacetic acid. Alkali metal cations (K+ and Cs+) can be exchanged in reactively landed peptide samples to provide the corresponding cationized peptide ions by LDI. Multiple charged trypsin cations were reactively landed into a layer of 2-(4-hydroxyphenylazo)benzoic acid and ionized by LDI. The ionization mechanisms for LDI of surface-deposited peptides are briefly discussed.

Borehole X-ray Fluorescence Spectrometer (XRFS): User's Manual, Software Description, and Performance Report

Kelliher, W.C., I.A. Carlberg, W.T. Elam, and E. Willard-Schmoe, "Borehole X-ray Fluorescence Spectrometer (XRFS): User's Manual, Software Description, and Performance Report," APL-UW TR 0703, December 2007.

30 Dec 2007

Reducing the Size of the Borehole X-ray Fluorescence Spectrometer (XRFS) Probe: Preliminary Design Study

Elam, W.T., W.C. Kelliher, and I.A. Carlberg, "Reducing the Size of the Borehole X-ray Fluorescence Spectrometer (XRFS) Probe: Preliminary Design Study," APL-UW TR 0503, June 2007.

30 Jun 2007

Deconvolving instrumental and intrinsic broadening in core-shell x-ray spectroscopies

Fister, T.T., G.T. Seidler, J.J. Rehr, J.J. Kas, W.T. Elam, J.O. Cross, and K.P. Nagle, "Deconvolving instrumental and intrinsic broadening in core-shell x-ray spectroscopies," Phys. Rev. B, 75, doi:10.1103/PhysRevB.75.174106, 2007.

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15 May 2007

Intrinsic and experimental mechanisms frequently lead to broadening of spectral features in core-shell spectroscopies. For example, intrinsic broadening occurs in x-ray absorption spectroscopy (XAS) measurements of heavy elements where the core-hole lifetime is very short. On the other hand, nonresonant x-ray Raman scattering (XRS) and other energy loss measurements are more limited by instrumental resolution. Here, we demonstrate that the Richardson-Lucy (RL) iterative algorithm provides a robust method for deconvolving instrumental and intrinsic resolutions from typical XAS and XRS data. For the K-edge XAS of Ag, we find nearly complete removal of ~9.3 eV full width at half maximum broadening from the combined effects of the short core-hole lifetime and instrumental resolution. We are also able to remove nearly all instrumental broadening in an XRS measurement of diamond, with the resulting improved spectrum comparing favorably with prior soft x-ray XAS measurements. We present a practical methodology for implementing the RL algorithm in these problems, emphasizing the importance of testing for stability of the deconvolution process against noise amplification, perturbations in the initial spectra, and uncertainties in the core-hole lifetime.

Micro-XRF excitation in an SEM

Haschke, M., F. Eggert, and W.T. Elam, "Micro-XRF excitation in an SEM," X-Ray Spectr., 36, 254-259, 2007.

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8 May 2007

Electron microscopes are often used for position-sensitive elemental analysis of non-homogeneous material by electron-probe-micro-analysis (EPMA). Due to the high spectral background, this method is limited in sensitivity. The availability of x-ray optics allows the generation of focussed x-ray beams with spot sizes in the micrometer range. The x-ray excited spectra have a better peak-to-background ratio and, therefore, a higher sensitivity. Further, the excitation efficiency for both electrons and photons varies with the atomic number. Therefore, light elements can be analysed better with electron excitation. The combination of analytical results from electron and x-ray excitation, therefore, should improve the accuracy of quantification. The paper presents a μ-XRF excitation unit for scanning electron microscopes (SEMs) and describes the quantification model that is prepared for this device. The quantification is performed for few samples. These results show that the standardless quantification give a good accuracy. Especially in case of presence of light elements like C, O or N in the matrix, the XRF results can be improved by consideration of results from EPMA.

Enhanced in-vitro blood compatibility of 316L stainless steel surfaces by reactive landing of hyaluronan ions

Volny, M., W.T. Elam, B.D. Ratner, and F. Turecek, "Enhanced in-vitro blood compatibility of 316L stainless steel surfaces by reactive landing of hyaluronan ions," J. Biomed. Mater. Res. B: Applied Biomaterials, 505-510, doi: 10.1002/jbm.b.30624, 2007

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1 Feb 2007

A novel dry process for immobilization of hyaluronan on stainless steel surfaces is presented. This process that we call reactive landing is based on an interaction of hyperthermal gas-phase hyaluronan ions with plasma-cleaned and activated stainless steel surfaces. Reactive landing is performed on a unique instrument that combines an in-situ plasma reactor with an electrospray ion source and ion transfer optics. Gas-phase hyaluronan anions are obtained by electrospray ionization of sodium hyaluronan solutions and immobilized by reactive landing on large-area stainless steel surfaces. The immobilized hyaluronan withstands extensive washing with polar solvents and solutions, and the washed surfaces maintain the protective properties against blood platelet activation. The mechanism of hyaluronan discharge and immobilization is discussed.

Multi-element spectrometer for efficient measurement of the momentum transfer dependence of inelastic x-ray scattering

Fister, T.T., G.T. Seidler, L. Wharton, A.R. Battle, T.B. Ellis, J.O. Cross, A.T. Macrander, W.T. Elam, T.A. Tyson, and Q. Qian, "Multi-element spectrometer for efficient measurement of the momentum transfer dependence of inelastic x-ray scattering," Rev. Sci. Instrum., 77, 063901, doi:10.1063/1.2204581, 2006.

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14 Jun 2006

Nonresonant x-ray Raman scattering (XRS) is the inelastic scattering of hard x rays from the K shell of low-Z elements or the less tightly bound shells of heavier elements. In the limit of low momentum transfer q, XRS is determined by the same transition matrix element as is measured by x-ray absorption spectroscopies. However, XRS at higher q can often access higher order multipole transitions which help separate the symmetry of various contributions to the local density of states. The main drawback of XRS is its low cross section—a problem that is compounded for a q-dependent study. To address this issue, we have constructed a multielement spectrometer to simultaneously measure XRS at ten different values of q. By means of example, we report new measurements of the XRS from the L- and K-edges of Mg. This instrument is now available to general users at the Advanced Photon Source as the lower energy resolution inelastic x-ray scattering (LERIX) spectrometer.

Examination of coherent surface reflection coefficient (CSRC) approximations in shallow water propagation

Williams, K.L., E.I. Thorsos, and W.T. Elam, "Examination of coherent surface reflection coefficient (CSRC) approximations in shallow water propagation," J. Acoust. Soc. Am., 116, 1975-1984, doi:10.1121/1.1785617, 2004.

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1 Oct 2004

The parabolic wave equation (PE) code of Rosenberg [J. Acoust. Soc. Am. 105, 144-153 (1999)] is used as a benchmark to study acoustic propagation in an ocean waveguide with a rough air/water interface. The PE results allow a close examination of the ability of a ray code [i.e., Gaussian RAy Bundle (GRAB)] to accurately estimate coherent field propagation using a coherent reflection coefficient derived from scattering theory. Comparison with PE implies that the Beckmann–Spizzichino model, as given within the GRAB software package, does not give accurate predictions of the coherent field at long ranges. Three other coherent reflection coefficient approximations are tested: the perturbation, the small slope, and the Kirchhoff approximations. The small slope approximation is the most accurate of the models tested. However, the Kirchhoff approximation is perhaps accurate enough for some purposes and would be simpler to implement as a module within GRAB.

Development of an electrospray approach to deposit complex molecules on plasma modified surfaces

Kitching, K.J., H.-N. Lee, W.T. Elam, E.E. Johnston, H. MacGregor, R.J. Miller, F. Turecek, and B.D. Ratner, "Development of an electrospray approach to deposit complex molecules on plasma modified surfaces," Rev. Sci. Instrum. 74, 4832-4839, doi:10.1063/1.1618013, 2003.

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30 Oct 2003

Two established techniques have been coupled to allow surfaces to be precision engineered. Electrospray ionization to bring large, complex, intact molecular ions into the gas phase has been interfaced with a radio frequency (rf) plasma reactor to treat surfaces making them receptive to the deposition of active biomolecules. The new instrument has been designed and used successfully to deposit a number of high molecular weight molecules including the polysaccharide, sodium hyaluronan (HA), that has an important role in a number of physiological functions. Substrate material is treated using a rf glow discharge plasma chamber, to clean and activate the surface in a controlled manner, then exposed to a beam of multiply charged ions in the gas phase that have been generated using electrospray techniques. The ions are deposited gently onto the substrate and become covalently bound. The molecular integrity and stability of HA surfaces prepared in this way was established using x-ray photoelectron spectroscopy, changes in the observed contact angle, time-of-flight secondary ion mass spectrometry, scanning electron microscopy, and a biological assay–platelet adhesion to the surface.

Inventions

Reactive landing for modification of graphene and other nanocarbon materials

Record of Invention Number: 46967

Tim Elam, Joe Rolfs, Frantisek Turecek, Michael Volny

Disclosure

27 May 2014

Reactive Landing Resistance Biosensors

Record of Invention Number: 45652

Tim Elam, Frantisek Turecek, Michael Volny

Disclosure

8 Jun 2011

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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