Frank W. DelRio

National Institute of Standards and Technology, GAI, Maryland, United States

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Publications (48)152.33 Total impact

  • Frank W. DelRio, Robert F. Cook, Brad L. Boyce
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    ABSTRACT: Silicon devices are ubiquitous in many micro- and nano-scale technological applications, most notably microelectronics and microelectromechanical systems (MEMS). Despite their widespread usage, however, issues related to uncertain mechanical reliability remain a major factor inhibiting the further advancement of device commercialization. In particular, reliability issues related to the fracture of MEMS components have become increasingly important given continued reductions in critical feature sizes coupled with recent escalations in both MEMS device actuation forces and harsh usage conditions. In this review, the fracture strength of micro- and nano-scale silicon components in the context of MEMS is considered. An overview of the crystal structure and elastic and fracture properties of both single-crystal silicon (SCS) and polycrystalline silicon (polysilicon) is presented. Experimental methods for the deposition of SCS and polysilicon films, fabrication of fracture-strength test components, and analysis of strength data are also summarized. SCS and polysilicon fracture strength results as a function of processing conditions, component size and geometry, and test temperature, environment, and loading rate are then surveyed and analyzed to form overarching processing-structure-property-performance relationships. Future studies are suggested to advance our current view of these relationships and their impacts on the manufacturing yield, device performance, and operational reliability of micro- and nano-scale silicon devices.
    Applied Physics Reviews 06/2015; 2(2):021303. DOI:10.1063/1.4919540
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    ABSTRACT: We present the design and validation of a micromachined gripper array that enables reliable transmission of forces of at least 14 mN. The gripper is constructed with polycrystalline silicon (polysilicon), a brittle material, and is compatible with polysilicon surface micromachining. Two ingressive snap-and-lock array designs are presented. After developing design guidelines, it is shown that the first gripper array is functional. However, a risk remains that the gripper array rather than the tensile bar that it grips in its intended application fails. Therefore, an improved geometry is designed and it is shown that it is robust with respect to failure. Scanning confocal Raman imaging directly confirms that the local peak tensile stresses in the robust gripper array are approximately 50% of the lower bound material strength, and also resolves a 25% stress variation across the array.
    Journal of Micromechanics and Microengineering 01/2015; 25(1). DOI:10.1088/0960-1317/25/1/015009 · 1.73 Impact Factor
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    ABSTRACT: Stress mapping of micromachined polycrystalline silicon devices with components in various levels of uniaxial tension was performed. Confocal Raman microscopy was used to form two-dimensional maps of Raman spectral shifts, which exhibited variations on the scale of the component and on the scale of the microstructure. Finite element analysis models enabled direct comparison of the spatial variation in the measured shifts to that of the predicted stresses. The experimental shifts and model stresses were found to be linearly related in the uniaxial segment, with a proportionality constant in good agreement with calculations based on an opto-mechanical polycrystalline averaging analysis.
    Applied Physics Letters 05/2014; 104(19):191908-191908-5. DOI:10.1063/1.4878616 · 3.52 Impact Factor
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    ABSTRACT: We report a systematic study of the controlled formation of discrete-size gold nanoparticle clusters (GNCs) by interaction with the reducing agent dithiothreitol (DTT). Asymmetric-flow field flow fractionation and electrospray differential mobility analysis were employed complementarily to determine the particle size distributions of DTT-conjugated GNCs (DTT-GNCs). Transmission electron microscopy was used to provide visualization of DTT-GNCs at different states of aggregation. Surface packing density of DTT and the corresponding molecular conformation on the Au surface were characterized by inductively coupled plasma mass spectrometry and X-ray photoelectron spectroscopy. Results show that DTT increases the aggregation rate of gold nanoparticles (AuNPs) up to ≈ 100×. A mixed conformation (i.e., combining vertically aligned, horizontally aligned, and cross-linking modes) exists for DTT on the Au surface for all conditions examined. The primary size of AuNPs, concentration of DTT, and the starting concentration of AuNPs influence the degree of aggregation for DTT-GNCs, indicating the collision frequency, energy barrier, and surface density of DTT are the key factors that control the aggregation rate. DTT-GNCs exhibit improved structural stability compared to the citrate-stabilized GNCs (i.e., unconjugated) following reaction with thiolated polyethylene glycol (SH-PEG), indicating that cross-linking and surface protection by DTT suppresses disaggregation normally induced by the steric repulsion of SH-PEG. This work describes a prototype methodology to form ligand-conjugated GNCs with high quality and well-controlled material properties.
    Langmuir 03/2014; 30(12). DOI:10.1021/la500044y · 4.46 Impact Factor
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    ABSTRACT: The extracellular matrix (ECM) environment plays a critical role in organism development and disease. Surface sensitive microscopy techniques for studying the structural and chemical properties of ECMs are often performed in high vacuum (HV) environments. In this report, we examine the affect HV conditions have on the bioactivity and mechanical properties of type I collagen fibrillar matrices. We find that HV exposure has an unappreciable affect on the cell spreading response and mechanical properties of these collagen fibril matrices. Conversely, low vacuum environments cause fibrils to become mechanically rigid as indicated by force microscopy, resulting in greater cell spreading. Time-of-flight secondary ion mass spectrometry results show no noticeable spectral differences between HV-treated and dehydrated matrices. While previous reports have shown that HV can denature proteins in monolayers, these observations indicate that HV-exposure does not mechanically or biochemically alter collagen in its supramolecular configuration. These results may have implication for complex ECM matrices such as decellularized scaffolds.
    Biointerphases 12/2013; 8(1). DOI:10.1186/1559-4106-8-2 · 2.68 Impact Factor
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    ABSTRACT: The extracellular matrix (ECM) consists of a complex mixture of biochemical and physical stimuli that together regulate cell behavior. In this study, we engineer a model ECM consisting of fibrillar Type-1 collagen plus fibronectin that allows systematic examination of the effects of matrix composition and mechanics on cells. On this combined protein matrix, cells exhibit intermediate degrees of spreading and proliferation compared to their responses on collagen or fibronectin alone. Adhesion to the combination matrix could be blocked by peptides containing the sequence Arginine-Glycine-Aspartic acid (RGD) and by antibodies against a1 integrin, suggesting cell-matrix engagement was mediated by a combination of integrin receptors that recognize fibronectin and collagen. Regardless of integrin engagement, cells were sensitive to the mechanical properties of the combination ECM, suggesting that cells could process biochemical and mechanical cues simultaneously and independently. Biotechnol. Bioeng. © 2013 Wiley Periodicals, Inc.
    Biotechnology and Bioengineering 10/2013; 110(10). DOI:10.1002/bit.24921 · 4.16 Impact Factor
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    ABSTRACT: Frictional properties of native and fibronectin (FN)-functionalized type I collagen (COL) thin films were studied via atomic force microscopy. The COL lateral contact stiffness was dependent only on the hydration state, indicating that shear deformation was invariant with FN. In contrast, the COL coefficient of friction and shear strength varied with both functionalization and hydration state. The changes in shear strength were found to correlate well with changes in mean cell spread area on the same thin films, suggesting that shear strength is a better indicator of cell spreading than heretofore considerations of film, and thus extracellular matrix, stiffness alone.
    Applied Physics Letters 09/2013; 103(14):143703-143703-5. DOI:10.1063/1.4824685 · 3.52 Impact Factor
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    ABSTRACT: A methodology to decouple irregular small-scale roughness and regular long-range features on deep reactive ion etched (DRIE) silicon surfaces is presented. Height-height correlations of three different DRIE silicon surfaces are evaluated via atomic force microscopy height data and fit to an analytic, five-parameter model based on a phenomenological scaling function for the small-scale roughness and a Bessel function for the long-range features. The resulting roughness parameters are constant for all three surfaces at small lateral length scales, indicating self-affine roughness inherent to the DRIE process, but dependent on the etch process at large lateral length scales, increasing by a factor of five as the controlled portion of the DRIE process decreased. The results from the analysis are also compared to fracture strengths from recently introduced “theta” test samples with the same etch features as an example of the potential of the analysis in providing an unbiased assessment of the processing-structure-property relationships for DRIE silicon surfaces.
    Journal of Applied Physics 09/2013; 114(11):113506-113506-6. DOI:10.1063/1.4821899 · 2.19 Impact Factor
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    ABSTRACT: In this study, an electrospray-differential mobility analyzer (ES-DMA) was operated with an aerosol flow-mode, temperature-programmed approach to enhance its ability to characterize the particle size distributions (PSDs) of nanoscale particles (NPs) in the presence of adsorbed and free ligands. Titanium dioxide NPs (TiO2-NPs) stabilized by citric acid (CA) or bovine serum albumin (BSA) were utilized as representative systems. Transmission electron microscopy (TEM) and inductively coupled plasma mass spectrometry were used to provide visual information and elemental-based PSDs, respectively. Results show that the interference resulting from electrospray-dried nonvolatile salt residual nanoscale particles (S-NPs) could be effectively reduced using the thermal treatment process: PSDs were accurately measured at temperatures above 200 °C for CA-stabilized TiO2-NPs and above 400 °C for BSA-stabilized TiO2-NPs. Moreover, TEM confirmed the volumetric shrinkage of S-NPs due to thermal treatment, and also showed that the primary structure of TiO2-NPs was relatively stable over the temperature range studied (i.e., below 700 °C). Conversely, the shape factor for TiO2-NPs decreased after treatment above 500 °C, possibly due to a change in the secondary (aggregate) structure. S-NPs from BSA-stabilized TiO2-NPs exhibited higher global activation energies toward induced volumetric shrinkage than those of CA-stabilized TiO2-NPs, suggesting that activation energy is dependent on ligand size. This prototype study demonstrates the efficacy of using ES-DMA coupled with thermal treatment for characterizing the physical state of NPs, even in a complex medium (e.g., containing plasma proteins) and in the presence of particle agglomerates induced by interaction with binding ligands.
    Langmuir 08/2013; 29(36). DOI:10.1021/la402311c · 4.46 Impact Factor
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    ABSTRACT: A new theta geometry was developed for microscale bending strength measurements. This new “gap” theta specimen was a modification of the arch theta specimen that enabled microscale tensile testing. The gap theta specimen was demonstrated here on single-crystal silicon, microfabricated using two different etch processes. The resulting sample strengths were described by three-parameter Weibull distributions derived from parameters determined using established arch theta strengths, assuming a specimen-geometry and -size invariant flaw distribution and an approximate loading configuration.
    MRS Communications 06/2013; 3(02). DOI:10.1557/mrc.2013.18 · 1.55 Impact Factor
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    ABSTRACT: The etching processes used to produce microelectromechanical systems (MEMS) leave residual surface features that typically limit device strength and, consequently, device lifetime and reliability. In order to optimize MEMS device reliability, it is therefore necessary to determine the effects that these etching processes have on MEMS component strength. The microscale theta specimen, which is shaped like the Greek letter $Theta$, acts as a tensile test specimen when loaded in compression by generating a uniform tensile stress in the central web region of the specimen. Three sets of single-crystal silicon theta specimens are fabricated using two deep reactive ion etching recipes and a temperature-controlled cryogenic plasma etching recipe, each set resulting in a different specimen surface structure. The resulting strength distributions are analyzed in two ways. First, the strength data are fit to a three-parameter Weibull distribution function to determine the lower bound, or threshold strength, of each distribution. Second, the strength data are used in conjunction with various loading schemes to assess their effect on the lifetime spectrum of the device. In both approaches, the theta specimen is used to great effect to gain quantitative insight into the role of etching-induced surface features on the manufacturing yield and operational reliability of MEMS components.$hfill$[2012-0302]
    Journal of Microelectromechanical Systems 06/2013; 22(3):589-602. DOI:10.1109/JMEMS.2012.2234724 · 1.92 Impact Factor
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    ABSTRACT: Microelectromechanical systems are especially sensitive to adhesion as a result of their large surface area-to-volume ratios, small surface separations, and compliant components. Interfacial forces that can contribute to the overall adhesion between micromachined surfaces include van der Waals, capillary meniscus, electrostatic, and solid bridging forces. In this chapter, we focus on van der Waals and capillary meniscus forces between polycrystalline silicon micromachined surfaces and describe a joint experimental-modeling technique that examines in depth when these forces are active and how they change with different processing and environmental conditions. In the experiments, microcantilever test structures were brought into contact with a landing pad in an environmental chamber. Adhesion energies were extracted from measured deflection profiles using finite element analysis. As roughness increased, the adhesion at a given relative humidity (RH) decreased, while the RH at which adhesion abruptly jumped, or the threshold RH, increased. Once the jump occurred, the adhesion increased toward the upper limit of 2γ \cos θ , where γ is the liquid-vapor surface energy and θ is the contact angle. A detailed model based on the topography of the polysilicon surfaces as measured by atomic force microscopy was developed. Below the threshold RH, the adhesion could be modeled with only van der Waals forces active. Above the threshold RH, the adhesion was modeled by assuming that capillary menisci had nucleated. It was found that the effect of asperity plasticity was small while the effects of topographic surface correlations and disjoining pressure were important. Several possible mechanisms that might explain the threshold RH are examined.
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    ABSTRACT: Dithiothreitol (DTT)-based displacement is widely utilized for separating ligands from their gold nanoparticle (AuNP) conjugates, a critical step for differentiating and quantifying surface-bound functional ligands and therefore the effective surface density of these species on nanoparticle-based therapeutics and other functional constructs. The underlying assumption is that DTT is smaller and much more reactive toward gold compared with most ligands of interest, and as a result will reactively displace the ligands from surface sites thereby enabling their quantification. In this study, we use complementary dimensional and spectroscopic methods to characterize the efficiency of DTT displacement. Thiolated methoxypolyethylene glycol (SH-PEG) and bovine serum albumin (BSA) were chosen as representative ligands. Results clearly show that (1) DTT does not completely displace bound SH-PEG or BSA from AuNPs, and (2) the displacement efficiency is dependent on the binding affinity between the ligands and the AuNP surface. Additionally, the displacement efficiency for conjugated SH-PEG is moderately dependent on the molecular mass (yielding efficiencies ranging from 60 to 80 % measured by ATR-FTIR and ≈90 % by ES-DMA), indicating that the displacement efficiency for SH-PEG is predominantly determined by the S-Au bond. BSA is particularly difficult to displace with DTT (i.e., the displacement efficiency is nearly zero) when it is in the so-called normal form. The displacement efficiency for BSA improves to 80 % when it undergoes a conformational change to the expanded form through a process of pH change or treatment with a surfactant. An analysis of the three-component system (SH-PEG + BSA + AuNP) indicates that the presence of SH-PEG decreases the displacement efficiency for BSA, whereas the displacement efficiency for SH-PEG is less impacted by the presence of BSA.
    Analytical and Bioanalytical Chemistry 10/2012; 404(10). DOI:10.1007/s00216-012-6418-4 · 3.58 Impact Factor
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    ABSTRACT: We report on a systematic investigation of molecular conjugation of tumor necrosis factor-α (TNF) protein onto gold nanoparticles (AuNPs) and the subsequent binding behavior to its antibody (anti-TNF). We employ a combination of physical and spectroscopic characterization methods, including electrospray-differential mobility analysis, dynamic light scattering, polyacrylamide gel electrophoresis, attenuated total reflectance-Fourier transform infrared spectroscopy, fluorescence assay, and enzyme-linked immunosorbent assay. The native TNF used in this study exists in the active homotrimer configuration prior to conjugation. After binding to AuNPs, the maximum surface density of TNF is (0.09 ± 0.02) nm(-2) with a binding constant of 3 × 10(6) (mol L(-1))(-1). Dodecyl sulfate ions induce desorption of monomeric TNF from the AuNP surface, indicating a relatively weak intermolecular binding within the AuNP-bound TNF trimers. Anti-TNF binds to both TNF-conjugated and citrate-stabilized AuNPs, showing that non-specific binding is significant. Based on the number of anti-TNF molecules adsorbed, a substantially higher binding affinity was observed for the TNF-conjugated surface. The inclusion of thiolated polyethylene glycol (SH-PEG) on the AuNPs inhibits the binding of anti-TNF, and the amount of inhibition is related to the number ratio of surface bound SH-PEG to TNF and the way in which the ligands are introduced. This study highlights the challenges in quantitatively characterizing complex hybrid nanoscale conjugates, and provides insight on TNF-AuNP formation and activity.
    Nanoscale 04/2012; 4(10):3208-17. DOI:10.1039/c2nr30415e · 6.74 Impact Factor
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    ABSTRACT: A necessary step in advancing the use of polyethylene glycol (PEG) surface coatings in critical biotechnological applications such as cancer treatments is to provide direct and reliable nanoscale property characterization. Measurements for such characterization are currently provided by scanning probe methods, which are capable of assessing heterogeneity of both surface coverage and properties with nanoscale spatial resolution. In particular, atomic force microscopy (AFM) can be used to detect and quantify the heterogeneity of surface coverage, whereas atomic force spectroscopy can be used to determine mechanical properties, thereby revealing possible heterogeneity of properties within coatings. In this work, AFM and force spectroscopy were used to characterize the morphology and mechanical properties of thiol-functionalized PEG surface coatings on flat gold substrates in aqueous PEG solution. Thiol-functionalized PEG offers a direct and simple method of attachment to gold substrates without intermediate anchoring layers and therefore can be exploited in developing PEG-functionalized gold nanoparticles. AFM was used to investigate the morphology of the PEG coatings as a function of molecular weight; the commonly observed coverage was in the form of sparse, brushlike islands. Similarly, force spectroscopy was utilized to study the mechanical properties of the PEG coatings in compression and tension as a function of molecular weight. A constitutive description of the mechanical properties of PEG brushes was achieved through a combinatorial analysis of the statistical responses acquired in both compression and tension tests. Such a statistical characterization provides a straightforward procedure to assess the nanoscale heterogeneity in the morphology and properties of PEG coverage.
    The Journal of Physical Chemistry B 03/2012; 116(10):3138-47. DOI:10.1021/jp211256f · 3.38 Impact Factor
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    ABSTRACT: The stress in silicon surrounding a tungsten-filled through-silicon via (TSV) is measured using confocal Raman microscopy line scans across the TSV both before and after etch removal of an oxide stack used as a mask to define the TSV during fabrication. Stress in the silicon arose in response to both athermal deposition and thermal expansion mismatch effects. The complex three-dimensional stress and strain field in silicon surrounding the TSV is modeled using finite element analysis, taking into account both athermal and thermal effects and the elastic anisotropy of silicon. Comparison of the measurements and model results shows that no one component of the stress tensor correlates with the Raman peak shift generated by the deformed silicon. An analysis is developed to predict the Raman shift in deformed silicon that takes into account all the components of the stress or strain tensor; the results of the model are then used as inputs to the analysis for direct comparison with measured peak shifts as a function of distance from the TSV. Good agreement between the measured and predicted peak shifts is obtained for the case of the intact oxide stack. A discrepancy between the measured and predicted shifts was observed adjacent to the TSV with the oxide stack removed; further modeling suggests the discrepancy is explained by the formation of a small void at the TSV-silicon interface during etching. The combined measurement-modeling approach serves to both validate the model, in this case for TSV design, and to extend the measurement capability of confocal Raman microscopy to complex stress fields.
    Journal of Applied Physics 10/2011; 110(7). DOI:10.1063/1.3644971 · 2.19 Impact Factor
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    ABSTRACT: Single-crystal silicon test specimens, fabricated by lithography and deep reactive ion etching (DRIE), were used to measure microscale deformation and fracture properties. The mechanical properties of two specimen geometries, both in the form of a Greek letter Θ (theta), were measured using an instrumented indentation system. The DRIE process generated two different surface structures leading to two strength distributions that were specimen geometry independent: One distribution, centered about 2.1 GPa, was controlled by 35 nm surface roughness of scallops; the second distribution, centered about 1.4 GPa, was controlled by larger, 150 nm, pitting defects. Finite element analyses (FEA) converted measured loads into strengths; tensile elastic measurements validated the FEA. Fractographic observations verified failure locations. The theta specimen and testing protocols are shown to be extremely effective at testing statistically relevant (hundreds) numbers of samples to establish processing–structure–property relationships at ultrasmall scales and for determining design parameters for components of microelectromechanical systems.
    Journal of Materials Research 10/2011; 26(20):2575-2589. DOI:10.1557/jmr.2011.319 · 1.82 Impact Factor
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    ABSTRACT: Surface-sensitive quantitative studies of competitive molecular adsorption on nanoparticles were conducted using a modified attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy method. Adsorption isotherms for thiolated poly(ethylene glycol) (SH-PEG) on gold nanoparticles (AuNPs) as a function of molecular mass (1, 5, and 20 kDa) were characterized. We find that surface density of SH-PEG on AuNPs is inversely proportional to the molecular mass (M(m)). Equilibrium binding constants for SH-PEG, obtained using the Langmuir adsorption model, show the binding affinity for SH-PEG is proportional to M(m). Simultaneous competitive adsorption between mercaptopropionic acid (MPA) and 5 kDa SH-PEG (SH-PEG5K) was investigated, and we find that MPA concentration is the dominant factor influencing the surface density of both SH-PEG5K and MPA, whereas the concentration of SH-PEG5K affects only SH-PEG5K surface density. Electrospray differential mobility analysis (ES-DMA) was employed as an orthogonal characterization technique. ES-DMA results are consistent with the results obtained by ATR-FTIR, confirming our conclusions about the adsorption process in this system. Ligand displacement competitive adsorption, where the displacing molecular species is added after completion of the ligand surface binding, was also interrogated by ATR-FTIR. Results indicate that for SH-PEG increasing M(m) yields greater stability on AuNPs when measured against displacement by bovine serum albumin (BSA) as a model serum protein. In addition, the binding affinity of BSA to AuNPs is inhibited for SH-PEG conjugated AuNPs, an effect that is enhanced at higher SH-PEG M(m) values.
    Langmuir 08/2011; 27(15):9302-13. DOI:10.1021/la2005425 · 4.46 Impact Factor
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    ABSTRACT: Structure–property relationships for methyl-terminated alkyl self-assembled monolayers (SAMs) are developed using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and atomic force microscopy (AFM). NEXAFS C K-edge spectra are used to compute the dichroic ratio, which provides a quantitative measure of the molecular structure. AFM data are analyzed with an elastic adhesive contact model, modified by a first-order elastic perturbation method to include substrate effects, to extract the monolayer mechanical properties. Using this approach, the measured mechanical properties are not influenced by the substrate, which allows universal structure–property relationships to be developed for methyl-terminated alkyl SAMs.
    Chemical Physics Letters 08/2011; 512(4):243-246. DOI:10.1016/j.cplett.2011.07.045 · 1.99 Impact Factor

Publication Stats

627 Citations
152.33 Total Impact Points

Institutions

  • 2008–2013
    • National Institute of Standards and Technology
      • • Material Measurement Laboratory (MML)
      • • Materials Science and Engineering Division
      GAI, Maryland, United States
    • Sandia National Laboratories
      • Semiconductor Material and Device Sciences Department
      Albuquerque, New Mexico, United States
  • 2007–2008
    • University of California, Berkeley
      Berkeley, California, United States
  • 2005–2007
    • University of Colorado at Boulder
      • Department of Mechanical Engineering (ME)
      Boulder, CO, United States
  • 2005–2006
    • University of Colorado
      • Department of Mechanical Engineering
      Denver, Colorado, United States