Publications (16)56.44 Total impact
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Article: Characterization of composition C4 explosives using time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy.
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ABSTRACT: The application of surface analytical techniques such as time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) is explored as a means of differentiating between composition C4 plastic explosives (C-4). Three different C-4 samples including U.S. military grade C-4, commercial C-4 (also from the United States), and C-4 from England (PE-4) were obtained and analyzed using both ToF-SIMS and XPS. ToF-SIMS was able to successfully discriminate between different C-4 samples with the aid of principal component analysis, a multivariate statistical analysis approach often used to reduce the dimensionality of complex data. ToF-SIMS imaging was also used to obtain information about the spatial distribution of the various additives contained within the samples. The results indicated that the samples could potentially be characterized by their 2-D chemical and morphological structure, which varied from sample to sample. XPS analysis also showed significant variation between samples, with changes in the atomic concentrations, as well as changes in the shapes of the high-resolution C 1s and O 1s spectra. These results clearly demonstrate the feasibility of utilizing both ToF-SIMS and XPS as tools for the direct characterization and differentiation of C-4 samples for forensic applications.Analytical Chemistry 09/2010; 82(17):7237-48. · 5.86 Impact Factor -
Article: Investigation of Damage Mechanisms in PMMA during ToF-SIMS Depth Profiling with 5 and 8 keV SF5+ Primary Ions
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ABSTRACT: Cluster secondary ion mass spectrometry (cluster SIMS) has been proven to be a useful technique for the surface and in-depth characterization of molecular films. In this study, an SF5+ polyatomic primary ion source is utilized for depth profiling in poly(methyl methacrylate) (PMMA) bulk and thin films (200 nm). The effects of SF5+ ion beam energy are discussed in detail. Both 5 and 8 keV ion beam energies are utilized for depth profiling experiments, where the chemistry of sputtering is investigated using surface analytical tools such as X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) in conjunction with SIMS. Thin film depth profiles acquired with 5 keV SF5+ display evidence of significant damage accumulation at the interface in the form of a highly cross-linked polymer gel. There is very little evidence of similar damage accumulation at the interface for the corresponding 8 keV SF5+depth profile. AFM and XPS analysis of the sputtered crater bottoms also indicates that very different chemistries and morphologies are present at the interface when employing 5 keV vs 8 keV SF5+. For PMMA bulk samples, greater erosion depths were achieved when employing higher beam energies, similar to what has been observed previously with C60n+ depth profiling.(1) These increased erosion depths are attributed to the increased sputter rates of the PMMA at 8 keV SF5+ as compared to 5 keV SF5+, thus allowing for increased amounts of material to be removed prior to the approach of the gel point of the PMMA (dose at which a 3-D cross-linked structure is formed). Despite these increased erosion depths, the 8 keV SF5+ beam imparts greater initial structural damage, as indicated by decreased C═O contents in the C1s XPS spectra and increased amounts of graphitic type peaks in the corresponding SIMS spectra. Overall, the results indicate that, for thicker samples, one should employ higher beam energies for optimum results. However, for thinner films, in which the gel effect does not play a significant role, lower beam energies are preferred.08/2010; -
Article: Fluorinated copolymer nanoparticles for multimodal imaging applications.
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ABSTRACT: Nanomaterials have emerged as valuable tools in biomedical imaging techniques. Here, the synthesis and characterization of a novel fluorinated nanoparticle with potential applications as an MRI contrast agent is reported. Particles were synthesized using a free radical polymerization technique. Secondary ion mass spectrometry analysis showed that the particles' surface contained fluorinated groups and nitrogen-containing groups. Solid-state NMR spectroscopy suggested the presence of two distinct fluorine resonances, which conforms to the structure of the fluorinated monomer. Ongoing studies aim to evaluate the performance of the nanoparticles as MRI contrast agents both in vitro and in vivo.Macromolecular Rapid Communications 01/2010; 31(1):87-92. · 4.60 Impact Factor -
Article: Three-dimensional time-of-flight secondary ion mass spectrometry imaging of a pharmaceutical in a coronary stent coating as a function of elution time.
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ABSTRACT: Three-dimensional (3D) chemical images reveal the surface and subsurface distribution of pharmaceutical molecules in a coronary stent coating and are used to visualize the drug distribution as a function of elution time. The coronary stent coating consists of 25% (w/w) sirolimus in a poly(lactic-co-glycolic acid) (PLGA) matrix and is spray-coated onto metal coupons. Information regarding the 3D distribution of sirolimus in PLGA as a function of elution time was obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS) imaging using a Au(+) ion beam for analysis in conjunction with a C(60)(+) ion beam for sputter depth profiling. The examined formulation is shown to have large areas of the surface as well as subsurface channels that are composed primarily of the drug, followed by a drug-depleted region, and finally, a relatively homogeneous dispersion of the drug in the polymer matrix. Elution is shown to occur from the drug-enriched surface region on a relatively short time scale and more gradually from the subsurface regions of homogeneously dispersed drug. Bulk composition was also probed by X-ray photoelectron spectroscopy (XPS) depth profiling and confocal Raman imaging, the results of which substantiate the TOF-SIMS 3D images. Finally, the effectiveness of a C(60)(+) ion beam for use in 3D characterization of organic systems is demonstrated against another polyatomic ion source (e.g., SF(5)(+)).Analytical Chemistry 11/2009; 81(24):9930-40. · 5.86 Impact Factor -
Article: Phase separation at the surface of poly(ethylene oxide)-containing biodegradable poly(L-lactic acid) blends.
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ABSTRACT: The surface chemistry and in-depth distribution of the composition of a poly(ethylene oxide) (PEO)-containing biodegradable poly(L-lactic acid) (PLLA) blend matrix system have been investigated using X-ray photoelectron spectroscopy (XPS). This study reports detailed quantitative compositional information using a novel numerical method for determining depth profiles. The PEO system studied is an amphiphilic Pluronic P104 surfactant, PEO-b-poly(propylene oxide) (PPO)-b-PEO. The extent of phase separation is analyzed by determining the surface enrichment of the PEO component via measurement of chemical composition at the polymer-air interface. For this blend system, the combination of the PPO component in the Pluronic surfactants drives the formation of a surface excess of Pluronic in the blends with PLLA. The surface excess profile shows a rapid increase in Pluronic surface composition versus bulk Pluronic mass fractions of 1-5%, but the profile levels off above bulk Pluronic mass fractions of 5%.Langmuir 09/2009; 25(19):11467-71. · 4.19 Impact Factor -
Article: Cluster secondary ion mass spectrometry of polymers and related materials.
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ABSTRACT: Cluster secondary ion mass spectrometry (cluster SIMS) has played a critical role in the characterization of polymeric materials over the last decade, allowing for the ability to obtain spatially resolved surface and in-depth molecular information from many polymer systems. With the advent of new molecular sources such as C(60)(+), Au(3)(+), SF(5)(+), and Bi(3)(+), there are considerable increases in secondary ion signal as compared to more conventional atomic beams (Ar(+), Cs(+), or Ga(+)). In addition, compositional depth profiling in organic and polymeric systems is now feasible, without the rapid signal decay that is typically observed under atomic bombardment. The premise behind the success of cluster SIMS is that compared to atomic beams, polyatomic beams tend to cause surface-localized damage with rapid sputter removal rates, resulting in a system at equilibrium, where the damage created is rapidly removed before it can accumulate. Though this may be partly true, there are actually much more complex chemistries occurring under polyatomic bombardment of organic and polymeric materials, which need to be considered and discussed to better understand and define the important parameters for successful depth profiling. The following presents a review of the current literature on polymer analysis using cluster beams. This review will focus on the surface and in-depth characterization of polymer samples with cluster sources, but will also discuss the characterization of other relevant organic materials, and basic polymer radiation chemistry.Mass Spectrometry Reviews 06/2009; 29(2):247-93. · 10.46 Impact Factor -
Article: Three-dimensional compositional analysis of drug eluting stent coatings using cluster secondary ion mass spectrometry.
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ABSTRACT: Cluster secondary ion mass spectrometry (cluster SIMS) employing an SF5+ polyatomic primary ion sputter source in conjunction with a Bi3+ analysis source was used to obtain three-dimensional molecular information in polymeric-based drug-eluting stent coatings. The formulations of the coatings varied from 0% to 50% (w/w) sirolimus drug in poly(lactic-co-glycolic acid) and were prepared on both MP35N metal alloy coupons and bare metal stents. All cluster SIMS depth profiles obtained indicated a drug-enriched surface region, followed by a drug-depletion region, and finally a constant bulk composition region, similar to previous data obtained in polymeric blend systems. The drug overlayer thickness was determined to increase with increasing sirolimus content. Sample temperature was determined to play an important role in the resulting depth profiles, where it was shown that the best profiles were obtained at low temperatures (-100 degrees C). At these temperatures, molecular signals typically remained constant through the entire depth of the film (approximately 6.5 microm) in some cases, as opposed to the typical 1 microm-2 microm depth limit, which is achievable at room temperature. The 3-D imaging capabilities of cluster SIMS were successfully demonstrated and indicated a significant amount of subsurface domain formation in the 25% and 50% sirolimus samples, but not in the 5% sample, which was homogeneous. These results clearly illustrate the utility of cluster SIMS for probing the 3-D structure in polymeric-based drug delivery devices.Analytical Chemistry 03/2008; 80(3):624-32. · 5.86 Impact Factor -
Article: Temperature-Controlled Depth Profiling of Poly(methyl methacrylate) Using Cluster Secondary Ion Mass Spectrometry. 2. Investigation of Sputter-Induced Topography, Chemical Damage, and Depolymerization Effects
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ABSTRACT: Poly(methyl methacrylate) (PMMA) thin films (150 nm) on silicon were bombarded with SF5+ polyatomic primary ion projectiles at −75 °C, 25 °C, and 125 °C. The crater bottoms were then characterized using a combination of atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS). AFM results indicated increased sputter-induced topography formation in the order of −75 °C < 125 °C < 25 °C, consistent with earlier SIMS depth profile results which illustrated optimum depth profile characteristics at low temperatures and less favorable characteristics at room temperature.1 XPS results indicated that there was a significant amount of C remaining at the crater bottom at 25 °C, suggesting that there is a large amount of organic material remaining despite the loss in characteristic PMMA secondary ion signal in the SIMS depth profile. Specifically, C/Si ratios increased in the following order: −75 °C < 125 °C < 25 °C, consistent with the trend in topography observed in the AFM results. High-resolution C(1s) spectra of the PMMA film indicated a decrease in the O−CO component with sputtering at both −75 °C and 25 °C. However, there was very little change in the C(1s) spectra in samples sputtered at 125 °C. This was determined to be a result of ion-induced depolymerization which is expected to occur at higher temperatures in PMMA. Residual gas analysis (RGA) gave results that were consistent with this hypothesis, showing increased amounts of PMMA monomer at higher temperatures. Principle components analysis (PCA) of SIMS spectra showed increased PMMA secondary ion intensities coupled with increased O signal in PMMA sputtered at 125 °C. Conversely, SIMS spectra acquired in the sputtered PMMA at −75 °C, and to a smaller degree at 25 °C, showed increased C signals, decreased O intensities, and the appearance of peaks indicative of polycyclic aromatic hydrocarbons, all consistent with increased chemical damage. Overall, these results indicate that while there is increased damage occurring at −75 °C, there is still a significant improvement in the depth profile characteristics. It is concluded that the enhancement in low-temperature depth profiles in PMMA results mainly from the changes in the physical properties of the PMMA at low temperatures, yielding a significant reduction in sputter-induced topgraphy.12/2006; -
Article: Temperature-Controlled Depth Profiling of Poly(methyl methacrylate) Using Cluster Secondary Ion Mass Spectrometry. 1. Investigation of Depth Profile Characteristics
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ABSTRACT: Secondary ion mass spectrometry employing an SF5+ polyatomic primary ion source was used to depth profile poly(methyl methacrylate) (PMMA) at a series of temperatures ranging from −75 °C to 125 °C, where the primary glass transition for PMMA occurs at 105 °C. The depth profile characteristics (e.g., interface widths, sputter rates, damage accumulation factors, normalized intensities, and overall secondary ion stability or constancy) were monitored as a function of temperature. It was found that, at low temperatures, the quality of the depth profiles improved considerably, having decreased damage accumulation, higher normalized intensities, and decreased interface widths, particularly at −75 °C. Higher temperatures were correlated with increased sputter rates. However, the improvements in interfacial widths and decreased damage accumulation were not as prevalent as observed at low temperatures. The importance of glass transition temperature (Tg) on the depth profile characteristics was also apparent. The resulting PMMA depth profile characteristics were compared with that of poly(lactic acid) (PLA), considered to be one of the more successful cases of polymer depth profiling (very low damage accumulation, high sputter rates, small interface widths). The measured interface widths and damage accumulation factors in PMMA characterized at low temperatures were comparable to PLA at room temperature. These results indicate that temperature is an important parameter in the sputtering of polymeric materials and should be optimized.12/2006; -
Article: Characterization of gunpowder samples using time-of-flight secondary ion mass spectrometry (TOF-SIMS).
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ABSTRACT: Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was utilized to obtain characteristic mass spectra from three different smokeless powders and six different black powder samples. In these mass spectra, peaks indicative of both the organic and inorganic additive constituents in the gunpowders were observed. TOF-SIMS was able to successfully differentiate between the different black and smokeless gunpowder samples analyzed with the aid of principal components analysis (PCA), a multivariate statistical analysis approach often used to reduce the dimensionality of complex data. TOF-SIMS was also used to obtain information about the spatial distribution of the various additives contained within the gunpowder samples. SIMS imaging demonstrated that that the samples could potentially be characterized by their 2-D structure, which varied from sample to sample. These results clearly demonstrate the feasibility of utilizing TOF-SIMS as a tool for the characterization and differentiation of gunpowder samples for general forensic applications.Forensic Science International 05/2006; 158(1):39-51. · 2.30 Impact Factor -
Article: Investigating activated sludge flocs using microanalytical techniques: demonstration of environmental scanning electron microscopy and time-of-flight secondary ion mass spectrometry for wastewater applications.
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ABSTRACT: Environmental scanning electron microscopy (ESEM) with an energy-dispersive X-ray spectrometer (EDS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were demonstrated to be useful analytical tools for investigating surface and bulk components of individual floc particles from both full- and bench-scale activated sludge systems. Detailed surface imaging of various hydrated biological floc particles by ESEM revealed substantial differences in surface features between treatment systems, while EDS identified spatial differences in the iron and the aluminum distributions. The ToF-SIMS spectra had signature fragments of protein and polysaccharide material from the floc surface, suggesting that this technique is capable of surface profiling extracellular polymeric substances. Principal-component analysis of the positive ion ToF-SIMS spectra from the mixed-liquor-suspended solid (MLSS) samples and reference aquatic organic materials found slight differences between the full- and bench-scale MLSS surface properties but substantial differences among MLSS and treated effluent from the same facility.Water Environment Research 05/2006; 78(4):381-91. · 0.88 Impact Factor -
Article: Cellular response to phase-separated blends of tyrosine-derived polycarbonates.
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ABSTRACT: Two-dimensional thin films consisting of homopolymer and discrete compositional blends of tyrosine-derived polycarbonates were prepared and characterized in an effort to elucidate the nature of different cell responses that were measured in vitro. The structurally similar blends were found to phase separate after annealing with domain sizes dependent on the overall composition. The thin polymer films were characterized with the use of atomic force microscopy (AFM), water contact angles, and time-of-flight secondary ion mass spectrometry (TOF-SIMS) and significant changes in roughness were measured following the annealing process. Genetic expression profiles of interleukin-1beta and fibronectin in MC3T3-E1 osteoblasts and RAW 264.7 murine macrophages were measured at several time points, demonstrating the time and composition-dependent nature of the cell responses. Real-time reverse transcriptase polymerase chain reaction (RT-PCR) depicted upregulation of the fibronectin gene copy numbers in each of the blends relative to the homopolymers. Moreover, the interleukin-1beta expression profile was found to be compositionally dependent. The data suggest strongly that optimal composition and processing conditions can significantly affect the acute inflammatory and extracellular matrix production responses.Journal of Biomedical Materials Research Part A 04/2006; 76(3):491-502. · 2.63 Impact Factor -
Article: Depth profiling of poly(L-lactic acid)/triblock copolymer blends with time-of-flight secondary ion mass spectrometry.
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ABSTRACT: Time-of-flight secondary ion mass spectrometry employing an SF5+ polyatomic primary ion source was utilized to obtain a series of in-depth profiles from PLLA/Pluronic-P104 (poly(ethylene oxide-co-propylene oxide) triblock copolymer) blends in attempts to quantify the in-depth surface segregated Pluronic region. The resultant in-depth profiles were consistent with theoretical models describing the surface segregated region in polymeric blends and copolymer systems, with a surface enriched Pluronic-P104 region, followed by a P104 depletion layer, and finally a constant composition bulk region. These results were consistent over a range of concentrations (1-25%). The depth profiles obtained using cluster SIMS were compared to information obtained using X-ray photoelectron spectroscopy. The results demonstrate that, with cluster primary ion bombardment, we are for the first time able to quantify the polymeric composition as a function of depth within certain multicomponent polymer blends. This success can be attributed to the sputter characteristics of polyatomic primary ion bombardment (SF5+) as compared to monatomic primary ion beams.Analytical Chemistry 07/2005; 77(11):3570-8. · 5.86 Impact Factor -
Article: Depth Profiling of Poly(l-lactic acid)/Triblock Copolymer Blends with Time-of-Flight Secondary Ion Mass Spectrometry
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ABSTRACT: Time-of-flight secondary ion mass spectrometry employing an SF5+ polyatomic primary ion source was utilized to obtain a series of in-depth profiles from PLLA/Pluronic-P104 (poly(ethylene oxide-co-propylene oxide) triblock copolymer) blends in attempts to quantify the in-depth surface segregated Pluronic region. The resultant in-depth profiles were consistent with theoretical models describing the surface segregated region in polymeric blends and copolymer systems, with a surface enriched Pluronic-P104 region, followed by a P104 depletion layer, and finally a constant composition bulk region. These results were consistent over a range of concentrations (1−25%). The depth profiles obtained using cluster SIMS were compared to information obtained using X-ray photoelectron spectroscopy. The results demonstrate that, with cluster primary ion bombardment, we are for the first time able to quantify the polymeric composition as a function of depth within certain multicomponent polymer blends. This success can be attributed to the sputter characteristics of polyatomic primary ion bombardment (SF5+) as compared to monatomic primary ion beams.04/2005; -
Article: Depth profiling of 4-acetamindophenol-doped poly(lactic acid) films using cluster secondary ion mass spectrometry.
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ABSTRACT: The feasibility of using cluster secondary ion mass spectrometry for depth profiling of drug delivery systems is explored. The behavior of various biodegradable polymer films under dynamic SF(5)(+) primary ion bombardment was investigated, including several films doped with model drugs. The SF(5)(+) depth profiles obtained from these biodegradable polymer films showed very little degradation in secondary ion signal as a function of increasing primary ion dose, and it was discovered that the characteristic ion signals for the polymers remained constant for ion doses up to approximately 5 x 10(15) ions/cm(2). These results suggest that the polyester structure of the biodegradable polymers studied here allows for a greater ability to depth profile due to ease of main chain scission. Attempts were also made to depth profile through a series of poly(lactic acid) (PLA) films containing varying concentrations of the drug 4-acetamidophenol. The depth profiles obtained from these films show very little decrease in both the 4-acetamidophenol molecular ion and PLA fragment ion signals as a function of increasing SF(5)(+) primary ion dose. Similar results were obtained with theophylline-doped PLA films. These results show that, in some drug delivery devices, it is possible to monitor the distribution of a drug as a function of depth by using cluster primary ion beams.Analytical Chemistry 07/2004; 76(11):3199-207. · 5.86 Impact Factor -
Article: Performance of a C60+ ion source on a dynamic SIMS instrument
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ABSTRACT: An IonOptika1 C60+ ion source has been fitted onto a CAMECA1 ims-4f. Stable ion beams of C60+ and C602+ have been obtained with typical currents approaching 20 nA under conditions that allow for several days of source operation. The beam has been able to be focussed into a spot size of ∼3 μm with an anode voltage of 10 keV and scanning ion images have been acquired. We have performed analyses to characterize the performance of C60+ and C602+. Depth profiles of a Cr–Ni multi-layer and polymer films with C60+ have produced excellent results. We have discovered that, under bombardment energies of <12 keV on Si, C60+ will sputter material from the sample but will also produce deposition at a rate that exceeds the sputter rate. The performance of the source and our experiences with its operation will be discussed and some characteristic analysis data will be shown.Applied Surface Science 252(19):7312-7314. · 2.10 Impact Factor
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Institutions
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2004–2009
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National Institute of Standards and Technology
Gaithersburg, MD, USA
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