Cluster analysis in soft X-ray spectromicroscopy: Finding the patterns in complex specimens

Lerotic, Mirna; Jacobsen, C.; Gillow, J. B.; Francis, A.J.; Wirick, S.; Vogt, Stefan; Mäser, J.

doi:10.1016/j.elspec.2005.01.158

Cited by 92 publications

(80 citation statements)

References 6 publications

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“…The maps in this image stack were then aligned using techniques described in Jacobsen et al (2000), and carbon-XANES spectra were derived for each pixel in the image stack. We used "cluster analysis," described in Lerotic et al (2005), to compare the C-XANES spectra from each pixel in an image stack and to select and identify groups having similar spectra. Improvements to this STXM provided the spatial stability necessary to characterize the carbonaceous grain coatings by X-ray Absorption Near-Edge Structure (XANES) spectroscopy.…”

Section: Analytical Techniquementioning

confidence: 99%

Organic grain coatings in primitive interplanetary dust particles: Implications for grain sticking in the Solar Nebula

2013

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The chondritic porous interplanetary dust particles (CP IDPs), fragments of asteroids and comets collected by NASA high-altitude research aircraft from the Earth's stratosphere, are recognized as the least altered samples of the original dust of the Solar Nebula available for laboratory examination. We performed high-resolution, ∼25 nm/pixel, x-ray imaging and spectroscopy on ultramicrotome sections of CP IDPs, which are aggregates of >10 4 grains, and identified and characterized ∼100 nm thick coatings of organic matter on the surfaces of the individual grains. We estimated the minimum tensile strength of this organic glue to be ∼150 to 325 N/m 2 , comparable to the strength of the weakest cometary meteors, based on the observation that the individual grains of ∼5 μm diameter aggregate CP IDPs are not ejected from the particle by electrostatic repulsion due to charging of these IDPs to 10 to 15 volts at 1 A.U. in space. Since organic coatings can increase the sticking coefficient over that of bare mineral grains, these organic grain coatings are likely to have been a significant aid in grain sticking in the Solar Nebula, allowing the first dust particles to aggregate over a much wider range of collision speeds than for bare mineral grains.

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Section: Analytical Techniquementioning

confidence: 99%

Organic grain coatings in primitive interplanetary dust particles: Implications for grain sticking in the Solar Nebula

2013

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“…After deWning a background correction area (I 0 ) and orthogonalizing and noise-Wltering the data, principal component and cluster analyses (PCA_GUI 1.0, Lerotic et al 2004) were used to identify sample regions with similar spectra. From 2 to 4 components and 20 clusters were used based on the eigenvalues, eigenimages, and eigenspectra (Beauchemin et al 2002;Lerotic et al 2005). The goal was to select components due to systematic variations of spectral signals from pixel to pixel and to discard random Xuctuations of signal beyond which noise eVects will occur.…”

Section: ¡1mentioning

confidence: 99%

Organic matter stabilization in soil microaggregates: implications from spatial heterogeneity of organic carbon contents and carbon forms

2007

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This study investigates the spatial distribution of organic carbon (C) in free stable microaggregates (20-250 m; not encapsulated within macroaggregates) from one Inceptisol and two Oxisols in relation to current theories of the mechanisms of their formation. Two-dimensional micro-and nano-scale observations using synchrotron-based Fourier-transform infrared (FTIR) and near-edge X-ray absorption Wne structure (NEXAFS) spectroscopy yielded maps of the distribution of C amounts and chemical forms. Carbon deposits were unevenly distributed within microaggregates and did not show any discernable gradients between interior and exterior of aggregates. Rather, C deposits appeared to be patchy within the microaggregates. In contrast to the random location of C, there were micronscale patterns in the spatial distribution of aliphatic C-H (2922 cm ). Aliphatic C forms and the ratio of aliphatic C/ aromatic C were positively correlated (r 2 of 0.66-0.75 and 0.27-0.59, respectively) to the amount of O-H on kaolinite surfaces (3695 cm ¡1 ), pointing at a strong role for organomineral interactions in C stabilization within microaggregates and at a possible role for molecules containing aliphatic C-H groups in such interactions. This empirical relationship was supported by nanometer-scale observations using NEXAFS which showed that the organic matter in coatings on mineral surfaces had more aliphatic and carboxylic C with spectral characteristics resembling microbial metabolites than the organic matter of the entire microaggregate. Our observations thus support models of C stabilization in which the initially dominant process is adsorption of organics on mineral surfaces rather than occlusion of organic debris by adhering clay particles.

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“…26 Subsequently, a cluster analysis was performed to classify pixels according to similarities in their spectra. 27 The pixel size used in the image sets was 100 Â 100 nm.…”

Section: Scanning Transmission X-ray Microscopymentioning

confidence: 99%

Styrene oligomerization as a molecular probe reaction for Brønsted acidity at the nanoscale

Aramburo

Wirick

Miedema

et al. 2012

Phys. Chem. Chem. Phys.

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The Brønsted acid-catalyzed oligomerization of 4-fluorostyrene has been studied on a series of H-ZSM-5 zeolite powders, steamed under different conditions, with a combination of UV-Vis micro-spectroscopy and Scanning Transmission X-ray Microscopy (STXM). UV-Vis microspectroscopy and STXM have been used to monitor the relative formation of cyclic and linear dimeric carbocations as a function of the steaming post-treatment (i.e., parent vs. steaming at 600, 700 and 800 1C). It was found that the UV-Vis band intensity ratios of linear to cyclic dimeric species increase from 0.79 (parent H-ZSM-5) over 1.41 (H-ZSM-5 steamed at 600 1C) and 1.88 (H-ZSM-5 steamed at 700 1C) to 2.33 (H-ZSM-5 steamed at 800 1C). STXM confirms this trend in reaction product selectivity, as the relative intensities of the transitions attributed to the presence of the cyclic dimer in the carbon K-edge spectra decrease with increasing severity of the steaming post-treatment. Furthermore, STXM reveals spatial heterogeneities in reaction product formation within the H-ZSM-5 zeolite powders at the nanoscale. More specifically, a shrinking carbon core-shell distribution was detected within the zeolite aggregates, in which the relative amount of cyclic dimeric species is higher in the core relative to the shell of the zeolite aggregate and the relative amount of cyclic dimeric species in the zeolite core gradually decreases with increasing severity of the steaming post-treatment. These differences are rationalized in terms of spatial differences in Brønsted acidity within H-ZSM-5 zeolite powders as well as by changes in the formation process of linear and dimeric carbocations within H-ZSM-5 micro-and mesopores.

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Cluster analysis in soft X-ray spectromicroscopy: Finding the patterns in complex specimens

Cited by 92 publications

References 6 publications

Organic grain coatings in primitive interplanetary dust particles: Implications for grain sticking in the Solar Nebula

Organic grain coatings in primitive interplanetary dust particles: Implications for grain sticking in the Solar Nebula

Organic matter stabilization in soil microaggregates: implications from spatial heterogeneity of organic carbon contents and carbon forms

Styrene oligomerization as a molecular probe reaction for Brønsted acidity at the nanoscale

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