Near‐Edge X‐ray Absorption Fine Structure Spectroscopy as a Tool for Investigating Nanomaterials

Hemraj‐Benny, Tirandai; Banerjee, Sarbajit; Sambasivan, Sharadha; Balasubramanian, Mahalingam; Fischer, Daniel A.; Eres, Gyula; Puretzky, Alexander A.; Geohegan, David B.; Lowndes, D. H.; Han, Wei‐Qiang; Misewich, James A.; Wong, Stanislaus S.

doi:10.1002/smll.200500256

Cited by 162 publications

(152 citation statements)

References 45 publications

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“…The dependence of the intensity of the detected spectral features on the orientation of the final state orbital with respect to the electric field vector of the incident photon beam 58 also allows the surface molecular orientation of nanomaterials [59][60][61] and adsorbates 62 to be investigated.…”

Section: Introductionmentioning

confidence: 99%

Quantitative Evaluation of the Carbon Hybridization State by Near Edge X-ray Absorption Fine Structure Spectroscopy

2016

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The characterization of the local bonding configuration of carbon in carbon-based materials is of paramount importance since the properties of such materials strongly depend on the distribution of carbon hybridization states, the local ordering, and the degree of hydrogenation. Carbon 1s near edge X-ray absorption fine structure (NEXAFS) spectroscopy is one of the most powerful techniques for gaining insights into the bonding configuration of near-surface carbon atoms. The common methodology for quantitatively evaluating the carbon hybridization state using C1s NEXAFS measurements, which is based on the analysis of the sample of interest and of a highly ordered pyrolytic graphite (HOPG) reference sample, was reviewed and critically assessed, noting that inconsistencies are found in the literature in applying this method. A theoretical rationale for the specific experimental conditions to be used for the acquisition of HOPG reference spectra is presented together with the potential sources of uncertainty and errors in the correctly computed fraction of sp 2 -bonded carbon. This provides a specific method for analyzing the distribution of carbon hybridization state using NEXAFS spectroscopy. As an illustrative example, a hydrogenated amorphous carbon film was analyzed using this method, and showed good agreement with X-ray photoelectron spectroscopy (which is surface sensitive).Furthermore, the results were consistent with analysis from Raman spectroscopy (which is not surface sensitive), indicating the absence of a structurally different near-surface region in this particular thin film material. The present work can assist surface scientists in the analysis of NEXAFS spectra for the accurate characterization of the structure of carbon-based materials.3

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Section: Introductionmentioning

confidence: 99%

Quantitative Evaluation of the Carbon Hybridization State by Near Edge X-ray Absorption Fine Structure Spectroscopy

2016

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“…In NEXAFS, a plot of the π* intensity in polymers with exposed catechols increases slightly with an increasing incident angle (Fig. 2b), indicating a slightly ordered orientation of aromatic rings on the surface, whereas in polymers with blocked catechols random distribution is evident 25,26 (Fig. 2c).…”

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confidence: 99%

“…2d), suggesting that removal of the silyl groups may enable more catechols to populate the interface. Given the low uncertainty of the NEXAFS measurements, the differences are likely to be significant 25,26 . Consistent with NEXAFS, X-ray photoelectron spectroscopy showed ∼10% decrease in the Si 2p signal following acid treatment ( Supplementary Fig.…”

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confidence: 99%

Surface-initiated self-healing of polymers in aqueous media

et al. 2014

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Polymeric materials that intrinsically heal at damage sites under wet or moist conditions are urgently needed for biomedical and environmental applications [1][2][3][4][5][6] . Although hydrogels with self-mending properties have been engineered by means of mussel-inspired metal-chelating catechol-functionalized polymer networks 7-10 , biological self-healing in wet conditions, as occurs in self-assembled holdfast proteins in mussels and other marine organisms 11,12 , is generally thought to involve more than reversible metal chelates. Here we demonstrate self-mending in metal-free water of synthetic polyacrylate and polymethacrylate materials that are surface-functionalized with mussel-inspired catechols. Wet self-mending of scission in these polymers is initiated and accelerated by hydrogen bonding between interfacial catechol moieties, and consolidated by the recruitment of other non-covalent interactions contributed by subsurface moieties. The repaired and pristine samples show similar mechanical properties, suggesting that the triggering of complete self-healing is enabled underwater by the formation of extensive catechol-mediated interfacial hydrogen bonds.All polymeric materials suffer damage in the course of their functional lifetimes. Few, if any, completely heal at damage sites. Despite recent progress in the design of self-mending polymeric materials based on crack-activated crosslinking 1 , light 2 , heat 3 or other external stimuli 4 , these remain less than perfectly healed, and, in the case of polymers in wet environments, self-healing technologies are even more limited than those engineered for dry conditions. Mussel adhesive holdfasts exhibit significant self-healing capabilities 11,12 , although the molecular mechanisms involved are poorly understood. Notwithstanding this, the selfmending adhesion and cohesion of isolated dopa (3,4-dihydroxyphenyl-L-alanine)-containing adhesive proteins were shown to rely critically on maintaining dopa in an acidic and reducing environment 13,14 . Significantly different conditions are required to recapitulate the self-healing cohesion of tris-dopa-Fe 3+ -mediated complexes in proteins and polymers [7][8][9]15 . Such results increasingly suggest the importance of dopa, but also its subtle and diverse interfacial reactivity vis-à-vis the traditional and still widely held view that dopa, and catechols generally, function primarily as crosslinkers after their 2-electron oxidation to quinones 16 . To better assess the contribution of catechol to polymer selfhealing in a reducing (pH 3), metal-free wet environment, we prepared a material from common, water-insoluble synthetic acrylic polymers having a catechol-functionalized surface. These materials are completely self-healing in a process initiated by catecholmediated interfacial hydrogen bonding, and consolidated by followup interactions (for example, hydrophobic and steric) after a brief compression (∼6 × 10 4 Pa). The crucial and robust roles played by

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“…Near-edge X-ray absorption spectroscopy (XAS) techniques are well established for characterizing element-specific electronic structure with extremely high surface sensitivity, making it an ideal tool for the study of graphene 11 . The peak positions and lineshapes of the observed XAS resonances represent, to first approximation, a replica of the unoccupied atom-projected density of states modified by core-hole interactions.…”

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confidence: 99%

Imaging local electronic corrugations and doped regions in graphene

et al. 2011

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Electronic structure heterogeneities are ubiquitous in two-dimensional graphene and profoundly impact the transport properties of this material. Here we show the mapping of discrete electronic domains within a single graphene sheet using scanning transmission X-ray microscopy in conjunction with ab initio density functional theory calculations. scanning transmission X-ray microscopy imaging provides a wealth of detail regarding the extent to which the unoccupied levels of graphene are modified by corrugation, doping and adventitious impurities, as a result of synthesis and processing. Local electronic corrugations, visualized as distortions of the π*cloud, have been imaged alongside inhomogeneously doped regions characterized by distinctive spectral signatures of altered unoccupied density of states. The combination of density functional theory calculations, scanning transmission X-ray microscopy imaging, and in situ near-edge X-ray absorption fine structure spectroscopy experiments also provide resolution of a longstanding debate in the literature regarding the spectral assignments of pre-edge and interlayer states.

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Near‐Edge X‐ray Absorption Fine Structure Spectroscopy as a Tool for Investigating Nanomaterials

Cited by 162 publications

References 45 publications

Quantitative Evaluation of the Carbon Hybridization State by Near Edge X-ray Absorption Fine Structure Spectroscopy

Quantitative Evaluation of the Carbon Hybridization State by Near Edge X-ray Absorption Fine Structure Spectroscopy

Surface-initiated self-healing of polymers in aqueous media

Imaging local electronic corrugations and doped regions in graphene

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