Methods in carbon K-edge NEXAFS: Experiment and analysis

Watts, Benjamin; Thomsen, Lars; Dastoor, Paul C.

doi:10.1016/j.elspec.2005.11.006

Cited by 159 publications

(128 citation statements)

References 20 publications

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“…Normalization was performed using reference scans from a clean Si(100) surface together with the flux signal from a 50% transmissive gold grid placed upstream of the sample. 44 We note that at high photon intensity the triethylenediamine-dosed Si(100) surface was susceptible to beam-induced changes in surface composition. However, we were able to strongly limit the deleterious effects of the photon beam on our sample by reducing the intensity of the beam.…”

Section: Experimental and Computational Methodsmentioning

confidence: 99%

Adsorption and Dissociation of a Bicyclic Tertiary Diamine, Triethylenediamine, on a Si(100)-2 × 1 Surface

et al. 2016

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This study investigates the adsorption and thermal transformations of a bicyclic tertiary amine, triethylenediamine, on the clean Si(100)-2 × 1 surface. Below room temperature, triethylenediamine adsorption leads to the formation of a strong dative bond between one of the nitrogen atoms of this compound and the silicon surface. In contrast to previously studied amines, the datively adsorbed triethylenediamine features a second tertiary amine entity that is not bonded to the surface, with a lone pair orbital that is directed away from the surface and is available for further reactions. The thermal chemistry and electronic properties of triethylenediamine on silicon are studied using thermal desorption spectroscopy, infrared spectroscopy, and Xray photoelectron spectroscopy. Near-edge X-ray absorption fine structure measurements are utilized to clarify the geometry of the adsorbates at room temperature. Density functional theory calculations are used to describe the binding geometry and electronic properties of the resulting surface species and the likely reaction paths at elevated temperatures.

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Section: Experimental and Computational Methodsmentioning

confidence: 99%

Adsorption and Dissociation of a Bicyclic Tertiary Diamine, Triethylenediamine, on a Si(100)-2 × 1 Surface

et al. 2016

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“…TEY was measured by monitoring the drain current to the sample, PEY was measured with a channeltron detector with a retarding voltage of ≈200 V, and FY was measured by a multichannel plate detector with a retarding field of 2600 V. Dark levels were measured and subtracted from the data, and double normalization was done using a gold mesh corrected by a www.afm-journal.de www.MaterialsViews.com photodiode. [83] Peak fitting and tilt angle calculations were done using the Quick AS NEXAFS Tool. [84] All tilt angles are calculated from a peak fit of structure at lower energies than 286 eV, which is in the π* manifold, corresponding to transition dipole moments normal to the face of a conjugated core, along the direction of the carbon π orbitals.…”

Section: Field-effect Transistor Fabrication and Characterizationmentioning

confidence: 99%

High‐Mobility Naphthalene Diimide and Selenophene‐Vinylene‐Selenophene‐Based Conjugated Polymer: n‐Channel Organic Field‐Effect Transistors and Structure–Property Relationship

Sung

Luzio

Park

et al. 2016

Adv Funct Materials

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Interdependence of chemical structure, thin-film morphology, and transport properties is a key, yet often elusive aspect characterizing the design and development of high-mobility, solution-processed polymers for large-area and flexible electronics applications. There is a specific need to achieve >1 cm 2 V −1 s −1 field-effect mobilities (μ) at low processing temperatures in combination with environmental stability, especially in the case of electron-transporting polymers, which are still lagging behind hole transporting materials. Here, the synthesis of a naphthalene-diimide based donor-acceptor copolymer characterized by a selenophene vinylene selenophene donor moiety is reported. Optimized field-effect transistors show maximum μ of 2.4 cm 2 V −1 s −1 and promising ambient stability. A very marked film structural evolution is revealed with increasing annealing temperature, with evidence of a remarkable 3D crystallinity above 180 °C. Conversely, transport properties are found to be substantially optimized at 150 °C, with limited gain at higher temperature. This discrepancy is rationalized by the presence of a surface-segregated prevalently edge-on packed polymer phase, dominating the device accumulated channel. This study therefore serves the purpose of presenting a promising, high-electron-mobility copolymer that is processable at relatively low temperatures, and of clearly highlighting the necessity of specifically investigating channel morphology in assessing the structure-property nexus in semiconducting polymer thin films.

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“…This can lead to significant errors when analyzing elements that are simultaneously present in multiple layers. In particular, for carbon-based materials previously exposed to air, their carbon K-edge NEXAFS spectra, even when corrected using any of the approaches outlined by Watts et al 52 , are a convolution of the spectrum of the sample of interest and the spectrum of the adventitious carbon contamination on its surface since the thickness of the latter (typically <2 nm 55 ) is smaller than the information depth at the carbon K-edge ( Figure 1). While the thickness of the adventitious carbon contamination has been shown to depend on the sample preparation procedure and history 55,56 , no comprehensive characterization of its composition and structure has yet been published.…”

Section: Introductionmentioning

confidence: 99%

“…While the approaches outlined by Watts et al are effective for addressing the issues commonly encountered in the evaluation of NEXAFS data 52 , the corrected spectra they yield represent the photo-absorption spectra of the specimens under the assumption of structural and compositional homogeneity within the nanometer-scale depth probed by NEXAFS spectroscopy. For electron yield NEXAFS spectroscopy of low-Z elements, the information depth (the specimen thickness measured normal to the surface from which a specified percentage of typically 95% of the detected signal originates) is usually less than 5 nm 1 .…”

Section: Introductionmentioning

confidence: 99%

“…One key set of challenges derive from the presence of artifacts in the as-collected experimental data caused by the adventitious carbon contamination (subsequently modified by X-ray exposure) of X-ray optics in synchrotron beamlines 52 . Recently, Watts et al reviewed and implemented the numerous methods of calibration, normalization, and artifact removal for NEXAFS spectra (with a particular focus upon carbon K-edge spectra) reported in the literature 52 .…”

Section: Introductionmentioning

confidence: 99%

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Accounting for Nanometer-Thick Adventitious Carbon Contamination in X-ray Absorption Spectra of Carbon-Based Materials

et al. 2014

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Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is a powerful technique for characterizing the composition and bonding state of nanoscale materials and the top few nanometers of bulk and thin film specimens. When coupled with imaging methods like photoemission electron microscopy, it enables chemical imaging of materials with nanometerscale lateral spatial resolution. However, analysis of NEXAFS spectra is often performed under the assumption of structural and compositional homogeneity within the nanometer-scale depth probed by this technique. This assumption can introduce large errors when analyzing the vast majority of solid surfaces due to the presence of complex surface and near-surface structures such as oxides and contamination layers. An analytical methodology is presented for removing the contribution of these nanoscale overlayers from NEXAFS spectra of two-layered systems to provide a corrected photo-absorption spectrum of the substrate. This method relies on the subtraction of the NEXAFS spectrum of the overlayer adsorbed on a reference surface from the spectrum of the two-layer system under investigation, where the thickness of the overlayer is independently determined by X-ray photoelectron spectroscopy (XPS). This approach is applied to NEXAFS data acquired for one of the most challenging cases: air-exposed hard carbon-based materials with adventitious carbon contamination from ambient exposure. The contribution of the adventitious carbon was removed from the as-acquired spectra of ultrananocrystalline diamond (UNCD) and hydrogenated amorphous carbon (a-C:H) to determine the intrinsic photoabsorption NEXAFS spectra of these materials. The method alters the calculated fraction of sp 2 -hybridized carbon from 5 to 20%, and reveals that the adventitious contamination can be

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Methods in carbon K-edge NEXAFS: Experiment and analysis

Cited by 159 publications

References 20 publications

Adsorption and Dissociation of a Bicyclic Tertiary Diamine, Triethylenediamine, on a Si(100)-2 × 1 Surface

Adsorption and Dissociation of a Bicyclic Tertiary Diamine, Triethylenediamine, on a Si(100)-2 × 1 Surface

High‐Mobility Naphthalene Diimide and Selenophene‐Vinylene‐Selenophene‐Based Conjugated Polymer: n‐Channel Organic Field‐Effect Transistors and Structure–Property Relationship

Accounting for Nanometer-Thick Adventitious Carbon Contamination in X-ray Absorption Spectra of Carbon-Based Materials

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