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Daniel Fischer

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Nadine Gergel-Hackett

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D. Yogi Y Goswami

University of South Florida

Barbara Vercelli

Consiglio Nazionale delle Ricerche (CNR)

Gildênia Moura de Araújo Almeida

Daiana Capdevila

Indiana University

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Papers by Daniel Fischer

Electrical and Physical Characterization of Bilayer Carboxylic Acid Functionalized Molecular Layers

Journal of Physical Chemistry C, Jan 30, 2013

We have used flip chip lamination (FCL) to form monolayer and bilayer molecular junctions of carb... more We have used flip chip lamination (FCL) to form monolayer and bilayer molecular junctions of carboxylic acidcontaining molecules with Cu atom incorporation. Carboxylic acid-terminated monolayers are self-assembled onto ultrasmooth Au by using thiol chemistry and grafted onto n-type Si. Prior to junction formation, monolayers are physically characterized by using polarized infrared absorption spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy, confirming the molecular quality and functional group termination. FCL was used to form monolayer junctions onto H-terminated Si or bilayer junctions of carboxylic acid monolayers on Au and Si. From the electrical measurements, we find that the current through the junction is attenuated as the effective molecular length within the junction increases, indicating that molecules are electrically active within the junction. We find that the electronic transport through the bilayer junction saturates at very thick effective distances possibly because of another electron-transport mechanism that is not nonresonant tunneling as a result of trapped defects or sequential tunneling. In addition, bilayer junctions are fabricated with and without Cu atoms, and we find that the electron transport is not distinguishably different when Cu atoms are within the bilayer.

Investigation of BARC-Resist Interfacial Interactions

With the increasing drive towards smaller feature sizes in integrated circuits and the consequent... more With the increasing drive towards smaller feature sizes in integrated circuits and the consequent use of shorter exposure wavelengths, the imaging resist layer and underlying bottom anti-reflective coating (BARC) layer are becoming thinner. At this scale, the performance of chemically amplified resists can be adversely affected by the BARC-resist interfacial interactions. These interactions can cause distortion of resist profiles and lead to footing, undercut, or pattern collapse. -BARC components can immensely influence the deprotection and dissolution properties of the resist. A thorough understanding of the physico-chemical interactions at these interfaces is essential to design and develop new material platforms with minimal adverse interactions and maximum compatibility between BARC and resist. Results are reported from studies of (A) surface versus bulk chemistry of BARC materials as a function of cure temperature, (B) the dependence of the thickness and composition of the res...

Core level spectroscopies locate hydrogen in the proton transfer pathway – identifying quasi-symmetrical hydrogen bonds in the solid state

Physical Chemistry Chemical Physics, 2020

Snapshots of hydrogen locations between non-ionic and ionic states with XPS reveal hydrogen centr... more

Origins of Diamond Surface Noise Probed by Correlating Single-Spin Measurements with Surface Spectroscopy

Physical Review X, 2019

Blade Coating Aligned, High-Performance, Semiconducting-Polymer Transistors

Chemistry of Materials, 2018

Recent demonstration of mobilities in excess of 10 cm 2 V-1 s-1 have energized research in soluti... more Recent demonstration of mobilities in excess of 10 cm 2 V-1 s-1 have energized research in solution deposition of polymers for thin film transistor applications. Due to the lamella motif of most soluble, semiconducting polymers, the local mobility is intrinsically anisotropic. Therefore, fabrication of aligned films is of interest for optimization of device performance. Many techniques have been developed to control film alignment, including solution deposition via directed flows and deposition on topologically structured substrates. We report device and detailed structural analysis (ultraviolet-visible absorption, IR absorption, near-edge X-ray absorption (NEXAFS), grazing incidence X-ray diffraction, and atomic force microscopy) results from blade coating two high performing semiconducting polymers on unpatterned and nanostructured substrates. Blade coating exhibits two distinct operational regimes: the Landau-Levich or horizontal dip coating regime and the evaporative regime. We find that in the evaporative deposition regime, aligned films are produced on unpatterned substrates with the polymer chain director perpendicular to the coating direction. Both NEXAFS and device measurements indicate the coating induced orientation is nucleated at the air interface. Nanostructured substrates produce anisotropic bottom contact devices with the polymer chain at the buried interface oriented along the direction of the substrate grooves, independent of coating regime and coating direction. Real time studies of film drying establish that alignment occurs at extremely high volume-fraction conditions, suggesting mediation via a lyotropic phase. In all cases, the final films appear to exhibit high degrees of crystalline order. The independent control of alignment at the air and substrate interfaces via coating conditions and substrate treatment, respectively, enable detailed assessment of structure-function relationships that suggest the improved performance of the nanostructure aligned films arise from alignment of the less ordered material in the crystallite interphase regions.

Evolution of redox couples in Li- and Mn-rich cathode materials and mitigation of voltage fade by reducing oxygen release

Nature Energy, 2018

Voltage fade is a major problem in battery applications for high-energy lithium-and manganese-ric... more Voltage fade is a major problem in battery applications for high-energy lithium-and manganese-rich (LMR) layered materials. As a result of the complexity of the LMR structure, the voltage fade mechanism is not well understood. Here we conduct both in situ and ex situ studies on a typical LMR material (Li 1.2 Ni 0.15 Co 0.1 Mn 0.55 O 2) during charge-discharge cycling, using multi-lengthscale X-ray spectroscopic and three-dimensional electron microscopic imaging techniques. Through probing from the surface to the bulk, and from individual to whole ensembles of particles, we show that the average valence state of each type of transition metal cation is continuously reduced, which is attributed to oxygen release from the LMR material. Such reductions activate the lower-voltage Mn 3+ /Mn 4+ and Co 2+ /Co 3+ redox couples in addition to the original redox couples including Ni 2+ /Ni 3+ , Ni 3+ /Ni 4+ and O 2− /O − , directly leading to the voltage fade. We also show that the oxygen release causes microstructural defects such as the formation of large pores within particles, which also contributes to the voltage fade. Surface coating and modification methods are suggested to be effective in suppressing the voltage fade through reducing the oxygen release.

Strain and bond length dynamics upon growth and transfer of graphene by NEXAFS spectroscopy from first principles and experiment

Langmuir : the ACS journal of surfaces and colloids, Jan 29, 2017

As the quest towards novel materials proceeds, improved characterization technologies are needed.... more As the quest towards novel materials proceeds, improved characterization technologies are needed. In particular, the atomic thickness in graphene and other 2D materials renders some conventional technologies obsolete. Characterization technologies at wafer levels are needed with enough sensitivity to detect strain in order to inform fabrication. In this work, NEXAFS spectroscopy was combined with simulations to predict lattice parameters of graphene grown on copper and further transferred to a variety of substrates. The strains associated with the predicted lattice parameters are in agreement with experimental findings. The approach presented here holds promise to effectively measure strain in graphene and other 2D systems at wafer levels to inform manufacturing environments.

Monitoring Deformation in Graphene Through Hyperspectral Synchrotron Spectroscopy to Inform Fabrication

The Journal of Physical Chemistry C, 2017

The promise from graphene to produce devices with high mobilities and detectors with fast respons... more The promise from graphene to produce devices with high mobilities and detectors with fast response times is truncated in practice by strain and deformation originating during growth and subsequent processing. This work describes effects from graphene growth, multiple layer transfer, and substrate termination on out of plane deformation, critical to device performance. Synchrotron spectroscopy data was acquired with a state-of-the-art hyperspectral large-area detector to describe growth and processing with molecular sensitivity at wafer lengthscales. A study of methodologies used in data analysis discouraged dichroic ratio approaches in favor of orbital vector approximations and data mining algorithms. Orbital vector methods provide a physical insight into mobility-detrimental rippling by identifying ripple frequency as main actor, rather than intensity; which was confirmed by data mining algorithms, and in good agreement with electron scattering theories of corrugation in graphene. This work paves the way to efficient information from mechanical properties in graphene in a high throughput mode throughout growth and processing in a Materials by Design approach.

NEXAFS Chemical State and Bond Lengths of p-Aminobenzoic Acid in Solution and Solid State

Journal of Physics: Conference Series, 2016

Solid-state and solution pH-dependent NEXAFS studies allow direct observation of the electronic s... more Solid-state and solution pH-dependent NEXAFS studies allow direct observation of the electronic state of para-aminobenzoic acid (PABA) as a function of its chemical environment, revealing the chemical state and bonding of the chemical species. Variations in the ionization potential (IP) and 1s→p* resonances unequivocally identify the chemical species (neutral, cationic, or anionic) present and the varying local environment. Shifts in s* shape resonances relative to the IP in the NEXAFS spectra vary with C-N bond length, and the important effect of minor alterations in bond length is confirmed with nitrogen FEFF calculations, leading to the possibility of bond length determination in solution.

Roles of surface chemistry and structural defects of activated carbons in the oxidative desulfurization of benzothiophenes

Fuel, 2016

A range of different activated carbons was characterized and evaluated for promotion of the oxida... more A range of different activated carbons was characterized and evaluated for promotion of the oxidative desulfurization (ODS) of JP-8 fuel using H 2 O 2 oxidant and acetic acid. Wood-based carbons activated by acid treatment showed much higher effectiveness than all other carbon types, regardless of source or activation method. Under identical test conditions designed to differentiate material performance, the most effective carbon material yielded 69% oxidation of 2,3-dimethylbenzothiophene (2,3-DMBT) whereas the ineffective materials scarcely out-performed the control (10% oxidation). To understand the characteristics most associated with reaction promotion, the textural, chemical, and defect features of the carbon materials were examined using a battery of

Prestrain relaxation in non-covalently modified ethylene-vinyl acetate | PyChol | multiwall carbon nanotube nanocomposites

APL Materials, 2014

Effects of aging on chemical structure and molecular dynamic behaviour of strained thermally acti... more Effects of aging on chemical structure and molecular dynamic behaviour of strained thermally active ethylene-vinyl acetate | multiwall carbon nanotube (EVA|MWCNT) composites were investigated by spectroscopy and microscopy techniques. Aged composites showed spatial inhomogeneity due to system relaxation. Inhomogeneity is attributed to segregation of non-covalently linked cholestryl 1-pyrenecarboxylate, acting as MWCNT dispersant and polymer compatibilizer. Analysis of molecular interplay between filler and matrix upon in situ temperature variation showed a lack of synchronicity, which had been observed in fresh composites. Reduced synchronous interplay allowed quantification of degraded π-π interactions, promoting PyChol unlatching as a result of both sonication and strained-derived π-π degradation.

High-resolution X-ray emission spectroscopy with transition-edge sensors: present performance and future potential

Journal of Synchrotron Radiation, 2015

X-ray emission spectroscopy (XES) is a powerful element-selective tool to analyze the oxidation s... more X-ray emission spectroscopy (XES) is a powerful element-selective tool to analyze the oxidation states of atoms in complex compounds, determine their electronic configuration, and identify unknown compounds in challenging environments. Until now the low efficiency of wavelength-dispersive X-ray spectrometer technology has limited the use of XES, especially in combination with weaker laboratory X-ray sources. More efficient energy-dispersive detectors have either insufficient energy resolution because of the statistical limits described by Fano or too low counting rates to be of practical use. This paper updates an approach to high-resolution X-ray emission spectroscopy that uses a microcalorimeter detector array of superconducting transition-edge sensors (TESs). TES arrays are discussed and compared with conventional methods, and shown under which circumstances they are superior. It is also shown that a TES array can be integrated into a table-top time-resolved X-ray source and a so...

Fluorescence yield near edge spectroscopy of π-bonded CO on Fe(100)

Surface Science, 1989

Utilizing Near Edge X-ray Absorption Fine Structure to Probe Interfacial Issues in Photolithography

ACS Symposium Series, 2004

Control of the shape, critical dimension (CD), and roughness is critical for the fabrication of s... more Control of the shape, critical dimension (CD), and roughness is critical for the fabrication of sub 100 nm features, where the CD and roughness budget are approaching the molecular dimension of the resist polymers 1. Here we utilize near edge X-ray absorption fine structure (NEXAFS) to provide detailed chemical insight into two interfacial problems facing sub-100 nm patterning. First, chemically amplified photoresists are prone to surface phenomenon, which causes deviations in the pattern profile near the interface. Striking examples include T-topping, closure, footing, and undercutting. NEXAFS was used to illustrate that the surface extent of deprotection in a model resist film can be different than the bulk deprotection. Second, line edge roughness becomes increasingly critical with shrinking patterns, and may be intimately related to the line edge deprotection profile. A NEXAFS technique to surface depth profile for compositional gradients is described with the potential to provide detailed chemical information about the resist line edge.

Probing surface and bulk chemistry in resist films using near edge x-ray absorption fine structure

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2002

The performance of chemically amplified photoresists is extremely sensitive to interfacial and su... more The performance of chemically amplified photoresists is extremely sensitive to interfacial and surface phenomena, which cause deviations in the pattern profile near an interface. Striking examples include T-topping or closure near the air/resist interface and footing or undercutting near the resist/substrate interface. One focus of our research is to identify mechanisms that cause lithographic patterns to deviate near interfaces. Near edge x-ray absorption fine structure (NEXAFS) is a powerful tool that can be developed and adapted to probe for detailed chemical information near lithographically relevant interfaces. NEXAFS showed that our model resist films exhibited significant surface segregation of the photo acid generator (PAG) at the air interface. The PAG surface mole fraction was 20–70 times greater than the bulk mole fraction and the amount of surface segregation was dependent on the polarity of the polymer. NEXAFS also revealed that the PAG surface fraction was reduced afte...

Conservation of artists' acrylic emulsion paints: XPS, NEXAFS and ATR‐FTIR studies of wet cleaning methods

Surface and Interface Analysis, 2014

Works of art prepared with acrylic emulsion paints became commercially available in the 1960s. It... more Works of art prepared with acrylic emulsion paints became commercially available in the 1960s. It is increasingly necessary to undertake and optimise cleaning and preventative conservation treatments to ensure their longevity. Model artists' acrylic paint films covered with artificial soiling were thus prepared on a canvas support and exposed to a variety of wet cleaning treatments based on aqueous or hydrocarbon solvent systems. This included some with additives such as chelating agents and/or surfactants, and microemulsion systems made specifically for conservation practice. The impact of cleaning (soiling removal) on the paint film surface was examined visually and correlated with results of attenuated total reflection Fourier transform infrared, XPS and near-edge X-ray absorption fine structure analysesthree spectroscopic techniques with increasing surface sensitivity ranging from approximately À 1000, 10 and 5 nm, respectively. Visual analysis established the relative cleaning efficacy of the wet cleaning treatments in line with previous results. X-ray spectroscopy analysis provided significant additional findings, including evidence for (i) surfactant extraction following aqueous swabbing, (ii) modifications to pigment following cleaning and (iii) cleaning system residues.

Ordering in Poly (3-alkylthiophene) Thin Films Determined with Polarized Optical Spectroscopies

We measured the molecular order of poly(3-alkylthiophene) chains in thin films before and after m... more We measured the molecular order of poly(3-alkylthiophene) chains in thin films before and after melting through the combination of several polarized photon spectroscopies: infrared (IR) absorption, variable angle spectroscopic ellipsometry (SE), and near-edge X-ray absorption fine structure (NEXAFS). The data from the various techniques can be uniformly treated in the context of the dielectric constant tensor for the film. The combined spectroscopies allow determination of the orientation distribution of the main-chain axis (SE and IR), the conjugated π system normal (NEXAFS), and the side-chain axis (IR). We find significant improvement in the backbone order of the films after recrystallization of the material at temperatures just below the melting temperature. Less aggressive thermal treatments are less effective. IR studies show that the changes in backbone structure occur without significant alteration of the structure of the alkyl side chains. The data indicate that the side chains exhibit significant disorder for all films regardless of the thermal history of the sample.

Spectromicroscopy of Poly(ethylene terephthalate): Comparison of Spectra and Radiation Damage Rates in X-ray Absorption and Electron Energy Loss

The Journal of Physical Chemistry B, 1997

The C 1s and O 1s X-ray absorption spectra of poly(ethylene terephthalate) (PET) have been record... more The C 1s and O 1s X-ray absorption spectra of poly(ethylene terephthalate) (PET) have been recorded using transmission, fluorescence, and electron yield detection. The corresponding electron energy loss spectra (EELS) have been recorded in a scanning transmission electron microscope. These results are compared to the C 1s and O 1s spectra of gas phase 1,4-dimethyl terephthalate (the monomer of PET) recorded using EELS. The comparison of monomer and polymer materials in different phases and with different techniques has aided the understanding of the relative strengths and limitations of each technique as well as assisting the spectral interpretation. Good agreement is found in the overall shape and the energies of the spectral features. Relatively minor differences in intensities can be understood in terms of the properties of the individual spectroscopic techniques. The critical dose for radiation damage by 100 keV electrons incident on PET at 100 K is found to be (1.45 (0.15) × 10 3 eV nm-3. In contrast, the critical dose for radiation damage by 302 eV X-rays incident on PET at 300 K is (1.2 (0.6) × 10 4 eV nm-3. A figure of merit involving the product of critical energy dose and spectral efficiency (as expressed by the appropriate G value) is developed. This indicates that, for near-edge studies involving a 20 eV spectral width, there is ∼500-fold advantage of X-ray absorption studies on room temperature PET relative to electron energy loss studies of cooled PET.

Hydrogen-induced CO displacement from the Pt(111) surface: an isothermal kinetic study

Surface Science, 1991

Chemisorbed CO can be completely removed from the Pt(ll1) surface in the temperature range 318 to... more Chemisorbed CO can be completely removed from the Pt(ll1) surface in the temperature range 318 to 348 K for hydrogen pressures above 2 X lo-' Torr. Thermal desorption of CO in this temperature range in the absence of hydrogen removes only a fraction of the adsorbed CO. A series of in situ isothermal kinetic experiments are presented in this paper which show that CO displacement in the presence of 0.2 Torr of hydrogen is a first-order process in CO coverage with an activation energy of 10.9 kcal/mol. We propose that the origin of this effect is that repulsive intereactions between coadsorbed atomic hydrogen and carbon monoxide induce high desorption rates of CO characteristic of high CO coverages, presumably due to lower values of the desorption activation energy. The importance of these results is to show that high coverages of coadsorbed hydrogen resulting from substantial overpressures of Ha may substantially modify desorption activation energies, and thus the coverages and kinetic pathways available, even for strongly chemisorbed species. These phenomena may play an important role in surface reactions which occur at high pressure.

Separation of Recollision Mechanisms in Nonsequential Strong Field Double Ionization of Ar: The Role of Excitation Tunneling

Physical Review Letters, 2001

Vector momentum distributions of two electrons created in double ionization of Ar by 25 fs, 0.25 ... more Vector momentum distributions of two electrons created in double ionization of Ar by 25 fs, 0.25 PW͞cm 2 laser pulses at 795 nm have been measured using a "reaction microscope." At this intensity, where nonsequential ionization dominates, distinct correlation patterns are observed in the two-electron momentum distributions. A kinematical analysis of these spectra within the classical "recollision model" revealed an ͑e, 2e͒-like process and excitation with subsequent tunneling of the second electron as two different ionization mechanisms. This allows a qualitative separation of the two mechanisms demonstrating that excitation-tunneling is the dominant contribution to the total double ionization yield.

Electrical and Physical Characterization of Bilayer Carboxylic Acid Functionalized Molecular Layers

Journal of Physical Chemistry C, Jan 30, 2013

We have used flip chip lamination (FCL) to form monolayer and bilayer molecular junctions of carb... more We have used flip chip lamination (FCL) to form monolayer and bilayer molecular junctions of carboxylic acidcontaining molecules with Cu atom incorporation. Carboxylic acid-terminated monolayers are self-assembled onto ultrasmooth Au by using thiol chemistry and grafted onto n-type Si. Prior to junction formation, monolayers are physically characterized by using polarized infrared absorption spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy, confirming the molecular quality and functional group termination. FCL was used to form monolayer junctions onto H-terminated Si or bilayer junctions of carboxylic acid monolayers on Au and Si. From the electrical measurements, we find that the current through the junction is attenuated as the effective molecular length within the junction increases, indicating that molecules are electrically active within the junction. We find that the electronic transport through the bilayer junction saturates at very thick effective distances possibly because of another electron-transport mechanism that is not nonresonant tunneling as a result of trapped defects or sequential tunneling. In addition, bilayer junctions are fabricated with and without Cu atoms, and we find that the electron transport is not distinguishably different when Cu atoms are within the bilayer.

Investigation of BARC-Resist Interfacial Interactions

With the increasing drive towards smaller feature sizes in integrated circuits and the consequent... more With the increasing drive towards smaller feature sizes in integrated circuits and the consequent use of shorter exposure wavelengths, the imaging resist layer and underlying bottom anti-reflective coating (BARC) layer are becoming thinner. At this scale, the performance of chemically amplified resists can be adversely affected by the BARC-resist interfacial interactions. These interactions can cause distortion of resist profiles and lead to footing, undercut, or pattern collapse. -BARC components can immensely influence the deprotection and dissolution properties of the resist. A thorough understanding of the physico-chemical interactions at these interfaces is essential to design and develop new material platforms with minimal adverse interactions and maximum compatibility between BARC and resist. Results are reported from studies of (A) surface versus bulk chemistry of BARC materials as a function of cure temperature, (B) the dependence of the thickness and composition of the res...

Core level spectroscopies locate hydrogen in the proton transfer pathway – identifying quasi-symmetrical hydrogen bonds in the solid state

Physical Chemistry Chemical Physics, 2020

Snapshots of hydrogen locations between non-ionic and ionic states with XPS reveal hydrogen centr... more

Origins of Diamond Surface Noise Probed by Correlating Single-Spin Measurements with Surface Spectroscopy

Physical Review X, 2019

Blade Coating Aligned, High-Performance, Semiconducting-Polymer Transistors

Chemistry of Materials, 2018

Recent demonstration of mobilities in excess of 10 cm 2 V-1 s-1 have energized research in soluti... more Recent demonstration of mobilities in excess of 10 cm 2 V-1 s-1 have energized research in solution deposition of polymers for thin film transistor applications. Due to the lamella motif of most soluble, semiconducting polymers, the local mobility is intrinsically anisotropic. Therefore, fabrication of aligned films is of interest for optimization of device performance. Many techniques have been developed to control film alignment, including solution deposition via directed flows and deposition on topologically structured substrates. We report device and detailed structural analysis (ultraviolet-visible absorption, IR absorption, near-edge X-ray absorption (NEXAFS), grazing incidence X-ray diffraction, and atomic force microscopy) results from blade coating two high performing semiconducting polymers on unpatterned and nanostructured substrates. Blade coating exhibits two distinct operational regimes: the Landau-Levich or horizontal dip coating regime and the evaporative regime. We find that in the evaporative deposition regime, aligned films are produced on unpatterned substrates with the polymer chain director perpendicular to the coating direction. Both NEXAFS and device measurements indicate the coating induced orientation is nucleated at the air interface. Nanostructured substrates produce anisotropic bottom contact devices with the polymer chain at the buried interface oriented along the direction of the substrate grooves, independent of coating regime and coating direction. Real time studies of film drying establish that alignment occurs at extremely high volume-fraction conditions, suggesting mediation via a lyotropic phase. In all cases, the final films appear to exhibit high degrees of crystalline order. The independent control of alignment at the air and substrate interfaces via coating conditions and substrate treatment, respectively, enable detailed assessment of structure-function relationships that suggest the improved performance of the nanostructure aligned films arise from alignment of the less ordered material in the crystallite interphase regions.

Evolution of redox couples in Li- and Mn-rich cathode materials and mitigation of voltage fade by reducing oxygen release

Nature Energy, 2018

Voltage fade is a major problem in battery applications for high-energy lithium-and manganese-ric... more Voltage fade is a major problem in battery applications for high-energy lithium-and manganese-rich (LMR) layered materials. As a result of the complexity of the LMR structure, the voltage fade mechanism is not well understood. Here we conduct both in situ and ex situ studies on a typical LMR material (Li 1.2 Ni 0.15 Co 0.1 Mn 0.55 O 2) during charge-discharge cycling, using multi-lengthscale X-ray spectroscopic and three-dimensional electron microscopic imaging techniques. Through probing from the surface to the bulk, and from individual to whole ensembles of particles, we show that the average valence state of each type of transition metal cation is continuously reduced, which is attributed to oxygen release from the LMR material. Such reductions activate the lower-voltage Mn 3+ /Mn 4+ and Co 2+ /Co 3+ redox couples in addition to the original redox couples including Ni 2+ /Ni 3+ , Ni 3+ /Ni 4+ and O 2− /O − , directly leading to the voltage fade. We also show that the oxygen release causes microstructural defects such as the formation of large pores within particles, which also contributes to the voltage fade. Surface coating and modification methods are suggested to be effective in suppressing the voltage fade through reducing the oxygen release.

Strain and bond length dynamics upon growth and transfer of graphene by NEXAFS spectroscopy from first principles and experiment

Langmuir : the ACS journal of surfaces and colloids, Jan 29, 2017

As the quest towards novel materials proceeds, improved characterization technologies are needed.... more As the quest towards novel materials proceeds, improved characterization technologies are needed. In particular, the atomic thickness in graphene and other 2D materials renders some conventional technologies obsolete. Characterization technologies at wafer levels are needed with enough sensitivity to detect strain in order to inform fabrication. In this work, NEXAFS spectroscopy was combined with simulations to predict lattice parameters of graphene grown on copper and further transferred to a variety of substrates. The strains associated with the predicted lattice parameters are in agreement with experimental findings. The approach presented here holds promise to effectively measure strain in graphene and other 2D systems at wafer levels to inform manufacturing environments.

Monitoring Deformation in Graphene Through Hyperspectral Synchrotron Spectroscopy to Inform Fabrication

The Journal of Physical Chemistry C, 2017

The promise from graphene to produce devices with high mobilities and detectors with fast respons... more The promise from graphene to produce devices with high mobilities and detectors with fast response times is truncated in practice by strain and deformation originating during growth and subsequent processing. This work describes effects from graphene growth, multiple layer transfer, and substrate termination on out of plane deformation, critical to device performance. Synchrotron spectroscopy data was acquired with a state-of-the-art hyperspectral large-area detector to describe growth and processing with molecular sensitivity at wafer lengthscales. A study of methodologies used in data analysis discouraged dichroic ratio approaches in favor of orbital vector approximations and data mining algorithms. Orbital vector methods provide a physical insight into mobility-detrimental rippling by identifying ripple frequency as main actor, rather than intensity; which was confirmed by data mining algorithms, and in good agreement with electron scattering theories of corrugation in graphene. This work paves the way to efficient information from mechanical properties in graphene in a high throughput mode throughout growth and processing in a Materials by Design approach.

NEXAFS Chemical State and Bond Lengths of p-Aminobenzoic Acid in Solution and Solid State

Journal of Physics: Conference Series, 2016

Solid-state and solution pH-dependent NEXAFS studies allow direct observation of the electronic s... more Solid-state and solution pH-dependent NEXAFS studies allow direct observation of the electronic state of para-aminobenzoic acid (PABA) as a function of its chemical environment, revealing the chemical state and bonding of the chemical species. Variations in the ionization potential (IP) and 1s→p* resonances unequivocally identify the chemical species (neutral, cationic, or anionic) present and the varying local environment. Shifts in s* shape resonances relative to the IP in the NEXAFS spectra vary with C-N bond length, and the important effect of minor alterations in bond length is confirmed with nitrogen FEFF calculations, leading to the possibility of bond length determination in solution.

Roles of surface chemistry and structural defects of activated carbons in the oxidative desulfurization of benzothiophenes

Fuel, 2016

A range of different activated carbons was characterized and evaluated for promotion of the oxida... more A range of different activated carbons was characterized and evaluated for promotion of the oxidative desulfurization (ODS) of JP-8 fuel using H 2 O 2 oxidant and acetic acid. Wood-based carbons activated by acid treatment showed much higher effectiveness than all other carbon types, regardless of source or activation method. Under identical test conditions designed to differentiate material performance, the most effective carbon material yielded 69% oxidation of 2,3-dimethylbenzothiophene (2,3-DMBT) whereas the ineffective materials scarcely out-performed the control (10% oxidation). To understand the characteristics most associated with reaction promotion, the textural, chemical, and defect features of the carbon materials were examined using a battery of

Prestrain relaxation in non-covalently modified ethylene-vinyl acetate | PyChol | multiwall carbon nanotube nanocomposites

APL Materials, 2014

Effects of aging on chemical structure and molecular dynamic behaviour of strained thermally acti... more Effects of aging on chemical structure and molecular dynamic behaviour of strained thermally active ethylene-vinyl acetate | multiwall carbon nanotube (EVA|MWCNT) composites were investigated by spectroscopy and microscopy techniques. Aged composites showed spatial inhomogeneity due to system relaxation. Inhomogeneity is attributed to segregation of non-covalently linked cholestryl 1-pyrenecarboxylate, acting as MWCNT dispersant and polymer compatibilizer. Analysis of molecular interplay between filler and matrix upon in situ temperature variation showed a lack of synchronicity, which had been observed in fresh composites. Reduced synchronous interplay allowed quantification of degraded π-π interactions, promoting PyChol unlatching as a result of both sonication and strained-derived π-π degradation.

High-resolution X-ray emission spectroscopy with transition-edge sensors: present performance and future potential

Journal of Synchrotron Radiation, 2015

X-ray emission spectroscopy (XES) is a powerful element-selective tool to analyze the oxidation s... more X-ray emission spectroscopy (XES) is a powerful element-selective tool to analyze the oxidation states of atoms in complex compounds, determine their electronic configuration, and identify unknown compounds in challenging environments. Until now the low efficiency of wavelength-dispersive X-ray spectrometer technology has limited the use of XES, especially in combination with weaker laboratory X-ray sources. More efficient energy-dispersive detectors have either insufficient energy resolution because of the statistical limits described by Fano or too low counting rates to be of practical use. This paper updates an approach to high-resolution X-ray emission spectroscopy that uses a microcalorimeter detector array of superconducting transition-edge sensors (TESs). TES arrays are discussed and compared with conventional methods, and shown under which circumstances they are superior. It is also shown that a TES array can be integrated into a table-top time-resolved X-ray source and a so...

Fluorescence yield near edge spectroscopy of π-bonded CO on Fe(100)

Surface Science, 1989

Utilizing Near Edge X-ray Absorption Fine Structure to Probe Interfacial Issues in Photolithography

ACS Symposium Series, 2004

Control of the shape, critical dimension (CD), and roughness is critical for the fabrication of s... more Control of the shape, critical dimension (CD), and roughness is critical for the fabrication of sub 100 nm features, where the CD and roughness budget are approaching the molecular dimension of the resist polymers 1. Here we utilize near edge X-ray absorption fine structure (NEXAFS) to provide detailed chemical insight into two interfacial problems facing sub-100 nm patterning. First, chemically amplified photoresists are prone to surface phenomenon, which causes deviations in the pattern profile near the interface. Striking examples include T-topping, closure, footing, and undercutting. NEXAFS was used to illustrate that the surface extent of deprotection in a model resist film can be different than the bulk deprotection. Second, line edge roughness becomes increasingly critical with shrinking patterns, and may be intimately related to the line edge deprotection profile. A NEXAFS technique to surface depth profile for compositional gradients is described with the potential to provide detailed chemical information about the resist line edge.

Probing surface and bulk chemistry in resist films using near edge x-ray absorption fine structure

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, 2002

The performance of chemically amplified photoresists is extremely sensitive to interfacial and su... more The performance of chemically amplified photoresists is extremely sensitive to interfacial and surface phenomena, which cause deviations in the pattern profile near an interface. Striking examples include T-topping or closure near the air/resist interface and footing or undercutting near the resist/substrate interface. One focus of our research is to identify mechanisms that cause lithographic patterns to deviate near interfaces. Near edge x-ray absorption fine structure (NEXAFS) is a powerful tool that can be developed and adapted to probe for detailed chemical information near lithographically relevant interfaces. NEXAFS showed that our model resist films exhibited significant surface segregation of the photo acid generator (PAG) at the air interface. The PAG surface mole fraction was 20–70 times greater than the bulk mole fraction and the amount of surface segregation was dependent on the polarity of the polymer. NEXAFS also revealed that the PAG surface fraction was reduced afte...

Conservation of artists' acrylic emulsion paints: XPS, NEXAFS and ATR‐FTIR studies of wet cleaning methods

Surface and Interface Analysis, 2014

Works of art prepared with acrylic emulsion paints became commercially available in the 1960s. It... more Works of art prepared with acrylic emulsion paints became commercially available in the 1960s. It is increasingly necessary to undertake and optimise cleaning and preventative conservation treatments to ensure their longevity. Model artists' acrylic paint films covered with artificial soiling were thus prepared on a canvas support and exposed to a variety of wet cleaning treatments based on aqueous or hydrocarbon solvent systems. This included some with additives such as chelating agents and/or surfactants, and microemulsion systems made specifically for conservation practice. The impact of cleaning (soiling removal) on the paint film surface was examined visually and correlated with results of attenuated total reflection Fourier transform infrared, XPS and near-edge X-ray absorption fine structure analysesthree spectroscopic techniques with increasing surface sensitivity ranging from approximately À 1000, 10 and 5 nm, respectively. Visual analysis established the relative cleaning efficacy of the wet cleaning treatments in line with previous results. X-ray spectroscopy analysis provided significant additional findings, including evidence for (i) surfactant extraction following aqueous swabbing, (ii) modifications to pigment following cleaning and (iii) cleaning system residues.

Ordering in Poly (3-alkylthiophene) Thin Films Determined with Polarized Optical Spectroscopies

We measured the molecular order of poly(3-alkylthiophene) chains in thin films before and after m... more We measured the molecular order of poly(3-alkylthiophene) chains in thin films before and after melting through the combination of several polarized photon spectroscopies: infrared (IR) absorption, variable angle spectroscopic ellipsometry (SE), and near-edge X-ray absorption fine structure (NEXAFS). The data from the various techniques can be uniformly treated in the context of the dielectric constant tensor for the film. The combined spectroscopies allow determination of the orientation distribution of the main-chain axis (SE and IR), the conjugated π system normal (NEXAFS), and the side-chain axis (IR). We find significant improvement in the backbone order of the films after recrystallization of the material at temperatures just below the melting temperature. Less aggressive thermal treatments are less effective. IR studies show that the changes in backbone structure occur without significant alteration of the structure of the alkyl side chains. The data indicate that the side chains exhibit significant disorder for all films regardless of the thermal history of the sample.

Spectromicroscopy of Poly(ethylene terephthalate): Comparison of Spectra and Radiation Damage Rates in X-ray Absorption and Electron Energy Loss

The Journal of Physical Chemistry B, 1997

The C 1s and O 1s X-ray absorption spectra of poly(ethylene terephthalate) (PET) have been record... more The C 1s and O 1s X-ray absorption spectra of poly(ethylene terephthalate) (PET) have been recorded using transmission, fluorescence, and electron yield detection. The corresponding electron energy loss spectra (EELS) have been recorded in a scanning transmission electron microscope. These results are compared to the C 1s and O 1s spectra of gas phase 1,4-dimethyl terephthalate (the monomer of PET) recorded using EELS. The comparison of monomer and polymer materials in different phases and with different techniques has aided the understanding of the relative strengths and limitations of each technique as well as assisting the spectral interpretation. Good agreement is found in the overall shape and the energies of the spectral features. Relatively minor differences in intensities can be understood in terms of the properties of the individual spectroscopic techniques. The critical dose for radiation damage by 100 keV electrons incident on PET at 100 K is found to be (1.45 (0.15) × 10 3 eV nm-3. In contrast, the critical dose for radiation damage by 302 eV X-rays incident on PET at 300 K is (1.2 (0.6) × 10 4 eV nm-3. A figure of merit involving the product of critical energy dose and spectral efficiency (as expressed by the appropriate G value) is developed. This indicates that, for near-edge studies involving a 20 eV spectral width, there is ∼500-fold advantage of X-ray absorption studies on room temperature PET relative to electron energy loss studies of cooled PET.

Hydrogen-induced CO displacement from the Pt(111) surface: an isothermal kinetic study

Surface Science, 1991

Chemisorbed CO can be completely removed from the Pt(ll1) surface in the temperature range 318 to... more Chemisorbed CO can be completely removed from the Pt(ll1) surface in the temperature range 318 to 348 K for hydrogen pressures above 2 X lo-' Torr. Thermal desorption of CO in this temperature range in the absence of hydrogen removes only a fraction of the adsorbed CO. A series of in situ isothermal kinetic experiments are presented in this paper which show that CO displacement in the presence of 0.2 Torr of hydrogen is a first-order process in CO coverage with an activation energy of 10.9 kcal/mol. We propose that the origin of this effect is that repulsive intereactions between coadsorbed atomic hydrogen and carbon monoxide induce high desorption rates of CO characteristic of high CO coverages, presumably due to lower values of the desorption activation energy. The importance of these results is to show that high coverages of coadsorbed hydrogen resulting from substantial overpressures of Ha may substantially modify desorption activation energies, and thus the coverages and kinetic pathways available, even for strongly chemisorbed species. These phenomena may play an important role in surface reactions which occur at high pressure.

Separation of Recollision Mechanisms in Nonsequential Strong Field Double Ionization of Ar: The Role of Excitation Tunneling

Physical Review Letters, 2001

Vector momentum distributions of two electrons created in double ionization of Ar by 25 fs, 0.25 ... more Vector momentum distributions of two electrons created in double ionization of Ar by 25 fs, 0.25 PW͞cm 2 laser pulses at 795 nm have been measured using a "reaction microscope." At this intensity, where nonsequential ionization dominates, distinct correlation patterns are observed in the two-electron momentum distributions. A kinematical analysis of these spectra within the classical "recollision model" revealed an ͑e, 2e͒-like process and excitation with subsequent tunneling of the second electron as two different ionization mechanisms. This allows a qualitative separation of the two mechanisms demonstrating that excitation-tunneling is the dominant contribution to the total double ionization yield.