Nano-scale chemical imaging of a single sheet of reduced graphene oxide

Zhou, Jigang; Wang, Jian; Sun, Chia‐Liang; Maley, Jason; Sammynaiken, Ramaswami; Sham, Tsun‐Kong; Pong, W. F.

doi:10.1039/c1jm11071c

Cited by 62 publications

(93 citation statements)

References 46 publications

(61 reference statements)

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“…30,31 Scanning photoelectron microscopy (SPEM) and XMCD measurements were also performed, and they supported the claim that defects and/or vacancies and O 2p orbitals are playing critical roles in inducing d 0 ferromagnetism in ZnO nanostructures. The X-ray-based microscopic and spectroscopic techniques used in this study include extended X-ray-absorption ne structure (EXAFS) spectroscopy, X-ray-excited optical luminescence (XEOL) spectroscopy, scanning transmission X-ray microscopy (STXM) and the corresponding X-ray-absorption near-edge structure (XANES) spectroscopy.…”

Section: Introductionmentioning

confidence: 57%

Observation of the origin of d⁰magnetism in ZnO nanostructures using X-ray-based microscopic and spectroscopic techniques

et al. 2014

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Efforts have been made to elucidate the origin of d(0) magnetism in ZnO nanocactuses (NCs) and nanowires (NWs) using X-ray-based microscopic and spectroscopic techniques. The photoluminescence and O K-edge and Zn L3,2-edge X-ray-excited optical luminescence spectra showed that ZnO NCs contain more defects than NWs do and that in ZnO NCs, more defects are present at the O sites than at the Zn sites. Specifically, the results of O K-edge scanning transmission X-ray microscopy (STXM) and the corresponding X-ray-absorption near-edge structure (XANES) spectroscopy demonstrated that the impurity (non-stoichiometric) region in ZnO NCs contains a greater defect population than the thick region. The intensity of O K-edge STXM-XANES in the impurity region is more predominant in ZnO NCs than in NWs. The increase in the unoccupied (occupied) density of states at/above (at/below) the conduction-band minimum (valence-band maximum) or the Fermi level is related to the population of defects at the O sites, as revealed by comparing the ZnO NCs to the NWs. The results of O K-edge and Zn L3,2-edge X-ray magnetic circular dichroism demonstrated that the origin of magnetization is attributable to the O 2p orbitals rather than the Zn d orbitals. Further, the local density approximation (LDA) + U verified that vacancies in the form of dangling or unpaired 2p states (due to Zn vacancies) induced a significant local spin moment in the nearest-neighboring O atoms to the defect center, which was determined from the uneven local spin density by analyzing the partial density of states of O 2p in ZnO.

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Section: Introductionmentioning

confidence: 57%

Observation of the origin of d⁰magnetism in ZnO nanostructures using X-ray-based microscopic and spectroscopic techniques

et al. 2014

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“…[17][18] Successful investigations of the electronic structure and surface defects of individual (hetero-) nanostructure using STXM make it an extremely desirable technique in modern nanoresearch. [17][18][19][20][21][22][23] Two-dimensional X-ray absorption near edge structure−X-ray excited optical luminescence (2D XANES−XEOL) spectroscopy, an advanced spectroscopic technique to study the interplay of structural and optical properties of nanostructures, has also been used in this study. [24][25][26] XANES reveals the local symmetry and unoccupied electronic states associated with the absorbing atom.…”

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confidence: 99%

Nanoscale Clarification of the Electronic Structure and Optical Properties of TiO₂ Nanowire with an Impurity Phase upon Sodium Intercalation

Wang¹,

Zhao²,

Wang

et al. 2015

J. Phys. Chem. C

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The electronic structure and optical property of heterostructural TiO 2 nanowire (NW) synthesized by a hydrothermal process have been extensively studied. X-ray diffraction (XRD) and X-ray absorption near edge structure (XANES) were used to probe the crystal structure, and the local structure and bonding (unoccupied electronic states) of the as-obtained TiO 2 NW, respectively. Discrepancy between XRD and XANES results without spatial resolution was observed and interpreted on the basis of the inhomogeneous distribution of a sodium titanate impurity phase among the "bulk" pristine TiO 2 phase. Scanning transmission X-ray microscopy (STXM), on the other hand, provides nanoscale clarification for the divergence with a spatial resolution of 30 nm. Using STXM, the nature of the sodium titanate impurity phase and pristine TiO 2 phase was thoroughly characterized by comparing the XANES at the Na K-edge, Ti L 3,2 -edge and O K-edge. The local effect of sodium intercalation into the TiO 2 matrix together with the presence of sodium titanate impurity to the electronic structure of the entire NW specimen was addressed. Analysis was also conducted using 2D XANES−XEOL (X-ray Excited Optical Luminescence) spectroscopy. The optical interplay with structural properties reveals the element and site specificity of the observed luminescence. Of these, the dominant green emission and minor near-infrared (NIR) luminescence were attributed to the defect states from both Ti and O sites within the minor sodium titanate phase and the dominant rutile TiO 2 phase, respectively.The relationship between the observed luminescence intensity ratio and the phase content ratio of rutile and sodium titanate is discussed.

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“…and the D peak is associated with the aromatic rings only. 19 The 2D band at ∼2660 cm −1 is related to disorder-induced defects,and its shape is highly sensitive to the number of grapheme layers. 19,20 The spectra of GNFs:N and…”

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confidence: 99%

Nitrogen-Functionalized Graphene Nanoflakes (GNFs:N): Tunable Photoluminescence and Electronic Structures

et al. 2012

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This study investigates the strong photoluminescence (PL) and X-ray excited optical luminescence observed in nitrogen-functionalized 2D graphene nanoflakes (GNFs:N), which arise from the significantly enhanced density of states in the region of π states and the gap between π and π* states. The increase in the number of the sp 2 clusters in the form of pyridine-like N−C, graphite-N-like, and the CO bonding and the resonant energy transfer from the N and O atoms to the sp 2 clusters were found to be responsible for the blue shift and the enhancement of the main PL emission feature. The enhanced PL is strongly related to the induced changes of the electronic structures and bonding properties, which were revealed by the X-ray absorption near-edge structure, X-ray emission spectroscopy, and resonance inelastic X-ray scattering. The study demonstrates that PL emission can be tailored through appropriate tuning of the nitrogen and oxygen contents in GNFs and pave the way for new optoelectronic devices.

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Nano-scale chemical imaging of a single sheet of reduced graphene oxide

Cited by 62 publications

References 46 publications

Observation of the origin of d⁰magnetism in ZnO nanostructures using X-ray-based microscopic and spectroscopic techniques

Observation of the origin of d⁰magnetism in ZnO nanostructures using X-ray-based microscopic and spectroscopic techniques

Nanoscale Clarification of the Electronic Structure and Optical Properties of TiO₂ Nanowire with an Impurity Phase upon Sodium Intercalation

Nitrogen-Functionalized Graphene Nanoflakes (GNFs:N): Tunable Photoluminescence and Electronic Structures

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Nano-scale chemical imaging of a single sheet of reduced graphene oxide

Cited by 62 publications

References 46 publications

Observation of the origin of d0magnetism in ZnO nanostructures using X-ray-based microscopic and spectroscopic techniques

Observation of the origin of d0magnetism in ZnO nanostructures using X-ray-based microscopic and spectroscopic techniques

Nanoscale Clarification of the Electronic Structure and Optical Properties of TiO2 Nanowire with an Impurity Phase upon Sodium Intercalation

Nitrogen-Functionalized Graphene Nanoflakes (GNFs:N): Tunable Photoluminescence and Electronic Structures

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Observation of the origin of d⁰magnetism in ZnO nanostructures using X-ray-based microscopic and spectroscopic techniques

Observation of the origin of d⁰magnetism in ZnO nanostructures using X-ray-based microscopic and spectroscopic techniques

Nanoscale Clarification of the Electronic Structure and Optical Properties of TiO₂ Nanowire with an Impurity Phase upon Sodium Intercalation