scholarly journals X-Ray Absorption Spectroscopy from H-Passivated Porous Si and Oxidized Si Nanocrystals

1994 ◽  
Vol 375 ◽  
Author(s):  
S. Schuppler ◽  
S. L. Friedman ◽  
M. A. Marcus ◽  
D. L. Adler ◽  
Y.-H. Xie ◽  
...  
Keyword(s):  
Fine Structure ◽  
Quantum Confinement ◽  
Ir Absorption ◽  
X Ray ◽  
Coordination Numbers ◽  
Absorption Fine ◽  
Visible Luminescence ◽  
Si Nanocrystals ◽  
Wide Range ◽  
X Ray Absorption

AbstractQuantum confinement in nanoscale Si structures is widely believed to be responsible for the visible luminescence observed from anodically etched porous silicon (por-Si), but little is known about the actual size or shape of these structures. Extended x-ray absorption fine structure data from a wide variety of por-Si samples show significantly reduced average Si coordination numbers due to the sizable contribution of surface-coordinated H. (The H/Si ratios, as large as 1.2, were independently confirmed by ir-absorption and α-recoil measurements.) The Si coordinations imply very large surface/volume ratios, enabling the average Si structures to be identified as crystalline particles (not wires) whose dimensions are typically <15 Å. Comparison of the size-dependent peak luminescence energies with those of oxidized Si nanocrystals, whose shapes are known, shows remarkable agreement. Furthermore, near-edge x-ray absorption fine structure measurements of the nanocrystals shows the outer oxide and interfacial suboxide layers to be constant over a wide range of nanocrystal sizes. The combination of these results effectively rules out surface species as being responsible for the observed visible luminescence in por-Si, and strongly supports quantum confinement as the dominant mechanism occurring in Si particles which are substantially smaller than previously reported or proposed.

Near Edge X-Ray Absorption Fine Structure (NEXAFS) Microscopy: Chemical Analysis at Sub Visible Spatial Resolution

1997 ◽  
Vol 3 (S2) ◽  
pp. 851-852
Author(s):  
H. Ade
Keyword(s):  
Fine Structure ◽  
Compositional Analysis ◽  
High Sensitivity ◽  
Linear Dichroism ◽  
X Rays ◽  
X Ray ◽  
Absorption Fine ◽  
Nexafs Spectroscopy ◽  
Wide Range ◽  
X Ray Absorption

Infrared, Raman, and fluorescence/luminescence microspectroscopy/microscopy in many instances seek to provide high sensitivity compositional and functional information that goes beyond mere elemental composition. This goal is shared by NEXAFS microscopy, in which Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy is employed to provide chemical sensitivity and can be relatively easily adopted in a scanning transmission x-ray microscope (STXM). In addition to compositional information, NEXAFS microscopy can exploit the dependence of x-ray absorption resonances on the bond orientation relative to the linearly polarized x rays (linear dichroism microscopy). For compositional analysis, NEXAFS microscopy is analogous to Electron Energy Loss Spectroscopy (EELS) in an electron microscope. However, when utilizing near edge spectral features, NEXAFS microscopy requires a considerable lower dose than EELS microscopy which makes it very suitable to studying radiation sensitive materials such as polymers. NEXAFS has shown to have excellent sensitivity to a wide range of moieties in polymers, including sensitivity to substitution isomerism.

Reflected extended X-ray absorption fine structure study of the surface region of layered samples

2011 ◽  
Vol 1 (SRMS-7) ◽  
Author(s):  
A. Muñoz-Páez ◽  
V. López-Flores ◽  
S. Díaz-Moreno ◽  
D. T. Bowron ◽  
S. Ramos ◽  
...  
Keyword(s):  
Fine Structure ◽  
Surface Region ◽  
Structure Study ◽  
Molybdenum Nitride ◽  
X Ray ◽  
Absorption Fine ◽  
Wide Range ◽  
Two Samples ◽  
X Ray Absorption ◽  
Layered Samples

We present preliminary reflection extended X-ray absorption fine structure results on reactive magnetron sputtering molybdenum nitride (MoN) layered samples, with different compositions and surface layer thickness. The results obtained over a wide range of incidence angles show significant differences between two samples where the outer layer is either Mo metal or MoN.

An Automated System for Extended X-Ray Absorption Measurements

1964 ◽  
Vol 8 ◽  
pp. 180-188
Author(s):  
G. D. Christofferson ◽  
T. R. Hughes ◽  
R. F. Klaver
Keyword(s):  
Fine Structure ◽  
Wavelength Region ◽  
Fortran Program ◽  
Automated System ◽  
Clock Frequency ◽  
Absorption Data ◽  
X Ray ◽  
Absorption Fine ◽  
Wide Range ◽  
X Ray Absorption

AbstractIn the study of X-ray absorption fine structure, one is faced with the task of measuring sample absorbance over an extended wavelength region. For the sake of accuracy, these measurements are often carried out on a fixed-count basis. Manual collection of the data at a hundred or more spectrometer settings is a tedious and time-consuming chore. This paper describes an automated system for accumulating absorption data.The equipment is used in conjunction with a Philips wide-range goniometer employed as a single-crystal spectrometer. It consists of: (1) a four-position sample changer, (2) a fixed-count selector for each sample position, (3) a five-digit counter and paper tape printer which register and record sample identification and counting times based on a 60-cps clock frequency, and (4) a programmer. The spectrometer advance is accomplished using the Philips step-scan arrangement. An IBM 7094 FORTRAN program for data reduction and computation will be described. The possibility of using X-ray absorption fine-structure measurements as a quantitative method for determining the various absorbing species will be discussed.

X-ray absorption spectroscopy principles and practical use in materials analysis

2020 ◽  
Vol 5 (4) ◽  
Author(s):  
Wolfgang Grünert ◽  
Konstantin Klementiev
Keyword(s):  
Fine Structure ◽  
Structural Analysis ◽  
Disordered Systems ◽  
Structural Information ◽  
Research Strategies ◽  
Edge Structure ◽  
X Ray ◽  
Absorption Fine ◽  
Wide Range ◽  
X Ray Absorption

AbstractThe X-ray Absorption Fine Structure (XAFS) with its subregions X-ray Absorption Near-edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) is a powerful tool for the structural analysis of materials, which is nowadays a standard component of research strategies in many fields. This review covers a wide range of topics related to its measurement and use: the origin of the fine structure, its analytical potential, derived from the physical basis, the environment for measuring XAFS at synchrotrons, including different measurement geometries, detection modes, and sample environments, e. g. for in-situ and operando work, the principles of data reduction, analysis, and interpretation, and a perspective on new methods for structure analysis combining X-ray absorption with X-ray emission. Examples for the application of XAFS have been selected from work with heterogeneous catalysts with the intention to demonstrate the strength of the method providing structural information about highly disperse and disordered systems, to illustrate pitfalls in the interpretation of results (e. g. by neglecting the averaged character of the information obtained) and to show how its merits can be further enhanced by combination with other methods of structural analysis and/or spectroscopy.

Synthesis and characterization of 1,2,3,4 tetrahydroquinoline intercalated into MoS2 in search of cleaner fuels

2007 ◽  
Vol 22 (10) ◽  
pp. 2747-2757 ◽  
Author(s):  
Karina Castillo ◽  
Felicia Manciu ◽  
J.G. Parsons ◽  
Russell R. Chianelli
Keyword(s):  
Fine Structure ◽  
Infrared Spectroscopy ◽  
Synthesis And Characterization ◽  
X Ray Diffraction ◽  
X Ray ◽  
Coordination Numbers ◽  
Absorption Fine ◽  
Diffraction Patterns ◽  
X Ray Absorption

Two different morphologies of MoS2 (short and long sheets) were utilized to elucidate the intercalation mechanism of 1,2,3,4 tetrahydroquinoline (THQ). MoS2 (short sheets) and molybdenite (MB) (long sheets) were exfoliated and restacked in the presence of THQ. The x-ray diffraction patterns of both samples show a new reflection in the 001 plane, which implies a lowering of symmetry and corresponds to an expansion of the layers by approximately 12.3 Å. In the MoS2-THQ sample, 80% of the MoS2 was intercalated and 20% remained stacked. In the MB-THQ sample, 30% of MB was intercalated while 70% remained stacked. X-ray absorption structure (XAS) studies showed changes in atomic geometry and coordination. The x-ray absorption near-edge spectra showed shifts in the geometry of the intercalated MoS2 and MB sample compared to the unintercalated samples. Extended x-ray absorption fine structure studies showed lower coordination numbers compared to the untreated samples. Infrared spectroscopy characterization of these same samples suggests intercalation and partial dehydrogenation of the THQ.

scholarly journals Size, Shape, and Crystallinity of Luminescent Structures in Oxidized Si Nanoclusters and H-Passivated Porous Si

1994 ◽  
Vol 358 ◽  
Author(s):  
S. Schuppler ◽  
S. L. Friedman ◽  
M. A. Marcus ◽  
D.L. Adler ◽  
Y.-H. Xie ◽  
...  
Keyword(s):  
Visible Region ◽  
Weighted Average ◽  
Ir Absorption ◽  
Porous Si ◽  
Emission Data ◽  
X Ray ◽  
Visible Luminescence ◽  
Si Nanocrystals ◽  
X Ray Absorption ◽  
Average Structures

ABSTRACTNear-edge and extended x-ray absorption fine structure measurements from a wide variety of H-passivated porous Si samples and oxidized Si nanocrystals, combined with electron microscopy, ir-absorption, α-recoil, and luminescence emission data, provide a consistent structural picture of the species responsible for the luminescence observed in these systems. For luminescent porous Si samples peaking in the visible region, i. e., ≤700nm, their mass-weighted-average structures are determined here to be particles–not wires, whose short-range character is crystalline – not amorphous, and whose dimensions – typically <15 Å – are significantly smaller than previously reported or proposed. These results depend only on sample luminescence behavior, not on sample preparation details, and thus have general implications in describing the mechanism responsible for visible luminescence in porous silicon. New results are also presented which demonstrate that the observed luminescence is unrelated to either the photo-oxidized Si species in porous Si or the interfacial suboxide species in the Si nanocrystals.

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