Extended x-ray absorption fine structure investigation on buried InAsP/InP interfaces

X-ray absorption and emission spectroscopies, supported by quantum mechanical calculations, were used to determine the architecture of Ti(IV) sites in Ti aluminophosphate AlPO 4 -5. The chemical sensitivity of the Kβ 2,5 X-ray emission lines of Ti was exploited to monitor its local environment, proving that it mainly substitutes P in the framework, with a not negligible fraction substituting Al. Local structure of the substituted sites was found to be considerably deformed with respect to the AlPO 4 -5 original framework.

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“…This is, e.g. , the case of titanium or gallium substituting silicon in zeolites, or arsenic substituting phosphorus in InP …”

Section: Discussionmentioning

confidence: 99%

Architecture of the Ti(IV) Sites in TiAlPO-5 Determined Using Ti K-Edge X-ray Absorption and X-ray Emission Spectroscopies

et al. 2014

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“…EXAFS evidences the distortion of the local geometry from the tetrahedral one finding R AC and R BC bond lengths much closer to those of the pure AC and BC binary compounds, than foreseen from the VCA approximation. [145][146][147][179][180][181] Another example comes from mixed oxides with brownmillerite ABO 2.5 structure; brownmillerite exhibits an alternation of BO 6 octahedra layers with BO 4 tetrahedra. While BO 6 octahedra do not show any preferred orientation, BO 4 tetrahedra does.…”

Section: Interactive Xrpd Exafs and Ab Initio Structural Refinement: ...mentioning

confidence: 99%

X-ray absorption spectroscopies: useful tools to understand metallorganic frameworks structure and reactivity

et al. 2010

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The large unit cells, the enormous flexibility and variation in structural motifs of MOFs represent a big challenge in the characterization of MOF materials, particularly in cases where single crystal diffraction data are not available. In this critical review it is shown that in cases where only powder diffraction data are available additional structural information, particularly regarding local coordination within the inorganic cluster, are often mandatory in order to solve the structure. There are also cases where the inorganic cluster does not follow the symmetry of the overall structure. In such cases diffraction techniques will just "see" an average structure, missing the local structure: a lack that may be critical for understanding the specific properties of the material. In both cases, EXAFS spectroscopy is the tool that provides complementary structural information on the inorganic cluster and the way it binds to the ligand. Selected examples will show how EXAFS will be relevant in: (i) confirming the structure obtained from diffraction refinements; (ii) highlighting that the inorganic cornerstone has a lower symmetry with respect to that of the organic framework; (iii) obtaining the local structure of the inorganic cluster in the desolvated material when desolvation causes a partial loss of long range order; (iv) obtaining the local structure of the inorganic cluster in the desolvated material after coordination of a probe (or reactant) molecule, including cluster deformation upon molecule coordination and metal-molecule binding distance; (v) evidencing the presence of impurities in the form of amorphous extra-phases (339 references).

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“…EXAFS evidence shows the distortion of the local geometry from the tetrahedral one finding R AC and R BC bond lengths much closer to those of the pure AC and BC binary compounds than foreseen from the VCA approximation. [47][48][49][50][51][52] Another example comes from mixed oxides with the brownmillerite ABO 2.5 structure; brownmillerite exhibits an alternation of BO 6 octahedra layers with BO 4 tetrahedra. While BO 6 octahedra do not show any preferred orientation, BO 4 tetrahedra do.…”

Section: Introductionmentioning

confidence: 99%

Disclosing the Complex Structure of UiO-66 Metal Organic Framework: A Synergic Combination of Experiment and Theory

et al. 2011

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Through a combined use of experimental and theoretical approaches such as XRPD, EXAFS, IR, and UV−vis spectroscopies and ab initio periodic DFT calculations, we report a detailed characterization of structural, vibrational, and electronic properties of UiO-66 (Zr-BDC MOF) in its hydroxylated and dehydroxylated forms. The stability of the materials with respect to the most common solvents, acids, and bases is determined by combining XRPD and TGA/MS techniques. The structures of the two forms of UiO-66 are refined through an interactive XRPD/EXAFS approach and validated by ab initio calculations. Experimental and calculated IR spectra are reported and compared to enlighten the nature of vibrational modes upon dehydroxylation and to show the complete reversibility of the dehydration/hydration phenomenon. Experimental and calculated band gaps are also reported and compared. In this work, we show the necessity to combine, in a synergic way, different experimental techniques and periodic ab initio approaches to disclose and fully understand the nature of complex novel materials such as UiO-66 on structural, vibrational, and electronic grounds. The correct structure refinement could not be possible using one of these three approaches alone, in particular, XRPD data were unable to detect an important distortion of the Zr6O6 units of the dehydrated material that was, however, foreseen in the ab initio calculations and measured in the EXAFS spectra.

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Extended x-ray absorption fine structure investigation on buried InAsP/InP interfaces

Cited by 31 publications

References 19 publications

Architecture of the Ti(IV) Sites in TiAlPO-5 Determined Using Ti K-Edge X-ray Absorption and X-ray Emission Spectroscopies

Architecture of the Ti(IV) Sites in TiAlPO-5 Determined Using Ti K-Edge X-ray Absorption and X-ray Emission Spectroscopies

X-ray absorption spectroscopies: useful tools to understand metallorganic frameworks structure and reactivity

Disclosing the Complex Structure of UiO-66 Metal Organic Framework: A Synergic Combination of Experiment and Theory

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