In the last couple of decades, there has been a great effort in the realization of low-dimensioned systems, because confinement represents a impressive tool for tuning the structural, physical, chemical, electronic, optical etc… properties of materials. Confinement can be achieved in one, two or three directions resulting in 2D, 1D and 0D systems, respectively. Due to evident important interests on both fundamental and applied grounds, low-dimensioned systems have represented, and still represent, a frontier in science where Material Science, Physics, Chemistry and Engineering overlap constructively. The complexity of such heterostructures and the extremely low number of atoms present in the confined regions has requested an effort in the characterization techniques. Among them X-ray absorption spectroscopy (XAS) has been one of the most powerful. The main reasons for its success are: (i) its atomic selectivity, allowing to obtain signal coming from the atoms forming the confined phase only (being those of the hosting matrix silent); (ii) the high photon flux of synchrotron radiation sources, allowing the investigation of highly diluted systems; (iii) the high penetration depth of hard x-rays, allowing the study of buried nanostructures; (iv) the possibility to tune the depth sensitivity of the technique by selecting different acquisition modes (transmission, fluorescence yield and electron yield). In this chapter, after a brief introduction to the technique itself and its different acquisition modes, selected examples of its use in the characterization of 2D, 1D and 0D systems are reported. For 2D systems classical semiconductors quantum wells and superlattices for optoelectronic and monolayer-thin oxide films epitaxially grown on metals are discussed in details. The overall discussion on 1D and 0D systems has a broader character and covers both the “bulk down” and the “atom up” approaches. Then, the atomically defined –O-Ti-O-Ti-O- quantum wires of ETS-10 titanosilicates and the three-dimensionally ordered [Cu2C4O8] units of HKURST-1 metal organic framework have been chosen as original examples of 1D and 0D systems, respectively.
Characterization of low dimensional systems by X-ray absorption spectroscopy: a selection of 2D, 1D and 0D systems
BORDIGA, Silvia;GROPPO, Elena Clara;AGOSTINI, Giovanni;LAMBERTI, Carlo
2008-01-01
Abstract
In the last couple of decades, there has been a great effort in the realization of low-dimensioned systems, because confinement represents a impressive tool for tuning the structural, physical, chemical, electronic, optical etc… properties of materials. Confinement can be achieved in one, two or three directions resulting in 2D, 1D and 0D systems, respectively. Due to evident important interests on both fundamental and applied grounds, low-dimensioned systems have represented, and still represent, a frontier in science where Material Science, Physics, Chemistry and Engineering overlap constructively. The complexity of such heterostructures and the extremely low number of atoms present in the confined regions has requested an effort in the characterization techniques. Among them X-ray absorption spectroscopy (XAS) has been one of the most powerful. The main reasons for its success are: (i) its atomic selectivity, allowing to obtain signal coming from the atoms forming the confined phase only (being those of the hosting matrix silent); (ii) the high photon flux of synchrotron radiation sources, allowing the investigation of highly diluted systems; (iii) the high penetration depth of hard x-rays, allowing the study of buried nanostructures; (iv) the possibility to tune the depth sensitivity of the technique by selecting different acquisition modes (transmission, fluorescence yield and electron yield). In this chapter, after a brief introduction to the technique itself and its different acquisition modes, selected examples of its use in the characterization of 2D, 1D and 0D systems are reported. For 2D systems classical semiconductors quantum wells and superlattices for optoelectronic and monolayer-thin oxide films epitaxially grown on metals are discussed in details. The overall discussion on 1D and 0D systems has a broader character and covers both the “bulk down” and the “atom up” approaches. Then, the atomically defined –O-Ti-O-Ti-O- quantum wires of ETS-10 titanosilicates and the three-dimensionally ordered [Cu2C4O8] units of HKURST-1 metal organic framework have been chosen as original examples of 1D and 0D systems, respectively.
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