Low-Dimensional Physics of Organic-Inorganic Multilayers

<p>This thesis demonstrates the rich low-dimensional physics associated with the class of organic-inorganic hybrid materials based on atomic layers of a metal oxide separated by organic spacer molecules. Hybrid materials based on tungsten oxide and also transition metal tungstates (with manganese, iron, cobalt, nickel and copper) were synthesised and characterised using a variety of techniques. The materials in question represent one example of the huge variety of systems classed as 'organic-inorganic hybrids' and have the potential to combine the high-electron mobility of the metal oxide layers with the propensity for self-assembly of the organic layers. The crystal structures of the compounds were investigated using powder X-ray diffraction and electron diffraction, and compared with structural information obtained using IR, Raman, and extended X-ray absorption fine structure (EXAFS) spectroscopies. This data confirmed the presence of a 2- dimensional layered structure. The electronic properties of the hybrids were studied using optical spectroscopy and confirmed via ab initio calculations. The band gaps of the tungsten oxide hybrids were found to be independent of interlayer spacing, and in all cases were larger than that observed in the three dimensional WO3 'parent' material. For the transition metal tungstate hybrids there appeared to be significant interactions between the organic amines and the transition metal ions within the inorganic layers. The magnetic properties of the hybrids incorporating transition metal ions were also studied in detail. Many of these metal tungstate hybrids display magnetic transitions at low temperatures indicating a crossover from 2-dimensional to 3-dimensional behaviour. This illustrates the importance of the low-dimensional nature of the inorganic layers in these hybrid materials and thus their potential in nano-structural applications.</p>

Low-Dimensional Physics of Organic-Inorganic Multilayers

<p>This thesis demonstrates the rich low-dimensional physics associated with the class of organic-inorganic hybrid materials based on atomic layers of a metal oxide separated by organic spacer molecules. Hybrid materials based on tungsten oxide and also transition metal tungstates (with manganese, iron, cobalt, nickel and copper) were synthesised and characterised using a variety of techniques. The materials in question represent one example of the huge variety of systems classed as 'organic-inorganic hybrids' and have the potential to combine the high-electron mobility of the metal oxide layers with the propensity for self-assembly of the organic layers. The crystal structures of the compounds were investigated using powder X-ray diffraction and electron diffraction, and compared with structural information obtained using IR, Raman, and extended X-ray absorption fine structure (EXAFS) spectroscopies. This data confirmed the presence of a 2- dimensional layered structure. The electronic properties of the hybrids were studied using optical spectroscopy and confirmed via ab initio calculations. The band gaps of the tungsten oxide hybrids were found to be independent of interlayer spacing, and in all cases were larger than that observed in the three dimensional WO3 'parent' material. For the transition metal tungstate hybrids there appeared to be significant interactions between the organic amines and the transition metal ions within the inorganic layers. The magnetic properties of the hybrids incorporating transition metal ions were also studied in detail. Many of these metal tungstate hybrids display magnetic transitions at low temperatures indicating a crossover from 2-dimensional to 3-dimensional behaviour. This illustrates the importance of the low-dimensional nature of the inorganic layers in these hybrid materials and thus their potential in nano-structural applications.</p>

Intercalated Iron Chalcogenides: Phase Separation Phenomena and Superconducting Properties

Organic molecule-intercalated layered iron-based monochalcogenides are presently the subject of intense research studies due to the linkage of their fascinating magnetic and superconducting properties to the chemical nature of guests present in the structure. Iron chalcogenides have the ability to host various organic species (i.e., solvates of alkali metals and the selected Lewis bases or long-chain alkylammonium cations) between the weakly bound inorganic layers, which opens up the possibility for fine tuning the magnetic and electrical properties of the intercalated phases by controlling both the doping level and the type/shape and orientation of the organic molecules. In recent years, significant progress has been made in the field of intercalation chemistry, expanding the gallery of intercalated superconductors with new hybrid inorganic–organic phases characterized by transition temperatures to a superconducting state as high as 46 K. A typical synthetic approach involves the low-temperature intercalation of layered precursors in the presence of liquid amines, and other methods, such as electrochemical intercalation, intercalant or ion exchange, and direct solvothermal growths from anhydrous amine-based media, are also being developed. Large organic guests, while entering a layered structure on intercalation, push off the inorganic slabs and modify the geometry of their internal building blocks (edge-sharing iron chalcogenide tetrahedrons) through chemical pressure. The chemical nature and orientation of organic molecules between the inorganic layers play an important role in structural modification and may serve as a tool for the alteration of the superconducting properties. A variety of donor species well-matched with the selected alkali metals enables the adjustment of electron doping in a host structure offering a broad range of new materials with tunable electric and magnetic properties. In this review, the main aspects of intercalation chemistry are discussed, involving the influence of the chemical and electrochemical nature of intercalating species on the crystal structure and critical issues related to the superconducting properties of the hybrid inorganic–organic phases. Mutual relations between the host and organic guests lead to a specific ordering of molecular species between the host layers, and their effect on the electronic structure of the host will be also argued. A brief description of a critical assessment of the association of the most effective chemical and electrochemical methods, which lead to the preparation of nanosized/microsized powders and single crystals of molecularly intercalated phases, with the ease of preparation of phase pure materials, crystal sizes, and the morphology of final products is given together with a discussion of the stability of the intercalated materials connected with the volatility of organic solvents and a possible degradation of host materials.

Dielectric polarization effect and transient relaxation in FAPbBr3 films before and after PMMA passivation

In organic–inorganic hybrid lead halide perovskites with a naturally arranged layered structure, the dielectric polarization effect caused by the dielectric mismatch between the organic and inorganic layers takes effect in their optical responses.

Mechanism of ultrafast energy transfer between the organic–inorganic layers in multiple-ring aromatic spacers for 2D perovskites

2D hybrid perovskites are stoichiometric compounds consisting of alternating inorganic metal–halide sheets and organic cations. Here we show ultrafast energy transfer pathways between lead halide excitons and chromophore singlet or triplet states.

Synthesis of Core–Double Shell Nylon-ZnO/Polypyrrole Electrospun Nanofibers

Core–double shell nylon-ZnO/polypyrrole electrospun nanofibers were fabricated by combining three straightforward methods (electrospinning, sol–gel synthesis and electrodeposition). The hybrid fibrous organic–inorganic nanocomposite was obtained starting from freestanding nylon 6/6 nanofibers obtained through electrospinning. Nylon meshes were functionalized with a very thin, continuous ZnO film by a sol–gel process and thermally treated in order to increase its crystallinity. Further, the ZnO coated networks were used as a working electrode for the electrochemical deposition of a very thin, homogenous polypyrrole layer. X-ray diffraction measurements were employed for characterizing the ZnO structures while spectroscopic techniques such as FTIR and Raman were employed for describing the polypyrrole layer. An elemental analysis was performed through X-ray microanalysis, confirming the expected double shell structure. A detailed micromorphological characterization through FESEM and TEM assays evidenced the deposition of both organic and inorganic layers. Highly transparent, flexible due to the presence of the polymer core and embedding a semiconducting heterojunction, such materials can be easily tailored and integrated in functional platforms with a wide range of applications.

Correction: Comparison of organic and inorganic layers for structural templating of pentacene thin films

Correction for ‘Comparison of organic and inorganic layers for structural templating of pentacene thin films’ by Dong Kuk Kim et al., Mater. Horiz., 2019, DOI: 10.1039/c9mh00355j.

Ab initio modeling of 2D and quasi-2D lead organohalide perovskites with divalent organic cations and a tunable band gap

We describe theoretically the structure and properties of layered lead organohalide perovskites, considering purely bi-dimensional (2D) PbI4 layers, and quasi-2D systems where the inorganic layers are formed by more than one lead iodide sheet.

Comparison of organic and inorganic layers for structural templating of pentacene thin films

Effective control over the molecular orientation of pentacene was achieved with copper(i) iodide and results in a change in the functional properties with increases in both visible light absorption and work function.