The Synthesis Of Indium Based Semiconductor Nanomaterials And Their High-pressure Studies

Semiconductor nanomaterials have been attracting considerable attention in recentyears due to their novel physical and chemical properties, which differ significantlyfrom those of their bulk counterparts, and their potential applications in a wide field.As we all known that the properties of nanostructures not only depend on thecomposition of materials, but also on their monodispersity and characteristics,including sizes, shapes, crystal phases, exposed surface and so on. With thedevelopment of research on preparation and properties of nanomaterials, varioussynthetic strategies were designed and developed to provide control over thesenanostructure characteristics, such as physical evaporation technique, chemicalvapour deposition(CVD), laser ablation technique, hydrothermal/solvothermalmethods, sol-gel method, and others. Nowadays, the controllable preparation ofsemiconductor nanomaterials with definite characteristics has become an importantresearch focus.High-pressure studies on nanostructured materials have also attracted considerablescientific interest since nanocrystal systems exhibit novel compression behaviorsdifferent from those of their bulk counterparts. It may offer the opportunities to revealsome novel properties of nanomaterials, and then make it possible to establish somenew concepts and theories to guide the preparation of novel materials.As an important class of semiconductor nanomaterials, the indium basedsemiconductor which including In2O3, InOOH, InN, etc. has received substantialattention in a variety of technological applications, such as solar cells, light-emittingdiodes, field-emission devices, liquid-crystal displays, and gas sensors. So, takeingthese prepared indium based semiconductor nanomaterials as examples in thisdissertation. And due to the convenient equipment, low cost and environmentally friendly closed system, the hydrotherma/solvothermal technique and chemical vapourdeposition method are used to prepare different In2O3, InOOH and InN nanostructures.Then, takeing these prepared indium based semiconductor nanomaterials as examples,we have carried on the high pressure studies by using the diamond anvil cell (DAC)technique. And the phase transition behaviors of the In2O3and InN nanostructures areall investigated in detail. The details are as follow:1. A solvothermal reaction is generally considered to be governed by the chemicaland thermodynamic parameters. Yet, the effects of the heating rate on the nucleationand growth of the target materials within solvothermal processes have been rarelyreported. In this dissertation, taking the solvothermally synthesized InOOH/In2O3asthe sample system, we intend to illustrate that the heating rate plays an important rolein the nucleation and growth in solvothermal reactions. Especially, it is found thatheating rate may trigger different growth mechanisms in the solvothermal system, andsubsequently influence the microstructure of the products. Thus it is anticipated thatcontrolling the heating rate may be a potential route to tailor the morphology,microstructure, and even the properties of materials via solvothermal processes.2. The differences between the compression behaviors of nanocrystal systems andtheir bulk counterparts are generally attributed to the size and morphology effects.However, these effects may not be simply employed to deal with the contradictoryresults about In2O3bulk and nanomaterials under high pressures. In this dissertation,we intend to show that other than size and morphology, the effects of microstructureshould play a key role in the compression behavior and phase transition routine ofIn2O3cubical-shaped nanocrystals under high pressures. Thus, it is anticipated thatcontrolling the microstructures of nanomaterials may be a potential route to modulatetheir structural and elastic behaviors under pressures.3. Uniform InN nanowires were synthesized through chemical vapour deposition(CVD) mehod and then studied under pressures by using in situ synchrotron radiationx-ray diffraction technique at room temperature. An anomalous phase transitionbehavior has been discovered. Contrary to the results in the literature, which indicateInN undergoes fully reversible phase transition from the wurtzite to the rocksalt type structure in general, the InN nanowires in this study showed unusually a partiallyirreversible phase transition. The released sample contained the metastable rocksaltphase as well as the starting wurtzite one. The experimental findings of this study alsoreveal the potentiality of high pressure techniques to synthesize InN nanomaterialswith the metastable rocksalt type structure, in addition to the generally obtainedzincblende type one.