The Synthesis Of Cu/Ag Doped ZnO Nanomaterials And Their High-pressure Studies

zinc oxide (ZnO) is one kind of semiconductor material with direct wide band gap and a large exciton binding energy, which is widely used for production of green, blue-ultraviolet, optoelectronics, mechanical properties, piezoelectric constants, lattice dynamics, vibrational processes, thermal properties, and white light-emitting devices. Thus, ZnO is considered to be one of the most promising materials in science and technology. ZnO has the most abundant kinds of nano structures. It exhibited many strange properties, such as surface effect, small size effect, quantum confinement effect , which made ZnO to be an attractive candidate for nano-optoelectronic devices and nano-electronic devices. In addition, the diffusion of transition metal into ZnO can cause variations in its lattice structure and, correspondingly, in the interrelated physical properties. Tuning the micro-mechanism of ZnO by doping with transition metal can get the giant negative magnetoresistance, magneto-optical enhancement effect, anomalous Hall effect. These experimental and theoretical research promoted the potential applications of the zinc oxide-based diluted magnetic semiconductor materials in various fields. Some groups have claimed that ferromagnetism in TM-doped ZnO comes from impurities, precipitation of magnetic clusters or other secondary magnetic phases. On the other hand, there are many reports that support the idea that the FM is an intrinsic property. It is necessary to do more systematic experimental and theoretical analysis to figure out the controversies in ZnO based diluted magnetic semiconductor.In recent years, the high-pressure studies on nanomaterials have been the topic of current interest. However,the high-pressure behavior of zinc oxide-based diluted magnetic semiconductor is rare known.In this paper, we report the synthesis of various morphologies of Cu/Ag doped ZnO nanostructures. which includes a systematic investigation of the lattice structure, the electrical structure, the Raman vibration mode, optical properties and magnetic properties. We also venture our experimental observations to highlight more informed contemplation of the possible mechanisms.In addition,we report a high-pressure study on the synthesized Cu doped ZnO nanostructures nano particles using an in situ synchrotron radiation X-ray diffraction technique in diamond anvil cell.The obtained main results are as follow:1. We have synthesized ZnO and Cu doped ZnO nano particles by a sol-gel method. It is clearly seen that the peak position of the heavier sample shifts to lower angles as compared with pure ZnO, which indicates an increment in the lattice parameters a and c. Room temperature FM was observed in Cu doped ZnO nanoparticles. XRD and XPS results provide evidence that Cu ions are mainly in the divalent state and incorporated into the ZnO lattice at the Zn2+ site. The Cu doping makes nonmagnetic ZnO nanocrystallites ferromagnetic.2. we synthesized Cu-doped ZnO nanorod and nanoflower through a hydrothermal process. These nanoflowers consist of many pricklelike nanopetals. The tubes obtained were grown epitaxially on sapphire (0001) substrates with both the ZnO c axis. The ZnO bandgap turned broad due to Cu doping. Room temperature FM was observed in Cu doped ZnO3. We have synthesized ZnO andAg doped ZnO nano particles by a sol-gel method. It is clearly seen that the peak position of the heavier sample shifts to lower angles as compared with pure ZnO, which indicates an increment in the lattice parameters a and c. The sp-d exchange interactions between the band electrons and the localized d electrons of he Agt ions substituting metal ions are responsible for the andgap renormalization effect. The s-d and p-d exchange nteractions give rise to a negative and a positive correction o the conduction-band and valence-band edges, respectively, esulting in shrinkage of the bandgap.4. We report the structural and optical properties of flower-shaped undoped and Ag-doped ZnO nanostructures synthesized through a hydrothermal process. These nanoflowers consist of many pricklelike nanopetals. The photoluminescence (PL) spectrum of Ag-doped ZnO nanoflowers shows a remarkably enhanced emission band compared with undoped ZnO nanostructures with similar morphology. Ag doping decreases ZnO bandgap and excellently tunes the luminescence properties. Due to the doping and morphological effects, the Ag-doped ZnO flower-shaped structures may find applications in various areas such as the fabrication of field emission devices, photovoltaics, sensors, microfluidics, electromechanical coupled devices, and transducers.5. We demonstracted the Cu doping effects on the wurtzite to cubic phase transformation in Zn1-xCuxO (x=0.005 and 0.011). As the pressure increases, phase transformations from the wurtzite structure to the rocksalt structure are observed in both samples, with the transition pressures at 9.8 GPa and 7.9 GPa, respectively. The chemical bonding characteristics and their relationships with compressibility are explored. With the increasing of the Cu-doping concentration in ZnO, crystalline parameters, the bulk moduli and the Zn-O bond lengths all increased, meanwhile, the transition pressures decreased. The evolution of the Zn-O bond lengths under high pressure provides an insight toward understanding the differences in the pressure-induced phase transition properties between these two samples. The results show that the Cu dopants significantly promote the formation of B1 phase. The doping effects on chemical bonding of crystals can play an important role in the research of the physical properties such as compressibility and bulk modulus determination. Pressure induced phase transition of hexagonal Zn0.854Cu0.146O is studied by using synchrotron angle dispersive X-ray diffraction (ADXRD) up to 43.1 GPa at room temperature. A structural transformation from a hexagonal phase to a cubic phase is observed, which starts at 10.2 GPa and finishes at about 16.1 GPa. The phase transition leads to a volume collapse of 17% at 10.2 GPa. The cubic phase of Zn0.854Cu0.146O remains stable up to the highest experiment pressure. The pressure-volume data are fitted with the Birch-Murnaghan equation of state. The bulk modulus obtained upon compression from the fitting are 175±2 GPa and 259±6 GPa for the hexagonal and cubic phases, respectively.