Strain-engineered Properties Of Cinfined Nanoparticles

The investigation of the influence of strain on the crystal microstructure and physical properties of embedded nanoparticles,the interplay between the size,morphology and microstructure of nanoparticles is an important project.The study of this project will be especially useful for researcher to expand their knowledge of nanomaterials and the physics of strain.The contents of this thesis are as following:(1)Understanding the physics that correlate strain and microstructures of quantum dots(QDs)is extremely essential for technology applications.In this paper,GaAs QDs confined in Al2O3 matrix are synthesized using the pulsed laser deposition method and rapid thermal annealing technique.It is revealed that the confined GaAs QDs experience compressive strain during growth process.The strain can be used to improve and tailor the optical properties of confined GaAs QDs by engineering the bandgap and thus the photoluminescence emission band to a distinct wavelength.These findings presented here can engineer the properties of GaAs QDs for potential application in optoelectronic and photonic devices.(2)It is well known that the face-centered cubic(fcc)Fe is thermodynamically unstable at ambient conditions.In this paper,we theoretically and experimentally demonstrated that thermodynamically stable fcc Fe nanocrystals can be induced by external strain at room temperature.Fe nanocrystals confined in non-magnetic Al2O3 matrix were fabricated using pulsed laser deposition method and rapid thermal annealing technique.During the growth process,the confined Fe nanocrystals experience net deviatoric strain from Al2O3 matrix,which can modify the microstructure of the confined Fe nanocrystals and lead to the thermodynamically stable fcc Fe nanocrystals(space group Fm-3m)at room temperature.First-principles calculations also clearly demonstrated that strained Fe nanostructure with fcc phase is more thermodynamically stable.A typical behavior of weakly interacting Fe nanocrystals is observed,characterized by a superparamagnetic regime and a blocking of particle moments centered at TB(~9 K).(3)Au nanoparticles confined in Al2O3 matrix are synthesized using pulsed laser deposition method and rapid thermal annealing technique.The confined Au nanoparticles experience compressive strain during the growth process.It is demonstrated that hydrogen passivation can be used to enhance and tailor the optical properties of confined Au nanoparticles by engineering the strain and defect states of the confined Au nanoparticles.The findings provide a physical insight and useful methodology to improve the emission efficiency of noble metal nanoparticle based materials for potential application in optoelectronic and photonic devices.