مطالعه ي ابتدا به ساكن و تجربي نيمرساناي مغناطيسي رقيق بر پايه ي اكسيد روي

چكيده انگليسي :

First Principles and Experimental Investigation of ZnO Based Diluted Magnetic Semiconductor Ismaeil Abdolhosseini Sarsari i abdolhosseini@ph iut ac ir 10 14 2012 Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran Degree PhD Language Persian Supervisor Dr H Salamati salamati@cc iut ac ir Advisor Dr S J Hashemifar hashemifar@cc iut ac ir Abstract In this thesis ZnO nanoparticles with different cobalt concentration were prepared by a simple and rapid method This method is based on a short time solid state milling and calcinations of zinc acetate cobalt acetate and citric acid powders The physical properties of the samples were characterized using X ray diffraction XRD Field Emission Scanning Electron Microscopy FE SEM Fourier Transform Infrared FTIR photoluminescence and UV vis spectroscopy It was shown that a very low substitution of Co less than 10 percent of molecular weight has little effect on the lattice param eters of ZnO and significantly decreases the band gap Eg value of the synthesized ZnO Co nanopar ticles Calculation based on the XRD data shows that the average crystallite sizes of ZnO particles are nearly 18 nm Photoluminescence spectroscopy shows that many defects such as interstitial zinc zinc vacancy and exciton recombination are responsible for the observed optical properties Magnetiza tion measurements which were recorded by a superconducting quantum interference device SQUID magnetometer determine the paramagnetic behaviour for all samples due to the absence of enough oxygen vacancy To study the nature of magnetic properties of this system Density functional theory was employed DFT can not predict correct band gap in semiconductor due to self interaction error so for predicting correct band gap and properties related that the many body GW approximation and ASIC approach was used First single shot GW G0W0 and self consistent GW scGW quasiparticle density of states upon GGA GGA U and HSE03 for Co doped zinc oxide are investigated The wurtzite crystal field split minority 3d Co states to e and t which the location of them is in doubt especially with LDA and GGA calculation In consideration to new many body scenario GW and its reputation to predict Eg and d binding energy in wide band semiconductor such as ZnO ZnS and LiF we have predicted the position of t to be equal to 1 4 4 3 eV above the conduction band minimum i e it is impossible to predict the presence of ferromagnetism in the absence of defects in zinc oxide doped with cobalt Then In order to better understand the role of extended defect structures in stabilizing long range magnetic order in this material the electronic structure of transition metal Co doped ZnO grain bound aries GBs was studied Recent experimental work has shown that grain boundaries and defects as sociated to them possibly play a fundamental role in the observed ferromagnetism of Co doped ZnO This observed correlation between the presence of GBs and ferromagnetism will be investigated in this work with the help of ab initio electronic structure calculations Identifying qualitative as well as quantitative differences between the electronic structures of Co dopant in the bulk material and at the grain boundary is key to understand this phenomenon Then we shall be employing self interaction corrected density functional theory DFT methods incorporated into the SIESTA platform And at the end the density functional full potential computations are performed to study the ring to cage structural crossover in the small ZnO n n 2 16 clusters and its effects on electronic and vibrational thermodynamic behaviour of the system The origin of this structural crossover which is found to occurs at n 10 is studied by the investigation of the behavior of the Zn O Zn bond angle

عبدالحسيني سارسري، اسماعيل

مطالعه ي ابتدا به ساكن و تجربي نيمرساناي مغناطيسي رقيق بر پايه ي اكسيد روي

اكسيد روي آلاييده به كبالت , تقريب بس ذره اي GW , تقريب تصحيح خود برهمكنش اتمي ASIC و خوشه هاي اكسيد روي