【作者】 徐静；

【导师】 王海英；

【作者基本信息】 河南师范大学 ， 材料科学与工程， 2019， 硕士

【摘要】 稀磁半导体由于结合了半导体的电学性质和磁性材料的磁学性质,并且在自旋场效应晶体管和随机磁性存储器方面广范的应用,受到研究学者的广泛关注。关于TiO₂基材料稀磁特性的研究主要集中在元素掺杂,比如Co,Mn,Ru,Mo,Fe等。但是对于稀磁半导体的稀磁特性来源仍然没有统一的结论。有报道指出,磁性来源于样品中Ti³⁺离子的存在,也有报道指出磁性来源于样品中存在氧空位。为了更深入的研究二氧化钛掺杂样品磁性的来源,本研究采用非金属元素N和金属元素（Ru,Ag,W）共同掺杂的方式,研究TiO₂掺杂材料的稀磁特性来源,本论文主要包含以下方面:（1）通过第一性原理和阳极氧化法相结合的方法研究了不掺杂,N掺杂,Ru掺杂,Ru/N共掺杂TiO₂的稀磁特性来源。实验制备的所有样品均为锐钛矿结构并且在室温下表现出铁磁行为。实验中测得不掺杂,N掺杂,Ru掺杂,Ru/N共掺杂TiO₂的饱和磁矩分别为0.065emu/g,0,015 emu/g,0.155 emu/g,0.073 emu/g。而采用第一性原理磁距计算结果为Ru掺杂>Ru/N共掺杂>不掺杂>N掺杂。实验和理论结果高度的吻合。氧空位的存在对TiO₂稀磁特性来源有着关键的作用。而且计算结果表明,Ru 4d,N 2p,O 2p的杂化导致了Ru 4d,N 2p,O 2p轨道的劈裂,对样品的磁性产生重要的作用。（2）采用TiO₂单晶基片,光化学沉积方法制备了Ag掺杂和Ag/N共同掺杂TiO₂薄膜。采用不同的测试手段研究了制备样品的光学特性和磁性。X射线衍射结果未显示任何氧化银相关的峰,表明Ag可能作为Ag原子存在于Ag掺杂的TiO₂单晶薄膜中。XPS结果表明Ag和Ti以Ag⁰和Ti⁴⁺的形式存在在Ag/N共掺杂TiO₂单晶薄膜中。结果表明Ag以Ag原子形式沉积在TiO₂单晶薄膜表面。并且Ag原子可以提高Ag掺杂TiO₂单晶薄膜的铁磁性。Ag和N共同掺杂TiO₂单晶片的实验结果表明Vos和Ag原子的存在共同影响Ag/N共同掺杂TiO₂单晶薄膜的铁磁性。（3）采用直流磁控方法制备了不掺杂,N掺杂,WO₃负载的不掺杂,WO₃负载的N掺杂TiO₂金红石单晶基片。N掺杂和WO₃负载分别用来增加和减少样品中Vos的浓度。XRD结果表明N掺杂和WO₃负载并没有改变TiO₂样品的峰。XPS结果表明,W元素主要以WO₃负载TiO₂金红石单晶基片上。UV结果表明WO₃负载的不掺杂,WO₃负载的N掺杂TiO₂金红石单晶吸收边有略微的红移,导致带隙的减小。PL谱表明由于退火氛围的影响,所有样品中均存在Vos,N掺杂增加样品中Vos的浓度,WO₃负载减少样品中Vos的浓度。样品中的饱和磁矩顺序为:N掺杂TiO₂>WO₃负载的N掺杂TiO₂>不掺杂TiO₂>WO₃负载的不掺杂TiO₂,和样品中Vos的顺序一致。N掺杂提高了样品饱和磁化强度,WO₃负载降低了样品饱和磁化强度。更多还原

【Abstract】 Diluted magnetic oxide semiconductors（DMOSs）have been extensively studied because of the combined transport properties and magnetic properties,which are desirable for spintronic applications,such as spin field-effect transistors and magnetoresistance random access memory.The investigations mainly focus on element doped TiO₂,such as Co,Mn,Ru,Mo,Fe.Researchers reported that,the origin of RTFM mainly comes from the Ti³⁺exists in samples;others researchers reported that the origin of RTFM mainly comes from the Vos exists in samples.To study the RTFM origin of TiO₂ doped samples,non-metal element（N）and the metal element（Ru,Ag,W）co-doped TiO₂ samples were investigated.The details are shown follows:（1）The room temperature ferromagnetism（RTFM）of the undoped,N doped,Ru doped,and Ru-N co-doped anatase TiO₂ nanotubes（TNTs）films are investigated combined with experiments and first principles approaches.All samples display anatase structures and ferromagnetism at room temperature.The values of the saturation magnetization（Ms）of undoped TiO₂,N doped TiO₂,Ru doped TiO₂,and Ru/N codoped TiO₂,respectively,are 0.065emu/g,0.015emu/g,0.155emu/g,and 0.073emu/g.The calculated net moment is in the order of Ru doped>Ru/N co-doped>un-doped>N doped.The oxygen vacancies play an important role in RTFM of TNTs.The experiments are highly consistent with the theory calculations.Moreover,the hybridization of Ru 4d,N 2p,and O 2p led to the spin-spilt of Ru 4d,N 2p,and O 2p which is devoted to the system magnetism.（2）We employ TiO₂ single-crystal films as a substrate and use photochemical deposition method to prepare Ag doped and Ag/N co-doped TiO₂ single-crystal films.We also investigate the optical and magnetic properties of the samples using various measurements.No diffraction peaks related to silver oxide appear in the X-ray diffraction（XRD）spectra,which implies the existence of Ag atoms in Ag-doped TiO₂ single-crystal films.X-ray photoelectron spectroscopy（XPS）spectra indicate the existence of Ti⁴⁺and Ag⁰ in Ag/N co-doped TiO₂ single crystal films.It is found that Ag is deposited on a TiO₂single-crystal film surface in the form of Ag particles.Meanwhile,Ag particles can slightly enhance ferromagnetism in Ag-doped TiO₂ single-crystal films compared with the TiO₂ single-crystal film sample.Oxygen vacancies and Ag particle synergy influence ferromagnetism in Ag/N co-doped TiO₂ single-crystal films.（3）In this work,undoped,N-doped,WO₃-loaded undoped,and WO₃-loaded with N-doped TiO₂ rutile single-crystal wafers were fabricated by direct current（DC）magnetron sputtering.N-doping into TiO₂ and WO₃ loading onto TiO₂ surface were used to increase and decrease oxygen vacancies.Various measurements were conducted to analyze the structural and magnetic properties of the samples.X-ray diffraction results showed that the N-doping and WO₃ loading did not change the phase of all samples.X-ray photoelectron spectroscopy results revealed that W element loaded onto rutile single-crystal wafers existed in the form of WO₃.UV-Vis spectrometer results showed that the absorption edge of WO₃-loaded undoped and WO₃-loaded with N-doped TiO₂ rutile single-crystal wafers had red shift,resulting in a slight decrease in the corresponding band gap.Photoluminescence spectra indicated that oxygen vacancies existed in all samples due to the post annealing atmosphere,and oxygen vacancies density increased with N-doping,while decreasing with WO₃ loading onto TiO₂ surface.The magnetic properties of the samples were investigated,and the saturation magnetization values were in the order N-doped>WO₃-loaded with N-doped>undoped>WO₃-loaded undoped rutile single-crystal wafers,which was the same order as the oxygen vacancy densities of these samples.N-doping improved the saturation magnetization values,while WO₃-loaded decreased the saturation magnetization values.This paper reveals that the magnetic properties of WO₃-loaded with N-doped rutile single-crystal wafers originate from oxygen vacancies.更多还原