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TFA-MOD方法制备YBCO超导薄膜研究 总被引:4,自引:1,他引:3
采用TFA-MOD方法在LaAlO3(001)单晶基片上制备了性能良好的YBCO超导薄膜:临界电流密度(Jc)可达3MA/cm2(77K,0T),超导转变温度Tc≈90K,转变宽度ΔTc=0.5K,其一次涂层厚度达338nm.通过X射线衍射(XRD)分析表明YBCO具有纯c-轴取向、无a-轴取向的晶粒存在.ω扫描分析表明该YBCO薄膜具有很好的面外外延性,其摇摆曲线的半高宽(FWHM)为0.653°. 用SEM分析也表明膜的表面无裂纹存在,表面平整,没有a轴晶粒生长. 相似文献
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本文对 Bi 系中可能存在一种 T_c>100K 的2212相作了进一步的论证.化学分析显示普通的2212相中 Cu~(3+)含量为~10%,而2223相和 T_c>100K 的2212相中 Cu~(3+)的含量却大于30%.从 DTA-TG 实验中观察到普通2212相和2223相失去晶格氧的量为0.8%,而含 T_c>100K 的2212相的样品失去晶格氧的量为~2%,说明这种2212相受氧含量影响更大.文中还介绍了一种简易判断样品中是否存在2223相和普通2212相的经验方法. 相似文献
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微波处理技术在材料科学工程中的应用 总被引:6,自引:0,他引:6
本文介绍了微波处理技术在材料科学与工程中的应用及原理,以及微波 技术的特点和优势,并指出了应用中的技术难点。 相似文献
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Sodium beta-alumina thin films as gate dielectrics for A1GaN/GaN metal-insulator-semiconductor high-electron-mobility transistors 下载免费PDF全文
<正>Sodium beta-alumina(SBA) is deposited on AlGaN/GaN by using a co-deposition process with sodium and Al2O3 as the precursors.The X-ray diffraction(XRD) spectrum reveals that the deposited thin film is amorphous.The binding energy and composition of the deposited thin film,obtained from the X-ray photoelectron spectroscopy(XPS) measurement,are consistent with those of SBA.The dielectric constant of the SBA thin film is about 50.Each of the capacitance-voltage characteristics obtained at five different frequencies shows a high-quality interface between SBA and AlGaN.The interface trap density of metal-insulator-semiconductor high-electron-mobility transistor(MISHEMT) is measured to be(3.5~9.5)×1010 cm-2·eV-1 by the conductance method.The fixed charge density of SBA dielectric is on the order of 2.7×1012 cm-2.Compared with the AlGaN/GaN metal-semiconductor heterostructure high-electronmobility transistor(MESHEMT),the AlGaN/GaN MISHEMT usually has a threshold voltage that shifts negatively. However,the threshold voltage of the AlGaN/GaN MISHEMT using SBA as the gate dielectric shifts positively from—5.5 V to—3.5 V.From XPS results,the surface valence-band maximum(VBM-EF) of AlGaN is found to decrease from 2.56 eV to 2.25 eV after the SBA thin film deposition.The possible reasons why the threshold voltage of AlGaN/GaN MISHEMT with the SBA gate dielectric shifts positively are the influence of SBA on surface valence-band maximum (VBM-EF),the reduction of interface traps and the effects of sodium ions,and/or the fixed charges in SBA on the two-dimensional electron gas(2DEG). 相似文献
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采用基于密度泛函理论的分子动力学方法,对α-Al2O3(0001)表面 Al,O原子空位缺陷及其对ZnO吸附进行了理论计算.电子局域函数显示了表面空位处的电子密度变化,表面Al原子空缺处有非常明显的缺电子区域,悬挂键临近O的电子密度增大,有利于对Zn的吸附;O原子空缺处的Al原子处存在孤立电子,其ELF值为005—03,将有利于同电负性较大的O或O2-结合.通过吸附动力学模拟与体系能量的计算发现,表面缺陷显著增强了表面 的化学吸附,空缺原子处都被吸附原子填补,吸附结合能远大于单晶表面的情况.在Al空缺的表面,由于ZnO的O与表面O形成双键,破坏了α-Al2O3(0001)表面O六 角对称结构,减小了 O的表面扩散,从而不利于规则的ZnO薄膜生长.相反,O的空缺表面,弥补了α-Al2O3(0001)表面O空位缺陷,不影响基片表面O六角对称结构. 相似文献
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Density functional theory is used to investigate the surface structures and the energies of two possible terminated LaAlO3 (001) surfaces with oxygen vacancies, i.e. LaO- and AlO2-terminated surfaces. The large displacements of ions, deviated from their crystalline sites, can lead to the formation of the surface rumpling. From thermodynamics analysis, the AlO2-terminated surface with oxygen-vacancies is less stable than the LaO-terminated one. Some states in the gap lie under the Fermi level by about -1eV in the LaO-terminated surface with oxygen vacancies. For the AlO2- terminated oxygen-vacancy surface, some O 2p states move into the mid-gap region and become partially unoccupied. The two types of termination surfaces exhibit conduction related to oxygen vacancies. Our results can contribute to the application of LAO films to high dielectric constant materials. 相似文献