PZT/NFO/LSMO多层磁电外延薄膜微观结构研究

用脉冲激光沉积法在(110)取向的SrTiO3(STO)单晶衬底上制备了Pb(Zr0.52Ti0.48)O3/NiFe2O4/La0.7Sr0.3MnO3(PZT/NFO/LSMO)磁电复合外延薄膜,并用X射线衍射和透射电镜技术研究了外延薄膜的物相和显微结构。原子力显微镜结果表明PZT、NFO和LSMO薄膜表面均平整,晶粒尺寸分布均匀,表面粗糙度分别为1.8,1.7和0.2 nm。X射线衍射、选区电子衍射和高分辨透射电子显微镜(HRTEM)测试结果均证明各层薄膜沿(110)STO衬底外延生长,其外延关系为(110)PZT//(110)NFO//(110)LSMO//(110)STO和[001]PZT//[001]NFO//[001]LSMO//[001]STO。HRTEM结果显示,NFO/LSMO界面和LSMO/STO界面平整外延性好,无缺陷,而PZT/NFO界面较粗糙;NFO薄膜表面呈锯齿状,锯齿状面为立方NFO的能量最低{111}面,而PZT薄膜表面呈岛状,进一步的显微结构分析认为PZT薄膜为层状-岛状生长模式。     

半导体Si（001）基片上制备的超薄SrTiO3薄膜的透射电镜及电子全息研究

随着半导体技术的发展，Si基体上生长的高介电常数的钙钛矿晶体氧化物薄膜如SrTiO3（STO）也受到了广泛关注。SrTiO3（a=0.3905nm）在沿Si（001）方向旋转45℃之后和Si（d=0.384nm）之间的点阵错配很小（-1.7%），同时也有各种晶体氧化物薄膜在Si基体上生长很好的缓冲材料。本文主要利用透射电子显微镜和电子全息技术对薄膜的截面样品进行了界面微结构的研究。     

庞磁电阻La0.8Sr0.2MnO3薄膜的微结构研究

利用激光分子束外延方法在(001)SrTiO3衬底上制备庞磁电阻La0.8Sr0.2MnO3薄膜.发现高密度、尺度均匀的纳米聚集物弥散地分布在La0.8Sr0.2MnO3薄膜中.Z衬度像、EDS及电子衍射综合分析表明,这些纳米聚集物的内部成分出现起伏,主要特征是富Mn贫La,Mn/La的比值在其核心处达到极大值,形成立方结构的第二相MnO.LSMO薄膜由两种正交结构的取向畴组成.MnO与畴1的取向关系为[101]LSMO,1//[100]MnO和(010)LSMO,1//(010)MnO;与畴2的关系为[101]LSMO,2//[100]MnO和(010)LSMO,2//(001)MnO.在LSMO/STO外延体系中,还观察到大量的失配位错.失配位错的类型分为刃型失配位错,位错线沿<100>方向;螺型失配位错,位错线沿<110>方向.刃型位错是基中原有位错在薄膜生长过程中沿生长表面的扩展造成的;螺型失配位错的形成与降温过程中LSMO正交结构的取向畴的形成有关.     

La0.9Sr0.1MnO3/Si体系界面的电子显微学研究

本文利用透射电子显微术,研究了通过激光分子束外延方法在Si基体上生长的La0.9Sr0.1MnO3功能薄膜的显微结构特征及界面处的微区成分分布规律.结果表明,在Si基体上生长的La0.9Sr0.1MnO3薄膜由单相多晶体构成.这些多晶体颗粒以柱状结构生长,柱状晶垂直于界面并一直贯穿整个LSMO薄膜.La0.9Sr0.1MnO3薄膜具有正交点阵结构,其颗粒大小为10 nm～20 nm.在LSMO/Si的界面处发现了由化学反应引起的两个纳米尺度的非晶层.     

Cu—Ni—Be高导电耐磨合金时效析出的TEM研究

本文用TEM确定了Cu—Ni—Be合金时效时G·P区和γ’析出相(NiBe)是合金硬度、电导率变化的重要原因,同时确立了NiBe与母相之间的相位关系:(110)_P//(100)_M,[001]_P//[001]_M;惯析面为[001]。     

在(001)SrRuO_3/(001)SrTiO_3上外延生长c轴取向Bi_(3.15)Nd_(0.85)Ti_3O_(12)铁电薄膜的显微结构研究

用脉冲激光沉积在(001)SrRuO3,(001)SrTiO3上外延生长了c轴取向的Bi3.15Nd0.85Ti3O12(BNdT)铁电薄膜.SrRuO3底电极层厚约117 nm,BNdT薄膜厚～35nm.X射线衍射(XRD)和透射电镜(TEM)观察证实了SrRuO3层和BNdT薄膜的外延生长.通过TEM平面样品观察,在SrRuO3/BNdT界面附近看到了两种村度处于不同高度的失配位错网,位错线沿<110>走向,其柏格斯矢量沿[110]或[110]方向有分量,在[001]方向上可能没有分量.讨论了位错的形成机制.     

Si(001)外延ZnSe薄膜界面原子的结合与成键

基于密度泛函理论的第一性原理计算,通过对Si(001)和氮化Si(001)表面单层Zn/Se原子结合的方式,模拟ZnSe外延薄膜的二维生长模式,从单层原子结合能、界面原子电子得失、共价结合成键的角度解释了Zn/Se原子在衬底表面的黏附性问题,阐述了薄膜生长初期界面无定形Se出现等现象,分析了氮化Si(001)表面对薄膜二维均匀生长的作用,结果显示N的引入缓和了Si衬底的非极性共价结合与ZnSe原子间的极性离子键结合之间的异质差异。     

Mo基底的粗糙度对C轴择优取向AlN的影响

通过物理气相沉积的方法制备出Si／非晶／Mo／AlN多层膜器件,利用透射电子显微学方法研究了截面样品和AlN薄膜平面样品,确定了AlN和 Mo的界面形态和生长方式。研究表明二者取向关系为[2110] AlN／／[111]Mo,（0002）AlN／／（110）Mo,且Mo表面的粗糙程度对AlN的生长有影响,因此本文为改进器件性能提供了参考方向。     

In_xGa_(1-x)As/GaAs应变超晶格的电子结构

用有效质量理论研究了[001]和[111]方向生长的In_xGa_(1-x)As/GaAs应变超晶格的电子结构.具体计算了价带能级的色散曲线和光吸收曲线.沿[001]方向生长的光吸收曲线与实验进行了比较.内应变使重轻空穴能级发生上升和下降.由于压电效应,[111]方向生长的超晶格应变层内存在很强的内电场(1.5×10~5V/cm),而对[001]方向生长的应变超晶格不产生内电场.     

多铁性BiFeO3/SrTiO3多层膜的透射电镜研究

本文利用透射电子显微镜（TEM）研究了由磁控溅射法生长的多铁性BiFeO3/SrTiO3多层膜的微观结构。衍衬分析及高分辨电子显微（HRTEM）像显示出界面清晰的各个单层。BiFeO3外延生长在SrTiO3（001）衬底上,生长方向沿基体c轴。随着薄膜厚度的增加,即多层膜周期的加长,层与层之间界面不再平直。原子序数Z衬度成像,EDS线扫以及各种元素的能量过滤综合分析确定了多层膜的成分变化特征。     

Characterization of crystalline MOCVD SrTiO3 films on SiO2/Si(100)

SrTiO₃ thin films (STO), were deposited on Si(100) covered by 2 nm of SiO₂, at different temperatures from 450 °C to 850 °C using liquid injection MOCVD, the bimetallic precursor being Sr₂Ti₂(OiPr)₈(tmhd)₄. The STO films were analysed by XRD, FTIR, SIMS and TEM. An amorphous layer was observed between STO and SiO₂/Si. The nature and thickness of the interlayer were determined, as well as the most favourable conditions for a good quality crystalline STO film, and a reduced interlayer.     

Determination of absolute thickness and mean free path of thin foil specimen by zeta-factor method

The zeta-factor method is applied to the thickness determination of thin amorphous specimens where the convergent-beam electron diffraction method is not applicable. Characteristic X-ray intensities are first measured using standard specimens in order to determine zeta-factors. These zeta-factors are then used to determine local thicknesses of an amorphous Si and an amorphous Al alloy. Electron energy-loss spectroscopy (EELS) spectra are acquired at the same positions as for the X-ray measurements. Thus, using the thicknesses measured from the zeta-factor method, the electron mean-free path is determined through the EELS log-ratio method. The mean free path is measured as a function of the collection semi-angle, beta, and specimen thickness, and it is also compared with theoretical values. Furthermore, the mean free path of amorphous Si is compared with that of the crystalline Si.     

非晶态SiO2过渡层对生长C轴取向LiNbO3薄膜的影响

采用磁控溅射方法,在Si衬底和LiNbO3薄膜之间引入SiO2过渡层制备LiNbO3薄膜。采用X射线衍射（XRD〉、傅里叶变换红外吸收光谱（FT-IR）和扫描电子显微镜（SEM）对LiNbO3薄膜的结晶取向、组成成分和表面形貌进行了表征,重点研究了非晶态SiO2过渡层对LiNbO3薄膜C轴取向的影响。结果表明,非晶态S...     

a-SiN_x/nc-Si/a-SiN_x三明治结构的电荷存储效应

采用等离子体增强化学气相淀积 (PECVD)生长技术结合限制性结晶原理 ,采用与硅平面工艺相兼容的准静态热退火方法 ,使 a-Si:H层晶化 ,制备出了高密度的、尺寸均匀的 nc-Si薄膜 ;利用 Raman散射和透射电镜 (TEM)技术 ,分析了样品的结构特性 ;采用 C-V测量方法 ,通过对退火和未退火样品的对比分析 ,对该三明治样品的电学性质进行了研究 ,观察到 nc-Si薄膜的电荷存储现象 ,并且该现象与 nc-Si层的厚度有着明显的关系。     

Catalyst‐Free Synthesis and Characterization of Metastable Boron Carbide Nanowires

Catalyst‐free growth of boron carbide nanowires is achieved by pyrolysis of diborane and methane at 650–750 °C and around 500 mTorr in a quartz tube furnace. Electron‐diffraction analysis using a novel diffraction‐scanning transmission electron microscopy (D‐STEM) technique indicates that the crystalline nanowires are single‐crystal orthorhombic boron carbide. TEM images show that the nanowires are covered by a 1–3 nm thick amorphous layer of carbon. Elemental analysis by electron energy loss spectroscopy (EELS) shows only boron and carbon while energy‐dispersive X‐ray spectroscopy (EDX) and X‐ray photoelectron spectroscopy (XPS) show the presence of oxygen as well as boron and carbon.     

Praseodymium Silicate as a High‐k Dielectric Candidate: An Insight into the Pr2O3‐Film/Si‐Substrate Interface Fabricated Through a Metal–Organic Chemical Vapor Deposition Process

Praseodymium‐containing thin films have been deposited on Si(001) substrates by metal–organic chemical vapor deposition (MOCVD) from the Pr(tmhd)₃ (H‐tmhd = 2,2,6,6‐tetramethyl‐3,5‐heptanedione) precursor. The structural, compositional, and morphological film characterization has been investigated using X‐ray diffraction (XRD), angle‐resolved X‐ray photoelectron spectroscopy (AR‐XPS), and transmission electron microscopy (TEM). Detailed studies of the deposition parameters indicate that the MOCVD process is governed by a kinetic regime and that some reactive phenomena occur at the film/substrate interface, forming a praseodymium silicate layer. A possible explanation for interfacial interaction has been proposed, taking into account the diffusion of Si from the substrate towards the bulk and that of oxygen from the film surface toward the substrate/film interface. Finally, the electrical characterization of the praseodymium silicate layer has been carried out in order to evaluate its potential implementation as an alternative dielectric. Its dielectric constant has been evaluated to be ～ 8.     

Physical and electrical characterization of polysilicon vs. TiN gate electrodes for HfO2 transistors

The effects of pre-deposition substrate treatments and gate electrode materials on the properties and performance of high-k gate dielectric transistors were investigated. The performance of O₃ vs. HF-last/NH₃ pre-deposition treatments followed by either polysilicon (poly-Si) or TiN gate electrodes was systematically studied in devices consisting of HfO₂ gate dielectric produced by atomic layer deposition (ALD). High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) using X-ray spectra and Electron Energy Loss Spectra (EELS) were used to produce elemental profiles of nitrogen, oxygen, silicon, titanium, and hafnium to provide interfacial chemical information and to convey their changes in concentration across these high-k transistor gate-stacks of 1.0–1.8 nm equivalent oxide thickness (EOT). For the TiN electrode case, EELS spectra illustrate interfacial elemental overlap on a scale comparable to the HfO₂ microroughness. For the poly-Si electrode, an amorphous reaction region exists at the HfO₂/poly-Si interface. Using fast transient single pulse (SP) electrical measurements, electron trapping was found to be greater with poly-Si electrode devices, as compared to TiN. This may be rationalized as a result of a higher density of trap centers induced by the high-k/poly-Si material interactions and may be related to increased physical thickness of the dielectric film, as illustrated by HAADF-STEM images, and may also derive from the approximately 0.5 nm larger EOT associated with polysilicon electrodes on otherwise identical gate stacks.     

Characterization of hafnium oxide grown on silicon by atomic layer deposition: Interface structure

Ultra-thin films of hafnium oxide deposited on Si(1 0 0) substrates by means of atomic layer deposition using tetrakis(diethylamino)hafnium as the hafnium precursor are characterized. These films and interface structures are probed using Fourier transform infrared spectroscopy along with Z-contrast imaging and electron energy loss spectroscopy (EELS) of a scanning transmission electron microscope. The interface structure of HfO₂/Si(1 0 0) is further investigated using angle resolved X-ray photoelectron spectroscopy to probe the core level orbitals (Hf 4f, Si 2p, O 1s) at high resolution. The interfacial differences are also examined by probing the Hf 4f bonding with normal incidence XPS in thin and thick films. The XPS studies show that the binding energies remain unchanged with film depth and that there is no apparent signature of silicate structure in the as-deposited films. EELS spectra taken at the interface and XPS measurements suggest the interface is mainly silicon oxide. Two different cleaning methods used show difference only in the thickness of the silicon oxide interlayer.