铁电相BiFeO3对多铁复合薄膜CoFe2O4-BiFeO3铁磁性能的影响

为了研究铁电相BiFeO₃对复合薄膜磁性能的影响,在LaNiO₃ (LNO)缓冲层的Si (100)衬底上旋涂制备了含有0、6、9、10层等不同厚度BiFeO₃的层状CoFe₂O₄-BiFeO₃ (CFO-BFO) 多铁复合薄膜。采用XRD、SEM以及TEM对其结构和形貌进行了表征,采用振动样品磁强计测量磁性,研究了不同厚度BFO对复合薄膜磁性的影响。结果表明: CFO和BFO在异质结构薄膜中共存。缓冲层LNO和铁磁相CFO薄膜具有精细微观结构及明显界面。铁电相BFO的厚度对CFO-BFO复合薄膜的磁性能产生了很大影响。在含有不同层数铁电相BFO的复合薄膜中,含有9层BFO复合薄膜的饱和磁化强度最大,达到了230 emu·cm^-3,相比无铁电相BFO的薄膜,饱和磁化强度提高了18.6%。初步讨论认为: 随着铁电相BFO厚度的增加,CFO与BFO之间的应力传导引起了复合薄膜饱和磁化强度的提高。     

残余应力对SrRuO3薄膜磁学及电输运性能的影响

采用射频磁控溅射法在单晶SrTiO₃ (STO)衬底和硅(Si)衬底上制备出不同取向的SrRuO₃ (SRO)薄膜, 对薄膜的残余应力进行了分析, 并研究了应力对不同取向SRO薄膜磁学性能与电输运特性的影响。根据X射线衍射(XRD)结果分析可知, Si基SRO薄膜为多晶单轴取向薄膜, 且应力来源主要为热失配拉应力; STO基SRO薄膜为外延薄膜, 其应力主要为热失配压应力和外延压应力; 磁学性能测试表明, (001)取向SRO薄膜比(110)取向薄膜拥有更高的居里温度T_C; 压应力提高了(001)取向SRO薄膜的T_C, 却降低了(110)取向薄膜的T_C。电阻性能测试表明, 对于在同种类型衬底上沉积的SRO薄膜, (001)取向的薄膜的剩余表面电阻比(RRR)高于(110)取向的薄膜。另外, 拉应力引起了薄膜微结构的无序度增加, 弱化了表面电阻率的温度依赖性, 提高了金属绝缘体转变温度(T_MI)。     

Sol-gel法制备LaNiO3/Bi4Ti3O12异质薄膜及性能研究

采用Sol-gel(溶胶-凝胶)法在Si衬底上制备LaNiO3/Bi4Ti3O12(LNO/BTO)叠层薄膜,并研究了不同退火温度下BTO薄膜的生长行为和铁电、介电性能.试验表明,与单晶Si直接作衬底制备的Bi4Ti3O12薄膜相比,引入过渡层LNO降低了Bi4Ti3O12薄膜与衬底的晶格失配度,减少了热应力和外应力,缓解了薄膜龟裂的现象,而且制备出的Ag/BTO/LNO/Si异质薄膜电容具有优良的介电性质.     

新型硅基双异质外延SOI材料Si/γ-Al2O3/Si制备

异质外延法是目前制备新型SOI材料的技术途径之一。采用低压化学气相沉积技术(LPCVD)在硅衬底上先外延γ-Al2O3绝缘单晶薄膜，制备出硅衬底上外延氧化物外延结构γ-Al2O3/Si(EOS)，然后采用类似SOS薄膜生长的常压CVD(APCVD)方法在EOS上外延硅单晶薄膜，形成新型硅基双异质SOI材料Si／γ-Al2O3／Si。利用反射高能电子衍射(RHEED)、X射线衍射(XRD)、俄歇电子能谱(AES)及MOS电学测量等技术表征分析了Si(100)／γ-Al2O3(100)／Si(100)SOI异质结构的晶体结构、组分和电学性能。测试结果表明，已成功实现了高质量的新型双异质外延SOI结构材料Si(100)／γ-Al2O3(100)／Si(100)，γ-Al2O3与Si外延薄膜均为单晶，γ-Al2O3薄膜具有良好绝缘性能，SOI结构界面清晰陡峭，该SOI材料可应用于CMOS电路的研制。     

衬底温度对Si(111)衬底上MBE异质外延3C-SiC薄膜的影响

利用固源分子束外延(SSMBE)技术, 在Si(111)衬底上异质外延生长3C-SiC单晶薄膜, 通过RHEED、XRD、AFM、XPS等实验方法研究了衬底温度对薄膜结构、形貌和化学组分的影响. 研究结果表明, 1000℃生长的样品具有好的结晶质量和单晶性. 在更高的衬底温度下生长, 会导致大的孔洞形成, 衬底和薄膜间大的热失配使降温过程中薄膜内形成更多位错, 从而使晶体质量变差. 在低衬底温度下生长, 由于偏离理想的化学配比也会导致薄膜的晶体质量降低.     

不同衬底上LaNiO3导电氧化物薄膜的制备和研究

通过MOD法和快速热处理过程,在Si(100)和Pt(111)/Ti/SiO2/Si衬底上制备了LaNiO3(LNO)导电氧化物薄膜.经XRD结构分析表明,所制备的LNO薄膜具有纯的钙钛矿结构,并且以(100)方向择优取向.经SEM和AFM分析表明,LNO薄膜具有表面均匀、无裂纹.经标准四探针法测试表明,LNO薄膜具有好的金属特性,其室温电阻率为7.6×10-4Ω·cm.铁电性能测试表明,LNO薄膜可以提高PZT铁电薄膜的剩余极化强度.     

CdIn2S4光电薄膜材料的制备及光电性能研究

以氯化镉(CdCl₂·2.5H₂O)、氯化铟(InCl₃·4H₂O)和硫代乙酰胺(TAA)为原料，利用水热法在FTO导电基底上制备CdIn₂S₄薄膜材料。利用X射线粉末衍射仪(XRD)、扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、紫外-可见漫反射光谱(UV-Vis)等手段对所得薄膜的物相结构、表面形貌、成分及光吸收性能等进行表征。借助瞬态表面光电压(TSPV)技术探究CdIn₂S₄薄膜的光生载流子的分离、传输及复合过程。结果表明：制备的CdIn₂S₄薄膜结晶良好、表面均匀平整且具有良好的光吸收性能和光电响应。构建了以CdIn₂S₄和P3HT为吸收层、TiO₂为电子传输层的异质结薄膜太阳能电池器件(FTO/TiO₂/CdIn₂S₄     

异质外延MgO/SrTiO3薄膜中界面应力研究

本文利用激光分子束外延(LMBE)技术在SrTiO3(100)单晶基片上外延生长MgO薄膜，同时又在MgO(100)单晶基片上外延生长SiO3(STO)薄膜。通过反射高能电子衍射(RHEED)仪原位实时监测薄膜生长，研究薄膜的生长过程。并结合X射线衍射(XRD)仪来分析在不同的生长条件下，不同应力对薄膜外延生长的影响。在压应力情况下，MgO薄膜在STO基片上以单个晶胞叠层的方式生长，即以“Cubicon Cubic”方式进行外延；在张应力情况下，由于膜内位错较多，STO薄膜在MgO基片上以晶胞镶嵌的方式进行生长，即以“Mosaic”结构进行外延；提高生长温度，可以减少膜内位错，提高外延质量，使STO薄膜在MgO基片上以较好的层状方式外延生长。     

BST类铁电薄膜低温外延层状生长研究

利用激光分子束外延技术(LMBE)在SrTiO₃(100)单晶基片上外延生长SrTiO₃(STO)、BaTiO₃(BTO)、Ba_0.6Sr_0.4TiO₃(BST)铁电薄膜.通过反射高能电子衍射(RHEED)实时监测薄膜生长,并结合原子力显微镜(AFM)分析薄膜的生长模式,根据RHEED衍射强度振荡曲线及衍射图样的变化确定动态和静态控制最低晶化温度,发现STO、BTO、BST三种铁电薄膜可以分别在280、330、340℃的低温下实现外延层状生长.     

偏轴磁控溅射法外延BiFeO3薄膜的介电性能与阻变效应

利用偏轴射频磁控溅射法, 在(001) SrTiO₃(STO)单晶基片上制备了Pt/BiFeO₃/La_0.5Sr_0.5CoO₃/STO (Pt/BFO/ LSCO/STO)异质结电容器。研究了BiFeO₃薄膜的结构和物理性能。原子力显微镜(AFM)和X射线衍射(XRD)分析表明: BFO薄膜结晶质量良好, 且为单相(00l)外延钙钛矿结构。介电性能测试结果发现: 在5 V驱动电压下, Pt/BFO/LSCO电容器呈现饱和的蝶形回线, 调谐率和介电损耗分别为14.1%和0.19。此外, 阻变机制研究表明: 在0→5→0 V正向电压和0→-5→0 V负向电压下, 阻变均为高阻向低阻转变规律, 呈现为铁电二极管的阻变开关行为。通过I-V曲线拟合, 得到0→5→0→-5 V时阻变机制为空间电荷限制电流陷阱能级的填充和脱陷, 而-5→0 V时符合界面限制的F-N隧穿机制。     

Low-temperature epitaxial growth of conductive LaNiO3 thin films by RF magnetron sputtering

Epitaxial growth of LaNiO₃ (LNO) thin films was successful on CeO₂/YSZ/Si(100), MgO(100) and SrTiO₃ (STO)(100) substrates by RF magnetron sputtering at 300 °C, although pulsed laser deposition requires 600 °C to prepare epitaxial LNO films according to the literature. Epitaxial LNO films deposited on CeO₂/YSZ/Si(100) and STO(100) had single orientation of LNO[100]//CeO₂[110]//YSZ[110]//Si[110]) and LNO[100]//STO[100], respectively. On the other hand, epitaxial LNO films deposited on MgO(100) had mixed orientations of LNO[100]//MgO[100] and LNO[100]//MgO[110]. The lattice parameter, composition and resistivity of the LNO thin films were strongly dependent on the substrate temperature. The minimum resistivity of LNO films was approximately 5×10⁻⁶ Ω m, which value almost agrees with the resistivity in the literature. It was found that the temperature to achieve minimum resistivity was 200 °C, irrespective of the type of substrate. The surface of the LNO films was smooth and flat.     

Comparative analysis for the crystalline and ferroelectric properties of Pb(Zr,Ti)O3 thin films deposited on metallic LaNiO3 and Pt electrodes

The crystalline quality and ferroelectricity of the Pb(Zr,Ti)O₃ (PZT) films deposited on the metallic LaNiO₃ (LNO) and Pt electrodes were comparatively analyzed to investigate the possibility for their application to non-volatile memory devices. LNO thin films were successfully deposited on various substrates by using r.f. magnetron sputtering even at a low temperature ranging from 250 to 500 °C, and the ferroelectric PZT thin films were spin-coated onto the LNO and Pt bottom electrodes. Metallic LNO thin films exhibited [100] orientation irrespective of the substrate species and PZT films coated onto LNO films had highly a- and c-axis orientations, while those with Pt bottom electrode were polycrystalline. PZT films with LNO bottom electrode had smaller grain size and larger dielectric constant compared to those grown on the Pt electrode. The ferroelectric thin films fabricated on LNO bottom electrode displayed an asymmetric D–E hysteresis loop, which was explained by the defect effects formed at the interface. Especially, the LNO/PZT/LNO capacitor was found to significantly improve the polarization fatigue and the effects of the LNO electrodes to the fatigue were discussed.     

Fabrication of epitaxial conductive LaNiO3 films on different substrates by pulsed laser ablation

LaNiO₃ (LNO) thin films were deposited on (1 0 0) MgO, SrTiO₃ (STO) and LaAlO₃ (LAO) crystal substrates by pulsed laser deposition (PLD) under 20 Pa oxygen pressure at different substrate temperatures from 450 to 750 °C. X-ray diffraction (XRD), ex situ reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) were employed to characterize the crystal structure of LNO films. LNO films deposited on STO and LAO at a temperature range from 450 to 700 °C exhibit high (0 0 l) orientation. XRD ψ scans and RHEED observations indicate that LNO films could be epitaxially grown on these two substrates with cubic-on-cubic arrangement at a wide temperature range. LNO films deposited at 700 °C on MgO (1 0 0) substrate have the (l l 0) orientation, which was identified to be bicrystalline epitaxial growth. La₂NiO₄ phase appears in LNO films deposited at 750 °C on three substrates. The epitaxial LNO films were tested to be good metallic conductive layers by four-probe method.     

Alkoxide route to La0.5Sr0.5CoO3 epitaxial thin films on SrTiO3

An all alkoxide based sol–gel route was investigated for preparation of epitaxial La_0.5Sr_0.5CoO₃ (LSCO) films on 100 SrTiO₃ (STO) substrates. Films with 20–30 to 80–100 nm thickness were prepared by spin-coating 0.2–0.6 M (metal) solutions on the STO substrates and heat treatment to 800 °C at 2 °C min^− 1, 30 min, in air. The films were epitaxial with a cube-on-cube alignment and the LSCO cell was strained to match the STO substrate of 3.905 Å closely; a and b = 3.894 Å and 3.897 Å for the 20–30 and 80–100 nm films, respectively. The c-axis was compressed to 3.789 Å and 3.782 Å for the 20–30 and 80–100 nm films, respectively, which resulted in an almost unchanged cell volume as compared to polycrystalline film and nano-phase powders prepared in the same way. The SEM study showed mainly very smooth, featureless surfaces, but also some defects. A film prepared in the same way on an -Al₂O₃ substrate was dense and polycrystalline with crystallite sizes in the range 10–50 nm and gave cubic cell dimensions of a_c = 3.825 Å. The conductivity of the ca 30–40 nm thick polycrystalline film was 1.7 mΩcm, while the epitaxial 80–100 nm film had a conductivity of around 1.9 mΩcm.     

Heteroepitaxial growth of tungsten oxide films on sapphire for chemical gas sensors

The performance of chemiresistive gas sensors made from semiconducting metal oxide films is influenced by film stoichiometry, crystallographic structure, surface morphology and defect structure. To obtain well-defined microstructures, heteroepitaxial WO₃ films were grown on r-cut and c-cut single crystal sapphire substrates using rf magnetron Ar/O₂ reactive sputtering of a W target. On r-cut sapphire, an epitaxial tetragonal WO₃ phase is produced at a 450°C deposition temperature whereas 650°C growth stabilizes an epitaxial monoclinic WO₃ phase. On c-cut sapphire, a metastable hexagonal WO₃ phase is formed. RHEED and X-ray diffraction indicate that the films have a ‘polycrystalline epitaxial structure’ in which several grains are present, each having the same crystallographic orientation. STM analysis of the film surfaces reveals morphological features that appear to be derived from the substrate symmetries. The monoclinic phase has a step/terrace growth structure, has the smallest mosaic spread in XRD rocking curves and exhibits the highest degree of reproducibility suggesting that it is the best suited for sensor applications. Measurements of film conductivity versus temperature indicate that the charge transport mechanisms are also dependent on the crystallographic phase and microstructure of the WO₃ films.     

Stoichiometry determination of VOx thin films by O-RBS spectrometry

This paper reports on the stoichiometry determination of epitaxially grown vanadium monoxide (VO_x) thin films on MgO(100) substrates. The epitaxial growth was confirmed by RHEED, LEED and XRD techniques. The oxygen content of VO_x thin films, as a function of oxygen flux, was determined using Rutherford backscattering spectrometry. The ¹⁸O isotope was used for film growth, in order to distinguish between the oxygen of film and substrate. The upper and lower stoichiometry limit found are consistent with the ones known for bulk material.     

Fabrication of LSS bottom electrode by PLD

Polycrystalline LaNiO₃/SrTiO₃/Si(100) (LSS) conducting substrates were fabricated by pulsed laser deposition (PLD) technique. LSS substrate is a potential candidate for the multiferroic materials for use as bottom electrode. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) equipped with EDX system, atomic force microscopy (AFM) and electrical resistivity were employed to characterize the films. Buffer layer SrTiO₃ (STO) deposited at 700 °C resulted in dense, smooth and with crack free features. XRD studies confirmed bi-crystalline [(100), (110)] growth of STO on Si(100) substrate. Deposition of bottom electrode LaNiO₃ (LNO) epitaxially followed the buffer layer. EDX analyses determined the chemical composition of the films. The role of oxygen partial pressure during deposition affecting the crystallinity and resistivity of the films was explored in detail. Atomic force microscopy revealed the atomic scale features of the films desirable for functional devices. Resistivity of the conducting film (LNO) was ∼10⁻⁴ Ω cm at room temperature. Thus it is demonstrated that LNO/STO/Si(100) is a suitable conducting substrate for growth of the multiferroic functional materials.