衬底温度和N_2流量比对SI基GaN薄膜的影响

为了获得高质量的GaN薄膜,首先用射频磁控溅射的方法在Si基片合成Ga_2O_3薄膜,再通过高温氨化法与NH_3自组装形成GaN薄膜。然后分别用扫描电子显微镜和X-射线衍射仪对薄膜的形貌和结构进行了表征。结果发现GaN薄膜是纤锌矿结构并沿着晶面(002)方向择优生长。GaN薄膜的生长速率随着衬底温度的升高逐渐下降,结晶质量随着衬底温度的升高逐渐变差。同时晶粒表面较为平整;随着N_2流量比的适量增加,薄膜的结晶质量提高,晶体颗粒较为均匀,通过分析薄膜的生长机理,给出了GaN薄膜的最佳工艺条件。     

钙钛矿La_(1-x)Zn_xMnO_3薄膜结构及巨磁电阻

采用射频磁控溅射法分别在LaAlO3(LAO)(001)和SrTiO3(STO)(001)单晶基片上沉积了La1-xZnxMnO3(x=0.3,0.5,0.7)系列薄膜。通过X射线衍射,原子力显微镜,X射线光电子能谱和四探针法等分别研究了在基片LAO和基片STO上沉积的La1-xZnxMnO3薄膜的相结构、微形貌、表面化学态和磁电阻等性质。结果表明:薄膜在空气中900℃退火2h后,晶粒与基片之间形成了稳定的外延结构。La0.5Zn0.5MnO3和La0.7Zn0.3MnO3薄膜的晶粒生长良好。在温度为300K,磁场为1.5T的条件下,在LAO上沉积的La0.5Zn0.5MnO3薄膜和在STO上沉积的La0.7Zn0.3MnO3薄膜的巨磁电阻变化分别高达25%和28%。     

同质外延钛酸锶薄膜的生长模式图谱

利用激光分子束外延技术在SrTiO3(100)单晶基片上同质外延生长SrTiO3铁电薄膜.通过反射高能电子衍射原位实时监测薄膜生长,结合原子力显微镜等表征手段,分析了薄膜的表面微观结构,确定了薄膜的生长模式.根据反射高能电子衍射强度振荡曲线及衍射图样,通过改变薄膜的生长条件,实现了对薄膜生长模式的控制,绘制了SrTiO3薄膜的生长模式图谱:在高温、低沉积速率时,薄膜以二维层状模式生长为主;而在低温、高沉积速率下,薄膜则以三维岛状生长模式为主.从二维模式生长向三维模式生长的过渡区则表现为层状和岛状混合的Stranski-Krastanov生长模式.系统研究了生长条件对生长模式的影响,发现生长温度是影响薄膜生长过程中Ehrilich-Schwoebel扩散势垒的主要因素,而扩散势垒和沉积速率的变化决定了生长模式的改变.     

Pt/Na_(0.5)Bi_(0.5)TiO_(3)/La_(0.5)Sr_(0.5)CoO_(3)电容器的结构和铁电疲劳特性EI北大核心CSCD

采用偏轴磁控溅射法,以单晶钛酸锶(001)SrTiO_(3)(STO)为衬底,不同沉积温度下外延生长了La_(0.5)Sr_(0.5)CoO_(3)(LSCO)氧化物底电极。X射线衍射仪(XRD)和原子力显微镜(AFM)结构表征以及四探针方阻测试结果表明:LSCO薄膜外延(00l)取向最优温度沉积条件为550℃。此外,利用脉冲激光沉积法,以LSCO/STO异质结为模板,构架了Pt/Na_(0.5)Bi_(0.5)TiO_(3)(NBT)/LSCO/STO铁电电容器。XRD和AFM结构表征表明:NBT薄膜为(00l)外延结构。电流密度-电压测试曲线结果表明,室温变为70℃时,Pt/NBT/LSCO异质结漏电流密度有所增加,但未改变导电机制:低压下为欧姆导电和高压下为陷阱的空间电荷限制电流导电。在5 V驱动电压下,室温和70℃时,Pt/NBT/LSCO电容器具有饱和的电滞回线和保持特性,且经过10^(10)翻转后,均未产生疲劳。     

衬底温度对Al2O3(0001)表面外延6H-SiC薄膜的影响

采用固源分子束外延技术,以α-Al2O3(0001)为衬底,在不同衬底温度下制备了6H-SiC薄膜.利用反射式高能电子衍射,原子力显微镜、X射线衍射对生长样品的结构和结晶质量进行了表征.结果表明:在衬底温度为1100℃时生长的薄膜质量较好,在较低温度(1000℃)和较高温度(1200℃)条件下生长的薄膜质量较差.同时发...     

MSF-g-COOH/IFR阻燃复合薄膜的制备及性能研究

以季戊四醇(PEG)和三聚氰胺(MEL)为原料制备一种水溶性膨胀型阻燃剂(IFR),然后采用氯乙酸接枝剑麻纤维素微纤自制纳米纤维素(MSF-g-COOH)为基体,通过抽滤和自组装吸附的方法,制备了一种MSF-gCOOH/IFR阻燃复合薄膜。研究了IFR对MSF-g-COOH薄膜材料阻燃性和热性能的影响,并利用X射线分析仪(XPS)和扫描电子显微镜(SEM)对IFR的合成、MSF-g-COOH/IFR阻燃复合薄膜表面形貌的微观结构以及燃烧后的炭层结构进行分析。结果表明:当IFR自组装吸附在MSF-g-COOH薄膜表面后,MSF-g-COOH/IFR阻燃复合薄膜具有较好的阻燃性和热稳定性;其初始热分解温度相比纯MSF-g-COOH薄膜提高了20℃;经IFR自组装吸附后的MSF-g-COOH/IFR阻燃复合薄膜在燃烧过程中,其表面形成炭支撑保护层,可阻止火势蔓延。     

沉积温度对Na_(0.5)Bi_(0.5)TiO_3铁电薄膜结构与性能的影响

利用脉冲激光沉积法和磁控溅射法在(001)SrTiO_3单晶基片上构架了铁电异质结电容器Pt/La_(0.5)Sr_(0.5)CoO_3/Na_(0.5)Bi_(0.5)TiO_3/La_(0.5)Sr_(0.5)CoO_3/SrTiO3(LSCO/NBT/LSCO/STO)。利用原子力显微镜(AFM)、X射线衍射仪(XRD)、铁电测试仪和压电力显微镜(PFM)研究了沉积温度对Na_(0.5)Bi_(0.5)TiO_3(NBT)铁电薄膜的表面形貌、微结构和电学性能的影响。AFM结果表明,NBT薄膜晶粒尺寸随着沉积温度的增加先变小后增大。XRD结果显示,不同沉积温度下生长的NBT薄膜均为(00l)择优取向结构。铁电测试仪和PFM结果表明,NBT薄膜的铁电和压电性能随着沉积温度的增加先增大后减小,650℃生长的薄膜具有最高的剩余极化强度(19.6μC/cm2)和最大的有效压电系数(146 pm/V)。     

两种衬底对La_(0.7)Sr_(0.3)MnO_3薄膜的性能影响研究

采用脉冲激光溅射法分别在Sr Ti O3(STO)和Si(001)衬底上制备出La0.7Sr0.3Mn O3(LSMO)薄膜。通过X射线衍射仪、原子力显微镜、能谱仪以及磁性测量系统研究了薄膜晶体结构、表面形貌、成分以及电阻-温度特性。结果表明:STO衬底上的LSMO薄膜比Si衬底上的LSMO薄膜电阻低,金属-绝缘转变温度高。     

液相自组装Ce、W掺杂VO2薄膜的制备及其性能研究

利用三氯十八烷基硅烷(octadecyltrichlorosilane--OTS)为模板,以草酸、五氧化二钒,硝酸铈、钨酸铵、为原料,利用自组装薄膜技术,在玻璃基片上成功制备了氧化钒薄膜。测量了紫外光照射后OTS薄膜的亲水性。通过X射线衍射研究了自组装氧化钒薄膜的晶体结构,利用扫描电镜观察了薄膜的表面形貌,表明通过自组装制备的氧化钒薄膜通过退火处理后,可以良好的在玻璃基片上成膜,薄膜质量良好。通过FTIR测试表明,1%Ce和1.5%W共掺杂的VO2薄膜其相变温度从65℃降低到28℃。     

温度对LaMnO3+δ薄膜材料功函数影响机制研究

通过磁控溅射的方法制备了LaMnO_3+δ薄膜材料。掠入射X射线衍射(GIXRD)测试结果表明，薄膜材料为单一相结构的多晶氧化物，结构为正交畸变钙钛矿LaMnO_3+δ;利用开尔文探针显微镜(KPFM)测得LaMnO_3+δ薄膜接触电势差(CPD)的高分辨率图像，并通过CPD结果计算得知，在30～80℃温度范围内，随着温度的升高材料的功函数由4.452 eV升至4.644 eV,这是由于材料内部高价阳离子Mn⁴⁺浓度增加所致。该结果在XPS测试中得到进一步验证，Mn⁴⁺/Mn³⁺含量随温度的升高而升高。采用自组装电阻-温度测试系统的测试结果表明，薄膜材料在30～80℃范围内具有一定的负温度系数热敏特性。     

Effects of compressive and tensile stress on the growth mode of epitaxial oxide films

Oxide films were deposited on different substrates by laser molecular beam epitaxy. Reflection high-energy electron diffraction was performed to in situ investigate the change of growth mode and the lattice relaxation during the growth. An asymmetrical phenomenon was found in the two kinds of strain states, compressive stress and tensile stress of heterostructures with different lattice mismatch. In the case of BaTiO₃/SrTiO₃ (2.2%), 2D layer-by-layer growth mode without lattice relaxation can be maintained for a longer period for BTO films on STO with compressive stress, comparing to STO films on BTO with tensile stress. When MgO films were deposited on SrTiO₃ with a large mismatch of 7.8%, compressive stress leads to rapid lattice relaxation with a very thin wet layer, and 3D strained island were observed. As a comparison, SrTiO₃ films on MgO with tensile stress were configured. No RHEED patterns can be observed duo to a large tensile stress.     

(SrZrO_3)_(10)(SrTiO_3)_(90)缓冲层对PZT结晶及性能的影响

采用Sol-gel法制备了PbZr0.52Ti0.48O3 (PZT)薄膜,并研究了(SrZrO3)10(SrTiO3)90((SZO)10(STO)90)缓冲层对PZT薄膜结晶和性能的影响.X射线衍射(XRD)结果表明:(SZO)10(STO)90缓冲层对PZT薄膜结晶有取向诱导作用,由(SZO)10(STO)90诱导的PZT薄膜有很强的(111)择优取向,缓冲层将PZT薄膜的取向度α由45.0%提高到了90.1%以上;PZT的(111)择优取向提高了薄膜的电性能,使剩余极化强度Pr从26.8 μC/cm2增大到38.8 μC/cm2.     

Growth and structural characteristics of perovskite-wurtzite oxide ceramics thin films

Wurtzite ZnO thin films were grown on single-crystal perovskite SrTiO₃(STO) (1 0 0) substrates at various temperatures. The ZnO/STO thin films thus formed exhibit a preferred (1 1 0)-orientation at a growth temperature of 600-700 °C. A high growth temperature enhances not only the (1 1 0)-texture of ZnO/STO thin films but also the crystalline quality of the film. (La_0.7Sr_0.3)MnO₃ (LSMO) thin films were subsequently grown on ZnO(1 1 0)/STO(1 0 0) substrates with various thicknesses, and were polycrystalline. A thicker LSMO film has a stronger (0 0 l)-preferred orientation than the thinner one. The lattice distortion of LSMO decreases as the LSMO thickness increases. Magnetization vs. temperature curves show that both crystalline quality and lattice distortion influence the magnetic properties of LSMO thin films. The physical properties of the manganite oxide can be modulated by forming a heterostructure with wurtzite ZnO.     

Relaxation behavior of PbZrO3-SrTiO3 thin film for enhancing energy storage performances

In recent years, antiferroelectric materials have attracted significant attention as energy storage materials in pulsed power systems. In this study, (1-x)PbZrO₃-xSrTiO₃ (PZO-STO) antiferroelectric films were prepared, and the effects of the STO content on the microstructure and energy storage performance of the thin films were investigated in detail. The results showed that when the PZO/STO ratio was near the morphotropic phase boundary, the long-range PZO-STO-ordered structure could be broken by the paraelectric nanograins generated at the grain boundary. The number of nanoparticles increased gradually with an increase in the STO content, thereby leading to the microstructure transformation of the thin films from antiferroelectric to relaxation ferroelectric. When the STO content was 20%, the as-prepared thin film had a maximum energy storage density of 15.26 J/cm³, which was 117.14% higher than that of the pure PZO thin film.     

Electro-optical performances of nanostructured SrTiOx films: The effect of plasma power,Ar/O2 ratio and annealing

The present work evaluates the effects of plasma power and oxygen mixing ratios (OMRs) on structural, morphological, optical, and electrical properties of strontium titanate SrTiO_x (STO) thin films. STO thin films were grown by magnetron sputtering, and later thermal annealing at 700°C for 1 h was applied to improve film properties. X-ray diffraction analysis indicated that as-deposited films have amorphous microstructure independent of deposition conditions. The films deposited at higher OMR values and later annealed also showed amorphous structure while the films deposited at lower OMR value and annealed have nanocrystallinity. In addition, all as-deposited films were highly transparent (~80%–85%) in the visible spectrum and exhibited well-defined main absorption edge, while the annealing improved transparency (90%) within the same spectrum. The calculated direct and indirect optical band gaps for films were in the range of 3.60-4.30 eV as a function of deposition conditions. The refractive index of the films increased with OMRs and the postdeposition annealing. The frequency dependent capacitance measurements at 100 kHz were performed to obtain film dielectric constant values. High dielectric constant values reaching up to 100 were obtained. All STO samples exhibited more than 2.5 μC/cm² charge storage capacity and low dielectric loss (less than 0.07 at 100 kHz). The leakage current density was relatively low (3 × 10⁻⁸Acm⁻² at +0.8 V) indicating that STO films are promising for future dynamic random access memory applications.     

Optical properties of epitaxial BiFeO3 thin film grown on SrRuO3-buffered SrTiO3 substrate

The BiFeO₃ (BFO) thin film was deposited by pulsed-laser deposition on SrRuO₃ (SRO)-buffered (111) SrTiO₃ (STO) substrate. X-ray diffraction pattern reveals a well-grown epitaxial BFO thin film. Atomic force microscopy study indicates that the BFO film is rather dense with a smooth surface. The ellipsometric spectra of the STO substrate, the SRO buffer layer, and the BFO thin film were measured, respectively, in the photon energy range 1.55 to 5.40 eV. Following the dielectric functions of STO and SRO, the ones of BFO described by the Lorentz model are received by fitting the spectra data to a five-medium optical model consisting of a semi-infinite STO substrate/SRO layer/BFO film/surface roughness/air ambient structure. The thickness and the optical constants of the BFO film are obtained. Then a direct bandgap is calculated at 2.68 eV, which is believed to be influenced by near-bandgap transitions. Compared to BFO films on other substrates, the dependence of the bandgap for the BFO thin film on in-plane compressive strain from epitaxial structure is received. Moreover, the bandgap and the transition revealed by the Lorentz model also provide a ground for the assessment of the bandgap for BFO single crystals.     

Crystallographic Domain Structure of an Epitaxial (Pr0.7Ca0.3)MnO3 Thin Film Grown on a SrTiO3 Single Crystal Substrate

We characterized the structure of the crystallographic domain of a (Pr_0.7Ca_0.3)MnO₃ (PCMO ( x =0.3)) thin film epitaxially grown on a (001)SrTiO₃ (STO) single-crystal substrate. We found that the domain structure exhibited an atomically smooth coherent interface with the STO substrate with no misfit dislocations. The crystallographic relationships between the domains and the substrate in their planes were interpreted to be PCMO ( x =0.3)[110][001]//STO[100][010] and PCMO ( x =0.3)[001][1-10]//STO[100][010]. The domain structure of PCMO ( x =0.3)[110][1-10]//STO[100][010] has less possibility of having the larger anisotropic strain energy found in a monoclinically distorted pseudo-cubic perovskite unit cell of PCMO ( x =0.3). This epitaxial growth structure is totally different from the previously reported PCMO ( x =0.5) epitaxial thin-film structure on STO substrate. Our observations suggested that an x value change strongly influences the structure of epitaxial PCMO thin films.     

脉冲准分子激光扫描沉积(PLD)高c轴取向V2O5/Si薄膜及结构分析

采用脉冲准分子激光大面积扫描沉积技术,在Si(111)单晶衬底上沉积了多晶V2O5薄膜,经300℃以上退火处理得到了具有高c-轴取向生长的V2O5膜。300℃以上热退火处理的薄膜表面具有正常的化学计量比（无氧缺位）,晶粒间界明显,晶粒呈针棒状,晶粒尺寸在100－200nm之间。采用X射线衍射（XRD）、Raman光谱（RS）、Fourier红外光谱（FT－IR）及透射电镜扫描附件（STEM）对沉积及不同温度下退火处理的样品进行了结构分析。研究结果表明：V2O5/Si薄膜经400℃热处理后表面部分处于低价态的钒离子已被氧化为V2O5。     

Fabrication of Pb(Zr,Ti)O3 thin films utilizing unconventional powder magnetron sputtering (PMS)

Pb(Zr,Ti)O3 (PZT) ferroelectric ceramic films exhibit highly superior ferroelectric, pyroelectric and piezoelectric properties which are promising for a number of applications including non-volatile random access memory devices, non-linear optics, motion and thermal sensors, tunable microwave systems and in energy harvesting (EH) use. In this research, a thin layer of PZT was deposited on two different substrates of Strontium Titanate (STO) and Strontium ruthenate (SRO) by powder magnetron sputtering (PMS) system. The preliminary powders, consisting of PbO, ZrO₂ and TiO_2, were manually mixed and placed into the target holder of the PMS. The deposition was performed at an elevated temperature reaching up to 600 °C via a ceramic heater. This high temperature is required for PZT thin film crystallinity, which is never achieved in conventional physical vapour deposition processes. The phase structure, crystallite size, stress-strain and surface morphology of deposited thin films were characterized using X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The composition of the PZT thin films were also analysed by X-ray photoelectron spectroscopy (XPS). The mechanical properties of the thin films were evaluated with micro-scratch adhesive strength and micro hardness equipment. FESEM results showed that the PZT thin films were successfully deposited on both SRO and STO substrates. The surfaces of the coated samples were free from cracks, relatively smooth, uniform and dense. The profile of X-ray diffraction confirmed the formation of single-c-domain/single crystal perovskite phase grown on both substrates. The XPS analysis have shown that the PZT thin film grown by this method and that a target of PZT+10% PbO is a proper target for growing nominal PZT thin films. The adhesion strength and micro hardness results have confirmed the stability and durability of the thin film on the substrates, although higher values have been reported for thin film of PZT deposited on SRO surfaces.     

Gallium oxide films deposition by RF magnetron sputtering; a detailed analysis on the effects of deposition pressure and sputtering power and annealing

In this study, gallium oxide (Ga₂O₃) thin films were deposited on sapphire and n-Si substrates using Ga₂O₃ target by radio frequency magnetron sputtering (RFMS) at substrate temperature of 300 °C at variable RF power and deposition pressure. The effects of deposition pressure and growth power on crystalline structure, morphology, transmittance, refractive index and band gap energy were investigated in detail. X-ray diffraction results showed that amorphous phase was observed in all the as-deposited thin films except for the thin films grown at low growth pressure. All the films showed conversion to poly-crystal β-Ga₂O₃ phase after annealing process. When the deposition pressure increased from 7.5 mTorr to 12.20 mTorr, change in the 2D growth mode to 3D columnar growth mode was observed from the SEM images. Annealing clearly showed formation of larger grains for all the thin films. Lower transmission values were observed as the growth pressure increases. Annealing caused to obtain similar transmittance values for the thin films grown at different pressures. It was found that a red shift observed in the absorption edges and the energy band gap values decrease with increasing growth pressure. For as-deposited and annealing films, increasing sputtering power resulted in the increase refractive index.