Equivalent refractive index of multilayer films of different materials

The variation of the equivalent refractive index with composition of multilayer films of ZnS-MgF₂-SiO, ZnS-Na₃AlF₆ and Ge-ZnS, prepared by depositing alternate layers of different materials, has been investigated. It has been established that, for small step thicknesses (much less than the wavelength of light to be used for measurements) of each layer, the composite multilayer films are optically equivalent to homogeneously mixed films of the same materials of corresponding relative compositions. Further, the results show that the indices of the multilayer films of ZnS-MgF₂-SiO and ZnS-Na₃AlF₆ are in good agreement with the values predicted on the basis of the Lorentz-Lorenz theory. The refractive index of Ge-ZnS multilayer films is in agreement with the Drude theory. Our studies also show that the refractive index of a multilayer film composed of three materials, two of which react chemically in the molten and vapour states, as, for example, ZnS and SiO in ZnS-MgF₂-SiO films, is equivalent to that expected theoretically for a homogeneously mixed film of the same materials. The controlled and predictable equivalent behaviour of multilayer films suggests their use to produce variable refractive index optical coatings by selecting any number of materials which may or may not react with each other chemically.     

Infrared optical properties of Bi2Ti2O7 thin films by spectroscopic ellipsometry

Bi₂Ti₂O₇ thin films have been grown directly on n-type GaAs (1 0 0) by the chemical solution decomposition technique. X-ray diffraction analysis shows that the Bi₂Ti₂O₇ thin films are polycrystalline. The optical properties of the thin films are investigated using infrared spectroscopic ellipsometry (3.0–12.5 μm). By fitting the measured ellipsometric parameter (Ψ and Δ) data with a three-phase model (air/Bi₂Ti₂O₇/GaAs), and Lorentz–Drude dispersion relation, the optical constants and thickness of the thin films have been obtained simultaneously. The refractive index and extinction coefficient increase with increasing wavelength. The fitted plasma frequency ω_p is 1.64×10¹⁴ Hz, and the electron collision frequency γ is 1.05×10¹⁴ Hz, and it states that the electron average scattering time is 0.95×10⁻¹⁴ s. The absorption coefficient variation with respect to increasing wavelength has been obtained.     

Controllable formation of Er–Yb codoped Al2O3 films by the non-aqueous sol–gel method

1 mol%Er³⁺–10 mol%Yb³⁺ codoped Al₂O₃ thin films have been prepared on thermally oxidized SiO₂/Si(110) substrates by a dip-coating process in the non-aqueous sol–gel method from the hydrolysis of aluminum isopropoxide [Al(OC₃H₇)₃] under isopropanol environment. Addition of N,N-dimethylformamide (DMF) as a drying control chemical additive (DCCA) into the sol suppresses formation of the cracks in the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films when the rare-earth ion is doped with a high doping concentration. Homogeneous, smooth and crack-free Er³⁺–Yb³⁺ codoped Al₂O₃ thin films form at the conditions by a molar ratio of 1:1 for DMF:Al(OC₃H₇)₃. A strong photoluminescence spectrum with a broadband extending from 1.400 to 1.700 µm centered at 1.533 µm is obtained for the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films, which is unrelated to the addition of DMF. Controllable formation of the Er³⁺–Yb³⁺ codoped Al₂O₃ thin films may be explained by the fact that the DMF assisted the deprotonation process of Al–OH at the surfaces of gel particles, resulting in enhancement of the degree of polymerization of sols and improvement of the mechanical properties of gel thin films.     

Ferroelectric/superconductor heterostructures

This review covers the fabrication and characterization of ferroelectric/superconductor heterostructures such as Pb(Zr_xTi_1−x)O₃/YBa₂Cu₃O_7−δ (YBCO), BaTiO₃/YBCO and Ba_xSr_1−xTiO₃/YBCO etc. on various single crystal substrates. Pulsed laser deposition, laser molecular beam epitaxy, and magnetron-sputtering methods are compared. This report shows that pulsed laser deposition equipped with in situ reflection high-energy electron diffraction is a good method to control the growth mode of YBCO thin films. Furthermore, laser molecular beam epitaxy is a superb method for research of complex oxide films and their superlattices. Atomic force microscopy and transmission electron microscopy showed the ferroelectric films grown on the rough surface of the YBCO films produced high-density planar defects in the film and is detrimental to the ferroelectric/dielectric properties of the heterostructures. Therefore, for device usage, it is more advantageous to use SrRuO₃ than YBCO as the bottom electrode material. For growing atomically smooth surface films step-flow mode is highly recommended. Prospects of microwave device application of the ferroelectric/superconductor heterostructures are discussed, and proposed the BSTO films as the best candidate for passive microwave components.     

磷酸处理对多孔SiO2薄膜质子导电特性和双电层薄膜晶体管性能的影响

采用等离子体增强化学气相沉积法(PECVD)制备了多孔SiO₂薄膜, 系统地研究了不同浓度磷酸处理对多孔SiO₂薄膜的质子导电特性、双电层电容和以此多孔SiO₂薄膜为栅介质的铟锌氧(IZO)双电层薄膜晶体管性能的影响。结果表明: 多孔SiO₂薄膜的质子电导率和双电层电容随磷酸浓度升高而增大, 60%浓度磷酸处理后多孔SiO₂薄膜质子电导率和双电层电容分别达到1.51×10^-4 S/cm和6.33 μF/cm²。随磷酸浓度升高, 双电层薄膜晶体管的工作电压降低, 并且, 电流开关比也变大。其中60%浓度磷酸处理后器件工作电压为1.2 V, 迁移率为20 cm²/(V·s), 电流开关比为4×10⁶。这种双电层薄膜晶体管有望应用在化学和生物传感等领域。     

纳米Al_2O_3/聚酰亚胺复合薄膜的介电与力学性能

采用原位聚合与热亚胺化的方法,成功制备了一系列不同纳米Al_2O_3粒子质量分数的纳米Al_2O_3/聚酰亚胺(PI)复合薄膜。通过SEM、TEM、XRD、FTIR、LCR数字电桥、高压电源及电子万能材料试验机对纳米Al_2O_3/PI复合薄膜的微观结构、介电性能及力学性能进行了表征和测试。结果表明:纳米Al_2O_3粒子在均匀地分散在PI基体中;当纳米Al_2O_3粒子质量分数为8%时,纳米Al_2O_3/PI复合薄膜的击穿强度和拉伸强度均达到了最大值;纳米Al_2O_3/PI复合薄膜的介电常数随纳米Al_2O_3质量分数的增加而增加。     

衬底温度和生长氧压对La0.67Sr0.33MnO3:Ag0.08薄膜激光感生电压效应的影响

通过化学共沉淀法制备了La_0.67Sr_0.33MnO₃:Ag_0.08 (LSMO:Ag_0.08)多晶材料, 然后采用脉冲激光沉积(PLD)技术在LaAlO₃ (LAO)倾斜衬底上制备了LSMO:Ag_0.08薄膜。研究了衬底温度和生长氧压对薄膜结构、电输运特性及激光感生电压(LIV)效应的影响。结果表明: 当衬底温度为790℃、生长氧压为45 Pa时, 薄膜具有最大峰值电压(U_p)、优值(F_m)和各向异性Seebeck系数(ΔS); 在优化的衬底温度和生长氧压条件下, 长程Jahn-Teller协变引起ΔS数值提高, 这是LIV信号增强的主要原因。     

Photon frequency dependent electron relaxation time in noble metals: effect of voids

Optical properties of noble metals at frequencies below the interband transitions are well described by a simple Drude model of the free electron gas. However, a photon frequency dependent electron relaxation time τ(gW)⁻¹ = τ_o⁻¹ + βΩ² has been reported frequently for experimental data. Also, the parameters of the Drude model of silver were found to be influenced by fluids (H. Gugger et al., Phys. Rev. B, 30 (1984) 4189). On the other hand, thin silver films condensed on cold substrates contain a large amount of voids with elongated shape, which cause a strong absorption around λ ≈ 450 nm. Borensztein et al. (Surf. Sci., 211/212 (1989) 775) modelled this absorption band with an effective medium theory (EMT), taking into account the shape of the voids. In the present work it is shown that both the frequency-dependent relaxation time and the effects of fluids can be explained by this EMT.     

WO3/TiO2复合薄膜的制备及其电致变色性能

使用水热法在掺氟SnO₂涂覆的导电玻璃（FTO）基板上生长TiO₂纳米线,随后在TiO₂纳米线上采用水热法生长WO₃纳米线,制备出WO₃/TiO₂复合薄膜。通过循环伏安法（CV）、计时电流法（CA）、计时电量法（CC）等电化学测试技术研究了WO₃/TiO₂复合薄膜的电致变色性能;采用紫外分光光度计对薄膜的着色﹑漂白状态的响应时间进行测试。通过以上测试,计算得到了薄膜的循环稳定性﹑光调制﹑着色效率和切换时间（Y和X）等参数。结果显示WO₃/TiO₂复合薄膜的电致变色性明显提高,其中WO₃/TiO₂复合薄膜可逆性增加了6%,着色效率提高了40.96 cm2/C。      

Ti掺杂MoS2薄膜的抗氧化性和电学性能

用磁控溅射在硅片上制备MoS₂和Ti-MoS₂薄膜,并将其在恒温恒湿箱中在AT 30℃、RH 70%条件下存储360 h。使用XRD谱、XPS谱和紫外-可见分光光度计、四探针测试仪表征分析薄膜的结构、在恒温恒湿条件下存储前后的表面化学状态和电学性能,研究了Ti掺杂对薄膜抗氧化性和电学性能的影响。结果表明：Ti掺杂影响MoS₂薄膜的晶体取向。随着Ti靶电流的增大薄膜的结晶性变差,Ti靶电流为0.6A时薄膜呈无定型结构且禁带宽度减小、电导率提高;在恒温恒湿条件下存储后薄膜的部分氧化而呈MoS₂与MoO₃的复合状态,随着Ti靶电流的增大I_Mo-O/I_Mo-S比提高、禁带宽度略有增大,Ti靶电流为0.4A的Ti-MoS₂薄膜其化学稳定性较高。     

Sc2W3O12薄膜制备及其负热膨胀性能

采用脉冲激光沉积法制备了斜方相Sc₂W₃O₁₂薄膜。利用X射线衍射仪(XRD)和场发射扫描电镜(FESEM)对Sc₂W₃O₁₂靶材和Sc₂W₃O₁₂薄膜组分、表面形貌和靶材断面形貌进行表征, 研究衬底温度与氧分压对薄膜制备的影响。采用变温XRD和热机械分析仪(TMA)分析了Sc₂W₃O₁₂陶瓷靶材和薄膜的负热膨胀特性。实验结果表明: 经1000℃烧结6 h得到结构致密的斜方相Sc₂W₃O₁₂陶瓷靶材, 其在室温到600℃的温度范围内平均热膨胀系数为-5.28×10^-6 K^-1。在室温到500℃衬底温度范围内脉冲激光沉积制备的Sc₂W₃O₁₂薄膜均为非晶态, 随着衬底温度的升高, 薄膜表面光滑程度提高; 随着沉积氧压强增大, 表面平整性变差。非晶膜经1000℃退火处理7 min后得到斜方相Sc₂W₃O₁₂多晶薄膜, 在室温到600℃温度区间内, Sc₂W₃O₁₂薄膜的平均热膨胀系数为-7.17×10^-6 K^-1。     

Growth of calcium carbonate by the atomic layer chemical vapour deposition technique

Thin films of CaCO₃ (calcite) have been grown with the atomic layer chemical vapour deposition (ALCVD) technique, using Ca(thd)₂ (Hthd=2,2,6,6-tetramethylheptan-3,5-dione), CO₂, and ozone as precursors. Pulse parameters for the ALCVD-type growth are found and self-limiting reaction conditions are established between 200 and 400 °C. Calcium carbonate films have been deposited on soda-lime glass, Si(100), -Al₂O₃(001), -Al₂O₃(012), -SiO₂(001), and MgO(100) substrates. The observed textures were: in-plane oriented films with [100](001)CaCO₃ [100](001)Al₂O₃ and [100](001)CaCO₃[110](001)Al₂O₃ on -Al₂O₃(001), amorphous films on -Al₂O₃(012) when grown at 250 °C, and columnar oriented films on soda-lime glass, Si(001), -SiO₂(001), and MgO(100) substrates with (00l) and (104) parallel to the substrate plane at 250 and 350 °C, respectively. The film topography was studied by atomic force microscopy and AC impedance characteristics were measured on as-deposited films at room temperature. The films were found to be insulating with a dielectric constant (_r) typically approximately 8. Thin films of CaO were obtained by heat treatment of the carbonate films at 670 °C in a CO₂-free atmosphere, but the thermal decomposition led to a significant increase in surface roughness.     

Coverage properties of silicon nitride film prepared by the Cat-CVD method

The coverage properties of silicon nitride (Si₃N₄) films prepared by the catalytic chemical vapor deposition (Cat-CVD) technique were systematically studied. By increasing the catalyzer–substrate distance, the coverage was improved from 46 to 67% on a 1.0-μm line and space pattern. The etching rate of Cat-CVD Si₃N₄ film measured using 16BHF solution was independent of the deposited position of the micro-patterns deposited, and was approximately 3 nm/min, one order of magnitude lower than that of plasma-enhanced CVD (PE-CVD) Si₃N₄ film. This means that Cat-CVD Si₃N₄ films are denser than PE-CVD Si₃N₄ films, and that the quality at the side wall is equivalent to that on the top surface. That is, Cat-CVD Si₃N₄ films show a passivation effect, which was excellent, even at the side wall of micro-patterns. These results suggest that Si₃N₄ films prepared by Cat-CVD are suitable for the passivation films in microelectronic devices having a step configuration, such as TFT-LCDs and ULSIs.     

Characterization of activated reactive evaporated MoO3 thin films for gas sensor applications

Thin films of molybdenum trioxide (MoO₃) were prepared by activated reactive evaporation technique on Pyrex glass substrates. The influence of oxygen partial pressure, substrate temperature and glow power on the structure, surface morphology and optical properties of MoO₃ thin films was studied. The MoO₃ films deposited in an oxygen partial pressure of 1×10⁻³ Torr, glow power of 10 W and substrate temperature of 573 K exhibited predominantly a (0 k 0) orientation corresponding to the orthorhombic layered structure of -MoO₃. The evaluated optical band gap was 3.24 eV. The sensing property of these MoO₃ films for gases like NH₃ and CO was also studied to see the applicability for environmental monitoring. We have observed that the MoO₃ thin films of -phase are capable of detecting NH₃ and CO gases at concentrations lower than 10 ppm in dry air.     

Growth of La2Mo2O9 films on porous Al2O3 substrates by radio frequency magnetron sputtering

Synthesis conditions of La₂Mo₂O₉ thin film by radio frequency (RF) sputtering technique on Al₂O₃ ceramic substrates are studied. It is found that the deposition temperature and oxygen partial pressure are the most important factors for obtaining pure La₂Mo₂O₉ films. Varying both parameters, Mo-rich, stoichiometric, and Mo-deficient films are obtained. With increasing the La:Mo ratio, films become denser. A crust layer is observed on top of the Mo-rich and the Mo-deficient films. The formation of the La₂Mo₂O₉ phase is discussed with respect to the sputtering mechanism.     

Epitaxial growth of RuO2 thin films by metal-organic chemical vapor deposition

Conductive RuO₂ thin films were epitaxially grown on LaAlO₃(100) and MgO(100) substrates by metal-organic chemical vapor deposition (MOCVD). The deposited RuO₂ films were crack-free, and well adhered to the substrates. The RuO₂ film is (200) oriented on LaAlO₃ (100) substrates at deposition temperature of 600°C and (110) oriented on MgO(100) substrates at deposition temperature of 350°C and above. The epitaxial growth of RuO₂ on MgO and LaAlO₃ is demonstrated by strong in-plane orientation of thin films with respect to the major axes of the substrates. The RuO₂ films on MgO(100) contain two variants and form an orientation relationship with MgO given by RuO₂(110)//MgO(100) and RuO₂[001]//MgO[011]. The RuO₂ films on LaAlO₃(100), on the other hand, contain four variants and form an orientation relationship with LaAlO₃ given by RuO₂(200)//LaAlO₃(100) and RuO₂[011]//LaAlO₃[011]. Electrical measurements on the RuO₂ thin films deposited at 600°C show room-temperature resistivities of 40 and 50 μΩ cm for the films deposited on the MgO and LaAlO₃ substrates, respectively.     

Preparation of Aluminum Nitride Thin Films by CVD

AlN films were prepared by CVD using aluminum halide (AlCl₃) and aluminum alkyl ((CH₃)3Al) precursors. The appropriate deposition conditions to obtain polycrystalline AlN films using A1C1₃ precursor were found at T_dep = 1173 K, P_tot = 66.6 Pa and N₂/NH₃ = 0.75. It was found that AlN films of different crystallinity can be obtained from (CH₃)₃Al precursor at T_de = 973-1023 K, P_tot = 1.99 kPa, only under a H₂ atmosphere. AlN films can be grown highly oriented in the (210) direction on amorphous quartz substrates depending on their thicknesses. The 0.1 -0.2 μm thick AlN films were transparent and their refractive indexes were about 1.4-1.6.     

Si3N4/FePd/Si3N4薄膜的晶体结构和磁性能研究

采用磁控溅射的方法制备了Si₃N₄/FePd/Si₃N₄三层膜, 研究了非磁性材料Si₃N₄作为插入层对磁记录FePd薄膜结构与磁性能的影响。结果表明, 热处理后Si₃N₄分布在FePd纳米颗粒之间, 抑制了FePd晶粒的生长, 与纯FePd薄膜相比, Si₃N₄/FePd/Si₃N₄薄膜的颗粒明显得到细化; 通过添加Si₃N₄层, FePd薄膜的晶体学参数c/a从0.960减小到0.946, 表明Si₃N₄可以有效促进FePd薄膜的有序化进程, 同时提升了矫顽力和剩磁比, 分别提高到249 kA/m、0.86; 随着600℃退火时间的进一步延长, 添加Si₃N₄的薄膜磁性没有迅速下降, 在较宽的热处理时间范围内磁性能保持在比较高的水平, 提高了抗热影响的能力。Si₃N₄作为插入层对FePd薄膜的磁性能具有较大的提升作用, 这对磁记录薄膜的发展具有重要意义。     

Highly conductive microcrystalline silicon carbide films deposited by the hot wire cell method and its application to amorphous silicon solar cells

Microcrystalline silicon carbide (μc-Si_1−xC_x) films were successfully deposited by the hot wire cell method using a gas mixture of SiH₄, H₂ and C₂H₂. It was confirmed by Fourier transform infrared and X-ray diffraction analyses that the films consisted of μc-Si grains embedded in a-Si_1−xC_x tissue. The p-type μc-Si_1−xC_x films were deposited using B₂H₆ as a doping gas. A dark conductivity of 0.2 S/cm and an activation energy of 0.067 eV were obtained. The p-type μc-Si_1−xC_x was used as a window layer of a-Si solar cells, in which the intrinsic layer was deposited by photo-chemical vapor deposition, and an initial conversion efficiency of 10.2% was obtained.     

Fabrication and characterization of (1−x)SrBi2Ta2O9–xBi3TaTiO9 layered structure solid solution thin films for ferroelectric random access memory (FRAM) applications

We report on the properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ solid solution thin films for ferroelectric non-volatile memory applications. The solid solution thin films fabricated by modified metalorganic solution deposition technique showed much improved properties compared to SrBi₂Ta₂O₉. A pyrochlore free crystalline phase was obtained at a low annealing temperature of 600°C and grain size was found to be considerably increased for the solid solution compositions. The film properties were found to be strongly dependent on the composition and annealing temperatures. The measured dielectric constant of the solid solution thin films was in the range 180–225 for films with 10–50% of Bi₃TaTiO₉ content in the solid solution. Ferroelectric properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ thin films were significantly improved compared to SrBi₂Ta₂O₉. For example, the observed remanent polarization (2P_r) and coercive field (E_c) values for films with 0.7SrBi₂Ta₂O₉–0.3Bi₃TaTiO₉ composition, annealed at 650°C, were 12.4 μC/cm² and 80 kV/cm, respectively. The solid solution thin films showed less than 5% decay of the polarization charge after 10¹⁰ switching cycles and good memory retention characteristics after about 10⁶ s of memory retention. The improved microstructural and ferroelectric properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ thin films compared to SrBi₂Ta₂O₉, especially at lower annealing temperatures, suggest their suitability for high density FRAM applications.