Effect of the laser fluence on structural and optical characterization of thin CdS films synthesized by femtosecond pulsed laser deposition

CdS thin films have been grown on Si(1 1 1) and quartz substrates using femtosecond pulsed laser deposition. X-ray diffraction, atomic force microscopy, photoluminescence measurement, and optical transmission spectroscopy were used to characterize the structure and optical properties of the deposited CdS thin films. The influence of the laser fluence (laser incident energy in the range 0.5–1.5 mJ/pulse) on the structural and optical characterizations of CdS thin films has been studied. The results indicate that the structure and optical properties of the CdS thin films can be improved as increasing the per pulse output energy of the femtosecond laser to 1.2 mJ. But when the per pulse output energy of the femtosecond laser is further increased to 1.5 mJ, which leads to the degradation of the structure and optical properties of the CdS thin films.     

On the effective magnetization and uniaxial anisotropy of permalloy films

The values of the effective magnetization and uniaxial induced anisotropy were measured on permalloy films, vacuum deposited on unheated glass slides, by the method of local ferromagnetic resonance. The double resonance curves of these films indicate the existence of two magnetically different components; to both components there correspond different values of the effective magnetization and uniaxial anisotropy. These quantities have different local and time variations for each component. The results of measurement agree with the recently proposed model of the stratification of thin ferromagnetic films.The authors thank J. Kaczér and F. Kroupa for valuable discussions.     

Room-temperature ferromagnetism in CuO sol-gel powders and films

Both CuO nanopowders and thin films prepared by sol-gel method exhibit room-temperature ferromagnetism (FM), even though CuO bulk presents a paramagnetism (PM) at room temperature above its antiferromagnetic Néel temperature. For CuO nanopowders at room temperature, FM likely occurs at surfaces of nanograins, while PM may remain in the inner of grains. The vacuum annealing greatly enhances room-temperature FM, and the air reheating after vacuum annealing reduces FM again, indicating that the observed FM in CuO sol-gel powders and thin films are connected with oxygen vacancies. The room-temperature FM of CuO nanograins decreases with an increase of grain size, possibly due to the decrease of oxygen vacancy concentrations at surfaces of nanograins.     

VO2光学薄膜的脉冲激光损伤特性测试

为评价VO2光学薄膜在光电器件中的工作可靠性,搭建了可输出连续渐变激光能量密度的脉冲激光照射实验平台,运用1对1与s对12种激光损伤测试手段进行激光辐射照射实验,采用线性外推法和测量计算法2种方法对实验结果进行了处理并得出VO2薄膜在重复频率10 kHz、中心波长532 nm、脉冲宽度15 ps脉冲激光辐射下的损伤特性。结果表明:VO2薄膜损伤几率与脉冲激光的单脉冲能量密度呈线性关系,重复辐射的激光脉冲对VO2薄膜造成的损伤具有积累效应,且重复辐射的激光脉冲次数越多损伤积累效果越明显。     

多层铁电陶瓷击穿分析及优化

建立了多层串联PZT95/5爆电换能组件3维数值模型,对固化封装条件下陶瓷介质击穿问题进行了计算分析,计算结果表明:在不改动器件外部结构尺寸条件下,采用等厚度PZT95/5叠片结构布局对进一步提高输出电压方面存在瓶颈。为克服上述影响以及降低爆电换能组件击穿概率,提出了PZT95/5铁电陶瓷非等厚度布局解决方案。为实现上述设想,通过引入不等式约束条件计算得到一组非等厚度优化布局,将爆电换能组件所用PZT95/5铁电陶瓷数量减至19片,同时有效实现该布局下,各片PZT95/5陶瓷电压均低于对应厚度击穿电压的优化目标。     

多层铁电陶瓷击穿分析及优化

建立了多层串联PZT95/5爆电换能组件3维数值模型,对固化封装条件下陶瓷介质击穿问题进行了计算分析,计算结果表明：在不改动器件外部结构尺寸条件下,采用等厚度PZT95/5叠片结构布局对进一步提高输出电压方面存在瓶颈。为克服上述影响以及降低爆电换能组件击穿概率,提出了PZT95/5铁电陶瓷非等厚度布局解决方案。为实现上述设想,通过引入不等式约束条件计算得到一组非等厚度优化布局,将爆电换能组件所用PZT95/5铁电陶瓷数量减至19片,同时有效实现该布局下,各片PZT95/5陶瓷电压均低于对应厚度击穿电压的优化目标。     

Orientation dependence of the electrocaloric effect of ferroelectric bilayer thin films

An analytical thermodynamic theory is applied to investigate the electrocaloric effect of ferroelectric BaTiO₃/SrTiO₃ bilayer thin films with different orientations at room temperature. Theoretical analysis indicates that the strong electrostatic coupling between the layers results in the suppression of ferroelectricity at a critical relative thickness which occurs approximately at 50%, 23%, and 12% of SrTiO₃ fraction in the (001), (110), and (111) bilayer thin films, respectively. The ferroelectric bilayer thin films are respected to have the largest electrocaloric effect at this critical relative thickness. Moreover, the electrocaloric effect strongly depends on the orientation and the (110) oriented bilayer thin films have the largest electrocaloric effect. Consequently, control of the orientation and the relative thickness of SrTiO₃ layer can be used to adjust the electrocaloric effect of ferroelectric bilayer thin films, which may provide the potential for practical application in refrigeration devices.     

Effect of the growth conditions on infrared upconversion efficiency of CaS: Eu, Sm thin films

High-quality electron-trapping thin films CaS: Eu, Sm with red light output have been successfully deposited on quartz and single-crystal silicon substrates by electron beam evaporation (EBE) and radio frequency (RF) magnetron sputtering in vacuum and H₂S partial pressures. Infrared upconversion efficiency of CaS: Eu, Sm thin films under different growth conditions has been investigated by using ultrashort infrared (IR) laser pulse with 20 ps (full width at half-maximum (FWHM)). The results show that upconversion efficiency of CaS: Eu, Sm thin films depends strongly on growth conditions in spite of the existence of “exhaustion” phenomena. Microstructures identified by X-ray diffraction (XRD) indicate that crystallinity of CaS films relies on both substrate materials and growth conditions. The stoichiometric composition of CaS films was measured by secondary-ion mass spectrometry (SIMS). The post-annealing process was found to promote grain growth and activate strong luminescence so that it could obviously improve upconversion efficiency of CaS: Eu, Sm films, even though it had negative influence on transmittance and spatial resolution of these films. Received: 5 June 2000 / Accepted: 7 June 2000 / Published online: 23 August 2000     

基于金属掺杂ITO透明导电层的紫外LED制备

为降低ITO薄膜对紫外波段的光吸收,制备低电压高功率的紫外LED,研究了一种基于金属掺杂ITO透明导电层的365 nm紫外LED的制备工艺。利用1 cm厚的石英片生长了不同厚度ITO薄膜以及在ITO上掺杂不同金属的新型薄膜,并研究了在不同的退火条件下这种薄膜的电阻和透过率,分析了掺杂金属ITO薄膜的带隙变化。将这种掺杂的ITO薄膜生长在365 nm外延片上并完成电极生长,制备成14 mil×28 mil的正装LED芯片。利用电致发光（EL）设备对LED光电性能进行测试并对比。实验结果表明:掺Al金属的ITO薄膜能够相对ITO薄膜的带隙提高0.15 eV。在600℃退火后,方块电阻降低6.2 Ω/□,透过率在356 nm处达到90.8%。在120 mA注入电流下,365 nm LED的电压降低0.3 V,功率提高14.7%。ITO薄膜掺金属能够影响薄膜带隙,改变紫光LED光电性能。     

Structural relaxation of spin-cast glassy polymer thin films as a possible factor in dewetting

Reiter [1] has recently reported a situation in which the dewetting of quasi-solid films is linked to plastic deformation - rather than viscous flow - resulting from capillary forces. Herein we propose that, in thin films of some glassy polymers - especially poly(methyl methacrylate) (PMMA) - prepared by spin-casting from solvent, structural relaxation might impart sufficient stress to cause plastic deformation. We find that PMMA films decrease in thickness by several percent, which is sufficient to create significant stress in those cases in which the film is attached to a rigid substrate. The floating technique, which can take tens of minutes, might allow most of the structural relaxation to occur prior to dewetting experiments.Received: 1 August 2003PACS: 65.40.De Thermal expansion; thermomechanical effects - 82.60.Lf Thermodynamics of solutions - 61.41. + e Polymers, elastomers, and plasticsM. Sferrazza: Current address: Département de Physique, Université Libre de Bruxelles, Boulevard du Triomphe, CP223, 1050 Bruxelles, Belgium     

Effect of ionizing radiations on the crystalline structure and electric resistivity of cadmium sulphide thin films

The effect of ionizing radiations on semiconductor thin films has been less investigated.^1.2 In Ref. 1 the authors studied the effect of electron irradiation on the resistivity of thin epitaxial silicon films. The effects of electron irradiation at energies varying between 11 keV and 100 keV confirmed those obtained with monocrystals.³ The variation of electrical conductivity and of the distribution of carriers in the silicon epitaxial thin films due to the simultaneous action of silicon ion implantation and evaporation in vacuum was studied in Ref. 4.     

Mechanical properties of sol-gel derived lead zirconate titanate thin films by nanoindentation

Lead zirconate titanate (PZT) thin films are deposited on platinized silicon substrate by sol-gel process. The crystal structure and surface morphology of PZT thin films are characterized by X-ray diffraction and atomic force microscopy. Depth-sensing nanoindentation system is used to measure mechanical characteristics of PZT thin films. X-ray diffraction analyses confirm the single-phase perovskite structures of all PZT thin films. Nanoindentation measurements reveal that the indentation modulus and hardness of PZT thin films are related with the grain size and crystalline orientation. The increases of the indentation modulus and hardness with grain size are observed, indicating the reverse Hall-Petch effect. Furthermore, the indentation modulus of (1 1 1)-oriented PZT thin film is higher than those of (1 0 0)- and random-oriented films. The consistency between experimental data and numerical results of the effective indentation moduli for fiber-textured PZT thin films using Voigt-Reuss-Hill model is obtained.     

Oxidation temperature dependent optical properties of bismuth oxide thin films: Effect of vapour chopping and air exposure

The optical properties of vapour chopped and nonchopped bismuth oxide thin films of two thicknesses 1500 Å and 2000 Å have been studied. The films were prepared by thermal oxidation in air; of vacuum evaporated vapour chopped and nonchopped bismuth thin films. As revealed by XRD studies, multiphase and polycrystalline bismuth oxide thin films were obtained. The refractive index was found to increase with the thickness and exposure to air for 40 days. The vapour chopped films showed higher refractive index, band gap and lower grain size than those of nonchopped films. The films showed high transmittance in the visible spectrum. The ageing effect on the vapour chopped films was found low.     

Bi-Sb-Te基热电薄膜温差电池离子束溅射制备与表征

本文采用离子束溅射Bi/Te和Sb/Te二元复合靶,直接制备n型Bi₂Te₃热电薄膜和p型Sb₂Te₃热电薄膜.在退火时间同为1 h的条件下,对所制备的Bi₂Te₃薄膜和Sb₂Te₃薄膜进行不同温度的退火处理,并对其热电性能进行表征.结果表明,在退火温度为150 ℃时,制备的n型Bi₂Te₃关键词： 薄膜温差电池 2Te₃薄膜')" href="#">Sb₂Te₃薄膜 2Te₃薄膜')" href="#">Bi₂Te₃薄膜 离子束溅射     

Effect of excimer laser annealing on the properties of ZnO thin film prepared by sol-gel method

Pristine ZnO thin films have been deposited with zinc acetate [Zn(CH₃COO)₂], mono-ethanolamine (stabilizer), and isopropanol solutions by sol-gel method. After deposition, pristine ZnO thin films have been irradiated by excimer laser (λ = 248, KrF) source with energy density of 50 mJ/cm² for 30 sec. The effect of excimer laser annealing on the optical and structural properties of ZnO thin films are investigated by photoluminescence and field emission scanning electron microscope. As-grown ZnO thin films show a huge peak of visible region and a wide full width at half maximum (FWHM) of UV region due to low quality with amorphous ZnO thin films. After KrF excimer laser annealing, ZnO thin films show intense near-band-edge (NBE) emission and weak deep-level emission. The optically improved pristine ZnO thin films have demonstrated that excimer laser annealing is novel treatment process at room temperature.     

Modeling of In2O3-10 wt% ZnO thin film properties for transparent conductive oxide using neural networks

Effects of deposition process parameters on the deposition rate and the electrical properties of In₂O₃–10 wt% ZnO (IZO) thin films were modeled and analyzed by using the error back-propagation neural networks (BPNN). Output models were represented by response surface plots and the fitness of models was estimated by calculating the root mean square error (RMSE). The deposition rate of IZO thin films is affected by the RF power and the substrate temperature. The electrical properties of the IZO thin films are mainly controlled by O₂ ratio and the substrate temperature. The predicted output characteristics by BPNN can sufficiently explain the mechanism of IZO deposition process. Thus, neural network models can provide the reliable explanation of IZO film deposition.     

The role of copper ions on the structural and magnetic characteristics of MgZn ferrite nanoparticles and thin films

In this study Cu_xMg_0.5−xZn_0.5Fe₂O₄ (x=0-0.5) nanoparticles and thin films were prepared by sol-gel processing. The morphologies of nanoparticles were observed by transmission electron microscope (TEM). The Mössbauer spectroscopy (MS) was employed to determine the site preference of the constitutive elements. Magnetic dynamics of the nanoparticles was studied by the measurement of AC magnetic susceptibility versus temperature at different frequencies. The phenomenological Néel-Brown and Vogel-Fulcher models were employed to distinguish between interacting or non-interacting system. Results exhibited that there is strong interaction between fine particles. X-ray diffraction (XRD) patterns of the thin films indicate the formation of single-phase cubic spinel structure. Atomic force microscope (AFM) was employed to evaluate the surface morphologies of the prepared thin films. Vibrating sample magnetometer (VSM) was employed to probe magnetic properties of samples. It was found that with an increase in the amount of copper, the saturation of magnetization and initial permeability increase.     

Synthesis and characterization of single- and co-doped SnO2 thin films for optoelectronic applications

Doped SnO₂ thin films have been prepared by sputtering from two different targets: antimony doped tin oxide (ATO) and antimony and zinc doped tin oxide (AZTO). In the case of ATO ceramic, the antimony amount only reaches 0.012 mol per formula unit due to its evaporation at high temperature while the presence of Zn²⁺ in AZTO prevents the antimony evaporation, greatly enhances the ceramic density and allows the deposition of thin films with a high deposition rate. Both types of thin films have a dense morphology with a smooth surface and they are polycrystalline. For post-annealed ATO thin films, the Drude model was applied to deduce the carrier concentration, the optical mobility as well as the resistivity. The carrier concentration is around ten times higher for ATO thin films compared to AZTO. The two combined effects (higher carrier concentration and mobility) for ATO thin films doped with 1.2% of Sb lead to the best optoelectronic performances, confirming previous results obtained with ceramics. Nevertheless, we have a better opportunity to modulate the conductivity in the case of AZTO thin films.     

Magnetic field annealing effects on self-oriented BiFeO3 thin films prepared by chemical solution deposition

Self-oriented BiFeO₃ (BFO) thin films are prepared via chemical solution deposition method with magnetic field in-situ annealing process. The effects of magnetic annealing on the microstructure, magnetic and dielectric properties as well as magnetoelectric coupling effect of the BFO thin films are investigated. With increasing the annealing magnetic field, the crystallization quality, texture, grain boundary connectivity and densification of the films are enhanced, which is attributed to the improvement of connection and diffusion of components. The magnetization of the field-annealing films and dielectric constant as well as remanent polarization increases with increasing the strength of annealing magnetic field. In addition, it is observed that magnetocapacitance value of the magnetic-field-annealing BFO thin film is higher than the non-field-annealing one. Moreover the BFO thin films annealed at 3 kOe magnetic field show the magnetoelectric effect with 4% under 2 kOe at room temperature.     

Dielectric properties of multilayered SrTiO3 thin films with graded oxygen vacancy concentration

SrTiO₃ (STO) thin films were homo-epitaxially grown on Nb-doped STO substrates at varying oxygen pressures, and the effect of oxygen vacancy concentration on the dielectric properties of the STO thin films was studied and is presented herein. Although the STO thin films with low oxygen vacancy concentration demonstrated low zero-bias permittivity, low dielectric tunability, and high dielectric dissipation, the STO thin films, however, could withstand a large electric field. While the STO thin films with high oxygen vacancy concentration exhibited reduced dielectric loss and high dielectric tunability, they exhibited a low breakdown electric field. In order to make use of the respective advantages of the STO thin films with different oxygen vacancy concentrations, a trilayered structure was obtained by varying the oxygen pressure during deposition and combining one thin STO layer with large oxygen vacancy concentration sandwiched by two STO thin films with low oxygen vacancy concentration. The microstructure and dielectric properties of the trilayer were then studied. X-ray diffraction analysis indicated that the trilayer was a relaxed STO multilayer formed by two STO thin layers with different lattice parameters. An improved optimization of high tunability and low loss was achieved in the relaxed trilayer. PACS 77.84.Bw; 68.55; 77.22.Ch; 68.35.Ct; 74.80.Dm