PtMn层厚度对NiFe/PtMn双层膜交换偏置形成及热稳定性的影响

采用磁控溅射的方法制备了一组以(Ni_0.81Fe_0.19)_1-xCr_x作为缓冲层的NiFe/PtMn双层膜样品，研究了NiFe/PtMn双层膜的形成过程和热稳定性.实验表明，Cr成分的不同会引起NiFe/PtMn双层膜中PtMn层晶粒尺寸的不同，使NiFe/PtMn双层膜的交换偏置场与PtMn层厚度之间呈现不同的变化关系.热稳定性实验表明，PtMn晶粒尺寸较大的样品，出现交换偏置现象所需要的临界厚度较小，热稳定性好，这与Mauri的理论模型一致. 关键词： NiFe/PtMn双层膜 交换偏置场 热稳定性     

Quick preparation and thermal transport properties of nanostructured β-FeSi2 bulk material

This paper reports that the nanostructured β-FeSi2 bulk materials are prepared by a new synthesis process by combining melt spinning(MS) and subsequent spark plasma sintering(SPS).It investigates the influence of linear speed of the rolling copper wheel,injection pressure and SPS regime on microstructure and phase composition of the rapidly solidified ribbons after MS and bulk production respectively,and discusses the effects of the microstructure on thermal transport properties.There are two crystalline phases(α-Fe2Si5 and ε-FeSi) in the rapidly solidified ribbons;the crystal grains become smaller when the cooling rate increases(the 20 nm minimum crystal of ε-FeSi is obtained).Having been sintered for 1 min above 1123 K and annealed for 5 min at 923 K,the single-phase nanostructured βFeSi2 bulk materials with 200-500 nm grain size and 98% relative density are obtained.The microstructure of β-FeSi2 has great effect on thermal transport properties.With decreasing sintering temperature,the grain size decreases,the thermal conductivity of β-FeSi2 is reduced remarkably.The thermal conductivity of β-FeSi2 decreases notably(reduced 72% at room temperature) in comparison with the β-FeSi2 prepared by traditional casting method.     

Comparative study of optical parameters of fullerene C60 film at different temperatures

Fullerene C₆₀ thin films on glass substrate (around 2000 ? thickness) were prepared by thermal evaporation technique. The structural, surface morphology and optical properties of the films were studied. The optical properties of fullerene C₆₀ were investigated in the spectral range 200 nm to 900 nm using a UV-Vis spectrophotometer at room temperature as well as at liquid nitrogen temperature (77 K). The optical band gap at room temperature is found to be 2.30 eV, which gradually decreases with lowering the temperature and reaches to 2.27 at 77 K. The thickness and refractive index of fullerene C₆₀ film were calculated by ellipsometry. From the X-ray analysis, we have calculated the grain size, dislocation density, number of crystallite per unit area, and strain of the film at room temperature. The surface morphology of film was analyzed by scanning electron microscope (SEM). The present result show that the fullerene C₆₀ film becomes more conducting at low temperature.     

Structural,morphologic and optical characterization of In(2−x)Al x S3

Aluminum-doped indium sulfide thin films are deposited on glass by spray pyrolysis technique. The structure and the surface morphology of these films were characterized by X-ray diffraction and atomic force microscopy. The effects of aluminum ratio z and substrate temperature T _s, on the film structure and grain size are discussed. The influence of aluminum ratio on surface morphology is revealed by scanning electron microscope. Besides, energy dispersive spectrometry technique is used to compare atomic aluminum concentration in the film with aluminum ratio z in spray solution. Optical properties are studied by a spectrophotometer in the wavelength range 350–850 nm, at room temperature. Optical transmission and grain size are found to be maximal for z = 1.8 %. Moreover, band-gap energy is found to increase with aluminum ratio.     

Crystallization-dependent magnetic properties of Mn1.56Co0.96Ni0.48O4 thin films

The effects of magnetic property dependence of the Mn_1.56Co_0.96Ni_0.48O₄ (MCN) films on crystallization are investigated in the growth temperature of 450-750 °C. With the growth temperature increase, both the crystalline quality and the grain size improve. The MCN films exhibit paramagnetic to ferromagnetic transition and the paramagnetic parts fit to the modified Curie-Weiss law. The ferromagnetic couplings of the magnetic ions in the MCN films enhance at elevated growth temperature. The saturation magnetization at 5 K increases with increasing growth temperature, but coercive field decreases monotonously. The magnetic properties of the MCN films strongly depend on their microstructures.     

Effect of the sintering temperature of ceramic manganites La0.7Mn1.3O3 ± Δ on their grain sizes, magnetic and electrical properties

The effect of the sintering temperature from 1070 to 1670 K of ceramic samples of lanthanum manganite La_0.7Mn_1.3O₃ on their grain size, structure, magnetic and resistive properties has been studied. An increase in the sintering temperature to 1270 K is shown to lead to an insignificant increase in the grain size and an increase in the density, fraction of the ferromagnetic phase in a grain, and colossal magnetoresistance. The ceramics sintering at temperatures higher than 1470 K is found to sharply increase the grain size; simultaneously, the grain takes a layered structure. The grain growth at these temperatures is established to be accompanied by manganese precipitation at the grain boundaries and likely in the grain interior. The increase in the sintering temperature is accompanied by appearance of a magnetically phase heterogeneity and a decrease in the Curie temperature and magnitude of the colossal magnetoresistance effect.     

Pulsed laser deposition of NdNiO3 thin films

We report the structural and transport properties of NdNiO₃ thin films prepared via pulsed laser deposition over various substrates. The films were well textured and c-axis oriented with good crystalline properties. The electrical resistivity of the films undergoes a metal-insulator transition, depending on the deposition process. Well-defined first order metal-insulator phase transition (T_MI) was observed in the best quality films without high pressure processing. Various growth conditions such as substrate temperature, oxygen pressure and thickness were varied to see their influence on T_MI. Deposition temperature was found to have a great impact on the electrical and structural properties of these films. Further the films deposited on LaAlO₃ substrate were found to be highly oriented with uniform grain size as observed from X-ray diffraction and atomic force microscopy, whereas those on Si substrate were polycrystalline, dense and randomly oriented.     

Quantum confinement effects of CdTe nanocrystals sequestered in TiO2 matrix: effect of oxygen incorporation

Thin films of TiO₂ with high volume fraction (40–55%) and crystallite size (6–40 nm) of CdTe nanoparticles had been prepared by rf magnetron sputtering from a composite TiO₂:CdTe target at room temperature and 373 K. A detailed optical properties of nanocrystalline CdTe:TiO₂ films as-deposited and after thermal treatment (300 °C) are studied. The absorbance of the TiO₂ films with CdTe nanocrystallite dispersions depends both on the nanocrystallite size and volume fraction. The blue-shifts of the optical absorption edge concurrent with the CdTe nanocystal size reduction for as-deposited and after thermal treatment of nanocrystalline CdTe:TiO₂ thin films with respect to the bulk semiconductor agrees quite well with the strong quantum confinement theory. A slight deviation in absorption edge values than the predicted values from the strong quantum confinement model can be attributed to change in interplanar distance due to oxygen incorporation and inhomogeneous size distribution of CdTe nanocrystallites in these films.     

Quantum states in fabricating poly-Si films

The quantum states are presented in these processions of fabricating poly-Si films. Amorphous silicon films prepared by PECVD has been crystallized by conventional furnace annealing (FA) and rapid thermal annealing (RTA), respectively. It is found that the thin films grain size present quantum states with the increasing of the gas flow ratios of SiH₄, H₂ mixture, substrate temperatures, frequency power, annealing temperature and time.     

Successive occurrence of ferromagnetic and shape memory properties during crystallization of NiMnGa freestanding films

Ni₅₀Mn₃₀Ga₂₀ films of 13 μm thickness were fabricated by DC magnetron sputtering on unheated glass substrates. The As-deposited films are partially crystalline and crystallize during rapid annealing. The successive appearance of ferromagnetic and shape memory properties was observed as the annealing temperature was increased. Ferromagnetic properties evolved after annealing at 400 °C for 0.5 h, while thermal annealing of at least 600 °C for 0.5 h led to polycrystalline films that transformed reversibly and martensitically as shown by structural analysis and differential scanning calorimetry and confirmed by mechanical spectroscopy data. Magnetic measurements also revealed the influence of the post deposition annealing on the ferromagnetic hysteresis. Transition temperatures and reaction enthalpies of the martensitic phase transformation were strongly influenced by the temperature of the rapid annealing process. X-ray absorption fine-structure (XAFS) spectroscopy proved these changes to be related to the change in the chemical order. It is proposed that the annealing data reflect the evolution of the crystalline state. Ferromagnetic order is established already in nano-grained samples whereas the shape memory effect is only observed above a critical grain size.     

Material and device properties of Cu(In,Ga)Se2 absorber films prepared by thermal reaction of InSe/Cu/GaSe alloys to elemental Se vapor

The aim of this work was to study the influence of selenization temperature on the morphological and structural properties of CuIn_1−xGa_xSe₂ (CIGS) polycrystalline thin films prepared by a two-step method. The compound and metallic precursors were deposited sequentially using GaSe, InSe and Cu sources by thermal evaporation. These identical InSe/Cu/GaSe precursors are then selenized with Se vapor in a vacuum system. All the CIGS films showed chalcopyrite structure and presence of secondary phases observed at low temperatures. High temperature treatment led to better crystalline and an increase in grain size. Solar cell devices are fabricated and J–V measurements performed under AM1.5 global solar spectra conditions at 25 °C are presented.     

Structural and dielectric properties of Bi4Ti3O12 thin films prepared by metalorganic solution deposition

Ferroelectric Bi₄Ti₃O₁₂ thin films with single phase and nanosized microstructure were prepared on Pt/Ti/SiO₂/Si(111) substrate by metalorganic solution deposition using titanium butoxide and bismuth nitrate at relatively low annealing temperatures. The internal strain in Bi₄Ti₃O₁₂ thin films was calculated from the peak shifts and broadening of XRD patterns. With increase in annealing temperature, the uniform strain decreased from positive to zero and then to negative, and the non-uniform strain decreased and was negative. The total strain was negative and in the range of -0.2%–-1.0%, from which the stress of the films was calculated to be about -1.4×10⁹ N/m². The mode values of strain decreased with increase in annealing temperature and increased with increase in film thickness. The dielectric constant increased with increase in annealing temperature and film thickness. The dielectric properties were interpreted by considering the influence of strain, grain size, and grain boundaries. The strain lowered the polarization and increased the dielectric constant. The larger the grain size and the thinner the grain boundary, the greater the dielectric constant. The influence of grain size and grain boundary was stronger than that of the strain. Received: 23 September 1998 / Accepted: 6 January 1999 / Published online: 24 March 1999     

Study of the microstructure influence on the transport properties of Bi86.5Sb13.5 polycrystalline alloy

This study is focused on the investigation of the transport properties of Bi_86.5Sb_13.5 polycrystalline alloys. Bulk materials were prepared by cold pressing ultrafine powders of alloy and by annealing the resulting pellets. Special care was taken to avoid contamination of the powders. Starting with powders of average grain size of 0.06 μm bulk semi-conducting sample with mean grain size respectively of 0.1, 0.8, 2.5 and 200 μm were obtained. The influence of the grain size on both electrical resistivity, thermal conductivity, thermoelectric power, thermoelectric figure of merit is presented within the range 80-330 K. The thermoelectric properties are discussed and compared with those of single crystals presented in previous studies.     

Hysteresis loop construction for the metal-semiconductor phase transition in vanadium dioxide films

Thermal hysteresis of the reflectivity of vanadium dioxide films observed upon the metal-semiconductor phase transition is studied. The major hysteresis loop is assumed to form when the phase equilibrium temperature in film grains and the grain size vary and correlate with each other. Within the suggested concept of hysteresis loop formation, it is demonstrated that the major loop may be asymmetric, i.e., broadened (shifted) toward lower temperatures. Unlike hysteresis branches for VO₂ bulk single crystal, those for VO₂ films are extended along the temperature axis and may exhibit a step if the grain size distribution has several maxima. The validity of the concept is verified experimentally. It is also shown that atomic force microscopy (AFM) data for the grain size distribution can serve to determine the distribution parameters from the phase equilibrium temperatures without constructing a complete set of minor hysteresis loops, as was required before.     

Structural and magnetic properties of sol-gel Co2xNi0.5−x Zn0.5−xFe2O4 thin films

Nanocrystalline Co_2xNi_0.5−xZn_0.5−xFe₂O₄ (x=0−0.5) thin films have been synthesized with various grain sizes by a sol-gel method on polycrystalline silicon substrates. The morphology as well as magnetic and microwave absorption properties of the films calcined at 1073 K were studied using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. All films were uniform without microcracks. The Co content in the Co-Ni-Zn films resulted in a grain size ranging from 15 to 32 nm while it ranged from 33 to 49 nm in the corresponding powders. Saturation and remnant magnetization increased with increase in grain size, while coercivity demonstrated a drop due to multidomain behavior of crystallites for a given value of x. Saturation magnetization increased and remnant magnetization had a maximum as a function of grain size independent of x. In turn, coercivity increased with x independent of grain size. Complex permittivity of the Co-Ni-Zn ferrite films was measured in the frequency range 2-15 GHz. The highest hysteretic heating rate in the temperature range 315-355 K was observed in CoFe₂O₄. The maximum absorption band shifted from 13 to 11 GHz as cobalt content increased from x=0.1 to 0.2.     

Focused ion beam fabrication and magneto-electrical transport properties of La0.67Ca0.33MnO3 nanobridge

La_0.67Ca_0.33MnO₃ particle films with an average particle size of ~150 nm were grown on single-crystal silicon substrate using pulsed electron deposition technique and then focused ion beam was introduced to fabricate nanobridge in size of 300 × 900 nm on the particle film. The magneto-transport properties of both samples were studied. For the film, there is only one resistance peak at 182 K in temperature-dependent resistance (R–T) curves, which is far lower than ferromagnetic–paramagnetic transition temperature (T _C) of 250 K. When compared to the film, double peaks were observed in both R–T curves and magnetoresistance dependent on temperature (MR–T) curves of the nanobridge, one peak is at 186 K, which is very close to metal–insulator transition temperature (T _P) of film, the other one is at 250 K, which is close to the T _C of film, and these two peaks caused separately by grain and grain boundary (GB), which demonstrated that the electrical transport behavior of grain was separated from that of GB.     

晶界对庞磁电阻颗粒薄膜的磁学和输运性能的影响

采用脉冲电子束沉积技术，在Si(100)单晶衬底上沉积庞磁电阻La_0.67Ca_0.33MnO₃颗粒薄膜，并对它的磁学性能和电学输运性能进行了表征.研究晶界对庞磁电阻薄膜的物理性能的影响，结果表明，晶界的存在使得晶粒之间的耦合变弱，在变温磁化过程中表现出团簇玻璃态行为，金属—绝缘体转变温度(T_p)远远低于铁磁—顺磁转变温度(T_c).低温下电子输运具有弱局域化行为.在低磁场下，晶界的存在掩盖了La_0.67Ca_0.33MnO₃的本征磁电阻行为. 关键词： 脉冲电子束沉积 晶界 磁学和电学输运性能 庞磁电阻     

基片温度对SiNx薄膜结晶状态及机械性能的影响

利用微波电子回旋共振增强磁控反应溅射法在不同基片温度下制备无氢SiN_x薄膜.通过傅里叶变换红外光谱、透射电子显微镜、台阶仪、纳米硬度仪等表征技术,研究了基片温度对SiN_x薄膜结晶状态、晶粒尺寸、晶体取向等结晶性能以及薄膜的生长速率、硬度等机械性能的影响,并探讨了薄膜结晶性能与机械性能之间的关系.研究结果表明,在基片温度低于300℃时制备的SiN_x薄膜以非晶状态存在,硬度值仅为18GPa左右;基片温度 关键词： x')" href="#">SiN_x 磁控溅射 微观结构 硬度     

Preparation and characterization of thermally evaporated titanium phthalocyanine dichloride thin films

Titanium phthalocyanine dichloride (TiPcCl₂) thin films are prepared on glass substrates by vacuum-sublimation technique. The optical constants of thin films are obtained by means of thin film spectrophotometry. Planar structures for the study of electrical properties are fabricated with TiPcCl₂ as active layer and silver as the contact electrodes. The effects of post-deposition annealing on the optical band gap have been studied. The optical transition is found to be direct allowed in nature. The invariance in the optical band gap shows the thermal stability of the material. The activation energies are determined using the Arrhenius plots between electrical conductivity and inverse temperature. The variation in activation energy with post-deposition annealing is investigated. The unit cell dimensions of TiPcCl₂ thin films are also determined by indexing the powder diffraction data. The variations of the surface morphology and grain size with annealing have also been studied.     

Grain Size Effects in Sensor Response of Nanostructured SnO2- and In2O3-Based Conductometric Thin Film Gas Sensor

Based on the experimental results, obtained by studying both structural and gas-sensing properties of the SnO₂ and In₂O₃ films deposited by the spray pyrolysis method, we analyzed the influence of crystallite size on the parameters of the SnO₂- and In₂O₃-based thin film solid-state gas sensors. For comparison, the behavior of ceramic-type gas sensors was considered as well. In particular, we examined the correlation between the grain size and parameters of conductometric-type gas sensors such as the magnitude of sensor signal, the rate of sensor response, thermal stability, and the sensitivity of sensor signal to air humidity. Findings confirmed that that grain size is one of the most important parameters of metal oxides, controlling almost all operating characteristics of the solid state gas sensors fabricated using both the ceramic and thin film technologies. However, it was shown that there is no single universal requirement for the grain size, because changes in grain size could either improve, or worsen of operating characteristics of gas sensors. Therefore, the choice of optimal grain size should be based on the detailed consideration of all possible consequences of their influence on the parameters of sensors designed.