PZT铁电薄膜纳米尺度铁电畴的场致位移特性

利用扫描力显微术的压电响应模式，并基于逆压电效应原理，研究了梯度组成的PZT铁电薄膜纳米尺度铁电畴的场致位移特性.获得了源于纳米尺度铁电畴的压电效应和电致伸缩效应贡献的场致位移回滞线，以及源于线性压电效应和电畴反转效应综合贡献的纳米尺度压电位移 场强蝶形曲线，证实了Caspari Merz理论在纳米尺度上的有效性.发现了梯度铁电薄膜存在纳米尺度印刻现象，认为该现象的内因源于薄膜中的内偏场. 关键词： PZT铁电薄膜 场致位移 纳米尺度 扫描力显微术     

SERS activity of pulsed laser ablated silver thin films with controlled nanostructure

The surface‐enhanced Raman scattering (SERS) activity of silver thin films deposited by the pulsed laser ablation technique was investigated. The samples were grown in a controlled Ar atmosphere at pressures ranging between 10 and 70 Pa, and changing the number of laser pulses. Different surface morphologies, from isolated nearly spherical nanoparticles (NPs) to larger islands with smooth edges, were observed by means of scanning and transmission electron microscopies, as a function of the different deposition conditions adopted. SERS measurements were performed by soaking the samples in rhodamine 6G aqueous solutions over the concentration range between 1.0 × 10⁻⁴ and 5.0 × 10⁻⁸ M . Raman spectra were acquired using both the 632.8 and 514.5 nm excitation sources. The dependence of the SERS activity of the samples on the observed surface morphology is presented and discussed. The presence of the so called hot spots is envisaged. Copyright © 2011 John Wiley & Sons, Ltd.     

Morphology and orientation of iron oxide precipitates in epitaxial BiFeO3 thin films grown under two non-optimized oxygen pressures

Microstructures of multiferroic BiFeO₃ thin films epitaxially grown on SrRuO₃-buffered SrTiO₃ (001) substrates by laser molecular-beam epitaxy under two non-optimized oxygen pressures were characterized by means of transmission electron microscopy. The results showed that the films grown under oxygen pressures of 1 Pa and 0.3 Pa contain a secondary phase embedded in the BiFeO₃ matrix. High-angle annular dark-field imaging, elemental mapping and composition analysis in combination with selected area electron diffraction revealed that the parasitic phase is mainly antiferromagnetic α-Fe₂O₃. The α-Fe₂O₃ particles are semi-coherently embedded in the BiFeO₃ films, as confirmed by high-resolution transmission electron microscopy. In addition to the α-Fe₂O₃ phase, ferromagnetic Fe₃O₄ precipitates were found in the BiFeO₃ films grown under 0.3 Pa and shown to accumulate in areas near the film/substrate interfaces. In our heteroepitaxy systems, very low density misfit dislocations were observed at the interfaces between the BiFeO₃ and SrRuO₃ layers implying that their misfit strains may be relieved by the formation of the secondary phases. Using X-ray photoelectron spectroscopy it was found that Fe exists in the +3 oxidation state in these films. The possible formation mechanisms of the secondary phases are discussed in terms of film growth conditions.     

PZT铁电薄膜纳米尺度畴结构的扫描力显微术研究

利用扫描力显微术中压电响应模式原位研究了（111）择优取向的PZT60/40铁电薄膜的纳米尺度畴结构及其极化反转行为.铁电畴图像复杂的畴衬度与晶粒中的畴排列和晶粒的取向密切相关.直接观察到极化反转期间所形成的小至30nm宽的台阶结构，该台阶结构揭示了（111）取向的PZT60/40铁电薄膜在极化反转期间其畴成核与生长机理主要表现为铁电畴的纵向生长机理. 关键词： 畴结构 反转机理 PZT薄膜 扫描力显微术     

Enhancement of photosensitivity in bismuth doped Cu2ZnSnS4 thin films

In this paper, the effect of bismuth doping on the structural, morphological, optical and electrical properties of Cu₂ZnSnS₄ (CZTS) films has been investigated. The undoped and bismuth doped CZTS films (0, 0.5, 1, 1.5 and 2 mol%) were deposited on glass substrates by solution based method. The XRD result shows a significant improvement in the crystallinity of the films with increase in bismuth concentration. The Raman spectra of the films show the dominant peak at 334 cm^–1 corresponding to A₁ vibrational mode of CZTS kesterite phase. The FESEM micrographs of the films show an enhancement in the grain size and densification with the addition of bismuth ion concentration. The optical bandgap of the films was found to vary (1.59–1.40 eV) with the doping of bismuth ions. The I –V characteristics indicate twofold increment in the photoconductivity for the bismuth doped CZTS films under 100 mW/cm² illumination suggesting their potential application in photovoltaic devices. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Nano-scale and surface precipitation of metallic particles in laser interference patterned noble metal-based thin films

Laser interference patterning (also known as “laser interference metallurgy”) is used to locally tailor the microstructure of oxide (Pd_0.25Pt_0.75O_x) and nitride (Cu₃N) thin films to induce a chemical decomposition, which is responsible for a decrease of electrical resistivity. This technique allows hereby a laser-induced chemical decomposition of as-deposited oxide and nitride films, resulting locally in a porous microstructure due to the simultaneous emission of gaseous nitrogen and oxygen. The process locally generates at the nanometer scale metal precipitatation of Pt or Cu in the oxide or nitride matrix. Thus, isolated metallic clusters with low resistivity coexist with a high resistivity phase, establishing a preferential electrical conduction path and giving the system a lower effective resistivity. The decomposition process is investigated by four-point probe method, X-ray diffraction, spectrophotometry, white light interference, scanning and transmission electron microscopies.     

Structural characterization and magnetoresistance of manganates thin films and Fe-doped manganates thin films

Perovskites thin films with the composition La_0.6Ca_0.4MnO₃ doped with 20% Fe, were prepared by pulsed reactive crossed beam laser ablation, where a synchronized reaction gas pulse interacts with the ablation plume. The films were grown on various substrates and the highest colossal magnetoresistance ratio (CMR) was detected by Hall measurements for films grown on LaAlO₃ (1 0 0), which was selected as substrate for further investigations.Several growth parameters, such as substrate temperature and target to substrate distance were varied to analyze their influence on the film properties.The structure of the deposited thin films was characterized by X-ray diffraction and atomic force microscope, while Rutherford backscattering (RBS) was used to determine the film stoichiometry. The electrical properties were determined by Hall effect measurements in a magnetic field of 0.51 T.These measurements reveal that the amplitude of the CMR ratio depends strongly on the substrate and that the oxygen content influences the temperature where the transition from semiconductor to metal is observed.     

一种在线测量微机械薄膜残余应力的新结构

提出了一种利用临界屈曲法在线测量微机械薄膜残余应力的新结构，并采用表面微加工技术制作了两种测试样品.搭建了在线观测实验装置来实时监控释放过程中结构出现的临界屈曲变形模态，由此判断出结构内部的应力状态，同时在测得临界刻蚀深度的情况下，采用有限元方法计算出残余应力大小.借助有限元方法，先研究了多个参数对临界屈曲应力的影响，然后利用这种新结构对薄膜残余应力进行了实际测量，所得结果与微旋转结构的应力测量结果基本吻合.分析及实验表明，新结构在测量薄膜残余应力方面有许多优点，具有较高的实用价值，不仅能满足大量程的应力检测要求，而且只用一个结构就可以同时测量压应力和拉应力，从而极大提高了器件版图空间的利用率.     

基底温度对电子束蒸发制备氧化铝薄膜的影响

为了考察基底温度对氧化铝薄膜折射率以及沉积厚度的影响情况,在不同基底温度环境下,通过离子辅助电子束蒸发方式,在玻璃基底上制备了同一Tooling因子条件下所监测到相同厚度的Al2O3薄膜,利用分光光度计测量光谱透过率,依据光学薄膜相关理论,计算了基底温度在25℃～300℃范围内获得的膜层实际物理厚度为275.611 nm～348.447 nm,以及膜层折射率的变化。通过对实验结果的数值计算和曲线模拟,给出了基底温度对于薄膜的折射率和实际厚度的影响情况。     

Structural and optoelectronic properties of amorphous GaN thin films

Amorphous gallium nitride (a-GaN) thin films were deposited on glass substrate by electron beam evaporation technique at room temperature and high vacuum using N ₂ as carrier gas. The structural properties of the films was studied by X-ray diffraction (XRD) and scanning electron microscope (SEM). It was clear from XRD spectra and SEM study that the GaN thin films were amorphous. The absorbance, transmittance and reflectance spectra of these films were measured in the wavelength range of 300–2200 nm. The absorption coefficient spectral analysis in the sharp absorption region revealed a direct band gap of E _g = 3:1 eV. The data analysis allowed the determination of the dispersive optical parameters by calculating the refractive index. The oscillator energy E ₀ and the dispersion energy E _d, which is a measure of the average strength of inter-band optical transition or the oscillator strength, were determined. Electrical conductivity of a-GaN was measured in a different range of temperatures. Then, activation energy of a-GaN thin films was calculated which equalled E _a = 0:434 eV.     

Mechanism of two-dimensional chiral growth of 6,13-pentacenequinone thin films on Si(1 1 1)

Thin film growth of 6,13-pentacenequinone (C₂₄H₁₂O₂, PnQ) on Si(1 1 1)-7 × 7 at room temperature (RT) was studied by low-energy electron microscopy (LEEM) and ab initio density functional theory (DFT) calculations. Our experiments yielded direct microscopic observation of enantiomorphic evolution mechanism in the initial stage of the chiral-like growth of PnQ islands, under kinetic growth conditions. We observed that the faster growth direction aligns with the direction of easier molecule incorporation, or lowest kink formation energy, rather than along the lowest energy step. Real time observation of the growth and subsequent relaxation of island shape revealed that kinetically stiff direction differs from the thermodynamic one. This feature together with anisotropic mass incorporation determines the enantiomorphic evolution and rotational arrangement of crystallites during the growth of elongated organic molecules, like PnQ.     

Determination of the nanoscale dielectric properties in ferroelectric lead zirconate titanate (PZT) thin films

We report on nanoscale experiments with <100 nm lateral resolution being able to differentiate the effective dielectric polarisation P_z, deposited charge density σ, surface dielectric constant ε_surface, its voltage dependence ε_surface(U), as well as the built-in electric bias voltage U_int in ferroelectric lead zirconate titanate (PZT) thin films. This is possible by combining piezoresponse force microscopy (PFM) and pull-off force spectroscopy (PFS), both methods based on scanning force microscopy (SFM). The differentiation becomes possible since both P_z and σ contribute additively in PFS, while they are subtractive in PFM, hence allowing the two contributions to be separated. ε_surface can be quantified by means of the experimental PFS data and the calculated effective penetration depth of PFM developed in a finite element modelling. Finally, U_int and ε_surface(U) are derived by an absolute matching of the P_z values measured by PFM and PFS.Our nanoscale results obtained on PZT thin films reveal values for the above specified quantities that have the same order of magnitude as those obtained from macroscopic measurements reflecting the integral response using large electrode areas. However, we stress that the data reported here reveal physical properties deduced on the nanometer scale. Furthermore, they are recorded during one single experimental investigation, using one single set-up only.     

Microwave magnetic properties of soft magnetic thin films

We review our works that focus on the microwave magnetic properties of metallic,ferrite and granular thin films.Soft magnetic material with large permeability and low energy loss in the GHz range is a challenge for the inforcom technologies.GHz magnetic properties of the soft magnetic thin films with in-plane anisotropy were investigated.It is found that several hundreds of permeability at the GHz frequency was achieved for Co100-xZrx and Co90Nb10 metallic thin films because of their high saturation magneti...     

纳米晶氧化锡薄膜的接触特性

在 Ar和 O2 气体中 ,基片温度在 15 0～ 40 0℃的条件下 ,用直流磁控溅射的方法可以制备纳米晶透明导电薄膜。实验利用 TL M模型测试了纳米晶 Sn O2 透明导电薄膜的方块电阻、单位面积薄膜的接触电阻和电极与薄膜的结合力随热处理温度的变化情况     

Atomic-scale study of precipitates (NbC and Cu-rich phase) at the twin boundary in the long time ageing austenitic stainless steel

ABSTRACT

Microstructures of Cu-rich phases and NbC precipitated phases have been studied in a long time ageing austenitic stainless steel by high resolution scanning transmission electron microscopy. The interaction difference between the twins and the second phases found to be dependent on the nature of the precipitates. The Cu-rich phases were identified to be twinned at the twin boundary. Nevertheless, the NbC precipitates not only twinned at the twin boundary but also induced the twin boundary bypass them. A particle size dependence of the generation of misfit dislocations also was detected at interface between precipitates and the austenitic matrix.     

Nanoporous nickel oxide thin films and its improved electrochromic performance: Effect of thickness

Electrochromic properties of chemically bath deposited nanoporous NiO thin films were investigated as a function of film thickness using Ni sulphate precursor, aqueous ammonia and potassium persulphate as complexing and oxidizing agents respectively. The films were characterized for their structural, morphological, optical and electrochromic properties using X-ray diffraction, scanning electron microscopy, FT-IR spectroscopy, cyclic voltammetry, chronoamperometry and optical transmittance studies. X-ray diffraction patterns show that the films are polycrystalline, consisting of NiO cubic phase. Infrared spectroscopy results show the presence of free hydroxyl ion and water in NiO thin films. SEM micrographs revealed nanoporous nature composed of interconnected nanoporous network, forming well defined 3D nano envelopes. The optical band gap energy was found to be decreased from 3.22 to 2.80 eV with increasing film thickness. The electrochromic properties of all the films were investigated in aqueous (KOH) and non aqueous (LiClO₄-PC) electrolyte by means of cyclic voltammetry (CV), chronocoulometry (CC) and optical studies. The transmittance modulations or optical density differences during the coloring/bleaching process were found to be increased with the film thickness. This increment in optical differences led to an increase in coloration efficiency (CE) to about 95 cm²/C, which is two times more than that observed in KOH and response time of 2.9 s for bleaching (reduction) and 3.5 s for coloration (oxidation) observed for the film deposited at 60 min with excellent electrochemical stability up to 3000 c/b cycles in LiClO₄-PC electrolyte.     

Switching phenomena in CdIn2S4 thin films

Summary Two kinds of switching phenomena in CdIn₂S₄ polycrystalline and amorphous thin films which were prepared by the vacuum evaporation method and the d.c. sputtering method, respectively, were studied. One is the so-called memory switching phenomenon arising from the low resistive filament path. Another is a characteristic switching phenomenon in which the resistivity abruptly changes whenever the ambient temperature reaches a critical value. The switching time is fast and about 100 ns. This switching phenomenon is related to the native defects in the CdIn₂S₄ lattice, because they can be observed in the polycrystalline as well as in the amorphous thin films. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

The role of interfacial morphology in multilayers based on high T c YBa2Cu3O7-x

The interfacial microstructures in CaTiO₃/YBa₂Cu₃O_7-x /SrTiO₃/LaAlO₃/CaRuO₃ multilayers grown on (001) LaAlO₃ substrates has been characterized using transmission electron microscopy in combination with scanning electron microscopy. The morphology of films grown on both flat surfaces and on stepped surfaces patterned by ion beam milling were interpreted in terms of effects that influence epitaxial orientation relationships, nucleation of Y₂O₃ particles, and pinhole formation. The general conclusions are that a-axis oriented YBa₂Cu₃O_7-x particles should be avoided in multilayer structures. The particles give rise to cracking and pinhole formation. Local surface roughness, which may be due to ion beam milling or to the growth mechanism of YBCO, induces Y₂O₃ particle nucleation and pinhole formation. Very steep surface slopes cause the formation of a-axis YBa₂CU₃O_7-x particles. A critical size effect of the Y₂O₃ particles is suggested.     

Oxidation-induced changes in the electro-optical properties of thin copper films

Summary The room temperature oxidation of vapour deposited copper films has been investigated as a function of film thickness and time by the sheet resistance and optical transmittance measurements. An increase of both sheet resistance and transmittance with a tendency to saturation has been observed. Time variation of the sheet resistance shows that the kinetics of oxidation could be described by a model whereby an initial logarithmic oxide growth changes to an inverse logarithmic one as time progresses; the thicker the film, the longer the change-over time. Absorption coefficients of oxidized films show that the resulting oxide is most probably Cu₂O. Evaluation of the oxidized films for possible use as transparent electrode material shows the existence of an optimum thickness value.

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Riassunto Si è studiata l’ossidazione a temperatura ambiente di pellicole di rame depositate per vaporizzazione in funzione dello spessore della pellicola e del tempo mediante la resistenza del foglio e misurazioni di trasmittenza ottica. Si è osservato un aumento sia della resistenza del foglio, sia della trasmittenza con una tendenza alla saturazione. La variazione temporale della resistenza del foglio mostra che la cinetica di ossidazione potrebbe essere descritta da un modello con cui un’iniziale crescita logaritmica dell’ossido cambia in una logaritmica inversa al crescere del tempo; più spessa è la pellicola più lungo è il tempo del cambiamento. I coefficienti di assorbimento delle pellicole ossidate mostrano che l’ossido risultante è molto probabilmente il Cu₂O. La valutazione delle pellicole ossidate per un possibile uso come materiale di elettrodo trasparente mostra l’esistenza di un valore ottimo dello spessore.

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Резюме Исследуется окисление при комнатной температуре пленок меди в зависимости от толщины пленки и времени, используя измерения сопротивления слоя и оптической прозрачности. Наблюдается увеличение сопротивления слоя и прозрачности с тенденцией к насыщению. Временное изменение сопротивления слоя показывает, что кинетика окисления может быть описана с помощью модели, согласно которой начальный логарифмический рост окисла изменяется на обратно логарифмический, когда время увеличивается; для более толстой пленки изменение происходит при больщих временах. Коэффициенты поглощения окисленных пленок показывают, что результирующий окисел представляет Cu₂O. Оценка возможности использования окисленных пленок в качестве прозрачного материала электродов указывает на существование оптимальной толщины пленки.

     

溶胶-凝胶VO2薄膜转换特性研究

利用溶胶凝胶法在SiO2Si衬底上沉积高取向的V2O5薄膜,在压强低于2Pa,温度高于400℃的条件下,对V2O5薄膜进行真空烘烤,获得了电阻率变化3个数量级以上、弛豫宽度为62℃的VO2多晶薄膜.以X射线衍射(XRD)、扫描电子显微镜(SEM)图和电阻率转换特性等实验结果为依据,详细分析了溶胶凝胶薄膜在真空烘烤时从V2O5向VO2的转化,它经历了从VnO2n+1(n=2,3,4,6)到VO2的过程.实验证明,根据选择合适的成膜热处理条件和真空烘烤条件是实现溶胶凝胶V2O5结构向VO2结构成功转换的关键 关键词： 溶胶-凝胶法 氧化钒薄膜 VO2膜转换特性