Dissolution Kinetics in Langmuir-Blodgett Films of Solid State Polymerized ω-Tricosenoic Acid

ω-tricosenoic acid in L.B. films undergoes a solid state, lattice controlled polymerization. This molecule exhibits high contrast under short time development when used as an electron-resist in microlithography. This high contrast seems to be due to two factors : the monodispersity of the polymer and the compactness of the film. To check for a relationship between these factors and contrast, a model for the dissolution rate of partially polymerized L.B. films is presented, which includes monodispersity and compactness as basic hypotheses.

Since this model is able to fit all the set of experimental results in spite of its crude simplicity and the small number of adjustable parameters, it is believed to actually represent the real dissolution mechanism. The necessity of introducing a long penetration period is an expected consequence of the compact, trans-zigzag structure of the fatty acids. Polymer monodispersity is a second consequence of the model. A possible mechanism for it (stress limited propagation) is presented.     

Magnetic resonances of Fe and Ni nanoparticles in films of silicon suboxide produced by ion irradiation of triethoxysilane gels containing Fe or Ni solute atoms

The structure and magnetic properties of composite films obtained by ion irradiation or thermal treatment of triethoxysilane gels containing iron or nickel in solution are investigated by means of X-ray diffraction, electron microscopy and electron spin resonance. Ion irradiated gels are converted into silica glasses containing metallic nanoparticles with a narrow range of sizes. These particles exhibit a magnetic resonance with a preferential alignment of magnetic moments perpendicular to the surface. This unusual out of plane anisotropy seem to be ascribed to an interaction of the moments with radiation defects. The magnetization in irradiated film is comparable to that in films of same materials submitted to a thermal conversion at 1000 °C in vacuum. But the latter films are porous and contain particles of metal and silicide or silicate with a wider range of sizes.     

钝化剂乙酰水杨酸对钙钛矿太阳能电池性能影响的研究

有机-无机杂化钙钛矿太阳能电池因其优异的光电性能和低廉的制备成本,成为目前光伏领域内的研究热点。然而,钙钛矿薄膜表面和晶界处存在大量缺陷,这易于导致载流子非辐射复合,并进而影响太阳能电池的光电转换效率。本工作通过在两步法制备钙钛矿的铅盐前驱液中引入钝化剂乙酰水杨酸(acetylsalicylic acid, ASA),利用吸收/光致发光光谱、扫描电镜和电学测试等技术手段研究了ASA分子对钙钛矿薄膜质量与器件性能的影响。结果表明:适量的ASA分子可以通过路易斯酸碱相互作用增大钙钛矿晶粒尺寸,并有效降低钙钛矿薄膜的缺陷密度;当ASA的浓度为2.5 mmol/L时,所制得的钙钛矿电池取得了19.83%的最高光电转换效率,明显高于对照器件的转换效率(17.47%)。本工作首次报道了ASA对钙钛矿薄膜缺陷的良好钝化效果,并为提高钙钛矿太阳能电池性能提供了一种简单有效的制备方法。     

Investigation into the structure of Langmuir-Blodgett films prepared from salts of acetylenic acids

Langmuir-Blodgett films are prepared from lead, cadmium, and copper salts of carboxylic acids, namely, 23-tetracosynoic acid HC≡C(CH₂)₂₁COOH (with the terminal triple bond) and 2-docosynoic acid CH₃(CH₂)₁₈C≡CCOOH (with the internal triple bond). The structural transformations in the films during polymerization under exposure to UV radiation are investigated using X-ray reflectomertry. It is found that the X-ray reflectograms of the initial films prepared from salts of both acids exhibit no less than four or five pronounced intense Bragg reflections. This suggests that the initial films have good layer ordering. The bilayer periods for all the films are determined, and the influence of the salt type on the bilayer period is analyzed. It is established that, under exposure to UV radiation, the structural transformations in the films prepared from the salts of 23-tetracosynoic acid occur without substantial disturbances and defects, as can be judged from the absence of significant changes in the location and intensity of the Bragg reflections. An increase in the time of irradiation of the films prepared from the salts of 2-docosynoic acid leads to an increase in the bilayer period. This effect is especially pronounced for the lead and copper salts. However, upon long-term exposure to UV radiation, the salts undergo photolysis, the bilayer period decreases, and the structure of the film begins to break down.     

Forty Years Study of Fivefold Twinned Structures in Small Particles and Thin Films

Multiple twinning in crystalline solids forming quintuples of twins is known since 1957 (Segall ). It ever has attracted the attention not only of crystal growth and crystallography research, but also of cluster physics, physical chemistry, surface science, thin films and materials research. This review gives a comprehensive record of four decades work on fivefold twinned structures (frequently named ‘multiply twinned structures’) in small particles and thin films. After introducing crystallographic aspects of fivefold twinning, an historical review reports on beginning and spread out of the exploration as well as its broad extension to various fields, techniques and materials. The main issues of fivefold twinned structures, i.e. materials and processes involved, formation mechanisms, and stability and lattice defects, respectively, are treated in detail and illustrated by various examples. Accompanied by an almost complete list of references this review may not only make available results and experience of previous work in a greater context, but also stimulate future studies on this phenomenon.     

Ba1-xSrxTiO3薄膜的Sol-gel制备技术与微结构

研究了利用钡、锶的碳酸盐代替醋酸盐作原料,采用新的Sol-gel技术制备Ba1-xSrxTiO3(BST)铁电薄膜的技术.采用碳酸钡、碳酸锶和钛酸四丁酯作原料配制BST溶胶;通过TG/DTA分析确定了BST薄膜的制膜工艺;使用XRD、SEM、AFM技术分析了薄膜的微结构.研究结果表明,采用碳酸盐作为钡、锶的原料,用冰醋酸和乙二醇甲醚混合液作溶剂,可配制出澄清透明、能长时间放置的溶胶,用此溶胶制备出了膜厚均匀、表面光洁致密、没有裂纹的全钙钛矿相的BST薄膜;采用扫描探针显微镜的压电响应模式(PFM)观察到了BST薄膜中的具有纳米结构的a畴和c畴.     

Surface excitations in liquid helium nanofilms

The structural dynamic factor S(Q, ω) of liquid ⁴He has been measured by inelastic neutron scattering in films of different thickness at temperatures from 0.6 to 0.05 K. The measurements were performed on an IN6 spectrometer (Institut Laue-Langevin, France). Analysis of the obtained experimental data on S(Q, ω) made it possible to establish the main parameters of surface excitations arising in a helium film and their dependences on the film temperature and thickness. The measurements showed that surface excitations arise in a helium film at a thickness of about two to three atomic layers, and the film thickness plays a decisive role in the formation of surface excitations.     

Morphology of cells at the grain boundaries of an anisotropic material

We have studied the formation of ridges on the grain boundaries of an anisotropic crystal known as pivalic acid. These results are compared with very well studied another isotropic material succinonitrile to understand the formation of defects in anisotropic crystals. Preliminary results show that along with anisotropy, orientation has a large influence on the morphology of solid-liquid interface formed after planar interface becomes unstable. The formation of ridges and hence the defects at the interfaces are more favoured in highly anisotropic materials.     

Properties of oriented TTF-TCNQ thin films

Vapour deposited thin films of the organic molecular complex tetrathiafulvaliniumtetracyanoquinodimethane (TTF-TCNQ) are investigated by electrical and electronmicroscopical methods. Morphology studies by means of electron micrographs show, that the thin films up to thicknesses of 300 nm consist of small crystals of a size of 1.2 · 0.2 μm² (deposited on cleaved (100) faces of NaCl) or 15 · 2 μm² (on glass substrate). Dependend on deposition conditions and on material of the substrate thin films are produced with strong or statistic orientation of this crystals. Strong oriented thin films exhibit conductivities up to σ = 65 ω⁻¹ cm⁻¹ and activation energies of W_A = 0.02 eV. The found dependences of the conductivity on electrical field strength. temperature, and size of microcrystals are explained by a linear hopping model.     

Thin chalcogenide films prepared by pulsed laser deposition – new amorphous materials applicable in optoelectronics and chemical sensors

Principles, advantages, applications and drawbacks of pulsed laser deposition (PLD) technique for thin films preparation are reviewed. The PLD method is promising for preparation of thin films of complex composition, including rare-earth and Ag-doped chalcogenide films; all components of the target can be evaporated at once. Low volatility and refractory materials can be also deposited. The deposition in vacuum, inert or reactive atmosphere is possible. Results obtained in a study of chalcogenide films are discussed and the current state-of-the-art is reviewed. The composition and structure of PLD films can be different from thermally evaporated films and new materials or materials with new properties applicable in optics and optoelectronics can be prepared. The method can be used for fabrication of different chalcogenide-based sensors and memory materials of complex composition. Photoinduced changes of structure and properties of PLD films and chalcogenides exposed to intense laser pulses are also discussed. The intense laser pulses can change the properties of the materials prepared and can be used for fabrication of chalcogenide-based waveguides, diffractive elements and high-density optical data storage media.     

Microcrystalline germanium thin films prepared by the reactive RF sputtering method

We focus on thin film microcrystalline germanium (μc-Ge) as narrow gap semiconductor materials for high infrared sensitivity and consider applying it to thermo-photo-voltaic (TPV). The μc-Ge films were prepared on glass substrates by the reactive RF sputtering method with Ar and H₂ gas mixtures. We could successfully produce photosensitive μc-Ge films. Higher crystallinity structures do not always result in better carrier properties. Probably, the amorphous portions between crystalline grains have important roles to suppress the grain boundary defects. We applied the μc-Ge to i-layers of pin structure devices, and observed the photovoltaic effect for the first time.     

高功率直流电弧等离子体喷射法制备的金刚石厚膜中黑色缺陷的研究

借助激光标记的方法,对采用高功率直流电弧等离子体喷射法制备的金刚石膜中的黑色缺陷进行了定点表征.结合使用光学显微镜、激光扫描共焦显微镜、扫描电子显微镜、电子背散射衍射技术等多种表征方法,对同一样品的特定微观标记区域进行了多角度的分析.实验结果表明:金刚石膜内部的黑色缺陷是一种存在于晶界处的孔洞与质量较低的金刚石相的复合体,它的形成应与金刚石膜中某些晶界处的生长环境有关.     

Colour centre studies in MoO3 films

The growth of defects in vacuum-evaporated MoO₃ films has been studied by optical absorption in the present work. The as-grown films were subjected to different kinds of treatment such as thermal annealing, UV and X-ray irradiation, and their optical absorption spectra were recorded between 300 and 1500 nm at room temperature as well as at liquid N₂ temperature The films were found to be amorphous from X-ray and electron-microscopic studies. From these studies it is observed that in addition to point defects, defect aggregates similar to the colloidal centres in silver and alkali halides, are present in these films.     

Nonlinear Optical Properties of Benzylic Amide [2] Catenanes: A Novel Versatile Photonic Material

Abstract

Benzylic amide catenanes are a class of synthetically-accessible interlocked molecular rings which can rotate one through the other depending on the nature of the local environment. The rings contain four phenyl units each and interlocking also affords their packing in novel, highly interacting ways that may lead to unexpected properties thus opening up the possibility of developing new materials. Third harmonic generation in benzylic amide catenane solutions was measured at a wavelength of γ = 1064 nm, with the fundamental and the harmonic wavelengths in the region of transparency of the material. The thoroughly non resonant value of the hyperpolarisability γ(-3ω; ω, ω, ω) was found to be (6.5 ± 0.7) × 10^?35 esu with a negligible imaginary part, in agreement with the value of (6.8 ± 0.9) × 10^?35 esu calculated from a bond-additivity model of hyperpolarisability. The static second order hyperpolarisability predicted by a Molecular Orbital model was about a factor four less than the experimental value. Second hyperpolarizability values of several solvents were also measured at the fundamental wavelength of γ = 1064 nm.     

ZnO薄膜结构缺陷与发光性能研究(一)

在ZnO发光材料中存在的各种结构缺陷是制约ZnO发光性能的一个关键因素。本文总结了ZnO薄膜材料中可能存在的缺陷类型,并就点缺陷的性质及其对发光性能影响的研究现状做了重点评述。对ZnO薄膜发光光谱常见的三个发光带,即紫外、绿光和黄光而言,紫外发光普遍被认为是带-带直接辐射复合发光或激子发光;而对可见光,尤其是绿光的发光机理却有着不同的说法,人们早期认为是铜杂质,近年来普遍认为是氧空位、锌空位等点缺陷所致,确切机理仍有争论。此外,点缺陷作为非辐射中心对ZnO薄膜的发光寿命有一定的影响。     

面向器件应用的PEDOT:PSS薄膜的光电稳定性研究

PEDOT:PSS(聚3, 4-亚乙基二氧噻吩-聚苯乙烯磺酸盐)薄膜因其良好的导电性、透光性、机械柔韧性以及溶液可加工性而被广泛应用。提高PEDOT材料的电导率以及光电稳定性对其器件应用有重要意义。在本文中,首先用旋涂法制备PEDOT:PSS薄膜,然后采用硫酸后处理技术提高其电导率,并将硫酸处理后的薄膜分别放置于空气、氧气、氮气中以及太阳光照下30 d,研究薄膜的光电稳定性及老化机制。实验结果表明:太阳光照是影响薄膜光电性能稳定性的主要因素,而硫酸处理有效地去除了过量的PSS成分,使薄膜的稳定性变好。通过比较老化前后薄膜的光吸收谱和光电子能谱(XPS)发现,在老化过程中薄膜发生了光氧化降解,这是影响薄膜光电稳定性的原因之一。     

FTIR and absorption edge studies on tungsten oxide based precursor materials synthesized by sol-gel technique

The sol-gel technique has been employed for synthesizing three precursor materials for the deposition of tungsten oxide based electrochromic films. The ion-exchange route yields tungstic acid precursor (ITA) which has a strong tendency to polymerize rapidly. Addition of hydrogen peroxide and/or acetic acid suppresses the gelation process and an ethanol soluble precursor material (AIPTA) possessing a low degree of polymerization and high chemical stability is obtained. Another precursor material APTA endowed with similar desirable characteristics is produced from direct reaction between tungsten metal powder and a mixture of hydrogen peroxide and acetic acid. These materials were characterized by FTIR and absorption edge studies and compared in terms of their degree of polymerization and modes of association of various functionalities with the tungsten metal ion.     

Crystallographic defects in epitaxial layers of cadmium sulphide

Thin epitaxial films of CdS deposited in high vacuum on ionic single crystal substrates have been studied by transmission electron microscopy. The (100), (110) and (111) faces of NaCl and the (111) face of BaF₂ were used as substrate surfaces. Both cubic sphalerite and hexagonal wurtzite structure films have been produced. The orientations of the sphalerite structure films were (100) and (110) and were produced on substrate faces having the same two orientations. The wurtzite structure films were in (0001) orientation and grew on (111) oriented substrate faces. For a fixed rate of deposition both the number and type of defects found in the films appear to be dependent upon the growth temperature and the crystal structure. Annealing the films at a high temperature has been tested as a means for reducing their defect content and the effect is very different for the two crystal structures. A reduction in the defect content of the wurtzite structure films is induced but no change in the crystal structure occurs. In contrast to this, the sphalerite structure films undergo a progressive phase transformation to the wurtzite stucture while at the same time losing a high proportion of their defects.