Low-frequency vibrations of bacteriochlorophyll

Frequencies and normal vibrational modes of bacteriochlorophyll are calculated using the semiempirical quantum-mechanical MNDO-PM3 method. To analyze the structure of normal modes, the indices of delocalization of the vibrations and the distribution functions of normal modes over atoms in the molecule are introduced. It is shown that normal vibrational modes of bacteriochlorophyll in the region from 3 to 20 cm^?1 represent “intermolecular” vibrational modes of phytol and tetrapyrrole macrocycle. As the vibrational frequency increases, the normal modes delocalized both on phytol and tetrapyrrole atoms alternate with the modes that are delocalized only on phytol atoms or only on tetrapyrrole atoms. The structural properties of some modes are considered in the aspect of their possible involvement in the formation of absorption spectra of the pigments of reaction centers in photosynthesis and in the formation in them of the coordinate of a primary reaction of the intermolecular electron transfer.     

The influence of the nature of the coordinated metal atom on the photoelectrochemical activity of thin films of tetrapyrrole compounds

The photopotentials and photocurrents of thin films of various metal derivatives of tetrapyrrole compounds (TPCs) were compared to determine the photoelectrochemical activity of organic TPC semiconductors. The high reliability and reproducibility of the results were provided by a small spread of the parameters of the pigmented electrodes studied, a large statistical sampling, and thorough selection of determining measurement conditions. The results obtained for the photoelectrochemical reduction of oxygen show that TPC complexes with transition metals are effective in dark catalysis, because the special structure of their d shells provides strong overlapping with acceptor orbitals and dark electron transfer with a change in the valence of metals. Covalent bonds with ligands and a high electron density on the central atom contribute to this effect. In complexes of constant-valence metals with ionic bonds, acceptor coordination and reduction likely occur on pyrrole rings. The effectiveness of photoreduction increases as the ionization potential of TPCs decreases and electron density on the periphery of molecules grows.     

Jet flow of vapors in an electric arc and its uses in spectral analysis (a survey)

The effect of the migratory motion of atoms on line intensity in dc arc spectra is considered. Increase in the jet character of vapor flow are accompanied by increases in the fraction of atoms entering the excitation zone. Sensitivity of spectral analysis can be increased by providing for jet flow of iodine vapor through the discharge gap. The use of a carrier (Ga₂O₃) also makes it possible to augment the jet character of the flow at lower vapor flow velocities.     

Gas sensing behavior of SnO1.8:Ag films composed of size-selected nanoparticles

Size-selected SnO_1.8:Ag mixed nanoparticle films have been prepared using a gas phase condensation method. Transmission electron microscopy showed that the applied size-selection technique yields well-defined, monodisperse and spherical SnO_1.8 and Ag nanoparticles, both with a fixed diameter of 20 nm. The technique allows an independent variation of the particle size of both materials as well as the concentration of Ag. It allows to assess the influence of these parameters on the gas-sensing properties of the films, here for ethanol vapor in synthetic air. SnO_1.8:Ag nanoparticle films show optimal values of the sensor signal and response time at a Ag nanoparticle concentration of 5%. Due to the fact that the Ag nanoparticles are clearly distinct from the SnO_1.8 nanoparticles in the film, the most probable mechanism leading to improved sensor properties is chemical sensitization via a spill-over effect.     

Microtopography and field emission properties of carbon films grown in a microwave gas discharge plasma

Graphite-like carbon films are grown in an ethanol vapor plasma in a microwave gas discharge. The electrical parameters controlling the microtopography and electronic properties of carbon films are determined. It is shown that electron bombardment affects the fine structure of graphite-like nanocrystallites and their emissive power with characteristics close to those of carbon nanotubes. The emission properties of layered graphite-like films can be improved by metal (cadmium) impurity doping. For nanocrystalline graphite-like films, emission currents with a density of 0.3 A/cm² are induced at an electric field strength of less than 7 V/μ m in the gap. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 2, 2004, pp. 367–371. Original Russian Text Copyright ? 2004 by Suzdal’tsev, Yafarov.     

Non-metal doped TiO2 nanotube arrays for high efficiency photocatalytic decomposition of organic species in water

Titanium dioxide is a well-known photoactive semiconductor with a variety of possible applications. The procedure of pollutant degradation is mainly performed using TiO₂ powder suspension. It can also be exploited an immobilized catalyst on a solid support. Morphology and chemical doping have a great influence on TiO₂ activity under illumination. Here we compare photoactivity of titania nanotube arrays doped with non-metal atoms: nitrogen, iodine and boron applied for photodegradation of organic dye - methylene blue and terephtalic acid. The doped samples act as a much better photocatalyst in the degradation process of methylene blue and lead to the formation of much higher amount of hydroxyl radicals (•OH) than undoped TiO₂ nanotube arrays. The use of a catalyst active under solar light illumination in the form of thin films on a stable substrate can be scaled up for an industrial application.     

Secondary electron emission characteristics of graphene films with copper substrate

For modern and future circular accelerators, especially high-intensity proton synchrotrons or colliders, the electron cloud effect is a key issue. So, in order to reduce the electron cloud effect, exploring very low secondary electron yield (SEY) material or coating used in vacuum tubes becomes necessary. In this article, we studied the SEY characteristics of graphene films with different thicknesses which were deposited on copper substrates using chemical vapor deposition. The SEY tests were done at temperatures of 25℃ and vacuum pressure of (2-6)×10^-9 torr. The properties of the deposited graphene films were investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The SEY curves show that the number of graphene layers has a great effect on the SEY of graphene films. The maximum SEY of graphene films decreases with the increase of the number of layers. The maximum SEY of 6-8 layers of graphene film is 1.25. These results have a great significance for next-generation particle accelerators.     

Surface modification of a polyamide 6 film by He/CF4 plasma using atmospheric pressure plasma jet

Polyamide 6 (PA 6) films are treated with helium(He)/CF₄ plasma at atmospheric pressure. The samples are treated at different treatment times. The surface modification of the PA 6 films is evaluated by water contact angle, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The etching rate is used to study the etching effect of He/CF₄ plasma on the PA 6 films. The T-peel strengths of the control and plasma treated films are measured to show the surface adhesion properties of the films. As the treatment time increases, the etching rate decreases steadily, the contact angle decreases initially and then increases, while the T-peel strength increases first and then decreases. AFM analyses show that the surface roughness increases after the plasma treatment. XPS analyses reveal substantial incorporation of fluorine and/or oxygen atoms to the polymer chains on the film surfaces.     

掺杂金刚石薄膜的缺陷研究

利用多普勒增宽谱和电子顺磁共振研究了掺硼和掺硫金刚石薄膜的缺陷状态.多普勒增宽谱的结果表明，不同杂质元素掺杂的金刚石薄膜，其中使正电子湮没的缺陷种类是相同的；正电子与不同杂质元素硼、硫之间的相互作用不明显；少量硼可使金刚石膜中的空位浓度减少.EPR结果表明，各掺杂样品的顺磁信号主要来自于金刚石的碳悬键. 关键词： 金刚石 掺杂 多普勒增宽谱 电子顺磁共振     

氢的强化刻蚀对金刚石薄膜品质的影响与sp2杂化碳原子的存在形态

用化学气相沉积方法制备了金刚石薄膜.在制备过程中，通过间歇式关闭甲烷气体，强化了氢对sp2杂化碳原子的刻蚀.用拉曼光谱和金相显微镜对薄膜进行了分析表征.结果表明，氢对sp2杂化碳原子的强化刻蚀并未影响金刚石薄膜的品质和微观结构.这一结论说明，在金刚石薄膜中，sp2杂化碳原子主要存在于金刚石晶粒表面和晶界碳原子之间,而不是以石墨或无定形碳颗粒为主要存在方式. 关键词： 化学气相沉积 金刚石薄膜 拉曼光谱 强化刻蚀     

Effect of diluent gas on silicon film deposition from a free jet of monosilane-diluent mixture activated by electron-beam plasma

Thin silicon films were synthesized by the gas-jet electron beam plasma chemical vapor deposition method from monosilane-argon, monosilane-argon-helium, and monosilane-argon-hydrogen mixtures. Addition of argon to the argon-silane mixture increased the deposition rate of silicon films, whereas addition of helium and hydrogen to the same mixture decreased the growth rate. It is shown that the process of silicon film deposition by this method from argon-monosilane mixture is primarily governed by fast secondary electrons, and argon dilution of mixture leads to increasing concentration of fast secondary electrons and increasing deposition rate of silicon films. Dilution of the initial mixture with helium or hydrogen causes a decrease in the deposition rate either due to gas-dynamic behavior of the supersonic jet of the mixture of light and heavy gases, or due to the etching effect of metastable helium atoms or hydrogen atoms on the surface of the growing silicon film.     

Spectral luminescence properties of hydroporphyrazine metallo complexes

We have studied the spectral luminescence properties of a zinc complex of dibenzobarreleno-substituted tetraazaisobacteriochlorin (a synthetic tetrapyrrole pigment which is the structural analog of the biologically important chromophore isobacteriochlorin) and a palladium complex of dibenzobarreleno-substituted tetraazachlorin. We have shown that despite the substantial effect of aza-substitution on the electronic structure and the electronic spectra of the tetrapyrrole molecules, the effect of hydrogenation of adjacent pyrrole rings on the spectral luminescence properties is similar in compounds with nitrogen and carbon bridges. As in the free base case, the fluorescence of the studied zinc complex is strongly quenched at 293 K but flares up at 77 K (temperature and viscosity-dependent quenching). To study the substituted Zn-tetraazaisobacteriochlorin, we determined the position of the 0-0 band of the low-intensity transition S₀ → S₂ and showed that the S₂ → S₁ energy difference increases with bridge aza substitution. For the Pd complex of dibenzobarreleno-substituted tetraazachlorin, we could not detect phosphorescence in the near IR region (to 1150 nm); we detected weak fluorescence. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 700–707, September–October, 2008.     

退火温度对硼掺杂纳米金刚石薄膜微结构和p型导电性能的影响

采用热丝化学气相沉积法制备硼掺杂纳米金刚石 (BDND) 薄膜, 并对薄膜进行真空退火处理, 系统研究退火温度对BDND薄膜微结构和电学性能的影响. Hall效应测试结果表明掺B浓度为5000 ppm (NHB) 的样品的电阻率较掺B浓度为500 ppm (NLB) 的样品的低, 载流子浓度高, Hall迁移率下降. 1000 ℃退火后, NLB和NHB 样品的迁移率分别为53.3和39.3 cm²·V^-1·s^-1, 薄膜的迁移率较未退火样品提高, 电阻率降低. 高分辨透射电镜、紫外和可见光拉曼光谱测试结果表明, NLB样品的金刚石相含量较NHB样品高, 高的硼掺杂浓度使薄膜中的金刚石晶粒产生较大的晶格畸变. 经1000 ℃退火后, NLB和NHB薄膜中纳米金刚石相含量较未退火时增大, 说明薄膜中部分非晶碳转变为金刚石相, 为晶界上B扩散到纳米金刚石晶粒中提供了机会, 使得纳米金刚石晶粒中B浓度提高, 增强纳米金刚石晶粒的导电能力, 提高薄膜电学性能. 1000 ℃退火能够恢复纳米金刚石晶粒的晶格完整性, 减小由掺杂引起的内应力, 从而提高薄膜的电学性能. 可见光Raman光谱测试结果表明, 1000℃退火后, Raman谱图中反式聚乙炔 (TPA) 的1140 cm^-1峰消失, 此时薄膜电学性能较好, 说明TPA减少有利于提高薄膜的电学性能. 退火后金刚石相含量的增大、金刚石晶粒的完整性提高及TPA含量的大量减少有利于提高薄膜的电学性能. 关键词： 硼掺杂纳米金刚石薄膜 退火 微结构 电学性能     

Carrier transport of doped nanocrystalline Si formed by annealing of amorphous Si films at various temperatures

Phosphorus- and boron-doped hydrogenated amorphous silicon thin films were prepared by the plasma-enhanced chemical vapor deposition method. As-deposited samples were thermally annealed at various temperatures to get nanocrystalline Si with sizes around 10 nm. X-ray photoelectron spectroscopy measurements demonstrated the presence of boron and phosphorus in the doped films. It is found that the nanocrystallization occurs at around 600 °C for the B-doped films, while it is around 700-800 °C for the P-doped samples. For the P-doped samples, the dark conductivity decreases at first and then increases with the annealing temperature. While for the B-doped samples, the dark conductivity monotonously increases with increasing annealing temperature. As a result, the carrier transport properties of both P- and B-doped nanocrystalline Si films are dominated by the gradual activation of dopants in the films. The conductivity reaches 22.4 and 193 S cm⁻¹ for P- and B-doped sample after 1000 °C annealing.     

Features of the structure and defect states in hydrogenated polymorphous silicon films

The structural and electronic properties of thin hydrogenated polymorphous silicon films obtained by plasma-enhanced chemical vapor deposition from hydrogen (H₂) and monosilane (SiH₄) gas mixture have been studied by means of transmission electron microscopy, electron paramagnetic resonance (EPR) spectroscopy, and Raman spectroscopy. It has been established that the studied films consist of the amorphous phase containing silicon nanocrystalline inclusions with the average size on the order of 4–5 nm and the volume fraction of 10%. A signal was observed in the hydrogenated polymorphous silicon films during the EPR investigation that is attributed to the electrons trapped in the conduction band tail of microcrystalline silicon. It has been shown that the introduction of a small fraction of nanocrystals into the amorphous silicon films nonadditively changes the electronic properties of the material.     

Optical and physicochemical properties of hydrogenated silicon nitride thin films: Effect of the thermal annealing

The effect of thermal annealing on the optical and physicochemical properties of hydrogenated silicon nitride films was studied. These films were deposited by plasma-enhanced chemical vapor deposition from a mixture of silane, ammonia, and nitrogen. Subsequently, the films were annealed at various temperatures ranging from 400°C to 1000°C. The properties of the films were studied using ellipsometry and Fourier transform infrared spectroscopy. The Maxwell Garnet model considers the silicon nitride material as heterogeneous with three distinct phases: silicon, stoichiometric silicon nitride, and hydrogen. Based on the ellipsometric analysis, the annealing treatment leads to reduce the volume fraction of both hydrogen and silicon. As a result, the stoichiometry parameter significantly increases from 1.24 to 1.32 making it closer to the stoichiometric silicon nitride one. According to the infrared data, a noticeable decrease in the total hydrogen concentration in the films was obtained with respect to the annealing temperature.     

Zn1-xMnxS(001)稀磁半导体薄膜的能量稳定性、磁性和电子结构

通过基于广义梯度近似的总能密度泛函理论研究不同Mn掺杂浓度的ZnS(001)薄膜的电学和磁学特性. 计算单个Mn原子和两个Mn原子处于各种掺杂位置及不同的磁耦合状态时的能量稳定性.计算了单个Mn原子掺杂和两个Mn原子掺杂的ZnS(001)薄膜的态密度. 不同掺杂组态的p-d杂化的程度不同. 不同掺杂组态,Mn原子所处的晶场环境不同,所以不同掺杂组态的Mn的3d分波态密度峰的劈裂有很大的不同. 掺杂两个Mn原子时,得到三种稳定组态的基态都是反铁磁态. 分析了以上三种能量稳定的组态中,两个Mn原子在不同磁耦合状态下的3d态密度图. 当两原子为铁磁耦合时,由于d-d电子相互作用,使反键态的态密度峰明显加宽. 随着Mn掺杂浓度的增加,Mn原子有相互靠近,并围绕S原子形成団簇的趋势. 对于这样的组态,Mn原子之间为反铁磁耦合能量更低.     

非晶态Sm-Fe和Sm-Co薄膜的低温磁性

研究了非晶态Sm-Fe和Sm-Co薄膜在1.5—300K的磁性。发现Sm-Fe薄膜中Fe原子磁矩取向存在分散性,Sm-Co薄膜中Co原子有效磁矩随Sm含量的变化与Nd-Co非晶薄膜很相似。决定了Sm-Fe薄膜具有散铁磁结构,Sm-Co薄膜为共线铁磁性结构。Sm原子磁矩≈0。报道了这两个非晶合金系列的矫顽力H_c与成份和温度的依赖关系。发现Sm-Fe薄膜的H_c较高于Sm-Co的值;前者随Sm含量增加而急剧上升,并随温度升高而陡降;后者的H_c在Sm含量≈43at％有极大值,并以指数形式随温度升高而减小。发现低温范围内磁化强度随温度变化与自旋波激发和Stoner激发都有关系。 关键词：     

Optical permittivity,thermo-optical and electrical properties of nickel oxide nanostructures with heavy cupper doping

In this research, physical properties of nickel oxide nano-structured layers doped with various amount of Cu atoms (20–60 at.%) is studied using spray pyrolysis method on the glass substrate. The FESEM images show formations of nanostructures of about 20–60 nm and the XRD patterns show layers have a polycrystalline cubic structure nature with (111) as the preferred direction that its intensity reduces as the doping density increases. Analyzing transmittance UV. Vis spectra shows the variations of optical band gap of the samples are due to occurrence of doping atoms and quantum confined effects. Optical permittivity of different doped films have been compared using new numerical method and show the prominent effect of doping percent to real and imaginary parts of electrical permittivity. Also Hall effect results shows that Cu atoms substituted by Ni atoms sites play as acceptor atoms in the crystalline lattice. Finally, thermo-optical properties of the films have been studied using Nd–YAG laser illumination.     

氩气退火对氢掺杂AZO薄膜电学性能的影响

采用射频磁控溅射法,在石英玻璃衬底上制备出了性能良好的H掺杂AZO透明导电薄膜,通过XRD、Hall、UV-Vis等测试手段,研究了氩气气氛中退火温度对薄膜电学热稳定性的影响。实验结果显示,随着退火温度的升高,薄膜中载流子的浓度和迁移率下降。分析认为,这与薄膜中氢的逸出密切相关。