Characterization of lysozyme films produced by matrix assisted pulsed laser evaporation (MAPLE)

Thin lysozyme films of thickness up to more than 100 nm have been produced in a dry environment by MAPLE (matrix assisted pulsed laser evaporation) from a water ice matrix. Analysis of the films demonstrates that a significant part of the lysozyme molecules is transferred to the substrate without decomposition and that the protein activity is preserved. The film deposition rate for 1 wt% lysozyme has a maximum at 2 J/cm² of about 1 ng/cm² per laser shot. During the film production the deposition rate is constant without any sign of depletion or accumulation effects in the water ice target or in the growing film. Scanning electron microscopy (SEM) images demonstrate that the silicon substrate is completely covered by lysozyme films thicker than 100 nm. Deposition was also made from a target with pressed (100%) solid lysozyme, but the deposition was difficult to handle and with a much slower rate than that from a water ice matrix.     

Effects of the ZnSe concentration on the structural and optical properties of ZnSe/PVA nanocomposite thin film

This study investigated the effects of ZnSe nanoparticles (NPs) on the structural and (linear and nonlinear) optical properties of polyvinyl alcohol (PVA) thin film. Three samples of ZnSe NP-doped PVA thin films with different concentrations of ZnSe were produced on a glass substrate. The ZnSe NPs were synthesized by pulsed laser ablation of the ZnSe bulk target immersed in distilled water using a 1064 nm wavelength and a high frequency pulsed Nd:YAG laser. The optical bandgap energies of the films were extracted from their UV-Vis-NIR absorption spectra. The corresponding energy bandgaps of the nanocomposite films declined as the ZnSe NPs doping concentration increased. X-ray diffraction analysis was used to characterize the crystalline phases of the ZnSe/PVA nanocomposite films. The concentration-dependent nonlinear optical absorption and nonlinear refraction behaviors of the films after exposure to 532-nm nanosecond laser pulses were investigated using the Z-scan technique. The nonlinear absorption response of the films was positive when measured using an open aperture scheme, which was attributed to the two-photon absorption mechanism. In addition, the nonlinear refraction indices had a negative value and they increased as the concentration of ZnSe NPs in the films increased.     

Effect of Vacuum on the Laser-Induced Damage of Anti-Reflection Coatings

In the comparison of damage modifications, absorption measurement and energy dispersive x-ray analysis, the effect of vacuum on the laser-induced damage of anti-reflection coatings is analyzed. It is found that vacuum decreases the laser-induced damage threshold of the films. The low laser-induced damage threshold in vacuum environments as opposed to air environments is attributed to water absorption and the formation of the O/Si, O/Zr sub-stoichiometry in the course of laser irradiation.     

Surface sensitivity in cluster-ion-induced sputtering

The ion beam-induced removal of thin water ice films condensed onto Ag and bombarded by energetic Au, Au2, Au3, and C60 projectiles is examined both experimentally and with molecular dynamics computer simulations. For water overlayers of thicknesses greater than 10 A, the yields of sputtered Ag+ secondary ions decay exponentially with increasing ice thickness, revealing characteristic decay lengths of 24, 20, 18, and 7.0 A, respectively. It is shown that these values manifest the characteristic depths of projectile energy loss, rather than escape depths of the sputtered Ag atoms through the water ice overlayer. Computer simulations show that the mechanism of ejection involves the sweeping away of overlayer water molecules, allowing for an unimpeded escape of ejected Ag atoms. The relevance of these data with respect to surface sensitivity in secondary ion mass spectrometry is discussed.     

非链式重复频率HF激光器激光介质净化技术

开展了分子筛对非链式电激励重频HF激光器中基态HF分子吸附技术研究,设计了新型的分子筛吸附装置,进行了大量的吸附实验,结果表明: 3A分子筛为有效的吸附剂,实现了HF激光器在50 Hz/20 s条件下运行时平均激光能量下降率小于5%,大大提高了激光能量的稳定性,延长了激光介质的使用寿命。开展了激光器工作于不同频率条件下使用3A型分子筛吸附装置时的激光能量情况研究,并通过实验方法获得了3A型分子筛的再生活化方法。     

稀土夹心双酞菁铥的LB膜及其光谱特性

采用表面压-面积(π～A)等温曲线和紫外-可见吸收光谱研究了稀土夹心双酞菁铥(TmPc2)分子在Langmuir膜及其Langmuir-Blodgett(LB)膜中分子的排列状态和光谱特性。发现TmPc2分子在纯膜中以edge-on方式面对面的排列,在与花生酸(AA)的混合膜中TmPc2分子以face-on方式平躺排列。纯的TmPc2分子在亚相表面可以形成稳定的Langmuir膜,但不易转移到固体基片上,加入花生酸混合后不仅可以在亚相表面形成稳定的Langmuir膜,而且可以较好地转移到固体基片上,制成多层LB膜。TmPc2氯仿溶液和LB膜的紫外-可见吸收光谱具有明显的Soret吸收带和Q吸收带,Soret吸收带有2个吸收峰,分别对应184—187*和178—186的轨道电子跃迁。而Q吸收带有4个吸收峰,分别对应于186—189*,190*和185—187*,188*的轨道电子跃迁。由于分子间的相互作用,TmPc2分子在LB膜中紫外-可见吸收谱的各个吸收峰与氯仿溶液中的吸收峰相比较都发生了红移。层内分子的相互作用比层间分子的相互作用强。     

SiO2 films fabricated by F2 laser-induced chemical deposition using silicone rubber

Silicon dioxide (SiO₂) films were selectively fabricated on a Si substrate at room temperature by illuminating both the silicone rubber target and the substrate with an F₂ laser (157 nm). The laser fluence was much less than the ablation threshold. Absorption due to absorbed water (H₂O) and hydrogen-bonded silanol (SiOH) groups were observed in addition to absorption due to Si-O-Si stretching mode in the Fourier transform infrared spectroscopy (FT-IR) spectra of the films. The illumination with higher laser fluence caused an increase of Si-O-Si/OH peak ratio in the FT-IR spectra, a decrease of etching rate in hydrofluoric acid (HF) solution, and an increase in the refractive index close to the value of a thermal SiO₂ film. These results indicate that the quality of the grown SiO₂ films was improved. The high photon energy of F₂ laser induced photodissociation of main chains and side chains of silicone and oxygen (O₂), and bonds between the ejected gaseous molecules including Si and O(¹D) to form SiO₂ films. PACS 61.80.Ba; 81.15.Fg; 82.50.Hp     

Growth of anthracene thin films by matrix-assisted pulsed-laser evaporation

Thin films of anthracene (C₁₄H₁₀) have been grown by matrix-assisted pulsed-laser evaporation. Frozen solutions of 2 wt% anthracene (solute) in ortho-xylene or in chloroform were used as targets and were irradiated by a frequency-quadrupled Nd:YAG laser (266 nm). The deposited films were studied by the complementary use of infrared absorption and photoluminescence emission. The vibrational bands and fluorescence emission of bulk anthracene were clearly identified in the films. This means that the organic molecules were not modified by photochemical reactions during the laser irradiations, despite the strong absorption of anthracene at 266 nm. Among the growth parameters, the laser fluence was found to be critical in order to avoid the fragmentation of the anthracene molecules. The results show that matrix-assisted pulsed-laser evaporation is suitable for growing thin films of organic materials even if they absorb at the irradiating wavelength. PACS 81.15.Fg; 78.55.Kz; 33.20.Ea; 71.20.Rv     

Surface morphology of thin lysozyme films produced by matrix-assisted pulsed laser evaporation (MAPLE)

Thin films of the protein, lysozyme, have been deposited by the matrix-assisted pulsed laser evaporation (MAPLE) technique. Frozen targets of 0.3-1.0 wt.% lysozyme dissolved in ultrapure water were irradiated by laser light at 355 nm with a fluence of 2 J/cm². The surface quality of the thin lysozyme films of different thickness deposited on 7 mm × 7 mm Si-〈1 0 0〉-wafers was investigated with scanning electron microscopy and atomic force microscopy. Already at comparatively low thickness, ∼20 nm, the substrate is covered by intact lysozyme molecules and fragments. The concentration of lysozyme in the ice matrix apparently does not play any significant role for the morphology of the film. The morphology obtained with MAPLE has been compared with results for direct laser irradiation of a pressed lysozyme sample (i.e. pulsed laser deposition (PLD)).     

Volume absorption laser energy meter for high energy laser by water absorption

Since the energy density of high energy laser can be extremely high and destructive, it is difficult to directly measure the laser energy with custom methods. A volume absorption method directly using water as absorption substance is introduced. In the energy meter, water is pumped into an absorption cavity sealed by a quartz window, and energy increment of water by laser is calculated. The new energy meter has excellent power and energy linearity and is almost not affected by power, energy and flow, its relative deviation to norm middle-power energy meter is 1.9 %, which infers that the new energy meter can measure higher laser energy and maintain higher precision as well.     

Fundamental studies of the cluster ion bombardment of water ice

The fundamental sputtering properties of water ice are of interest for molecular depth profiling of biological samples in their native environment. We report on a method of studying amorphous water ice films of precise thicknesses in which pure water vapor is condensed onto a pre-cooled, silver-coated quartz crystal microbalance (QCM). This scheme allows for the determination of water ice sputter yields for any primary projectile as well as providing a means for studying escape depths of atoms and molecules beneath the deposited water ice layer. Specifically, we find a removal of approximately 2500 water molecule equivalents/20 keV C₆₀⁺ projectile with an underlying silver ion escape depth of 7.0 Å.     

IR spectroscopic study of surface properties of amorphous water ice

The state of the surface of amorphous ice with a specific surface area of about 160 m²/g obtained by the condensation of water vapor at 77 K is studied by IR spectroscopy. As the temperature increases to 130–160 K, absorption bands of surface hydroxyl groups vanish, whereas changes in bands characteristic of hydroxyl groups in the bulk of ice are indicative of a phase transition of ice from amorphous to the polycrystalline structure. The surface sites of amorphous ice are characterized with low-temperature adsorption of carbon monoxide. It is shown that there are two types of CO adsorption sites, free hydroxyl groups and oxygen atoms of surface coordinately unsaturated water molecules. Upon adsorption of nitrogen, methane, and carbon monoxide, in addition to the perturbation of surface OH groups, reversible changes in the spectrum are observed in the region of vibrations of bulk hydroxyls, which indicate that the strength of hydrogen bonds between water molecules in the surface layer of icy particles increases approaching the strength of these bonds in the crystal and that the ice surface becomes less amorphous. These results indicate that the properties of the ice surface layer substantially depend on the presence of adsorbed molecules.     

电场诱导水的太赫兹透射特性研究

许多生物分子自身的转动、振动或分子团的整体振动模式都位于太赫兹波段内,因此可以利用太赫兹光谱技术对生物分子进行检测。同时又由于太赫兹波的光子能量仅为毫电子伏量级,不会对分子的内部结构造成破坏,所以太赫兹时域光谱技术在生物检测方面具有良好的应用前景。众所周知,绝大多数的生物分子只有在液体条件下才能发挥其生物活性,所以研究液体环境下生物分子之间的相互作用就非常必要。然而水分子的转动模式、振动模式以及和氢键有关的能量均处于太赫兹波段,从而对其产生强烈的吸收;另外,水分子为极性分子,而极性分子对太赫兹波有强烈的共振吸收,这就使利用太赫兹技术对生物分子活性进行动态表征产生了困难。因此在研究溶液中的生物分子与太赫兹波的相互作用时,最大限度地减小水分子对太赫兹波的吸收就成为近年来的研究热点。目前,减少水对太赫兹波吸收的主要方法有：在溶液样品中加入抑制氢键缔合的离子来减小水对太赫兹的吸收;通过改变溶液的温度来调节水对太赫兹的吸收;利用微流控芯片技术,通过减小被测样品与太赫兹波的作用距离来减小水对太赫兹波的吸收。另外,激光的激励、电场或磁场的处理,也能改变水对太赫兹波的吸收,将盛有去离子水的微流控芯片放于电场中,研究经电场处理不同时间的去离子水对太赫兹吸收强度的影响。结果发现,太赫兹波的透射强度随着去离子水在电场当中静置时间的增加而增强,当在电场中静置60 min时,太赫兹的频谱强度达到最大,与空气的频谱强度接近。由此可以推断外加电场使水分子的偶极矩发生了变化,从而对整体水分子的振动和转动产生了影响,并且改变了水中的氢键结构,导致了太赫兹透射光谱强度的增强。     

The primary stages of the charge carrier photogeneration in C60 films studied by the 100-fs laser pulse pump-probe method

The primary stages of photoinduced processes are studied in thin C₆₀ films by the femtosecond laser pump-probe method. The films were excited by 100-fs laser pulses with photon energies above (wavelengths 345 and 367 nm) and below (645 nm) the mobility threshold, the fraction of excited molecules being no more than several percent. Upon probing in the spectral range from 400 to 1100 nm, several regions with substantially different decay kinetics were observed in the difference spectrum, which is caused by the simultaneous presence of several relaxing components. The appearance of the 465-and 500-nm bleaching bands in the difference spectrum upon excitation by photons with energies both above and below the mobility threshold, which are typical for electroabsorption spectra, suggests that charge carriers are produced in both these cases. The observed dependence of relaxation on the oxygen amount in the sample volume suggests that during excitation both charged (electrons and holes) and neutral (excited molecules) components are produced. The fraction of charged components is greater upon excitation into the fundamental band. The appearance of the 500-nm absorption band delayed by 10^?13–10^?14 s, the delay being increased in the presence of oxygen, was attributed to the formation of excited anions due to the capture of electrons by C₆₀ molecules. It is concluded that upon excitation of the films by photons with the energy below the mobility threshold, charge carriers are produced due to two-photon absorption rather than due to singlet-singlet annihilation. When the films are excited by photons above the mobility threshold, the primary charge carriers are produced by direct optical excitation.     

在磁场作用下水的特性的变化和它的变化机理

我们研究了在磁场作用下水的光学性质和电学性质等的变化,实验发现它们的这些特性和未受磁场作用的水有重大改变特别是在红外光谱和拉曼光谱中的变化更加明显,这种现象就称为水的磁化。我们从水的中红外光谱得知在3000~3800 cm-1的范围内有奇特的六个峰值存在,从水分子结构和红外光谱的特性出发了解到它们分别代表了自由水分子的OH键的对称与反对称的振动,众多水分子通过氢键连接而成的线性链和环形链的OH键的对称与反对称振动,于是从这个实验我们看到了在这个水中存在有众多水分子结合成的环形氢键链的存在。我们用水分子的极化特性,一阶相变的特性和实验进一步证实了这些环形链的客观存在,根据质子或氢离子在氢键系统中传递理论得知在磁场的罗仑兹力作用下处于水中环形氢键链中质子能够进行传导产生环形电流.这些环形电流象一个分子电流或是个小磁体,它们能彼此相互作用或与外加磁场相互作用,从而改变了水分子的分布和结构状态,导致了水的一些特性的变化,这就是水的磁化的分子机理,我们用这个机理解释了我们从实验中所发现的磁处理过的水的特性如饱和效应和记忆效应等,因此这是非常有趣的实验和现象.     

Effect of laser incident energy on the structural,morphological and optical properties of Cu2ZnSnS4 (CZTS) thin films

The polycrystalline Cu₂ZnSnS₄ (CZTS) thin films have been prepared by pulsed laser deposition (PLD) method at room temperature. The laser incident energy was varied from 1.0 at the interval of 0.5–3.0 J/cm². The effect of laser incident energy on the structural, morphological and optical properties of CZTS thin films was studied by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and optical absorption. The studies reveal that an improvement in the structural, morphological and optical properties of CZTS thin films with increasing laser incident energy up to 2.5 J/cm². However, when the laser incident energy was further increased to 3.0 J/cm², leads to degrade the structural, morphological and optical properties of the CZTS thin films.     

Polymer films filled with organic molecules by CO2 laser evaporation in vacuum

A new p-type of material for organic field-effect transistors (OFETs) is 5,5′-di(9,9′-di-(butyl)-fluorene′)-2,2′-bithiophene (DBFBT). DBFBT films have been prepared by casting, by thermal evaporation in vacuum, and by means of CO₂ laser evaporation. The photon energy from a CO₂ laser is too small to break chemical bonds of the DBFBT molecule, but the heating rate is extremely high. Pressed pellets of powders composed of DBFBT and polychlorotrifluoroethylene (PCTFE) were used as targets for the fabrication of films. These targets were irradiated by a laser beam of 40 W cw-power and 0.5 cm diameter. The deposition rate was 30-50 nm/s. The films have been characterised by optical spectroscopy and by AFM. The structure of DBFBT films produced by casting from solution and thermal deposition is composed of elongated crystals, while the laser deposited layers show cluster structure. By FTIR the films show the absorption band of pure DBFBT, with intensity proportional to the DBFBT concentration in the PCTFE matrix. The absorption bands for a pure DBFBT film, for a film with 22 vol.% and with 34 vol.% of DBFBT in the PCTFE matrix are situated at 274, 298 and 402 nm, where the latter is the most intense one. No significant difference in the band positions of all samples has been found. We concluded that no interaction between chromophore and matrix occurs. The DBFBT molecules in the PCTFE matrix did not oxidize during storage under ambient condition over a period of a year.     

Matrix assisted growth of nanoparticles and nanoporous films

Since the inception of matrix assisted pulsed laser evaporation (MAPLE), a large body of research has focused on the structure and property preservation of soft materials. Departing from this precedent, a variation of MAPLE to grow complex inorganic nanoparticles and nanoporous thin films from acetate precursors is presented. While some aspects of MAPLE are retained, a weakly absorbing matrix solvent is used to promote absorption by the precursors, leading to photothermal decomposition. The diffusion of ions within the laser interaction volume results in the formation of nanoparticles, which are then ejected by subsequent pulses. The acetate precursors were processed into colloidal suspensions in deionized water and frozen to form solid targets, followed by irradiation with a pulsed excimer laser at fluences ranging from 0.25 to 0.75 J/cm². Nanoparticles and nanoporous films of unary, binary, and ternary metallic and oxide systems were deposited at room temperature onto substrates of Si and electron-transparent grids. Size distributions varied between different material systems with negligible pressure and energy effects, with distribution extrema ranging from 2 to 100 nm in diameter. Characterization of the nanoparticles was performed by high resolution scanning and transmission electron microscopy, and energy dispersive x-ray spectroscopy.     

激光驱动飞片过程中激光烧蚀深度的计算

利用激光体烧蚀模型,数值模拟了激光驱动飞片的加速过程,包括激光的吸收和飞片的速度历史等。在光强为GW/cm2量级的激光作用下,激光烧蚀产生的等离子体的流体力学运动可用改编的1维La-grange流体力学计算程序SSS来描述。通过计算得到不同激光能量下的飞片密度剖面,由此给出金属薄膜的烧蚀深度与实验测量值进行比对,二者符合得较好。     

Reactive ion scattering from ice in a molecular dynamics perspective

This is a study into the scattering dynamics of the alkaline ions Cs⁺, K⁺, Na⁺, and Li⁺ from an ice surface, and the process of abstracting water molecules by the scattered ions to form ion–water clusters as a result of the ion–dipole attraction. In a classical molecular dynamics computer simulation a semi-empirical ion–water interaction potential and a modified version of the TIP3P ice model are employed.The thickness of the ice structure at the surface greatly affects the abstraction efficiency. From a thin ice overlayer all alkaline ions exhibit similar scattering probabilities, but Cs⁺ abstracts water molecules most efficiently; its lower speed facilitates a mechanism where the Cs⁺ in its outgoing trajectory pulls water molecules out of the ice structure. From a thick ice structure the scattering probabilities decrease dramatically due to an effective energy transfer to the ice structure. A more grazing angle of incidence reduces the energy transfer and enhances the scattering probabilities for the lighter alkaline ions. The deprived formation of ion–water clusters in the simulations confirms that from thick ice the cluster formation probability is reduced by at least three orders of magnitude.