聚(ε-己内酯)薄膜结晶形貌及分子取向研究

用匀胶机通过溶液铸膜方法在硅片和铝箔基板上分别制备具有不同厚度的聚(ε-己内酯)(PCL)薄膜. 通过原子力显微镜(AFM)和偏光衰减全反射傅里叶红外光谱(ATR-FTIR)对薄膜中PCL的结晶形貌、 片晶生长方式及分子链取向进行了研究. AFM结果表明, 在200 nm或更厚的薄膜中, PCL主要以侧立(edge-on)片晶的方式生长; 对于厚度小于200 nm的薄膜, PCL片晶更倾向于以平躺(flat-on)的方式生长. 这种片晶生长方式的改变在硅片和铝箔基板上都表现出同样的倾向. 此外, 在15 nm或更薄的薄膜中, PCL结晶由通常的球晶结构变为树枝状晶体. 偏光ATR-FTIR结果表明, 当膜厚小于200 nm时, 薄膜结晶中PCL分子链沿垂直于基板表面方向取向, 并且膜越薄, 取向程度越高, 与AFM的观测结果一致.     

聚3-羟基丁酸酯薄膜结晶的ATR-FTIR研究

使用匀胶机(spincoater),通过溶液铸膜的方法,在铝箔基板上制备出具有不同厚度的聚3羟基丁酸酯(PHB)薄膜.20℃室温条件下,通过衰减全反射傅立叶红外光谱(ATRFTIR)原位观测了不同厚度薄膜的结晶过程,并通过偏光ATRFTIR对薄膜中PHB分子的取向进行了研究.ATRFTIR原位观测结果显示,PHB在薄膜中的结晶速率以及结晶度均随着薄膜厚度的减小而逐渐降低;同时,偏光ATRFTIR测试结果表明,随膜厚减小,薄膜中结晶部分的PHB分子逐渐倾向于沿垂直于基板表面方向取向,膜越薄,倾向越明显.可以认为,PHB分子与基板间的相互作用以及扩散控制结晶导致了上述现象的产生.     

Self-assembly of star ABC triblock copolymer thin films: self-consistent field theory

Microphase separation and morphology of star ABC triblock copolymers confined between two identical parallel walls (symmetric wetting or dewetting) are investigated with self-consistent field theory (SCFT) combined with the "masking" technique to describe the geometric confinement of the films. In particular, we examine the morphology of confined near-symmetric star triblock copolymers under symmetric and asymmetric interactions as a function of the film thickness and the surface field. Under the interplay between the degree of spatial confinement, characterized by the ratio of the film thickness to bulk period, and surface field, the confined star ABC triblock copolymers are found to exhibit a rich phase behavior. In the parameter space we have explored, the thin film morphologies are described by four primary classes including cylinders, perforated lamellae, lamellae, and other complex hybrid structures. Some of them involve novel structures, such as spheres in a continuous matrix and cylinders with alternating helices structure, which are observed to be stable with suitable film thickness and surface field. In particular, complex hybrid network structures in thin films of bulk cylinder-forming star triblock copolymers are found when the natural domain period is not commensurate with the film thickness. Furthermore, a strong surface field is found to be more significant than the spatial confinement on changing the morphology of star triblock copolymers in bulk. These findings provide a guide to designing novel microstructures involving star triblock copolymers via geometric confinement and surface fields.     

PM IRRAS investigation of thin silica films deposited on gold. Part 1. Theory and proof of concept

Polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) was successfully used for the first time to characterize an optically transparent thin oxide film. SiO2 layers of 7 nm thickness were synthesized by plasma enhanced chemical vapor deposition (PECVD) on 200 nm thick gold covered glass slides. Despite the fact that silica is transparent and absorptive to IR radiation when deposited in the form of thin films on a gold surface, it preserves the high metallic reflectivity for the IR light. At grazing angles of incidence of the IR beam, the enhancement of the normal component of the electric field at the interface is comparable to that of Au alone. In addition, the analysis of the structure of a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid monolayer deposited using the Langmuir-Blodgett technique is demonstrated.     

Photooxidation of some metallocenes in a polymer matrix

The changes in the electronic absorption spectra (UV-Vis) of some metallocene-doped poly(methyl methacrylate) (PMMA) thin films containing chloroform molecules as impurities were studied after photoexcitation in the nitrogen atmosphere. Photoexcitations were made by monochromatic radiation (using a Xe-lamp source and a monochromator) at an interval of few nanometers in the spectral range 210-750 nm. The changes in spectra were studied as a function of photoexcitation time (duration), amount of metallocene in the film and the amount of chloroform molecules present in the film. Occurrence of photoinduced charge-transfer between some metallocenes and chloroform molecules confined in the PMMA thin films was observed, which indicated photooxidation of the metallocenes in the polymer matrix. Photoresponse in the case of ferrocene derivatives was observed to decrease with the increase in the value of para- Hammett constant for the substituent attached to the ferrocene unit and also with increasing half-wave potential for the ferrocene derivatives. Photoeffects on the metallocenes having different central metal atom were studied and it was noticed that the photoeffects on the metallocenes with "18 valence electrons", as in ferrocene and ruthenocene, favored the occurrence of photoinduced charge-transfer between the metallocene and chloroform molecules present in a PMMA film. The photooxidation of a metallocene in a PMMA thin film resulted in an enhanced photoconductivity of the polymeric film.     

Optical Spectra of Polygermane/Mesoporous Silica Nanocomposites

Summary: The monitoring of poly(di-n-hexylgermane) (PDHG) optical spectra in a variety of structures ranging from a bulk film to a nanosize polymer confined into a nanopore of SBA-15 was performed using the fluorescence and fluorescence excitation spectra in the temperature range from 5 to 240 K as well as the absorption and FTIR spectra at room temperature. The observed data were compared with those obtained for poly(di-n-hexylsilane). It was shown that PDHG film absorption and fluorescence spectra strongly depend on the polymer thickness and consist of a number of bands which were assigned to centers with different amount of trans- and gauche- conformers of the polymer chains. Conformations of the polymer chains found in a thin film and in a 10 nm pore are similar while differing from the conformations of a thick film. Optical spectra of the confined PDHG are blue-shifted relative to those of a thin film. The PDHG polymer chain conformation becomes disordered with the decrease of the polymer film thickness and the nanopore size from 10 to 6 nm.     

Self-assembly of ABC star triblock copolymer thin films confined with a preferential surface: a self-consistent mean field theory

The microphase separation and morphology of a nearly symmetric A(0.3)B(0.3)C(0.4) star triblock copolymer thin film confined between two parallel, homogeneous hard walls have been investigated by self-consistent mean field theory (SCMFT) with a pseudospectral method. Our simulation experiments reveal that under surface confinement, in addition to the typically parallel, perpendicular, and tilted cylinders, other phases such as lamellae, perforated lamellae, and complex hybrid phases have been found to be stable, which is attributed to block-substrate interactions, especially for those hybrid phases in which A and B blocks disperse as spheres and alternately arrange as cubic CsCl structures, with a network preferred structure of C block. The results show that these hybrid phases are also stable within a broad hybrid region (H region) under a suitable film thickness and a broad field strength of substrates because their free energies are too similar to being distinguished. Phase diagrams have been evaluated by purposefully and systematically varying the film thickness and field strength for three different cases of Flory-Huggins interaction parameters between species in the star polymer. We also compare the phase diagrams for weak and strong preferential substrates, each with a couple of opposite quality, and discuss the influence of confinement, substrate preference, and the nature of the star polymer on the stability of relatively thinner and thick film phases in this work.     

In situ FTIR spectroscopic studies of CO adsorption on electrodes with nanometer-scale thin films of ruthenium in sulfuric acid solutions

A nanometer-scale thin film of ruthenium supported on glassy carbon (nm-Ru/GC) was prepared by electrochemical deposition under cyclic voltammetric conditions. Scanning tunneling microscopy (STM) was used to investigate the structure and to measure the thickness of the thin film. It has been found that the Ru thin film is composed of layered Ru crystallites that appear in a hexagonal form with dimensions of about 250 nm and thickness around 30 nm. In situ FTIR spectroscopic studies demonstrated that such a nanostructured Ru thin film exhibits abnormal infrared effects (AIREs) for CO adsorption (G.Q. Lu et al., Langmuir 16 (2000) 778). In comparison with CO adsorbed on a massive Pt electrode, the IR absorption of CO_ad on nm-Ru/GC was significantly enhanced. Moreover, the direction of CO_ad bands is inverted and the full width at half maximum of CO_ad bands is increased. It has been revealed that the enhancement factor of IR absorption of CO adsorbed on nm-Ru/GC electrodes depends strongly on the thickness of the Ru film. An asymmetrical volcano relationship between the enhancement factor and the thickness of the Ru film has been obtained. The maximum value of the enhancement factor was measured as 25.5 on a nm-Ru/GC electrode of Ru film thickness around 86 nm. The present study has contributed to exploration of the particular properties of nanostructured Ru film material and to the origin of the abnormal infrared effects.     

CdS Thin Films Deposited by CBD Method on Glass

CdS thin films were prepared by chemical-bath-deposited method and the effect of tempera-ture and time on the properties of CdS thin films was studied. Independent of the deposited temperature, the growth was mainly controlled by the ion-by-ion growth mechanism at the beginning of the film deposition, then the cluster-by-cluster mechanism came to be domi-nant. The growth rate increased faster with the increasing of temperature until the thickness reached the limitation, then thickness instead become thinner. The scanning electron micro-scope results revealed that the morphology of the CdS film changed from pinholes to rough,inhomogeneous surface with increasing deposition time and deposition temperature. The X-ray diffraction results showed the film structure was a mixture of two phases: hexagonal and cubic, and it was very important to controll deposition time to the film's crystal phase. All films in depth of approximate 100 nm existed above 65% transmittance, the absorption edge became 〝red-shift〞 with temperature rising. At 60 and 70 oC, with 20 min deposited-time, the energy band gap was more than 2.42 eV and decreased with time, while at 80 and 90 oC, the energy band gap was less than 2.42 eV and increased little when the time changed from 10 min to 15 min at 80 oC.     

Spinodal instability and pattern formation in thin liquid films confined between two plates

The instability, morphology and pattern formation engendered by the van der Waals force in a thin liquid film of thickness h confined between two closely placed solid surfaces (at distance d > h) are investigated based on nonlinear 3D simulations. The initial and the final stages of dewetting and pattern formation are found to be crucially dependent on the volumetric (thickness) ratio of air and liquid and its deviation from the location of the maximum of the spinodal parameter versus volumetric ratio curve. On a low energy surface, relatively thinner films and wider air gaps favor initial dewetting of the lower plate by the formation of holes, whereas thicker films with thinner air gaps initially evolve by the formation of columns/bridges that join the upper plate. In the later stage of evolution, the initial holes in thinner films evolve into columns/drops, while a rapid coalescence of columns in the thicker films eventually causes formation of holes. Thus, a phase inversion, either from liquid-in-air to air-in-liquid dispersion or vice versa, occurs during the final stages of evolution. A thin film confined between two high-energy solid surfaces forms columns (bridges) only when its mean thickness, h0, is greater than a critical thickness (hc) or the air gap is smaller than a critical distance. The patterns can be aligned by using a topographically patterned confining surface. Conditions on pattern periodicity, amplitude, and the volumetric ratio of air and liquid in the gap are explored for the formation of various types of ordered patterns including annular rings of columns, concentric ripples, parallel channels and a rectangular array of complex features. The results are of significance in soft lithographies such as LISA, soft stamping and capillary force lithography.     

Surface enhanced infrared absorption observed with attenuated total reflection (ATR-SEIRA): modeling the optical response

The gain in sensitivity due to Surface Enhanced Infrared Absorption (SEIRA) when analyzing an adsorbate on a metal island film was calculated for the ATR configuration under full consideration of the anisotropy of the film. Modeling the islands as spheroids coated with the dielectric adsorbate leads to such extraordinarily high refractive indices and low absorption indices as experimentally observed and to an enhancement of the absorption bands of the coating. Simulation of the ATR reflectance indicated further enhancement as a result of the optical properties of the island film. The predicted total level of enhancement was about one order of magnitude superior to what commonly is found in experiments. This was attributed to percolation of the metal islands which almost inevitably occurred in practice: the resulting lateral conductivity was found to have a strongly decreasing effect on the enhancement.     

Transport of ions through the oil phase of W(1)/O/W(2) double emulsions

Using a capillary video microscopy technique, the ion transport at liquid-liquid interfaces and through a surfactant-containing emulsion liquid membrane was visually studied by preparing a double emulsion globule within the confined space of a thin-walled, transparent, cylindrical microtube. NaCl and AgNO(3) were selected as the model reactants and were prepared to form a NaCl/AgNO(3) pair across the oil film. By observing and measuring the formed AgCl deposition, it was found that both Cl(-) and Ag(+) could transport through a thick oil film and Ag(+) was transported faster than Cl(-). Interestingly, the ion transport was significantly retarded when the oil film became extremely thin (<1 microm). The results suggested that the transport of ions mainly depends on the "reverse micelle transport" mechanism, in which reverse micelles with entrapped ions and water molecules can be formed in a thick oil film and their construction will get impeded if the oil film becomes extremely thin, leading to different ion transport rates in these two cases. The direction of ion transport depends on the direction of the osmotic pressure gradient across the oil film and the ion transport is independent of the oil film thickness in the investigated thick range. Ions with smaller Pauling radii are more easily entrapped into the formed reverse micelles and therefore will be transported faster through the oil film than bigger ions. Oil-soluble surfactants facilitate ion transport; however, too much surfactant in the oil film will slow down the ion migration. In addition, this study showed no support for the "molecular diffusion" mechanism of ion transport through oils.     

Different surface corrugations occurring during drainage of axisymmetric thin liquid films

This paper deals with the different surface corrugations observable during the thinning of axisymmetric thin and large aqueous films, stabilized by saponin. The films are observed using a thin film balance under a constant driving pressure. This device allows measurement of the thicknesses of the film surface shapes arising all along the drainage, as well as the following-up of their evolution before equilibrium is attained. Depending on the electrolyte (NaCl) concentration, three different sorts of corrugation were originally observed in such suspended thin liquid films. At the lowest NaCl concentrations, corresponding to repulsive potential between film walls, only the hydrodynamic corrugations deformed the film surfaces. Regarding the higher NaCl concentrations, when van der Waals forces become predominant, and following the thickness of the first-established thin film, the experiments disclose either that the thinner films are broken up by spinodal decomposition, or that the thicker ones are broken by nucleation and growth of black film. In addition, an original aspect of these works appears in the fact that these observations of the spontaneous decomposition of suspended thin films are relatively similar to those usually described for dewetting experiments on solid substrates, and are well fitted by the existing theoretical models.     

Interfacial effects on moisture absorption in thin polymer films

Moisture absorption in model photoresist films of poly(4-hydroxystryene) (PHOSt) and poly(tert-butoxycarboxystyrene) (PBOCSt) supported on silicon wafers was measured by X-ray and neutron reflectivity. The overall thickness change in the films upon moisture exposure was found to be dependent upon the initial film thickness. As the film becomes thinner, the swelling is enhanced. The enhanced swelling in the thin films is due to the attractive nature of the hydrophilic substrate, leading to an accumulation of water at the silicon/polymer interface and subsequently a gradient in concentration from the enhancement at the interface to the bulk concentration. As films become thinner, this interfacial excess dominates the swelling response of the film. This accumulation was confirmed experimentally using neutron reflectivity. The water rich layer extends 25 +/- 10 A into the film with a maximum water concentration of approximately 30 vol %. The excess layer was found to be polymer independent despite the order of magnitude difference in the water solubility in the bulk of the film. To test if the source of the thickness dependent behavior was the enhanced swelling at the interface, a simple, zero adjustable parameter model consisting of a fixed water rich layer at the interface and bulk swelling through the remainder of the film was developed and found to reasonably correspond to the measured thickness dependent swelling.     

Influence of local structure on local electric field in Island‐like silver films

The infrared absorption enhancement phenomenon in the normal configuration of vacuum‐evaporated metal films on a transparent substrate is known to depend not only on the metal film morphology but also on the local structures of metal particles. To date, however, few studies have examined the effect of local structure on the phenomenon. Size distributions of islands and gaps, along with the volume fractions of Ag in thin films, were measured using scanning electron microscopy as a function of film thickness. The local structure of Ag nano clusters deposited on silicon substrates was investigated using a total conversion electron yield X‐ray absorption fine structure (XAFS) method at the Ag K‐edge. We observed a correlation between the electromagnetic field intensity at the surface as evaluated by IR measurement and the coordination numbers evaluated by XAFS. We found that the film morphology had a greater effect on resonant and nonresonant contributions than did the local structure of a particle. Copyright © 2006 John Wiley & Sons, Ltd.     

Surface enhanced infrared absorption observed with attenuated total reflection (ATR-SEIRA): modeling the optical response

The gain in sensitivity due to Surface Enhanced Infrared Absorption (SEIRA) when analyzing an adsorbate on a metal island film was calculated for the ATR configuration under full consideration of the anisotropy of the film. Modeling the islands as spheroids coated with the dielectric adsorbate leads to such extraordinarily high refractive indices and low absorption indices as experimentally observed and to an enhancement of the absorption bands of the coating. Simulation of the ATR reflectance indicated further enhancement as a result of the optical properties of the island film. The predicted total level of enhancement was about one order of magnitude superior to what commonly is found in experiments. This was attributed to percolation of the metal islands which almost inevitably occurred in practice: the resulting lateral conductivity was found to have a strongly decreasing effect on the enhancement. Received: 23 December 1997 / Revised: 9 March 1998 / Accepted: 15 March 1998     

Dielectric interlayers for increasing the transparency of metal films for mid-infrared attenuated total reflection spectroscopy

By depositing a continuous, thin metal film on a substrate coated with a mid-infrared (IR) transparent dielectric film that fulfils the role of an index-matching, anti-reflective coating for the metal, the transparency of the metal in the IR wavelength range can be significantly enhanced. This effect is used to yield enhanced absorption in attenuated total internal reflection infrared (ATR-IR) spectroscopy in the presence of continuous thin metal films. The main limitation of the ATR technique when using continuous metal films is the low transparency of metals, especially for infrared light. Computations and experiments show an enhancement in the absorbance of a sample in contact with the metal at certain wavenumbers when the dielectric interlayer is present. The realisation of the setup is the stratified system consisting of zinc selenide-germanium (~1 μm)-gold (40 nm and 20 nm) using the organic solvent acetonitrile as sample. Enhancement is stronger in s- than in p-polarisation. In s-polarisation, enhancement factors of up to 4 have been observed so far in experiments, but calculations show a route to higher enhancements. In addition to the increased absorption, the absorbance spectra show interference fringes which are due to a mismatch in the real part of the refractive index of the sample in contact with the metal film compared to a reference measurement.     

溶液法制备的碳纳米管薄膜的结构分析与场致电子发射机理研究

结合紫外光电子能谱和拉曼光谱对溶液法制备的碳纳米管薄膜的场致电子发射性能进行研究。采用溶液滴涂法制备的碳纳米管薄膜的场致电子发射开启电场约为3.33 MV/m,阈值电场约为5.44 MV/m,以福勒-诺得海姆(Fowler-Nordheim,FN)理论对电子发射进行解释,其发射的增强因子接近103。通过对紫外光电子能谱的分析,发现碳纳米管薄膜的低能量截止端在外加电场作用下逐步降低,表明纳米管薄膜的表面有效势垒在外加电场作用下逐步下降,从而使得碳纳米管薄膜的电子更加容易发射进入真空。结合拉曼光谱和电学特性的研究,发现界面过渡层的接触电阻与碳纳米管薄膜中的非晶碳成分均可以增强场致电子发射。     

SELF ASSEMBLY OF ABC TRIBLOCK COPOLYMER THIN FILMS ON A BRUSH-COATED SUBSTRATE

Self assemblies of ABC triblock copolymer thin films on a densely brush-coated substrate were investigated by using the self-consistent field theory.The middle block B and the coated polymer form one phase and the alternating phase A and phase C occur when the film is very thin either for the neutral or selective hard surface(which is opposite to the brushcoated substrate).The lamellar phase is stable on the hard surface when it is neutral and interestingly,the short block tends to stay on this hard surf...     

Photoinduced charge-transfer between ferrocene derivatives and chloroform molecules confined in poly(methyl methacrylate) thin films

The changes in the electronic absorption spectra (UV-Vis) (after photoexcitations) of poly(methyl methacrylate) (PMMA) thin films doped with a ferrocene derivative and containing chloroform molecules as impurities, have been studied as a function of photoexcitation wavelength (210–750 nm), photoexcitation time (duration), amount of ferrocene derivative in the film and amount of chloroform molecules present in the film. Occurrence of photoinduced charge-transfer between some ferrocene derivatives and chloroform molecules confined in the PMMA thin films has been observed. The effects of the substitution group (attached to the ferrocene unit) on the photoinduced changes are discussed.