Sol-gel silica thin films with copper selenide

The silica sol-gel films with copper selenide produced by the selenization of metallic copper nanoparticles were fabricated. The composition of the films was studied with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and optical absorption spectroscopy. Several copper selenide phases were detected with XRD and contribute into the complicated behavior of core levels (Cu2p, Se3d, and Si2p) and Auger levels (Cu) in the XPS analysis. The optical absorption features of the films in the visible and near-infra red range are presented. The consistent interpretation of experimental data is proposed based on assumption of copper multivalence in the system “particles-silica matrix”.     

Structural aspects of Langmuir-Blodgett and cast films of zinc phthalocyanine and zinc hexadecafluorophthalocyanine

The processing of macrocyclic phthalocyanines (Pc) in the form of thin, nanostructured films has been usually carried out via evaporation techniques, owing to the low solubility exhibited by these compounds. The fabrication of Pc ultrathin films via the Langmuir-Blodgett technique may be advantageous from a technological point of view, since parameters such as film architecture and organization can be achieved without post-thermal treatments. In this study, a parent zinc phthalocyanine (ZnPc) and its fluorinated derivative (F₁₆ZnPc) were synthesized and manipulated in the form of LB films. The morphological and structural features of ZnPc and F₁₆ZnPc Langmuir-Blodgett films containing up to 31 layers were investigated using Fourier transform infrared spectroscopy (FTIR), micro-Raman spectroscopy and X-ray diffraction analyses and were compared to ZnPc and F₁₆ZnPc cast films. The interplanar distance obtained by X-ray specular reflection decreases from 12.64 Å for ZnPc to 12.16 Å for F₁₆ZnPc. FTIR spectra indicated absence of order in the LB films from ZnPc and F₁₆ZnPc, at least in the direction perpendicular to the substrate surface. Therefore, the order observed in the X-ray diffractograms means that the molecules might be organized in crystallites that are randomly oriented in the film.     

Stability of dimethyldioctadecylammonium bromide Langmuir-Blodgett films on mica in aqueous salt solutions—implications for surface force measurements

Langmuir-Blodgett (LB) monolayer films of dimethyldioctadecylammonium bromide (DDOA) on muscovite mica have been studied using Wilhelmy plate type wetting measurements, surface force measurements, atomic force microscopy (AFM), and Brewster angle microscopy (BAM) on insoluble monolayers of DDOA before deposition. In particular, the effect of exposure to aqueous KBr salt solutions was investigated. BAM shows a heterogeneous monolayer with small condensed domains of dendritic shape under conditions normally used for deposition. A stick-jump behaviour of the meniscus is seen during deposition, leading to a large-scale heterogeneity measurable in wetting studies. These also show breakdown and hydrophilization of the LB film at the three-phase contact line (meniscus) and when exposed to salt solutions of approximately 10⁻² M concentration. The advancing contact angle against water is approximately 105°. Surface force measurements show long-range attraction in water, but also a surface charge which depends on salt concentration, and breakdown when surfaces are brought into contact in high salt concentrations. AFM images of untreated films show small holes, and breakdown when exposed to salt solution, especially at the three-phase line. The LB film is judged to be less suitable as a model hydrophobic surface owing to its heterogeneity and instability in salt solution.     

Ferroelectricity of ultrathin ferroelectric Langmuir-Blodgett polymer films on conductive LaNiO3 electrodes

LaNiO₃ (LNO) films with a surface roughness rms of 0.384 nm and a sheet resistance of about 200 Ω were prepared on SrTiO₃ and Si/SiO₂ substrates respectively by rf magnetron sputtering technique. The surface of LNO on Si/SiO₂ substrate is smoother than that on SrTiO₃ substrate. A nominal 2-monolayer (ML) poly(vinylidenefluoride-trifluoroethylene) film with a thickness of about 3 nm was deposited on LNO coated Si/SiO₂ substrate by Langmuir-Blodgett (LB) technology. Piezoresponse force microscopy (PFM) measurements show that the LB films demonstrate an obvious feature of polarization switching and good voltage durability. The results suggest that the ultrathin polymer films may be utilized to explore ferroelectric tunnel junctions.     

Effect of subphase divalent ions on optical second harmonic properties of hemicyanine Langmuir-Blodgett films interleaved with compatible spacer

The surface pressure-area (π-A) isotherms of 1.10-bistearyl-4.6.13.15-tetraene-8-nitrogen-crown-6 (NC) monolayers at the air-water interface, the UV-visible absorption spectra and optical nonlinear properties of Y-type hemicyanine/NC interleaving Langmuir-Blodgett (LB) multilayers containing divalent ions in the subphase (such as Cd²⁺, Ba²⁺ and Co²⁺) were investigated in the paper. It was found that the π-A isotherms of the NC monolayer, the peak position of absorption spectra and the optical second harmonic intensity in the alternating LB multilayers strongly depend on the divalent ions in the subphase. The 2ω resonance effect of molecular hyperpolarizability β was responsible for the change of the observed second order polarizability χ⁽²⁾ of LB multilayers.     

LB薄膜技术在尖端材料制备中的应用

LB(Langmuir-Blodgett)薄膜技术可以在分子水平上进行材料设计,是实现分子工程的重要手段.LB膜可以方便地沉积纳米级的功能微粒和薄膜,也是制备梯度功能材料的方法之一.简要综述了LB薄膜技术在功能晶体、纳米半导体及铁电体等尖端材料制备中的应用,并展望了其相关应用研究的重要前景.     

Spectroscopic properties of mixed Langmuir-Blodgett films of rhodamine dyes and poly(N,N-diallyl-N-octadecylamine-alt-maleic acid)

Langmuir-Blodgett (LB) films of poly(N,N-diallyl-N-octadecylamine-alt-maleic acid) as well as mixed films consisting of polyampholyte and two amphiphilic fluorophores - alkyl substituted rhodamine dyes - were prepared and investigated. The π-A isotherm of the polyampholyte at air-water interface is typical for monolayer in the liquid state. Mixed monolayers of polyampholyte and rhodamine amphiphiles show improved packing of the hydrophobic chains. Absorption and fluorescence spectroscopic studies of the mixed LB films reveal the aggregation of dyes in the densely packed multilayer films.     

Amplitude-dependent internal friction in copper thin films on silicon substrates

Internal friction in copper thin films 0.2–1.5 μm thick on silicon substrates has been measured between 180 and 340 K as a function of strain amplitude. Analysis of the amplitude-dependent internal friction in the copper films shows the relation between the plastic strain of the order of 10⁻⁹ and the effective stress on dislocation motion. The stress–strain curves thus obtained for the copper films tend to shift to a higher stress with decreasing film thickness and also with decreasing temperature, both indicating a suppression of microplastic flow. It is concluded that the microflow stress at a constant level of the plastic strain varies inversely with the film thickness at all temperatures examined. The film thickness effect in the microplastic range can be explained on the basis of a dislocation-bowing model.     

Characterization of copper phthalocyanine Langmuir-Blodgett films

Asymetrically substituted copper phthalocyanine (as-CuPc) Langmuir-Blodgett (LB) films are prepared on metal-coated quartz substrates and the electronic behaviour of sandwich structures of metal/CuPc LB film/metal are studied under normal laboratory ambients. The results show that CuPc films are very stable and reproducible. D.c. measurements produce ohmicI(V) characteristics while the a.c. conductance shows a power-law dependence on the frequency.     

Semifluorinated TTF derivatives in Langmuir-Blodgett films

New semifluorinated tetrathiafulvalene (TTF) derivatives were prepared and used in Langmuir and Langmuir-Blodgett (LB) films. Transfer onto a solid substrate of such pure monolayers can be easily achieved leading to organized LB films in which the fluorinated chains are tilted with respect to the normal of the substrate as demonstrated by infrared and X-ray experiments. Doping of such films by iodine does not induce change in the layer spacing on the contrary to already published studies concerning alkyl derivatives of TTF. Such structural stability and values of the layer thickness suggest some interdigitation between TTF groups within the LB film. Depending on the exact chemical structure of the TTF moiety, the iodination is stabilized or not. When the doped film is stabilized in a mixed valency state, conductivity of approx. 10⁻² S cm⁻¹ was measured at room temperature.     

Photopatterning of heterostructured polymer Langmuir-Blodgett films

Heterostructured polymer Langmuir-Blodgett (LB) film prepared by using poly(N-dodecylacrylamide-co-t-butyl 4-vinylphenyl carbonate) (p(DDA-tBVPC53)) and poly(N-neopentyl methacrylamide-co-9-anthrylmethyl methacrylate) (p(nPMA-AMMA10)) polymer LB films which can act as photogenerator layers were investigated. Patterns with a resolution of 0.75 μm were obtained on heterostructured polymer LB films composed of 4 layers of p(nPMA-AMMA10) LB film (top layers) and 40 layers of p(DDA-tBVPC53) LB film (under layers) on a silicon wafer by deep UV irradiation followed by development with 1% tetramethylammonium hydroxide aqueous solution. The sensitivity of the heterostructured polymer LB films was improved without loss of the resolution compared with p(DDA-tBVPC53) LB film. The etch resistance of the heterostructured polymer LB films was sufficiently good to allow patterning of a copper film suitable for photomask fabrication.     

Structural,optical and electrical properties of chemically deposited copper selenide films

Stoichiometric and nonstoichiometric thin films of copper selenide have been prepared by chemical bath deposition technique at temperature below 60°C on glass substrate. The effect of nonstoichiometry on the optical, electrical and structural properties of the film was studied. The bandgap energy was observed to increase with the increase in at % of copper in composition. The grain size was also observed to increase with the decrease of at % of copper in composition. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), absorption spectroscopy, and AFM. The results are discussed and interpreted.     

Ultrathin polymer Langmuir-Blodgett films for microlithography

We describe photolithographic properties of poly(N-dodecylmethacrylamide-co-t-butyl 4-vinylphenyl carbonate) [p(DDMA-tBVPC)], which has a structure being subject to main chain scission and deprotection of t-butoxycarbonyloxy group by deep UV irradiation. Positive-tone patterns of the p(DDMA-tBVPC) Langmuir-Blodgett (LB) film with 60 layers were obtained by deep UV light irradiation followed by development with alkaline aqueous solution. The resolution of the pattern was 0.75 μm, which is the resolution limit of the photomask employed. The etching resistance of p(DDMA-tBVPC) LB film deposited for the pattern of the gold film is also investigated.     

Control of oxidation state of copper in flame deposited films

The deposition of thin copper based films onto carbon steel surface is described, using premixed flames with different oxygen/methane ratios doped with aqueous copper nitrate as precursor. We investigated the chemical properties of the copper as a function of oxygen/methane ratio. Using fuel rich flames (equivalence ratio 0.665), the deposited copper film was entirely metallic. When the equivalence ratio was increased to 0.850 or greater the copper film contained predominantly Cu^2 +. Furthermore, the flame can be used for post deposition modification, as demonstrated by reduction of Cu^2 + containing films to Cu metal. All the films were characterised by X-ray diffraction, Raman and scanning electron microscopy (SEM). A rotating sample holder was employed to avoid over heating of the sample and the critical variables such as sample height in the flame and deposition time were optimised. Deposition for 20 min, which translated to a total residence time in the flame of approx. 76 s, produces metallic copper films of thickness 169 ± 18 nm as determined by anodic stripping and SEM. The microstructure of the metallic films was clearly composed of fused copper spheres of 100-150 nm, which are probably formed in the flame and subsequently deposited on the surface with good adhesion.     

Influence of the glycosylphosphatidylinositol anchor in the morphology and roughness of Langmuir-Blodgett films of phospholipids containing alkaline phosphatases

The morphology of phospholipid Langmuir-Blodgett films containing a glycosylphosphatidylinositol-anchored rat osseous plate alkaline phosphatase was studied by atomic force microscopy. Two forms of the enzyme were used in this study: an anchor-containing detergent-solubilized form, and a phospholipase-solubilized form, without the hydrophobic moiety. Direct measurements of catalytic activity in enzyme/phospholipid mixed films, and nanogravimetric estimations by quartz crystal microbalance confirmed the adsorption of both forms of alkaline phosphatase. Atomic force microscopy analysis showed that both enzyme forms originated aggregates when adsorbed on phospholipid Langmuir-Blodgett films. However, the phospholipase-solubilized form showed a higher roughness when compared to the detergent solubilized alkaline phosphatase. A model suggesting different alignments of the major axis of the ellipsoid polypeptide moiety relative to the film surface is proposed. This model, supported by surface density and catalytic activity data, might explain the difference of roughness observed for films containing each enzyme form adsorbed onto a phospholipid-modified solid support.     

Experimental studies on substituted copper phthalocyanine Langmuir-Blodgett films

Using the Langmuir-Blodgett (LB) technique, novel copper bis(3-hydroxypropyloxy-hexaisopentyloxy)phthalocyanine molecules were deposited on quartz substrates. It is argued on the basis of pressure-area isotherms that films are deposited as monolayers. Optical absorption spectroscopy suggests that the deposited films were uniform. A.c. measurements were performed on LB films in a planar configuration at different temperatures. The power-law dependence of the conductivity on frequency is explained in terms of electronic conduction through hopping over a coulombic barrier 0.66 eV high. The Debye relaxation time is estimated to be of the order 811 µs at room temperature.     

LB膜技术及其用于膜分离过程的研究

介绍了ＬＢ（Ｌａｎｇｍｕｉｒ－Ｂｌｏｇｄｇｅｔｔ）膜的材料，制备技术及物注表征，并对ＬＢ膜在膜分离中应用及存在问题作评述。     

Molecular order in Langmuir-Blodgett assembled films of an azobenzene amphiphile

Alternating multilayers of amphiphile, 4-{4-[Methyl-(4-octadecylcarbamoyl-butyl)-amino]-phenylazo}-benzenesulfonic acid (S-azo-C₁₈), and stearic acid were deposited on hydrophobized silica surfaces using the Langmuir-Blodgett technique. Ellipsometry, UV-visible spectroscopy, and second harmonic generation were used to characterize the films, demonstrating reproducible deposition and suggesting a well ordered film structure. Despite the appearance of order at the macroscopic level, neutron and X-ray scattering results unequivocally show that there is considerable disorder, with significant interpenetration between the stearic acid and S-azo-C₁₈ layers. These results suggest that molecular disorder in Langmuir-Blodgett deposited multilayer films may often go unrecognized mainly because the macroscopic probes based on these optical measurements are not adequate for determining the molecular level structural order.     

Structural, optical and electrical properties of chemically deposited nonstoichiometric copper indium diselenide films

Thin films of copper indium diselenide (CIS) were prepared by chemical bath deposition technique onto glass substrate at temperature, 60°C. The studies on composition, morphology, optical absorption, electrical conductivity and structure of the films were carried out and discussed. Characterization included X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray analysis (EDAX) and absorption spectroscopy. The results are discussed and interpreted.     

On the correlation between morphology and electronic properties of copper phthalocyanine (CuPc) thin films

The morphology of vacuum deposited copper phthalocyanine (CuPc) thin films surface deposited on Si(111) have been studied using the contact mode Atomic Force Microscope (AFM). The influence of substrate temperature during deposition and of the post-deposition UHV annealing on surface roughness as well as on the average and maximum grain height was determined. The observed changes of surface morphology were in a good correlation with the shift of surface Fermi level position in the band gap after O₂ exposure determined in our recent photoemission studies.