Some aspects of AFM nanomechanical probing of surface polymer films

We analyzed how the approach developed for the microindentation of non-uniform elastic solids can be adapted to analyze the atomic force microscopy (AFM) probing of ultrathin (1-100 nm thick) polymer films on a solid substrate, as well as polymer films with a multilayered structure. We suggested that recent Johnson's modification of the contact mechanics model that included a viscoelastic contribution could also be utilized to analyze rate-dependent loading data for polymer surfaces. The graded model proposed for microindentation experiments was modified allowing to account not only for variable elastic moduli within different layers but also for the gradient of properties between layers within a transition zone. Two examples of a recent application of this model for molecularly thick hyperbranched polymer monolayers (<3 nm thick) and tri-layered polymer films (20-40 nm thick) tethered to a solid substrate were presented and discussed. In both cases, complex shapes of both loading curves and elastic modulus depth profiles obtained from experimental AFM data were successfully fitted by the graded model with realistic structural parameters.     

Direct imaging of nanoscale acidic clusters in a polymer electrolyte membrane

One of the factors hindering the development of technologies that rely on the use of proton-conducting polyelectrolyte membranes is the lack of control over the membrane morphology on the nanoscale. Of particular importance is the rearrangement and clustering of acidic groups, which may seriously degrade the electrical properties. Although electron microscopy is capable of imaging the morphology of the clusters, images of unmodified membranes with sufficient quality to discriminate between different proposed cluster morphology models have not been presented. Here we show the first determination of the cluster size distribution in a model polymer electrolyte membrane from electron micrographs of individual acidic clusters. Imaging of the sulfur-rich clusters by dark-field microscopy was facilitated by the spontaneous formation of thin, cluster-containing layers on the top and bottom surfaces of free-standing films with a thickness of ~35 nm.     

Electron Backscattering from Real and In-Situ Treated Surfaces

 Significant differences in backscattered electron (BSE) yields exist between the surfaces cleaned by methods used in electron microscopy and spectroscopy. These differences have been observed for Au, Cu and Al specimens, and are interpreted on the basis of simulated BSE yields. Composition and thickness of the surface contamination layers, responsible for the differences, are estimated. The results (7 nm of carbon on Au or 3 nm of oxide on Al) remain within expectation and indicate that the BSE yield measurements and BSE images should be interpreted cautiously. Peculiar results are obtained for Cu, perhaps due to a different cleaning procedure. A new concept of an information depth for the BSE signal is introduced as a depth within which the total BSE yield can be modelled as composed of the yields of layers proportional to their thickness weighted by the escape depths. This concept proved satisfactory for thin surface layers and brought the information depth values 2 to 4 times smaller than first estimated, i.e. half the penetration depth.     

Investigation of ion-bombarded conducting polymer films by scanning electrochemical microscopy (SECM)

Scanning electrochemical microscopy (SECM) was used to investigate the effect of ion bombardment on thin films of the conducting polymers poly[3-ethoxy-thiophene] (PEOT) and poly[ethylenedioxy-thiophene] (PEDT). Bombardment with Ar+-ions converts the topmost 30 nm thick layer to an essentially insulating material. SECM approach curves as well as two dimensional scans prove the existence of regions of different conductivity within the irradiated regions that did not show a significant dependence on ion dosage. PEDT layers patterned by ion bombardment through microscopic masks are investigated as prototypes of miniaturized printed circuit boards that can be formed by galvanic copper deposition onto conducting PEDT. Defects in conducting polymer patterns were analyzed by SECM imaging before any deposition of copper. Appropriate representations of SECM images for the evaluation of this technologically important question are discussed.     

Investigation of ion-bombarded conducting polymer films by scanning electrochemical microscopy (SECM)

Scanning electrochemical microscopy (SECM) was used to investigate the effect of ion bombardment on thin films of the conducting polymers poly[3-ethoxy-thiophene] (PEOT) and poly[ethylenedioxy-thiophene] (PEDT). Bombardment with Ar⁺-ions converts the topmost 30 nm thick layer to an essentially insulating material. SECM approach curves as well as two dimensional scans prove the existence of regions of different conductivity within the irradiated regions that did not show a significant dependence on ion dosage. PEDT layers patterned by ion bombardment through microscopic masks are investigated as prototypes of miniaturized printed circuit boards that can be formed by galvanic copper deposition onto conducting PEDT. Defects in conducting polymer patterns were analyzed by SECM imaging before any deposition of copper. Appropriate representations of SECM images for the evaluation of this technologically important question are discussed.     

Quantitative comparison of ATR-IR spectra of LB and bulk layers of 22-tricosenic acid on inorganic supports

The availability of ATR devices equipped with a diamond internal reflection element makes it possible to obtain IR absorption spectra of organic substances deposited on inorganic substrates, for example, metals, glass or quartz. The quantitative comparison of these spectra performing mass calibration by Langmuir-Blodgett (LB) layers are reported. The measurements were made in the common configuration with the specimen placed between the internal reflection element and the non-transparent support and in a second configuration with a thin transparent substrate (silicon) placed between the specimen and the internal reflection element. The band areas of the CH₂ bands near 2900 cm^–1 measured for the two ATR configurations were compared with those obtained from transmission measurements. The results can be partially interpreted by the equation for the effective thickness of thin layers on internal reflection elements. The relative absorbances of several bands of the TSE spectra obtained under different measuring conditions were also investigated.     

Surface Engineering of Poly(DL‐lactic acid) by Entrapment of Biomacromolecules

Alginate, chitosan and gelatin were deposited on the surface of PDL‐LA films via an entrapment method. ATR‐FT‐IR, XPS and contact‐angle analyses revealed the formation of stable thin biomacromolecule layers on the PDL‐LA film, thus enhancing the hydrophilicity of the films. Confocal laser scanning microscopy showed the existence of entrapment areas of approximately 10–20 μm in depth. This simple surface‐treatment method may have the potential for many biomedical applications.     

Adsorption of phenylphosphonic acid on GaAs (100) surfaces

The adsorption of phenylphosphonic acid (PPA) on GaAs (100) surfaces from solutions in acetonitrile/water mixtures was studied using Fourier transform infrared spectroscopy in attenuated total reflection in multiple internal reflections (ATR/MIR), X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS), and atomic force microscopy (AFM). ATR/MIR in situ showed that the accumulation of PPA molecules near the GaAs surface increased with the water concentration in the solution. For water contents lower than 4%, ATR/MIR and XPS results are consistent with the formation of a low-density monolayer. A mechanism is proposed for H2O percentages lower than 4% involving the creation of interfacial bonds through a Br?nsted acid-base reaction, which involves the surface hydroxyl groups most probably bound to Ga. It was found that the morphology of the final layer depended strongly on the water concentration in the adsorbing solution. For water concentrations equal to or higher than 5%, the amount of adsorbed molecules drastically increased and was accompanied by modifications in the infrared spectral region corresponding to P-O and P=O. This sudden change indicates a deprotonation of the acid. XPS studies revealed the presence of extra oxygen atoms as well as gallium species in the layer, leading to the conclusion that phosphonate and hydrogenophosphonate ions are present in the PPA layer intercalated with H3O+ and Ga3+ ions. This mechanism enables the formation of layers approximately 10 times thicker than those obtained with lower H2O percentages. HREELS indicated that the surface is composed of regions covered by PPA layers and uncovered regions, but the uncovered regions disappeared for water contents equal to or higher than 5%. XPS results are interpreted using a model consisting of a monolayer partially covering the surface and a thick layer. This model is consistent with AFM images revealing roughness on the order of 7 nm for the thick layer and 0.2-0.5 nm for the thin layer. Sonication proves to be an effective method for reducing layer thickness.     

ESR imaging and FTIR study of thermally treated poly(acrylonitrile-butadiene-styrene) (ABS) containing a hindered amine stabilizer: Effect of polymer morphology, and butadiene and stabilizer content

Electron spin resonance imaging (ESRI) was applied to the study of thermal degradation at 393 K of poly(acrylonitrile-butadiene-styrene) (ABS) prepared by emulsion polymerization and containing 25% wt butadiene (ABS-25B). The polymer was doped with 1 or 2% wt Tinuvin 770 as the hindered amine stabilizer (HAS). The spatial distribution of the HAS-derived nitroxide radicals, obtained by 1D ESRI, was initially homogeneous, but became heterogeneous through sample depth with increasing treatment time, t. The spatial variation of ESR line shaping with sample depth was visualized by 2D spectral-spatial ESRI. ESR spectra along the sample depth, obtained by nondestructive (“virtual”) slicing of the 2D images, were used to deduce the relative intensity of nitroxide radicals present in two dynamically distinct sites; the sites were assigned to butadiene-rich (fast component) and SAN-rich domains (slow component), respectively. 1D and 2D ESRI allowed the determination of the extent of degradation within morphologically-distinct domains as a function of sample depth and treatment time. The results from the ESRI experiments were substantiated by attenuated total reflectance (ATR)-FTIR spectroscopy of the outer layer (500 μm thick) of the polymer. Both techniques indicated faster degradation of polymer samples that contained the higher HAS content, 2% wt. Comparison with the results obtained for a parallel study of ABS prepared by mass polymerization and containing 10% wt butadiene (ABS-10B) indicated clearly that the rate of degradation of the polymer prepared by emulsion polymerization (ABS-25B) is significantly reduced. This result can be explained by the formation of cross-linked “composite” networks during emulsion polymerization, which leads to greater thermal stability.     

Preparation of nanocrystalline titania films with different porosity by water-based chemical solution deposition

This study describes the synthesis of nanocrystalline titania layers on silicon and glass substrates by chemical solution deposition, using a water-based citratoperoxo-Ti(IV) precursor solution. The same aqueous solution–gel precursor is used for deposition of, both, thin dense layers by spin-coating and thicker porous layers by tape-casting. In the latter, the precursor solution is modified by the addition of polyvinyl alcohol (PVA), which acts as a thickener and pore-forming agent. Phase composition, film morphology, and the hydrophilic character of the films are studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–VIS transmission measurements, variable angle spectroscopic ellipsometry (VASE), and by contact angle measurements. The thin 180 nm titania film, deposited from the unmodified precursor solution, shows a density of about 96%. Upon ultraviolet illumination, it acquires a highly hydrophilic surface. One hour of illumination is sufficient to obtain a water contact angle of almost 0°. Furthermore, the hydrophilisation process shows to be reversible. Tape-casting and thermal treatment of the modified precursor solution gives rise to the formation of a 500 nm thick, porous, pure anatase film. The nanocrystalline thick film is composed of 20–40 nm particles, and contains clearly defined pores of 20 nm, homogeneously distributed along the surface.     

SURFACE MOLECULAR STRUCTURE DETERMINATION OF LITHIUM SALT OF 10,12-NONACOSADIYNOIC ACID MONOMER AND POLYMER LANGMUIR-BLODGETT FILMS BY SCANNING FORCE MICROSCOPY COMPARED TO ELECTRON DIFFRACTION RESULTS

Langmuir-Blodgett films of lithium salts of 10,12-nonacosadiynoic acid monomer (Li/16-8 DA) and polymer (Li/16-8 PDA) were characterized by scanning force microscopy (SFM or AFM) to study their surface molecular structure. Based on analysis of these images, a two-dimensional oblique unit mesh is assigned for Li/16-8 DA monomer LB film with unit mesh parameter c = 0.549 ± 0.040 nm and b = 0.541 ± 0.060 nm with an angle of 113°. A hexagonal unit mesh is assigned for Li/16-8 PDA with unit mesh parameter c = 0.497 ± 0.052 nm and b = 0.497 ± 0.060 nm. We then report the comparison of two-dimensional, fast Fourier transform (FFT) of SFM images to the electron diffraction images. From the viewpoint of a three-dimensional structure projected onto a plane, centered rectangular nets can be assigned for both Li/16-8 DA and Li/16-8 PDA. The monomer unit cell parameters are c = 0.460 ± 0.040 nm and b = 1.020 ± 0.060 nm. The polymer cell parameters are c = 0.485 ± 0.080 nm and b = 0.820 ± 0.010 nm. The correlation between the two very different methods of surface structure determination is excellent. However, care must be taken in assigning the unit net (two-dimensional representation) and the projected unit cell (three-dimensional) vectors.     

Surface plasmon near-field imaging of very thin microstructured polymer layers

We report on the near-field imaging of microstructured polymer layers deposited on an homogeneous metal thin film on which a surface plasmon mode is excited. The microstructures in the polymer layers are designed by electron beam lithography, and the near-field imaging is performed with a photon scanning tunneling microscope (PSTM). We show that, despite their very small height, the microstructures can be conveniently imaged with a PSTM thanks to the field enhancement at the surface of the metal thin film supporting the surface plasmon. The influence of the illumination conditions on the contrast of the PSTM images is discussed. In particular, we show that both the field enhancement and the near-field intensity distribution around the microstructures depend dramatically upon the illumination conditions, leading to the conclusion that the PSTM is well suited for spatially resolved near-field surface plasmon sensing purposes.     

Modeling of glancing incidence X-ray for depth profiling of thin layers

In this work, we present a method to obtain quantitative information about the thickness of thin, polycrystalline layers. This non-destructive method is based on Glancing-Incidence X-ray Diffraction (GIXRD) experiments at different incidence angles. At different incidence angles, information about phases lying at different depths is obtained. The diffracted X-ray intensities' dependence on the glancing angle was analyzed and compared with simulations performed by means of a simple optico-geometrical model taking into account the Fresnel coefficients, X-ray absorption, and the effective scattered volume. The depth profile of polycrystalline Au layers was evaluated to test the procedure. The results of the GIXRD and the simulations are in very good agreement with the thickness obtained by means of X-ray reflectivity (XRR) technique.     

Combined Fourier-transform infrared imaging and desorption electrospray-ionization linear ion-trap mass spectrometry for analysis of counterfeit antimalarial tablets

This paper reports use of a combination of Fourier-transform infrared (FTIR) spectroscopic imaging and desorption electrospray ionization linear ion-trap mass spectrometry (DESI MS) for characterization of counterfeit pharmaceutical tablets. The counterfeit artesunate antimalarial tablets were analyzed by both techniques. The results obtained revealed the ability of FTIR imaging in non-destructive micro-attenuated total reflection (ATR) mode to detect the distribution of all components in the tablet, the identities of which were confirmed by DESI MS. Chemical images of the tablets were obtained with high spatial resolution. The FTIR spectroscopic imaging method affords inherent chemical specificity with rapid acquisition of data. DESI MS enables high-sensitivity detection of trace organic compounds. Combination of these two orthogonal surface-characterization methods has great potential for detection and analysis of counterfeit tablets in the open air and without sample preparation.     

Growth process and molecular packing of a self-assembled lipid nanotube: phase-contrast transmission electron microscopy and XRD analyses

Phase-contrast transmission electron microscopy (PC-TEM) and quick freezing method have been combined to study the initial growing process of a self-assembled lipid nanotube in water. The PC-TEM enabled us to detect thin lamellar edge structure and the very fast growth of the newborn edge to a thin tube with high contrast. The thin tube acts as a core structure for further growth into thick complete lipid nanotube. The initially formed nanotube structure is denoted as a "core tube". The core tube has uniform wall structure that consists of five lamellar layers and the inner and outer diameters of the core tube are 130 and 180 nm, respectively. The evaluated lamellar spacing of 4.6 nm is well compatible with that measured by X-ray diffraction. We also discussed the molecular packing of the nanotube from the pitch angle determined by the PC-TEM images, X-ray diffraction pattern in wide-angle region, and IR spectroscopy. The subcell structure of the nanotube is assigned to an orthorhombic type. The twisting angle between the neighboring lipid molecules is determined as ca. 0.26 degrees for the first time; it is a crucial parameter for the formation of a lipid nanotube in chiral packing but has not been elucidated before.     

Ultrathin films of variable polarity and crystallinity obtained from 1,2-polybutadiene nanoparticle dispersions

Characterization of ultrathin films of different polymer nanoparticles obtained at room temperature via spin-coating of aqueous dispersions and their morphology are described. Very small nanoparticles of semicrystalline 1,2-polybutadiene (PB), noncrystalline poly(1-butene) (PH), and poly(1-butenal) (PHF) were prepared via catalytic emulsion polymerization and subsequent hydrogenation or hydroformylation. The prefabricated nanoparticles were used as building blocks. The thin films obtained are continuous and transparent (n=1.5; κ=0). The properties of these films, formed from different constituents, are analyzed. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) images show that the PB-films are very smooth (rms roughness=10 nm) and polycrystalline. Recrystallization of these PB films reveals that edge-on lamellae are the constituent units. Films with very low roughness values (rms roughness <2 nm) are obtained with PH nanoparticles, due to the soft character of the nanoparticles. The AFM profile of the PHF films reveals that the surface remains structured after drying due to the high degree of the internal cross-linking that occurs in the nanoparticles. Quantification of the films' polarity (I(3)/I(1)=0.89, 1.3, and 2.1 for PHF, PB, and PH, respectively) agrees well with the previous values obtained for the polymer dispersions. Surfactant molecules are desorbed during the film formation; however, these aggregates can be removed by rinsing with water with no undesirable effects observed on the films.     

聚酯低聚物和聚乙二醇醚对蒙脱土的插层与剥离作用

高分子基 /层状硅酸盐钠米复合材料的制备得益于自然界存在的一类层状硅酸盐 .它具有阳离子可交换性和在一些介质中的可膨润性 .在层状硅酸盐中蒙脱土是使用较普遍的一种 .它的晶胞系由两层Ｓｉ—Ｏ四面体中间夹一层Ａｌ—Ｏ(ＯＨ)八面体组成 .晶胞呈平行迭置 .层内有剩余电子而使其带负电荷 ,它与层间的自由阳离子Ｎａ+、Ｋ+、Ｃａ2 +、Ｍｇ2 +等达到电荷平衡 ,保持其整体的电中性 .利用蒙脱土的阳离子可交换特性 ,将有机离子插层剂或反应单体插入ＭＭＴ层间 ,使其层间距撑大 ,并增加其在反应体系中的膨润性 ,使ＭＭＴ在反应体系中剥离 ,…     

Performance evaluation of mapping and linear imaging FTIR microspectroscopy for the characterisation of paint cross sections

Different Fourier transform infrared microspectroscopic techniques, using attenuated total reflection (ATR) mode and single-element mercury–cadmium–telluride (MCT) detector (mapping) or multielement MCT detector (raster scanning), are compared with each other for the characterisation of inorganic compounds and organic substances in paint cross sections. All measurements have been performed on paint cross sections embedded in potassium bromide, a transparent salt in the mid-infrared region, in order to better identify the organic materials without the interference of the usual embedding resin. The limitations and advantages of the different techniques are presented in terms of spatial resolution, data quality and chemical information achieved. For all techniques, the chemical information obtained is found to be nearly identical. However, ATR mapping performed with a recently developed instrumentation shows the best results in terms of spectral quality and spatial resolution. In fact, thin organic layers (∼10 μm) have been not only identified but also accurately located. This paper also highlights the recent introduction of multielement detectors, which may represent a good compromise between mapping and imaging systems.     

具有双螺旋链的新型二维无机-有机骨架晶体材料Ni(PDC)(H2O)2的合成与结构

本文报道由H2PDC合成的新型维层状无机-有机骨架晶体Ni(PDC)(H2O)2(H2PDC=吡啶-2,5-二羧酸), 该化合物的一层是由右手螺旋Ni—O—C链与左手螺旋Ni-pdc链组成, 而邻近的一层则是由左手螺旋Ni—O—C链与右手螺旋Ni-pdc链组成, 层与层之间通过氢键作用形成了三维超分子结构. 用ICP、TG、IR和X射线单晶衍射分析等手段对其结构进行表征.     

Structure of polypropylene crystallized in confined nanolayers

Films with a thousand alternating layers of isotactic polypropylene (PP) and polystyrene (PS) were prepared by layer‐multiplying coextrusion. The crystal structure of extremely thin PP layers confined between PS layers was studied by optical light microscopy (OM), atomic force microscopy (AFM), differential scanning calorimetry (DSC), small‐angle X‐ray scattering (SAXS), and wide‐angle X‐ray scattering (WAXS). Changes in structure were observed as the PP layer thickness decreased to the nanoscale. The thin PP discoids were largely composed of edge‐on lamellae with (040) planes lying flat on the interface. In layers 65 and 10‐nm thick, compressed d‐spacings in the directions perpendicular to the chains and loss of registry along the chain axis were suggestive of smectic packing of conformationally distorted chains. Even so, crystalline lamellae were distinguishable in the AFM images. In addition to the crystal population with (040) planes parallel to the interface, the WAXS from layers 65‐nm thick revealed another crystal fraction with (110) planes parallel to the interface and (040) planes perpendicular to the interface. This fraction was more evident in layers 10‐nm thick, where it accounted for approximately 10–20% of the crystallinity. Decreasing layer thickness resulted in a change of the crystal growth plane from the usual (110) to the more rare (010). The new crystal structure possibly served to fill‐in the radial structure of the dendritic discoids when a limitation to the thickness of the layer left only a little space for secondary nucleation of the crosshatched lamella. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3380–3396, 2004