A comparative study between inductively and capacitively coupled plasma deposited polystyrene films: chemical and morphological characterizations

Thin polystyrene films were deposited on stainless steel substrates by capacitively and inductively coupled radio frequency glow discharge plasma, in order to compare their chemical and morphological properties. The films were characterized by Fourier‐transform infrared spectroscopy (FTIR), X‐Ray photoelectron spectroscopy (XPS), time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS), atomic force microscopy (AFM) and scanning electron microscope (SEM). Wettability properties were also determined by contact angle measurements. Ageing effect was studied by analysing films aged for 15 min and for 1 week. Results from both capacitively and inductively plasma polymerized polystyrene (pPS) films aged for 15 min showed that the chemical structure of the bulk, chemical composition of the surface (depth < 10 nm) and wettability properties were rather similar. Only their microstructures were very different: the pPS_capa film's microstructure showed homogeneous distribution of spherical particles of about 100 nm in diameter but the pPS_ind film's microstructure seemed to be mainly influenced by the surface of the metallic substrate: orientated ‘lamellae‐like layers’ of polymers were observed on each metallic grain. Ageing for 1 week in ambient air induced low oxygen uptake in the surface of both pPS films. The pPS_ind topmost surface (depth < 3 nm) was more oxidized than that of pPS_capa but no modification of the chemical structure of the bulk or of the morphology was noticed after ageing. Copyright © 2006 John Wiley & Sons, Ltd.     

Closing the Nanographene Gap: Surface‐Assisted Synthesis of Peripentacene from 6,6′‐Bipentacene Precursors

The thermally induced cyclodehydrogenation reaction of 6,6′‐bipentacene precursors on Au(111) yields peripentacene stabilized by surface interactions with the underlying metallic substrate. STM and atomic‐resolution non‐contact AFM imaging reveal rectangular flakes of nanographene featuring parallel pairs of zig‐zag and armchair edges resulting from the lateral fusion of two pentacene subunits. The synthesis of a novel molecular precursor 6,6′‐bipentacene, itself a synthetic target of interest for optical and electronic applications, is also reported. The scalable synthetic strategy promises to afford access to a structurally diverse class of extended periacenes and related polycyclic aromatic hydrocarbons as advanced materials for electronic, spintronic, optical, and magnetic devices.     

Microscopic study of ultra-thin gold layers on polyethyleneterephthalate

Continuous and discontinuous gold layers sputtered on polyethyleneterephthalate (PET) were characterized using atomic force microscopy (AFM), scanning electron microscopy (SEM) and by reflection of microwave radiation. The changes in the surface morphology of the continuous and discontinuous gold layers as a function of the sputtering time were clearly observed by AFM technique. SEM imaging of very thin gold layers was adversely affected by specimen charging. For medium sputtering times, when a continuous gold coverage is already formed, the SEM technique still show the presence of regions with very thin gold coverage which gradually disappear at longer sputtering times. Both, the AFM and SEM techniques confirmed that in the course of the gold deposition the initially small gold clusters grow and finally associate in a continuous layer. It was shown that the sub-microne metallic structures could be modeled by artificial, significantly larger structures prepared on PET by lithographic etching.     

Effect of atmospheric-pressure plasma on adhesion characteristics of polyimide film

In this work, the effect of atmospheric-pressure plasma treatments on surface properties of polyimide film are investigated in terms of X-ray photoelectron spectroscopy (XPS), contact angles, and atomic force microscopy (AFM). The adhesion characteristics of the film are also studied in the peel strengths of polyimide/copper film. As experimental results, the polyimide surfaces treated by plasma lead to an increase of oxygen-containing functional groups or the polar component of the surface free energy, resulting in improving the adhesion characteristics of the polyimide/copper foil. Also, the roughness of the film surfaces, confirmed by AFM observation, is largely increased. These results can be explained by the fact that the atmospheric-pressure plasma treatment of polyimide surface yields several oxygen complexes in hydrophobic surfaces, which can play an important role in increasing the surface polarity, wettability, and the adhesion characteristics of the polyimide/copper system.     

Surface characteristic of poly(p‐phenylene terephthalamide) fibers with oxygen plasma treatment

Oxygen plasma is widely employed for modification of polymer surfaces. Plasma treatment process is a convenient procedure that is also environmentally friendly. This study reports the effects of oxygen plasma treatment on the surface properties of poly(p‐phenylene terephthalamide) (PPTA) fibers. The surface characteristics before and after oxygen plasma treatment were analyzed by XPS, atomic force microscopy (AFM) and dynamic contact angle analysis (DCAA). It was found that oxygen plasma treatment introduced some new polar groups (O? C?O) on the fiber surface, increased the fiber surface roughness and changed the surface morphologies obviously by plasma etching and oxidative reactions. It is also shown that the fiber surface wettability was improved significantly by oxygen plasma treatment. Copyright © 2008 John Wiley & Sons, Ltd.     

Surface modification of polypropylene under argon and oxygen-RF-plasma conditions

Polypropylene fabrics samples were surface functionalized under Ar and O₂ RF plasma conditions. Survey and high resolution photoelectron spectroscopy and attenuated total reflectance FTIR comparative evaluation of virgin and plasma treated substrat surfaces, and their pentafluorophenyl hydrazine-derivatized correspondents, indicate that both Ar and O₂-discharge treated PP surfaces undergo intense oxidation. C=O, O−C=O, and C−O linkages were identified on both inert and reactive gas plasma exposed surfaces. It was found that the relative surface atomic concentrations and the relative ratios of newly created functionalities are controlled by the external plasma parameters (RF power and treatment time). The oxidation of Ar-plasma treated surfaces has been related toex situ post plasma mechanisms. Dynamic contact angle measurements from unmodified and plasma exposed substrates demonstrated the presence of increased surface polarity, and its dependence on plasma parameters. AFM evaluations of plasma treated samples indicate the presence of rough surface morphologies. Paper based on the results presented during the workshop of the Engineering Research Center for Plasma-Aided Manufacturing held in Madison, Wisconsin, in Spring 1996.     

Excellent anti‐bacterial activity and surface properties of polyamide‐6 films modified with argon‐plasma and methyl diallyl ammonium salt‐graft

In this study, the effect of argon‐plasma treatment on the grafting of methyl diallyl ammonium salt (MDAA) onto polyamide‐6 film and the anti‐bacterial and surface properties of the plasma‐ and graft‐treated film were investigated. The grafting amounts of MDAA caused by argon‐plasma treatment increased with the increase in the plasma exposure time and plasma power. The analyses of Fourier transform infrared (FT‐IR) spectroscopy and electron spectroscopy for chemical analysis (ESCA) spectra revealed that the epoxy and vinyl groups of MDAA could be grafted on the argon‐plasma treated polyamide‐6 film. The survey spectra of ESCA, the patterns of atomic force microscopy (AFM), and the spectra from scanning electron microscopy (SEM) were employed to certify the surface modification of argon‐plasma treated and the argon‐plasma treated/MDAA grafted polyamide‐6 films. Argon‐plasma treatment could generate the functional group and increase the roughness on the surface of polyamide‐6 film. This phenomenon could enhance the grafting effect of MDAA. The anti‐bacterial property of argon‐plasma treated/MDAA grafted polyamide‐6 film was excellent. This argon‐plasma treated/MDAA grafted polyamide‐6 film was expected to be applied on the field of packing. Copyright © 2008 John Wiley & Sons, Ltd.     

Elaboration of nano-structured grafted polymeric surface

The surface grafting of multi-polymeric materials can be achieved by grafting as components such as polymers poly(N-isopropylacrylamide) and/or surfactant molecules (hexatrimethylammonium bromide, polyoxyethylene sorbitan monolaurate). The chosen grafting techniques, i.e. plasma activation followed by coating, allow a large spectrum of functional groups that can be inserted on the surface controlling the surface properties like adhesion, wettability and biocompatibility. The grafted polypropylene surfaces were characterized by contact angle analyses, XPS and AFM analyses. The influence of He plasma activation, of the coating parameters such as concentrations of the various reactive agents are discussed in terms of hydrophilic character, chemical composition and morphologic surface heterogeneity. The plasma pre-activation was shown inevitable for a permanent polymeric grafting. PNIPAM was grafted alone or with a mixture of the surfactant molecules. Depending on the individual proportion of each component, the grafted surfaces are shown homogeneous or composed of small domains of one component leading to a nano-structuration of the grafted surface.     

Atomic force microscopy investigation of cold‐plasma‐treated poly(ethyleneterephthalate) textiles

Atomic force microscopy (AFM) has been applied to investigate the morphological and topographical surface modifications induced by radiofrequency cold plasma processing of poly(ethyleneterephthalate) textiles. Surface effects are analysed in low‐pressure air plasma for different plasma exposure times. The results show a progressive degradation of the surface with increasing roughness. The analysis suggests that modification of the surface during textile treatment may be ascribed to a plasma‐induced physical process. Copyright © 2003 John Wiley & Sons, Ltd.     

Plasma pretreatment of polycarbonate substrates for indium zinc oxide film deposition

The influence of plasma treatment of polycarbonate (PC) substrates on the morphological, electrical, and adhesion properties of deposited amorphous transparent indium zinc oxide (IZO) by direct current magnetron sputtering was investigated by analyzing atomic force microscopy, contact angles, Hall, and nano‐scratch measurements. The surfaces of PC substrates were performed by plasma treatment at various processing times in Ar/O₂ mix atmosphere. The atomic force microscopy images indicated that the microstructure of the substrates considerably influenced the surface morphology of deposited IZO films, and the least surface roughness of IZO was obtained after 5‐s plasma treatment. The IZO film deposited on PC with 5‐s plasma treatment presented an improved electrical conductivity and thermal stability after annealing at 120 °C in air, whereas the significant decrease in carrier concentration and increase in resistivity with extending plasma treatment time were observed, which was attributed to the elevated oxygen adsorption during annealing for a loosely packed structure. Moreover, the adhesion properties of IZO films with PC substrates decreased after 30‐s plasma treatment because of the significant difference on the surface polarity between the PC and thin films and the increased roughness caused by plasma etching. Copyright © 2016 John Wiley & Sons, Ltd.     

A study of atmospheric-pressure CHF3/Ar plasma treatment on dielectric characteristics of polyimide films

In this work, the influence of atmospheric-pressure CHF(3)/Ar plasma treatment on surface dielectric properties of polyimide films was investigated using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and contact angle measurements. The dielectric characteristics of the films were studied using a dielectric spectrometer. From the results, it was found that the plasma treatment introduced fluorine functional groups onto the polyimide surfaces. F 1s/C 1s ratios of the polyimides were enhanced with the increase of plasma treatment time. Consequently, the fluorine groups led to a decrease of the surface free energy and dielectric constant of the polyimide films, which can largely be attributed to the decrease of the deformation polarizability or London dispersive component of surface free energy of the solid surface studied.     

Functional lipid microstructures immobilized on a gold electrode for voltammetric biosensing of cholera toxin

Redox functionalized microstructures of diacetylene lipids containing cell surface ligand GM1 have been prepared for the construction of an electrochemical biosensor for cholera toxin from Vibrio cholerae. Incorporation of lipid molecules with disulfide functionality into the microstructures allows for firm attachment of the microstructures on a gold surface to form a sensing interface. The observed morphology of the microstructures is platelet, with size around 240 nm as determined by dynamic light scattering and transmission electron microscopy. The electrochemical response stems from electron transfer between the electrode and the redox sites on the microstructures, and the Faradaic current is influenced by the binding events of protein toxins to the ligands displayed on the crystalline surface. Electrochemical characterization indicates that electron transfer of surface ferrocene on the gold electrode is facile. Differential pulse voltammetry was used to measure the current magnitude as a function of toxin concentration, and a working range expanding from 1.0 x 10(-8) to 5.0 x 10(-7) M was obtained. Bovine serum albumin (BSA) was used as a control agent with which no interference to Faradaic response was found in the same concentration range. Atomic force microscopy (AFM) was used to characterize the morphology and distribution of microstructures on the gold surface. The effectiveness of the design for bypassing surface fouling of proteins in electrochemical detection has been demonstrated, and a binding regulated electron hopping mechanism for the observed electrochemical behavior has been proposed.     

Chemical force titrations of amine- and sulfonic acid-modified poly(dimethylsiloxane)

Chemical force titrations-measurements of the adhesive interaction between a pair of suitably chemically modified atomic force microscopy (AFM) tip and sample surfaces as a function of pH-have been carried out for various combinations of silanol, amine, carboxylic acid, and sulfonic acid functional groups on both tip and sample. The primary surface material studied was poly(dimethylsiloxane) (PDMS). Surface modification was carried out using a plasma oxidation process to form silanol sites; further modification with amine or sulfonic acid sites was carried out by reaction of the silanol sites with the appropriate trialkoxysilane derivative. AFM tips were also modified using trialkoxysilane compounds. In the cases of tip/sample combinations with the same functional group on each, surface pK(1/2) values could be determined. In several "mixed" tip/sample combinations, a peak appeared in the titration curve midway between the surface pK(1/2) values of the tip and sample, consistent with an ionic H-bonding model for the interactions. The amine/sulfonic acid pair showed more complex behavior; the amine-terminated tip/sulfonic acid-terminated PDMS surface force titration curve consisted of two peaks centered at pH 4 and pH 8. Reversing the tip/sample pair resulted in the peak positions being shifted upward by 1.0 pH unit. The peak appearing at lower pH is assigned to electrostatic interactions between the two oppositely charged surfaces, whereas the higher pH peak is believed to arise due to ionic H-bonding interactions. AFM images show the effects on surface patterning of amine- and sulfonic acid-modified PDMS surfaces that have undergone two different oxidation methods (air plasma oxidation and Tesla coil oxidation). The surface morphologies of freshly prepared and 24 h aged air plasma oxidized PDMS are also discussed in this study.     

The Origin of the “Snap‐In” in the Force Curve between AFM Probe and the Water/Gas Interface of Nanobubbles

The long‐range attractive force or “snap‐in” is an important phenomenon usually occurring when a solid particle interacts with a water/gas interface. By using PeakForce quantitative nanomechanics the origin of snap‐in in the force curve between the atomic force microscopy (AFM) probe and the water/gas interface of nanobubbles has been investigated. The snap‐in frequently happened when the probe was preserved for a certain time or after being used for imaging solid surfaces under atmospheric conditions. In contrast, imaging in liquids rarely induced a snap‐in. After a series of control experiments, it was found that the snap‐in can be attributed to hydrophobic interactions between the water/gas interface and the AFM probe, which was either modified or contaminated with hydrophobic material. The hydrophobic contamination could be efficiently removed by a conventional plasma‐cleaning treatment, which prevents the occurring of the snap‐in. In addition, the adsorption of sodium dodecyl sulfate onto the nanobubble surface changed the water/gas interface into hydrophilic, which also eliminated the snap‐in phenomenon.     

Surface Energy and Wettability of Plasma-treated Polyacrylonitrile Fibers

Polyacrylonitrile fibers were treated with a nitrogen glow-discharge plasma. The surfaces of untreated and treated fibers were examined with contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Surface energy calculations of the fibers were carried out from contact angle measurements using the relationships developed by Fowkes. It is found that plasma treatment causes a reduction in water contact angle on the fiber surfaces. The dispersion component of surface energy changes slightly, while the polar component is increased significantly from 14.6 mN/m to 58.7 mN/m and the total surface energy increase is 139%. The increase of surface energy is mainly caused by the introduction of hydrophilic groups on the fiber surfaces after plasma treatment.     

铝合金表面原位自组装超疏水膜层的制备及耐蚀性能

采用阳极氧化法在铝合金表面原位构造粗糙结构, 经表面自组装硅氧烷后得到超疏水自清洁表面, 与水滴的接触角最大可达157.5°±2.0°, 接触角滞后小于3°. 通过傅立叶变换红外(FT-IR)光谱分析仪、场发射扫描电子显微镜(FE-SEM)、能谱仪(EDS)、原子力显微镜(AFM)和接触角测试对阳极氧化电流密度、硅氧烷溶液中水的含量和自组装时间等参数进行了分析, 并得到制备超疏水自清洁表面的最优工艺参数. FE-SEM及AFM的测试结果表明, 由自组装硅氧烷膜层的无序性形成的纳米结构和阳极氧化构造的微米级粗糙结构与硅氧烷膜层的低表面能的协同作用构成了稳定的超疏水表面. 电化学测试(动电位极化)的结果表明, 原位自组装超疏水膜层极大地提高了铝合金的耐蚀性.     

Narrow‐band UVB‐induced Externalization of Selected Nuclear Antigens in Keratinocytes: Implications for Lupus Erythematosus Pathogenesis†

The aim of this study was to analyze whether sera obtained from patients with lupus erythematosus (LE) react with membrane structures found on keratinocytes irradiated with narrow‐band ultraviolet B (NB‐UVB). We applied atomic force microscopy (AFM) to visualize cell surface structures expressing nuclear antigens upon apoptosis following NB‐UVB irradiation. Immortalized human keratinocytes (HaCaT) were cultured under standard conditions, irradiated with 800 mJ cm^?2 NB‐UVB light and imaged by AFM mounted on an inverted optical microscope. It was observed that NB‐UVB irradiation provoked significant alterations of the keratinocyte morphology and led to the membrane expression of antigens recognized by anti‐La and anti‐Ro 60 kDa sera but not by antidouble‐strand DNA sera. The presence of La and Ro 60 kDa antigens on keratinocyte surfaces after NB‐UVB irradiation was limited mainly to the small bleb‐like protrusions found on the keratinocytes by AFM. A closer investigation by AFM also revealed that some structures positively stained with anti‐Ro 60 kDa serum were also located submembranously. We hypothesize that the externalization of some nuclear antigens because of NB‐UVB exposure might be responsible for exacerbation of skin symptoms in patients suffering from LE.     

Stability of polycarbonate and polystyrene surfaces after hydrophilization with high intensity oxygen RF plasma

A general drawback observed with plasma treatment is the limited stability of the hydrophilic-treated surfaces toward washing, storage, or heating. It has recently been found that oxygen, air, or argon radiofrequency plasmas with higher intensities than normally used can give hydrophilic surfaces having good wash stability. High intensity oxygen plasma treatment of polystyrene and polycarbonate surfaces was therefore carried out using two different capacitively coupled RF reactors with internal shelf electrodes. The obtained surface characteristics and stability were evaluated using contact angle measurements, XPS, AFM, and nanoindentation. For both materials, low water contact angles were found to correlate with high surface oxygen content. Only the surfaces exposed to relatively intense treatments, with self-bias voltages above 140 V (polystyrene) or 240 V (polycarbonate), could withstand washing in ethanol and remain highly hydrophilic. Substantial amounts of nonsoluble material were observed on the plastic substrates after treatment. Furthermore, for polycarbonate Young's modulus of the surface was found to increase with increasing intensity of the plasma. These observations were taken as an indication that extensive cross-linking of the surface layer took place. After more than 6 months of storage, the samples treated with the most intense plasmas (self-bias voltages in the range of 480-600 V) still had water contact angles around 20 degrees .     

Quantitative determination of surface energy using atomic force microscopy: the case of hydrophobic/hydrophobic contact and hydrophilic/hydrophilic contact

Atomic force microscopy (AFM) has been used to determine the surface energy of chemically modified surfaces at a local scale. In order to achieve this aim, it was necessary to graft both the AFM tip and the substrate with the same chemical functional groups. Two different organothiols terminated either by hydrophilic or hydrophobic chemical functionalities were used. Grafting process classically reported shows that after UV/ozone treatment for 30 min, the tip is coated by thermal deposition with 4‐5‐nm‐thick titanium layer followed by a 30‐nm‐thick gold layer. Finally, the tip is grafted by organothiols. The thickness of the layer deposited on the tip is of the same order of magnitude as the tip radius. To avoid the use of Ti and to decrease the thickness of the gold layer, we have developed a new way of grafting by using organic molecules like (3‐mercaptopropyl)triethoxysilane (MPS) as a linkage agent. Then this way of grafting was checked. Finally, AFM force‐distance curves, between grafted tips and chemically modified surface, were carried out in contact mode. Calibration of the various parts of the apparatus and especially of the cantilever (spring constant and tip radius) is of major importance to reach quantitative data. Finally, by applying a suitable theory of contact, we were able to determine the surface energy of our system. Copyright © 2005 John Wiley & Sons, Ltd.     

Comparative characterisation by atomic force microscopy and ellipsometry of soft and solid thin films

Ellipsometry and atomic force microscopy (AFM) were used to study the film thickness and the surface roughness of both ‘soft’ and solid thin films. ‘Soft’ polymer thin films of polystyrene and poly(styrene–ethylene/butylene–styrene) block copolymer were prepared by spin‐coating onto planar silicon wafers. Ellipsometric parameters were fitted by the Cauchy approach using a two‐layer model with planar boundaries between the layers. The smooth surfaces of the prepared polymer films were confirmed by AFM. There is good agreement between AFM and ellipsometry in the 80–130 nm thickness range. Semiconductor surfaces (Si) obtained by anisotropic chemical etching were investigated as an example of a randomly rough surface. To define roughness parameters by ellipsometry, the top rough layers were treated as thin films according to the Bruggeman effective medium approximation (BEMA). Surface roughness values measured by AFM and ellipsometry show the same tendency of increasing roughness with increased etching time, although AFM results depend on the used window size. The combined use of both methods appears to offer the most comprehensive route to quantitative surface roughness characterisation of solid films. Copyright © 2007 John Wiley & Sons, Ltd.