Characterization of the morphology and composition of commercial negative resists used for lithographic processes

We present a spectroscopic and microscopic characterization of the chemical composition, structure, and morphology of two commercial negative resists using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). For this purpose, films of a novolak-based resist (ma-N 2400) and hydrogen silsesquioxane (HSQ) are treated under different conditions (temperature, deep ultraviolet (DUV) exposure, CHF₃ plasma). Topographic AFM images show that both heating and DUV exposure strongly affect the surface morphology of as-prepared ma-N 2400 resist films. These different treatment conditions also lead to decreasing roughnesses, which indicates structural reorganization. Furthermore, the decrease of the photoactive compound (bisazide) in the ma-N 2400 resist films, observed in FTIR spectra, suggests cross-linking of the resist after CHF₃ plasma treatment, heating, or DUV exposure. XPS measurements on different CHF₃ plasma-treated surfaces reveal that a structurally homogeneous fluorine-containing polymer is generated that is responsible for an enhanced etch resistance. FTIR measurements of HSQ films show a correlation between the degree of HSQ cross-linking and baking time.     

Real-time monitoring of polymer swelling on the nanometer scale by atomic force microscopy

The swelling of a polymer surface has been monitored in real time on the nanometer scale by atomic force microscopy (AFM). After modification by oxygen plasma treatment, poly(p-phenylene terephthalamide) (PPTA) displays a characteristic nanostructured surface morphology consisting of high-lying features alternating with topographically depressed areas. Selective swelling of the least cross-linked, depressed areas after the adsorption of ambient water or water from saturated humid atmospheres was observed by tapping mode AFM operated in the attractive interaction regime. The swollen areas could be distinguished from the nonswollen ones by local variations in the sample indentation made by the AFM tip when imaging in the tapping mode repulsive interaction regime. Monitoring the swelling of the plasma-treated polymer surface provided a means to reveal the nanometer-scale heterogeneity that this type of treatment creates on the polymer surface, which is something that would not be possible otherwise. Measurement of AFM tip-sample adhesion forces evidenced rapid water adsorption onto the oxygen plasma-treated surface, supporting the idea of water-induced swelling. This high hydrophilicity was interpreted as arising from the incorporation of polar oxygen functionalities, as demonstrated by X-ray photoelectron spectroscopy (XPS).     

Chemical modifications of inert organic monolayers with oxygen plasma for biosensor applications

In this paper we present a study of using oxygen plasma for chemically modifying inert hydrocarbon self-assembled monolayers of octadecyltrichlorosilane (OTS-SAMs) and rendering active surfaces for protein immobilization. Detailed surface modification and protein immobilization were characterized by using ellipsometry, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared-attenuated total reflectance spectroscopy, and fluorescence microscopy. Our XPS results showed that the surface reaction between OTS-SAMs and oxygen plasma can generate new surface functional groups such as alcohol (C-O), aldehyde (C=O), and carboxylic acid (O-C=O), and their compositions can be controlled by using different treatment times and powers. A short treatment time ( approximately 1 s) and high power (10 W) can lead to a higher density of aldehyde groups, which can serve as linker groups for protein immobilization through the formation of Schiff bases with the amine groups of proteins. By using the fluorescence immunostaining method, we confirmed that human immunoglobulin (IgG) can be immobilized on a glass slide, only if the surface was decorated with OTS-SAMs and if the OTS-SAMs were pretreated with oxygen plasma. The protein immobilized on the oxygen-plasma-treated surface can only be recognized by using a highly specific antibody, FITC-anti-IgG, but not FITC-anti-biotin.     

Surface modification of acrylate intraocular lenses with dielectric barrier discharge plasma at atmospheric pressure

Surface modification with dielectric barrier discharge (DBD) plasma was carried out at atmospheric pressure (argon as the discharge gas) to improve the biocompatibility of hydrophobic acrylate intraocular lens (IOL). Changes of the plasma-treated IOL surface in chemical composition, morphology and hydrophilicity were comprehensively evaluated by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and water contact angle (WCA) measurements. The surface biocompatibility of the untreated and plasma-treated IOLs was compared with the adhesion behavior of platelets, macrophages and lens epithelial cells (LECs) in vitro. After DBD plasma treatment, the hydrophilicity of the IOL surface was obviously improved. The changes in WCA with treatment extension may be attributed to both the introduction of oxygen or/and nitrogen-containing polar groups and the increase of surface roughness induced by plasma etching effect. The existence of low molecular weight oxidized material (LMWOM) was proved on the plasmatreated IOL which was caused by the chain scission effect of the plasma treatment. The plasma-treated IOLs resisted the adhesion of platelets and macrophages significantly. The LECs spreading and proliferation were postponed on the IOLs plasma-treated for more than 180 s, with a well maintained epithelial phenotype of LECs. The IOL biocompatibility was improved after the DBD plasma treatment. We speculate that slighter foreign-body reaction and later incidence of anterior capsule opacification (ACO) may be expected after implantation of the argon DBD plasma-treated IOL. Supported by the Zhejiang Natural Science Foundation of China (Grant No. 2004C23003)     

Chemical force titrations of antigen- and antibody-modified poly(methylmethacrylate)

Poly(methylmethacrylate) (PMMA) is a versatile polymer that displays desirable properties for development of cheap and disposable microfluidic devices for sensing biomolecular interactions. Atomic force microscopy (AFM) and chemical force titrations were used to determine the efficacy of surface modifications made to accommodate protein-substrate linkage. AFM images show the effects on surface morphology of carboxylated-, amine-, hCG antigen- and anti-hCG antibody-modified PMMA substrates. Confocal microscopy was used to determine the fluorescent intensity of labeled antibody species on the PMMA substrate, confirming the success of surface antigen/antibody immobilization. Surface pK(1/2) value for carboxylic acid and amine species grafted on PMMA were determined. When carboxylic acid or amine-terminated tips were titrated against PMMA samples terminated with the hCG antigen and anti-hCG antibody, peaks appeared in the force titration curve consistent with the pI range of the antigen or antibody species. Strong adhesive forces were present at pH values above 7.0 when the antigen was present on the PMMA substrate, and these were attributed to hydrophobic interactions between the antigen and the alkane "linker" chain attaching the amine or carboxylate group to the AFM tip. Such hydrophobic interactions were not observed with the carboxylic acid or amine/antibody combinations suggesting that the surface-linked antibody was more resistant to denaturation under higher pH. The results demonstrated the feasibility of using AFM approaches for interrogating protein grafting strategies in the fabrication of PMMA-based microsystems.     

Influence of O2 Plasma on Surface Properties of PC-TiO2 Nanocomposite Film

In this work, polycarbonate-TiO₂ nanocomposite films were prepared with different percentages. The aim was to consider the effect of O₂ LF plasma (50 Hz) on the hydrophilicity, surface energy, and surface morphology of polycarbonate and polycarbonate-TiO₂ nanocomposite. Structure of samples was determined by using X-ray diffraction analysis. In comparison with the reference sample, the samples’ structure did not change after plasma treatment. Surface properties of polycarbonate and polycarbonate-TiO₂ nanocomposite films were studied by X-ray photoelectron spectroscopy (XPS), contact angle measurement, atomic force microscopy (AFM), and Vickers microhardness tester. XPS analysis showed that the surface of samples became more oxidized due to plasma treatment. The water contact angle significantly decreased from 88° to 15° after plasma treatment. It was observed that the hardness of the nanocomposite films was not modified after plasma treatment.     

Plasma Assisted Synthesis and Physicochemical Characterizations of Ni–Co/Al2O3 Nanocatalyst Used in Dry Reforming of Methane

To assess the effects of plasma treatment a Ni–Co/Al₂O₃ nanocatalyst (10 % Ni and 3 % Co) was prepared via impregnation method followed by treatment with a non-thermal plasma to be investigated in a catalytic dry reforming of methane. The impregnated and plasma-treated nanocatalysts were characterized using XRD, FESEM, EDX, TEM, BET, FTIR, and XPS techniques. The XRD patterns confirmed the presence of nickel as NiO and NiAl₂O₄ and cobalt as Co₃O₄ on alumina support. Small NiO, NiAl₂O₄, and Co₃O₄ crystals observed in plasma-treated nanocatalyst, exhibited a good dispersion of active phase in this catalyst. The average particles size in plasma-treated sample obtain by FESEM micrograph were shown to be smaller than that of impregnated sample and the morphology was more homogenous and relatively agglomeration-free in plasma-treated Ni–Co/Al₂O₃ nanocatalyst. According to BET analysis, specific surface area of plasma-treated sample was 58 % higher than the non-treated catalyst. TEM analysis showed that particles of active phase were fairly small and well-dispersed on Al₂O₃ as a result of the plasma treatment. Better dispersion of active metal on the surface of plasma-treated sample was confirmed by XPS analysis. The plasma-treated sample showed higher yield and conversion at all temperature ranges investigated and was more resistant to coke formation compared to the non-treated sample. The results from the characterization and reaction studies suggests that plasma treatment may be a promising method for obtaining more active and stable nanocatalysts for dry reforming of methane.     

Influence of oxygen plasma treatment on poly(ether sulphone) films

Poly(ether sulphone) (PES) is one of the most widely used materials in the micro-electronics industry and a good candidate for the substrates of flexible optoelectronic devices. In this work, the influences of oxygen plasma treatment on the surface chemical composition, surface morphology and optical transparency of PES films were investigated by means of X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and UV-visible spectrophotometry. The possible relations between the optical transparency of the substrate and the surface roughness and chemical composition were also studied. The oxygen plasma treatment seriously changed the surface chemical composition and made the surface more rough. Considerable amounts of sulphate species were found on the plasma-treated surface and the surface roughness values (R_a) increased monotonically with the increase of the treatment time. The PES films treated by 5 min, 15 min, 30 min and 45 min oxygen plasma demonstrated transmission of approximately 98, 94, 68 and 46%, respectively, in the wavelength range of 400-780 nm. The oxygen plasma induced decline of optical transparency of PES films might be attributed to both the increase of surface roughness and the changes of chemical composition of the film surface.     

Covalent attachment of trypsin on plasma polymerized allylamine

This paper focuses on the immobilization of a proteolytic enzyme, trypsin, on plasma polymerized allylamine (ppAA) films. The later have been deposited onto silicon substrate by means of radiofrequency glow discharge. The covalent attachment of the enzyme was achieved in three steps: (i) activation of the polymer surface with glutaraldehyde (GA) as a linker, (ii) immobilization of trypsin and (iii) imino groups reduction treatment. The effects and efficiency of each step were investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Fluorescent spectroscopy was used to evaluate the change of the biological activity following the immobilization steps. The results showed that enzyme immobilization on GA-modified substrate increases the enzyme activity by 50% comparing to adsorbed enzymes, while the imino reduction treatment improves the enzyme retention by about 30% comparing to untreated samples. In agreement with XPS and AFM data, UV–vis absorption spectroscopy, used to quantify the amount of immobilized enzyme, showed that allylamine plasma polymer presents a high adsorption yield of trypsin. Although the adsorbed enzymes exhibit a lower activity than that measured for enzymes grafted through GA linkers, the highest catalytic activity obtained was for the enzymes that underwent the three steps of the immobilization process.     

等离子体改性聚氯乙烯的TiO2光催化降解研究

聚氯乙烯(PVC)是一种通用型塑料,无论采用挤出、注射或浸渍等方法均有优异的成型性能,至今仍是大量使用的弹性体.……     

Atmospheric‐pressure spin plasma jets processing of polymethylmethacrylate surface using experimental design methodology

Atmospheric‐pressure spin plasma jets (APSPJs) have been developed to induce surface modifications on polymethylmethacrylate (PMMA). In this study, an experimental design methodology was used to investigate the influence of process parameters [such as radio frequency (RF) power, processing gap, and number of treatment cycles] on the characteristics of PMMA surface treated by APSPJs. It was observed from the atomic force microscope (AFM) and scanning electron microscope (SEM) results that the surface morphology of PMMA treated by direct plasma is much rougher than that treated by remote plasma. The direct plasma used in APSPJs processing created a substantial amount of nanostructure grains. Moreover, the measured XPS results showed that the O/C ratios of the PMMA surface were substantially increased and subsequently water contact angle decreased on direct plasma treatment. This decrease is due to an increase of oxygen‐containing functional groups on the PMMA surface by the APSPJs processing. From the statistical analysis, the RF power and the processing gap were found to play a major role in enhancing the hydrophilic properties of PMMA surface. In contrast, the number of treatment cycles played only a secondary role in this case. Finally, in this study the APSPJs processing was demonstrated to be an effective method for surface modification of PMMA by controlling processing parameters during the treatment process. Copyright © 2009 John Wiley & Sons, Ltd.     

Surface modification of low density polyethylene (LDPE) film by low pressure O2 plasma treatment

In this work, low pressure glow discharge O₂ plasma has been used to increase wettability in a LDPE film in order to improve adhesion properties and make it useful for technical applications. Surface energy values have been estimated using contact angle measurements for different exposure times and different test liquids. In addition, plasma-treated samples have been subjected to an aging process to determine the durability of the plasma treatment. Characterization of the surface changes due to the plasma treatment has been carried out by means of Fourier transformed infrared spectroscopy (FTIR) to determine the presence of polar species such as carbonyl, carboxyl and hydroxyl groups. In addition to this, atomic force microscopy (AFM) analysis has been used to evaluate changes in surface morphology and roughness. Furthermore, and considering the semicrystalline nature of the LDPE film, a calorimetric study using differential scanning calorimetry (DSC) has been carried out to determine changes in crystallinity and degradation temperatures induced by the plasma treatment. The results show that low pressure O₂ plasma improves wettability in LDPE films and no significant changes can be observed at longer exposure times. Nevertheless, we can observe that short exposure times to low pressure O₂ plasma promote the formation of some polar species on the exposed surface and longer exposure times cause slight abrasion on LDPE films as observed by the little increase in surface roughness.     

Microwave plasma treatment of polymer surface for irreversible sealing of microfluidic devices

Microwave plasma was generated in a glass bottle containing 2-3 Torr of oxygen for plasma treatment of a polymer surface. A "kitchen microwave oven" and a dedicated microwave digestion oven were used as the power source. Poly(dimethylsiloxane)(PDMS) slabs treated by a 30 W plasma for 30-60 s sealed irreversibly to form microfluidic devices that can sustain solution flow of an applied pressure of 42 psi without leaking. Experimental set up and conditions for the production of a homogeneous plasma to activate the PDMS surface for irreversible sealing are described in detail. The surface of a microwave plasma-treated PDMS slab was characterized using atomic force microscopy (AFM) and attenuated total reflection-Fourier Transform infrared spectroscopy (ATR-FTIR). The plasma-treated surface bears silica characteristics.     

Surface modifications of PET in argon atmospheric pressure plasma: Gas flow rate effect

The correlation between plasma optical properties and the treated polyethylene terephthalate (PET) surface characteristics have been studied at various Ar flow rate. The rotational T_rot and vibrational T_vib temperatures of APPJ were determined from SPS emission band. The pristine and plasma-treated PET surfaces were characterized by several techniques including X-ray photoelectrons spectroscopy (XPS), Raman spectroscopy, contact angle (CA), and atomic force microscope (AFM). The CA decreased rapidly in the flow rate range 1–3 L/min and weakly dependent as flow rate > 3 L/min. XPS results showed that C 1s % of plasma-treated PET surfaces decreases and has a minimum for samples treated at 3–4 L/min, while O 1s has a maximum at the same flow rate range. The carbon C 1s peak of pristine and plasma treated PET samples resolved into five subcomponents: C–C, C–O, C=O, O–C=O, and π–π bonds with variable percentage ratio accordance to the plasma gas flow rate. Raman data revealed a partial loss in the crystallinity of the treated PET samples and also confirm the incremental of C–O band at Ar flow rate of 3 L/min. AFM images showed that the surface roughness of treated PET films increases as Ar flow rate increases.     

Microchip-based ELISA strategy for the detection of low-level disease biomarker in serum

A simple and sensitive method has been proposed to determine a trace level of α-fetoprotein (AFP), hepatocellular carcinoma biomarker, using poly(methyl methacrylate) (PMMA) microfluidic chips coupled with electrochemical detection system. The PMMA microchannels have been modified with poly(ethyleneimine) (PEI) containing abundant NH₂ groups to covalently immobilize AFP monoclonal antibody. Afterward, the antigen AFP and horseradish peroxidase (HRP)-conjugated AFP antibody can sequentially bind through antigen-antibody specific interaction. Atomic force microscopy (AFM) and confocal fluorescence microscope (CFFM) were utilized to characterize the surface topography and protein immobilization after modification. Coupled with three-electrode electrochemical detection system, the immunochip can perform the detection limit of AFP down to 1 pg mL⁻¹, and achieve a detectable linear concentration range of 1-500 pg mL⁻¹ by differential pulse voltammetry (DPV). The on-chip immunoassay platform can not only provide rapid and sensitive detection for target proteins but also be resistant to non-specific adsorption of proteins, which contributes to the detection of low-level protein in real sample. Finally, AFP existing in healthy human serum was detected to demonstrate the utility of the immunochip. The result shows that the proposed approach is feasible and has the potential application in clinical analysis and diagnosis.     

Dendrimer-functionalized self-assembled monolayers as a surface plasmon resonance sensor surface

We report here a multistep route for the immobilization of DNA and proteins on chemically modified gold substrates using fourth-generation NH(2)-terminated poly(amidoamine) dendrimers supported by an underlying amino undecanethiol (AUT) self-assembled monolayer (SAM). Bioactive ultrathin organic films were prepared via layer-by-layer self-assembly methods and characterized by fluorescence microscopy, variable angle spectroscopic ellipsometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR). The thickness of the AUT SAM base layer on the gold substrates was determined to be 1.3 nm from ellipsometry. Fluorescence microscopy and AFM measurements, in combination with analyses of the XPS/ATR-FTIR spectra, confirmed the presence of the dendrimer/biopolymer molecules on the multilayer sensor surfaces. Model proteins, including streptavidin and rabbit immunoglobulin proteins, were covalently attached to the dendrimer layer using linear cross-linking reagents. Through surface plasmon resonance measurements, we found that sensor surfaces containing a dendrimer layer displayed an increased protein immobilization capacity, compared to AUT SAM sensor surfaces without dendrimer molecules. Other SPR studies also revealed that the dendrimer-based surfaces are useful for the sensitive and specific detection of DNA-DNA interactions. Significantly, the multicomponent films displayed a high level of stability during repeated regeneration and hybridization cycles, and the kinetics of the DNA-DNA hybridization process did not appear to be influenced by surface mass transport limiting effects.     

Thermal and surface study of phenolic resin from cashew nut shell liquid cured by plasma treatment

In this study, phenolic resins from cashew nut shell liquid (CNSL) were applied as coating on Carbon Steel 1020 samples and successfully cured by plasma treatment or with hexamethylenetetramine (HMTA). The crosslinked samples were characterized by thermal analysis using thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), and atomic force microscopy (AFM) techniques in order to evaluate the thermal stability of these samples, as well as understand and study the curing process. TG/DTG curves showed that the thermal stability of the HMTA-cured resin was slightly higher than the resin treated by plasma. According to the DSC curves, HMTA-cured resin and plasma-treated resin exhibited only transition temperatures, so both resins were predominantly amorphous. Images generated by AFM provided qualitative evaluation of the resin surfaces, demonstrating that the coating surface with best homogeneity was cured by plasma treatment.     

Reversible Addition‐fragmentation Chain Transfer Polymerization Grafted from Silicon Surface to Prepare Poly(methyl methacrylate) Brushes

通过共价键锚固链转移剂4-氰基-4-二硫代苯甲酰基戊酸琥珀酯于硅片表面,然后采用可逆加成-断裂链转移（RAFT）自由基聚合方法制备了聚甲基丙烯酸甲酯（PMMA）高分子刷. 聚合动力学研究表明,在反应进行2小时后,PMMA的厚度随聚合时间的增大而几乎呈线性增大,具有明显的活性聚合特征. 用椭圆偏光仪、X-光电子能谱（XPS）、原子力显微镜（AFM）及接触角测试对硅片表面的PMMA高分子刷进行了表征.     

Nanoscale investigation of the structural and chemical changes induced by oxidation on carbon black surfaces: a scanning probe microscopy approach

Scanning tunneling microscopy (STM) and noncontact tapping mode atomic force microscopy (AFM) have been employed to study on a local scale the structural and, for the first time, the chemical changes of carbon black (CB) particles following plasma oxidation. STM imaging of the pristine, untreated particles revealed a relatively ordered structure of tiny crystallites with a few amorphous regions. After plasma treatment, the crystallites were no longer observed and the CB particle surface exhibited a noticeable and ubiquitous increase in atomic-scale disorder. Phase contrast images obtained with noncontact tapping mode AFM indicated that the untreated CB particles were essentially hydrophobic as a pristine basal surface of graphite, but with occasional hydrophilic patches. By contrast, their plasma-treated counterparts displayed enhanced hydrophilicity as a result of the introduction of oxygen onto the CB surface, the presence of which was evidenced by X-ray photoelectron spectroscopy, but most significantly, such enhancement was observed to be quite uniform at a local scale of individual particles. The possibility of investigating on a very local scale the chemical behavior of oxidized CB particles should be useful for the control and optimization of their dispersion properties in different systems.     

Influence of antibody immobilization strategy on molecular recognition force microscopy measurements

A systematic evaluation of the effects of antibody immobilization strategy on the binding efficiency and selectivity (e.g., ability to distinguish between specific and nonspecific interactions) of immunosurfaces prepared with F(ab') antibody fragments of rabbit Immunoglobulin G (IgG) is described. F(ab') was attached to gold surfaces either (1) directly via the formation of a gold-thiolate bond or (2) indirectly through a series of a bifunctional linkers containing an alkane chain or ethylene glycol spacer. Immobilization of F(ab') via the sulfhydryl reactive group located opposite the antigen binding site ensured optimum orientation of the antigen binding site. X-ray photoelectron spectroscopy (XPS) and surface plasmon resonance (SPR) were used to confirm surface modification with the bifunctional linkers and antibody immobilization, respectively. Binding efficiency assays performed with SPR indicated that increasing the length of the linker increased the antigen binding efficiency. Atomic force microscopy (AFM) adhesion force measurements indicated that AFM probes functionalized with directly immobilized F(ab') more effectively discriminated between specific and nonspecific surface-bound proteins than probes modified indirectly via linker-immobilized F(ab'). In addition, a greater number of antibody-antigen binding events were observed with directly immobilized F(ab')-functionalized probes.