Influence of argon plasma treatment on polyethersulphone surface

Polyethersulphone (PES) was modified to improve the hydrophilicity of its surface, which in turn helps in improving its adhesive property. The modified PES surface was characterized by contact angle measurement, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and Vicker’s microhardness measurement. The contact angles of the modified PES reduces from 49° to 10° for water. The surface free energy (SFE) calculated from measured contact angles increases from 66.3 to 79.5 mJ/m² with the increase in plasma treatment time. The increase in SFE after plasma treatment is attributed to the functionalization of the polymer surface with hydrophilic groups. The XPS analysis shows that the ratio of O/C increases from 0.177 to 0.277 for modified PES polymer. AFM shows that the average surface roughness increases from 6.9 nm to 23.7 nm due to the increase in plasma treatment time. The microhardness of the film also increases with plasma treatment.     

Excimer laser-assisted chemical process for formation of hydrophobic surface of Si (001)

Silicon (Si) wettability is one of the important parameters in the development of Si-based biosensing and lab-on-chip devices. We report on UV laser induced hydrophobicity of Si (001) wafers immersed in methanol during the irradiation with an ArF excimer laser. The irradiation with 800 pulses of the laser operating at 65 mJ/cm² allowed to significantly increase the hydrophobicity of investigated samples as characterized by the static contact angle change from 77° to 103°. Owing to the irradiation with relatively low laser fluence, no measurable change in surface morphology of the irradiated samples has been observed with atomic force microscopy measurements. The nature of the hydrophobic surface of investigated samples is consistent with X-ray photoelectron spectroscopy analysis that indicates formation of Si–O–CH₃ bonds on the surface of the laser-irradiated material.     

Wettability and surface energy of parylene F deposited on PDMS

For the first time, the wettability and surface energy of parylene F were investigated. The results showed that parylene F had a hydrophobic surface with an eigen water contact angle of 104.7 ± 0.6°. We found that 3.5 μl probe liquid was an optimal value for the contact angle measurement of parylene F. Moreover, we found that the Lifshitz–van der Waals/acid–base approach was unsuitable for determining the surface energy of parylene F, whereas the Owens–Wendt–Kaelble approach and the limitless liquid–solid interface wetting system were compatible. The surface energy of parylene F was estimated to be 27.06 mJ/m² (Owens–Wendt–Kaelble) and 40.41 mJ/m² (Limitless liquid-solid interface wetting system). Furthermore, this investigation also provided a reference for the applications of empirical and physics-based semi-empirical approaches for the estimation of surface energy.     

几种微构件材料的表面能及纳观黏附行为研究

对微机电系统（MEMS）中几种常用构件材料的表面能及其主要影响因素进行了探讨,并与材料表面的纳观黏附性能进行了分析比较.用Owens二液法计算出硅基材料的表面能在60—75 mJ/m²之间,它们之间总表面能的差异主要归结为表面能极性分量的差异,表面粗糙度的存在使表观表面能有所偏高.施加自组装分子膜后的表面能大为降低,粗糙度的存在可以使其表面能进一步减小.纳观黏附力和表面能之间有一定的对应关系.另外,在研究中发现表面粗糙度对纳观黏附行为的影响较小. 关键词： MEMS 表面能 纳观黏附 粗糙度     

Fluorination of polymethylmethaacrylate with tetrafluoroethane using DC glow discharge plasma

Fluorination of polymer surfaces has technological applications in various fields such as microelectronics, biomaterials, textile, packing, etc. In this study PMMA surfaces were fluorinated using DC glow discharge plasma. Tetrafluoroethane was used as the fluorinating agent. On the fluorinated PMMA surface, static water contact angle, surface energy, optical transmittance (UV-vis), XPS and AFM analyses were carried out. After the fluorination PMMA surface becomes hydrophobic with water contact angle of 107° without losing optical transparency. Surface energy of fluorine plasma-treated PMMA decreased from 35 mJ/cm² to 21.2 mJ/cm². RMS roughness of the fluorinated surface was 4.01 nm and XPS studies revealed the formation of C-CF_x and CF₃ groups on the PMMA surface.     

Oxygen plasma and high pressure H<Subscript>2</Subscript>O vapor heat treatments used to fabricate polycrystalline silicon thin film transistors

Oxygen plasma and high pressure H₂O vapor heat treatment were applied to fabrication of n-channel polycrystalline silicon thin film transistors (poly-Si TFTs). 13.56 MHz-oxygen-plasma treatment at 250 °C, 100 W for 5 min effectively reduced defect states of 25-nm-thick silicon films crystallized by 30 ns-pulsed XeCl excimer laser irradiation. 1.3×10⁶-Pa-H₂O vapor heat treatment at 260 °C for 3 h was carried out in order to improve electrical properties of SiO_x gate insulators and SiO_x/Si interfaces. A carrier mobility of 470 cm²/V s and a low threshold voltage of 1.8 V were achieved for TFTs fabricated with crystallization at 285 mJ/cm². Received: 18 November 2002 / Accepted: 25 November 2002 / Published online: 11 April 2003 RID="*" ID="*"Corresponding author. Fax: +81-42/388-7109, E-mail: tsamesim@cc.tuat.ac.jp     

Wetting behavior of Al–Si–Mg alloys on Si3N4/Si substrates: optimization of processing parameters

The wetting behavior of Al–Si–Mg alloys on Si₃N₄/Si substrates has been investigated using the sessile drop technique. Based on a Taguchi experiment design, the effect of the following processing parameters on the contact angle (θ) and surface tension (σ_LV) was studied: processing time and temperature, atmosphere (Ar and N₂), substrate surface condition (with and without a silicon wafer), as well as the Mg and Si contents in the aluminium alloy. In nitrogen, non-wetting conditions prevail during the isothermal events while in argon a remarkable non-wetting to wetting transition leads to contact angles θ as low as 11±3° and a liquid surface tension σ_LV of 33± 10×10^-5 kJ/m². According to the multiple analysis of variance (Manova), the optimum conditions for minimizing the values of θ and σ_LV are as follows: temperature of 1100 °C, processing time of 90 min, argon atmosphere, no use of a silicon wafer, and the use of the Al-18% Mg-1% Si alloy. A verification test conducted under the optimized conditions resulted in a contact angle of θ=9±3° and a surface tension of σ_LV=29± 9×10^-5 kJ/m², both indicative of excellent wetting. PACS 68.03.Cd; 81.05.Bx; 68.08.Bc; 05.70.-a; 61.10.Nz     

Point-defect properties of and sputtering events in the {001} surfaces of Ni3Al I. Surface and point-defect properties

Constant-area and fully relaxed molecular dynamics methods are employed to study the properties of the surface and point defects at and near {001} surfaces of bulk and thin-film Ni, Al and Ni₃Al respectively. The surface tension is larger than the surface energy for all {001} surfaces considered in the sequence: Al (1005?mJ?m^?2)<?Ni₃Al (mixed Ni–Al plane outermost, 1725?mJ?m^?2)<?Ni₃Al (all-Ni-atoms plane outermost, 1969?mJ?m^?2)<?Ni (1993?mJ?m^?2). For a surface of bulk Ni₃Al crystal with a Ni–Al mixed plane outermost, Al atoms stand out by 0.0679?Å compared with the surface Ni atoms and, for the all-Ni-atoms surface, Al atoms in the second layer stand out by 0.0205?Å compared with Ni atoms in the same layer. Vacancy formation energies are about half the bulk values in the first layer and reach a maximum in the second layer where the atomic energy is close to the bulk value but the change in embedding energy of neighbouring atoms before and after vacancy formation is greater than that in the bulk. Both the vacancy formation energy and the surface tension suggest that the fourth layer is in a bulk state for all the surfaces. The formation energy of adatoms, antisite defects and point-defect pairs at and near {001} surfaces of Ni₃Al are also given.     

不同射频输入功率下制备的氟化类金刚石碳膜疏水性研究

以高纯石墨作靶、氩气（Ar）和三氟甲烷（CHF₃）为源气体,用反应磁控溅射法在不同射频功率下制备了氟化类金刚石碳（F-DLC）膜,并对其疏水性进行研究.双蒸水液滴与膜表面接触角的测试结果表明,所制备薄膜表面的最大水接触角可达115°左右.通过原子力显微镜获得的薄膜表面AFM图谱、拉曼光谱以及傅里叶变换红外光谱探讨了影响薄膜的疏水性的因素.结果表明,薄膜的疏水性与薄膜的表面粗糙度和表面键结构直接相关,表面粗糙度越大,疏水性越好,但与薄膜中的F含量和sp³/sp²的比值并未呈单调增加或减小的对应关系.射频输入功率影响着薄膜的沉积速率,与薄膜表面粗糙度、薄膜中芳香环单核的比例以及薄膜表面的键结构（F的接入方式）直接相关. 关键词： 疏水性 反应磁控溅射 氟化类金刚石膜 射频功率     

Wettability of ZnO: A comparison of reactively sputtered; thermally oxidized and vacuum annealed coatings

We have studied the wettability of sputter deposited ZnO, thermally oxidized Zn-ZnO and vacuum annealed ZnO coatings. The X-ray diffraction patterns showed the formation of hexagonal-wurtzite structure of ZnO, which was further confirmed by micro-Raman spectroscopy data. The X-ray photoelectron spectroscopy data indicated that the sputter deposited ZnO coatings were more stoichiometric than thermally oxidized Zn-ZnO and vacuum annealed ZnO coatings. The wettability measurements indicated that water contact angles of 158.5° and 155.2° with sliding angles of 2° and 4° were achieved for thermally oxidized Zn-ZnO and vacuum annealed ZnO coatings, respectively. The superhydrophobicity observed in thermally oxidized Zn-ZnO and vacuum annealed coatings is attributed to the nanorod cluster like morphology along with the presence of high fraction of micron scale air pockets. The water droplet on such surfaces is mostly in contact with air pockets rather than solid surface, leading to high contact angle. Whereas, the sputter deposited ZnO coatings exhibited a maximum water contact angle of 110.3°. This is because the sputter deposited ZnO coatings exhibited a densely packed nanograin-like microstructure without any air pockets. The work of adhesion of water was very low for thermally oxidized Zn-ZnO (5.06 mJ/m²) and vacuum annealed ZnO coatings (6.71 mJ/m²) when compared to reactively sputtered ZnO coatings (90.41 mJ/m²). The apparent surface free energy (SFE) for these coatings was calculated using Neumann method and the SFE values for sputter deposited ZnO, thermally oxidized Zn-ZnO and vacuum annealed ZnO coatings were 32.95, 23.21 and 18.78 mJ/m², respectively.     

Preparation of Y2O3:Eu thin films by excimer-laser-assisted metal organic deposition

Europium-doped yttrium oxide (Y₂O₃:Eu) thin films were successfully deposited on quartz and ITO/glass substrates by excimer-laser-assisted metal organic deposition (ELAMOD) at low temperatures. The effects of laser wavelength and thermal temperature on the films’ crystallinity and photoluminescence properties were investigated. Films irradiated by an ArF laser at 80 mJ/cm² and 400–500°C were highly crystallized compared with those prepared by thermal MOD. In contrast, when the film was irradiated by a KrF laser at 500°C, no crystalline Y₂O₃:Eu was formed. The Y₂O₃:Eu film irradiated by the ArF laser at 80 mJ/cm² and 500°C showed typical PL spectra of Eu³⁺ ions with cubic symmetry and a ⁵D₀→⁷F₂ transition at ∼612 nm. The PL intensity at 612 nm was much higher for the film prepared with ELAMOD than for that prepared by the thermal-assisted process, and the photoemission intensity of the film prepared with ELAMOD strongly depended on the substrate material.     

Modification of polyethylene powder with an organic precursor in a spiral conveyor by hollow cathode glow discharge

Hexamethyldisiloxane (HMDSO) films were deposited on polyethylene (PE, (C₂H₄)_n) powder by hollow cathode glow discharge. The reactive species in different HMDSO/Ar plasmas were studied by optical emission spectroscopy (OES). Increasing the HMDSO fraction in the gas mixture additional compounds like CH_x, OH, SiC and SiO can be identified. After deposition the formed silicon and carbon containing groups (C–O, C=O, SiC and SiO) on the PE powder surface have been analyzed by X-ray photoemission spectroscopy (XPS). Changes in wettability depending on the HMDSO fraction were investigated by contact angle measurements (CAM). The free surface energy of the PE powder decreases with increasing HMDSO fraction in the process gas and encapsulation of the powder particles occurs. An aging effect of the plasma treated PE surface was observed depending on the process gas composition. The higher the HMDSO fraction the less is the aging effect of the plasma treated PE surface.     

Exploring the influence of a XeCl laser treatment on biocompatibility of polyethersulfone film

The effect of XeCl laser irradiation on biocompatibility of polyethersulfone (PES) film surface was investigated. For this purpose, the surface of PES film was irradiated with different number of pulses at different fluences. The treated surfaces were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurements. The platelet adhesion and cell culture measurements were done on the treated surface for investigation of the biocompatibility. It was shown that, irradiation of surface with 500 pulses at a fluence of 25 mJ/cm² is the most optimal condition for improving the platelet adhesion on the PES surface with a XeCl laser.     

The super-hydrophobic IR-reflectivity TiO2 coated hollow glass microspheres synthesized by soft-chemistry method

The super-hydrophobic and IR-reflectivity hollow glass microspheres (HGM) was synthesized by being coated with anatase TiO₂ and a super-hydrophobic material. The super-hydrophobic self-cleaning property prolong the life time of the IR reflectivity. TBT and PFOTES were firstly applied and hydrolyzed on HGM and then underwent hydrothermal reaction to synthesis anatase TiO₂ film. For comparison, the PFOTES/TiO₂ mutual-coated HGM (MCHGM), PFOTES single-coated HGM (F-SCHGM) and TiO₂ single-coated HGM (Ti-SCHGM) were synthesized as well. The MCHGM had bigger contact angle (153°) but smaller sliding angle (16°) than F-SCHGM (contact angle: 141.2°; sliding angle: 67°). Ti-SCHGM and MCHGM both showed similar IR reflectivity with ca. 5.8% increase compared with original HGM and F-SCHGM. For the thermal conductivity, coefficients of F-SCHGM (0.0479 W/(m K)) was basically equal to that of the original HGM (0.0475 W/(m K)). Negligible difference was found between the thermal conductivity coefficients of MCHGM-coated HGM (0.0543 W/(m K)) and Ti-SCHGM (0.0546 W/(m K)).     

Stability of atmospheric-pressure plasma induced changes on polycarbonate surfaces

Polycarbonate films are subjected to plasma treatment in a number of applications such as improving adhesion between polycarbonate and silicon alloy in protective and optical coatings. The surfaces that undergo changes in surface properties due to plasma treatment have a tendency to revert back to their original states. Thus, the stability of the plasma induced changes on polymer surfaces over a desired time period is an important issue. The objective of this study was to examine the effect of ageing on atmospheric-pressure helium-plasma treated polycarbonate (PC) sample as a function of treatment time. The ageing effects were studied over a period of 10 days. The samples were plasma treated for 0.5, 2, 5 and 10 min. Contact angle made by water droplet on polymer surfaces were measured to study surface energy changes. Modification of surface chemical structure was examined using X-ray photoelectron spectroscopy (XPS). Contact angle decreased from 93° for untreated samples to 30° for samples treated with plasma for 10 min. After 10 days the contact angle for the 10 min plasma treated sample increased to 67°, but it never reverted back to that of the untreated surface. Similarly, the oxygen-carbon (O:C) ratio increased from 0.136 for untreated samples to 0.321 for 10 min plasma-treated samples, indicating an increase in surface energy.     

Surface modification of a polyamide 6 film by He/CF4 plasma using atmospheric pressure plasma jet

Polyamide 6 (PA 6) films are treated with helium(He)/CF₄ plasma at atmospheric pressure. The samples are treated at different treatment times. The surface modification of the PA 6 films is evaluated by water contact angle, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The etching rate is used to study the etching effect of He/CF₄ plasma on the PA 6 films. The T-peel strengths of the control and plasma treated films are measured to show the surface adhesion properties of the films. As the treatment time increases, the etching rate decreases steadily, the contact angle decreases initially and then increases, while the T-peel strength increases first and then decreases. AFM analyses show that the surface roughness increases after the plasma treatment. XPS analyses reveal substantial incorporation of fluorine and/or oxygen atoms to the polymer chains on the film surfaces.     

Effect of carbon powder thermal activation on characteristics of supercapacitor electrodes

The capacitors are increasingly being used as energy storage devices in various power systems. The scientists of the world are trying to maximize the electrical capacity of the supercapacitors. This research aims to use plasma spray technology in order to develop carbon electrodes with carbon powder thermally treated in the temperatures ranging from 100 °C to 900 °C in the environment of argon gas. The BET research on primary carbon powder reveal that the largest surface area is obtained at 100 °C heating temperature – 577 m²/g, and at 900 °C – 507 m²/g. Meanwhile, at 300–700 °C heating temperatures the powder surface area decreases up to 2.2 times. The measurements of supercapacitor specific capacitance indicate that the largest values, 15 F/g and 8.7 F/g, were obtained when the respective specific surface area of primary powders equalled 577 m²/g and 261 m²/g.     

Self-organisation of di(perfluorohexyl)hexane in Langmuir and LB films

Symmetrical triblock semifluorinated n-alkane, di(perfluorohexyl)hexane of the formula F(CF₂)₆(CH₂)₆(CF₂)₆F (abbreviated F₆H₆F₆), has been synthesised and investigated at the air/water interface. Our results show for the first time that this unusual film-forming material, completely hydrophobic in nature and possessing no polar group, is capable of stable film formation at the free water surface. The surface pressure–area isotherm of the studied compound exhibited two regions: corresponding to monotonous pressure rise, followed by a pseudo-plateau region. Visualisation of film structure with Brewster angle microscope (BAM) proved the formation of domains within the pseudo-plateau region. A closer insight into the structure of these domains with atomic force microscope (AFM) proved their ordered, circular shape. The average area of F₆H₆F₆ domain was found to depend on surface pressure value, as it is 4.98 ± 1.75 μm² at π = 1.2 mN/m to 16.54 ± 0.31 μm² at π = 1.7 mN/m. Following performed quantum-chemical calculations, it can be concluded that the observed surface aggregates from F₆H₆F₆ are formed by linear conformers with shifted CF and CH parts. The calculated domain thickness is between 20 and 21 Å, which perfectly agrees with the experimental value estimated from AFM measurements (20.3 ± 1.4 Å).     

Diffusion and chemical composition of TiNxOy thin films studied by Rutherford Backscattering Spectroscopy

Thickness and chemical composition of the TiN_xO_y thin films deposited by reactive magnetron sputtering from Ti target at controllable oxygen flow rate were determined by Rutherford Backscattering Spectroscopy (RBS) using 2 MeV He⁺ ions. The films were deposited on carbon foils and amorphous silica (a-SiO₂) substrates at 25 °C and 250 °C. The estimated film thickness is of 75-100 nm. The O/Ti atomic ratio in the films increases up to 1.5 with increasing oxygen flow rate, while that of N/Ti decreases from about 1.1 for TiN to 0.4 at the highest oxygen flow rate. Substantial out-diffusion of carbon from the substrate is observed which is independent of the substrate temperature. Films grown onto a-SiO₂ substrates can be treated as homogeneous single layers without interdiffusion. It is more difficult to determine the nitrogen and oxygen content due to superposition of RBS signals arising from film and substrate. RBS analysis of the depth profile indicates that for the investigated films the carbon diffusion and oxidation not only at the topmost surface layers but over the bulk of the films were found. Comparison with XPS results indicates substantial oxygen adsorption at the surface of TiN_x thin films obtained at zero oxygen flow rate.