Preparation of hydrophobic surface on steel by patterning using laser ablation process

Currently there is an increasing demand for the application of hydrophobic surface in industrial and biological processes. It has been found that the contact angle with liquid, closely related to hydrophobicity of a solid surface, is largely determined by micro-geometrical structure and chemistry of the said surface. In this investigation, the hydrophobicity of steel surface was achieved by implementing micro-patterns on substrate using laser ablation process, and depositing amorphous carbon (a-C) thin film using magnetron sputtering technique. For the patterning, a short pulse excimer laser with a wavelength of 248 nm was used to etch the substrate surface to form different controlled patterns. Based on the models built by Wenzel and Cassie-Baxter, the depth of etched grooves, d, the clearance between two grooves, a, and the width of grooves, b, were optimized to obtain the largest contact angle. It was found that when a pattern was set at a = 25 μm, b = 50 μm and d = 8 μm, the contact angle of the surface could be increased to about 130°, compared to the 68.5° found from a plain smooth steel surface (R_a ≤ 0.01 µm). As a preliminary investigation, an amorphous carbon (a-C) coating was deposited on the patterned surface. It shows that the contact angle was increased further by about 10°-20° on a patterned surface.     

Rapid and scalable method for direct and indirect microstructuring of vertical aligned carbon nanotubes

Multi-walled carbon nanotube (MWCNT) films are grown by chemical vapor deposition (CVD) on silicon substrates using an alumina buffer and a Fe/Co layer as catalyst with different Fe/Co ratios. For both coatings, a scalable wet-chemical technique is applied. The highest CNT forests (100–125 μm) are obtained with Fe content between 60 and 80 wt.%. After deposition of the films, direct laser interference patterning (DLIP) method is used for fabricating micro patterns of the CNTs, using a frequency tripled Nd:YAG laser emitting 10 ns pulses. Two different approaches for fabricating periodic MWCNT arrays are presented. The first approach is the direct patterning of the CNT layer itself (CNT-DLIP) obtaining well defined line-like structures with 10 μm spatial period. By adjusting the laser fluence (from 150 to 250 mJ cm^− 2) and the number of laser pulses (from 1 to 20), the morphology (structure depth and line width) of the fabricated arrays can be varied. Thermal simulations of the CNT ablation process validate the experimental observations. The second approach involves indirect patterning of the CNTs, by fabricating line-like structures on the iron/cobalt catalyst layer (CAT-DLIP). In the last case, moderate energy densities (100 mJ cm^− 2) permitted to remove the catalyst layer locally at the interference maxima positions. By altering the number of laser pulses from 1 to 20 the line width can be tuned. The CNT forests are subsequently grown on the patterned catalyst.     

Hydroxyapatite coatings prepared by a high power laminar plasma jet

For two hydroxyapatite (HA) powders, containing particles differing in mass by a factor of 20, a set of optimum deposition parameters was defined, leading to the coatings with high crystallinity (80-90%), high adhesion strength (60 and 40 MPa for the coating thicknesses of 120 μm and 350 μm, respectively) and excellent microstructure (coatings were without micro- or macro-cracks, without delaminating on substrate-coating surface contact, and possess low porosity, 1-2%). It was shown that higher plasma power (52 kW) did not necessarily lead to a higher HA decomposition.     

Micro-patterning of Si(100) surfaces by ethanol cluster ion beams

The irradiation of Si(100) surfaces by ethanol cluster ion beams exhibited high-rate sputtering and low-damage formation. The sputtered depth increased with increase of the acceleration voltage for ethanol cluster ions, and the sputtering yield was a few hundreds times larger than that by Ar monomer ion beams. Also, the RBS channeling measurement showed that the irradiation damage was much less than that by Ar monomer ion irradiation. Furthermore, the AFM image showed that the surface roughness of the irradiated Si(100) surface was less than 1 nm. As well as the Si(100) surface, the sputtered depth of the photo-resist surface increased with increase of the acceleration voltage for ethanol cluster ions.Based on these results, micro-patterning with various sizes in a range of 3 μm to 100 μm was performed on the Si(100) surfaces by the ethanol cluster ion irradiation. Various kinds of photo-resist mask patterns such as circle, square and line patterns were made on a Si(100) surface by photo-resist technique. The SEM observation showed that micro-patterns were prepared on the Si (100) surface by the ethanol cluster ion irradiation.     

Surface modification of silica glass by CHF3 plasma treatment and carbon negative-ion implantation for cell pattern adhesion

We have investigated a method for the patterning of cell adhesion on a silica glass by using two-steps of surface modification processes of CHF₃ plasma treatment and negative-ion pattern implantation. For the first step, exposure of CHF₃ plasma to silica glass (SG) was used to obtain hydrophobic surface, leading to eliminate cell-adhesion property. After treatment with RF power of 20 W and exposure time of 120 s, the hydrophobicity was occurred from the increase in contact angle of SG from 43° to 88° and its reason based on XPS analysis was due to formations of C―F, C―F₂, and C―F₃ bonds, so-called fluorocarbonated bonds. Culture of mesenchymal stem cells (MSC) and rat adrenal pheochromocytoma cells (PC12h) showed the degradation of cell adhesion property on the plasma-treated SG surface. For the second step, carbon negative-ion implantation into the hydrophobic fluorocarbonated-SG surface was used to pattern the hydrophilic region, leading to enhance cell adhesion property. The contact angle of C-modified surface decreased to 76° at conditions of 15 keV and 1 × 10¹⁵ ions/cm². XPS showed that the hydrophilicity was due to reduction of C―F_x bonds and formation of C―O and C═O bonds. After 3 days culture of MSC and PC12h on the C-implanted surface of the plasma-treated SG, a fairly good adhesion patterning of both cells was obtained on the ion-implanted regions.     

Nanoindentation on the surface of thermally sprayed coatings

The ability to quantify surface mechanical properties is valuable for assessing the quality of thermal spray coatings. This is especially important for prostheses where loading is placed directly on the surface. Hydroxyapatite was classified to small (20-40 μm), medium (40-60 μm) and large (60-80 μm) particle sizes and thermal sprayed to produce a coating from spread solidified hydroxyapatite droplets. It was revealed for the first time, that nanoindentation can be successfully used to determine the hardness and elastic modulus on the surface of well spread solidified droplets at the hydroxyapatite coating surface. Comparison with indentation results from polished cross-section exhibited comparable values and statistical variations. The hardness was 5.8 ± 0.6, 5.4 ± 0.5 and 5.0 ± 0.6 GPa on coatings produced from small, medium and large sized powder. Similarly, the elastic modulus decreased from 121 ± 7, 118 ± 7 to 114 ± 7 GPa, respectively. Use of several indentation loads gave comparable results with sintered hydroxyapatite suggesting good inter-splat bonding within the coating. MicroRaman spectroscopy and X-ray diffraction confirmed a larger degree of dehydroxylation for the smaller particles also revealing a lower elastic modulus. This shows the influence of particle size and possibly dehydroxylation of hydroxyapatite on the mechanical properties of the coating surface.     

Ion-assisted vapor deposition of acryl polymer thin films

Polymer thin films were prepared by an ion-assisted vapor deposition polymerization method that involves physical vapor deposition of monomer combined with low-energy ion irradiation. In a high vacuum environment, zinc diacrylate monomer was evaporated at a rate of 0.8 nm/min on gold-coated glass substrates under simultaneous irradiation by nitrogen ions of 20 nA/cm² at ion energy ranging from 500 to 2000 eV. The ion irradiation remarkably reduced the surface roughness of the deposited films. Infrared spectroscopy showed that the absorption bands of the vinyl group diminish with increasing ion energy. Formation of polymer molecules was confirmed by gel permeation chromatograph. Moreover, the film became insoluble to organic solvents when the ion energy was increased. These results indicate that polymer thin films can be prepared by vapor deposition of monomers under ion irradiation. The ion-assisted vapor deposition polymerization was also possible on insulating substrates.     

Characterization of thick ceramic and cermet coatings deposited by an industrial-scale LAFAD process

The unidirectional LAFAD dual-arc vapor plasma source yields 100% ionized metal vapor plasma flow and more than 50% ionized gaseous plasma in the coating chamber. The LAFAD technology deposits thick ceramic and cermet coatings with multi-elemental nanostructured architectures, nearly defect-free morphology and atomically smooth surfaces at high deposition rates. The productivity of one unidirectional LAFAD vapor plasma source integrated into an industrial-scale batch coating system ranges from 3-4 µm/h for nitride base coatings and up to 6 µm/h for oxi-ceramic coatings with good uniformity over large deposition areas, making it an attractive alternative to other PVD processes for a wide variety of applications. The 20 µm to 100 μm monolithic and Ti/TiN microlaminated LAFAD coatings exhibit low residual compressive stresses, i.e. < 1.5 GPa, resulting in exceptionally good adhesive and cohesive toughness. The fracture resistance of ultra-thick LAFAD coatings vs. coating architecture will be discussed.     

Characteristics of atmospheric pressure plasma jet generated by compact and inexpensive high voltage modulator

An atmospheric pressure plasma jet has been successfully generated using a compact high voltage modulator driven by 12 V alkaline batteries. A jet nozzle was composed of a quartz tube with two cylindrical electrodes. The grounded electrode was rolled on the tube and the powered one was inserted in the tube for discharging at lower voltage. V-Q Lissajous analysis of the plasma jet indicated that energy and power consumed for the plasma generation were linear along the distance between the electrodes. Length of the plasma plume from the tip of the tube was 11 mm for the gap length of 5 mm and the input voltage DC of 12 V. At the input voltage, the energy and power consumed for the plasma generation were 4.1 μJ and 0.12 W, respectively. Optical emission spectroscopy analysis of the plasma showed that the plasma contained hydroxyl radicals and exited nitrogen molecules which are chemically active species. The plasma jet can be applied to plasma cleaning for material surface though was generated with the alkaline batteries.     

Micropatterning of conducting polymer tracks on plasma treated flexible substrate using vapor phase polymerization-mediated inkjet printing

A facile strategy to pattern a conducting polymer on various flexible substrates is reported using vapor phase polymerization-mediated inkjet printing. Complex polypyrrole patterns were obtained via oxidation polymerization of vaporized monomer on the inkjet-printed oxidant patterns. The patterned lines are readily controlled by inkjet printing with the high resolution of micrometer scale. FT-IR attenuated total reflection analysis and X-ray photoelectron spectroscopy were conducted in order to confirm the polymerization of pyrrole monomer. This process provided highly conductive polymer patterns of polypyrrole with the sheet resistance of 2.8 × 10³ Ω/□, the minimum line width of ca. 60 μm and the film thickness of ca. 450 nm. Furthermore, metallic copper pattern was prepared on previously patterned polypyrrole architectures by electroless plating as a practical application.     

The use of a micro-cavity discharge array at atmospheric pressure to investigate the spatial modification of polymer surfaces

A micro-cavity discharge array (2500 cavities of 50 µm² size) was operated in neon at atmospheric pressure to modify polystyrene (PS), fluorinated ethylene-propylene co-polymer (FEP) and polytetrafluoroethylene (PTFE) polymer surfaces and, with the injection of a polymerisable monomer (acrylic acid), to deposit patterned, thin polymeric coatings. The aim of this study was to investigate the utility of these micro-discharge sources in the surface treatment of polymers and for the patterned deposition of polymeric material. The influence of the driving frequency, treatment time and sample-array distance on polymer surface treatment was investigated. X-ray photoelectron spectroscopy (XPS) was used to explore the surface chemistry of the treated polymer surfaces and of the polymer deposits. It was found that increasing the micro-cavity discharge source driving frequency and/or treatment time and decreasing the sample-array distance all led to a significant decrease in surface energy as determined by water contact angle measurements. For a period of time, post treatment surface hydrophilicity degraded due to the well known “ageing effect” but stabilized after two days. Finally, it was demonstrated that the device could be used for the localized, array sized, deposition of acrylic acid. High resolution XPS analysis of the deposit registered a C 1s spectra typical of poly(acrylic acid) with a prominent peak centred at approximately 289.3 eV indicating a relatively high level retention of the original monomer functionality. These results demonstrate that micro-cavity discharges, operated at or near atmospheric pressure, can be used to both modify and locally deposit polymeric material.     

Surface modification of PET films by atmospheric pressure plasma-induced acrylic acid inverse emulsion graft polymerization

In order to make polyester film surface hydrophilic, atmospheric pressure plasma jet (APPJ) is used to activate the film surface first followed by inverse emulsion grafting polymerization of acrylic acid (AA). The graft ratio and wettability test reveal that the effectiveness of APPJ on initiating graft polymerization increases with increasing plasma treatment duration and helium flow rate. As the jet-to-substrate distance increases, the graft efficiency goes through a maximum at 2 mm. When oxygen is added to the plasma treatment gas, the graft efficiency decreases substantially. Fourier transform infrared spectrometry (FTIR) analysis shows new bands appearing at 2500-3600 cm^− 1 and 1546 cm^− 1 for the plasma-grafted samples. Scanning electron microscopy (SEM) results show that the grafted layer is built with a large number of spherical particles at submicron or even nanoscale. With a high graft ratio, agglomeration of neighboring particles becomes more pronounced, and eventually a relatively continuous graft layer is obtained with a corresponding surface contact angle of 5° which is considered superhydrophilic.     

Development and irradiation performance of stencil masks for heavy-ion patterned implantation

Heavy-ion implantation is a powerful tool to conduct atomic injection and to create buried nanoparticles with good depth-controllability in dielectric material. Metal nanoparticle composites, especially, the metal ion implanted insulators (e.g. SiO₂) with patterned nanoparticles are promising for plasmonic applications, possessing an enhanced surface plasmon resonance and nonlinear optical property as compared with randomly implanted specimens [1]. Contact masked implantation is one practical method for patterned implantation, which has advantage of reliable 2D nanoparticle spatial controllability without any abreactions. In this experiment, the Si stencil mask was made from top Si layer of SOI wafer by using e-beam lithography and plasma deep etching. The mask can be fabricated with required aspect ratio (from 3 up to 100), fine pore shape, surface flatness, and mechanical hardness. 60 keV Cu ion irradiation damage test shows that, below the fluence of 1 × 10¹⁷ ions/cm², Si stencil mask can keep dimensional stability.     

Austenite modification of AISI 316L SS by pulsed nitrogen ion beams generated in dense plasma focus discharges

We present the results of a surface modification of AISI 316L stainless steel by surface irradiation with high energy, pulsed nitrogen ion beams generated with 0.8 kJ dense plasma focus. The surface characterization was done using GAXRD, Auger electrons spectroscopy, TEM and optical microscopy. After the irradiation, we found a modification of a 1 μm thick surface layer, on which a gradual lattice expansion of the austenite with the number of irradiation pulses, i.e. with the total nitrogen ion fluence, was observed.In addition, ~ 40 nm close to the surface layer, a disordered lattice structure had been observed through TEM analysis. Those results can be explained in terms of the extreme thermal effect induced on the surface through the fast high energy release during the pulsed ion interaction with the steel surface, followed by an also rapid cooling down process which limits the nitrogen diffusion to the bulk.     

Microstructure and mechanical performance of new Al0.5CrFe1.5MnNi0.5 high-entropy alloys improved by plasma nitriding

Effects of plasma nitriding at 525 °C on microstructure and mechanical performance of a brand-new Al_0.5CrFe_1.5MnNi_0.5 high-entropy alloy (HEA) were investigated. This alloy exhibits a large age hardening effect at temperatures from 600 to 800 °C and can be well-nitrided in the as-cast condition or the homogenized and furnace-cooled state. The nitrided layer has a thickness around 75 μm and a peak hardness level of Hv 1250 near the surface. The nitrided Al_0.5CrFe_1.5MnNi_0.5 alloys exhibit superior adhesive wear resistance to conventional nitrided steels by 25-54 times due to their much thicker highly-hardened layer and higher peak hardness than that of conventional steels.     

Al and Zn film deposition using a vacuum arc plasma source with a refractory anode

The radially expanding plasma plume generated in a Hot Refractory Anode Vacuum Arc was used to deposit thin Al and Zn films on glass substrates. The electrode separation was 10 mm, arc time varied up to 165 s, and current (I) was 100-225 A. The cathode was a water-cooled Al or Zn cylinder. A graphite anode with 9 or 30 mm height was used with the Al cathode, and 10 or 30 mm height Mo anode was used with the Zn cathode. A mechanical shutter controlled the substrate exposure onset and duration (15 s) to the anodic plasma. The distance from the arc axis to the substrate (L) was varied between 80 and 165 mm. The film thickness was measured with a profilometer, and macroparticle (MP) presence on the coating surface was examined by optical microscopy.It was found that the deposition rate increased as a function of time to a peak, and then decreased to a steady-state value. The peak occurred sooner using the 9 mm anode than with the 30 mm anode. The peak deposition rate increased and the peak time decreased with I. The steady-state deposition rate was larger for Zn (~ 2 μm/min) than for Al cathodes (~ 1 μm/min) at I = 225 A and L = 110 mm. The arc voltage for Al was ~ 20-22 V and for Zn it was 11 V. The deposition rate peak appeared due to MPs evaporating from the hot anode, where they had initially condensed during the conventional arc stage when the anode was still cold. This effect was significant with low melting temperature Al and Zn cathodes, and negligible with Cu and Ti cathodes studied previously.     

An investigation on the microstructure and oxidation behavior of laser remelted air plasma sprayed thermal barrier coatings

NiCrAlY bond-coat was coated on Inconel 718 substrate by air plasma spraying (APS) followed by APS ZrO₂-8 wt.%Y₂O₃ as top-coat. Using CO₂ laser of different energy densities, ceramic top-coat surface was remelted. Laser remelting with high energy density (4 J/mm²) produced a dense microstructure over the whole thickness of top-coat, while low energy density (0.67 J/mm²) laser remelting produced a ~ 50 μm thick dense layer on the top-coat surface. It was found that the volume fraction of monoclinic phase decreased from 9% in as-sprayed coating to 4% and 3% after laser remelting with high and low energy density respectively. After isothermal oxidation at 1200 °C for 200 h, the thickness of oxide layer (TGO) in the sample produced by low energy density laser remelting was ~ 5.6 μm, which was thinner than that of oxide layer in as-sprayed (~ 7.6 μm) and high energy density laser remelted (~ 7.5 μm) samples. A uniform and continuous oxide layer was found to develop on the bond-coat surface after low energy density laser remelting. Thicker oxide layer containing Cr₂O₃, NiO and spinel oxides was observed in both as-sprayed and high energy density laser remelted coatings. After cyclic oxidation at 1200 °C for 240 h, the weight gain per unit area of as-sprayed coating was similar to that of high energy density laser remelted coating while a significantly smaller weight gain was found in low energy density laser remelted coating.     

Nanofiltration membrane prepared from polyacrylonitrile ultrafiltration membrane by low-temperature plasma: 5. Grafting of styrene in vapor phase and its application

Low-temperature plasma techniques have widely been used to modify surface properties of polymer membranes. The NF membranes were prepared from PAN UF membrane by Ar low-temperature plasma treatment and subsequent grafting of the monomer styrene in vapor phase. FTIR-ATR spectroscopy, DSC analysis and contact angle measurement were used to characterize the chemical and physical changes of PAN membranes modified by plasma-induced graft polymerization in vapor phase. FTIR spectra and DSC analysis revealed that hydrophobic monomer, styrene, was successfully grafted onto PAN UF membrane surface. DSC analysis also indicated that the average pore size decreased and the pore size distribution was narrowed with increasing graft time. The contact angle measurement results showed that the hydrophobicity of the grafted membrane was significantly increased. The filtration performances including permeation flux (J) and rejection (R) were determined with a mixture containing dewaxed oil (M_w ≈ 450 g/mol) and dewaxing solvent (toluene and methyl ethyl ketone) in the range of temperature. For the feed composition of 83.94 wt.% dewaxed solvent, the solvent in permeate solution was 98.42 wt.%, and the rejection of lube oil was up to 90.2%, which implied that these PAN membranes may be potentially used to recover the dewaxing solvent from the dewaxed lube oil.     

Mechanisms of self-lubrication in patterned TiN coatings containing solid lubricant microreservoirs

The tribological mechanisms of friction and lubrication have been investigated in TiN coatings patterned to contain microscopic reservoirs for solid lubricant entrapment. Photo-lithography was used to fabricate three sets of samples on silicon wafers, varying the reservoir size (4 and 9 μm) and spacing (11 and 25 μm), which resulted in samples with a nominal reservoir area of either 2 or 10%. Pin-on-disk tests were run using lubricants of graphite and indium and counterfaces of alumina and steel (440C). In most cases, the samples with the 9 μm holes spaced 25 μm apart gave the lowest friction coefficients and longest wear life. Analysis of the wear tracks by SEM/EDS methods showed carbon to be present in the holes of the graphite/steel counterface samples, but TiO₂ was found in the holes of the graphite/alumina counterface samples. For the indium/steel counterface samples indium was detected within the microreservoirs, but iron was also found, transferred from the ball. These experiments highlight a variety of tribological mechanisms that can operate in microreservoir-patterned coatings.     

Glass capillary optics for producing nanometer sized beams and its applications

We have developed a method to produce micro/nano meter sized beams of keV energy highly charged ions (HCIs) and MeV energy protons/He ions with tapered glass capillary optics for application of surface modifications and a biological tool called “cell surgery”, respectively. The transmission through the tapered glass capillaries with inlet diameter of 0.8 mm?, outlet diameter from 900 nm? to several tens of microns and length of about 50 mm was performed using 8/64 keV Ar⁸⁺ beams. The transmitted beams had a density enhancement of about 10 and were guided through a capillary tilted by as large as ±100 mrad. The charge state of the beams was kept during the transmission. The combination of MeV proton/He ion beams and the capillary with a thin end window at its outlet can realize pinpoint energy deposition and three-dimensional selection of the bombarding point in an arbitrary position of a living cell or in any liquid object. We demonstrated that a real biological cell, HeLa cell with the nucleus labeled by green fluorescent protein (GFP), was irradiated with the microbeam, which was prepared by 4 MeV He²⁺ entering a capillary with an end window of 7.3 μm in thickness and outlet diameter of 9.6 μm?. The transmitted MeV ion beams had density enhancement up to 1000 according to the capillary outlet sizes, which are applicable to various material analyses employing microbeams.