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Based on electron backscatter diffraction (EBSD), hollow structures of Ni foam struts fabricated by electroplating on a chemically removable template were observed. Three-dimensional (3D) pore structures of Ni foams were also obtained using X-ray computed tomography (CT), and microstructural features such as porosity, pore size and strut thickness were statistically quantified. Evolution of microstructure and mechanical properties during ex situ compression of open-cell Ni-foams was investigated based on X-ray CT, and experimental results were compared with predictions by the finite element method (FEM). 3D microstructures obtained by X-ray CT revealed that the stress drop started with the buckling of struts at the center of the Ni-foams. The flow stress increased after the buckling of the struts spreads to most of the regions. For effective simulation of the compressive deformation and determination of the microstructural evolution, small domains of interest were selected from the entire set of observed 3D microstructures based on X-ray CT, and struts of Ni foams with a hollow structure were simplified with relevant thin-solid struts. Numerical 3D modeling comprehensively disclosed that compression caused the transverse buckling of the struts, with the bending and buckling of struts thus reducing the stress. Thickness variation of the struts causes a change in the porosity of Ni-foams without a change in pore shape or connectivity. The overall range of strut thickness was from 59 to 133 μm, and the range of porosity values was from 80% to 93.7%. A stress drop was predicted with a decrease in the strut thickness or an increase in the porosity, as measured experimentally. It was also found that the stress drop contributed to an increase in the calculated energy absorption efficiency.

Broadband light absorbers are highly desirable in various applications including solar-energy harvesting, thermo-photovoltaics, and photon detection. The Fabry–Perot (F–P) cavity comprising metal–i...

Vanadium oxide (V 2 O 5-x ) thin films with a thickness of about 4 nm were prepared by atomic layer deposition (ALD) to be used as a hole-transporting layer in an amorphous silicon solar cell. The ALD growth characteristics (growth rate, crystallinity, and surface morphology) of the V 2 O 5-x films were investigated while exposed to different pulse times of ozone (O 3 ), which was used as an oxidant. The effect of the different ozone pulse times, used in the V 2 O 5 layer, on the device performance was also investigated. At the ozone pulse time of 1 s, the maximum value of power conversion efficiency (PCE), i.e., 5.35%, was achieved, whereas at the ozone pulse time of 5 s, the PCE was 4.18%. Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) analyses confirmed that increasing the proportion of crystalline phase in the V 2 O 4 films with lower work function of V 2 O 5 resulted in decreased open-circuit voltage and conversion efficiency as the ozone pulse time increased.

The esthetic functions of metals are becoming increasingly significant, as their application fields are rapidly extending into mobile electronics, home appliances, surface decoration/art, and building interiors. Herein we present a simple surface structure that produces vivid structural colors on stainless steel (STS). The structure consists of a thin metal layer deposited on a dielectric film, in which the metal layer can adjust the amount of light incident onto the dielectric and strengthens the interference effect. A wide variety of colors, including blue, green, pink, purple, scarlet, and yellow, are produced simply by changing the thicknesses of the dielectric and metal layers. An important finding is that the refractive indices of the thermally evaporated Ag and Au layers are strongly thickness-dependent, which allows color tuning by varying the thickness of the metal layer only. Consequently, color images can also be printed by selectively depositing a metal layer (Au or Ag) on a uniform dielectric film. The results of this study provide a simple, scalable route to produce vivid structural colors on bulk metals and may find diverse applications, including surface decoration, product identification, perfect absorbers, and reflective color filters.

In this study, a novel process was developed for the fabrication of ultrafine electrodes on flexible substrates. Conductive fine electrodes using silver nano-ink on polyimide (PI) film were obtained by means of plasma-enhanced superhydrophobic technology. The plasma etching conditions were optimized for the formation of a superhydrophobic layer on the surface of the PI film. A micro-trench on the hydrophobic PI film was then formed by mechanical scratching, thus imparting hydrophilic properties only to the trench area. Finally, the fine electrode was realized by the selective deposition of aqueous silver nano-ink on the trench region. The electrical properties of the conductive electrodes fabricated using silver nano-ink with an average particle size of 50 or 200 nm were investigated and the microstructure of the electrodes was observed using an electron microscope at sintering temperatures ranging from 150 to 400 °C. In addition, the addition effect of silver nanowire to silver nano-ink was examined to assess the improvement on the conductive properties of electrode.

This study is carried out to develop the new process for the fabrication of ultra-fine electrodes on the flexible substrates using superhydrophobic effect. A facile method was developed to form the ultra-fine trenches on the flexible substrates treated by plasma etching and to print the fine metal electrodes using conductive nano-ink. Various plasma etching conditions were investigated for the hydrophobic surface treatment of flexible polyimide (PI) films. The micro-trench on the hydrophobic PI film fabricated under optimized conditions was obtained by mechanical scratching, which gave the hydrophilic property only to the trench area. Finally, the patterning by selective deposition of ink materials was performed using the conductive silver nano-ink. The interface between the conductive nanoparticles and the flexible substrates were characterized by scanning electron microscope. The increase of the sintering temperature and metal concentration of ink caused the reduction of electrical resistance. The sintering temperature lower than resulted in good interfacial bonding between Ag electrode and PI film substrate.

Poly(ethylene terephthalate) and poly(imide) surfaces pre-treated by plasma were modified by two-step plasma, and the plasma modified film surface were investigated with scanning probe microscopy, X-ray photoelectron spectroscopy, and contact-angle and surface energy to characterize the surfaces. The surface energies were calculated from measured contact angles between several solutions and film-based on geometric means and the Lewis acid-base method. The exposure of the PET and PI film surfaces pre-treated by plasma to the two-step plasma led to the decrease in surface roughness and increase of the contact angles of film in water and surfactant solution. Primarily because of the contribution of polar force, the surface energy and hydrophilicity of PET and PI film treated by plasma decreased greatly. Electron spectroscopy for chemical analysis (ESCA) indicated that the plasma treatment introduced fluorine functional groups led to a decrease of the surface energy and hydrophilicity of PET and PI film.

As a solid lubricant, silver-palladium (Ag-Pd) alloy coating was investigated for the application to high temperature stud bolt. A glue layer nickel (Ni) film was deposited on the surface of the hex bolt sample and then Ag-Pd alloy coating was performed on it using ion plating method. The friction coefficient of Ag-Pd alloy film coated bolt was lower than that of N-5000 oil coated bolt by the result of axial force measurement. The cyclic test of heat treatment was conducted to evaluate the durability of Ag-Pd alloy film coated bolt. In a cycle, sample was assembled into the block using torque wrench, followed by heating and disassembling. It was not successful to disassemble the N-5000 oil coated bolt from the block after only one cycle. However, the Ag-Pd alloy film coated bolt was able to be disassembled softly till 12 cycles.

This study was a preliminary investigation of the influence of surface characteristics of substrates on the detergency of particulate soil. A PET film was surface modified with NaOH and DMF for different times. The surface morphology of the film was scanned by AFM and the surface energies were calculated from the measured contact angles between several solutions and film based on a geometric mean and the Lewis acid base method. The surface morphology of the PET film treated with NaOH and DMF became more etched and swelled with an increased treatment time, respectively. The surface roughness and surface area of film treated with NaOH enlarged with increased treatment time. However, the coefficient of friction of film treated with NaOH and coefficient of friction, surface roughness, and surface area of film treated with DMF increased and then decreased with increased treatment time. The contact angle of film treated with DMF decreased with increased treatment time in water and surfactant solution; however, the effect of treatment time on the contact angle was different in both solutions for film treated with NaOH. By the treatment of PET film with NaOH and DMF, the polar group of the surface energy increased and the nonpolar group decreased; however, the change of total surface energy was not significant.

Multi-layer diamond-like carbon (DLC) coating, 150 and 220 nm thick were deposited by negative pulsed d.c. bias induced with magnetron sputtering. The objective of this research is to resolve a wear resistance in terms of DLC coating residual stress and mechanical properties. The bias was controlled from - 200 to 0 V during 10 second with point contacting controller. The surface structure was continuously fabricating to soft and hard-layer during deposition. It was shown that the compressive residual stress and hardness were 0.09, 18 GPa under multi-layer coating condition. The as-deposited DLC coating has a relatively higher wear resistance than unmodified DLC under nanoabrasive wear. It also showed that multi-layer DLC coating had no wear until 400 nN. The decreased residual stress and increased film hardness in the multi-layer coating gave a rise to increase wear resistance.

The silver-palladium(Ag-Pd) alloy coating as a solid lubricant was investigated for its application to the high temperature stud bolts used in nuclear power plants. A hex bolt sample was prepared in the following steps: 1) bolt surface treatment using alumina grit blasting for cleaning and increasing the surface area; 2) nickel(Ni) film coating as a glue layer on the surface of the bolt; and 3) Ag-Pd alloy coating on the Ni film. The films were deposited by using a direct current(DC) magnetron sputtering system. The thickness and composition of the Ag-Pd alloy film have effect on the friction coefficient, which was determined using axial force measurement. A 500 nm-thick Ag-Pd (80:20, molar ratio) alloy film has the lowest friction coefficient of 0.109. A cyclic test was conducted to evaluate the durability of bolts coated with either the Ag-Pd (80:20) alloy film or N-5000 oil. In a cycle, the bolts were inserted into a block using a torque wrench, which was followed by heating and disassembling. After only one cycle, it was not possible to remove the bolts coated with the N-5000 oil from the block. However, the bolts coated with the Ag-Pd (80:20) alloy could be easily removed up until 15 cycles.

Super-hydrophobic surfaces showed that contact angle of water was higher than 140 degrees. That surface could be made several methods such as Carbon nano tubes grown vertically, PDMS asperities arrays, hydrophobic fractal surfaces, and self assembled monolayers coated by CVD and so on. However, we fabricated super-hydrophobic surfaces with plasma treatments which were very cost efficient processes. Their surfaces were characterized by static contact angles, advancing, receding, and stability against UV irradiation. Optimal surfaces showed static contact angles were higher than 150 degrees. Super-hydrophobic property was remained after UV irradiation for one week. 1. 서 론 초소수성은 여러 산업 분야에서 관심을 끄는 표면특성이다. 이는 연꽃잎에서 보이는 자정효과를 분석하여 응용하려는 연구에서 시도 되었으며, 그 응용사례는 페인트, (1) 자동차용 유리, (2) 의류 3) , 오염되지 않는 표면 4) 등 다양하다. 이러한 초소수성 표면을 얻기 위하여 여러 가지 방법으로 제조되어 왔으며 5)~9) 최근에는 단분자막 코팅을 통해서도 얻을 수 있는 것으로 알려지고 있다. (10) 이에 대한 이론적인 연구는 1932년 Wenzel (11) 등이 주축이 되어 왁스의 표면 형상에 따른 물의 접촉각 거동을 연구한 것이 시초가 된다.

In this work, molybdenum and tungsten ions were implanted onto the DLC films deposited by filtered cathodic vacuum arc. We investigated the effects of ion species and doses on carbon related bonding property such as the ratio of sp 3 carbon to sp 2 phase, the chemical composition and tribological properties of the DLC films in the range of 200 to 600 °C. The oxidation starting temperature decreased with an increasing ion dose and ion mass owing to higher sp 2 carbon fraction. Oxidation of the implanted-metal element, however, keeps the DLC film from carbon sublimation by oxidation, offering stable tribological characteristics by covering it with a metal oxide layer at the high temperature.

Cr–Al–N, Cr–Si–N, Cr–Al–Si–N coatings were successfully deposited on WC–Co substrates by a hybrid coating system combining an arc ion plating technique using Cr target, and a magnetron sputtering method using Al and Si targets under N 2 /Ar atmosphere. XRD, HRTEM, and XPS analyses revealed that the synthesized Cr–Al–N coatings consisted of solid-solution (Cr,Al)N crystallites, and the Cr–Si–N and Cr–Al–Si–N coatings with Si content of ∼ 9 at.% were fine composites consisting of (Cr,Si)N and (Cr,Al,Si)N crystallites, respectively, embedded in an amorphous Si 3 N 4 /SiO 2 matrix. The hardness values of the Cr–Si–N (∼ 35 GPa) and the Cr–Al–Si–N (∼ 55 GPa) coatings were significantly increased compared with those of CrN (∼ 23 GPa) and Cr–Al–N (∼ 25 GPa) coatings. Besides, the average friction coefficients of the Cr–Si–N (∼ 0.30) and the Cr–Al–Si–N (∼ 0.57) coatings with Si content of about 9 at.% were largely decreased compared with those of CrN (∼ 0.50) and Cr–Al–N (∼ 0.84) coatings. A comparative study on microstructural characteristics among Cr–Al–N, Cr–Si–N, and Cr–Al–Si–N coatings is reported in this paper.

The so-called ‘black’ layer between PVD TiN coating and an ion nitrided surface was observed by SEM and TEM to investigate the detailed microstructure of the interface and the delamination mechanism of the TiN film. Two distinct sublayers were observed in the black layer. The upper sublayer was of very fine grains and the lower region of 10 times larger grains. The fine grains were irregular and around 50 nm in size. The larger grains of the lower sublayer were similar to the compound layer underneath. A Ti-based film was deposited on the surface of the black layer during Ti ion bombardment in a cathodic arc ion plating method and identified as TiN and Ti phase. The TiN film deposited during Ti ion bombardment was of a very fine grain size and had a strong preferential arrangement of (200) plane perpendicular to the surface. A lot of pores were observed along the interface between the TiN film and the upper sublayer. It is suggested that the cracking and delamination of the TiN film be initiated at these pores during the scratch adhesion test, which thereby decreased the adhesion strength of the TiN film.

In order to investigate the interfacial structure between TiN and iron nitride, an AISI 4140 steel was nitrided to form a layer of thickness 15 μm by DC ion nitriding, then the surface was bombarded with Ti ions and subsequently coated a TiN film of 5 μm by arc ion plating method. The interfacial microstructure between TiN and iron nitride was characterized by optical microscope, SEM and XRD. The so-called `black' layer was observed in the duplex treatment. It resulted from the decomposition of iron nitride during the bombardment. Its thickness was increased with increasing bombardment time at high bias voltage. But the thickness was greatly decreased when the iron nitride was bombarded with a nitrogen gas or at a reduced bias voltage. The adhesion strength of the top TiN coating was decreased with increasing thickness of the black layer. Furthermore, the reduced adhesion strength in this system was discussed in view of the interfacial structural relationship between TiN and iron nitride.

Cubic boron nitride (c-BN) is one of the hardest known materials (second after diamond). It has a high level of chemical resistance and high UV transmittance. In this study, a stamp for ultra-violet nanoimprint lithography (UV-NIL) was fabricated using a bi-layered BN film deposited on a quartz substrate. Deposition of the BN was done using RF magnetron sputtering. A hexagonal boron nitride (h-BN) layer was deposited for 30 min before c-BN was deposited for 30 min. The thickness of the film was measured as 160 nm. The phase of the c-BN layer was investigated using Fourier transform infrared (FTIR) spectrometry, and it was found that the c-BN layer has a 40% cubic phase. The deposited film was patterned using focused ion beam (FIB) lithography for use as a UV-NIL stamp. Line patterns were fabricated with the line width and line distance set at 150 and 150 nm, respectively. The patterning process was performed by applying different currents to observe the effect of the current value on the pattern profile. The fabricated patterns were investigated using AFM, and it was found that the pattern fabricated by applying a current value of 50 picoamperes (pA) has a better profile with a 65 nm line depth. The UV transmittance of the 160 nm thick film was measured to be 70–86%. The hardness and modulus of the BN was measured to be 12 and 150 GPa, respectively. The water contact angle of the stamp surface was measured at 75°. The stamp was applied to UV-NIL without coating with an anti-adhesion layer. Successful imprinting was proved via scanning electron microscope (SEM) images of the imprinted resin.

A cubic δ-TaN thin film with an electrical resistivity of 400 μΩ cm was successfully obtained by suppressing the formation of Ta 3 N 5 using two-step atomic layer deposition independent of NH 3 dosage. The deposition cycle involved two chemical reaction steps: The formation of elemental tantalum (Ta) by reducing tantalum pentafluoride (TaF 5 ) with hydrogen plasma and the subsequent nitridation of the preformed Ta with NH 3 at 200―350°C. The microstructure of the preformed Ta was β-Ta phase with an electrical resistivity of 220 μΩ cm, which was formed without regard to the deposition temperature. At a deposition temperature of less than 250°C, cubic δ-TaN with a Ta/N ratio of I was achieved independent of the NH 3 dosage. However, at a deposition temperature of greater than 300°C, the resistivity of Ta―N-based thin film increased abruptly as the NH 3 dosage exceeded 16.08 × 10 19 molecules/cm 3 due to the formation of Ta 3 N 5 .