• Macromolecular Research
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• v.12 no.4
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• pp.374-378
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• 2004

The biodegradable and biocompatible poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a copolymer of microbial polyester, was fabricated as nanofibrous mats by electrospinning. Image analysis of the electrospun nanofibers fabricated from a 2 wt% 2,2,2-trifluoroethanol solution revealed a unimodal distribution pattern of fiber diameters with an observed average diameter of ca. 185 nm. The fiber diameter of electrospun fabrics could be controlled by adjusting the electro spinning parameters, including the solvent composition, concentration, applied voltage, and tip-to-collector distance. Chondrocytes derived from rabbit ear were cultured on a PHBV cast film and an electrospun PHBV nano-fibrous mat. After incubation for 2 h, the percentages of attached chondrocytes on the surfaces of the flat PHBV film and the PHBV nanofibrous mat were 19.0 and 30.1 %, respectively. On the surface of the electrospun PHBV fabric, more chondrocytes were attached and appeared to have a much greater spreaded morphology than did that of the flat PHBV cast film in the early culture stage. The electro spun PHBV nanofabric provides an attractive structure for the attachment and growth of chondrocytes as cell culture surfaces for tissue engineering.

• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.3981-3986
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• 2012

Anatase nanocrystalline and its tungsten-doped (0.4, 2, and 4 mol %) powders have been synthesized by microwave irradiation through hydrolysis of titanium tetra-isopropoxide (TIP) in aqueous solution. The materials are characterized by XRD, Raman, SEM-EDX, TEM, FT-IR and UV-vis techniques. The nanocrystalline $TiO_2$ particles are 30 nm in nature and doping of tungsten ion decreases their size. As seen in TEM images, the crystallites of W (4 mol %) doped $TiO_2$ are small with a size of about 10 nm. The photocatalytic activity was tested on the degradation of 4-nitrophenol (4-NP). Catalytic activities of W-doped and pure $TiO_2$ were also compared. The results show that the photocatalytic activity of the W-doped $TiO_2$ photocatalyst is much higher than that of pure $TiO_2$. Degradation decreases from 96 to 50%, during 115 min, when the initial 4-NP concentration increases from 10 to 120 ppm. Maximum degradation was obtained at 35 mg of photocatalyst.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.12 s.255
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• pp.1611-1617
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• 2006

A compact and two-dimensional atomic force microscope (AFM) using an orthogonal sample scanner, a calibrated homodyne laser interferometer and a commercial AFM head was developed for use in the nano-metrology field. The x and y position of the sample with respect to the tip are acquired by using the laser interferometer in the open-loop state, when each z data point of the AFM head is taken. The sample scanner which has a motion amplifying mechanism was designed to move a sample up to $100{\times}100{\mu}m^2$ in orthogonal way, which means less crosstalk between axes. Moreover, the rotational errors between axes are measured to ensure the accuracy of the calibrated AFM within the full scanning range. The conventional homodyne laser interferometer was used to measure the x and y displacements of the sample and compensated via an X-ray interferometer to reduce the nonlinearity of the optical interferometer. The repeatability of the calibrated AFM was measured to sub-nm within a few hundred nm scanning range.

• Journal of the Korean Society of Combustion
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• v.21 no.2
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• pp.7-14
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• 2016

Evaporation and combustion characteristics of fuel droplet with carbon nanoparticle were investigated in a rapid compression machine(RCM). RCM is an experimental equipment to simulate one compression stroke of reciprocating engine. Nitrogen was charged into reaction chamber for evaporation experiment, while oxygen was charged for combustion experiment. N990 carbon black and n-heptane were used to synthesize the carbon nanofluids. Surfactant, span80, was used to make synthesis easier. The droplet pictures were taken using a high speed camera with 500 frames per second. Thermocouple, of which tip is $50{\mu}m$, was used not only to measure transient bulk temperature, but also to suspend the droplet. Reaction chamber temperature was calculated from pressure data. The evaporation rate of nanofluids was improved compared to pure fuel. The ignition delay was promoted due to the nanoparticle, but the burning rate was decreased.

• Korean Journal of Metals and Materials
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• v.48 no.9
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• pp.861-866
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• 2010

Tetrapod-shaped ZnO crystals were synthesized through a simple oxidation of metallic Zn powder in air without the presence of any catalysts or substrates. X-ray diffraction data revealed that the ZnO crystals had wurtzite structure. It is supposed that the growth of the tetrapod proceeded in a vapor-solid growth mechanism. As the amount of the source powder increased, the size of the tetrapod decreased. The tip morphology of the tetrapod changed from a needle-like shape to a spherical shape with the oxidation time. ZnO crystals with rod shape were fabricated via the oxidation of Zn and Sn mixture. Sn played an important role in the formation of ZnO crystals with different morphology by affecting the growth mode of ZnO crystals. The cathodoluminescent properties were measured for the samples. The strongest green emission was observed for the rod-shaped ZnO crystals, suggesting that the crystals had the high density of oxygen vacancies.

• Journal of the Korean institute of surface engineering
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• v.57 no.2
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• pp.71-85
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• 2024

This article provides an overview of Raman spectroscopy and its practical applications for surface analysis of semiconductor processes including real-time monitoring. Raman spectroscopy is a technique that uses the inelastic scattering of light to provide information on molecular structure and vibrations. Since its inception in 1928, Raman spectroscopy has undergone continuous development, and with the advent of SERS(Surface Enhanced Raman Spectroscopy), TERS(Tip Enhanced Raman Spectroscopy), and confocal Raman spectroscopy, it has proven to be highly advantageous in nano-scale analysis due to its high resolution, high sensitivity, and non-destructive nature. In the field of semiconductor processing, Raman spectroscopy is particularly useful for substrate stress and interface characterization, quality analysis of thin films, elucidation of etching process mechanisms, and detection of residues.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.4
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• pp.145-150
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• 2014

GaN nanorods were grown on the apex of GaN stripes by three dimensional selective growth method. $SiO_2$ mask was partially removed only on the apex area of the GaN stripes by an optimized photolithography for the selective growth. Metallic Au was deposited only on the apex of the GaN stripes and a selective growth of GaN nanorods was followed by a metal organic vapor phase epitaxy (MOVPE). We confirmed that the shape and size of the GaN nanorods depend on growth temperature and flow rates of group III precursor. GaN nanorods were grown having a taper shape which have sharp tip and triangle-shaped cross section. From the TEM result, we confirmed that threading dislocations were rarely observed in GaN nanorods because of the very small contact area for the selective growth. Stacking faults which might be originated from a difference of the crystal facet directions between the GaN stripe and the GaN nanorods were observed in the center area of the GaN nanorods.

• Journal of the Korean Vacuum Society
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• v.20 no.3
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• pp.211-216
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• 2011

In this study, the effects of growth temperature on structural and optical properties of hydrothermally grown ZnO nanorod arrays have been investigated. Zinc nitrate ($Zn(NO_3)_2$) and hexamethylenetetramine were used as precursors. The ZnO buffered Si(100) with a thickness of 40 nm was used as the substrates. The ZnO nanorods were grown on these substrates with the temperature ranging from 55 to $115^{\circ}C$. The results were characterized by scanning electron microscope, X-ray diffraction and room temperature photoluminescence measurements. Well-aligned ZnO nanorods arrays were obtained from all samples. The tips of nanorods were flat when the temperature was less than $95^{\circ}C$, and the sharp-tip nanoneedle-like morphologies were obtained with the temperature of $115^{\circ}C$. In addition, some bundles were on the nanorods arrays with $115^{\circ}C$ due to the non-equilibrium growth. The growth temperature could affect the crystal and optical properties of ZnO. For the effects on crystal properties, the intensity of (002) peak was increased as the temperature was increased to $75^{\circ}C$, then decreased as the temperature was further increased to $115^{\circ}C$. As for the effects on optical properties, the intensity ratio of UV peak to visible peak is increased with the temperature increasing and the strongest UV peak intensity was obtained with the growth temperature of $95^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.117-123
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• 2012

This paper discusses two different techniques used to measure the mechanical properties of thin films: the bulge test and the nanoindentation test. In the bulge test, a uniform pressure is applied to one side of the film. Measurement of the membrane deflection as a function of the applied pressure allows one to determine the mechanical properties such as Young's modulus, and the residual stress. A nanoindentation test is performed by pushing an indenter tip into the specimen and then withdrawing it, and then recording the indentation force as a function of the indenter position. A modified King's model is used to estimate the mechanical properties of the thin film in order to avoid the effects of the substrate layers. A combination of both the bulge test and the nanoindentation test can determine both Young's modulus and Poisson's ratio simultaneously.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.12
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• pp.1171-1176
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• 2012

The selective patterning of a carbon nanotube (CNT) forest on a Si substrate has been performed using a femtosecond laser. The high shock wave generated by the femtosecond laser effectively removed the CNTs without damage to the Si substrate. This process has many advantages because it is performed without chemicals and can be easily applied to large-area patterning. The CNTs grown by plasma-enhanced chemical vapor deposition (PECVD) have a catalyst cap at the end of the nanotube owing to the tip-growth mode mechanism. For the application of an electron emission and biosensor probe, the catalyst cap is usually removed chemically, which damages the surface of the CNT wall. Precise control of the femtosecond laser power and focal position could solve this problem. Furthermore, selective CNT cutting using a femtosecond laser is also possible without any phase change in the CNTs, which is usually observed in the focused ion beam irradiation of CNTs.