• Korean Journal of Materials Research
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• v.27 no.12
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• pp.705-709
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• 2017

The electronic and optical characteristics of molybdenum disulphide ($MoS_2$) film significantly vary with its thickness, and thus a rapid and accurate estimation of the number of $MoS_2$ layers is critical in practical applications as well as in basic researches. Various existing methods are currently available for the thickness measurement, but each has drawbacks. Transmission electron microscopy allows actual counting of the $MoS_2$ layers, but is very complicated and requires destructive processing of the sample to the point where it will no longer be useable after characterization. Atomic force microscopy, particularly when operated in the tapping mode, is likewise time-consuming and suffers from certain anomalies caused by an improperly chosen set point, that is, free amplitude in air for the cantilever. Raman spectroscopy is a quick characterization method for identifying one to a few layers, but the laser irradiation causes structural degradation of the $MoS_2$. Optical microscopy works only when $MoS_2$ is on a silicon substrate covered with $SiO_2$ of 100~300 nm thickness. The last two optical methods are commonly limited in resolution to the micrometer range due to the diffraction limits of light. We report here a method of measuring the distribution of the number of $MoS_2$ layers using a low voltage field emission electron microscope with acceleration voltages no greater than 1 kV. We found a linear relationship between the FESEM contrast and the number of $MoS_2$ layers. This method can be used to characterize $MoS_2$ samples at nanometer-level spatial resolution, which is below the limits of other methods.

• Proceedings of the Korean Magnestics Society Conference
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• 2004.12a
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• pp.219-220
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• 2004

Superparamagnetic regions and magnetic anisotropic properties in randomly orientated Co nano dots(NDs) were investigated as a function of dot diameter, spacing, and density. The Co NDs were fabricated by intentionally exposing a laser source on ultra thin film. Various dot sizes are ultimately realized by changing laser power, scan condition, and intial film thickness. Magnetic hysteresis loops, angle-dependent magnetization, and temperature dependence magnetization of the Co NDs were measured with a superconducting quantum interference device. The analysis of magnetization and hysteresis loops was effectively used to determine superparamagnetic regions of the Co NDs. Up to now, the experimentally observed results repeal that room temperature superparamagnetic limit of our Co NDs was about 30 nm in diameter, with the confirmation of high resolution transmission electron microscope.

• Bulletin of the Korean Chemical Society
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• v.34 no.9
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• pp.2737-2740
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• 2013

The layered $KTiNbO_5$ was successfully synthesized with titanium(IV) isopropoxide and niobium oxalate by a novel polymerized complex (PC) method. The morphology and structure of the as-prepared sample was characterized by means of High-Resolution Transmission Electron Microscope, powder X-ray diffraction, and Laser Raman Spectroscopy. The spectral response characteristic was recorded by using UV-vis Diffuse Reflectance Spectroscopy. Results show that $KTiNbO_5$ as-prepared by PC method presents an uniform morphology of nano-particles, the mean particle sizes is ca. 28 nm corresponding to the (002), and the crystal structure can be well indexed to the orthorhombic phase. The sample as-prepared by PC method has higher band gap energy than that of the sample prepared by a solid-state reaction method due to the quantum size effect.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.13-17
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• 2002

Ga$_2$O$_3$ nanomaterials were synthesized from mechanically ground GaN powders with thermal annealing Ga$_2$O$_3$ nanobelts were farmed in a nitrogen atmosphere, while Ga$_2$O$_3$ nanoparticles were formed inan oxygen atmosphere. The structural properties of the Ga$_2$O$_3$ nanomaterials were investigated by X-ray diffractometer (XRD) and high-resolution transmission eleotron microscope (HRTEM). The study of field emission scanning electron microscopy (FESEM) on the microstructures of nanomaterials revealed that the nanobelts are with the range of about 10∼200nm width and 10∼50nm thickness, and that nanoparticles are with the range of about 20∼50nm radius. On the basis of XRD and HRTEM data, we determined that the nanobelts grow toward a direction perpendicular to the (010) lattice plane and that they are enclosed by facets of the (10T) and (101) lattice planes. The formation of the nanobelts may be described by the vapor-solid(VS) mechanism, and the supersaturation device of gaseous phase may play an important role in the formation of Ga$_2$O$_3$ nanomaterials.

• Applied Microscopy
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• v.37 no.4
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• pp.259-269
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• 2007

In this paper we explored a possibility of observation for effects of higher-order Laue zone(HOLZ) reflections on high resolution transmission electron microscope(HRTEM) images for illumination along an off-zone axis of a crystal. The analysis of the observation could give useful three dimensional crystal structure information. For the image simulation the Howie-Whelan equation was used with modification of including HOLZ reflections. This study clearly indicates that HRTEM images for a very thin crystal tilted by a few degrees from a zone axis show the effects of HOLZ reflections and contain some information of atomic arrangements along the zone axis.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.480.1-480.1
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• 2014

In this study, we suggest the new emitter formation applied solid phase epitaxy (SPE) growth process using rapid thermal process (RTP). Preferentially, we describe the SPE growth of intrinsic a-Si thin film through RTP heat treatment by radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD). Phase transition of intrinsic a-Si thin films were taken place under $600^{\circ}C$ for 5 min annealing condition measured by spectroscopic ellipsometer (SE) applied to effective medium approximation (EMA). We confirmed the SPE growth using high resolution transmission electron microscope (HR-TEM) analysis. Similarly, phase transition of P doped a-Si thin films were arisen $700^{\circ}C$ for 1 min, however, crystallinity is lower than intrinsic a-Si thin films. It is referable to the interference of the dopant. Based on this, we fabricated 16.7% solar cell to apply emitter layer formed SPE growth of P doped a-Si thin films using RTP. We considered that is a relative short process time compare to make the phosphorus emitter such as diffusion using furnace. Also, it is causing process simplification that can be omitted phosphorus silicate glass (PSG) removal and edge isolation process.

• Journal of Powder Materials
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• v.24 no.5
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• pp.389-394
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• 2017

Ni wires with a diameter and length of 0.4 and 100 mm, respectively, and a purity of 99.9% are electrically exploded at 25 cycles per minute. The Ni nanopowders are successfully synthesized by a pulsed wire evaporation (PWE) method, in which Ar gas is used as the ambient gas. The characterization of the nanopowders is carried out using X-ray diffraction (XRD) and a high-resolution transmission electronmicroscope (HRTEM). The Ni nanopowders are classified for a multilayer ceramic condenser (MLCC) application using a type two Air-Centrifugal classifier (model: CNI, MP-250). The characterization of the classified Ni nanopowders are carried out using a scanning electron microscope (SEM) and particle size analysis (PSA) to observe the distribution and minimum classification point (minimum cutting point) of the nanopowders.

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.231-234
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• 2000

Vertically aligned carbon nanotubes were synthesized on Ni-coated Si substrates using microwave plasma-enhanced chemical vapor deposition. The grain size of Ni thin films was varied with the RF power density during the RF magnetron sputtering process. It was found that the diameter, growth rate, and density of carbon nanotubes could be controlled systematically by the grain size of Ni thin films. With decreasing the grain size of Ni thin films, the diameter of the nanotubes decreased, whereas the growth rate and density increased. High-resolution transmission electron microscope images clearly demonstrated synthesized nanotubes to be multiwalled. The number of graphitized wall decreased with decreasing the diameter. Field emission properties will be further presented.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1188-1194
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• 2013

Transparent $TiO_2$ thin films have been prepared by sol-gel spin coating method. The sols used for deposition of thin films were prepared with different ethanol content. The effect of ethanol (solvent) concentration and annealing temperature on the performance of $TiO_2$ thin film solar cells has been studied. The results indicate that the as deposited films are amorphous in nature. $TiO_2$ thin films annealed at temperatures above $350^{\circ}C$ exhibited crystalline nature with anatase phase. The results also indicated that the crystallinity of the films improved with increase of annealing temperature. The high resolution transmission electron microscope images showed lattice fringes corresponding to the anatase phase of $TiO_2$. The band gap of the deposited films has been found to decrease with increase in annealing temperature and increase with increase in ethanol concentration. The dependents of photovoltaic efficiency of the dye-sensitized $TiO_2$ thin film solar cells (DSSCs) with the amount of ethanol used to prepare thin films was determined from photocurrent-voltage curves.

• Bulletin of the Korean Chemical Society
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• v.30 no.11
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• pp.2713-2716
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• 2009

$CuInS_{2}$ nanoparticles were synthesized by a simple sonochemical method; First, Cu nanoparticles were prepared from $CuInS_{2}$ in methanol solution by a one pot reaction through the sonochemistry under multibubble sonoluminescence (MBSL) conditions. Second, the resulting Cu nanoparticles were treated with $InCl_3{\cdot}4H_2O$ and $CH_3CSNH_2$ (thioacetamide) at the same MBSL conditions to synthesize $In_2S_3$-coated Cu nanoparticles in methanol solution. Then, they were transformed into $CuInS_{2}$ (CIS) nanoparticles of 20 $\sim$ 40 nm size in diameter by thermal heating at 300 ${^{\circ}C}$ for 2 hr. The prepared CIS nanoparticles, of which band gap is 1.44 eV, were investigated by X-ray diffractometer, UV-Vis spectrophotometer, inductively coupled plasma spectrometer, and high resolution-transmission electron microscope.