Jihun Mun

Low-temperature growth of layered molybdenum disulphide with controlled clusters

Layered molybdenum disulphide was grown at a low-temperature of 350 °C using chemical vapour deposition by elaborately controlling the cluster size. The molybdenum disulphide grown under various sulphur-reaction-gas to molybdenum-precursor partial-pressure ratios were examined. Using spectroscopy and microscopy, the effect of the cluster size on the layered growth was investigated in terms of the morphology, grain size, and impurity incorporation. Triangular single-crystal domains were grown at an optimized sulphur-reaction-gas to molybdenum-precursor partial-pressure ratio. Furthermore, it is proved that the nucleation sites on the silicon-dioxide substrate were related with the grain size. A polycrystalline monolayer with the 100-nm grain size was grown on a nucleation site confined substrate by high-vacuum annealing. In addition, a field-effect transistor was fabricated with a MoS2 monolayer and exhibited a mobility and on/off ratio of 0.15 cm2 V−1 s−1 and 105, respectively.

Sensor based on chemical vapour deposition-grown molybdenum disulphide for gas sensing application

Over the past few decades, sensors based on field-effect transistors have drawn much attention. Initially three dimensional materials were used for sensing, which were later replaced by two dimensional materials because of their ease of manufacturing and large specific areas. Amongst the transition metal dichalcogenides, MoS2 has been widely used for the fabrication of sensors owing to its ability to differentiate between a charge donor and an acceptor analyte. In this work, we fabricated sensors using chemical vapour deposition grown-MoS2. MoS2 was grown on a p-Si/SiO2 substrate using Mo(CO)6 as a precursor, the growth was carried out by the sublimation of the precursor under a flow of high purity H2S at high temperature. The aim of this work is to achieve a level of sensitivity that would enable the detection of individual gas analytes upon adsorption to the MoS2 surface. To efficiently detect individual gas analytes upon adsorption to the surface, we used interdigitated electrodes in the device architecture to increase the area of the channels for analyte adsorption. We used CO2 and O2 gases, which acted as charge donors. A trilayer MoS2 film was examined, and the detection sensitivity for O2 was higher in comparison to CO2. The fabricated device showed significant sensitivity up to parts per million detection level.

Development of particle characteristics diagnosis system for nanoparticle analysis in vacuum

A particle characteristics diagnosis system (PCDS) was developed to measure nano-sized particle properties by a combination of particle beam mass spectrometry, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDS). It allows us to measure the size distributions of nano-sized particles in real time, and the shape and composition can be determined by in situ SEM imaging and EDS scanning. PCDS was calibrated by measuring the size-classified nano-sized NaCl particles generated using an aqueous solution of NaCl by an atomizer. After the calibration, the characteristics of nano-sized particles sampled from the exhaust line of the plasma-enhanced chemical vapor deposition process were determined using PCDS.

Controlled Synthesis of Horizontal Silicon Nanowires for Biosensor Application

Top-down silicon nanowire (SiNW) fabrication mechanisms for connecting electrodes are widely utilized because they provide good control of the diameter to length ratio. The representative mechanism for the synthesis of SiNWs, a top-down approach, has limitations on the control of their diameter following lithography technologies, requires a long manufacturing process and is not cost-effective. In this study, we have implemented the bottom-up growth of horizontal SiNWs(H-SiNWs) on Si/SiO2 substrates directly by plasma enhanced chemical vapor deposition (PECVD) under about 400°C. The HAuCl4 solution as a catalyst and SiH4 gas as a precursor are used for the synthesis of H-SiNWs. After optimization of synthesis conditions, we evaluated the photoelectric properties of the H-SiNWs under illumination with different light intensities. Further, we demonstrated the feasibility of H-SiNW devices for the detection of biotinylated DNA nanostructures and streptavidin interaction.

Measurement of the Particle Current Changes Associated with the Flatness of Deflector Mesh Surface in Particle Beam Mass Spectrometer System

Advanced Device Technology, University of Science & Technology, 305-350, Daejeon, KoreaReceived March 19, 2016; revised March 31, 2016; accepted March 31, 2016Abstract The surface flatness of metal meshes in a deflector of particle beam mass spectrometer (PBMS) requiredideally flat, and this can specify the particle trajectories which goes through the detector. In this research, chargedparticle current was measured using the different surface roughness deflectors. NaCl particles were generatedmonodispersed in its size by using differential mobility analyzer and the whole processes were followed the waycalibrating PBMS. The results indicate that the mesh surface morphology in the deflector can affect to the particle sizeand the concentration errors, and sensitivity of PBMS.Keywords: PBMS, Deflector, Nickel mesh, Electric field, Flatness

Theoretical analysis for quantitative evaluation of in-situ nanoparticle measurement probability.

A probability equation based on the proper assumptions of the particle trajectory and fundamental physics has been developed by analyze beam properties such as beam width and intensity distribution for an in situ particle monitor (ISPM). The radius coordinate which has the same intensity and portion of beam area for detection voltage range were analyzed to calculate particle measurement probability. The particle measurement probability is defined at a ratio of entire beam area to specified beam area which decided by detection voltage range. A probability measurement, given as a function of the detection voltage range, was performed 5 times using 200, 300, 500, 700 nm polystyrene latex standard particles at a pressure of 100 Torr with an in-house ISPM. The theoretical calculation results show good agreement with the experimental results and the maximum error is 20% by calculating probability differences between theoretical and experimental values. A calibration method based on the proposed probability equation enables to developed and increase accuracy of ISPM.