• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.251-251
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• 2016

For several decades, industrial processes consume a huge amount of raw water for various objects that consequently results in the generation of large amounts of wastewater. Wastewaters are consisting of complex mixture of different inorganic and organic compounds and some of them can be toxic, hazardous and hard to degrade. These effluents are mainly treated by conventional technologies such are aerobic and anaerobic treatment and chemical coagulation. But, these processes are not suitable for eliminating all hazardous chemical compounds form wastewater and generate a large amount of toxic sludge. Therefore, other processes have been studied and applied together with these techniques to enhance purification results. These include photocatalysis, absorption, advanced oxidation processes, and ozonation, but also have their own drawbacks. In recent years, electrochemical techniques have received attention as wastewater treatment process that could be show higher purification results. Among them, boron doped diamond (BDD) attract attention as electrochemical electrode due to good chemical and electrochemical stability, long lifetime and wide potential window that necessary properties for anode electrode. So, there are many researches about high quality BDD on Nb, Ta, W and Si substrates, but, their application in effluents treatment is not suitable due to high cost of metal and low conductivity of Si. To solve these problems, Ti has been candidate as substrate in consideration of cost and property. But there are adhesion issues that must be overcome to apply Ti as BDD substrate. Al, Cu, Ti and Nb thin films were deposited on Ti substrate to improve adhesion between substrate and BDD thin film. In this paper, BDD films were deposited by hot filament chemical vapor deposition (HF-CVD) method. Prior to deposition, cleaning processes were conducted in acetone, ethanol, and isopropyl alcohol (IPA) using sonification machine for 7 min, respectively. And metal layer with the thickness of 200 nm were deposited by DC magnetron sputtering (DCMS). To analyze microstructure X-ray diffraction (XRD, Bruker gads) and field emission scanning electron microscopy (FE-SEM, Hitachi) were used. It is confirmed that metal layer was effective to adhesion property and improved electrode property. Electrochemical measurements were carried out in a three electrode electrochemical cell containing a 0.5 % H2SO4 in deionized water. As a result, it is confirmed that metal inter layer heavily effect on BDD property by improving adhesion property due to suppressing formation of titanium carbide.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.65-65
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• 2015

In this talk, I will introduce two topics. The first topic is the polymer light emitting diodes (PLEDs) using graphene oxide quantum dots as emissive center. More specifically, the energy transfer mechanism as well as the origin of white electroluminescence in the PLED were investigated. The second topic is the facile synthesis of eco-friendly III-V colloidal quantum dots and their application to light emitting diodes. Polymer (organic) light emitting diodes (PLEDs) using quantum dots (QDs) as emissive materials have received much attention as promising components for next-generation displays. Despite their outstanding properties, toxic and hazardous nature of QDs is a serious impediment to their use in future eco-friendly opto-electronic device applications. Owing to the desires to develop new types of nanomaterial without health and environmental effects but with strong opto-electrical properties similar to QDs, graphene quantum dots (GQDs) have attracted great interest as promising luminophores. However, the origin of electroluminescence (EL) from GQDs incorporated PLEDs is unclear. Herein, we synthesized graphene oxide quantum dots (GOQDs) using a modified hydrothermal deoxidization method and characterized the PLED performance using GOQDs blended poly(N-vinyl carbazole) (PVK) as emissive layer. Simple device structure was used to reveal the origin of EL by excluding the contribution of and contamination from other layers. The energy transfer and interaction between the PVK host and GOQDs guest were investigated using steady-state PL, time-correlated single photon counting (TCSPC) and density functional theory (DFT) calculations. Experiments revealed that white EL emission from the PLED originated from the hybridized GOQD-PVK complex emission with the contributions from the individual GOQDs and PVK emissions. (Sci Rep., 5, 11032, 2015). New III-V colloidal quantum dots (CQDs) were synthesized using the hot-injection method and the QD-light emitting diodes (QLEDs) using these CQDs as emissive layer were demonstrated for the first time. The band gaps of the III-V CQDs were varied by varying the metal fraction and by particle size control. The X-ray absorption fine structure (XAFS) results show that the crystal states of the III-V CQDs consist of multi-phase states; multi-peak photoluminescence (PL) resulted from these multi-phase states. Inverted structured QLED shows green EL emission and a maximum luminance of ~45 cd/m2. This result shows that III-V CQDs can be a good substitute for conventional cadmium-containing CQDs in various opto-electronic applications, e.g., eco-friendly displays. (Un-published results).

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.188.2-188.2
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• 2015

The presence of the conduction interface in epitaxial $LaAlO_3/SrTiO_3$ thin films has opened up challenging applications which can be expanded to next-generation nano-electronics. The metallic conduction path is associated with two adjacent insulating materials. Such device structure is applicable to frequency-dependent impedance spectroscopy. Impedance spectroscopy allows for simultaneous measurement of resistivity and dielectric constants, systematic identification of the underlying electrical origins, and the estimation of the electrical homogeneity in the corresponding electrical origins. Such unique capability is combined with the intentional control on the interface composition composed of $SrTiO_3$ and $CaTiO_3$, which can be denoted by $SrxCa1-_xTiO_3$. The underlying $Sr_xCa1-_xTiO_3$ interface was deposited using pulsed-laser deposition, followed by the epitaxial $LaAlO_3$ thin films. The platinum electrodes were constructed using metal shadow masks, in order to accommodate 2-point electrode configuration. Impedance spectroscopy was performed as the function of the relative ratio of Sr to Ca. The respective impedance spectra were analyzed in terms of the equivalent circuit models. Furthermore, the impedance spectra were monitored as a function of temperature. The ac-based characterization in the 2-dimensional conduction path supplements the dc-based electrical analysis. The artificial manipulation of the interface composition will be discussed towards the electrical application of 2-dimensional materials to the semiconductor devices in replacement for the current Si-based devices.

• Journal of the Korean Vacuum Society
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• v.18 no.3
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• pp.236-243
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• 2009

Proton Engineering Frontier Project (PEFP) has supplied the metal ions to users by using an installed metal ion implanter of 120 keV. At present a feasibility study is being performed for a cobalt ion implantation. For a cobalt ion extraction we studied to sustain the high temperature($648^{\circ}C$) for metal ions vaporization from a cobalt chloride powder by using an alumina crucible in the ion source. The temperature condition of the crucible was satisfied with the plasma generation at the arc current of 120V and EHC power of 250W. The extracted beam current of $Co^+$ ions was dependent on the arc current in the plasma. The maximum beam current was $100{\mu}A$ at 0.18A of the arc current. The 3 peak currents of the extracted ions such as $Co^+$, $CoCl^+$ and $Cl^+$ were obtained by adjusting a mass analyzing magnet and the $Co^+$ ion beam peak current fraction as around 70% in the sum of the peak currents. The fluence of the implanted cobalt ions at the $10{\mu}A$ of the beam current and 90 minutes of the implantation time into an aluminum sample as measured around $1.74{\times}10^{17}#/cm^2$ by a quantitative analysis method of RBS (Rutherford Backscattering Spectrometry).

• Journal of the Korean Vacuum Society
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• v.22 no.3
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• pp.111-118
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• 2013

The influence of gas flow on the plasma generation in the atmospheric plasma jet is described with the theory of hydrodynamics. The plasma discharge is affected by the gas-flow streams with Reynolds number (Re) as well as the gas pressure with Bernoulli's theorem according to the gas flow rate inserted into the glass tube. The length of plasma column is varied with the flow types such as the laminar flow of Re<2,000 and the turbulent flow of Re>4,000 as it has been known in a general fluid experiments. In the laminar flow, the plasma column length is increased as the increase of flow rate. Since the pressure in the glass tube becomes low as the increase of flow velocity by the Bernoulli's theorem, the breakdown voltage of plasma discharge is reduced by the Paschen's law. Therefore, the plasma length is increased as the increasing flow rate with the fixed operation voltage. In the transition of laminar and turbulent flows, the plasma length is decreased. When the flow becomes turbulent as the flow rate is increasing, the plasma length becomes short and the discharge is shut down ultimately. In the discharge of laminar flow, the diameter of plasma beam exposed on the substrate surface is kept less than the glass diameter, since the gas flow is kept to the distinct distance from the nozzle of glass tube.

• Journal of the Korean Vacuum Society
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• v.22 no.5
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• pp.245-249
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• 2013

The $HfO_X$ thin film was deposited what it has been paid attention to the next generation oxide thin layer of MOSFET (metal-Oxide semiconductor field-effect-transistor) by rf magnetron sputter on Si (100) substrate. The $HfO_X$ thin film was deposited using a various oxygen gas flows (5, 10, 15 sccm). After deposition, $HfO_X$ thin films were annealed from 400 to $800^{\circ}C$ for 20 min in nitrogen ambient. The electrical characteristics of the $HfO_X$ thin film was improved by leakage current properties, depending on the increase of oxygen gas flow and annealing temperature. In particular, the properties of nano-mechanics of $HfO_X$ thin films were measured by AFM and Nano-indenter. From the results, the maximum indentation depth at the basis of maximum indentation force was increased from 24.9 to 38.8 nm according to increase the annealing temperature. Especially, the indentation depth was increased rapidly at $800^{\circ}C$. The rapid increasement of indentation depth was expected to be due to the change of residual stress in the $HfO_X$ thin film, and this result was caused by relative flux of oxygen outgasing during the annealing process.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.410-410
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• 2013

Next-generation nonvolatile memory (NVM) has attracted increasing attention about emerging NVMs such as ferroelectric random access memory, phase-change random access memory, magnetic random access memory and resistance random access memory (RRAM). Previous studies have demonstrated that RRAM is promising because of its excellent properties, including simple structure, high speed and high density integration. Many research groups have reported a lot of metal oxides as resistive materials like TiO2, NiO, SrTiO3 and ZnO [1]. Among them, the ZnO-based film is one of the most promising materials for RRAM because of its good switching characteristics, reliability and high transparency [2]. However, in many studies about ZnO-based RRAMs, there was a problem to get lower current level for reducing the operating power dissipation and improving the device reliability such an endurance and an retention time of memory devices. Thus in this paper, we investigated that highly reproducible bipolar resistive switching characteristics of W doped ZnO RRAM device and it showed low resistive switching current level and large ON/OFF ratio. This may be caused by the interdiffusion of the W atoms in the ZnO film, whch serves as dopants, and leakage current would rise resulting in the lowering of current level [3]. In this work, a ZnO film and W doped ZnO film were fabricated on a Si substrate using RF magnetron sputtering from ZnO and W targets at room temperature with Ar gas ambient, and compared their current levels. Compared with the conventional ZnO-based RRAM, the W doped ZnO ReRAM device shows the reduction of reset current from ~$10^{-6}$ A to ~$10^{-9}$ A and large ON/OFF ratio of ~$10^3$ along with self-rectifying characteristic as shown in Fig. 1. In addition, we observed good endurance of $10^3$ times and retention time of $10^4$ s in the W doped ZnO ReRAM device. With this advantageous characteristics, W doped ZnO thin film device is a promising candidates for CMOS compatible and high-density RRAM devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.73-75
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• 2013

Atomic force microscopy (AFM) [1] can now not only image individual atoms but also construct atom letters using atom manipulation method [2]. Therefore, the AFM is the second generation atomic tool following the well-known scanning tunneling microscopy (STM). The AFM, however, has the advantages that it can image even insulating surfaces with atomic resolution and also measure the atomic force itself between the tip-apex outermost atom and the sample surface atom. Noting these advantages, we have been developing a novel bottom-up nanostructuring system, as shown in Fig. 1, based on the AFM. It can identify chemical species of individual atoms [3] and then manipulate selected atom species to the designed site one-by-one [2] to assemble complex nanostructures consisted of many atom species at room temperature (RT). In this invited talk, we will introduce our results toward atom-by-atom assembly of composite nanomaterials based on the AFM at RT. To identify chemical species, we developed the site-specific force spectroscopy at RT by compensating the thermal drift using the atom tracking. By converting the precise site-specific frequency shift curves, we obtained short-range force curves of selected Sn and Si atoms as shown in Fig. 2(a) and 2(b) [4]. Then using the atom-by-atom force spectroscopy at RT, we succeeded in chemical identification of intermixed three atom species in Pb/Sn/Si(111)-(${\surd}3$'${\surd}3$) surface as shown in Fig. 2(c) [3]. To create composite nanostructures, we found the lateral atom interchange phenomenon at RT, which enables us to exchange embedded heterogeneous atoms [2]. By combining this phenomenon with the modified vector scan, we constructed the atom letters "Sn" consisted of substitutional Sn adatoms embedded in Ge adatoms at RT as shown in Fig. 3(a)~(f) [2]. Besides, we found another kind of atom interchange phenomenon at RT that is the vertical atom interchange phenomenon, which directly interchanges the surface selected Sn atoms with the tip apex Si atoms [5]. This method is an advanced interchangeable single atom pen at RT. Then using this method, we created the atom letters "Si" consisted of substituted Si adatoms embedded in Sn adatoms at RT as shown in Fig. 4(a)~(f) [5]. In addition to the above results, we will introduce the simultaneous evaluation of the force and current at the atomic scale using the combined AFM/STM at RT.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.334-334
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• 2013

In the past decade, the infrared detectors based on intersubband transition in quantum dots (QDs) have attracted much attention due to lower dark currents and increased lifetimes, which are in turn due a three-dimensional confinement and a reduction of scattering, respectively. In parallel, focal plane array development for infrared imaging has proceeded from the first to third generations (linear arrays, 2D arrays for staring systems, and large format with enhanced capabilities, respectively). For a step further towards the next generation of FPAs, it is envisioned that a two-dimensional metal hole array (2D-MHA) structures will improve the FPA structure by enhancing the coupling to photodetectors via local field engineering, and will enable wavelength filtering. In regard to the improved performance at certain wavelengths, it is worth pointing out the structural difference between previous 2D-MHA integrated front-illuminated single pixel devices and back-illuminated devices. Apart from the pixel linear dimension, it is a distinct difference that there is a metal cladding (composed of a number of metals for ohmic contact and the read-out integrated circuit hybridization) in the FPA between the heavily doped gallium arsenide used as the contact layer and the ROIC; on the contrary, the front-illuminated single pixel device consists of two heavily doped contact layers separated by the QD-absorber on a semi-infinite GaAs substrate. This paper is focused on analyzing the impact of a two dimensional metal hole array structure integrated to the back-illuminated quantum dots-in-a-well (DWELL) infrared photodetectors. The metal hole array consisting of subwavelength-circular holes penetrating gold layer (2DAu-CHA) provides the enhanced responsivity of DWELL infrared photodetector at certain wavelengths. The performance of 2D-Au-CHA is investigated by calculating the absorption of active layer in the DWELL structure using a finite integration technique. Simulation results show the enhanced electric fields (thereby increasing the absorption in the active layer) resulting from a surface plasmon, a guided mode, and Fabry-Perot resonances. Simulation method accomplished in this paper provides a generalized approach to optimize the design of any type of couplers integrated to infrared photodetectors.

• Journal of the Korean Vacuum Society
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• v.19 no.1
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• pp.14-21
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• 2010

Ge is one of the attractive channel materials for the next generation high speed metal oxide semiconductor field effect transistors (MOSFETs) due to its higher carrier mobility than Si. But the absence of a chemically stable thermal oxide has been the main obstacle hindering the use of Ge channels in MOS devices. Especially, the fabrication of gate oxide on Ge with high quality interface is essential requirement. In this study, $HfO_xN_y$ thin films were prepared by plasma-enhanced atomic layer deposition on Ge substrate. The nitrogen was incorporated in situ during PE-ALD by using the mixture of nitrogen and oxygen plasma as a reactant. The effects of nitrogen to oxygen gas ratio were studied focusing on the improvements on the electrical and interface properties. When the nitrogen to oxygen gas flow ratio was 1, we obtained good quality with 10% EOT reduction. Additional analysis techniques including X-ray photoemission spectroscopy and high resolution transmission electron microscopy were used for chemical and microstructural analysis.