Single-Walled Carbon Nanotubes as a Chemical Sensor for <tex> $\hbox{SO}_{2}$</tex> Detection

SeGi Yu,Whikun Yi IEEE 2007 IEEE TRANSACTIONS ON NANOTECHNOLOGY Vol.6 No.5

<P>Single-walled carbon nanotubes (SWNTs) are Introduced as a chemical sensor for the detection of sulfur dioxide (SO<SUB>2</SUB>) molecules. For a single bundle of SWNTs, current-voltage (I-V) curves were measured for a series of different temperatures under adsorption of SO<SUB>2</SUB> molecules. The I-V characteristics for a 'MAT'-type thin film SWNTs, with respect to the amount of SO<SUB>2</SUB> adsorbed, were measured at room temperature and compared directly with O<SUB>2</SUB> adsorption. The change in current upon the adsorption of SO<SUB>2</SUB> is distinctly higher than that of O<SUB>2</SUB>, and is also reversible for adsorption and successive evacuation. Thus, the results strongly suggested that a thin film of SWNTs can be used as a chemical sensor in the nanometer scale devices.</P>

Emission Stability of Semiconductor Nanowires

SeGi Yu(유세기),Taewon Jeong(정태원),Sang Hyun Lee(이상현),Jungna Heo(허정나),Jeonghee Lee(이정희),Cheol Jin Lee(이철진),Jinyoung Kim(김진영),HyungSook Lee(이형숙),YoonPil Kuk(국윤필),J.M. Kim(김종민) 한국진공학회(ASCT) 2006 Applied Science and Convergence Technology Vol.15 No.5

열 화학기상법으로 만든 GaN와 GaP 나노와이어에서 전계 방출과, 산소와 아르곤 분위기에서 안정성에 대해 조사하였다. GaN 나노와이어의 경우 산소 분위기에서 전계 방출이 급격하게 줄었으나, GaP에서는 그렇지 않았다. 두 나노와이어 모두 아르곤 분위기에서는 큰 변화가 없었다. GaP 나노와이어의 외부에 존재하는 산화물 층이 전자 방출 안정성에 크게 기여한 것으로 생각된다. 나노와이어에서 방출된 전자의 에너지 분포를 통해 반도체 나노와이어는 탄소 나노튜브와 그 전계 방출 메카니즘이 다름을 유추할 수 있었다. Field emission of GaN and GaP nanowires, synthesized by thermal chemical vapor deposition, and their emission stabilities under oxygen and argon environments were investigated. The field emission current of GaN nanowires was seriously deteriorated under oxygen environment, while that of GaP was not. Both wires did not show any noticeable change under argon environment. The existence of oxide outer shell layers in the GaP nanowires was proposed to be a main reason for this emission stability behavior. Field emission energy distributions of electrons from these nanowires revealed that field emission mechanism of the semiconductor nanowires were different from that of carbon nanotubes.

Secondary electron emission characteristics of microchannel plates

Yu, SeGi 한국외국어대학교 외국학종합연구센터 부설 기초과학연구소 2003 기초과학연구 Vol.16 No.-

The electron apmplification of microchannel plates (MCPs) through secondary electron emission were evaluated for three different shapes of MCPs. An MCP was made of an alumina green-sheet by punching, laminating, and firing, sequentially. The channel walls of pore arrays of an MCP was coated with an electron emissive layer by electroless copper plating, and a resistive layer was formed upon the emissive layer by sol-gel process, subsequently. The slant and chevron-shaped MCPs were fabricated by aligning the channel holes in the alumina green sheet during laminating process. The maximum secondary electron emission efficiencies of slant and chevron-shaped MCPs were found to be around 300 at the applied bias voltage of 3000 V on the MCP. The amplification gain of the straight MCP was increased from 90 to 860, when the primary electron beam current was decreased from 0.75 A to 0.05 ㎂.

Double - to one - humped secondary electron emission curve change for thermal silicon oxide layers

SeGi Yu,TaeWon Jeong,Whikun Yi,Jeonghee Lee,S.H. Jin,J.M. Kim,D. Jeon 한국진공학회 2000 한국진공학회 학술발표회초록집 Vol.- No.-

Metal sputtered graphene based hybrid films comprising tin oxide/reduced graphene oxide/Ni as electrodes for high-voltage electrochemical capacitors

Byun, Segi,Shin, Byungha,Yu, Jin Elsevier 2018 Carbon Vol.129 No.-

<P><B>Abstract</B></P> <P>The high voltage aqueous electrochemical capacitor (EC) is a promising energy storage device because of eco-friendliness and high electrochemical performance with a wide operational voltage and high energy density. However, it typically experiences a stability problem that includes cell aging and capacitance loss. Here, to overcome the stability issue, a thin metal layer of Ni is created on one side of a SnO<SUB>2</SUB>/reduced graphene oxide (rGO) hybrid film to produce a binder-free film of SnO<SUB>2</SUB>/rGO/Ni. Due to the formation of the highly conductive metal layer of Ni, the fabricated film can be well interconnected with the current collector and have lower contact resistance and open-circuit potential compared with untreated SnO<SUB>2</SUB>/rGO film, which results in a remarkable enhancement of electrochemical performance, including a wide operational voltage (1.8 V), semi-permanent cycle-life (95% retention after 10k cycles), and ultrahigh volumetric energy density with a high power density, all of which are superior values compared to bare SnO<SUB>2</SUB>/rGO film based devices. We anticipate that the fabricated SnO<SUB>2</SUB>/rGO/Ni film could be utilized as a promising electrode for high voltage ECs, and our simple surface engineering technique will provide an effective electrode design for the fabrication of high performance thin-film ECs.</P> <P><B>Graphical abstract</B></P> <P>Forming a highly conductive metal layer of Ni on the SnO<SUB>2</SUB>/rGO based electrode can be dramatically enhanced the electrochemical performance.</P> <P>[DISPLAY OMISSION]</P>

Microchannel plates for field emission displays

Sunghwan Jin,SeGi Yu,Jungna Heo,Taewon Jeong,Junghee Lee,Whikun Yi,Yongsoo Choi,Jongmin Kim 한국진공학회(ASCT) 2000 Journal of Korean Vacuum Science & Technology Vol.4 No.4

Microchannel plates (MCPs) have been developed by introducing new materials and process technologies. Main body was made of alumina by programmable punching, laminating, and firing. The channel walls of pore arrays of an MCP were deposited with thin films by electro1ess copper plating and sol-gel process. Our MCP has advantages such as easy fabrication, durability, high temperature endurance, and applicability to the large size comparing with the conventional MCPs. Experiments on the brightness of an MCP incorporated FED revealed that the FED with a MCP is three to four times brighter than a conventional FED. Moreover, the focusing in a FED is improved. Incorporating an MCP into a FED is one of promising methods to enhance the characteristics of the FED. In addition, amplification yield of the MCP is measured for varying the aspect ratio and the input current.

Dielectric characteristics of MXene-incorporated polymer composites

Jun So-Yeon,Yu SeGi 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.11

Polymer-based dielectric composites were developed by mixing barium titanium oxide (BaTiO3, BTO) with conducting two-dimensional nanomaterials called MXenes in a polymer matrix. MXene platelets were delaminated, or exfoliated, in dimethyl sulfoxide (DMSO) solvent using ultrasonication for varying length of time (0, 1, 2, and 3 h). The addition of conducting MXene platelets induced interfacial polarization and resulted in improved dielectric performance compared to the reference sample, with an increase in the dielectric constant of 12 ~29% and a low level of the dielectric loss of less than 0.06 at 1 kHz. Among the samples, the sample produced with 2 h of sonication time, rather than the longest time of 3 h, was found to have the best by balancing ultrasonication’s dual efects: delamination of individual MXene platelets and the breaking up of platelets into smaller pieces. A longer sonication time failed to suppress the dielectric loss, despite its high value in the dielectric constant, potentially due the formation of a percolative connection among numerous small MXene platelets generated by the severe sonication. Thus, careful optimization of MXene delamination is necessary by monitoring sonication time to prevent the disintegration of MXene platelets into numerous small ones.

건식 열산화로 성장시킨 SiO₂ 박막의 이차전자 방출 특성

정태원(Taewon Jeong),유세기(SeGi Yu),이정희(Jeonghee Lee),진성환(S.H. Jin),허정나(Jungna Heo),이휘건(Whikun Yi),전동렬(D. Jeon),김종민(J.M. Kim) 한국진공학회(ASCT) 2001 Applied Science and Convergence Technology Vol.10 No.1

열산화시킨 SiO₂ 박막의 두께와 입사 전류의 양에 따라 이차전자 방출 계수를 측정하였다. 930℃에서 열산화시킨 SiO₂ 박막 두께는 5.8㎚, 19㎚, 43㎚, 79㎚, 95㎚, 114㎚였으며 이들의 이차전자의 방출 특성이 박막 두께와 전류량에 따라 변화하는 것을 확인하였다. 박막 두께 43㎚ 이하의 얇은 박막에서는 대체적으로 universal curve의 형태를 따르지만 79㎚ 이상의 두꺼운 박막에서는 이차전자 방출곡선이 최고점이 2개인 형태로 변하며 그 값도 전반적으로 낮아진다. 또 입사시키는 일차전자 전류의 증가에 대해서도 이차전자 방출곡선이 전체적으로 낮아진다. 이 실험에서 측정된 최대 이차전자 방출 계수는 박막 두께 19㎚, 일차 전자 에너지 300eV, 일차 전류 0.97㎂일 때 3.35를 갖는다. 이차전자 방출계수가 최대인 입사에너지에서 전자의 시료내 침투깊이와 탈출깊이와의 관계식을 통하여 박막 두께를 이론적으로 계산하였으며, 실험값과 비교적 일치하는 것을 확인하였다. The secondary electron emission (SEE) yields for the thermally grown SiO₂ thin layers were measured by varying the thickness of the SiO₂ layer and the primary current. SiO₂ thin layers were thermally grown in a furnace at 930℃, whose thickness varied to be 5.8㎚, 19㎚, 43㎚, 79㎚, 95㎚, and 114㎚. When the SiO₂ layers were thinner than 43㎚, it was found that SEE curves followed the universal curve. However, for samples with a SiO₂ layer thicker than 79㎚, the SEE curves exhibited two maxima and the values of SEE yields were reduced. Additionally, as the current of primary electrons increased, the SEE yields were reduced. In this experiment, the maximum value of the SEE yield for SiO₂ layers was obtained to be 3.35 when the thickness of SiO₂ layer was 19㎚, with the primary electron energy 300 eV and the primary electron current 0.97 ㎂. The penetration and escape depth of an electron in the SiO₂ layers were calculated at the primary electron energy for the maximum value of the SEE yield and from these depths, it was calculated that the thickness of the SiO₂ layer.

Precisely Geometry Controlled Microsupercapacitors for Ultrahigh Areal Capacitance, Volumetric Capacitance, and Energy Density

Yoo, Jungjoon,Byun, Segi,Lee, Chan-Woo,Yoo, Chung-Yul,Yu, Jin American Chemical Society 2018 Chemistry of materials Vol.30 No.12

<P>Microsupercapacitors are microscale rechargeable energy storage devices that can support or replace batteries in ultrasmall electronic devices. Although the use of high-capacitive, two-dimensional materials is promising, other methods are needed to reach a high capacitance and energy density, which cannot be achieved by fully utilizing the surface of electrode materials. Here, we introduce an effective strategy to control the geometry of interdigital microelectrodes for achieving an ultrahigh capacitance by utilizing the edge effect of in-plane structured graphene and improving ion transport. Theoretical calculations are employed to investigate the electrochemical enhancement at the edge of reduced graphene oxide in a KOH electrolyte. The presence of edges is predicted to enhance the capacitance by electronic redistribution. We report areal and volumetric stack capacitances (40 mF/cm<SUP>2</SUP> and 98 F/cm<SUP>3</SUP>, respectively) and energy densities (5.4 μWh/cm<SUP>2</SUP> and 13.7 mWh/cm<SUP>3</SUP>, respectively) that are much higher than those of any other microsupercapacitors containing micrometer-thick interdigital electrodes. This improvement is attributed to synergistic effects between numerous edge planes fabricated by a high-resolution laser-drilling process and a well-matched electrolyte as well as the in-plane structure of heat-treated graphene oxide, which provides minimal channel space for efficient ion transport. Our strategy provides a versatile method for designing high-performance microsupercapacitors and is promising for the development of microenergy storage devices for subminiature electronics that require a high energy density.</P> [FIG OMISSION]</BR>

산소 플라즈마 처리후의 이차전자방출계수(γ)를 이용한 MgO 보호막의 일함수(φW) 변화

정재천,유세기,조재원,Jeong, Jae-Cheon,Yu, SeGi,Cho, Jaewon 한국전기전자재료학회 2005 전기전자재료학회논문지 Vol.18 No.3

The changes in secondary electron emission coefficient(${\gamma}$) and work function($\Phi$$_{\omega}$) have been studied on the surface of MgO protective layer aster plasma(Ar. $O_2$) treatment using ${\gamma}$-focused ion beam (${\gamma}$-FIB) system. The values of ${\gamma}$ varied as follows: $O_2$-treated MgO > Ar-treated MgO > Non-treated MgO, and the work functions varied in the reverse order. The result indicates that both the physical etching and the chemical reaction of $O_2$-plasma removed the contaminating materials from the surface of MgO.