MoS₂ gas sensor functionalized by Pd for the detection of hydrogen

Baek, Dae-Hyun,Kim, Jongbaeg Elsevier 2017 Sensors and actuators. B Chemical Vol.250 No.-

<P><B>Abstract</B></P> <P>A facile, scalable and low-cost strategy for fabricating hydrogen sensors with few-layered Pd-functionalized MoS<SUB>2</SUB> according to a simple solution process is reported. The sensors were prepared by drop-casting a MoS<SUB>2</SUB>-containing solution onto a SiO<SUB>2</SUB> substrate and functionalizing the surface of the MoS<SUB>2</SUB> with Pd using evaporation. Patterned deposition of Cr/Au on top of the MoS<SUB>2</SUB>-coated SiO<SUB>2</SUB> substrate was then performed using evaporation through a shadow mask to place the micro electrodes on the substrate. The fabricated Pd-MoS<SUB>2</SUB> sensors successfully detected hydrogen gas diluted by air at room temperature. With exposure to hydrogen gas, the Pd was converted to palladium hydride, which has a lower work function than MoS<SUB>2</SUB>, resulting in the transfer of electrons from palladium hydride to MoS<SUB>2</SUB>, thereby decreasing the resistance of the sensor. The functionalized MoS<SUB>2</SUB> showed a 35.3% resistance change when exposed to a 1% hydrogen-containing gas, while the pristine MoS<SUB>2</SUB> showed no reaction. The lower limit of detection of the resulting functionalized MoS<SUB>2</SUB> sensor was 50ppm.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We fabricated a sensor with high sensitivity toward H<SUB>2</SUB>. </LI> <LI> It was prepared by drop-casting MoS<SUB>2</SUB> solution and functionalization with Pd nanodots. </LI> <LI> Upon H<SUB>2</SUB> exposure, Pd was converted to Pd-hydride with lower work function than MoS<SUB>2</SUB>. </LI> <LI> Pristine MoS<SUB>2</SUB> showed no change when exposed to a 1% hydrogen-containing gas. </LI> <LI> However, functionalized MoS<SUB>2</SUB> showed a 35.3% resistance change. </LI> </UL> </P>

전기 방사를 이용한 1D / 2D 하이브리드 구조 고활성 MoS2 / CNF 수소 발생 촉매의 합성 및 특성 분석

이정훈,박유세,장명제,박성민,이규환,최우성,최승목,김양도 대한금속·재료학회 2018 대한금속·재료학회지 Vol.56 No.12

Molybdenum disulfide (MoS2) based electrocatalysts have been proposed as substitutes for platinum group metal (PGM) based electrocatalyst to hydrogen evolution reaction (HER) in water electrolysis. Here, we studied MoS2/CNFs hybrid catalyst prepared by electrospinning method with heat treatment for polymer electrolyte membrane(PEM) water electrolysis to improve the HER activity. The physicochemical and electrochemical properties such as average diameter, crystalline properties, electrocatalitic activity for HER of synthesized MoS2/CNFs were investigated by the Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM), Raman Spectroscopy (Raman) and Linear Sweep Voltammetry (LSV). The as spun ATTM/PVP nanofibers were prepared by sol-gel and electrospinning method. Subsequently, the MoS2/CNFs was dereived from reduction heat treatment of ATTM at the ATTM/PVP nanofibers and carbonization heat treatment. Synthesized MoS2/ CNFs electrocatalyst had an average diameter of 179±30 nm. We confirmed that the MoS2 layers in MoS2/ CNF electrocatalyst consist of 3~4 layers from the Raman results. In addition, We confirmed that the MoS2 layers in MoS2/CNF catalyst consist of 7.47% octahedral 1T phase MoS2, 63.77% trigonal prismatic 2H phase MoS2 with 28.75% MoO3 through the XRD, Raman and XPS results. It was shown that MoS2/CNFs had the overpotential of 0.278 V at 10 mA/cm2 and tafel slope of 74.8 mV/dec in 0.5 M sulfuric acid (H2SO4) electrolyte.

Highly Enhanced Gas Adsorption Properties in Vertically Aligned MoS₂ Layers

Cho, Soo-Yeon,Kim, Seon Joon,Lee, Youhan,Kim, Jong-Seon,Jung, Woo-Bin,Yoo, Hae-Wook,Kim, Jihan,Jung, Hee-Tae American Chemical Society 2015 ACS NANO Vol.9 No.9

<P>In this work, we demonstrate that gas adsorption is significantly higher in edge sites of vertically aligned MoS<SUB>2</SUB> compared to that of the conventional basal plane exposed MoS<SUB>2</SUB> films. To compare the effect of the alignment of MoS<SUB>2</SUB> on the gas adsorption properties, we synthesized three distinct MoS<SUB>2</SUB> films with different alignment directions ((1) horizontally aligned MoS<SUB>2</SUB> (basal plane exposed), (2) mixture of horizontally aligned MoS<SUB>2</SUB> and vertically aligned layers (basal and edge exposed), and (3) vertically aligned MoS<SUB>2</SUB> (edge exposed)) by using rapid sulfurization method of CVD process. Vertically aligned MoS<SUB>2</SUB> film shows about 5-fold enhanced sensitivity to NO<SUB>2</SUB> gas molecules compared to horizontally aligned MoS<SUB>2</SUB> film. Vertically aligned MoS<SUB>2</SUB> has superior resistance variation compared to horizontally aligned MoS<SUB>2</SUB> even with same surface area exposed to identical concentration of gas molecules. We found that electrical response to target gas molecules correlates directly with the density of the exposed edge sites of MoS<SUB>2</SUB> due to high adsorption of gas molecules onto edge sites of vertically aligned MoS<SUB>2</SUB>. Density functional theory (DFT) calculations corroborate the experimental results as stronger NO<SUB>2</SUB> binding energies are computed for multiple configurations near the edge sites of MoS<SUB>2</SUB>, which verifies that electrical response to target gas molecules (NO<SUB>2</SUB>) correlates directly with the density of the exposed edge sites of MoS<SUB>2</SUB> due to high adsorption of gas molecules onto edge sites of vertically aligned MoS<SUB>2</SUB>. We believe that this observation extends to other 2D TMD materials as well as MoS<SUB>2</SUB> and can be applied to significantly enhance the gas sensor performance in these materials.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-9/acsnano.5b04504/production/images/medium/nn-2015-04504g_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b04504'>ACS Electronic Supporting Info</A></P>

수열 압력 제조 조건이 MoS2 촉매 특성과 직접 메탄화 반응에 미치는 영향

박정환,김성수,김진걸 한국수소및신에너지학회 2018 한국수소 및 신에너지학회논문집 Vol.29 No.2

After MoS2 catalyst was prepared at 1, 30, and 70 atm, the hydrothermal pressure effect over preparation of MoS2 was investigated in terms of catalyst characterization and direct methanation. Multifaceted characterization techniques such as XRD, BET, SEM, TPR, EDS, and XPS were used to analyze and investigate the effect of high pressure over the preparation of surface and bulk MoS2 catalyst. Result from XRD, SEM, and BET demonstrated that MoS2 was more dispersed as preparation pressure was increased, which resulted finer MoS2 crystal size and higher surface area. EDS result confirmed that bulk composition was MoS2 and XPS result showed that S/Mo mole ratio of surface was about 1.3. TPR showed that MoS2 prepared at 30 atm possessed higher active surface sites than MoS2 prepared at 1 atm and these sites could contribute to higher CO yield during methanation. Direct methanation was used to evaluate the CO conversion of the both catalysts prepared at 1 atm and 30 atm and reaction condition was at feed mole ratio of H2/CO=1, GHSV=4800, 30 atm, temperature(℃) of 300, 350, 400, and 450. MoS2 prepared at 30 atm showed more stable and higher CO conversion than MoS2 prepared at 1 atm. Faster deactivation was occurred over MoS2 prepared at 1 atm, which indicated that preparation pressure of MoS2 catalyst was the dominant factor to improve the yield of direct methanation.

Controllable synthesis of MoS₂/graphene low-dimensional nanocomposites and their electrical properties

Long, Le Ngoc,Thi, Pham Tan,Trung Kien, Pham,Trung, Pham Thanh,Ohtani, Masataka,Kumabe, Yoshitaka,Tanaka, Hirofumi,Ueda, Shigenori,Lee, Hyoyoung,Thang, Phan Bach,Khai, Tran Van Elsevier 2020 APPLIED SURFACE SCIENCE - Vol.504 No.-

<P><B>Abstract</B></P> <P>In this study, a novel hydrothermal route has been developed for the synthesis of MoS<SUB>2</SUB>/graphene composite with controllable structures, in which ammonium molybdatetetrahydrate, as-prepared graphene oxide (GO), and thioacetamide were used as staring materials. Effects of Mo<SUP>4+</SUP>-to-C precursor ratios and crystalline time on the structures, components and morphologies of MoS<SUB>2</SUB>/graphene were investigated. MoS<SUB>2</SUB>/graphene samples were characterized using XRD, FESEM, HRTEM, FTIR, Raman spectroscopy, HAADF-STEM/EDS, HXPES and electrical measurements. The results show that petal-like MoS<SUB>2</SUB> nanostructures with ultrathin petals (~1–10 layers) and coexistence of 1T- and 2H-MoS<SUB>2</SUB> phases can be synthesized on graphene surface in a short time (~2 h). Comparison of crystallization conditions, we found that the crystallization time had a significant effect on the size of the MoS<SUB>2</SUB> nanopetals. The shorter the reaction time is, the thinner the petal-like MoS<SUB>2</SUB> nanoscale is. On the other hand, by adjusting the ratios of Mo<SUP>4+</SUP>to C (denoted as: MoS<SUB>2</SUB>/C (1:2), MoS<SUB>2</SUB>/C (3:2), MoS<SUB>2</SUB>/C (2.5:1) and MoS<SUB>2</SUB>/C (3:1)), different MoS<SUB>2</SUB>/graphene architectures including “sandwich-liked”, “layer–by–layer” and “anchored” can be obtained. On the basis of these results, a possible growth mechanism of MoS<SUB>2</SUB>nanopetals on GO was proposed. Interestingly, the as-synthesized material depicts its memristive behavior through the Volt-Ampere characteristics, suggesting a potential application in logic memory devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel hydrothermal route has been developed for the synthesis of MoS<SUB>2</SUB>/graphene composite with controllable structures. </LI> <LI> The effects of Mo<SUP>4+</SUP>-to-C precursor ratios and crystalline time on properties of MoS<SUB>2</SUB>/graphene were investigated by FESEM, HRTEM, XRD, FTIR, Raman spectroscopy, HAADF-STEM/EDS and HXPES. </LI> <LI> The memristive properties of the MoS<SUB>2</SUB>/graphenenanocomposite were presented. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

디지털 오디오 프로세서용 전류모드 소자의 성능 개선에 관한 연구

김성권,조주필,차재상 한국인터넷방송통신학회 2008 한국인터넷방송통신학회 논문지 Vol.8 No.5

본 논문은 디지털 오디오 신호처리의 고속 및 저전력 동작을 구현하기 위한 전류모드 신호처리의 고성능 회로에 관하여 설계방안을 제시한다. 디지털 오디오 프로세서는 FFT(fast Fourier transform)와 같은 디지털 연산 동작이 필요하며, FFT 프로세서는 그 설정 포인트에 따라, 전력이 많이 필요하게 되며, 또한 고속 동작의 요구에 따라, 전력의 부담은 증대되고 있다. 따라서, 디지털 오디오 프로세서에 SI(switched current) circuit을 이용하는 analog current-mode 신호처리의 응용이 적용되게 되었다. 그러나 SI circuit을 구성하는 current memory는 clock-feedthrough의 문제점을 갖기 때문에, 전류 전달 특성에 있어서 오차를 발생시킨다. 본 논문에서는 current memory의 문제점인 clock- feedthrough의 해결방안으로 switch MOS에 dummy MOS의 연결을 검토하고, 0.25um process로 제작하기 위하여 switch MOS와 dummy MOS의 width의 관계를 도출하고자 한다. 시뮬레이션 결과, memory MOS의 width가 20um, 입력전류와 바이어스전류의 비가 0.3, switch MOS의 width가 2~5um일 경우에 switch MOS와 dummy MOS의 width는 의 관계로 정의되고, switch MOS의 width가 5~10um일 경우에 width는 의 관계로 정의되는 것을 확인하였다. 이 때, 정의된 MOS transistor의 width관계는 memory MOS의 설계에 유용한 지침이 될 것이며, 저전력 고속 동작의 디지털 오디오 프로세서의 적용에 매우 유용할 것으로 기대된다.

Microscopic evidence of strong interactions between chemical vapor deposited 2D MoS2 film and SiO2 growth template

Sohn Woonbae,Kwon Ki Chang,서준민,Lee Tae Hyung,노광철,장호원 나노기술연구협의회 2021 Nano Convergence Vol.8 No.11

Two-dimensional MoS 2 film can grow on oxide substrates including Al 2 O 3 and SiO 2 . However, it cannot grow usually on non-oxide substrates such as a bare Si wafer using chemical vapor deposition. To address this issue, we prepared as-synthesized and transferred MoS 2 (AS-MoS 2 and TR-MoS 2 ) films on SiO 2 /Si substrates and studied the effect of the SiO 2 layer on the atomic and electronic structure of the MoS 2 films using spherical aberration-corrected scanning transition electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The interlayer distance between MoS 2 layers film showed a change at the AS-MoS 2 /SiO 2 interface, which is attributed to the formation of S–O chemical bonding at the interface, whereas the TR-MoS 2 /SiO 2 interface showed only van der Waals interactions. Through STEM and EELS studies, we confirmed that there exists a bonding state in addition to the van der Waals force, which is the dominant interaction between MoS 2 and SiO 2 . The formation of S–O bonding at the AS-MoS 2 /SiO 2 interface layer suggests that the sulfur atoms at the termination layer in the MoS 2 films are bonded to the oxygen atoms of the SiO 2 layer during chemical vapor deposition. Our results indicate that the S–O bonding feature promotes the growth of MoS 2 thin films on oxide growth templates.

Ab initio study of adsorption behaviors of molecular adsorbates on the surface and at the edge of MoS2

차장환,민경아,성동철,홍석륜 한국물리학회 2018 Current Applied Physics Vol.18 No.9

Two dimensional (2D) semiconducting materials such as MoS2 have been actively investigated for their applications in nanodevices and gas sensors (or detectors). In this connection, we have investigated atomic and electronic structures of specific adsorbates on the surface of MoS2 and the edge of MoS2 armchair nanoribbons (ANRs) using density functional theory (DFT) calculations. Our calculations reveal that molecular adsorbates are well adsorbed at the edge of MoS2 than on the surface of MoS2. Despite the weak van der Waals (vdW) interaction between molecular adsorbates and MoS2 surface, paramagnetic molecules such as NO and NO2 induce the reduced band gap in MoS2 by making the states within the bandgap. On the other hand, adsorbed CO, NO, NO2, and O2 at the edge of MoS2 ANRs have much influence on the band structures of MoS2 ANRs via dissociation into their constituent atoms, while adsorbed CO2, NH3, H2, and N2 at the edge of MoS2 ANRs do not much change the band structure of MoS2 ANRs due to no dissociation. Further, we identify that dissociated molecules rearrange the charge densities of MoS2 ANRs by making the states within the bandgap.

Effect of defect types in monolayer MoS2 on SO2 adsorption

Liu Ge,Liu Jianfei,Yan Jun,Chen Yunlin,Zhu Yabin,Tian Yahui 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.5

As a two-dimensional semiconductor material, molybdenum disulfde (MoS2) is extensively applied to sulfur dioxide (SO2) gas sensor. However, point defects will inevitably be produced in the preparation of MoS2, which signifcantly afect the adsorption properties of MoS2. Thus, understanding the properties of diferent point defects is essential for the successful application of MoS2. In this work, four types of point defects (VS-MoS2, VS2-MoS2, VMoS3-MoS2 and VMoS6-MoS2) of monolayers MoS2 were proposed, and the adsorption characteristics of SO2 on four typical defective MoS2 monolayers were investigated based on frst principles. The adsorption models were established to calculate the electronic properties and adsorption parameters of the adsorption systems. The results show that VMoS6-MoS2 defect has excellent adsorption properties for SO2 due to its largest adsorption energy, charge transfer and electrical response. The obtained results will contribute to the understanding of the efects on the MoS2 monolayers with diferent defects for SO2 sensing application.

MoS2 기반의 쇼트키 반도체 광전소자

반동균,박왕희,정복만,김준동 한국전기전자재료학회 2017 전기전자재료학회논문지 Vol.30 No.7

High-performing photoelectric device was realized for the MoS2-embedded Si device. MoS2-coating was performed by a large-scale available sputtering method. The MoS2-layer coating on the p-Si spontaneously provides the rectifying current flow with a significant rectifying ratio of 617. Moreover, the highly optical transmittance of MoS2-layer provides over 80% transmittance for broad wavelengths. The MoS2-embedded Si photodetector shows the sensitive photoresponse for middle and long wavelength photons due to the functional MoS2-layer, which resolves the conventional limit of Si for long wavelength detection. The functional design of MoS2-layer would provide a promising route for the enhanced photoelectric devices, including photovoltaics cells and photodetectors. MoS2-layer를 실리콘에 코팅하여, 고성능 광전소자를 개발하였다. MoS2-layer 를 p-Si 에 코팅하면, 자발적으로 다이오드가 형성되어, 전류의 정류특성이 확보된다. 본 연구에서는 매우 높은 정류비인 617의 값을 얻었다. 또한 MoS2-layer 는 광학성능이 매우 좋아서 넓은 파장대에서 80% 이상의 투과도를 보인다. 이러한 특성을 이용하여, 입사광에 대한 Photodetector 로 응용이 가능하다. 기존의 실리콘 소자는 장파장 신호에 대한 감지가 어려운데, MoS2-layer/p-Si 의 소자에서는 이러한 문제를 해결하고 매우 좋은 광반응을 보인다. 이러한 특성을 이용하게 되면 태양전지와 광센서를 포함한 다양한 광전소자에서의 성능을 크게 향상 시킬 수 있을 것으로 예상된다.