ZnO-TiO₂ core-shell nanowires decorated with Au nanoparticles for plasmon-enhanced photoelectrochemical water splitting

Park, Jinse,Deshmukh, P.R.,Sohn, Youngku,Shin, Weon Gyu Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.787 No.-

<P><B>Abstract</B></P> <P>The present work reports the development of Au-nanoparticle decorated ZnO-TiO<SUB>2</SUB> core-shell nanowires on the Si-wafer. The developed Au-nanoparticle decorated ZnO-TiO<SUB>2</SUB> core-shell nanowires exhibit a unique structure with uniform sensitization of Au-nanoparticles with the diameter in the range of 5–9 nm on the ZnO-TiO<SUB>2</SUB> core-shell heterostructure. This unique structure of Au-nanoparticle decorated ZnO-TiO<SUB>2</SUB> core-shell nanowires demonstrates an enhanced photocurrent density of 1.63 mAcm<SUP>−2</SUP> upon illumination by visible light unveiling high photoelectrochemical water splitting activity. This photocurrent density is higher than the pristine ZnO nanowires (0.51 mAcm<SUP>−2</SUP>) and ZnO-TiO<SUB>2</SUB> core-shell nanowires (1.23 mAcm<SUP>−2</SUP>). Furthermore, photoelectrochemical water splitting efficiency of Au-nanoparticle decorated ZnO-TiO<SUB>2</SUB> core-shell nanowires was found to be 0.70%, which is higher than the ZnO nanowires (0.22%) and ZnO-TiO<SUB>2</SUB> core-shell nanowires (0.53%) at the same applied potential of +0.8 V<SUB>RHE</SUB>. The improved photocurrent density and efficiency is due to the enhanced absorbance in the visible region owing to the surface plasmon resonance effect of Au-nanoparticle, effective withdrawal of hot electron from the Au-nanoparticle at the interface of metal/semiconductor due to Schottky barrier as well as excellent charge-separation and transportation originating from the core-shell nanowires.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Development of Au decorated ZnO-TiO<SUB>2</SUB> core-shell NWs by CVD and photo-deposition. </LI> <LI> Au decorated ZnO-TiO<SUB>2</SUB> core-shell NWs shows the photocurrent density of 1.63 mAcm<SUP>−2</SUP>. </LI> <LI> Au decorated ZnO-TiO<SUB>2</SUB> core-shell NWs shows the fast photoresponse. </LI> <LI> Au decorated ZnO-TiO<SUB>2</SUB> core-shell NWs shows photoconversion efficiency of 0.70%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

수열합성법을 이용한 ZnO 나노 막대의 선택 성장 연구

김아라,장판,김창회,김홍승 한국물리학회 2012 새물리 Vol.62 No.8

We have investigated the effects of surface pattern size on the characteristics of hydrothermally grown ZnO nanorods. The sputtered ZnO seed layer on a Si substrate was patterned with features of various sizes by using nano-imprint technology for the selective growth of ZnO nanorods. The diameters and the lengths of the ZnO nanorods depended on the pattern feature size within several micrometers. The ZnO nanorods grown on small-pattern regions had large diameters and small lengths relative to those grown on large-pattern regions. The observation in this study suggests that controlling the pattern size of the ZnO seed layer on a substrate can control the morphology of the ZnO nanorod array. 본 연구에서는 수열합성법을 이용하여 패턴 영역의 크기에 대한 산화아연(ZnO, zinc oxide) 나노 막대 성장을 살펴보았다. ZnO와 Si기판의 격자상수 차이를 이용하여 ZnO 나노 막대를 선택적 영역에 성장시키고자스퍼터링 시스템으로 증착된 ZnO 씨앗층을 원하는 크기와 모양으로패턴화 하고자 하였으며 사용된 노광 기법은 광원의 파장에 제약을 받지않고 비교적 나노 스케일의 패턴을 재현성 있게 제작 가능한나노임프린트 공정을 이용하였다. ZnO 나노 막대는 패턴된 ZnO 씨앗층영역에 선택적으로 성장하였으며, ZnO 나노 막대의 직경과 길이의 크기는패턴된 ZnO 씨앗층의 수 μm크기의 변화에 따라 큰 영향을 받아 패턴크기가 작아질수록 큰 직경과 짧은 길이를 가지는 ZnO 나노 막대가 성장되었다.

용액공정으로 제작한 ZnO/Ag/ZnO 다층구조의 광학적 특성 연구

이형인,김지완 한국마이크로전자및패키징학회 2018 마이크로전자 및 패키징학회지 Vol.25 No.4

Various ZnO/Ag/ZnO multilayers were fabricated and their optical properties were investigated. Top and bottom ZnO layers were formed by sol-gel method and mid-metal layers were deposited by spin coating. To find suitable deposition condition of Ag, we measure thickness and sheet resistance of Ag monolayer. After the optimization of Ag monolayer, we fabricate ZnO/Ag/ZnO multilayers. Transmittance of ZnO/Ag/ZnO multilayers increased to 63%. In near IR region, transmittance of ZnO/Ag/ZnO multilayers decreased to 35% when the concentration of Ag solution was 2.5wt%. 본 논문은 용액공정으로 제작한 ZnO/Ag/ZnO 다층구조의 투과도에 대해 연구하였다. 다양한 두께의 ZnO/Ag/ ZnO 다층구조를 스핀코팅을 이용해 제작하였고 광학적 특성을 측정하였다. ZnO는 졸겔법으로 제작하였고 Ag는 Ag 용액을 이용해 스핀코팅으로 증착하였다. 최적화된 Ag 두께를 찾기 위해 Ag 용액의 농도, 스핀코팅의 회전속도를 조절하고 두께와 면저항을 측정하였다. ZnO/Ag/ZnO 다층구조의 투과도는 가시광 영역에서 최대 63%까지 증가하였다. 적외선영역에서 ZnO/Ag/ZnO 다층구조의 투과도는 Ag 용액의 농도가 2.5wt%일 때 투과도가 35%까지 감소하였다.

AlN를 도핑시킨 ZnO박막의 전기적 및 전자적 특성

손이슬,김겸룡,이강일,강희재,박남석 한국물리학회 2011 새물리 Vol.61 No.6

For high-quality p-type ZnO thin films, AlN co-doped ZnO thin films were grown by using a RF magnetron co-sputtering system with ambient Ar and O₂gases. In the XPS measurement, the binding energy peak of the Zn2p_(3/2) and O1s for the AlN-doped ZnO thin films was lower than that of the undoped ZnO thin film. The AlN-doped ZnO thin film grown at 200℃ exhibited p-type semiconductor with a high hall concentration of 1.37×10^(18)cm^(-3), a mobility of 776 cm²/Vs and a low resistivity of 5.86×10^(-3)Ω‧m. For the undoped ZnO thin film and the AlN-doped thin film grown at a temperature of 600℃, which exhibited characteristics of an N-type semiconductor, no nitrogen atoms were measured in the SIMS depth profile while for the AlN-doped ZnO thin films grown at room temperature, 200℃and 400℃, which exhibited the characteristics of a p-type semiconductor, nitrogen atoms were measured in the SIMS depth profile. Thus, we conclude that nitrogen atoms doped in ZnO thin films play an important role in the p-type semiconductor nature of AlN-doped ZnO thin films. 고품질의 p-형 ZnO박막을 제작하기 위해 AlN를 도핑시킨 ZnO박막을 RF 마그네트론 스퍼터링 법을 이용하여 Ar과 O₂분위기에서 성장시켰다. XPS측정결과, AlN를 도핑시킨 ZnO박막의 Zn2p_(3/2)와 O1s피크는도핑을 시키지 않은 ZnO박막의 피크보다 낮은 결합에너지에서측정되었다. 박막의 홀 측정 결과, 기판을 200℃로 가열하면서성장시킨 박막이 p-형을 나타내었으며, 비저항이 5.86×10^(-3)Ω‧m, 캐리어 농도가 1.37×10^(18)cm^(-3), 이동도가 776 cm²/Vs이었다. SIMS의 측정결과 N이 포함된박막에서는 p-형 반도체 특성을 나타내며, N이 포함되지 않은 박막에서는n-형 반도체 특성을 나타내었다.

Magnetic Core-shell ZnFe₂O₄@ZnO@SiO₂ Nanoparticle의 합성과 성질에 관한 연구

유정열,이영기,김종규,Yoo, Jeong-Yeol,Lee, Young-Ki,Kim, Jong-Gyu 대한화학회 2015 대한화학회지 Vol.59 No.5

II-VI 족 무기 화합물 반도체인 ZnO는 폭 넓은 응용분야 때문에 많은 관심을 받고 있다. ZnO는 넓은 밴드갭(3.37 eV)과 큰 excitation binding energy(60 meV)를 가지고 있고 광학특성, 반도체, 압전특성, 자성, 항균성, 광촉매 등 여러 분야에 응용 가능한 물질로 알려져 있다. 특히 광촉매 분야에 적용할 때 재수득의 문제를 위해 자성을 갖는 물질과 core-shell 구조를 이루는 연구가 활발히 진행 되고 있다. 본 연구에서, magnetic core-shell ZnFe₂O₄@ZnO@SiO₂ nanoparticles(NPs)는 3단계 과정을 통해 성공적으로 합성하였다. 합성된 물질들의 구조적 특성을 확인하기 위해 X-ray diffraction(XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy(FT-IR)을 사용하였다. ZnFe₂O₄ spinel 구조와 ZnO wurtzite 구조는 XRD를 사용하여 확인되었고, 전구체의 농도별 분석을 통해 ZnO 생성 비율을 확인 하였다. 합성된 물질들은SEM을 통하여 표면의 변화를 확인하였다. SiO₂층의 형성과 ZnFe₂O₄@ZnO@SiO₂ NPs의 합성은 FT-IR을 통해 Fe-O, Zn-O 및 Si-O-Si 결합을 확인하였다. 합성된 물질들의 자기적 성질은 Vibrating sample magnetometer(VSM)을 사용 하여 분석하였다. ZnO층과 SiO₂ 층의 형성의 결과는 자성의 증가와 감소로 확인하였다. 합성된 ZnFe₂O₄@ZnO@SiO₂ NPs의 광촉매 효과는 오염물질 대신 methylene blue(MB)를 사용하여 UV 조사 하에 암실에서 실험하였다. ZnO, II-VI group inorganic compound semi-conductor, has been receiving much attention due to its wide applications in various fields. Since the ZnO has 3.37 eV of a wide band gap and 60 meV of big excitation binding energy, it is well-known material for various uses such the optical property, a semi-conductor, magnetism, antibiosis, photocatalyst, etc. When applied in the field of photocatalyst, many research studies have been actively conducted regarding magnetic materials and the core-shell structure to take on the need of recycling used materials. In this paper, magnetic core-shell ZnFe₂O₄@SiO₂ nanoparticles (NPs) have been successfully synthesized through three steps. In order to analyze the structural characteristics of the synthesized substances, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR) were used. The spinel structure of ZnFe₂O₄ and the wurtzite structure of ZnO were confirmed by XRD, and ZnO production rate was confirmed through the analysis of different concentrations of the precursors. The surface change of the synthesized materials was confirmed by SEM. The formation of SiO₂ layer and the synthesis of ZnFe₂O₄@ZnO@SiO₂ NPs were finally verified through the bond of Fe-O, Zn-O and Si-O-Si by FT-IR. The magnetic property of the synthesized materials was analyzed through the vibrating sample magnetometer (VSM). The increase and decrease in the magnetism were respectively confirmed by the results of the formed ZnO and SiO₂ layer. The photocatalysis effect of the synthesized ZnFe₂O₄ @ZnO@SiO₂ NPs was experimented in a black box (dark room) using methylene blue (MB) under UV irradiation.

Co₃O₄-loaded ZnO nanofibers for excellent hydrogen sensing

Lee, Jae-Hyoung,Kim, Jin-Young,Kim, Jae-Hun,Mirzaei, Ali,Kim, Hyoun Woo,Kim, Sang Sub Elsevier 2019 International journal of hydrogen energy Vol.44 No.50

<P><B>Abstract</B></P> <P>The development of outstanding H<SUB>2</SUB>-sensing materials is vital for the realization of ecofriendly devices using H<SUB>2</SUB>-based energy. ZnO nanofibers have excellent H<SUB>2</SUB>-sensing performance. In this study, we synthesized a series of Co<SUB>3</SUB>O<SUB>4</SUB>-loaded ZnO nanofibers with the formula (1-x)ZnO-xCo<SUB>3</SUB>O<SUB>4</SUB> (x = 0.03, 0.05, 0.1, and 0.15, representing the molar ratio of Co<SUB>3</SUB>O<SUB>4</SUB>) via electrospinning to improve the H<SUB>2</SUB>-sensing properties of pristine nanofibers. The sensing results indicated that a sensor with a nominal composition of 0.95ZnO-0.05Co<SUB>3</SUB>O<SUB>4</SUB> had the highest response of ~133 to 10 ppm H<SUB>2</SUB> gas, with good H<SUB>2</SUB> selectivity. The main mechanisms underlying the excellent H<SUB>2</SUB>-sensing capability of the optimized gas sensor involved ZnO surface/grain boundaries and Co<SUB>3</SUB>O<SUB>4</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The <I>n</I>-<I>p</I> ZnO–Co<SUB>3</SUB>O<SUB>4</SUB> composite nanofibers showed higher H<SUB>2</SUB> sensing response, superior to that of pristine <I>n</I>–ZnO nanofibers. </LI> <LI> The composite nanofibers with composition of 0.95 ZnO-0.05 Co<SUB>3</SUB>O<SUB>4</SUB> showed the highest response to H<SUB>2</SUB> at 300 °C. </LI> <LI> H<SUB>2</SUB> sensing was related to the H<SUB>2</SUB>-induced reduction of resistance in ZnO and formation p-Co<SUB>3</SUB>O<SUB>4</SUB>/n-ZnO heterojunctions. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Change of potential barriers at ZnO/ZnO homointerfaces in the H<SUB>2</SUB> atmospheres, energy levels of ZnO and Co<SUB>3</SUB>O<SUB>4</SUB> after intimate contact, and responses of Co<SUB>3</SUB>O<SUB>4</SUB> loaded ZnO to H<SUB>2</SUB>, CO, NO<SUB>2</SUB> gases.</P> <P>[DISPLAY OMISSION]</P>

원자층 증착법 기반 양이온-음이온 이중 도핑 효과에 따른 ZnO 박막의 전기적 특성 비교 연구

김동은,김건우,강경문,Akendra Singh Chabungbam,박형호 한국마이크로전자및패키징학회 2023 마이크로전자 및 패키징학회지 Vol.30 No.3

투명 전도성 산화물(TCO)를 대체할 수 있는 대표적인 물질로 알려진 ZnO는 3.37 eV의 bandgap과 60 meV의exciton binding energy를 가진 반도체 물질이다. 본 연구에서는 투명 전극으로 사용하기 위한 높은 전기적 특성을 확보하기 위해 원자층 증착법을 기반으로 양이온과 음이온의 단일 및 이중 도핑에 따라 성장한 ZnO 박막을 제작하였다. 3가 양이온 Al, Ga과 음이온 F이 단일 및 이중 도핑된 ZnO 박막의 구조적, 광학적 특성 및 전기적 특성을 확인하였다. 단일 도핑의 경우, ZnO에 donor로 작용하는 Al, Ga, F에 의해 캐리어 농도가 도핑 전에 비해 증가하였고 근자외선 영역에서의band-edge absorption이 증가하는 것을 확인하였다. 단일 도핑 중에서는 F이 ZnO 내 산소 공공 자리에 passivation 되면서높은 mobility와 함께 가장 높은 전도도를 보였다. 이중 도핑의 경우, 각 원소들의 도핑 효과가 더해지면서 단일 도핑에 비해 높은 전기적 특성을 보였다. 결과적으로 Ga-F에 비해 Al-F 도핑 시 ionic radius 차이에 의한 lattice distortion 감소 및delocalized 된 전자 상태의 증가로 가장 낮은 비저항 값을 보였으며 PDOS 분석을 통한 시뮬레이션 데이터로 측정 값과 일치하는 결과를 확인했다. Zinc oxide(ZnO) is a semiconductor material with a bandgap of 3.37 eV and an exciton binding energy of 60 meV for various applications. Recently ZnO has been proven to enhance its electrical properties for utilization as an alternative for transparent conducting oxide (TCO) materials. In this study, cation(Al, Ga)-anion(F) single and double doped ZnO thin films were grown by atomic layer deposition (ALD) to enhance the electrical properties. The structural and optical properties of doped ZnO thin films were analyzed, and doping effects were confirmed to electrical characteristics. In single doped ZnO, it was observed that the carrier concentration was increased after doping, acting as a donor to ZnO. Among the single doping elements, F doped ZnO(FZO) showed the highest mobility and conductivity due to the passivation effect of oxygen vacancies. In the case of double doping, higher electrical characteristics were observed compared to single doping. Among the samples, Al-F doped ZnO(AFZO) exhibited the lowest resistance value. This results can be attributed to an increase in delocalized electron states and a decrease in lattice distortion resulting from the differences in ionic radius. The partial density of states(PDOS) was also analyzed and observed to be consistent with the experimental results.

MgZnO/ZnO 이중 구조의 성장을 위한 사파이어 기판에서의 InZnO 버퍼층 연구

염아람,김홍승,안형수,장낙원 한국물리학회 2019 새물리 Vol.69 No.1

The replacement of Zn by Mg increases the bandgap of ZnO from 3.37 eV to 7.8 eV. The quantum-well structure of MgZnO/ZnO can be utilized as an active layer for ultra violet light-emitting diode (UV-LED) and high-mobility field effect transistor (HEMT). However, forming a high-quality MgZnO/ZnO heterostructure is difficult because of the lattice mismatch and surface roughness of the ZnO layer on a sapphire substrate. This study was carried out to introduce an InZnO buffer layer for the formation of a good-quality ZnMgO/ZnO quantum-well structure. Pulsed laser deposition (PLD) was used for this purpose, and X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to evaluate the structural properties. Atomic force microscopy (AFM) was also performed to observe surface changes. The addition of only a small amount of In improved the surface roughness of the buffer layers. This revealed that a buffer layer of InZnO is favorable for growing ZnMgO/ZnO thin films of high quality. Mg에 의한 Zn의 치환은 ZnO의 밴드 갭을 3.37 eV에서 7.8 eV로 증가시킨다. 이를 이용하여 ZnMgO/ZnO의 양자우물 구조 형성 시 UV-LED (ultra violet light-emitting diode) 및 ZnO 기반 고이동도 전계효과 트랜지스터의 활성층으로 활용할 수 있다. 하지만 양질의 ZnMgO/ZnO 구조를 사파이어 기판위에 형성 시 격자 불일치 및 ZnO 층의 표면 거칠기 등으로 양질의 이중 구조 박막의 형성이 어려운 실정이다. 본 연구는 양질의 ZnMgO/ZnO 양자우물 구조 형성을 위하여 InZnO 버퍼층을 도입하여 박막 표면의 변화를 관찰하고자 진행하였다. 이를 위하여 펄스 레이저 증착법을 이용하였고 형성된 InZnO의 구조적 특성 평가를 위하여 X-선 회절법 및 투과 전자현미경 분석을 행하였다. 또한 표면 변화 관찰을 위하여 원자력 현미경 분석도 실시하였다. 소량의 In 첨가로 InZnO 버퍼층은 ZnO 층에 비해 표면 거칠기가 급격히 감소하여 양질의 ZnMgO/ZnO 박막을 성장하기 위한 유리한 조건을 갖추었다.

La-doped p-type ZnO nanowire with enhanced piezoelectric performance for flexible nanogenerators

Kang, Leeseung,An, HyeLan,Park, Ji Young,Hong, Myung Hwan,Nahm, Sahn,Lee, Chan Gi Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.475 No.-

<P><B>Abstract</B></P> <P>In recent years, energy harvesting has attracted considerable attention as a promising method to convert waste energy to useful energy. In particular, piezoelectric energy harvesters are of significant interest, because they have a simple structure and can be used to harvest energy regardless of weather or other environmental conditions. In accordance with the miniaturization trend of electronic devices driven by low power, piezoelectric nanogenerators (PENGs) using various nanostructured materials are being developed. Among them, ZnO nanowires (NWs) are most widely used for the use of PENGs. However, while research on n-type ZnO NWs is extensive, studies on p-type ZnO NWs are insufficient owing to their poor stability. In this study, La-doped p-type ZnO (La:ZnO) NWs were synthesized by a hydrothermal method to expand the applications of p-type ZnO and determine their potential as PENGs. XRD analysis showed that La<SUP>3+</SUP> ions was well doped without the formation of any secondary phases and caused a change in the lattice parameter when compared to that of undoped ZnO. XPS analysis was performed to investigate the surface elemental compositions of La:ZnO NWs, and the morphology of La:ZnO NWs was investigated using SEM and TEM. We further studied the piezoelectric output performance of undoped and La-doped ZnO NWs, and found that La:ZnO NWs showed improved piezoelectric output performance as a result of electron screening effect of the p-type semiconductor.</P> <P><B>Highlights</B></P> <P> <UL> <LI> La-doped p-type ZnO (La:ZnO) NWs were synthesized by a hydrothermal method. </LI> <LI> Their physical and chemical properties are systemically investigated. </LI> <LI> La-doping can improve piezoelectric performance by electron screening effect. </LI> <LI> La:ZnO nanogenerators are good candidates for power sources in electronic devices. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

(ZnO/Co) 다층 박막에서 ZnO층의 두께가 상온강자성 특성에 미치는 영향

강성근,김성동 한국마이크로전자및패키징학회 2018 마이크로전자 및 패키징학회지 Vol.25 No.4

Room temperature ferromagnetism of Co doped ZnO was studied using (ZnO/Co) multilayer structure, and the effects of ZnO sub-layer thickness on the RT ferromagnetism was investigated. As for the as-deposited state, the diamagnetism was observed for (ZnO 20Å/Co xÅ) while the ferromagnetism was observed for (ZnO 40Å/Co xÅ). After vacuum-annealed, both showed the RT ferromagnetism and (ZnO 40Å/Co xÅ) structure interestingly showed negative remanence magnetization behavior. UV-Vis spectrometer revealed that Co atoms were substituted with Zn in ZnO and Co cluster was not found in XPS and HRTEM EDS analysis. (ZnO/Co) 다층박막 구조를 이용하여 Co 도핑한 ZnO의 상온강자성 특성을 조사하였으며, 특히 ZnO 박막층의 두께가 (ZnO/Co) 다층박막의 상온강자성 특성에 미치는 영향을 조사하였다. ZnO 박막층의 두께가 20Å, 40Å일 때 증착상태에서는 각각 반자성과 강자성 특성을 나타내었으며 진공열처리 후에는 모두 강자성 특성을 나타내었다. 특히(ZnO 40Å/Co xÅ)는 열처리 후에 음의 잔류자화 거동을 나타내었다. UV-Vis 분석을 통해서 Co 일부가 Zn와 치환되어위치하고 있음을 확인할 수 있었으며, 열처리 전후에 대한 XPS 및 HRTEM EDS 분석에서 Co 클러스터의 형성은 관찰되지 않았다.