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>

Controllable hydrothermal synthesis of bundled ZnO nanowires using cerium acetate hydrate precursors

Choi, Seok Cheol,Sohn, Sang Ho Elsevier 2018 Physica E, Low-dimensional systems & nanostructure Vol.104 No.-

<P><B>Abstract</B></P> <P>ZnO nanowire arrays were grown by the hydrothermal decomposition of zinc acetate dehydrate in precursor solutions containing cerium acetate hydrate. The effects of the Ce precursor on the hydrothermal synthesis of ZnO nanowires were investigated as a function of the Ce concentration. It was found that all the samples exhibited preferential orientation toward the c-plane and the Ce precursor had no effect on the lattice constant in the ZnO nanowires. ZnO nanowires grown in solutions containing 1 and 2 at% Ce precursors were bent and bundled, suggesting that solutions containing adequate amounts of Ce precursors enable the top surfaces of the vertically aligned ZnO nanowires to be either positively or negatively charged, and that electrostatic interactions among these local charges causes bending and bundling of the ZnO nanowires. Thus, Ce precursors in the solutions can control the morphology of the ZnO nanowires, causing them to be bent and bundled. We suggest that the bundled ZnO is applicable to Dye-sensitized solar cells because it can be enhanced adsorbed dye amounts in devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Bundled ZnO nanowires were synthesized by hydrothermal method using Ce precursor. </LI> <LI> Solutions containing 1 and 2 at% of Ce precursors lead to bundled nanowires. </LI> <LI> Bundling of ZnO nanowires was related to electrostatic interaction among nanowires. </LI> <LI> Controlling the Ce precursors gives a desired morphology of ZnO nanowires. </LI> </UL> </P>

Luminescence properties of MgO-sheathed and annealed ZnO nanowires

Jin, C.,Kim, H.,Hong, C.,Lee, J.,Lee, C. Elsevier 2011 CURRENT APPLIED PHYSICS Vol.11 No.4

ZnO nanowires were synthesized by the thermal evaporation of a mixture of ZnO and graphite powders (ZnO:C = 1:1) in an oxidative atmosphere without using a metal catalyst. The nanowires were 80-200 nm in diameter and a few tens of micrometers in length. Also, ZnO-core/MgO-shell nanowires were prepared by sheathing the ZnO nanowires with MgO via a hydrothermal route. Transmission electron microscopy and X-ray diffraction analyses revealed that the cores and shells of the as-prepared core-shell nanowires were single crystal wurtzite-type ZnO and amorphous MgO, respectively. Sheathing ZnO nanowires with MgO resulted in a significant increase in the intensity of the near-band edge emission (NBE) and some increase in the intensity of the deep level (DL) emission. Consequently, the intensity ratio of the NBE emission to the DL emission of the MgO-sheathed ZnO nanowires was ∼3.5. The enhancement of the NBE emission may be attributed to two factors: the quantum confinement of the photo-generated carriers inside the ZnO cores, which is due to the larger band gap of the MgO shells; and the suppression of carrier capture by surface states, which is due to the passivation of the ZnO cores by the MgO shells. Post-annealing resulted in a decrease in the DL emission intensity, but a further decrease in the NBE emission intensity.

수열합성법에 의해 성장된 ZnO 나노와이어의 전계방출 특성

노임준(Im-Jun No),김성현(Sung-Hyun Kim),신백균(Paik-Kyun Shin) 한국조명·전기설비학회 2010 조명·전기설비학회논문지 Vol.24 No.2

본 논문은 수열합성법에 의해 합성된 ZnO 나노와이어의 전계방출 특성을 연구하였다. ZnO 나노와이어는 핫플레이트 위에서 90[℃]의 온도로 Au 박막위에서 합성되었으며, ZnO 나노와이어의 팁을 형성하기 위한 캡핑 재료로 SDS(Sodium Dodecyl Sulfate) 를 0.05~0.3[wt%] 용액에 혼합하였다. 2시간동안 수열합성 후 체인 형태의 ZnO 나노와이어가 성장되었다. 고순도의 ZnO 나노와이어는 울자이트(Wurzite) 구조의 팁 형태를 보였으며, ZnO 나노와이어의 전계방출 특성은 고진공 챔버에서 측정하였고, 나노와이어의 턴-온전계는 0.1[㎂/㎠] 의 전류밀도에서 4.1[V/㎛]를 나타내었다. We fabricated FEDs(Filed emission devices) based on ZnO nanowires. The ZnO nanowires were synthesized on Au thin films by hydrothermal method at the temperature of 90[℃] on hot plate. In order to form tips of the ZnO nanowire, SDS(Sodium Dodecyl Sulfate) was mixed in 0.05~0.3[wt%] solution as capping material. After 2 hour growth, we obtained nanowires of chain form. The high-purity nanowires showed sharp tip geometry with a wurtzite structure. The field emission properties of the ZnO nanowires were investigated in high vacuum chamber. The turn-on field for the ZnO nanowires was found to be about 4.1[V/㎛] at a current density of 0.1[㎂/㎠].

Influence of a ZnO Coating on the Photoluminescence Properties of SnO2 Nanobelts

이종무,박성훈,김호형,이종우,김현우 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2

ZnO-coated SnO2 (SnO2-core/ZnO-shell) one-dimensional structures were prepared using a two-step method of thermal evaporation of Sn powders followed by atomic layer deposition (ALD) of ZnO. The influence of the ZnO layer's thickness on the photoluminescence (PL) properties of the nanostructure was investigated by using a room-temperature PL spectroscopy analysis. The intensity of the PL peak at about 595 nm, characteristic of the SnO2 core, decreases significantly and shifts to the lower wavelength region to form a broad emission peak ranging from 535 to 595 nm as the ZnO layer's thickness increases. Besides this broad peak a new emission peak, centered around 370 nm in the ultraviolet region also characteristic of ZnO, appears and increases with increasing thickness of the ZnO layer. Our results show that the wavelength of the emitted light can be controlled by coating SnO2 nanobelts with ZnO and optimizing the thickness of the ZnO-shell layer. The experimental results also suggest that the ZnO-coated SnO2 nanostructures can be enhanced by thermal annealing. The growth mechanism of SnO2 one-dimensional nanostructures by thermal evaporation is also discussed. ZnO-coated SnO2 (SnO2-core/ZnO-shell) one-dimensional structures were prepared using a two-step method of thermal evaporation of Sn powders followed by atomic layer deposition (ALD) of ZnO. The influence of the ZnO layer's thickness on the photoluminescence (PL) properties of the nanostructure was investigated by using a room-temperature PL spectroscopy analysis. The intensity of the PL peak at about 595 nm, characteristic of the SnO2 core, decreases significantly and shifts to the lower wavelength region to form a broad emission peak ranging from 535 to 595 nm as the ZnO layer's thickness increases. Besides this broad peak a new emission peak, centered around 370 nm in the ultraviolet region also characteristic of ZnO, appears and increases with increasing thickness of the ZnO layer. Our results show that the wavelength of the emitted light can be controlled by coating SnO2 nanobelts with ZnO and optimizing the thickness of the ZnO-shell layer. The experimental results also suggest that the ZnO-coated SnO2 nanostructures can be enhanced by thermal annealing. The growth mechanism of SnO2 one-dimensional nanostructures by thermal evaporation is also discussed.

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>

Controllability of Threshold Voltage of ZnO Nanowire Field Effect Transistors by Manipulating Nanowire Diameter by Varying the Catalyst Thickness

Lee, Sang Yeol The Korean Institute of Electrical and Electronic 2013 Transactions on Electrical and Electronic Material Vol.14 No.3

The electrical properties of ZnO nanowire field effect transistors (FETs) have been investigated depending on various diameters of nanowires. The ZnO nanowires were synthesized with an Au catalyst on c-plane $Al_2O_3$ substrates using hot-walled pulsed laser deposition (HW-PLD). The nanowire FETs are fabricated by conventional photo-lithography. The diameter of ZnO nanowires is simply controlled by changing the thickness of the Au catalyst metal, which is confirmed by FE-SEM. It has been clearly observed that the ZnO nanowires showed different diameters simply depending on the thickness of the Au catalyst. As the diameter of ZnO nanowires increased, the threshold voltage of ZnO nanowires shifted to the negative direction systematically. The results are attributed to the difference of conductive layer in the nanowires with different diameters of nanowires, which is simply controlled by changing the catalyst thickness. The results show the possibility for the simple method of the fabrication of nanowire logic circuits using enhanced and depleted mode.

Controllability of Threshold Voltage of ZnO Nanowire Field Effect Transistors by Manipulating Nanowire Diameter by Varying the Catalyst Thickness

이상렬 한국전기전자재료학회 2013 Transactions on Electrical and Electronic Material Vol.14 No.3

The electrical properties of ZnO nanowire field effect transistors (FETs) have been investigated depending on various diameters of nanowires. The ZnO nanowires were synthesized with an Au catalyst on c-plane Al2O3 substrates using hot-walled pulsed laser deposition (HW-PLD). The nanowire FETs are fabricated by conventional photo-lithography. The diameter of ZnO nanowires is simply controlled by changing the thickness of the Au catalyst metal, which is confirmed by FE-SEM. It has been clearly observed that the ZnO nanowires showed different diameters simply depending on the thickness of the Au catalyst. As the diameter of ZnO nanowires increased, the threshold voltage of ZnO nanowires shifted to the negative direction systematically. The results are attributed to the difference of conductive layer in the nanowires with different diameters of nanowires, which is simply controlled by changing the catalyst thickness. The results show the possibility for the simple method of the fabrication of nanowire logic circuits using enhanced and depleted mode.

GROWTH OF HIGH QUALITY ZINC OXIDE NANOWIRES BY SIMPLE OXIDATION OF ZINC POWDER IN AIR

TAE-WOONG KOO,DONGMOK WHANG 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2008 NANO Vol.3 No.6

Single-crystal ZnO nanowires are synthesized by direct oxidation of zinc particles in air at a temperature much lower than the melting temperature of zinc solids. This simple and low-cost technique produces dense and high-quality ZnO nanowires. SEM and TEM studies revealed that as-grown ZnO nanowires have a uniform diameter and defect-free single-crystal structure. The growth direction of ZnO nanowires is the a axis, which is different from the common growth direction of one-dimensional ZnO structure. Room temperature PL spectra of ZnO nanowires grown with different oxygen pressures indicated that the quality of ZnO nanowires grown in air is much better than that of wires grown at reduced oxygen pressure. The excellent property of ZnO nanowires grown in air was confirmed by electrical transport measurements of individual ZnO nanowire field effect transistors.

단일 ZnO 나노선의 광전 특성에 대한 에이징 효과

김기현(Keem, Ki-Hyun),강정민(Kang, Jeong-Min),정동영(Jeong, Dong-Young),김상식(Kim, Sang-Sig) 한국전기전자학회 2006 전기전자학회논문지 Vol.10 No.2

본 연구는 단일 ZnO 나노선의 광전 특성에 대한 에이징(aging) 효과에 관한 것이다. 합성 직후의 ZnO 나노선에 대하여 photoluminescence (PL), 광전류 스펙트럼, 전류-전압 특성 및 광응답 특성들을 측정하였고, ZnO 나노선을 3달 동안 공기 중에 노출시킨 후에 위의 실험을 반복하였다. 에이징된 나노선은 합성 직후의 나노선과 비교하여 넓은 영역의 PL 밴드는 약해졌고, 광전류의 크기는 증가하였으며, 광응답 속도는 느려졌다. 본 연구에서 PL를 통해 관찰된 에이징 효과는 나노선 내부에 산소 공극의 수가 감소함으로 인한 것이며, 광전류와 광응답 특성에서 에이징 효과는 나노선 표면 부근에 산소 공극의 형성으로 인한 것이다. The effect of aging on the optoelectronic properties of a single ZnO nanowire is investigated in this study. The photoluminescence (PL), photocurrent spectrum, current-voltage characteristics, and photoresponse were measured for the as-grown ZnO nanowire and for the same nanowire exposed to air for three months. For the aged nanowire, the broad PL band is weaker, the intensity of the photocurrent is strengthened, and the photoresponse is slower, compared with the as-grown nanowire. It Is suggested in this paper that the observed aging effect on the PL is due to the reduction in the number of oxygen vacancies within the nanowire and that the aging effect on the photocurrent and photoresponse originates from the formation of oxygen vacancies near the surface.