- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
European Microscopy Congress 2016: Proceedings || Defects in as-grown vs. annealed rutile titania nanowires and their effect on properties
摘要： Semiconducting metal oxides play a key role in electrochemical and photo physical applications like photo catalysis and as electrode material in solar cells and Li-ion batteries. Among these metal oxides, hydrothermally grown rutile TiO2 nanowire arrays are promising as the 1 D structure possesses a large surface area and a directed electron path towards the substrate. However, the efficiency of these devices is also influenced by the defects inside the nanowires (dislocations, stacking faults, titanium interstitials and oxygen vacancies). A previous study showed that as-grown nanowires have a high density of lattice defects.[1] However, these defects can be removed by an additional annealing step. Latest findings demonstrate that hybrid solar cells where those annealed nanowires are incorporated have significantly higher power-conversion efficiency.[2] However, the removal of the defects is not fully understood so far. In our present work, transmission electron microscopy (TEM) was used to study the changes within the nanowire during annealing. TEM investigations were performed at 200 kV using a JEOL JEM-2200FS and at 300 kV using a FEI Titan Themis 60-300. First results were obtained by ex-situ TEM analysis of as-grown TiO2 nanowires and nanowires, which were annealed at 500 °C for 4 h. These ex-situ analysis confirm that both, as-grown and annealed nanowires, have the rutile crystal structure. Defects, present in the as-grown state, can be removed by the thermal treatment. Concurrently, a structural transformation inside the nanowires occurs resulting in faceted voids of several nanometer in diameter. Using tilt series from -70° to +70° in high-angle annular dark-field (HAADF) scanning (S)TEM mode and the discrete iterative reconstruction technique (DIRT)[3], a TEM tomograph was obtained, which proved that these voids are solely formed inside the nanowire and not at the nanowire surface (Fig. 1). Further analysis including electron energy loss spectroscopy revealed changes of the oxidation state at the surface region of the voids during annealing, whereas the rutile TiO2 crystal structure was maintained. HAADF-STEM in-situ heating experiments, performed in a JEOL JEM-2200FS with a DENSsolutions heating holder, enabled the direct observation of the structural changes inside the rutile TiO2 nanowires (Fig. 2). Using a slow heating ramp of 3.3°C/min, a sudden formation of these voids at around 500 °C could be observed. Heating at lower temperatures did not affect the structure of the nanowire and also an additional heating after the transformation (600°C, 1h) did not change the size and shape of the voids. These ex-situ and in-situ observations are a decisive step to explain the mechanisms involved in this process in more detail. The results of our TEM investigation were correlated to the properties of as-grown and annealed TiO2 nanowires. Here, we could show that the healing of the lattice defects upon annealing not only increased the performance of hybrid solar cells but also affects other properties of the nanowires e.g. chemical stability.
关键词： in-situ TEM,TiO2 nanowire,defect healing
更新于2025-09-16 10:30:52
-
[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Composite transparent conductive electrode for printed electronic devices
摘要： The new transparent conductive electrode consists of three materials: silver nanowires (AgNWs), zinc oxide nanoparticles (ZnO), and reduced graphene oxide (rGO). We prepared a silver nanowire electrode by spin coating a silver nanowire solution on a glass substrate，the zinc oxide nanoparticles covered the silver nanowire grid and filled the gap of silver nanowire, which enhanced the adhesion of silver nanowire to the substrate. The outermost reduced graphene oxide provides protection for the material and improves the stability of the electrode in an air environment. The AgNWs/ZnO/rGO composite electrode prepared has a sheet resistance of about 9.96 ?/sq and a light transmittance of 71% (T550), which has good photoelectric properties. Experimental results show that the composite electrode has long-term stability in air.
关键词： composite electrode,silver nanowire,reduced graphene oxide,zinc oxide
更新于2025-09-16 10:30:52
-
Highly focused femtosecond laser directed selective boron doping in single SiC nanowire device for n-p conversion
摘要： In this work, site-selective Boron (B) doping in SiC nanowires has been demonstrated by utilizing focused femtosecond (fs) laser irradiation. Raman spectra and electrical performance indicate that the localized element doping in pristine n-type SiC nanowires can convert the segment into p-type. The formation of crystalline defects and vacancies in nanowires under fs laser irradiation, along with the simultaneous dissociation of the dopant molecules, can accelerate the doping process. Single SiC nanowire p-n junction and ?eld-effect transistors with a p-type segment have been fabricated based on the pristine n-type nanowire, showing a modi?ed electrical response as a logic gate to programmed voltage signals. This laser controlled selective doping may provide an alternative for precise element doping in semiconductors at the nanoscale, which can be promising for nanoelectronic unit fabrication.
关键词： SiC nanowire,femtosecond laser,n-p conversion,nanoelectronics,boron doping
更新于2025-09-16 10:30:52
-
Nitrogen plasma treatment of ZnO and TiO2 nanowire arrays for polymer photovoltaic applications
摘要： This work reports on a simple, yet unique approach to improving the opto-electronic properties of vertically-aligned arrays of rutile TiO2 and Wurzite ZnO nanowires by means of controlled nitrogen doping during exposure to highly kinetic radio-frequency generated N2 plasma radicals. Morphologically, the plasma treatment causes a distortion of the vertical alignment of the nanowires due to a dissociation of the weak Van der Waals force clustering the nanowires. Optical spectroscopy show that plasma treatment increases the light transmission of TiO2 arrays from 48% to 90%, with the ZnO arrays exhibiting an increase from 70% to 90% in the visible to UV range. The as-synthesized TiO2 array has an indirect band gap of 3.13 eV, which reduces to 3.03 eV after N2 treatment, with the ZnO equivalent decreasing from 3.20 to 3.17 eV post plasma exposure. A study of the 3d transition metal near edge fine structure of both Ti and Zn show that the N2 plasma treatment of the nanowires results in nitrogen doping of both TiO2 and ZnO lattices; this is confirmed by scanning transmission electron microscopy coupled with energy dispersive spectroscopy x-ray maps collected of single nanowires, which show a clear distribution of nitrogen throughout the metal-oxide. Application of these structures in P3HT:PCBM polymer blends shows progressive improvement in the photoluminescence quenching of the photoactive layer when incorporating both undoped and nitrogen-doped nanowires.
关键词： Electron energy loss spectroscopy,RF plasma nitrogen doping,One-dimensional nanowire arrays,Hydrothermal synthesis
更新于2025-09-16 10:30:52
-
Silicon Powder-Based Wafers for Low-Cost Photovoltaics: Laser Treatments and Nanowire Etching
摘要： In this study, laser-treated polycrystalline Si (pc-Si) wafers, fabricated by wire sawing of hot-pressed ingots sintered from Si powder, have been investigated. As-cut wafers and those with high-quality thin Si layers deposited on top of them by e-beam have been subjected to laser irradiation to clarify typical trends of structural modifications caused by laser treatments. Moreover, possibility to use laser-treated Si powder-based substrates for fabrication of advanced Si structures has been analysed. It is established that (i) Si powder-based wafers with thicknesses ~180 μm can be fully (from the front to back side) or partly (subsurface region) remelted by a diode laser and grain sizes in laser-treated regions can be increased; (ii) a high-quality top layer can be fabricated by crystallization of an additional a-Si layer deposited by e-beam evaporation on top of the pc-Si; and (iii) silicon nanowires can be formed by metal-assisted wet chemical etching (MAWCE) of polished Si powder-based wafers and as-cut wafers irradiated with medium laser power, while a surface texturing on the as-cut pc-Si wafers occur, and no nanowires can form in the region subject to a liquid phase crystallization (LPC) caused by high-power laser treatments.
关键词： polycrystalline Si wafers,nanowire etching,photovoltaics,laser treatments,silicon powder
更新于2025-09-16 10:30:52
-
Modal analysis for nanoplasmonics with nonlocal material properties
摘要： Plasmonic devices with feature sizes of a few nanometers exhibit effects which can be described by the nonlocal hydrodynamic Drude model. We demonstrate how to exploit contour integral methods for computing eigenfrequencies and resonant states of such systems. We propose an approach for deriving the modal expansion of relevant physical observables. We use the methods to perform a modal analysis for a metal nanowire. All complex eigenfrequencies in a large frequency range and the corresponding resonant states are computed. We identify those resonant states which are relevant for the extinction cross section of the nanowire.
关键词： extinction cross section,nanoplasmonics,hydrodynamic Drude model,modal analysis,nonlocal material properties,metal nanowire
更新于2025-09-16 10:30:52
-
Dispersion tailoring of silicon nanowire optical rectangular waveguide (SNORW)
摘要： Dispersion analysis on silicon nanowire optical rectangular waveguide (SNORW) has been presented in this paper by guiding light inside low refractive index region. Dispersion engineering is an essential study to utilize any photonic integrated circuit-based waveguide in linear and nonlinear optical devices. This paper exhibits distinctive dispersion characteristics recognized in the wavelengths of S, C and L bands by tailoring physical parameters of SNORW. Modal investigation and numerical analysis have been carried out by finite element method (FEM), which shows that SNORW configuration enables the flat and low negative dispersion behavior. This paper also demonstrates the utilization of cladding materials and structural parameters of SNORW to tune the magnitude and behavior of dispersion for flat dispersion profile.
关键词： Silicon nanowire,Photonic integrated circuits,Optical waveguide,Dispersion,Silicon photonics,Photonic structure,Nanophotonics
更新于2025-09-16 10:30:52
-
Loss compensation of surface plasmon polaritons in organic/metal nanowire heterostructures toward photonic logic processing; 有机/金属纳米线异质结中的SPPs损耗补偿用于 光学逻辑运算;
摘要： Surface plasmon polaritons (SPPs) are crucial for the development of next generation information and communication technologies. However, the ohmic losses inherent to all plasmonic devices seriously limit their practical application in on-chip photonic communications. Here, loss compensation of SPPs and their application in photonic logic processing was demonstrated in rationally designed organic/silver nanowire heterostructures. The heterostructures were synthesized by inserting silver nanowires (AgNWs) into crystalline organic microwires, which served as a microscale optical gain medium. These heterostructures with large organic/metal interfacial areas ensured the efficient energy transfer from excitons to SPPs. Gain for subwavelength SPPs in the heterostructure was achieved through stimulated emission of strongly confined SPPs. Furthermore, cascade gain was performed to realize basic nanoscale photonic devices, such as Boolean logic units. The results would pave an alternative avenue to incorporating SPP-enhanced devices into hybrid photonic circuitry.
关键词： organic nanowire,nanowire heterostructure,loss compensation,surface plasmon
更新于2025-09-12 10:27:22
-
Low reflecting hierarchically textured silicon by silver assisted chemical etching for potential solar cell application
摘要： Present study reports fabrication of silicon nanowires over micro-textured Si substrates. Silver assisted electroless chemical etching route has been adopted for fabrication of the nanowires. Influence of HF concentration on the formation kinetics has been investigated by using scanning electron microscopy. The hierarchical binary structures have been able to reduce solar weighted reflectance (SWR) to <3% in broad spectral range (300-1100 nm), from 38% SWR of the polished silicon without any additional coating. Such reduction in reflectivity is obtained for <1 μm nanowires length. It is observed that at relatively lower concentration of HF the nanowires are preferably formed only in <100> direction. However, with increase in the concentration, etching in both <100> and non-<100> directions such as <111> also occurs on the micro-pyramids of similar dimensions and results in the binary structures with slanted silicon nanowires on 3-dimansional micro-pyramids.
关键词： Nanowire,Micro-pyramid,Chemical Etching,Reflectance,Silicon Nanowire
更新于2025-09-12 10:27:22
-
Nanowire Quantum Dot Surface Engineering for High Temperature Single Photon Emission
摘要： Generating single photons at high temperature remains a major challenge, particularly for group III-As and III-P materials widely used in optical communication. Here, we report a high temperature single photon emitter based on a “surface-free” GaAs quantum dot in a GaAsP nanowire. By using self-catalyzed vapor-liquid-solid growth and simple surface engineering, we can significantly enhance the optical signal from the QDs with a highly polarized photoluminescence at 750 nm. The “surface-free” nanowire quantum dots show photon antibunching up to 160 K and well resolved exciton lines as high as 220 K.
关键词： surface engineering,photon antibunching,quantum dot,single photon source,nanowire
更新于2025-09-12 10:27:22