Showing papers by "Hong Jin Fan published in 2010"
TL;DR: In this paper, a sacrificial template-accelerated hydrolysis (STAH) approach was proposed for the synthesis of iron oxide-based nanotube arrays including hematite α-Fe2O3 and magnetite Fe3O4 on centimeterscale conducting alloy substrates.
Abstract: We report a novel “sacrificial template-accelerated hydrolysis” (STAH) approach to the synthesis of iron oxide-based nanotube arrays including hematite α-Fe2O3 and magnetite Fe3O4 on centimeter-scale conducting alloy substrates. ZnO nanowire arrays are chosen as the inexpensive and sacrificial templates that do not contribute to the component of final iron oxide nanotubes but can be in situ dissolved by the acid produced from the Fe3+ precursor hydrolysis. Interestingly, the ZnO template dissolution in turn accelerates the Fe3+ hydrolysis, which is essential to initiating the nanotube formation. Such a STAH approach provides a morphology-reservation transformation, when various shaped ZnO templates are adopted. Moreover, by introducing glucose into the precursor solution, we also successfully obtain carbon/hematite(C/α-Fe2O3) composite nanotube arrays on large-area flexible alloy substrate, with a large number of pores and uniform carbon distribution at a nanoscale in the nanotube walls. These arrays have...
318 citations
TL;DR: In this article, the surface plasmon of Au nanoparticles was used to enhance the ultraviolet emission of ZnO nanorods, while the defect-related emission was completely suppressed.
Abstract: The author observe sixfold enhancement in the near band gap emission of ZnO nanorods by employing surface plasmon of Au nanoparticles, while the defect-related emission is completely suppressed. Time-resolved photoluminescence indicates that the decay process becomes much faster by Au capping. The remarkable enhancement of the ultraviolet emission intensities and transition rates is ascribed to the charge transfer and efficient coupling between ZnO nanorods and Au surface plasmons. The suppression of the green emission might be due to a combined effect of Au surface plasmon and passivation of the ZnO nanorod surface traps.
251 citations
TL;DR: Highly ordered treelike Si/ZnO hierarchical nanostructures are successfully prepared in a large scale by combining two common techniques, viz., photolithography-assisted wafer-scale fabrication of Si nanopillars and bottom-up hydrothermal growth of ZnO nanorods.
Abstract: Highly ordered treelike Si/ZnO hierarchical nanostructures are successfully prepared in a large scale by combining two common techniques, viz., photolithography-assisted wafer-scale fabrication of Si nanopillars and bottom-up hydrothermal growth of ZnO nanorods. Silver nanoparticles are decorated onto the nanotrees by photochemical reduction and deposition. The Si/ZnO/Ag hybrid nanotrees are employed as SERS-active substrates, which exhibit good performance in terms of high sensitivity and good reproducibility. In addition to the SERS application, such ordered Si/ZnO arrays might also find potential applications in light-emitting diodes and solar cells.
198 citations
TL;DR: In this paper, a series of Fe, Mn, and Cu doped Ca3Co4O9 was investigated and the results indicated that Fe/Mn substitutes for Co in CoO2 layers whereas Cu substitutes for CO in Ca2CoO3 layers.
Abstract: We report the strongly correlated, electrical transport, magnetic, and thermoelectric properties of a series of Fe, Mn, and Cu doped Ca3Co4O9. The results indicate that Fe/Mn substitutes for Co in CoO2 layers whereas Cu substitutes for Co in Ca2CoO3 layers. Because of the different doping sites, the electronic correlations increase remarkably in Fe and Mn doped series while remaining unchanged in Cu doped series. Correspondingly, the transport mechanism, magnetic properties, and some characteristic parameters along with transition temperatures all exhibit two distinct evolutions for Fe/Mn doping and Cu doping. The thermoelectric characteristics are improved in each series. Nevertheless, the improvement of thermoelectric performance is most significant in Fe doped samples due to the unexpected changes in thermopower and resistivity. The unusual thermopower behavior can be well described by the variations of electronic correlation. Possible approaches for further improvement of the thermoelectric performanc...
136 citations
TL;DR: The results unambiguously demonstrate a close correlation between the structural distortions and TE characteristics in this family and a new approach is suggested to improve the TE performance by controlling the structure factors in such strongly correlated oxide systems.
Abstract: Detailed structures and thermoelectric (TE) properties are investigated for the perovskite La1−xCaxCoO3 and La1−xSrxCoO3 with 0 ≤ x ≤ 0.3. The monoclinic crystal structures for all samples are refi...
83 citations
TL;DR: Transmission electron microscopy investigation shows that the deposited ZnO shell is continuous and uniform, in contrast to the previously reported particle morphology, and has a good crystalline quality as indicated by Raman and photoluminescence measurements.
Abstract: In this article, direct coating of ZnO on PECVD-grown multi-walled carbon nanotubes (MWCNTs) is achieved using atomic layer deposition (ALD). Transmission electron microscopy investigation shows that the deposited ZnO shell is continuous and uniform, in contrast to the previously reported particle morphology. The ZnO layer has a good crystalline quality as indicated by Raman and photoluminescence (PL) measurements. We also show that such ZnO layer can be used as seed layer for subsequent hydrothermal growth of ZnO nanorods, resulting in branched CNT–inorganic hybrid nanostructures. Potentially, this method can also apply to the fabrication of ZnO-based hybrid nanostructures on other carbon nanomaterials.
66 citations
TL;DR: In this article, the photoluminescence properties of tin oxide (SnO2) nanowires were studied in detail using high spectral resolution spectroscopy in a temperature range of 10-300 K.
Abstract: Photoluminescence (PL) properties of tin oxide (SnO2) nanowires are studied in detail using high spectral resolution spectroscopy in a temperature range of 10-300 K. The nanowires have an average diameter of 86 nm. The high quality of the nanowires enables the observation of rich fine structures in the ultraviolet PL spectra at low temperatures. By carefully analyzing the temperature and excitation power dependent spectra, the following emissions are identified: recombination of donor-acceptor pairs, excitons bound to neutral and ionized donor impurities and optical transitions from free electrons to neutral acceptor impurities. Moreover, it is believed that the emission from recombination of free excitons is observed, which is unusual for SnO2, a dipole forbidden direct band gap semiconductor.
63 citations
TL;DR: In this article, the electrical, thermal, magnetic, and thermoelectric properties of Y-doped Ca(3)Co(4)O(9) from 300 down to 5 K were investigated.
Abstract: We report the electrical, thermal, magnetic, and thermoelectric properties of Y-doped Ca(3)Co(4)O(9) from 300 down to 5 K. The results indicate that with Y doping, the increase of resistivity originates from the decreases of carrier concentration and mobility, while the increase of Seebeck coefficient is caused by the reduction of carrier concentration together with the enhanced electronic correlation. Point-defect scattering, is the dominant thermal transport mechanism in this system. Due to the considerable difference in mass between Y(3+) and Ca(2+), thermal conductivity is observably suppressed by doping. The substitution of Y also disturbs the interlayer ferrimagnetic coupling. The ground state of this System converts front ferrimagnetism to paramagnetism gradually. The alteration of transport properties of Ca(3-x)Y(x)Co(4)O(9) reveals two Crossovers: the transition from Fermi-liquid-like metal to thermally activated semiconductor occuring at x approximate to 0.25, and the transition from thermally activated semiconductor to two-dimensional variable range hopping semiconductor occurring at x approximate to 0.5. The optimal thermoelectric response In Ca(3-x)Y(x)Co(4)O(9) is found to exist only at the critical state after which the doping-induced metal-insulator transition takes place. Oil the basis of these experimental results, a possible phase diagram for Ca(3-x)Y(x)Co(4)O(9) is proposed.
56 citations
47 citations
TL;DR: In this paper, the effect of shrinking pore size on filling uniformity was investigated in a stop-flow fill−hold−purge process in comparison with a continuous-flow pulse-purge procedure.
Abstract: Atomic layer deposition (ALD) is shown as a unique method to produce high aspect ratio (AR) nanostructures through conformal filling and replication of high AR templates. The stop-flow process is often used as an alternative to the conventional continuous flow process to obtain high step coverage. However, there is a need for understanding the deposition kinetics and optimizing the deposition process to fabricate defect-free nanostructures. In this Article, TiO2 ALD in high AR self-assembled opal photonic crystal templates was performed in stop-flow fill−hold−purge process in comparison with continuous flow pulse−purge process. Photonic band gap properties of opal templates were characterized and compared with simulated band diagrams for quantitative investigation of filling kinetics and the effect of shrinking pore size on filling uniformity. Γ−L bands in the transmittance spectra of ALD-infiltrated opals accurately represented the depth profile of the depositions without the need for expensive sample pr...
45 citations
TL;DR: In this paper, a simple method was proposed to synthesize single-crystalline La1−xSrxCoO3 nanowire compacts with an improved TE efficiency.
Abstract: Nanotechnology has brought novel and controllable thermoelectric (TE) characteristics to conventional materials. Here we report a simple method to synthesize single-crystalline La1−xSrxCoO3 nanowire compacts with an improved TE efficiency. The figure of merit ZT in the nanowires can reach 0.19 at 300 K, which is nearly twice that in the bulk, and this room-temperature ZT is very high among oxide materials. The enhancement of TE efficiency can be attributed to both extrinsic and intrinsic factors: First, the unique nanowire structure together with numerous interfaces in the compact samples strongly suppresses the phonon thermal transport. Second, the small dimensions of nanowires give rise to an unexpected increase in the thermopower due to a reduction of the effective bandwidth and variation of the electron configuration. Our results indicate that the TE response of conventional oxides can be effectively improved by the form of nanowires, which can be synthesized much easier than single crystals and epita...
TL;DR: Electroluminescence characteristics of a heterojunction light-emitting diode, which was fabricated by depositing a layer of randomly assembled n-SnO(2) nanowires on p-GaN:Mg/sapphire substrate via vapor transport method, were investigated at room temperature.
Abstract: Electroluminescence characteristics of a heterojunction light-emitting diode, which was fabricated by depositing a layer of randomly assembled n-SnO2 nanowires on p-GaN:Mg/sapphire substrate via vapor transport method, were investigated at room temperature. Peak wavelength emission at around 388 nm was observed for the diode under forward bias. This is mainly related to the radiative recombination of weakly bounded excitons at the shallow-trapped states of SnO2 nanowires, Under reverse bias, near bandedge emission from the p-GaN:Mg/sapphire leads to the observation of emission peak at around 370 nm.
TL;DR: In this paper, high quality vertical aligned arrays of ZnCdO/ZnO coaxial multiple-quantum-well (MQW) nanowire heterostructures are fabricated for the first time by combining a simple chemical vapor deposition (CVD) and pulsed laser deposition (PLD) method.
Abstract: High quality vertical-aligned arrays of ZnCdO/ZnO coaxial multiple-quantum-well (MQW) nanowire heterostructures are fabricated for the first time by combining a simple chemical vapor deposition (CVD) and pulsed laser deposition (PLD) method. The ZnO nanowire core enables epitaxial and dislocation-free growth of uniform ZnCdO/ZnO quantum wells. Both steady-state and time-resolved photoluminescence measurements of the MQW nanowires are performed in the temperature range of 10-300 K. Strong quantum confinement and carrier localization effect are verified. In addition, an S-shaped temperature dependence is observed for both the exciton emission energy (Ep) and their lifetime in ZnCdO MQWs, which has not previously been reported in ZnMgO MQWs. A simple phenomenological model was introduced to explain this anomalous behavior. Such ZnCdO/ZnO coaxial MQW nanowires might find applications in nanoscale laser sources and other oxide-based quantum devices.
TL;DR: The thermal transport properties of a series of electron-doped CaMnO(3) perovskites have been investigated in this article, where phonon thermal conductivity is dominant, and both electron and spin wave contributions are negligible.
TL;DR: Four- and eight-node quadrilateral finite element models which can readily be incorporated into the standard finite element program framework are devised for plane Helmholtz problems and are considerably more accurate than their single-field counterparts.
TL;DR: In this paper, the structure and magnetic properties of LaCoO3 nanowires are investigated as a function of the diameter in the temperature range of 5-300 K. The structure analysis reveals that LaO3 nano-connections exhibit a monoclinic distorted structure with I2/a space group in the entire investigated temperature range.
Abstract: The structure and magnetic properties of LaCoO3 nanowires are investigated as a function of the diameter in the temperature range of 5–300 K. Ferromagnetism below 85 K is observed in these nanowires, in agreement with the recent observations in LaCoO3 epitaxial thin films and nanoparticles. With the diameter of nanowires decreasing, the unit-cell volume increases, while both the global and local structural distortions lessen, accompanied by the gradual enhancement of ferromagnetism. The structure analysis reveals that LaCoO3 nanowires exhibit a monoclinic distorted structure with I2/a space group in the entire investigated temperature range. Different from bulks, there is no clear spin-state transition occurring with temperature in LaCoO3 nanowires. There exists a noticeable Jahn–Teller (JT) distortion in the nanowires even at the lowest temperature, namely, orbital-ordered JT active Co3+ ions with intermediate-spin (IS) state persist at low temperatures, which is not observed in bulk LaCoO3. These result...
TL;DR: In this article, the high-temperature transport and thermoelectric characteristics of Ca(3-x) Y (x) Co(4)O(9) (x = 0-0.75) series were studied up to 1000 K.
Abstract: The high-temperature transport and thermoelectric characteristics of Ca(3-x) Y (x) Co(4)O(9) (x=0-0.75) series were studied up to 1000 K. The results reveal that the substitution of Y(3+) for Ca(2+) not only increases resistivity but also gradually alters the transport mechanism. The localization of carriers narrows bandwidth, which induces the evolution of the system from metal to variable-range hopping semiconductor and then to thermally activated semiconductor. The increasing thermopower with doping originates from the reduction of carrier concentration along with enhanced electronic correlations. Thermoelectric figure of merit ZT of Ca(3)Co(4)O(9) system is improved by Y doping. However, the optimal thermoelectric performance is found to only exist at the critical doping level where doping-induced metal-semiconductor transition occurs. This result suggests an intrinsic correlation between transport mechanism and thermoelectric response in this system.
TL;DR: In this paper, surface plasmon effects of Au nanoparticles on the photoluminescence properties of ZnCdO/ZnO coaxial multiquantum-well nanowires fabricated using chemical vapor deposition and pulse laser deposition methods.
Abstract: The authors present the surface plasmon effects of Au nanoparticles on the photoluminescence properties of ZnCdO/ZnO coaxial multiquantum-well nanowires fabricated using chemical vapor deposition and pulse laser deposition methods. The spontaneous emission rate from ZnCdO quantum wells was increased by surface plasmon coupling by 1.29 times. The strong plasmon coupling between ZnO barriers and Au nanoparticles provides an extra fast decay channel for excitons generated in ZnO barrier layer and leads to exciton redistribution in ZnCdO/ZnO coaxial quantum wells, which promotes radiative recombination in ZnO barriers but reduces the number of excitons relaxing into the ZnCdO quantum wells.
TL;DR: In this paper, it was shown that ferromagnetic clusters are embedded in an antiferromagnetic matrix in the mix-valent R1−xCaxMnO3 (R denotes rare-earth element, x = 0.88−1) manganites at low temperature, namely, magnetic phase separation phenomenon.
Abstract: Combining transport and magnetic properties measurements, we find that ferromagnetic clusters are embedded in an antiferromagnetic matrix in the mix-valent R1−xCaxMnO3 (R denotes rare-earth element, x = 0.88−1) manganites at low temperature, namely, magnetic phase separation phenomenon. In contrast to the hole-doped manganites, ferromagnetic clusters in the electron-doped manganites are likely ellipsoidal-type rather than stripe-type, evidenced by modeling the low temperature electrical transport behavior. Percolative conduction transport between the ferromagnetic clusters takes place in the case of phase separation state. As the R ion content exceeds a certain level, colossal magnetoresistance is observed in a narrow range in this system. The rotation of ferromagnetic domains under magnetic field may underlie the magnetoresistance effect in the phase separation state of these electron-doped manganite systems.
TL;DR: In this article, the effects of the deposition temperature and film thickness on the morphology of the ZnO nanorods are studied, and it is shown that the ALD has its advantage over the conventional dipcoating method when being applied to three-dimensional (3D) substrates, as exemplified by the macroporous Si adn CNT arrays.
Abstract: Atomic layer deposition (ALD) ZnO film as seed layer for growing aligned ZnO nanorods arrays is demonstrated. The effects of the deposition temperature and film thickness to the morphology of the ZnO nanorods are studied. The ALD is found to have its advantage over the conventional dip-coating method when being applied to three-dimensional (3D) substrates, as exemplified by the macroporous Si adn CNT arrays. As one example, the CNT-ZnO 3D hybrid nanostructures are obtained which might be useful for energy-related applications.