Al Nanorods Research Articles

A highly selective and fast-response photoluminescence humidity sensor based on F− decorated NH2-MIL-53(Al) nanorods

NH2-MIL-53(Al) nanorods studded with F− were successfully synthesized via coordination modulation with HF as a modulator.

Dual Strong Couplings Between TPPS J-Aggregates and Aluminum Plasmonic States.

We report on the spectral properties of strong coupling between the localized surface plasmon resonances (LSPRs) of aluminum (Al) nanostructures and tetraphenylporphyrin tetrasulfonic acid hydrate (TPPS) J-aggregates. Because of their wide spectral range of LSPR bands from ultraviolet to near-infrared wavelengths by controlling structural size, Al nanodisks can realize strong coupling with different excitons of TPPS J-aggregates. The Rabi splitting energies of the excitons based on Soret and Q bands are 300 and 180 meV, respectively. In addition to extinction spectrum, we have also measured an excitation spectrum to determine the essential absorption of the hybrid states and successfully confirmed a shoulder peak corresponding to a lower branch of hybrid states. In Al nanorod systems, strong coupling with two excitons can also be selectively induced by merely rotating the polarization of the incident light, which constituted a simple platform for the dynamic control of exciton/plasmon coupling states.

Ferromagnetic behavior due to Al3+ doping into ZnO nanorods

Al doped ZnO nanorods (NR's) having Al concentration up to 10mol% were grown by the hydrothermal method. XRD measurements showed that the Al substituted ZnO NR's maintained the hexagonal wurtzite structure for all levels of Al substitution. EDX measurements of the ZnO:Al NR's indicated that the Al substitution created additional Zn vacancies in the wurtzite structure which is reflected in the enhanced photoluminescence emission in the visible light spectra between 450 and 550nm of the more heavily doped ZnO:Al NR's. SEM images of the heavier doped ZnO:Al nanorods showed nano nodules being formed on the surface of the hexagonal shaped NR's. The saturation magnetizations of the ZnO:Al NR's as measured by a SQUID magnetometer increased to 10.66×10−4emu/g as more Al was substituted in. The hysteresis loops for the ZnO:Al NR's began to exhibit novel effects, such as horizontal shift (exchange bias field 0.0382kOe for the 9mol% NR) and butterfly shapes.

Near-UV-enhanced broad-band large third-order optical nonlinearity in aluminum nanorod array film with sub-10 nm gaps.

Plasmonic nanostructures with sub-10 nm gaps possess intense electric field enhancements, leading to their high reputation for exploring various functional applications at nanoscale. Till now, although large amounts of efforts have been devoted into investigation of such structures, few works were emphased on the nonlinear optical properties in near-ultraviolet (UV) region. Here, by combining sputtering technique and an optimized anodic aluminum oxide (AAO) template growing method, we obtain aluminum (Al) nanorod array film (NRAF) with average rod diameter and gap size of 50 and 7 nm, respectively. The Al-NRAF exhibits large third-order optical nonlinear susceptibility (χ(3)) and high figure of merit (χ(3)/α) over a broad wavelength range from 360 to 900 nm, and reaches their maximums at the shortest measured wavelength. In addition, comparisons with Au-NRAF and Ag-NRAF samples further confirm that Al-NRAF has better nonlinear optical properties in the blue and near-UV wavelength regions. These results indicate that Al nanostructures are promising candidates for nonlinear plasmonic applications at blue and near-UV wavelengths.

Low-Cost Fabrication of UV Photodetector Based on Hexagonal Nanocrystal ZnO:Al/p-Si Heterojunction

ZnO:Al/p-Si heterojunction was fabricated by depositing a hexagonal nanocrystal ZnO:Al film on p-type Si substrate using a simple chemical bath deposition (CBD) method. The vertically aligned hexagonal ZnO:Al nanocrystals reduce the grain boundary scattering and provide good conductivity. The ZnO:Al/Si heterojunction shows obvious photocurrent under ultraviolet (UV) illumination. A high UV-to-visible rejection ratio of the ZnO:Al/Si heterojunction indicates that the hexagonal nanocrystal ZnO:Al film is a good material for fabricating UV photodetectors. Furthermore, the response speed of the photodetector based on ZnO:Al hexagonal nanocrystal film is faster than that of most previously reported photodetectors based on ZnO:Al nanorods. We infer it is because the ZnO:Al nanocrystals film has a smaller surface to volume ratio than the ZnO:Al nanorod array.

Enhanced electroluminescence of an organic light-emitting diode by localized surface plasmon using Al periodic structure

In this work, we investigate the emission enhancement of an organic light-emitting diode (OLED) by increasing the internal quantum efficiency of the organic materials thanks to localized surface plasmon resonance (LSPR). We, particularly, consider periodic arrays of Al nanorods fabricated by e-beam lithography. The intrinsic parameters of the nanoparticles (NPs) are optimized using 3D finite-difference time-domain numerical simulations in order to match the emission wavelength of the Alq3-based OLED (520 nm) with the LSPR of the NPs. The periodic structures were fabricated on top of an indium titanium oxide anode. Our results indicate that the luminance and the current density of the OLED incorporating the Al arrays is drastically increased with an overall luminance increase of 20% compared to the standard OLED without a NP plasmonic layer.

Plasmonic Fano resonances in compositional heterogenous Al- Au nanorod dimers

We have investigated theoretically the plasmon resonance coupling in compositional heterogenous Al-Au nanorod dimers organized in a close proximity by end-to-end. It has been proved that the destructive interference between the bright dipole mode from Al nanorod and the dark quadrupole mode from Au nanorod nearby results in the appearance of apparent Fano resonance in the extinction spectra. The Fano resonance response on the structural dimension modifications in the proposed nanorod dimers have been estimated and determined. The Al-Au heterogeneous nanorod dimer shows a high sensitivity to the surrounding environment with a local surface plasmon resonance figure of merit of 7.6, which enables its promising applications in plasmonic sensing and detection.

Non-scanning optical near-field microscopy for nanophotonic security

We propose a novel method for observing and utilizing nanometrically fluctuating signals due to optical near-field interactions between a probe and target in near-field optical microscopy. Based on a hierarchical structure of the interactions, it is possible to obtain signals that represent two-dimensional spatial patterns without requiring any scanning process. Such signals reveal individual features of each target, and these features, when appropriately extracted and defined, can be used in security applications—an approach that we call nanophotonic security. As an experimental demonstration, output signals due to interactions between a SiO2 probe and Al nanorods were observed by using near-field optical microscopy at a single readout point, and these signals were quantitatively evaluated using an algorithm that we developed for extracting and defining features that can be used for security applications.

Far- and near-field optical properties of Al nanorod by discrete dipole approximation

We report a detailed theoretical investigation about the influence of the nanorod length and incident polarization on the far-field and near-field optical properties of Al nanorod using the discrete dipole approximation. The results show that Al nanorod has great tunability in the UV-Vis-NIR region and much stronger near-field intensity at UV and NIR wavelengths. The band position of transverse mode (TM) for the nanorod has a little blueshifted as the length increases, while that of the longitudinal mode (LM) is linearly redshifted with the size. In addition, we investigate how the incident polarization affects the extinction position and efficiency of the TM and LM. Finally, the near-field distribution dependences of the nanorod length for the TM and the LM have been analyzed. It is shown that much enhanced near-field always occur in the lateral surface of the nanorod for TM and the tip of the nanorod for the LM, respectively. The maximum local field enhancement factor of the TM is found to be about two times higher than that of the LM, which is due to close the region of interband transitions at about nm. These results would be of great potential application in localized surface plasmon resonance sensor and UV-plasmonic device.

Enhanced light trapping and plasmonic properties of aluminum nanorods fabricated by glancing angle deposition

Vertically aligned arrays of aluminum (Al) nanorods were fabricated by glancing angle deposition (GLAD) method. Nanorods with maximum lengths of 200 and 350 nm were grown on 100 nm flat Al thin film. Total and diffuse reflectance profiles were measured using an ultraviolet–visible–near infrared (UV-Vis-NIR) spectrophotometer utilizing an integrating sphere to study detailed optical properties of Al nanorods in comparison to conventional planar Al thin film samples. Finite-difference-time-domain (FDTD) optical modeling method was utilized to simulate the optical response of Al nanorod array and thin film structures. FDTD simulations were carried out for periodic and random arrays of Al nanorods as well as for an isolated single nanorod in order to investigate effects of geometrical structure on plasmonic and light trapping effects. UV-Vis-NIR spectrum results reveal that total reflectance is inversely proportional with nanorod length, and decreases down to as low as ∼25%–30% in the visible spectrum at wavelengths smaller than ∼750 nm, while it stays at ∼85%–90% for flat Al thin films at those wavelengths. FDTD simulation results indicate significant light absorption by GLAD Al nanorods mainly originating from enhanced light trapping and surface plasmon resonance among the nanorods.

Increasing the Solubility Limit for Tetrahedral Aluminium in ZnO:Al Nanorods by Variation in Synthesis Parameters

Nanocrystalline ZnO:Al nanoparticles are suitable building blocks for transparent conductive layers. As the concentration of substitutional tetrahedral Al is an important factor for improving conductivity, here we aim to increase the fraction of substitutional Al. To this end, synthesis parameters of a solvothermal reaction yielding ZnO:Al nanorods were varied. A unique set of complementary techniques was combined to reveal the exact position of the aluminium ions in the ZnO lattice and demonstrated its importance in order to evaluate the potential of ZnO:Al nanocrystals as optimal building blocks for solution deposited transparent conductive oxide layers. Both an extension of the solvothermal reaction time and stirring during solvothermal treatment result in a higher total tetrahedral aluminium content in the ZnO lattice. However, only the longer solvothermal treatment effectively results in an increase of the substitutional positions aimed for.

Optical Properties of Al@Al2O3 Nanorod as a UV and Visible Wavelengths Plasmonic Nanostructure

Aluminum as a new plasmonic material shows deep ultraviolet plasmon resonances which are broadly tunable. The use of aluminum plasmonic nanostructures offers new approaches, such as access high energy regions of the spectrum, low-cost and sustainable material. Therefore, aluminum is capable of being alternative plasmonic material compared to conventional gold and silver nanostructures. In this research, surface plasmon resonance properties of Al@Al2O3 core@shell nanorods in different dielectric environments were investigated. Using boundary element method and MNPBEM simulation package the sensitivity of aluminum plasmon resonance to the presence of Al2O3 layer, different aspect ratios and different dielectric mediums were studied. Results show that in Al nanorods with diameter of 3nm increasing length from 3 to 7nm plasmon longitudinal peak wavelength monotonously increase from 138nm to 213nm. In Al@Al2O3 nanorods with the same size and presence of 0.5nm Al2O3 oxide layer the peak wavelengths dramatically shift to higher values from 307nm to 514nm in the middle of visible region. Plasmon resonance sensitivity to medium refractive index was also investigated. Both aluminum and Al@Al2O3 nanorods exhibit red shift of longitudinal plasmon resonance wavelength by increasing refractive index from 1 to 2. Furthermore, red shift of plasmon peak wavelength by refractive index is linear in both cases. Finally results show that plasmonic response of Al@Al2O3 nanorods depend sensitively on presence of oxide layer, size and dielectric medium. As a new plasmonic material, Al@Al2O3 nanorods are capable for tremendous application due to wide ranges of plasmon resonances from deep UV to the middle of visible region.

Tuning the plasmon band number of aluminum nanorod within the ultraviolet-visible region by gold coating

The localized surface plasmon (LSP) properties of Al nanorod with Au coating have been investigated by using the quasi-static calculation. Because of the anisotropic plasmon splitting and the plasmon coupling between the Al and Au surfaces, the band number of LSP in the Al-Au core-shell nanorod could be tuned from 2 to 4 continuously in the ultraviolet-visible region. Due to the non-spherical symmetry and the dielectric polarization-induced plasmon energy fading, the Au coating-dependent plasmon shift and split are further affected by the aspect ratio and the dielectric surrounding. When the aspect ratio or the surrounding dielectric constant has a small value, the band number of LSP could only be tuned from 2 to 3. However, the band number of LSP could only be tuned from 3 to 4 when the aspect ratio or the surrounding dielectric constant has a large value. This tunable band number of LSP in the Au-coated Al nanorod provides potential application for multichannel plasmonic nanosensors.

Vivid, full-color aluminum plasmonic pixels.

Aluminum is abundant, low in cost, compatible with complementary metal-oxide semiconductor manufacturing methods, and capable of supporting tunable plasmon resonance structures that span the entire visible spectrum. However, the use of Al for color displays has been limited by its intrinsically broad spectral features. Here we show that vivid, highly polarized, and broadly tunable color pixels can be produced from periodic patterns of oriented Al nanorods. Whereas the nanorod longitudinal plasmon resonance is largely responsible for pixel color, far-field diffractive coupling is used to narrow the plasmon linewidth, enabling monochromatic coloration and significantly enhancing the far-field scattering intensity of the individual nanorod elements. The bright coloration can be observed with p-polarized white light excitation, consistent with the use of this approach in display devices. The resulting color pixels are constructed with a simple design, are compatible with scalable fabrication methods, and provide contrast ratios exceeding 100:1.

Tunable Fano resonances in heterogenous Al–Ag nanorod dimers

We theoretically investigate the plasmonic coupling in heterogenous Al–Ag nanorod dimers. A pronounced Fano dip is found in the extinction spectrum produced by the destructive interference between the bright dipole mode from a short Al nanorod and the dark quadrupole mode from a long Ag nanorod nearby. This Fano resonance can be widely tuned in both wavelength and amplitude by varying the rod dimensions and end geometry, the separation distance and the local dielectric environment. The Al–Ag heterogeneous nanorod dimer shows a high sensitivity to the surrounding environment with a local surface plasmon resonance figure of merit of 7.0, which enables its promising applications in plasmonic sensing and detection.

Abnormal residual stress in nanostructured Al thin films grown on Ti/glass substrates

The residual stress and micro-structural properties of nanostructured Al thin films prepared by electron beam evaporator are studied. The films were grown on Ti/glass substrates at normal and oblique angles of inclination. The average aspect ratio of Al nanorods produced at an oblique angle of incidence of 85°, increased from 2.2 to 6.0, as the thickness of the films increased from 100 nm to 600 nm. The column tilt angle of Al nanorods was observed to be in close agreement with the theoretical value. The XRD pattern of nanostructured Al thin films showed (111) planes oriented parallel to the substrate surface. The crystallite size was observed to be ∼9 nm for all the films produced at oblique angle deposition (OAD). Abnormal residual stresses were determined in the films produced at OAD. The nanocrystalline films produced at normal angle, exhibited tensile residual stress, while, the residual stresses in the films produced at oblique angles of inclination (α = 65°, 75°), were observed to be compressive. Residual stress-free nanocolumnar Al films (Al nanorod films) were observed, when they were grown at an oblique angle of inclination of 85°.

Enhanced Light Trapping in Periodic Aluminum Nanorod Arrays as Cavity Resonator

ABSTRACTMetallic nanostructures can exhibit different optical properties compared to bulk materials mainly depending on their shape, size, and separation. We present the results of an optical modeling study on ordered arrays of aluminum (Al) nanorods with a hexagonal periodic geometry placed on an Al thin film. We used a finite-difference time-domain (FDTD) method to solve the Maxwell's equations and predict the reflectance of the nanorod arrays. The thickness of the base Al film was set to 100 nm, and diameter, height and nanorod center-to-center periodicity were varied. Incident light in the FDTD simulations was an EM-circular polarized plane wave and reflectance profiles were calculated in the wavelength range 200-1800 nm. In addition, we calculated spatial electric field intensity distributions around the nanorods for wavelengths 300, 500, and 700 nm. Our results show that average reflectance of Al nanorods can drop down to as low as ∼50%, which is significantly lower than the ∼90% reflectance of conventional flat Al film at similar wavelengths. In addition to the overall decrease in reflectance, Al nanorod arrays manifest multiple resonant modes (higher-order modes) indicated by several dips in their reflectance spectrums (i.e. multiple attenuation peaks in their absorption profiles). Positions of these dips in the reflectance spectrum and spatial EM field distribution vary with nanorod height and diameter. Multiple reflectance peaks are explained by cavity resonator effects. Spatial EM field distribution profiles indicate enhanced light trapping among the nanorods, which can be useful especially in optoelectronic and solar cell applications.

Electrochemical elaboration of electrodes and electrolytes for 3D structured batteries

The challenges associated with the fabrication of three-dimensional (3D) electrode and electrolyte materials for Li-ion batteries are discussed. The basic issues for achieving a solid 3D cell foundation, which can simultaneously offer sufficient electronic conductivity to enable stable cycling, as well as enough compatibility with the incorporation of complementary components, have been addressed. Various electrochemical strategies for elaborating such systems are discussed and critically examined. Several current collector systems are presented including electrochemically prepared Cu and Al nanorods and commercial aperiodic carbon structures. Further electrochemical coating approaches then provide a direct method for the deposition of thin layers of active materials successfully demonstrated here as coatings on both 3D metal structures and commercially available 3D-structured carbon substrates. Enhanced capacities per foot print area are demonstrated for a number of 3D electrode materials, namely polyaniline on reticulated vitreous carbon, Cu2O on copper nanorods and TiO2 on Al nanorods. The crucial points for achieving a thin conformal coating of the corresponding 3D electrode structures with solid polymer electrolytes are also carefully analysed and discussed. In this context electro-polymerisation is proposed as a viable route to form thin electrolyte layers with promising characteristics. The high versatility of electro-polymerisation in combination with the various structures and methodologies adopted here represents a further step towards the development of cost-effective 3D microbattery devices.

Plasmonic enhancement of blue emission from ZnO nanorods grown on the anodic aluminum oxide (AAO) template

Luminescent properties of ZnO nanorods covered with Ag nanoparticles are examined. Nanorods were synthesized on AAO templates using Atomic Layer Deposition (ALD) technique. Two types of the samples were prepared with different arrangement of ZnO nanorods and doping conditions. Nanorods of the second type were codoped with Al, to stimulate defect-related emissions. The ZnO material fills heterogeneously the interior of the AAO nanopores and has hexagonal, wurtzite structure. Both types of structures exhibit a broad defect-related emission at about 440 nm, most probably related to recombination at zinc interstitial (Zni) defects. This emission in samples with a random distribution of ZnO:Al nanorods and finer Ag nanoparticles is enhanced by factor of ∼2.5 upon Ag deposition. The so-obtained material is interesting from the point of view of its application in blue range emitting diodes.

Aluminum Plasmonic Nanoantennas

The use of aluminum for plasmonic nanostructures opens up new possibilities, such as access to short-wavelength regions of the spectrum, complementary metal-oxide-semiconductor (CMOS) compatibility, and the possibility of low-cost, sustainable, mass-producible plasmonic materials. Here we examine the properties of individual Al nanorod antennas with cathodoluminescence (CL). This approach allows us to image the local density of optical states (LDOS) of Al nanorod antennas with a spatial resolution less than 20 nm and to identify the radiative modes of these nanostructures across the visible and into the UV spectral range. The results, which agree well with finite difference time domain (FDTD) simulations, lay the groundwork for precise Al plasmonic nanostructure design for a variety of applications.