Effective photoluminescence in a large-area array of Ta2O5 nanodots

Temperature-dependent ultraviolet photoluminescence in hierarchical Zn, ZnO and ZnO/Zn nanostructures

The temperature-dependent effects on the ultraviolet (UV) photoluminescence (PL) enhancement, blueshift, thermal quenching, and chromaticity of the two-dimensional (2D) Zn nanosheets, 2D-hierarchical ZnO nanostructures, and 2D-hierarchical ZnO/Zn nanostructures are presented. In this study, 2D Zn nanosheets were synthesized using a hot-plate metal vapor deposition technique, after which 2D-hierarchical ZnO nanostructures and ZnO/Zn were prepared from the 2D Zn nanosheets by a simple thermal annealing method. The enhancement and blueshift of the UV PL emissions from the three nanostructures at low temperatures arose from three distinct PL mechanisms. For the ZnO nanostructures, the UV PL emission enhancements and blueshifts at low temperature were due to the conversion of the free excitons (FXs) to neutral-donor-bound-excitons (D⁰Xs). The ZnO/Zn nanostructures possessed the highest UV PL intensities among the three nanostructures, because the free electrons from the Zn portions across the metal-semiconductor heterojunctions greatly assisted in enhancing the PL emissions. The enhancement and thermal quenching were quantitatively analyzed with simple normalization methods. The results show that all three kinds of nanostructures are excellent candidates for use in UV light emitters.

Terahertz spin-wave waveguides and optical magnonics in one-dimensional NiO nanorods

The two-magnon (2M) spin waves with a magnon frequency of 43 THz, generated by a polarized laser, were first observed in one-dimensional (1D) NiO nanorods. The 1D NiO nanorods of ∼700 nm length, which have perfectly in-plane antiferromagnetic spins lying on the (200) and (100) faces, are the smallest spin-wave waveguides. Due to the magneto-optical Faraday effect (MOFE), the significant change in the Faraday intensity can show the 2M information in the NiO nanorods. There are only two 2M-on and 2M-off states at various applied alternating-current magnetic fields and laser-incident angles, which make the 1D NiO nanorods excellent optical nanomagnonics.

Impact of Nanosize on Supercapacitance: Study of 1D Nanorods and 2D Thin-Films of Nickel Oxide

We synthesized unique one-dimensional (1D) nanorods and two-dimensional (2D) thin-films of NiO on indium-tin-oxide thin-films using a hot-filament metal-oxide vapor deposition technique. The 1D nanorods have an average width and length of ∼100 and ∼500 nm, respectively, and the densely packed 2D thin-films have an average thickness of ∼500 nm. The 1D nanorods perform as parallel units for charge storing. However, the 2D thin-films act as one single unit for charge storing. The 2D thin-films possess a high specific capacitance of ∼746 F/g compared to 1D nanorods (∼230 F/g) using galvanostatic charge-discharge measurements at a current density of 3 A/g. Because the 1D NiO nanorods provide more plentiful surface areas than those of the 2D thin-films, they are fully active at the first few cycles. However, the capacitance retention of the 1D nanorods decays faster than that of the 2D thin-films. Also, the 1D NiO nanorods suffer from instability due to the fast electrochemical dissolution and high nanocontact resistance. Electrochemical impedance spectroscopy verifies that the low dimensionality of the 1D NiO nanorods induces the unavoidable effects that lead them to have poor supercapacitive performances. On the other hand, the slow electrochemical dissolution and small contact resistance in the 2D NiO thin-films favor to achieve high specific capacitance and great stability.

Doping-free bandgap tuning in one-dimensional Magnéli-phase nanorods of Mo4O11

We synthesized one-dimensional (1D) Magnéli-phase nanorods of Mo4O11 using the hot filament metal-oxide vapor deposition technique. The 1D Magnéli-phase Mo4O11 nanorods synthesized at 1000, 1050, 1100, 1150, and 1200 °C contain varying combinations of two orthorhombic (α) and monoclinic (η) phases, and various mixtures of Mo(4+), Mo(5+) and Mo(6+) cations, while those synthesized at a higher temperature look bluer. The shifts of the transmittance maximum and absorbance minimum of the 1D Magnéli-phase Mo4O11 nanorods are inversely and linearly proportional to the elevated temperature, verifying that the bandgaps (Eg) are inversely proportional to the elevated temperature. The bandgap (Eg) of the 1D Magnéli-phase Mo4O11 nanorods can be tuned by simply controlling the synthesis temperature without doping with other materials, giving the 1D Magnéli-phase Mo4O11 nanorods good potential for use in optoelectronic nanodevices and bandgap engineering.

Size-controllable synthesis of Bi/Bi2O3 heterojunction nanoparticles using pulsed Nd:YAG laser deposition and metal-semiconductor-heterojunction-assisted photoluminescence

We synthesized Bi/Bi2O3 heterojunction nanoparticles at various substrate temperatures using the pulsed laser deposition (PLD) technique with a pulsed Nd:YAG laser. The Bi/Bi2O3 heterojunction nanoparticles consisted of Bi nanoparticles and Bi2O3 surface layers. The average diameter of the Bi nanoparticles and the thickness of the Bi2O3 surface layer are linearly proportional to the substrate temperature. The heterojunctions between the Bi nanoparticles and Bi2O3 surface layers, which are the metal-semiconductor heterojunctions, can strongly enhance the photoluminescence (PL) of the Bi/Bi2O3 nanoparticles, because the metallic Bi nanoparticles can provide massive free Fermi-level electrons for the electron transitions in the Bi2O3 surface layers. The enhancement of PL emission at room temperature by metal-semiconductor-heterojunctions make the Bi/Bi2O3 heterojunction nanoparticles potential candidates for use in optoelectronic nanodevices, such as light-emitting diodes (LEDs) and laser diodes (LDs).

Promising field electron emission performance of vertically aligned one dimensional (1D) brookite (β) TiO2nanorods

The vertically aligned and uniformly dispersed β-TiO₂nanorods injected electrons direct toward emission sites, and prominently contributed to the low turn-on field of 3.9 V μm⁻¹at a current density of 10 μA and also enhance the emission stability.