Jin-Han Lin

Photoluminescence mechanisms of metallic Zn nanospheres, semiconducting ZnO nanoballoons, and metal-semiconductor Zn/ZnO nanospheres

We utilized a thermal radiation method to synthesize semiconducting hollow ZnO nanoballoons and metal-semiconductor concentric solid Zn/ZnO nanospheres from metallic solid Zn nanospheres. The chemical properties, crystalline structures, and photoluminescence mechanisms for the metallic solid Zn nanospheres, semiconducting hollow ZnO nanoballoons, and metal-semiconductor concentric solid Zn/ZnO nanospheres are presented. The PL emissions of the metallic Zn solid nanospheres are mainly dependent on the electron transitions between the Fermi level (EF) and the 3d band, while those of the semiconducting hollow ZnO nanoballoons are ascribed to the near band edge (NBE) and deep level electron transitions. The PL emissions of the metal-semiconductor concentric solid Zn/ZnO nanospheres are attributed to the electron transitions across the metal-semiconductor junction, from the EF to the valence and 3d bands, and from the interface states to the valence band. All three nanostructures are excellent room-temperature light emitters.

Laser oxidation and wide-band photoluminescence of thermal evaporated bismuth thin films

Bismuth (Bi) thin films of various microstructures were synthesized by thermal evaporation at varying substrate temperatures. The substrate temperature strongly affects the surface morphology and crystalline orientation of the Bi thin films. Peak shift and broadening of the Raman bands (Eg and A1g modes) observed with an increase in substrate temperature can be attributed to the phonon confinement and compressive stress effects. The Bi thin film depicts a laser-induced oxidation and phase transition as a function of varying laser power. Photoluminescence spectra show visible–near infrared broadband emission for polycrystalline Bi thin film prepared at high substrate temperature. This result indicates that polycrystalline Bi thin film can be a promising candidate for broadband optical fibre amplifiers and tunable lasers.

Electrochromic properties of large-area and high-density arrays of transparent one-dimensional β-Ta2O5 nanorods on indium-tin-oxide thin-films

We report on the synthesis, crystalline structure, and electrochromic properties of transparent one-dimensional (1D) orthorhombic (β) Ta2O5 nanorods grown in a large-area high-density array. The transparent 1D β-Ta2O5 nanorod array was synthesized on a conducting indium-tin-oxide thin-film via hot-filament metal-oxide vapor deposition. The array contained ∼1900 β-Ta2O5 nanorods per square micrometer, which were on average, ∼17 nm wide and ∼300 nm long. The good coloration/bleaching cycles, large ion-diffusion coefficient (∼2.35×10−8 cm2/s), and high reversibility (∼79.8%) demonstrate that the 1D β-Ta2O5 nanorods to be a potential electrochromic material for electrochromic devices or smart windows.

An efficient methodology for measurement of the average electrical properties of single one-dimensional NiO nanorods

We utilized a metal tantalum (Ta) ball-probe to measure the electrical properties of vertical-aligned one-dimensional (1D) nickel-oxide (NiO) nanorods. The 1D NiO nanorods (on average, ~105 nm wide and ~700 nm long) are synthesized using the hot-filament metal-oxide vapor deposition (HFMOVD) technique, and they are cubic phased and have a wide bandgap of 3.68 eV. When the 1D NiO nanorods are arranged in a large-area array in ohmic-contact with the Ta ball-probe, they acted as many parallel resistors. By means of a rigorous calculation, we can easily acquire the average resistance RNR and resistivity ρNR of a single NiO nanorod, which were approximately 3.1 × 1013 Ω and 4.9 × 107 Ω.cm, respectively.

Room-temperature wide-range photoluminescence and semiconducting characteristics of two-dimensional pure metallic Zn nanoplates

We explore the structural, electronic, photoluminescent, metallic, and semiconducting characteristics of 2D pure Zn-metal nanoplates. The 2D pure Zn-metal nanoplates are synthesized by the hot-filament metal-oxide vapor deposition (HFMOVD) technique. They have an average diameter and thickness of ∼520 and ∼144 nm, respectively. The results of the electronic and crystalline structure studies reveal the 2D nanoplates to be pure Zn hexagonal crystals, which can provide a wide-range photoluminescence from ultraviolet (UV) to red light emissions at room temperature. The measured valence-band and the calculated band-structure of the 2D pure Zn-metal nanoplates verify that the UV and blue light arise from the 3d–sp interband transitions, while the green, yellow, and red lights come from the valence-conduction interband transitions at a bandgap that is only present in the 2D nanoplates. Therefore, the 2D pure Zn-metal nanoplates possess not only metallic, but also semiconducting characteristics.

Electrical and chemical characteristics of probe-induced two-dimensional SiOx protrusion layers

Three two-dimensional SiOx (x ≡ O/Si content ratio and x > 2) protrusion layers of ∼0.5, ∼4, and ∼6 nm high were induced on a native SiO2 layer by atomic force microscopy (AFM) probes. X-ray photoemission spectroscopy (XPS) was used to reveal the elemental quantity of the photoelectrons, Si 2p core-levels, and Si oxidation states in the three SiOx protrusion layers and native SiO2 layer. Pt-coated conductive AFM probes were also exploited to acquire the rectifying current-voltage (IV) characteristics of the three SiOx protrusion layers and the native SiO2 layer, indicating all the three SiOx protrusion layers to be good Schottky diodes.

Effective photoluminescence in a large-area array of Ta 2 O 5 nanodots (PL of Ta 2 O 5 nanodots)

In this study we present the synthesis of the large-area Ta<inf>2</inf>O<inf>5</inf> nanodot array by utilizing hot filament metal vapor deposition technique. The Ta<inf>2</inf>O<inf>5</inf> nanodots were arranged in a large-area array on a Si wafer, and their average diameter is ∼ 35 nm. X-ray photoemission spectroscopy (XPS) revealed the stoichiometric Ta and O compositions of Ta<inf>2</inf>O<inf>5</inf> nanodots. Raman spectroscopy showed the Ta<inf>2</inf>O<inf>5</inf> nanodots to be of orthorhombic (β) crystal. Photoluminescence (PL) spectroscopy displayed that the β-Ta<inf>2</inf>O<inf>5</inf> nanodots provided green and red light emissions at room temperature.