Liang-Chiun Chao

Room-temperature visible and infrared photoluminescence from Pr-implanted GaN films by focused-ion-beam direct write

Visible and infrared photoluminescence (PL) have been obtained from Pr-implanted GaN films using focused-ion-beam (FIB) direct write utilizing a Pr–Pt liquid alloy ion source. FIB implantation was performed on GaN films grown by molecular-beam epitaxy (MBE), hydride vapor-phase epitaxy, and metalorganic chemical-vapor deposition. After annealing, strong room-temperature emission was observed in the red (at 650 nm) and in the infrared (at several wavelengths including 0.96, 1.3, and 1.9 μm). Essentially identical PL spectra were obtained in the implanted GaN films as in the in situ Pr-doped GaN films grown by MBE.

Rare earth focused ion beam implantation utilizing Er and Pr liquid alloy ion sources

We have developed procedures for the fabrication of Er–Ni and Pr–Pt liquid alloy ion sources (LAIS). Er2+beam with target current of ∼100 pA and Pr2+ beams with target current of ∼200 pA were obtained, which correspond to 50% and 80% of the total target current, respectively. Both Er–Ni and Pr–Pt alloys oxidize quickly once exposed to air. Er–Ni source lifetimes were generally larger than 200 μA h. The source lifetimes of Pr–Pt LAISs were approximately 30 μA h, limited by oxide contamination and wettability problems. Visible photoluminescence has been observed from Er- or Pr-doped GaN, Al2O3, and ZBLAN glass using focused ion beam direct write implantation.

Zinc oxide nanodonut prepared by vapor-phase transport process

Zinc oxide nanodonuts have been synthesized using vapor-phase transport method. Zinc oxide powder, graphite powder, and erbium oxide powder were mixed with a molar ratio of 1:1:0.2 and heated at 1050°C in a flowing argon environment. Perfectly donut-shaped nanostructures with outer diameters ranging from 450to850nm were observed. The inner diameter of the zinc oxide donut varies from 75to95nm and the vertical distance from the highest point to the lowest point vary from 85to130nm. The composition of the nanodonut was analyzed using Auger electron spectroscopy and was found to be mainly of zinc oxide. Diffusion of silicon into the zinc oxide layer was confirmed by secondary ion mass spectroscopy.

Upconversion luminescence of Er-implanted GaN films by focused-ion-beam direct write

Upconversion luminescence has been obtained from Er-implanted GaN films by focused-ion-beam (FIB) direct write. FIB implantation was performed on GaN films grown by molecular beam epitaxy, hydride vapor phase epitaxy, and metalorganic chemical vapor deposition. After implantation, the GaN samples were annealed at 1100 °C for 1 h in various ambients (Ar, N2, and O2). Strong green upconversion was observed at 523 and 546 nm under red (840 nm) and infrared (1.0 μm) excitation. Upconversion intensity was measured for Er doses ranging from 4.3×1012 to 2.4×1016 atoms/cm2. Maximum upconversion intensity at 546 nm was observed at a dose of 1–2×1015 atoms/cm2, which corresponds to an atomic percentage of 0.3%–0.6%.

Fabrication of zinc nanotip arrays by ion beam sputtering

Zinc nanotip arrays were fabricated on polycrystalline zinc foils using capillaritron ion beam sputtering. The geometry and structure of the nanotip are found to be dependent on the ion species, beam energy, and exposure fluence. After 12keV argon ion beam sputtering, zinc nanotips with end radii less than 5nm and aspect ratios larger than 20 were obtained. Cone-shaped nanostructures with an aspect ratio of 3 and tip radius of 25nm were found after oxygen ion beam sputtering. Energy dispersive x-ray spectroscopy and scanning electron microscopy analysis indicate that the high aspect ratio nanotip formation mechanism after argon ion beam sputtering is due to differential erosion and anisotropic hardness of zinc nanocrystal, while the formation mechanism of cone-shaped nanostructures after oxygen ion beam sputtering is due mainly to the formation of ZnO on the apex, acting as an etch stop. The field emission properties of zinc nanotips are presented.

ZnO nanoneedles prepared by ion implantation and thermal oxidation on metallic zinc foils

ZnO nanoneedles are prepared on polycrystalline metallic zinc foils by oxygen/nitrogen ion implantation and thermal oxidation. The ZnO nanoneedles are grown along the [1 1 0] direction and their orientations are dependent on the crystallographic grain orientations of the substrate. ZnO nanoneedles prepared by oxygen implantation and thermal oxidation exhibit a turn-on field of 6.5 V µm−1 and field emission properties are improved as exposure ion fluence increases. ZnO nanoneedles prepared by nitrogen implantation shows similar morphology but inferior field emission properties. Energy dispersive x-ray spectroscopy analysis indicates that ZnO nanoneedles prepared by oxygen implantation contain excess zinc, while those prepared by nitrogen implantation contain excess oxygen. The difference in stoichiometry is probably due to different degrees of porosity of the zinc foil after ion implantation.

Erbium-Doped ZnO Prepared by Vapor-Phase Transport

Erbium-doped ZnO has been prepared by vapor-phase transport. ZnO powder, graphite powder, and Er2O3 powder were mixed at a molar ratio of 1:1:0.2 and heated at 1054 °C. Erbium-doped ZnO was deposited on n-type (100)Si wafers located in the same temperature zone. The photoluminescence of the as-deposited sample shows a strong ZnO band-gap emission near 378 nm. After annealing, green emissions at 548, 566, 576, 585, and 595 nm were observed, which correspond to the 4 f inner shell transition of erbium from 2H11/2 to 4I15/2 and 4S3/2 to 4I15/2. Our results indicate that vapor-phase transport is an alternative route for doping ZnO with erbium.

ZnO nanostructures grown on zinc nanocones by thermal oxidation

ZnO nanostructures were grown on metallic zinc nanocones by thermal oxidation. The metallic nanocones are prepared by argon ion beam sputtering utilizing a capillaritron ion source. The aspect ratios of zinc nanocones are found to be dependent on ion beam energy and substrate temperatures. By maintaining the substrate temperature to be less than 60°C, the aspect ratio of zinc nanocones increases from 1.2 to 2.7 as ion beam energy increases from 6to12keV. Zn nanocones with aspect ratio larger than 25 are obtained by utilizing a 12keV ion beam and allowing the substrate to increase to ∼180°C by in situ ion beam heating. Thermal oxidation of zinc nanocones results ZnO nanowires and nanoblades grown outwardly from the shank. This provides a convenient route for the fabrication of ZnO nanowires for field emission flat panel display and dye-sensitized solar cell applications.

Growth and characterization of Er doped ZnO prepared by reactive ion beam sputtering

Er doped ZnO (EZO) has been deposited on Si substrate at 500°C by reactive ion beam sputtering utilizing a capillaritron ion source at various oxygen partial flow rates. All the EZO films exhibit a preferred (002) growth direction. Maximum Er emission at 984 nm (4I11/2 to 4I15/2) was achieved from EZO deposited with 12.5% oxygen partial flow rate. XPS analysis of the O 1s core level shows an additional peak centered at 532.5 eV, indicating the presence of erbium oxide.

Efficient electron sources utilizing the effect of field emission

W-Cs3Sb, W-TiO2, and W-TiO2-Cs field emission cathodes are fabricated and studied. All these cathodes outperform the conventional tungsten cathode in emission properties: the emission current is very stable and one-and-a-half to two orders of magnitude higher. Physical models of the new emitters are suggested and experimentally verified.