Nanoparticle-assisted Pulsed-laser Deposition Research Articles

Observation of ultraviolet whispering gallery modes in ZnMgO microrods

Abstract We report on the fabrication of ZnO and Zn0.9Mg0.1O microrods using nanoparticle assisted pulsed laser deposition (NAPLD). Micro-photoluminescence studies reveal that Zn0.9Mg0.1O microrods exhibited a blue shift in the ultraviolet (UV) emission relative to unintentionally doped ZnO that was attributed to the increase in bandgap due to Mg doping. High-resolution micro-photoluminescence clearly indicated the presence of whispering gallery modes (WGMs) for both ZnO and Zn0.9Mg0.1O. Transverse electric (TE) and transverse magnetic (TM) optical WGMs were identified using the existing plane-wave model. The observation of lower order WGM modes in Zn0.9Mg0.1O microrods may be of great interest for future UV WGM lasing.

Improvement of Junction Properties of ZnO Nanorod/GaN Heterojunction Using Selective Laser Processing

We fabricated the ZnO nanorod/GaN heterojunction light emitting diode by directly-growth of the ZnO nanorods on the GaN film using the nanoparticle-assisted pulsed laser deposition. Subsequently, selective laser irradiation to the p-n junction was applied to improve the junction properties. The UV emission was strongly enhanced by the laser irradiation. The peak wavelength of the UV emission is 377 nm, which is attributed to the near-band-emission of ZnO. In addition, the forward current was increased in the I-V characteristics by a factor of 6 at a bias voltage of 30 V.

Controlling ZnO nanowire surface density during its growth by altering morphological properties of a ZnO buffer layer by UV laser irradiation

Zinc oxide (ZnO) nanocrystals, which are characterized by their configurations and fine structures, are unique oxide semiconductors. In this report, it is demonstrated that the number density of ZnO nanowires can be controlled by proper treatments of the buffer layer with ultraviolet laser irradiation. ZnO nanowires were synthesized on the locally laser-irradiated ZnO buffer layer using nanoparticle-assisted pulsed-laser deposition (NAPLD). The number density of ZnO nanowires decreased in the region laser-irradiated with <300 mJ/cm2, whereas it increased in the region laser-irradiated with more than 400 mJ/cm2. Effects of laser irradiation on ZnO buffer layers were investigated by atomic force microscopy, Kelvin probe force microscopy (KPFM), Raman spectroscopy, and X-ray diffraction analyses. In particular, the effects of laser irradiation on the surface work functions of ZnO buffer layers were investigated by KPFM, which is reported for the first time. Additionally, periodically aligned ZnO sub-microcrystals were fabricated as an application of controlling the number density of ZnO nanowires on micropatterned ZnO buffer layers using the four-beam interfered third harmonic of a Nd:YAG laser followed by NAPLD. ZnO sub-microcrystals can be used to fabricate field emitter arrays and can be developed for the application of ZnO nano/microcrystals due to their high throughput.

Position-controlled and catalyst-free growth of ZnO nanocrystals by nanoparticle-assisted pulsed laser deposition

We have synthesized ZnO nanocrystals, such as nanowires, nanorods, and nanosheets, using a nanoparticle-assisted pulsed laser deposition (NAPLD) method. Recently, we achieved position-controlled growth of the ZnO nanocrystals by means of a ZnO buffer layer and laser irradiation without any catalyst. The periodic structure was formed on the ZnO buffer layer by multi-beam interference patterning, and then vertically aligned ZnO nanowalls, corresponding to the patterning, were grown on the buffer layer. It was found that the periodic ZnO nanowalls grew along the c-axis direction by X-ray diffraction measurement. The well-aligned ZnO nanowalls are expected to be utilized as building blocks for field emitters and UV LEDs. The proposed technique can be used as one of the effective methods to control the growth position of the ZnO nanocrystals because various structures can be easily fabricated by a laser writing and a spatial light modulator.

Patterned growth of ZnO nanowalls by nanoparticle-assisted pulsed laser deposition

We have succeeded in controlling the growth density of ZnO nanowires synthesized by nanoparticle-assisted pulsed laser deposition (NAPLD) using a ZnO buffer layer and laser irradiation. The density of the nanowires decreased with increasing thickness of the buffer layer. In addition, the nanowire density also decreased by laser irradiation to the buffer layer. Patterned growth of ZnO nanowalls using NAPLD was successfully achieved with the help of the buffer layer patterned by interfering laser beams.

Formation of one-dimensional ZnO nanowires from screw-dislocation-driven two-dimensional hexagonal stacking on diamond substrate using nanoparticle-assisted pulsed laser deposition

We report on the growth of ZnO nanowires on a p-type diamond substrate using nanoparticle-assisted pulsed laser deposition technique. Microstructural analysis on different growth stages reveals that the self-assembled 1D ZnO nanowires emerge on well-formed 2D hexagonal base with spiral-like structures. We explain the formation of screw-dislocation-driven spiral-like-hexagons invoking crystal growth velocities at different regions of the hexagons. High-resolution transmission electron microscopy and selective area electron diffraction studies show that the nanowires are single crystalline in nature and grow along 〈0 0 0 1〉 direction of the wurtzite hexagonal structure. Room temperature photoluminescence spectrum of the ZnO nanowire shows a strong near band edge emission at 3.2 eV with a linewidth of 136 meV.

Fabrication of nanowires of Al-doped ZnO using nanoparticle assisted pulsed laser deposition (NAPLD) for device applications

Aluminium doped zinc oxide (AZO) nanostructures have been successfully synthesized on sapphire substrates by using nanoparticle assisted pulsed laser deposition (NAPLD) in Ar atmosphere without using any catalyst. The growth of the AZO nanowires has been investigated by varying the argon flow rates. The coatings have been characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Atomic force microscopy (AFM), Diffuse Reflectance Spectroscopy (DRS), Laser Raman spectroscopy and Photoluminescence spectroscopy. The results of XRD indicate that the deposited films are crystalline ZnO with hexagonal wurtzite structure with (0 0 2) preferred orientation. FESEM images also clearly reveal the hexagonal structure and the formation of nanowires with aspect ratios between 15 and 20. The surface roughness value of 9.19 nm was observed from AFM analysis. The optical properties of the sample showed that under excitation with λ = 325 nm, an emission band was observed in UV and visible region. The characteristic Raman peaks were detected at 328, 380, 420, 430 cm−1.

Effect of Laser Annealing on Optical Properties of Ion-Implanted ZnO Nanorods

We report on the demonstration of the effectiveness of nanosecond laser annealing on optical properties of phosphorus ion (P)-implanted ZnO nanorods (NRs). Vertically-alligned ZnO NRs have been synthesized by nanoparticle-assisted pulsed laser deposition (NAPLD) on c-plane sapphire substrates. The pre-laser annealing was performed with the third harmonic (355 nm) of a Qwitched Nd:YAG laser at a fluence of 100mJ/cm for improving optical property and weakening ntype conduction of as-grown ZnO NRs. P-ions were implanted into the ZnO NRs followed by the post-laser annealing in the same way as the pre-laser annealing. The top part of the ZnO NRs were melted and recrystallized by laser annealing. The transitions of properties were investigated by the scanning electron microscope, the room temperature photoluminescence spectra, X-ray diffraction patterns, and I-V measurement. As a result, it turned out that laser annealing has potentiality for improving optical property and compensating donor-vacancies without reducing crystalline quality. Moreover, the effectiveness of post-laser annealing on recovering ion-implanted ZnO layer and activating acceptors was demonstrated. It is promising that straightforward and stable method of fabricating ZnO-based UV-LED is established by applications of nanosecond laser annealing process.

Structural and optical properties of Sb[sbnd]Al co-doped ZnO nanowires synthesized using Nanoparticle Assisted Pulsed Laser Deposition (NAPLD) with Sb as catalyst

The paper deals with study of SbAl co-doped ZnO nanowires synthesized using Nanoparticle Assisted Pulsed Laser Deposition (NAPLD). The nanowires were synthesized by using ZnO:Al as target and Sb coated Si as substrate. At a growth temperature of 750°C, random oriented high density nanowires with a diameter of about 1μm and a length up to a few tens of micro meters were synthesized. The samples were annealed at 450, 550 and 650°C. The SbAl co-doped ZnO nanowires annealed at 650°C showed a significant change in lattice constant of 0.06° from XRD and widening of lattice fringe spacing of 0.56nm from TEM. From the XPS analysis, a peak at 539.5eV a near binding energy of SbO bond and peak at 76.2eV corresponding to AlO bonds confirms the penetration of oxygen. The suppression of A1T modes and E1(L0) modes from Raman spectroscopy confirms the depletion of oxygen vacancies. Thus resulting in a strong improvement in UV emission and reduction in visible emission as observed from room temperature PL.

Synthesis of Core/Shell Nanowires Using Doped ZnO Targets

ZnO nanowires have attracted a great attention as building blocks for the optoelectronic devices. For the practical optoelectronic applications based on the ZnO nanowires, synthesis technique of ZnO nanowire with layered structures is significantly important in order to achieve a p-n junction, a core/shell structure, and a multiple quantum well structure. We have been succeeded in growing nanowires on the pre-deposited ZnO film and core/shell structure by a newly developed nanoparticle-assisted pulsed-laser deposition (NAPLD) using multi-target changer. In this paper, recent progresses of synthesis of layer-structured ZnO nanowires using doped ZnO target, such as a Li-Ni codoped ZnO, are described.

Influence of Sb as a catalyst in the growth of ZnO nano wires and nano sheets using Nanoparticle Assisted Pulsed Laser Deposition (NAPLD)

Abstract The methodology on the synthesis of Sb-doped ZnO nanostructures by considering dopant as a catalyst is proposed and demonstrated. The nanostructures were synthesized using intrinsic ZnO as target and Sb-coated Si as substrate, where Sb simultaneously acts as dopant and the catalyst. The catalyst Sb is highly sensitive to temperature conditions resulted in two different nanostructures, the nanowires and the nanosheets. The surface, structural and optical characteristics of the nanowires and the nanosheets are comparatively investigated through SEM, EDX, XRD, Raman spectroscopy and photo luminescence (PL) spectroscopy. The nanowires showed a strong green emission in the PL spectrum and the presence of oxygen vacancies is confirmed thorough Raman peak shift at 556 cm−1. In the case of nanosheets, the defect in oxygen vacancies is completely reduced, and improved UV emission is observed, which confirms the diffusion of Sb in the ZnO lattice.

Influence of Sb on a controlled-growth of aligned ZnO nanowires in nanoparticle-assisted pulsed-laser deposition

Single-crystalline ZnO nanowires on a sapphire substrate have been synthesized by a nanoparticle-assisted pulsed-laser deposition (NAPLD) using a pure and Sb2O3 doped ZnO target. Low density and vertically well-aligned ZnO nanowires were grown on hexagonal cone-shape ZnO cores by introduction of a ZnO buffer layer. More than 90% of the ZnO cores of the Sb-induced ZnO nanowires are formed in the same size of 400 nm. The ZnO nanowires consist of single-crystalline wurtzite ZnO crystal and grow along [0001] direction. The room-temperature photoluminescence spectrum exhibited a strong ultraviolet emission at around 380 nm and a relatively low broad band emission in the visible region, indicating a low concentration of structural defect in the nanowires. Sb can be used as one of the effective additives to control the morphology and alignment of ZnO nanowires synthesized by NAPLD.

Low-Temperature Photoluminescence of Nanostructured ZnO Crystal Synthesized by Pulsed-Laser Ablation

The optical properties of ZnO nanorods and nanowires grown by our newly developed nanoparticle-assisted pulsed-laser deposition (NAPLD) technique were studied by photoluminescence (PL) spectroscopy. This NAPLD technique, which does not require a catalyst for crystal growth, is expected to synthesize high-quality nanostructured ZnO crystals. The green luminescence (GL) band and ultraviolet luminescence (UVL) observed at low temperature were investigated for these crystals. The UVL band consists of several sharp emission lines due to free excitons, donor-bound excitons, donor-acceptor pair (DAP) transitions, and their longitudinal-optical (LO) phonon replicas. The free-exciton binding energy was estimated to be 59 meV and the band gap of these ZnO crystals was determined to be 3.435 eV at 10 K. The temperature variation for the energy positions of free-exciton emission was fitted by the Manoogian–Woolley equation and the Debye temperature was estimated to be 505 K. The low-temperature PL investigation of our nanostructured ZnO crystals that were easily synthesized by our newly developed NAPLD technique demonstrated their excellent crystallinity.

Aligned growth of ZnO nanowires by NAPLD and their optical characterizations

Not only vertically aligned ZnO nanowires but also horizontally aligned ZnO nanowires have been successfully grown on the annealed (0 0 0 1) c-cut and (1 1 2 0) a-cut sapphire substrates, respectively using catalyst-free nanoparticle-assisted pulsed-laser ablation deposition (NAPLD). The as-synthesized ZnO nanowires exhibit an ultraviolet emission at around 390 nm and the absent green emission under room temperature. The single ZnO nanowire was collected in the electrode gap by dielectrophoresis (DEP). Under the optical pumping, the single ZnO nanowire exhibited UV emission at around 390 nm with several sharp peaks whose energy spacings are almost constant, which greatly differs from the broad UV emission of the film with many nanowires, suggesting ZnO nanowires as candidates for laser media. The single ZnO nanowire showed polarized photoluminescence (PL). The as-synthesized ZnO nanowires could find many interesting applications in short-wavelength light-emitting diode (LED), laser diode and gas sensor.

Catalyst-free synthesis of vertically-aligned ZnO nanowires by nanoparticle-assisted pulsed laser deposition

Vertically aligned ZnO nanowires have been successfully synthesized on c-cut sapphire substrates by a catalyst-free nanoparticle-assisted pulsed-laser ablation deposition (NAPLD) in Ar and N2 background gases. In NAPLD, the nanoparticles formed in the background gas by laser ablation are used for the growth of the nanowires. The surface density of the nanowires can be controlled by varying the density of nanoparticles, which is in turn achieved by varying ablation laser parameters such as the energy and the repetition rate. When single ZnO nanowire synthesized in a N2 background gas was excited by 355 nm laser-pulse with a pulse-width of 8 ns, stimulated emission was clearly observed, indicating high quality of the nanowire.

Electroluminescence from ZnO nanowire-based p-GaN/n-ZnO heterojunction light-emitting diodes

Vertically aligned ZnO nanowires were successfully grown on the sapphire substrate by nanoparticle-assisted pulsed laser deposition (NAPLD), which were employed in fabricating the ZnO nanowire-based heterojunction structures. p-GaN/n-ZnO heterojunction light-emitting diodes (LEDs) with embedded ZnO nanowires were obtained by fabricating p-GaN:Mg film/ZnO nanowire/n-ZnO film structures. The current–voltage measurements showed a typical diode characteristic with a threshold voltage of about 2.5 V. Electroluminescence (EL) emission having the wavelength of about 380 nm was observed under forward bias in the heterojunction diodes and was intensified by increasing the applied voltage up to 30 V.

Aligned growth of ZnO nanowires and lasing in single ZnO nanowire optical cavities

Ordered ZnO nanowire arrays have been fabricated in N2 background gas by catalyst-free nanoparticle-assisted pulsed-laser deposition. A single ZnO nanowire was collected in an electrode gap by dielectrophoresis. Under the optical pumping above an exciting laser (λ= 355 nm) threshold of ∼ 334 kW/cm2, ultraviolet lasing action in a single ZnO nanowire was observed at room temperature, indicating that the as-synthesized nanowires in pure N2 background gas are of high quality. The crystalline facets of both ends of the nanowire acted to form an optical cavity. Therefore, the mode spacings corresponding to cavity lengths of the respective nanowires were observed in photoluminescence spectra.

Synthesis of ZnO Nanowires by Nanoparticle-Assisted Pulsed-Laser Deposition and Optical Characteristics of Single ZnO Nanowire

Technique for synthesis of the ZnO nanowires by Nanoparticle-Assisted Pulsed-Laser Deposition (NAPLD) and the characterization of their optical property are described. Vertically-aligned ZnO nanowires were successfully grown on sapphire substrates by NAPLD without any catalyst. The surface density of the nanowires on the substrate was controlled by changing the laser irradiation conditions, such as an energy and a repetition rate. When a nanowire was excited by the third harmonic of a Q-switched Nd: YAG laser, the stimulated emission due to a micro-cavity effect in single nanowire was observed with a lasing threshold of about 400 kW/cm2, indicating high crystalinity of ZnO nanowires.

Synthesis of Vertically-Aligned ZnO Nanowires by Nanoparticle- Assisted Pulsed Laser Deposition and Their Application to Photo-Devices

Vertically aligned ZnO nanowires have been successfully synthesized on annealed c-cut sapphire substrates by a catalyst-free nanoparticle-assisted pulsed-laser deposition (NAPLD) in Ar and N2 background gases. In NAPLD, the nanoparticles formed in the background gas by laser ablation are used as a starting material for the growth of the nanowires. The surface density of the nanowires can be controlled by varying the density of nanoparticles, which are accomplished by changing the energy of the ablation laser, the repetition rate of the laser and so on. When single ZnO nanowire synthesized in a N2 background gas was excited by 355 nm laser-pulse with a pulse-width of 8 ns, stimulated emission was clearly observed, indicating high quality of the nanowire. These nanowires were used as building blocks for an ultraviolet photo-sensor, field emitters and an ultraviolet light emitting diode with a structure of n-ZnO/ZnO nanowire/p-GaN.

Density-Controlled Growth of ZnO Nanowires Via Nanoparticle-Assisted Pulsed-Laser Deposition and Their Optical Properties

Vertically aligned ZnO nanowires with controllable density were successfully synthesized by nanoparticle-assisted pulsed-laser deposition (NAPLD), by which nanoparticles formed in the gas phase by the condensation of the ablated species are transported onto the substrate, and nanoparticles play an important role in density control. The effects of synthesis conditions on the density and optical properties of ZnO nanowires were investigated in detail. With the increase in repetition rate and laser energy, ZnO nanowires with a higher density can be obtained as a result of a larger quantity of nanoparticles formed in the gas phase. The density-controlled growth also depends on substrate–target distance. UV emission was observed from all the obtained nanowires at about 390 nm without visible fluorescence near 500 nm due to their excellent crystallinity and the oxygen-deficient defect.