Laser-assisted fabrication of new slab-coupled lithium niobate optical waveguide

Recently a new type of lithium niobate waveguide was suggested for potential nonlinear optic applications. The waveguide consists of a uniform large core and a leaky coupled slab for realizing a lateral optical confinement to support the fundamental spatial mode propagation. Inside the waveguide, the slab layer is required to have a refractive index slightly lower than that of the core, but higher than that of the substrate. Lithium niobate doped with magnesium oxides shows an increased refractive index that is dependent on the dopant's concentration. Therefore, in order to fabricate such waveguides, the pulsed laser deposition approach was used to study the growth of such composition-modified lithium niobate as the slab layer. The as-grown films were characterized on its expitaxy, structure, and optical performance, via X-ray diffraction analysis, optical guiding experiment, etc.     

脉冲激光气相沉积法制备钴纳米薄膜实验研究

 采用脉冲激光沉积技术制备了钴纳米薄膜，分析和讨论了不同背景气压和脉冲频率对钴纳米薄膜表面形貌的影响及纳米微粒的形成机理。实验结果表明：在低背景气压下，等离子体羽辉自身粒子之间的碰撞占主导作用，容易形成液滴；在较高背景气压下，等离子体羽辉边缘粒子和背景气体粒子之间的碰撞占主导作用，容易形成小岛并凝聚成微颗粒；在4Hz的脉冲重复频率和5Pa背景气压下生长出单分散性良好的钴纳米颗粒。     

Fabrication and properties of Li-doped ZnCoO diluted magnetic semiconductor thin films

Li-doped ZnCoO (ZnCoO:Li) diluted magnetic semiconductor thin films were prepared on SiO₂ substrates by pulsed laser deposition. In ZnCoO:Li films, Co²⁺ substituted Zn²⁺ and Li occupied the interstitial sites behaving as donors. The ZnCoO:Li films are of high electron concentration in the 10²⁰ cm⁻³ order and acceptable crystal quality with a hexagonal wurtzite structure. No cluster, precipitate, or second phase was found from the X-ray diffraction pattern and Co k-edge X-ray absorption near-edge structure measurements. The sp-d exchange interactions between the band electrons and the localized d electrons of Co ions substituting Zn ions were observed. The magnetization of ZnCoO:Li film is 0.61 μB/Co, higher than that of the ZnCoO film (0.49 μB/Co). The enhanced defect density and electron concentration due to the introduced Li donors may answer for the improvement of ferromagnetism at room temperature.     

Assessing the antimicrobial activity of zinc oxide thin films using disk diffusion and biofilm reactor

The electronic and chemical properties of semiconductor materials may be useful in preventing growth of microorganisms. In this article, in vitro methods for assessing microbial growth on semiconductor materials will be presented. The structural and biological properties of silicon wafers coated with zinc oxide thin films were evaluated using atomic force microscopy, X-ray photoelectron spectroscopy, and MTT viability assay. The antimicrobial properties of zinc oxide thin films were established using disk diffusion and CDC Biofilm Reactor studies. Our results suggest that zinc oxide and other semiconductor materials may play a leading role in providing antimicrobial functionality to the next-generation medical devices.     

Lithium electrochemistry of SiO2 thin film electrode for lithium-ion batteries

The lithium electrochemistry of SiO₂ thin film prepared by reactive radio frequency sputtering has been investigated for the first time. The reversible discharge capacities of SiO₂/Li cells cycled between 0.01 and 3.0 V are found in the range from 416 to 510 mAh/g during the first 100 cycles. By using ex situ transmission electron microscopy, selected-area electron diffraction and X-ray photo-electron spectroscopy measurements, both Li-Si alloying process and the reversible conversion reaction of SiO₂ into Li₂Si₂O₅ are proposed in the lithium electrochemical reaction of SiO₂. SiO₂ film electrode with high-reversible capacity and good cycle performance exhibits it potential anode material for future lithium-ion batteries.     

Effects of phase explosion in pulsed laser deposition of nickel thin film and sub-micron droplets

Nickel (Ni) thin films were deposited on glass substrates in high vacuum and at room temperature with third-harmonic or 355-nm output from a nanosecond Nd:YAG laser. At low laser fluence of 1 J/cm², the deposition rate was about 0.0016 nm/shot which increased linearly until 4 J/cm². Above 4 J/cm², the onset of phase explosion in the ablation abruptly increased the optical emission intensity from laser-produced Ni plume as well as thin-film deposition rate by about 6×. The phase explosion also shifted the size distribution and number density of Ni droplets on its thin-film surface. On the other hand, the surface structures of the ablated Ni targets were compared between the scan-mode and the fixed-mode ablations, which may suggest that droplets observed on the thin-film surface were caused by direct laser-induced splashing of molten Ni rather than vapour-to-cluster condensation during the plume propagation.     

Carbon anode thin films for lithium batteries

This paper describes a simple method to create carbon anode films for potential applications to the research field of lithium batteries. Carbon films were prepared using DC magneton sputtering with post-annealing process in the range from room temperature (RT) to 700 °C. Half cells assembled with lithium foils as the counter electrode and 1 M LiPF₆ in EC:DMC (1:1 v/v) electrolytic solution was used to evaluate the discharging capacity of prepared anode thin films. We showed that carbon film deposited at RT can be more suitable for an anode material than that of higher temperature annealed films above 400 °C. A variety of analysis methods including X-ray diffraction spectrometry (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were utilized to evaluate the defect density of the films; for example, the more defects on the film were identified when the carbon film was treated at a low temperature such as RT. It is envisioned that DC magnetron-sputtering with optimized process conditions can be useful for fabricating carbon based film anodes.     

Pulsed laser thin film growth of di-octyl substituted polyfluorene and its co-polymers

Matrix-assisted pulsed laser deposition (PLD) allows a controlled layer-by-layer growth of polymer films. Di-octyl substituted polyfluorene (PF8) and its copolymers were deposited as thin films using matrix-assisted PLD by employing a KrF excimer laser with a fluence of 125 mJ/pulses. The optical and structural properties of these films are compared with spincoated films via Raman spectroscopy, absorption and photoluminescence. The Raman spectra of both PLD and spincoated films are similar indicating that the polymer films deposited via PLD maintain their molecular structure. Both the spincoated and the PLD grown PF8 films that were cast from toluene show the presence of the β phase. Benzothiadiazole substituted PF8 (F8BT) and butyl phenyl-substituted PF8 (PFB) PLD grown films show a slightly broader emission compared to the spincoated films, which is attributed to an enhanced intermolecular interaction in the PLD grown thin films.     

Synthesis of heavy fermion CeCoIn5 thin film via pulsed laser deposition

CeCoIn₅ (Co115) thin films have been grown on Al₂O₃ (000l) substrates through the pulsed laser deposition (PLD). The films are grown mainly along the c-axis, with CeIn₃ and In-related alloys. The rock-salt type grains are nucleated, where Co115 grains mixed with excess indium are evenly distributed over the substrate. The electrical resistivity of the films shows a Kondo coherence peak near 47 K and the zero-resistance superconducting state at 1.8 K, which is the first observation in the PLD grown thin films of Co115. The Rietveld refinement of the thin films shows that the c/a ratio (tetragonality) is suppressed to 1.6312 from 1.6374 of single crystals, which is consistent with the linear relationship between the superconducting transition temperature and tetragonality. The good agreement indicates that the PLD could provide an alternative route to tune the 2D character of the critical spin fluctuations to understand the superconducting pairing mechanism of Co115.     

Microstructural studies of bulk and thin film GDC

Ceria rare earth solid solutions are known as solid electrolyte with potential application in oxygen sensors and solid oxide fuel cells. We report the preparation of gadolinia-doped ceria, Ce_0.90Gd_0.10O_1.95, by the conventional solid-state reaction method and the preparation of thin films from a sintered pellet of gadolinia-doped ceria by the pulsed laser deposition technique. The effect of process conditions, such as substrate temperature, oxygen partial pressure, and laser energy on microstructural properties of these films are examined using powder X-ray diffraction, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy.