穿孔顶头等离子喷涂涂层残余应力分析

提出采用在顶头上喷涂等离子涂层的方法来提高穿孔顶头表面性能,从而提高其使用寿命,降低生产成本。采用有限元计算软件ANSYS对等离子喷涂过程进行瞬态分析,得到穿孔顶头与涂层内部的温度分布状况,在此基础上分析顶头与涂层界面处和涂层内部的应力状态,讨论了顶头预热温度、涂层厚度、涂层材料等因素对残余应力的影响,得出合理的喷涂工艺,为提高穿孔顶头的使用寿命提供理论依据。     

The dry etching of a sol-gel deposited ZnO thin film in a high density BCl3/Ar plasma

The etching characteristics of zinc oxide (ZnO) including the etch rate and the selectivity of ZnO in a BCl₃/Ar plasma were investigated. It was found that the ZnO etch rate showed a non-monotonic behavior with an increasing BCl₃ fraction in the BCl₃/Ar plasma, along with the RF power, and gas pressure. At a BCl₃ (80%)/Ar (20%) gas mixture, the maximum ZnO etch rate of 50.3 nm/min and the maximum etch selectivity of 0.75 for ZnO/Si were obtained. Plasma diagnostics done with a quadrupole mass spectrometer delivered the data on the ionic species composition in plasma. Due to the relatively high volatility of the by-products formed during the etching by the BCl₃/Ar plasma, ion bombardment in addition to physical sputtering was required to obtain the high ZnO etch rates. The chemical state of the etched surfaces was investigated with X-ray Photoelectron Spectroscopy (XPS). Inferred from this data, it was suggested that the ZnO etch mechanism was due to ion enhanced chemical etching.     

Preparation and characterization of La-doped Ba(1 − x)SrxTiO3 powders and thin films

Ba_(1 − x)Sr_xTiO₃ powders with different Ba/Sr ratios (x = 0.10, 0.25, 0.40, 0.55, 0.70) and La-doped Ba_0.9Sr_0.1TiO₃·yLa powders (y = 0.002, 0.004, 0.006, 0.008, 0.010) have been prepared by sol-gel technology using dehydrated barium-acetate, strontium-carbonate, lanthanum-nitrate, and titanium-isopropoxide as raw materials. The experimental results show that the dielectric properties of Ba_(1 − x)Sr_xTiO₃ powders depend on the Ba/Sr ratios. When the Sr fraction is 0.10, the dielectric constant is relatively higher and the dielectric loss is relatively lower, which are more than 2000 and less than 2.0 × 10^− 2 at 1000 Hz, respectively, the most important is that this kind of powder has better frequency stability. La-doping can increase the dielectric constant distinctly, but the dielectric loss can also be increased. Their dielectric properties at 1.0 × 10³ Hz are better than those at 1.0 × 10⁵ Hz. At 1.0 × 10³ Hz the dielectric constant is much higher, while the dielectric loss is much lower. The dielectric constant of different La-doping contents is nearly 3.5 × 10⁴ and the dielectric loss is less than 0.20 when La fraction is 0.008. The La-doped BST sample also has better frequency stability, especially at high frequency. La-doped BST thin films are successfully deposited on mild steel substrates by using plasma spray system with suspension precursors of Ba_0.90Sr_0.10TiO₃·0.8La powders. The XRD patterns of Ba_0.90Sr_0.10TiO₃ and Ba_0.90Sr_0.10TiO₃·0.8La powders are almost the same. No new peaks appear after La-doping, but the peaks move slightly to a larger degree, which indicates that the element La has entered the lattice of the Ba_0.90Sr_0.10TiO₃ and has made the constant of the crystal cell reduce. The XRD pattern of the thin films is just like that of the Ba_0.90Sr_0.10TiO₃·0.8La powders except a peak corresponding to Fe substrate. The SEM results show that the thin films have a uniform and smooth surface. The morphology of cross-section shows a columnar grain structure indicating smooth surface and uniform thickness of the film. The thickness of the film is about 15 um. The thin films obtained are expected to be prospective material for applications in tunable microwave devices.     

Study of plasma enhanced chemical vapor deposition of ZnO films by non-thermal plasma jet at atmospheric pressure

Plasma enhanced chemical vapor deposition using a non-thermal plasma jet was applied to deposition of ZnO films. Using vaporized bis(octane-2,4-dionato)zinc flow crossed by the plasma jet, the deposition rate was as high as several tens of nm/s. From the results of infrared spectra, the films deposited at the substrate temperature T_sub = 100 °C contained a significant amount of carbon residue, while the films prepared at T_sub = 250 °C showed less carbon fraction. The experimental results confirmed that the plasma jet decomposed bis(octane-2,4-dionato)zinc in the gaseous phase and on the substrate, and that there should be the critical T_sub to form high-quality ZnO films in the range from 100 to 250 °C.     

Synthesis and characterization of plasma assisted chemically vapor deposited tantalum

This study focuses on the synthesis of tantalum (Ta) coatings on high strength steel by plasma assisted chemical vapor deposition using tantalum pentachloride (TaCl₅) as a preferred precursor and hydrogen (H₂) as a reducing agent. The interrelationships governing the growth kinetics, compositions, and coating properties are discussed as a function of deposition temperature, total pressure, and gas composition. The synthesized tantalum coatings are shown to be essentially pure with trace amounts of oxygen, carbon, and chlorine. The coatings are found to be dense and to exhibit conformal coverage. Preferential formation of the α-Ta phase is noted to occur when coatings are grown sequentially and in-situ on a TaN_x seed layer.     

Intrinsic stress effect on fracture toughness of plasma enhanced chemical vapor deposited SiNx:H films

The apparent fracture toughness for a series of plasma enhanced chemical vapor deposition SiN_x:H films with intrinsic film stress ranging from 300 MPa tensile to 1 GPa compressive was measured using nanoindentation. The nanoindentation results show the measured fracture toughness for these films can vary from as high as > 8 MPa⋅√m for films in compression to as low as < 0.5 MPa⋅√m for the films in tension. Other film properties such as density, Young's modulus, and hydrogen content were also measured and not observed to correlate as strongly with the measured fracture toughness values. Various theoretical corrections proposed to account for the presence of intrinsic or residual stresses in nanoindent fracture toughness measurements were evaluated and found to severely underestimate the impact of intrinsic stresses at thicknesses ≤ 3 μm. However, regression analysis indicated a simple linear correlation between the apparent fracture toughness and intrinsic film stress. Based on this linear trend, a stress free/intrinsic fracture toughness of 1.8 ± 0.7 MPa⋅√m was determined for the SiN_x:H films.     

The characteristics of fluorinated polycrystalline silicon oxides and thin film transistors by CF4 plasma treatment

This study describes a simple fluorinating technique by the tetrafluoromethane (CF₄) plasma treatment to form fluorinated polyoxides and polycrystalline silicon thin film transistors (TFTs). In comparison with the non-fluorinated device, the fluorinated polyoxides and devices exhibit a higher breakdown field (>8 MV/cm), low charge trapping rates, low off-state current, and low trap states. Furthermore, the performance and reliability of the fluorinated devices are also improved by the CF₄ plasma treatment. This is due to the fact that the incorporated fluorine can break strain bonds to form stronger silicon-fluorine (Si-F) bonds to passivate the generation of interface and trap states existing near the polyoxide/polysilicon interface and grain boundaries.     

A finite element model to predict the ablation depth in pulsed laser ablation

This work presents development of a two-dimensional finite element model to predict temperature distribution and ablation depth in a laser ablation process. The model considers a number of aspects of the process, which hitherto have been considered independently in the literature. The aspects considered include: temperature dependent material properties of the target material, effect of plasma shielding on the incident laser flux, and temperature dependent absorptivity and absorption coefficient of the target. It was evident that these considerations have resulted in a significant improvement in the ability of the model to predict the ablation depth. Finally, the predicted ablation depth was found to match extremely well with experimental results at lower laser fluences, though at higher fluences there is a marginal overestimation.     

Preparation of thermosensitive gold nanoparticles by plasma pretreatment and UV grafted polymerization

This work is to develop an easy method of plasma treatment and graft polymerization to prepare thermosensitive gold nanoparticles. Gold nanoparticles (Nano-Au) were reduced by trisodium citrate combined with hydrogen tetrachloroaurate(III) tetrahydrate (chloroauric acid) and modified with 11-mercaptoundecanoic acid (MUA) by the self-assembly monolayers (SAM). The surface graft polymerization of N-isopropylacrylamide (NIPAAm) was carried out by two steps, using O₂ plasma pretreatment of the surface on MUA SAM modified Nano-Au to form the peroxide groups on Nano-Au(MUA), and then subsequently using UV light to induce grafting with thermosensitive polymer. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to direct investigation of the particle size and morphology in situ. The diameters of the gold nanoparticles measured from the TEM images are in good agreement with data measured at room temperature which is about 15 nm. The thermosensitive gold nanoparticles were characterized by chemical structure of surface (ESCA) and Fourier-transform infrared spectroscopy (FTIR). ESCA result suggests that plasma treatments can be employed to generate peroxides on the Nano-Au(MUA) for the subsequent UV graft polymerization of PNIPAAm.     

Microstructural characterization of thin gold films on a polyimide substrate

The study of thin metal films on flexible substrates is of interest for manufacture of many devices, such as implantable electrode arrays consisting of gold film on polyimide substrates. Adhesion of the film to the substrate is of utmost importance for device durability. Gold adhesion to a polyimide has previously been shown to increase when a variety of substrate treatments are performed prior to gold sputter deposition, but little microstructural analysis has been made to complete the process-structure-properties relationship. Here, the grain size is shown to increase slightly but statistically significantly if an oxygen plasma etch and adhesion layer treatment of the film is performed prior to deposition of the gold. A log-normal grain size distribution is found for gold on each sample, and the grains are shown to be columnar. Gold deposited on non-treated polyimide shows a strong {111} texture, but a random texture is seen in both pretreated systems, indicating that the pretreatment affects the surface energy of the polyimide and alters the gold film growth.