Enhancing the adhesive bonding strength of NiTi shape memory alloys by laser gas nitriding and selective etching

Laser gas nitriding process (LGN) was applied on NiTi shape memory alloy to obtain an alloyed surface consisting of TiN dendrites in NiTi matrix. By applying subsequent selective etching process, the matrix material in the alloyed layer can be selectively removed and a three-dimensional network of TiN dendrites is left on the surface protruding from the metal substrate. The 3D dendritic network provides extra surface area and locking mechanism for the adhesion joint. The microstructures of such textured surface were examined. The adhesion jointing characteristics of the surfaces were studied. A 150% increase in the lap-joint strength was achieved in the laser gas nitrided and etched specimen as compared with the sandblasted and etched ones.     

Pulsed laser ablation deposition of thin films on large substrates

We have designed and built an ultra-high vacuum chamber which allows thin film deposition on large area (up to 100 mm diameter) flat substrates and on three-dimensional substrates (e.g. 100 mm long, 50 mm diameter cylinders) by the pulsed laser deposition and reactive pulsed laser deposition techniques. Heating of substrates during and after film deposition is possible using either resistive heaters or a lamp array. Metal (Cu) and metal nitride (TiN) and carbide (TiC) films were deposited on Si wafers (60 and 100 mm diameter), three-dimensional steel substrates (steel cylinders and screws), Teflon plates, and paper sheets.     

Synthesis of TiN thin films by a new combined laser/sol-gel processing technique

In this work a novel method for synthesising TiN coatings is reported. A high-power diode laser at different powers and traverse speeds was applied to a mild steel substrate, coated with a slurry of titania sol-gel, urea and graphite. The reaction chemical thermodynamics was investigated to estimate the compositions, temperature range, and the required reaction enthalpy for producing TiN. A one-dimensional heat transfer model was used to optimise the processing parameters. Surface morphology and microstructure of the deposited coatings and substrate surface layers were examined using optical microscopy, scanning electron microscope, and field emission gun scanning electron microscope which reveals deposition of very thin layer about 0.3 μm of pure TiN and the presence of sub-micron crystalline structure of TiN forming a metal matrix composite inter-layer with the substrate below the film which suggest a good metallurgically bonding with the substrate. Chemical composition was determined by energy dispersive X-ray analysis. The phases were identified by X-ray diffraction which confirms the synthesis of TiN film for all the samples. Results of nano-hardness measurements revealed a hardness value of the order of 22-27 GPa.     

Pulsed laser deposition and characterization of NiTi-based MEMS prototypes

We report the fabrication and characterization of microelectromechanical systems (MEMS) prototypes based on a microcantilever coated with a NiTi thin film. The NiTi film was deposited by laser ablation and deposition in ultra-high vacuum. The samples were characterized from the mechanical point of view by measuring the resonance frequency of the cantilever as a function of the temperature. Data show a clear phase transition of the NiTi film, with relevant transition temperatures close to those of the bulk, which demonstrates the congruency of the deposition method. We have also developed a technique to control the deflection of the NiTi-coated cantilever by all-optical means, both continuous and pulsed, the latter with typical time scales in the hundreds of s range. PACS 81.15.Fg; 85.85.+j; 81.30.Kf     

Characterization of calcium phosphate coatings doped with Mg, deposited by pulsed laser deposition technique using ArF excimer laser

Calcium phosphate layers were deposited on Ti6Al4V substrates with TiN buffer layers by use of pulsed laser deposition method. With this technique three pressed pellets consisted of tricalcium phosphate (TCP, Ca(3)(PO(4))(2)), hydroxyapatite (HA, Ca(10)(PO(4))(6)(OH)(2)) and hydroxyapatite-doped with magnesium (HA with 4% of Mg and trace amount of (Ca,Mg)(3)(PO(4))(2)) were ablated using ArF excimer laser (lambda=193 nm). The using of different targets enabled to determine the influence of target composition on the nature of deposited layers. The obtained deposits were characterized by means of Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction method (XRD). The obtained Fourier spectras revealed differences in terms of intensity of spectral bands of different layers. The analysis from XRD showed that Mg-doped HA layer has crystalline structure and TCP and HA layers composition is characterized by amorphous nature.     

Pulsed KrF laser deposited GaN/TiN/Si(111) heterostructures by sequential TiN and liquid Ga laser ablation

GaN/TiN heterostructures were deposited on 4° miscut Si(111) substrates by pulsed KrF laser ablation of TiN through vacuum, followed by reactive pulsed KrF laser ablation of liquid Ga through 70-75 mTorr of microwave-activated NH₃. Deposition temperatures of 950 °C and 1050 °C were employed for the TiN layer while 900 °C was employed for the GaN layer. The targets were positioned 5 cm from the substrate and ablated by using a reimaging beamline at a nominal energy density of 3-4 J/cm². X-ray diffraction (XRD) revealed a highly textured heterostructure with GaN(0001)//TiN(111)//Si(111) and with a rocking curve width for both GaN(0001) and TiN(111) equal to ~1.1°. The mosaic spread through the TiN(001) reflection was ~1.3°, whereas that of the GaN(101_1) was undetectable because of low S/N. Scanning electron microscopy revealed large oriented 10 7m-sized hexagonal crystallites decorating large depressions in the TiN film with many smaller pits also present. The effect of substrate processing and TiN film processing on pit formation was explored.     

Pulsed laser deposition and its current research status in preparing hydroxyapatite thin films

Pulsed laser deposition (PLD) is a conceptually and experimentally simple yet highly versatile tool for thin films and multi-layer film research. The mechanisms, advantages and disadvantages of pulsed laser deposition were reviewed. The process and some methods to resolve the drawbacks of PLD were discussed. Pulsed laser deposition of hydroxyapatite thin films was reviewed. Simple adjustment of PLD parameters can deposit hydroxyapatite in situ in crystalline form, amorphous films or HA with other calcium phosphate phases. Compared with plasma sprayed HA coatings the pulsed laser deposition HA thin films have higher coating/substrate adhesion and have minor undesirable phases under optimal conditions. Finally, we suggested some new researches should be done.     

Diamond-like-carbon films produced by magnetically guided pulsed laser deposition

We have compared the quality of carbon films deposited with magnetically guided pulsed laser deposition (MGPLD) and conventional pulsed laser deposition (PLD). In MGPLD, a curved magnetic field is used to guide the plasma but not the neutral species to the substrate to deposit the films while, in conventional PLD, the film is deposited with a mixture of ions, neutral species and clusters. A KrF laser pulse (248 nm) was focused to intensities of 10 GW/cm² on a carbon source target and a magnetic field strength of 0.3 T was used to steer the plasma around a curved arc to the deposition substrate. Electron energy loss spectroscopy was used in order to measure the fraction of sp³ bonding in the films produced. It is shown that the sp³ fraction, and hence the diamond-like character of the films, increased when deposited only with the pure ion component by MGPLD compared with films produced by the conventional PLD technique. The dependence of film quality on the laser intensity is also discussed. Received: 7 December 2000 / Accepted: 20 August 2001 / Published online: 2 October 2001     

The comparison between CdS thin films grown on Si(111) substrate and quartz substrate by femtosecond pulsed laser deposition

Two kinds of cadmium sulfate (CdS) thin films have been grown at 600 °C onto Si(111) and quartz substrates using femtosecond pulsed laser deposition (PLD). The influence of substrates on the structural and optical properties of the CdS thin films grown by femtosecond pulsed laser deposition have been studied. The CdS thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), photoluminescence (PL) and Raman spectroscopy. Although CdS thin films deposited both on Si(111) and quartz substrates were polycrystalline and hexagonal as shown by the XRD , SEM and AFM results, the crystalline quality and optical properties were found to be different. The size of the grains for the CdS thin film grown on Si(111) substrate were observed to be larger than that of the CdS thin film grown on quartz substrate, and there is more microcrystalline perpendicularity of c-axis for the film deposited on the quartz substrate than that for the films deposited on the Si substrate. In addition, in the PL spectra, the excitonic peak is more intense and resolved for CdS film deposited on quartz than that for the CdS film deposited on Si(111) substrate. The LO and TO Raman peaks in the CdS films grown on Si(111) substrate and quartz substrate are different, which is due to higher stress and bigger grain size in the CdS film grown on Si(111) substrate, than that of the CdS film grown on the amorphous quartz substrate. All this suggests that the substrates have a significant effect on the structural and optical properties of thin CdS films. PACS 81.15.Fg; 81.05.Ea; 78.20.-e; 78.67.-n; 42.62.-b     

Optimization of plasma parameters for high rate deposition of titanium nitride films as protective coating on bell-metal by reactive sputtering in cylindrical magnetron device

Nano-structured titanium nitride (TiN) thin film coating is deposited by reactive sputtering in cylindrical magnetron device in argon and nitrogen gas mixtures at low temperature. This method of deposition using DC cylindrical magnetron configuration provides high uniform yield of film coating over large substrate area of different shapes desirous for various technological applications. The influence of nitrogen gas on the properties of TiN thin film as suitable surface protective coating on bell-metal has been studied. Structural morphological study of the deposited thin film carried out by employing X-ray diffraction exhibits a strong (2 0 0) lattice texture corresponding to TiN in single phase. The surface morphology of the film coating is studied using scanning electron microscope and atomic force microscope techniques. The optimized condition for the deposition of good quality TiN film coating is found to be at Ar:N₂ gas partial pressure ratio of 1:1. This coating of TiN serves a dual purpose of providing an anti-corrosive and hard protective layer over the bell-metal surface which is used for various commercial applications. The TiN film's radiant golden colour at proper deposition condition makes it a very suitable candidate for decorative applications.     

Synthesis of titanium nitride thin films deposited by a new shielded arc ion plating

Thin films of titanium nitride (TiN) were deposited on stainless steel substrates by a modified deposition technique, double-layered shielded arc ion plating with vicarious circular holes (DL-SAIP). The results show that the TiN film with the distance of 10 mm between the double-layered shield plates had the least droplets. The deposition rate of the films prepared with the new technique was more homogeneous than that of all the other shielded arc ion plating. The film/substrate adhesion and microhardness values of the TiN films were higher than 40 N and 18 GPa, respectively. Thus such TiN thin films can be expected in applications.     

高脉冲功率能量PLD法制备MgZnO薄膜中的沉积机理

用PLD法成功制备了一系列高质量的MgZnO薄膜。实验中发现高脉冲能量沉积薄膜的结构和发光特性随基片温度的变化规律与低脉冲能量下的结果不一样:基片在室温时高脉冲能量制备薄膜的XRD峰的半峰全宽比高基片温度时的结果相对更小;AFM显示其颗粒变大,柱状生长突出;PL谱紫峰与绿峰强度比最大,结晶质量反而提高。另一方面,与低脉冲能量时相反,增大氧气压强后高脉冲能量沉积的薄膜XRD半峰全宽变窄。结合实验现象和表征,合理解释了高脉冲能量沉积的机理。室温制备高质量MgZnO薄膜的PLD沉积机理对于以后在柔性衬底上沉积薄膜的研究有重要的参考价值。     

Pulsed laser deposition of NiTi shape memory effect thin films

2 O₃(100) substrates. We also produced free-standing NiTi films by deposition on KBr substrates and subsequent substrate removal by immersion in water. The presence of the solid-solid phase transformation responsible for the shape memory effect has been demonstrated through temperature-dependent X-ray diffraction and four-probe resistance versus temperature measurements. On cooling the deposited film, the austenite-martensite transformation was measured at around 195 K; on heating the film the reverse transformation was around 250 K. Evidence of the shape-memory effect for free-standing films was obtained in a bending deformation-shape recovery experiment. Received: 31 July 1996/Accepted: 6 January 1997     

Effect of temperature on pulsed laser deposition of HgCdTe films

HgCdTe thin films have been deposited on Si(1 1 1) substrates at different substrate temperatures by pulsed laser deposition (PLD). An Nd:YAG pulsed laser with a wavelength of 1064 nm was used as laser source. The influences of the substrate temperature on the crystalline quality, surface morphology and composition of HgCdTe thin films were characterized by X-ray diffraction (XRD), selected area electron diffraction (SAED), atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDS). The results show that in our experimental conditions, the HgCdTe thin films deposited at 200 °C have the best quality. When the substrate temperature is over 250 °C, the HgCdTe film becomes thermodynamically unstable and the quality of the film is degraded.     

Biocompatible film deposition by using Nd:YAG pulsed laser

A Nd:YAG laser operating at the fundamental wavelength (1064 nm) and at the second harmonic (532 nm), with 9 ns pulse duration, 100–900 mJ pulse energy, and 30 Hz repetition rate mode, was employed to ablate in vacuum (10^?6 mbar) biomaterial targets and to deposit thin films on substrate backings. Titanium target was ablated at the fundamental frequency and deposited on near-Si substrates. The ablation yield increases with the laser fluence and at 40 J/cm ² the ablation yield for titanium is 1.2×10¹⁶ atoms/pulse. Thin film of titanium was deposited on silicon substrates placed at different distance and angles with respect to the target and analysed with different surface techniques (optical microscopy, scanning electron spectrosopy (SEM), and surface profile).

Hydroxyapatite (HA) target was ablated to the second harmonic and thin films were deposited on Ti and Si substrates. The ablation yield at a laser fluence of 10 J/cm ² is about 5×10¹⁴ HA molecules/pulse. Thin film of HA, deposited on silicon substrates placed at different distance and angles with respect to the target, was analysed with different surface techniques (optical microscopy, SEM, and Raman spectroscopy).

Metallic films show high uniformity and absence of grains, whereas the bio-ceramic film shows a large grain size distribution. Both films found special application in the field of biomaterial coverage.     

Deposition of Au/TiO2 film by pulsed laser

Au nanoparticles, which were photoreduced by a Nd:YAG laser in HAuCl₄ solution containing TiO₂ colloid and accompanied by the TiO₂ particles, were deposited on the substrate surface. The film consisting of Au/TiO₂ particles was characterized by the absorption spectra, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The adhesion between the film and substrate was evaluated by using adhesive tape test. It was found that the presence of TiO₂ dramatically enhanced the adhesion strength between the film and the substrate, as well as the deposition rate of film. The mechanism for the deposition of Au/TiO₂ film was also discussed.     

Effects of the substrate temperature on the bioglass films deposited by pulsed laser

Effects of the substrate temperature on the bonding configuration and adhesion strength of the bioglass films deposited by pulsed laser were investigated by Fourier transform infrared spectroscopy (FTIR) and scratch apparatus. Morphology of the films is compact with the particles on the surface of them and the structure is amorphous glass. Bonding configuration is different from that of the target. Si-O-NBO/Si-O-Si (s) intensity ratios of the films decline as compared with the target. Besides, this tendency is obvious as the substrate temperature decreases. This effect is attributed to the network rearrangement during the film growth, which is associated to special structure of glass and complex physical mechanisms of pulsed laser deposition (PLD). Scratch test results show that the film deposited at 200 °C has the highest adhesion strength.     

Surface phenomena of HA/TiN coatings on the nanotubular-structured beta Ti-29Nb-5Zr alloy for biomaterials

Surface phenomena of HA/TiN coatings on the nanotubular-structured beta Ti-29Nb-5Zr alloy for biomaterials have been investigated by several experimental methods. The nanotubular structure was formed by anodizing the Ti-29Nb-5Zr alloy in 1 M H₃PO₄ electrolytes with 1.0 wt.% NaF at room temperature. Hydroxyapatite (HA)/titanium nitride (TiN) films were deposited on Ti-29Nb-5Zr alloy specimens using a magnetron sputtering system. The HA target was made of human tooth-ash by sintering at 1300 °C for 1 h, and the HA target had an average Ca/P ratio of 1.9. The HA/TiN depositions were performed, using the pure HA target, on Ti-29Nb-5Zr alloy following the initial deposition of a TiN buffer layer coating. Microstructures and nanotubular morphology of the coated alloy specimens were examined by FE-SEM, EDX, XRD, and XPS. The Ti-29Nb-5Zr alloy substrate had small grain size and preferred orientation along the drawing direction. The HA/TiN coating was stable with a uniform morphology at the tips of the nanotubes.     

用激光分子束外延在Si衬底上外延生长高质量的TiN薄膜

采用激光分子束外延技术,利用两步法,在Si单晶衬底上成功地外延生长出TiN薄膜材料.原子力显微镜分析结果显示, TiN薄膜材料表面光滑,在10 μm×10 μm范围内,均方根粗糙度为0842nm.霍耳效应测量结果显示,TiN薄膜在室温条件下的电阻率为36×10^-5Ω·cm,迁移率达到5830 cm²/V·S,表明TiN薄膜材料是一种优良的电极材料.X射线θ—2θ扫描结果和很高的迁移率均表明,高质量的TiN薄膜材料被外延在Si衬底 关键词： 激光分子束外延 TiN单晶薄膜 外延生长     

On the interface between iron and thin films of titanium and titanium nitride

Very thin films of TiN and Ti/TiN were prepared by physical vapor deposition on iron at 500°C to investigate the phenomena occurring at the coating/substrate interface during deposition. By means of depth selective Mössbauer spectroscopy, it was found that preliminary depositions of Ti films lead to the formation of α-Fe(Ti) solid solutions. Depending on the amount of deposited Ti, the α-Ti(Fe) solid solution and Fe?Ti intermetallic compounds can form. The influence of interfacial phases on the film adhesion is discussed.