DPF emits intense X-rays hard as well as soft, neutrons and energetic charged particles beams ions and electrons. Various workers studied these emissions extensively since 1965(53-56). The emission of X-rays and ions from DPF device take place during radial phase. The low energy X-rays(soft X-rays) have thermal origin and are produced predominantly by electron Bremsstrahlung in the hot plasma where as high energy X-rays(hard X-rays) have known non-thermal origin and are emitted from the anode surface or anode vapor plasma because of interaction of electron beam with the anode . X-ray output of several joules has been reported in the literature depending on device parameters.
DPF as an ion source
The energetic ions have become a subject of current interest for its applications in ion implantation, surface modification, thin film deposition and ion-assisted coating. This chapter will review some of the more recent efforts on characterizing the ion beam and modifying the surface sensitive properties of materials by ion beam processes with an emphasis on applications oriented work.
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DPF being a pulsed coaxial plasma accelerator produces high-energy (up to few Mev), high fluency ion beams with a continuous energy distribution. These ion beams are accelerated down to coaxial accelerator in a conical fashion due to its self generated mechanisms. When a substrate is subjected to these accelerated ion beams, it interacts with the substrate in two ways. Firstly, the flux of energetic ion beams impinging on the substrate changes the physical properties of the outer layer of the substrate and secondly, it increases the surface temperature abruptly without changing its bulk temperature due to energy conversion. Thus the ions penetrate to a depth of the surface layer well beyond the ions energy range. No external heating arrangement is required for ion diffusion in this device. The whole process takes a few hundreds of nano-second. These features make the DPF device unique for material processing work compared to the other conventional devices.
Kelly et al.  reported the nitrogen ion spectrum generated from a low energy Mather-type Plasma Focus device, the main species of ions present are N+1, N+2, and N+3. It was found that its relative concentrations at a distance of several cm from the ion source are in agreement with those predicted for an equilibrium charge-state of the beam, and hence the spectrum of the neutral nitrogen was also derived. By taking into account the lateral spread of the beam due to multiple elastic scattering with the background gas, the derivation of absolute values for the total ion spectrum within the investigated energy range (>170 keV), the total number and total energy of the fast particles had been obtained.
Bhuyan et al.  fabricated nanosecond response Faraday Cup and employed to characterize pulsed ion beam of a 2.2 kJ Mather type Dense Plasma Focus Device. The Faraday Cup operating in bias ion collector mode was used to determine the energy spectrum and flux of fast nitrogen ion beam along the electrode axis (0 degrees) of the device. It had been possible to register the ion energy up to a lower kinetic energy threshold of similar to7 keV which was a value much lower than that obtained in any previous works. The correlation of the ion beam intensity with filling gas pressure was also reported.
Mohanty et al.  carried a comparative study on the ion emission characteristics such as flux and energy, and their variation in angular positions and operating gas pressures carried out in a nitrogen-filling plasma focus device. The ion emission characteristics were investigated by employing three Faraday cups at various angular positions. The ion flux depends on the operating gas pressure irrespective of the anode designs and the maximum ion flux was found to be in the pressure range 0.3 to 0.5 Torr for all the anode designs. The hemispherical anode yields highest ion flux while the hollow anode emitted lowest ions flux. The angular variation of ion flux was seen to be anisotropic irrespective of the anode designs with an ion dip at 0 degrees (axis of the device) and maximal at 5 degrees angular positions. The anisotropic character of ion emission was less in the case of the hemispherical anode than the hollow anode. The ion energy, measured by the time of flight method, shows its dependence on the anode designs. The maximum ion energy was found to be around 830 keV at an angular position 5 degree in the case of the hemispherical anode design. The most probable ions were found to be with energy less than 100 keV irrespective of the anode designs and the angular positions. This study indicated that the plasma focus device could be optimized to a great extent for optimal ions yield by using an appropriate anode design.
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Neog et al.  studied electron beam emission from a 2.2 kJ plasma focus device by using a charge collector. Multiple bunches of electron beams having short live been observed. The electron beam current was found to be strongly dependent on the operating pressure and the average electron beam current at 0.3 Torr of nitrogen (optimum pressure) was found to be around 13.5 kA. The highest value of electron beam charge and density were estimated at the optimum operating pressure and found to be around 7.5 µC and 4.5 x 1016 m-3, respectively. The electron energy distribution spreads from approximately 10 keV to more than 200 keV with a most probable distribution within 80 to 110 keV.
Namini et al.  investigated the characteristics of the Ar ion beam generated in a low energy plasma focus device. A Mather-type PF device filled with argon gas driven by an 11 µF single capacitor bank was used. A Faraday cup, operating in the bias ion collector mode, was used to estimate the energy spectrum and ion flux along the PF axis. The results of the experiments showed the dependence of the energy spectrum on the gas pressure and the anode shape.
2.1 Surface modification and film deposition using dense plasma focus device
During the recent past, the use of DPF devices for material processing has attracted attention because several experiments have shown good results in surface modification and thin film deposition. In ref. [63-65] the DPF has been used for nitrogen ion implantation on AISI 304 stainless steel, titanium and high carbon steel. Similarly, DPF ion induced structural and morphological changes of variety of thin films are reported in ref. [66-68]. Argon ions of DPF were also used for creating n-type doping on conducting polymer films, namely polyaniline . In addition, ions of DPF were successfully used to fabricate various well-adhered thin films like carbon, diamond like carbon, aluminum nitride and titanium carbide.
Feugeas et al.  first time used DPF to implant samples of AISI 304 stainless steel with nitrogen which showed a reduction of wear of 42 times with respect to the implanted ones, with a reduction, at the same time of the friction coefficient. X-ray diffraction and x-ray photoelectron spectroscopy analysis of nitrided samples showed the Fe2N precipitate formation, in almost homogeneous≈0.4 μm thick superficial layer.
Sagar et al.  achieved amorphization of crystalline CdS film for the first time due to irradiation of energetic argon ions generated in the dense plasma focus. A systematic XRD analysis of crystalline and irradiated CdS films and SEM micrographs showed significant structural changes.
Agarwala et al.  used highly energetic pulsed argon ions generated by the dense plasma focus (DPF) device, for the first time to achieve a complete phase of magnetite from hematite thin films. The films were exposed to the ions of the DPF device axially above the anode at various distances. XRD spectra of the ion-irradiated films showed the change from α-Fe2O3 phase to Fe3O4 phase in the film. SEM micrographs of Fe3O4 films indicated the presence of columnar grains of the order of 50 to 90 nm. The magnetization curves confirmed the change from non-magnetic α-Fe2O3 to magnetic Fe3O4 phase.
Rawat et al.  studied the effect of argon ion irradiation on vacuum-evaporated as-grown Sb2Te3 films in a dense plasma focused device (DPF) by structural, compositional, and morphological analyses. The as-grown films consisted of both stoichiometric and nonstoichiometric Sb2Te3 phases with traces of Te. Ion energy greater than 1 MeV promoted the formation of nonstoichiometric SbxTe1−x phase and the oxidation of Sb. Ion energy less than 1 MeV promoted the formation of single stoichiometric Sb2Te3 phase and a homogeneous distribution of grain size
Gupta et al.  successfully deposited Pb(Zr0.53Ti0.47)O3 (PZT) thin films on glass, silicon and Indium-Tin-Oxide (ITO) coated glass substrates by a 3.3 kJ Mather type dense plasma focus device. The x-ray diffraction spectra of the films deposited on glass substrates kept at a distance of 4.2 cm from the top of the anode with 10, 15 and 25 shots showed peaks at 2θ = 31.3° corresponding to the perovskite phase of PZT. Transmission electron microscopy showed the presence of 0.5 nm grains of PZT. The leakage current density was found to be 10−6 Acm−2 at a reverse voltage of 1V, from current density-voltage (J -V) characteristics. The capacitance-voltage (C-V) characteristics showed a counter-clockwise hysteresis loop with a memory window of 1.2V. The ferroelectric characteristic had been confirmed using the polarization-field hysteresis loop. The spontaneous polarization, remnant polarization and coercive field values were found to be 20.1μC cm−2, 8.6μC cm−2 and 79.9 kV cm−1, respectively.
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Ahmad et al.  reported the co-deposition process of TiN0.9 and (Fe,Cr)2N compounds on SS-321 substrate using a 2.3 kJ dense plasma focus device operated with N2 discharges. X-ray diffraction analysis was performed to investigate the ion-induced changes in the near surface structure of the SS-321. Scanning electron microscopy with the energy dispersive X-ray spectroscopy was carried out to analyse the surface morphology and the elemental composition of the nitrided samples. The results revealed that at the low fluence of ion bombardment, a non-stoichiometric tertiary phase (Fe,Cr)xN was developed, which transformed into a stable stoichiometric compound (Fe,Cr)2N by increasing the ion flux. Some CrN precipitates were also observed because of the thermal effect produced by the bombardment of energetic ion beam. Vickers micro-hardness values were increased more than twice for typical ion nitrided samples.
Malhotra et al.  synthesized Luminescent ZnO nanoparticles on silicon and quartz substrates under extremely non-equilibrium conditions of energetic ion condensation during the post-focus phase in a dense plasma focus (DPF) device. Ar+, O+, Zn+ and ZnO+ ions were generated as a result of interaction of hot and dense argon plasma focus with the surfaces of ZnO pellets placed at the anode. It was found that the sizes, structural and photoluminescence (PL) properties of the ZnO nanoparticles appear to be quite different on Si(100) and quartz substrates. The x-ray diffractometry and atomic force microscopy results showed that the ZnO nanoparticles are crystalline and range in size from 5-7 nm on Si(100) substrates to 10-38 nm on quartz substrates. Room-temperature PL studies revealed strong peaks related to excitonic bands and defects for the ZnO nanoparticles deposited on Si (100), whereas the excitonic bands were not excited in the quartz substrate case. Raman studies indicated the presence of E2 (high) mode for ZnO nanoparticles deposited on Si(100).
Mohanty et al.  demonstrated an ingenious method for fabricating network of polyaniline nanowires at room temperature in microsecond timescale using the pulsed electron beam of a plasma focus device. The electron beam of the plasma focus device having a wide range of energies (10-200 keV) was irradiated on to the freestanding polyaniline film. The growth of polyaniline nanowires on the surface of film sample is confirmed by field emission scanning electron microscope images showing nanowires of about 50-80 nm in diameter and up to few tens of micrometers in length.
Ijaz et al.  deposited Nanocrystalline zirconium carbonitride (ZrCN) composite films on zirconium substrates for multiple focus shots. X-ray diffraction analysis showed diffraction peaks corresponding to nitrides (ZrN, Zr2N and Zr3N4), carbide (ZrC) and carbonitride (Zr2CN), confirming the formation of ZrCN composite films. The average crystallite size estimated for ZrN (200) and Zr2CN (111) planes are found to vary from 10 to 20 nm. Maximum compressive stresses of similar to 3.9 GPa in Zr2N (002) plane for 30 focus shots and maximum tensile stresses of similar to 6.5 GPa in ZrN (200) plane for 20 focus shots are observed. Tensile stresses observed in Zr2CN (111) plane are transformed to compressive stresses for higher (40 and 50) focus shots. Raman analysis reveals the emergence of D and G bands related to carbide phases during the film deposition process. Scanning electron microscope analysis exhibits the nanocrystalline microstructure patterns of the composite films. Microstructure patterns showing agglomerates of 30-300 nm dimensions are also observed. Microhardness values of ZrCN composite films increases with increasing number of focus shots and is equal to 5.6 +/- 0.45 GPa for 10 g imposed load, which is 4.5 times that of the virgin one.
Ghareshabani et al.  deposited nanostructured multiphase Ti(C,N)/a-C films using a 3.3 kJ pulsed plasma focus device onto silicon (100) substrates at room temperature The plasma focus device, fitted with solid titanium anode instead of usual hollow copper anode, was operated with nitrogen and Ar/CH4 as the filling gas Films were deposited with different number of shots, at 80 mm from top of the anode and at zero angular position with respect to anode axis X-ray diffraction results show the diffraction peaks related to different compounds such as TiC2, TiN, Ti2CN, Ti and TiC confirming the deposition of multiphase titanium carbo-nitride composite films on silicon X-ray photoelectron spectroscopy confirms the formation of Ti-C. C-N, Ti-O and C-C bonds in the films. Scanning electron microscopy revealed that the nanostructure grains were agglomerates of smaller nanoparticles about 10-20 nm in size. Raman studies verified the formation of multiphase Ti(C,N) and also of amorphous graphite in the films. The maximum microhardness value of the composite film was 14.8 ± 1 3 GPa for 30 shots.
2.2 Study of TiN/Si3N4, TiAlN/Si3N4, Aluminum Nitride and Silicon nitride system synthesized by various techniques.
Deposition of the nitrides of transition metals is one of the most promising techniques for improving the tribological characteristics of surfaces. Thin films of transition metals are important in a large number of technological applications. The TiN coating was developed in the early 1970s, and this hard coating has played an important role in surface engineering parts for two decades because of high hardness over 20 GPa. However, the main limitation of this coating is the oxidation at 550 or 600 °C which can be reached during the machining processes. To overcome this problem, aluminum was alloyed to form a TiAlN coating in the 1990s, which significantly improved the hardness and oxidation resistance up to 800 °C due to the age hardening effect. Recently, with the development of new physical vapor deposition methods such as magnetron sputtering, cathodic arc method and hybrid method, much attention has been paid to the incorporation of substitutional elements such as silicon which forms the TiN- Si3N4 and Ti(Al)N-Si3N4 nanostructures in order to further improve the physical and chemical properties . In this section, a review of thin films of AlN, TiN, TiAlN, Si3N4, TiN/Si3N4, and TiAlN/Si3N4 prepared by several techniques including chemical vapor deposition, reactive sputtering, reactive evaporation, nitriding of evaporated transition metal in a glow discharge in nitrogen, and ion implantation is given:
Hirai et al.  produced first coating consisting of Ti-Si-N by CVD in 1982. They prepared chemically vapor-deposited (CVD) Si3N4-TiN composite on a graphite substrate using a mixture of SiCl4, TiCl4, NH3 and H2 gases. The deposits thus obtained appeared black. The Ti content in the composites ranged from 2.1 to 24.8 wt % and was found in the form of TiN. The structure of the Si3N4 matrices varied from amorphous (initially) to theagr- and β -type, with increasing deposition. Most of theagr and β-type deposits had a preferred orientation (001) parallel to the deposition surface. The deposition surface of the amorphous deposits showed a pebble like structure and the surfaces of theagr- and β -type deposits were composed of various kinds of facets. The heat-treating experiment suggested that β -Si3N4 obtained in the present work was formed directly via a vapor phase, and not from crystallization of amorphous Si3N4 or from transformation ofagr-Si3N4.
Munz et al.  produced TiAl films in various compositions by using the sputter ion plating process. Films sputtered reactively from a target with the composition of TiAl 50:50 at. % had been deposited with a composition of 27.5 at. % Ti, 28.9 at. % Al, and 43.6 at. % N. The crystal structure found was that of sodium chloride with a lattice parameter of 4.20 Å; the micro hardness of such films was found to be HV 2100-2300. The incorporation of Al into the nitride films improved the oxidation resistance as well as the cutting performances of TiAlN coated drills. TiN films started to oxidize at a temperature level of 550 °C, whereas TiAl coatings react with hot air at a temperature of 800 °C severely. TiAlN coated drills had been tested with two different steels and performed better by a factor >2 compared with TiN coated drills.
Biunno et al.  investigated the formation of polycrystalline of TiN films on Si (100) substrate using low-temperature laser processing method. The films were deposited by laser ablation of a TiN hot pressed plate in the presence of neutral or ionized nitrogen using XeClexcimer laser (wavelength 308nm, pulse duration 45 - 10-9 s, and energy density of 4-5 J cm-2). The substrate temperature was ranged from 25 to 550 oC. Plain and cross-section transmission electron microscopy studies showed that films were poly crystalline (average grain size ~ 100 Çº) with face-centered-cubic structure and lattice constant of 4.25 Çº. It was interesting to note that the average grain size remained approximately constant with substrate temperature up to 550 oC. Chemical composition was analyzed by Rutherford backscattering and Auger electron spectroscopy as a function of film depth. The result showed that the film reproduced closely the chemical composition of the TiN target which contained some oxygen, and that the oxygen content decreased with increased substrate temperature. Four point probe measurement and I-V characteristics showed that the film were metallic with a typical resistivity of ~150 µâ„¦-cm. The micro hardness values of these films were found to be as high as 17 GPa.
Grigorov et al.  examined two kinds of reactively evaporated titanium nitride films with columnar and fine-grained film structures, respectively, as diffusion barriers for preventing aluminium diffusion. The aluminium diffusion profiles have been investigated. The activation-energy values determined indicated a grain boundary diffusion mechanism. The difference between the diffusion values was determined implicitly by the microstructure of the layers. Thus, the porous B0 layers contained a considerable amount of oxygen absorbed in the intercolumnar voids and distributed throughout the film thickness. As found by AES depth profiling, this oxygen supply allowed the formation of Al2O3 during annealing the latter preventing the subsequent diffusion of the aluminium atoms.
Baumvol et al.  deposited dielectric thin films of silicon nitride and aluminum nitride by r.f. and d.c. magnetron reactive sputtering respectively. Titanium-aluminum nitride thin films were prepared by d.c.-r.f. magnetron reactive sputtering codeposition. Different film compositions and characteristics were obtained by varying the parameters of the sputtering deposition. The films were characterized by means of Rutherford backscattering spectrometry, nuclear reaction analysis and X-ray diffraction. From these analytical techniques, they obtained the thicknesses, the stoichiometric ratios N/Si, N/Al, Al/Ti and N/(Al + Ti), the depth profiles of these different elements, the contamination levels of O and C, as well as the crystalline structure of the films.
Huang et al.  investicated the grain morphology, microstructure, mechanical properties and fracture behavior of hot-pressed silicon nitride containing two different sizes of TiN particles in this study. No interfacial interactions were noticeable between TiN and Si3N4 up to a temperature of 1850 degrees C. The average aspect ratio and grain thickness of beta-Si3N4 grains decreased slightly with the addition of TiN particles. The amplitude and frequency of the propagating path, and the crack deflection angles, increased with the content of large TiN particles. The toughening mechanisms in TiN/Si3N4 were attributed to the crack deflection, microcrack toughening, and crack impedance by the periodic compressive stress in the beta-Si3N4 matrix. The fracture toughness of Si3N4 was enhanced by 35% with the addition of 20% large TiN particles, hot-pressed at 1850 degrees C.
Veprek et al.  discussed the search for superhard materials considered so far mainly metastable solids, such as diamond, c-BN and C3N4 and single- and polycrystalline superlattices. More recently, novel superhard nanocrystalline composites have been developed which appear superior to these materials in terms of stability, resistance against oxidation and relatively simple preparation by means of plasma CVD. The present status of the theoretical concept for their design and the experimental results which support it are briefly summarized.
Vaz et al.  investicated the (Ti,Si)N system and some of its properties characterised. For this, (Ti,Si)N films with thicknesses ranging from 1 to 3.3 µm and different contents of Ti and Si were deposited onto silicon wafers and polished high-speed steel substrates by r.f. reactive magnetron sputtering technique. The atomic composition of the samples were measured by Rutherford Backscattering Spectrometry (RBS). With regard to the structural properties, two cubic crystallographic structures were found, with lattice parameters of about a = 4.29 Angstrom and 4.18 Angstrom. The grain size, evaluated by Fourier analysis of X-ray peaks, ranged from 5 nm to 34 nm. Comparing the adhesion results, the Ti0.70Si0.30N and Ti0.83Si0.17N sample presented the best results in adhesion with a critical load for total failure around 115 N and 105 N, respectively.
Schuler et al.  deposited titanium aluminum nitride films (Ti-Al-N) by reactive magnetron cosputtering. Elemental compositions of these films had been determined by core level photoelectron spectroscopy. Scanning electron microscopy revealed a columnar film growth. This was also reflected by the topography of film surfaces as studied by atomic force microscopy. By x-ray diffraction a crystalline atomic structure was revealed. Single phase samples obtained, consisting of the substitutional solid solution (Ti, Al)N. Crystallites show preferential orientation. The optical properties of these films had been investigated by spectrophotometry in the UV-VIS-NIR wavelength range. Depending on the elemental composition, the optical constants vary from metallic to dielectric behavior. For film compositions with x <0.5 typical features were a tunable transmission maximum and reflection minimum in the visible spectral range, a high infrared reflection, and a low infrared absorption. Due to these optical properties, Ti-Al-N films are found promising candidates for applications such as coatings for solar control windows and optical selective solar absorbers.
Zhang et al.  prepared nanocomposite coatings of TiN/Si3N4 by ion beam assisted deposition (IBAD): simultaneous sputtering of Ti and Si targets and film bombardment by N2(+) ions at 1000 eV. The Si/Ti ratio in the film varied from 0 to 0.9. The coatings were composed of amorphous Si3N4 and RN nanocrystals with grain size of several nanometers. Such nanocomposites exhibited improved mechanical properties in comparison with TiN or Si3N4 deposited under the same conditions. The nanoindentation hardness of TiN/ Si3N4 film at the Si/Ti ratio of 0.3 reached a maximum of 42 GPa, compared with 22 GPa for TiN and 18 GPa for Si3N4. The wear resistance of AISI 52100 steel coated with these nanocomposite coatings was increased about three times.
Vennemann et al.  deposited coatings by reactive DC magnetron sputtering on high-speed steel. The composition of the coatings varied by the type of target used and the applied voltage to each target and was determined by glow discharge optical spectroscopy (GDOS). The coating thickness was derived from ball cratering and ranges between 3 and 6 µm. The adhesion of the coatings was analysed by the scratch test. The coated samples were subjected to an oxidation test, where they are exposed to a temperature of 800 or 1000 degrees C and an oxygen partial pressure ranging between 1 and 100 mPa for 1 h. The results of the TiAlSiN coatings were compared with TiAlN coatings to evaluate the influence of the silicon. Ultra-microhardness measurements were performed prior and after the oxidation tests. Changes in the composition due to diffusion processes were measured with GDOS over the whole coating thickness and the coating/substrate interface. X-ray photoelectron spectroscopy revealed changes of composition and binding energy in the near surface zone.
Moto et al.  deposited nc-(Ti,Al)N and h-AIN were deposited on steel substrate using plasma CVD technique and characterized by means of XRD, XPS, EDX. The effect of Al substitution shown by the decrease of the lattice parameters of TiN as the fraction of Al increases. As the fraction of Al further increased up to 0.8, the hexagonal AlN phase precipitates. The hardness of these coating were around 30 GPa higher than that prepared by other method
Zhang et al.  calculated bulk properties of stable binary fcc-TiN and hcp(beta)-Si3N4, hypothetical fcc-SiN and hcp(beta)- Ti3N4, and ternary Ti-Si-N phases by ab initio method. The values of total energies were then used for thermodynamic calculations of the lattice instabilities of hypothetical binary phases of fcc-SiN and hcp-Ti3N4, and of the interaction parameters of ternary Ti-Si-N phases. Based on these data, Gibbs free energy diagrams of the quasi-binary TiN-SiN system were constructed in order to study the relative phase stability of the metastable ternary fcc- and hcp-Ti-Si-N phases over the entire range of compositions. The results were supported by the published data from chemical and physical vapor deposition experiments. The constructed Gibbs free energy diagram and phase selection diagram of quasi-binary TiN-SiN system in fcc structure showed that metastable fcc-Ti-Si-N coatings should undergo chemically spinodal decomposition into coherent fcc-TiN and fcc-SiN. Due to a high lattice mismatch between fcc-TiN and hcp-Si3N4, and to much higher lattice instability of fcc-SiN with respect to stable hcp-Si3N4, only about one monolayer of pseudomorphic SiN interfacial phase was stable.
Xiao et al.  prepared the Si3N4 thin film by MWECR-PECVD at different deposition temperature and the structure of the Si3N4 thin film was investigated. The results indicated that the structure of the Si3N4 thin film prepared at low deposition temperature was in the amorphous phase. However, when the deposition temperature increases to 280 degrees centigrade, the Si3N4 thin film changed to crystalline alpha- Si3N4. With a further increase of the deposition temperature, the grain of the Si3N4 thin film became more fine, uniform and flat. XRD analysis showed that the structure of the Si3N4 thin film prepared at 280 degrees centigrade was of a crystalline structure.
Li et al.  investigated the processes that are responsible for the relaxation of nanostructure and/or self-hardening of superhard nc-TiN/a-Si3N4 and nc-(Ti,Al)N/a-Si3N4 nanocomposites upon annealing in nitrogen, using the internal friction measurements by means of torsion pendulum and vibrating reed method. It was shown that stable nanocomposites, which were deposited under conditions of a sufficiently high nitrogen pressure and temperature, in a plasma of intense glow discharge (power density at the surface of the growing film about 2-3 W/cm2), had a constant value of hardness (measured at room temperature after each annealing step) up to 1100 degrees C, and show no internal friction peak up to a temperature of 800 degrees C achievable in our internal friction measurements. In contrast, the unstable coatings that were deposited at a low temperature and/or low nitrogen pressure or low plasma density showed self-hardening and a distinct internal friction peak with well defined activation energy. This peak was due to thermally activated processes within the grain boundaries of the nanostructure whose formation due to phase segregation was not completed during the deposition. Upon the annealing to ≥ 700 degrees C, the phase segregation was completed, the hardness increases and remains stable up to 1100 degrees C, and the internal friction peak vanished.
Prochazka et al.  prepared superhard nanocomposite nc-TiN/a-Si3N4 coatings by reactive magnetron sputtering (RMS) and pulsed dc plasma-induced chemical vapour deposition (PCVD) on stainless steel substrates. The tribological behaviour of these coatings at room and elevated temperature was compared with that of TiN coatings deposited by RMS and PCVD. The results showed that the superhard nanocomposite nc-TiN/a- Si3N4 coatings had a somewhat higher friction coefficient of 0.55-0.7 at room temperature that decreased to about 0.4-0.5 at 550 degrees C. However, the friction coefficient of pure TiN coatings was 0.6 at room temperature and increased to 0.7 after a sliding distance of 0.1 km at 550 degrees C.
Barshilia et al.  synthesized superhard nanocomposite coatings of TiAlN/Si3N4 with varying silicon contents using reactive direct current (DC) unbalanced magnetron sputtering. The Si and TiAl targets were sputtered using an asymmetric bipolar-pulsed DC power supply and a DC power supply, respectively, in Ar + N2 plasma. The structural and mechanical properties of the coatings were characterized using X-ray diffraction (XRD) and nanoindentation techniques, respectively. The elemental composition of the TiAlN/ Si3N4 nanocomposite coatings was determined using energy-dispersive X-ray analysis and the bonding structure was characterized by X-ray photoelectron spectroscopy. The surface morphology of the coatings was studied using atomic force microscopy. The XRD data showed that the nanocomposite coatings exhibited, (111) and (200) reflections of cubic TiAlN phase. The broadening of the diffraction peaks with all increase in the silicon content in the nanocomposite coatings, suggested a decrease in the average crystallite size. The TiAlN/ Si3N4 nanocomposite coatings exhibited a maximum hardness of 43 GPa and an elastic modulus of 350 GPa at a silicon concentration of approximately 11 at%. The hardness and the elastic modulus of the nanocomposite coatings decreased significantly at higher silicon contents. Micro-Raman spectroscopy was used to characterize the structural changes as a result of heating of the nanocomposite coatings in air (400-850 degrees C) and in vacuum (900 degrees C). The Raman data of the nanocomposite coatings annealed in air and vacuum showed better thermal stability as compared to that of the TiAlN coatings. Similarly, the nanocomposite coatings deposited on mild steel substrates exhibited improved corrosion resistance.
Yin et al.  reported that oxidation of TiN occurs at 450 degrees C, and an oxide layer of about 2030 nm was formed after only a few minutes of heat treatment with oxygen. The thickness of the oxide layer is comparable to the thickness of the absorbing layer of the solar thermal selective absorbers, which can affect significantly the solar thermal performance. TiN produced at higher nitrogen pressure (2.1 Pa with 40% nitrogen in argon) could absorb oxygen more easily into bulk and was less oxidation resistant during the heat treatment than that produced at 0.4 Pa of 40% nitrogen in argon. The hardness after the oxidation treatment was slightly increased by approximately 10%, consistent with reported oxidation resistant properties of this material for mechanical protection applications. As a result of this study, TiN or TiAlN as an element may not be suitable candidates for use as solar selective absorbers in air-stable high temperature applications.
Akamaru et al.  modified ake-shaped fine particles with a thin TiN layer by a hexagonal-barrel-sptittering technique. To determine the optimum sputtering conditions. TiN films were deposited on a glass substrate by the reactive sputtering technique by varying the values of N2 percentage. total pressure, radial-frequency (RF) power. and Substrate temperature. From the analysis of XRD patterns, it was determined that a N2 percentage of 25%. a total pressure of 1.2 Pa. a RF power of 200 W. and room temperature were suitable for the preparation of TiN films. Under these optimized conditions, Al flakes were modified with a TiN by the barrel-sputtering technique. The results of optical microscopy. X-ray diffraction measurements. scanning electron microscopy. and energy-dispersive X-ray spectroscopy measurements revealed that the surface of each Al flake was successfully coated uniformly with a TiN layer.
Jose et al.  synthesized Ti-Al-N films by reactive magnetron co-sputtering with different aluminum compositions. X-ray diffraction, secondary ion mass spectrometry, nanoindentation, and atomic force microscopy (AFM) techniques were used to analyze these films. The as-deposited films were crystalline for concentrations of Al (35%, 40%, 55%, and 64%) and at 81% it became amorphous. Nanoindentation hardness increased with aluminum and started to decrease beyond 81% of aluminum. Continuous multicycle indentation technique was used to analyze the failure mode of the film with highest hardness. AFM topography analysis of this film exhibited edge cracks outside and inside the indentation area and sink-in when the penetration reaches the substrate.
Shishkovsky et al.  discussed the possibility of the layer-by-layer synthesis of 3D parts from nitrides of titanium or aluminum by selective laser sintering/melting. The relationship between laser processing parameters and structure and phase content of sintered/melted samples were studied by means of optical metallography, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. Optimal parameters of SLM process for AlN and TiN synthesis were determined. Solid 3D parts containing a TiN phase were produced from Ti powder. Distortion of the crystalline lattice of AlN and TiN phases is observed with the laser energy input.
Saoula et al.  related the properties of TiN films deposited by magnetron sputtering to their deposition conditions. The elaboration of films had been carried out by RF-Magnetron Sputtering (13.56 MHz) from a titanium metallic target in reactive N2/Ar gas mixture. The main variables investigated were the composition of the Ar/N2 gas mixture, the total pressure, the deposition time, the discharge power but in this work the attention is given to the effect of the substrate bias voltage. A study was carried out on the effects of these variations on the film growth rates, the film thickness and the properties of TiN films. The deposited films were characterized by energy dispersive spectroscopy (EDS), and observed by means of atomic force microscopy (AFM).
Yue et al.  prepared a series of TiAlN/Si3N4 nano-multilayer films with various Si3N4 layer thicknesses by reactive magnetron sputtering. These multilayers were then annealed at temperatures ranging from 600 to 900 degrees C in air for 1 hour. The composition, microstructure, and mechanical properties of the films were characterized by energy dispersive x-ray spectroscopy, x-ray diffraction, scanning electron microscopy, and nanoindentation. It revealed that under the template effect of TiAlN layers in multilayers, as-deposited amorphous Si3N4 was crystallized and grows coherently with TiAlN layers when Si3N4 layer thickness is below 0.6 nm Correspondingly, the hardness and elastic modulus of the multilayers increased significantly. With further increase in the layer thickness, Si3N4 transformed into amorphous, resulting in a decrease of hardness and modulus. The TiAlN/ Si3N4 nano-multilayers retained their superlattice structure even up to 900 degrees C. The small decrease in the hardness of multilayers annealed below 800 degrees C was correlated to the release of compressive stress in multilayers. However, oxidation was found on the surface of multilayers when annealed at 800 degrees C, which resulted in a marked decrease in the hardness of multilayers. The multilayers presented higher hardness as compared with the monolithic TiAlN film.
Park et al.  investigated thermal stability of the TiAlN/Si3N4 in terms of the nano-layered structure and hardness TiAlN/ Si3N4 nanoscale multilayered coatings with various thickness of Si3N4 layer were prepared by alternating deposition of TiAlN and Si3N4. In contrast to other nanoscale multilayered coating system such as AlN/CrN in which the intensity of the low angle XRD peaks decreased with increasing annealing temperature by interdiffusion between adjacent layers, the low angle XRD peak intensity of the nanoscale multilayered TiAlN/ Si3N4 coatings increased after heat-treatment in N2 atmosphere up to 800 degrees C. Such a thermal stability of the nano-layered structure was believed to be due to spinodal type phase separation of TiAlN and Si3N4, which increased the hardness value of the TiAlN/ Si3N4 coating at high temperatures.
Doll et al.  reported a post-CMOS compatible fabrication process for piezoelectric sensors and actuators on silicon using only standard CMOS metals. The piezoelectric properties of aluminum nitride (AlN) deposited on titanium (Ti) by reactive sputtering are characterized and microcantilever actuators are demonstrated. The film texture of the polycrystalline Ti and AlN films was improved by removing the native oxide from the silicon substrate in situ and sequentially depositing the films under vacuum to provide a uniform growth surface. The piezoelectric properties for several AlN film thicknesses were measured using laser doppler vibrometry on unpatterned wafers and released cantilever beams. The film structure and properties are shown to vary with thickness, with values of d(33f), d(31) and d(33) of up to 2.9, -1.9 and 6.5 pm V-1, respectively. These values were comparable with AlN deposited on a Pt metal electrode, but with the benefit of a fabrication process that uses only standard CMOS metals.
Lee et al.  fabricated TiN/Si3N4 nanocomposites from beta-Si3N4 and TiN nano powders by powder processing routes. The specimens were consolidated at 1600 degrees C for 3 min by spark plasma sintering, and nearly full densification was obtained in the resulting sintered bulk composites. The TiN phase growed rapidly and a typical twin structure of TiN observed in the composites. The grain size and distribution for TiN affected the electrical resistivity, leading to a pulse current through the sintering compact. The resulting microstructure for the composite containing 10 wt% TiN reveals that grain coarsening behavior for beta-Si3N4 based grains was accelerated, and the composite had the highest toughness of 4.9 MPa among all these composites. The other composites showed nanosized beta-Si3N4 based grains with a fracture toughness of nearly 4.2 MPa.
Lee et al.  prepared the (103) oriented AlN films on the silicon substrate by rf magnetron sputtering. Different temperatures (100 oC, 200 oC, 300 oC, and 400 oC) were used in this experiment process. The crystalline structure of films was determined by X-ray diffraction (XRD) and the surface microstructure was investigated by the atomic force microscope (AFM). The result exhibited the optimal substrate temperature is 300 oC. The optimal (103) oriented AlN films have the strongest XRD intensity, the smallest full width at half maximum (FWHM) value (0.6 degrees), the largest grain size (15.8 nm) and the smoothest surface (Ra = 3.259 nm).
Ren et al.  investigated the effects of thickness of AlN nucleation layer grown at high temperature on AlN epi-layer. Crystalline quality crack-free AlN samples with various nucleation thicknesses are grown on sapphire substrates by plasma-assisted molecular beam epitaxy. The AlN crystalline quality was analyzed by transmission electron microscope and x-ray diffraction (XRD) rocking curves in both (002) and (102) planes. The surface profiles of nucleation layer with different thicknesses after in situ annealing were also analyzed by atomic force microscope A critical nucleation thickness for realizing high quality AlN films was found. When the nucleation thickness was above a certain value, the (102) XRD full width at half maximum (FWHM) of AlN bulk increased with nucleation thickness increasing, whereas the (002) XRD FWHM showed an opposite trend These phenomena attributed to the characteristics of nucleation islands and the evolution of crystal grains during AlN main layer growth.
Mahmood et al.  prepared polycrystalline aluminum nitride (AlN) films by DC reactive magnetron sputtering followed by its characterization using advance electronic and optical techniques. Film quality had been optimized mainly using deposition parameters. Rutherford backscattering spectroscopy (RBS) and nuclear interaction (NR) techniques were used to analyze the film density (atoms/cm3), elemental composition and impurities of the grown film. Ion beam analysis (IBA) was based on the particle energy spectra bombarded with a low-energy deuterium beam. The corresponding linear thickness of the film was measured using a profilometer. X-Ray diffraction, spectroscopic ellipsometry and atomic force microscope had also been employed to reinforce the results. They found that highly dense and stoichiometric films could be obtained at higher plasma current. Under optimal deposition conditions, the film densities of similar to 2.45 g/cm3, FWHM similar to 0.125 and the surface roughness similar to 6.758 nm had been achieved successfully.