Laser/sol–gel synthesis: a novel method for depositing nanostructured TiN coatings in non-vacuum conditions

In this work results of experiments on the in situ production of titanium nitride by the reaction of titania sol–gel with a nitrogenous admixture under laser irradiation are reported. A diode laser beam at different powers and traverse speeds was applied to the mixture placed on EN43 mild steel and 316L stainless steel substrates. Composite coatings of titanium nitride and titanium oxide with a hardness of 17–21 GPa have been achieved by this new method. Surface morphology and microstructure of the deposited coatings and substrate surface layers were examined using optical microscopy, scanning electron microscopy, and field-emission gun scanning electron microscopy. Chemical composition was determined by energy-dispersive X-ray analysis. The phases were identified by X-ray diffraction. Results of microhardness and nanohardness at the top surface were evaluated. PACS 81.15.Fg; 81.20.Fw; 81.05.-t     

Investigation of etch pits on KDP crystals with porous sol–gel coatings

We have investigated etch-pit formation on potassium dihydrogen phosphate (KDP) crystals with porous anti-reflective coatings. Etch pits develop beneath the sol–gel coatings after exposure to ambient humidity. The etch pits are homogeneously distributed with a density and an average size governed by the relative humidity and the coating thickness. Furthermore, the etch pits are self-similar in shape and possess facets corresponding to low-energy planes of KDP. Results from optical microscopy, light scattering, and atomic force microscopy support the following model for etch-pit formation in this system. Water adsorbed from the environment into the porous sol–gel coating contacts the crystal surface, causing etch-pit nucleation at high undersaturation. The plume of KDP rising from an etch pit slowly diffuses laterally, reducing the undersaturation and shutting off nucleation in the surrounding area. Because surface kinetics are rapid compared to mass transport through the sol–gel, etch pits continually undergo equilibration to maintain a low-energy geometry and generate an average spacing. Growth continues until the reservoir of water in the sol–gel is saturated with KDP. Coarsening is only observed in high relative humidity environments. Received: 13 Juni 2001 / Accepted: 30 July 2001 / Published online: 30 October 2001     

Temperature dependent structural and optical properties of nanocrystallineCdO thin films deposited by sol–gel process

Nanocrystallites of cadmium oxide (CdO) thin films were deposited by sol–gel dip coating technique on glass and Si substrates. XRD and TEM diffraction patterns confirmed the nanocrystalline cubic CdO phase formation. TEM micrograph of the film revealed the manifestation of nano CdO phase with average particle size lying in the range 1.6–9.3 nm. UV–Vis spectrophotometric measurement showed high transparency (nearly 75% in the wavelength range 500–800 nm) of the film with a direct allowed bandgap lying in the range 2.86–3.69 eV. Particle size has also been calculated from the shift of bandgap with that of bulk value for the films for which the particles sizes are comparable to Bohr exitonic radius. The particle size increases with the increase in annealing temperature and also the intensity of XRD peaks increases which implies that better crystallinity takes place at higher temperature.     

Impedance studies of Sb doped SnO2 thin film prepared by sol gel process

Antimony-doped tin oxide thin films have a range of technological applications as conductive coatings, and sol-gel processing seems to offer some advantages over other coating techniques. In this study antimony-doped tin oxide (ATO) thin films have been prepared by the sol-gel dip-coating (SGDC) process, using tin (II) chloride dehydrate (SnCl₂, 2H₂O) and antimony (III) chloride (SbCl₃) as host and dopant precursors respectively. The structure of the (ATO) powders was analysed by X-ray diffraction (XRD) and the microstructure of the thin films by atomic force microscopy (AFM). These investigations show that the structure is tetragonal rutile type and that an increase in Sb-doping decreases the crystallite size of the (ATO) particles. To analyze the impedance spectroscopy data, the Nyquist (Z″ vs. Z′) plots as well as the representation of imaginary (Z″) and real (Z′) parts of impedance vs. frequency were used. The Nyquist plots suggest that only the grain boundaries are responsible in the conduction mechanism of the material. From the variation of lnσ vs. inverse of absolute T we have deduced the activation energy found to be 0.87 eV.     

Synthesis and characterization of LiFePO4 prepared by sol–gel technique

LiFePO₄ powder was synthesized by means of a new route, using a two step process. In the first step, an intermediate compound was synthesized by the sol–gel method. This precursor compound to LiFePO₄ was characterized by thermal analysis (TG/DTG and DSC), Mössbauer spectroscopy, Transmission Electronic Microscopy (TEM) and Small Angle Scattering (SAXS). In the second step, the precursor was sintered and analyzed by X-ray diffraction (XRD), showing the formation of the proposed single phase material.     

Density-modulated alumina-based nanometre films prepared by sol–gel technique

Alumina-based nanometre films produced by a sol–gel method are investigated by wide-angle X-ray scattering and X-ray reflectometry. Every dipping cycle of the sol–gel route results in formation of an X-ray amorphous film exhibiting a density gradient. Both withdrawal speed and drying temperature used as tuning parameters during coating preparation influence the thickness and density of the sol–gel film. An increase of the withdrawal speed results in a thicker film of a lower mean density. An opposite effect is observed with an increase of the drying temperature. The appearance of multilayer Bragg reflections in the reflectivity curves of successive stacked films is discussed in detail. The thermal stability of the density-modulated aluminium oxide-based nanometre multilayers is investigated in a temperature range of 300–1000 °C. Possible applications as X-ray optical elements are outlined. PACS  61.10.Kw; 68.60.Dv; 81.20.Fw     

Preparation and magnetic properties of magnetite nanoparticles by sol–gel method

 Magnetite (Fe₃O₄) nanoparticles have been successfully synthesized by sol–gel method combined with annealing under vacuum. The phase structures, morphologies, particle sizes, chemical composition, and magnetic properties of Fe₃O₄ nanoparticles have been characterized by X-ray diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectrometer and vibrating sample magnetometer (VSM). The results indicate that the size, the corresponding saturation magnetization value and coercivity value of Fe₃O₄ nanoparticles increase with the increase of synthesized temperature. And the phase transformation of Fe₃O₄ nanoparticles has been studied under different atmospheres and temperatures.     

Study of NiCuZn ferrite powders and films prepared by sol gel method

This paper reports that a series of NiCuZn ferrite powders and films are prepared by using sol-gel method.The effects of raw material composition and the calcinate temperature on magnetic properties of them are investigated.The NiCuZn ferrite powders are prepared by the self-propagating high-temperature synthesis method and subsequently heated at 700 C～1000 C.The results show that NiCuZn ferrite powders with single spinel phase can be formed after heat-treating at 750 C.Powders obtained from Ni 0.4 Cu 0.2 Zn 0.4 Fe 1.9 O 4 gel have better magnetic properties than those from gels with other composition.After heat-treating at 900 C for 3 h,coercivity H c and saturation magnetization M s are 9.7 Oe (1 Oe=80 A/m) and 72.4 emu/g,respectively.Different from the powders,NiCuZn films produced on Si (100) from the Ni 0.4 Cu 0.2 Zn 0.4 Fe 2 O 4 gel formed at room temperature possess high properties.When heat-treating condition is around 600 C for 6 min,samples with low H c and high M s will be obtained.The minimal H c is 16.7 Oe and M s is about 300 emu/cm 3.In comparison with the films prepared through long-time heat treating,the films prepared through short heat-treating time exhibits better soft magnetic properties.     

Laser backwriting process on glass via ablation of metal targets

Ablation of metal targets onto pyrex glass substrates, using a Q-switched Nd:YAG laser working at 355 nm, was used to study the potential of a laser backwriting process for the fabrication of optical waveguides via an index of refraction change. Metal foils of stainless steel, aluminum, copper, brass and gold have been used as blanks and irradiated by focusing the laser beam through a cylindrical lens under continuous movement in a direction perpendicular to the irradiation. An horizontal setup was found suitable to improve the effect of the plume in the sample. Results were obtained for two different configurations. Transversal profiles were analysed using a contact profilometer, comparing results obtained for the different configurations, traverse speeds and metal targets used. Two ablation regimes were identified, which are related to a critical laser fluence value of 2.7 J/cm². Surface micrographs obtained by scanning electron microscopy are discussed, together with the characteristics of the structures attained, taking into account the optical and thermal properties of the ablated metal blanks.     

Laser sintering of green compacts

Green Compact Laser Sintering (GCLS) is a new technique for sintering powder metallurgical components by laser irradiation. After mixing; powders are pressed into a green compact; which can then be sintered by laser irradiation. The properties of powder metallurgical alloys for GCLS and conventional sintering are compared.     

Electrical properties of nickel - YSZ composites prepared by a sol gel method

Composite materials containing metallic nickel and yttria stabilised zirconia (YSZ) have been prepared by a sol gel method. Microstructural investigations show that metal particles with a diameter of less than 300 nm still remain present after sintering. In the present work, the conductivity behaviour of such composites was investigated. Furthermore, ageing phenomena, in particular the influence of the nickel content, were studied. A possible application of such materials as anodes in solid oxide fuel cells will be discussed. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11 – 18 Sept. 1994     

Mössbauer and optical investigation of Co3−x Fe x O4 thin films grown by sol–gel process

Structural transformation and the related variation in magnetic and optical properties of Co_3?x Fe _x O₄ thin films grown by a sol–gel method have been investigated as the Fe composition varies up to x?=?2. The normal spinel phase is dominant below x?=?0.55 and the inverse spinel phase grows as x increases further. Conversion electron Mössbauer spectroscopy (CEMS) measurements indicate that the normal spinel phase have octahedral Fe³⁺ ions mostly while the inverse spinel phase contain octahedral Fe²⁺ and tetrahedral Fe³⁺ ions. For higher Fe composition (x?>?1.22), Co²⁺ ions are found to substitute the octahedral Fe²⁺ sites. The measured optical absorption spectra for the Co_3?x Fe _x O₄ films by spectroscopic ellipsometry support the CEMS interpretation.     

Structural and electrical characteristics of zirconium oxide layers derived by photo-assisted sol–gel processing

This paper reports the photo-assisted formation of ZrO₂ layers derived by sol–gel processing at low temperatures using intense radiation from ultraviolet (UV) excimer lamps. Excellent layer properties can be readily obtained for these sol–gel layers after 5-min exposure to the UV irradiation at around 300 °C. Analyses of the as-deposited sol–gel layers by UV/VIS spectrophotometry show that the organic species contained in the layers have been removed to a large extent after 5-min irradiation. This is further confirmed by X-ray photoelectron spectroscopy analyses of the same irradiated layers, which indicate the formation of ZrO₂ with little carbon contamination contributed by the organic species and less oxidation of Si at the interface. Electrical measurements of these layers are also reported. Received: 31 July 2001 / Accepted: 6 September 2001 / Published online: 17 October 2001     

Conductivity and dielectric properties of sol–gel derived porous zirconia

The 8-mol percentage Y₂O₃-stabilized Porous Zirconia was prepared using sol–gel method. Zirconium oxalate gel was prepared by the addition of appropriate amount of oxalic acid solution into the 1 M aqueous solution of zirconium-oxy chloride. A cubic phase zirconia powder was obtained by calcination and milling of the zirconium oxalate gel. Crystallization temperature was found about 450 °C from the Differential thermal analysis. The phase analysis by X-ray diffraction shows the presence of cubic phase. Pellets sintered at 1,350 °C were highly porous, and the electrical conductivity was found with lower value due to the porosity, and the hardness was about 8.0 GPa. Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006.     

Polytetrafluoroethylene piezoelectrets prepared by sintering process

Polytetrafluoroethylene (PTFE) films with a void structure are prepared by a sintering process. Such void PTFE films are piezoelectric after proper corona charging. The quasi-static piezoelectric d ₃₃ coefficients up to 250 pC/N are achieved for the samples which were made of compact and biaxial-tension porous PTFE layers. Pre-ageing treatment is an effective method to further improve the thermal stability. For the samples with pre-ageing treatment, the reduction of the d ₃₃ coefficients is around 2% per day when exposed to 120 °C.     

Effect of calcinations on the structural and magnetic properties of magnesium ferrite nanoparticles prepared by sol gel method

Magnesium ferrite nanoparticles calcined at 300 °C, 350 °C, 400 °C, 450 °C were synthesized by sol-gel method. The effects of calcinations on the cation distribution, structural and magnetic properties have been investigated. X-ray diffraction (XRD) and vibrating scanning magnetometer (VSM) were used to characterize the structural and magnetic properties. X-ray diffraction analysis revealed the formation of single phase MgFe₂O₄ in all the samples. Lattice constant and crystallite size increased with calcination. X-ray diffraction data were used to estimate the average cationic distribution among A site and B site. Cationic distribution shows that there is migration of cation between tetrahedral A site and octahedral B site. Saturation magnetization increased with particle size. Coercivity decreased with calcination temperature as a result of decrease in pinning effect at the grain boundary. Curie temperature (T_C) decreased slightly due to weakening of A-B exchange interaction. Low temperature magnetic measurement revealed that blocking temperature (T_B) increased due to strong magnetic interaction.     

Investigation of dielectric and electrical behavior of Mn doped YCrO3 nanoparticles synthesized by the sol gel method

In the present work Mn doped YCrO₃ nanoparticles are synthesized by the sol–gel method. Samples have been characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–vis absorption spectroscopy. The optical band gap of Mn doped YCrO₃ nanoparticles increases with increase of doping concentration. The dc resistivity of the prepared samples decreases with increasing temperature. The variation of ac conductivity with frequency has been explained by the Correlated Barrier Hoping (CBH) conduction mechanism. Dielectric permittivity of the samples was studied and it follows the power law ε^/(f)∝Tⁿ, where the temperature exponent n is found to be frequency dependent. The dielectric properties of the samples have been discussed in terms of electric modulus vector. Both activation energies due to dc resistance and dielectric response have been measured for the different samples and it is observed that it increases with the Mn content.     

Synthesis,magnetic properties and microstructure of Ni–Zn ferrite by sol–gel technique

In the study, the Ni–Zn ferrite powder of a Ni_0.3Zn_0.7Fe₂O₄ composition was synthesized by sol–gel route using metal acetates at low temperatures. Both the scanning electron microscope and X-ray diffraction analyses of various gel samples heated at different temperatures were used to identify the reaction stages where the amorphous-gel-to-crystalline phase transition occurred. The electrical, magnetic and microstructural properties of the toroidal cores were studied. It was found that the initial permeability increased with a large frequency band (0.1–31.39 MHz) and the magnetic loss was small. The electrical resistivity was higher as compared to the ones which were obtained by the conventional process. Therefore, well–defined polycrystalline microstructure nickel–zinc ferrite and a short processing time of gel preparation have become the major achievements of this study.     

Dielectric anomaly in Li-doped zinc oxide thin films grown by sol–gel route

Sol–gel route was employed to grow polycrystalline thin films of Li-doped ZnO thin films (Zn_1-xLi_xO, x=0.15). Polycrystalline films were obtained at a growth temperature of 400–500 °C. Ferroelectricity in Zn_0.85Li_0.15O was verified by examining the temperature variation of the real and imaginary parts of dielectric constant, and from the C–V measurements. The phase transition temperature was found to be 330 K. The room-temperature dielectric constant and dissipation factor were 15.5 and 0.09 respectively, at a frequency of 100 kHz. The films exhibited well-defined hysteresis loop, and the values of spontaneous polarization (P_s) and coercive field were 0.15 μC/cm² and 20 kV/cm, respectively, confirming the presence of ferroelectricity. PACS 77.22Ch; 77.22Ej; 77.80Bh