Structural and magnetic properties of single-step electrochemically deposited nanocrystalline cobalt ferrite thin films

In this paper, we study the structural, surface morphological and magnetic properties of single-step electrochemically deposited cobalt ferrite thin films. The prepared films were nanocrystalline with cubic crystal structure. Scanning electron micrograph image showed that the cobalt ferrite thin film was uniformly distributed over the substrate in addition to some random overgrowth of porous particles. The saturation magnetization of 298 emu/c was confirmed when films were used in magnetic studies.     

Preparation and characterization of Al doped ZnO thin films by PLD

This paper describes the effect of doping on the composition, surface morphology and optical, structural and electrical properties of Al doped ZnO thin films by pulsed laser deposition. SEM analysis shows that the crystalline nature of the deposited films decreases with an increase of Al doping concentration from 1% to 6%. In the AFM analysis, the surface roughness of the deposited films increases by increasing the doping concentration of Al. Al doping strongly influences the optical properties of the ZnO thin films. Optical transmittance spectra show a very good transmittance in the visible region (450–700 nm). The calculated optical band gap was found to be in the range from 3.405 to 3.464 eV. Structural analysis confirms that the increases of Al concentration decrease the crystallinity of the ZnO films and the particle size decreases from 45.7±0.09 to 28.0±0.02 nm. In the Raman analysis, the active mode of Al(=1%) doped ZnO films were observed at 434.81 cm⁻¹. The shifts of the active mode (_E2)$\left(E_2\right)$ show the presence of tensile stress in the deposited films. The electrical properties of the deposited films showed that the values of the Hall mobility was in the range between 2.51 and 10.64 cm²/V s and the carrier concentration between 15.7 and 0.78×10¹⁷ and the resistivity values between 1.59 and 10.97 Ωcm, depending on the doping concentration.     

Thickness dependent anomalous magnetic behavior in pulsed-laser deposited cobalt ferrite thin film

Cobalt ferrite thin films of different thicknesses were pulsed-laser deposited onto a fused quartz substrate held at ambient temperature (RT) by varying deposition time. The samples were ex-situ annealed at 750°C in air for 2 hours. All the films were characterized by X-ray diffraction, Raman spectroscopy and energy dispersive X-ray analysis. The spontaneous magnetization, 4πM _S , was found to be 6130 G for the 50 nm thick sample, and this is higher than that for the bulk cobalt ferrite of 5300 G, by 16%. The 4πM _S was found to decrease with the increase in film thickness and an overall decrease of 32% was observed, when the film thickness increased from 50 nm to 600 nm. In contrast the films of the same thicknesses, when deposited at substrate temperature of 750°C showed an increase of 4πM _S with the increase in film thickness. The thickness dependence of 4πM _S in these nanocrystalline thin films has been explained in terms of the cation distribution and the grain size, which are sensitive to the substrate temperature during deposition.     

Characterisation of porous doped ZnO thin films deposited by spray pyrolysis technique

Al or Sn doped ZnO films were deposited by spray pyrolysis using aqueous solutions. The films were deposited on either indium tin oxide coated or bare glass substrates. ZnCl₂, AlCl₃ and SnCl₂ were used as precursors. The effect of ZnCl₂ molar concentration (0.1-0.3 M) and doping percentage (2-4% AlCl₃ or SnCl₂) have been investigated. The main goal of this work being to grow porous ZnO thin films, small temperature substrates (200-300 °C) have been used during the spray pyrolysis deposition. It is shown that, if the X-ray diffraction patterns correspond to ZnO, the films deposited onto bare glass substrate are only partly crystallized while those deposited onto ITO coated glass substrate exhibit better crystallization. The homogeneity of the films decreases when the molar concentration of the precursor increases, while the grain size and the porosity decrease when the Al doping increases. The optical study shows that band tails are present in the absorption spectrum of the films deposited onto bare glass substrate, which is typical of disordered materials. Even after annealing 4 h at 400 °C, the longitudinal resistivity of the films is quite high. This result is attributed to the grain boundary effect and the porosity of the films. Effectively, the presence of an important reflection in the IR region in samples annealed testifies of a high free-carriers density in the ZnO crystallites. Finally it is shown that when deposited in the same electrochemical conditions, the transmission of a polymer film onto the rough sprayed ZnO is smaller than that onto smooth sputtered ZnO.     

Cathodoluminescence degradation of PLD thin films

The cathodoluminescence (CL) intensities of Y₂SiO₅:Ce³⁺, Gd₂O₂S:Tb³⁺ and SrAl₂O₄:Eu²⁺,Dy³⁺ phosphor thin films that were grown by pulsed laser deposition (PLD) were investigated for possible application in low voltage field emission displays (FEDs) and other infrastructure applications. Several process parameters (background gas, laser fluence, base pressure, substrate temperature, etc.) were changed during the deposition of the thin films. Atomic force microscopy (AFM) was used to determine the surface roughness and particle size of the different films. The layers consist of agglomerated nanoparticle structures. Samples with good light emission were selected for the electron degradation studies. Auger electron spectroscopy (AES) and CL spectroscopy were used to monitor changes in the surface chemical composition and luminous efficiency of the thin films. AES and CL spectroscopy were done with 2 keV energy electrons. Measurements were done at 1×10⁻⁶ Torr oxygen pressure. The formation of different oxide layers during electron bombardment was confirmed with X-ray photoelectron spectroscopy (XPS). New non-luminescent layers that formed during electron bombardment were responsible for the degradation in light intensity. The adventitious C was removed from the surface in all three cases as volatile gas species, which is consistent with the electron stimulated surface chemical reaction (ESSCR) model. For Y₂SiO₅:Ce³⁺ a luminescent SiO₂ layer formed during the electron bombardment. Gd₂O₃ and SrO thin films formed on the surfaces of Gd₂O₂S:Tb³⁺ and SrAl₂O₄:Eu²⁺,Dy³⁺, respectively, due to ESSCRs.     

Bismuth ferrite composite thin films

0.60Bi_0.90La_0.10FeO₃–0.40Pb(Zr_0.52Ti_0.48)O₃ composite thin films were deposited on Pt/TiO₂/SiO₂/Si(100) substrates by radio-frequency sputtering and their ferroelectric and fatigue properties were mainly investigated. The composite thin films have a low dielectric loss, a high dielectric constant, and enhanced ferroelectric properties of 2P _r～122.6 μC/cm² and 2E _c～479.3 kV/cm, together with a fatigue-free behavior at 200 kHz. Their fatigue behavior is strongly dependent on measurement frequencies, and the concentration of oxygen vacancies plays an important role in their fatigue behavior.     

Bandgap engineering of rare earth element doped nanostructured cadmium oxide thin films

Rare earth element (gadolinium) doped cadmium oxide (CdO:Gd) thin films were deposited using the pulsed laser deposition technique. X-ray diffraction analysis reveals that growth temperature has large impact on the preferred orientation of the films. The films grown at low temperature show (1 1 1) preferred orientation, while films grown at high temperature have (2 0 0) orientation. The effect of substrate temperature on optical and electrical properties shows widening in optical bandgap and improvement in electron mobility with increase in growth temperature. These wide bandgap transparent conducting films could be used in optoelectronic applications.     

Morphological and optical properties of silicon thin films by PLD

Silicon thin films have been prepared on sapphire substrates by pulsed laser deposition (PLD) technique. The films were deposited in vacuum from a silicon target at a base pressure of 10⁻⁶ mbar in the temperature range from 400 to 800 °C. A Q-switched Nd:YAG laser (1064 nm, 5 ns duration, 10 Hz) at a constant energy density of 2 J × cm⁻² has been used. The influence of the substrate temperature on the structural, morphological and optical properties of the Si thin films was investigated.Spectral ellipsometry and atomic force microscopy (AFM) were used to study the thickness and the surface roughness of the deposited films. Surface roughness values measured by AFM and ellipsometry show the same tendency of increasing roughness with increased deposition temperature.     

In-plane magnetization with high coercivity in terbium iron garnet thin films deposited on Pt/Si substrate by PLD

We report on the growth of terbium iron garnet (TbIG, Tb₃Fe₅O₁₂) thin films having anomalously large coercivity and in-plane easy axis of magnetization. The TbIG thin films were prepared at room temperature (RT) on Pt/Si(1 0 0) substrates by pulsed laser deposition technique. The films deposited at RT were X-ray amorphous and do not show any magnetic order. Annealing of the RT deposited film at 900 °C resulted into fully textured (532) TbIG film. Atomic force microscopy and cross-sectional scanning electron microscopy studies of the TbIG films showed good surface quality with an average surface roughness of 5.0 nm and thickness of about 300 nm, respectively. The M-H loops measured at 20 K for TbIG films, exhibit about an order of magnitude enhancement in the coercivity value (H_c) than the single crystal. In-plane and out-of-plane M-H loops revealed that the easy axis of the magnetization lies within the film’s plane. In-plane magnetization combining with large H_c value of the TbIG thin film may be of scientific interest for the possible applications.     

Laser deposited YBaCuO thin films

YBa₂Cu₃O_7-x thin films were deposited by laser ablation using KrF excimer laser. In deposition on polycrystalline ZrO₂/(1–102) sapphire substrates influence of deposition conditions on film properties were studied. Zero resistance temperatureT _z of 83 K of epitaxially grown YBaCuO films on poly-ZrO₂/sapphire substrates was reached. Epitaxially grown yttria stabilized zirconia (YSZ) buffer layers were deposited by laser ablation on (1–102) sapphire substrates. On YSZ/sapphire, SrTiO₃ and NdGaO₃ substrates, temperatures T_z between 89–90 K were measured. Results of X-ray diffraction and SEM are also presented.We would like to express our thanks to L. Cibulka, L. and L. Rouek, and J. Stránský for their efficient help during the solution of technological problems connected with the construction of experimental apparatus.     

Structural analysis of nickel doped cobalt ferrite nanoparticles prepared by coprecipitation route

Magnetic nanoparticles of nickel substituted cobalt ferrite (Ni_xCo_1−xFe₂O₄:0≤x≤1) have been synthesized by co-precipitation route. Particles size as estimated by the full width half maximum (FWHM) of the strongest X-ray diffraction (XRD) peak and transmission electron microscopy (TEM) techniques was found in the range 18–28±4 nm. Energy dispersive X-ray (EDX) analysis confirms the presence of Co, Ni, Fe and oxygen as well as the desired phases in the prepared nanoparticles. The selective area electron diffraction (SAED) analysis confirms the crystalline nature of the prepared nanoparticles. Data collected from the magnetization hysteresis loops of the samples show that the prepared nanoparticles are highly magnetic at room temperature. Both coercivity and saturation magnetization of the samples were found to decrease linearly with increasing Ni-concentration in cobalt ferrite. Superparamagnetic blocking temperature as determined from the zero field cooled (ZFC) magnetization curve shows a decreasing trend with increasing Ni-concentration in cobalt ferrite nanoparticles.     

Luminescent materials based on thin metal oxide films doped with rare earth ions

Luminescent films of TiO₂: Sm were prepared by the sol-gel method using the spray pyrolysis technique. Various techniques (including IR absorption, Raman, AFM, XPS, photoluminescence) were used to characterize the samples. After a thermal treatment up to 750°C, intense Sm³⁺ luminescence with a well-resolved fine structure was observed under optical excitation within the fundamental absorption band of the TiO₂ host. After further thermal treatments up to 950°C, the luminescence was quenched, although no anataseto-rutile phase transformation was observed. This behavior is attributed to nanocrystallinity and segregation of Sm ions in the surface layer. The text was submitted by the authors in English.     

Electrical and structural studies of lithium doped cobalt ferrite

Lithium doped cobalt ferrites (Li_0.2CoFe_1.8O₄) were prepared by a sol–gel combustion method by using Lithium nitrate, cobalt nitrate, and ferric nitrate as source materials. Here, Citric acid and polyvinyl alcohol used as a burning agent and agglomeration reducing agent respectively. The pH value of precursor was maintained between 7 and 8 while preparation of the sample. The average particle size of the ferrite obtained at 300°C about ～15–20 nm. Further, single phase spinel structure has been confirmed by X-ray diffraction (XRD) and Cubic morphology was confirmed by High resolution scanning electron microscopy (HR-SEM). The composition of elements has been confirmed by Infrared spectroscopy (FT-IR). Moreover, the electrical studies of the prepared sample have been analyzed by four point probe method. The observed results inferred that conductivity of the ferrite sample has been reduced by addition of lithium.     

Effect of oxygen partial pressure on PLD cobalt oxide films

Thin CoO oxide layers with superior properties in terms of crystallographic ordering, surface roughness and constant and controlled chemical compositions have been prepared by pulsed laser deposition in reactive O₂ atmosphere at 400 °C. Such systems are particularly suitable both for applications and for basic studies, any time high quality and controlled surfaces are required, for example in multilayered systems whose behaviour critically depends on interface properties, such as magnetically exchange-coupled systems. A structural and microstructural study of such films is presented, together with the compositional analysis for different process conditions. The best control on film stoichiometry was obtained by protecting the surface with a thin Pt cap-layer, before air exposure.     

Nanostructured silver thin films deposited by pulsed laser ablation

Nanostructured thin films were deposited by excimer laser ablation of silver targets in controlled atmospheres of He and Ar. The film structural properties were investigated by means of scanning electron microscope and transmission electron microscope imaging. The film growth mechanism was identified as the result of coalescence of nanometric clusters formed during plume flight. Cluster formation involves plume confinement as a consequence of the increased collisional rate among plasma species. Fast photography imaging of the laser-generated silver plasma allowed to identify plasma confinement, shock wave formation and plasma stopping.     

Electrochemically deposited bismuth telluride thin films

Thin films of bismuth telluride grown by electrochemical deposition technique on conducting glass and Mo sheet substrates, were characterized for their structural, morphological, optical and compositional analysis. These studies revealed polycrystalline anisotropic and layered structure of these films with different compositional stoichiometry. In the present work electrochemical deposition of bismuth telluride thin films is studied as a dopant material in II–VI group absorber materials for photovoltaic application since it has a narrow optical energy band gap of 0.13 eV. In this deposition process different film growth parameters were optimized to get good quality of compositionally uniform bismuth telluride thin film. XRD analysis revealed a hexagonal symmetry with large c-axis lattice constants (Bi₂Te₃, Bi_2+XTe_3−X).     

Crystallization of Ba-Me hexagonal ferrite thin films

Thin films of Ba-Me ferrites are synthesized by reactive rf diode sputtering of a BaO · nFe₂O₃ ceramic target. Quartz plates subjected to preliminary annealing are used as substrates. The influence of the barium ion content on the crystalline and magnetic properties and the microstructure of the prepared films is investigated, and the interrelation between the quantity dH _c /dT and the microstructure of the film is considered. The prepared films satisfy the requirements for materials used as information carriers with a superhigh recording density.     

Structural and optical properties of YSZ thin films grown by PLD technique

We report on the structural and optical properties of yttria stabilized zirconia (YSZ) thin films grown by pulsed laser deposition (PLD) technique and in situ crystallized at different substrate temperatures (T_s = 400 °C, 500 °C and 600 °C). Yttria-stabilized zirconia target of ∼1 in. diameter (∼95% density) was fabricated by solid state reaction method for thin film deposition by PLD. The YSZ thin films were grown on an optically polished quartz substrates and the deposition time was 30 min for all the films. XRD analysis shows cubic crystalline phase of YSZ films with preferred orientation along 〈1 1 1〉. The surface roughness was determined by AFM for the films deposited at different substrate temperatures. The nano-sized surface roughness is found to increase with the increase of deposition temperatures. For the optical analysis, a UV-vis-NIR spectrophotometer was used and the optical band gap of ∼5.7 eV was calculated from transmittance curves.     

Preparation and characterization of nano and microcrystalline ZnO thin films by PLD

Nano and microcrystalline ZnO thin films were prepared on glass substrates using pulsed laser deposition technique under a vacuum of 3 × 10⁻⁷ Torr at different laser power density. Composition analyses show that the films deposited at low laser power density have more structural defects than the film deposited at high laser power density. It confirms that the content of Zn in free-state decreased greatly at high laser power density. Atomic force microscopy analysis shows that the surface roughness of the deposited films increases with an increase in laser power density. X-ray diffraction analyses show that all the films are oriented along (0 0 2) direction independently on the laser power density applied. The structural quality increases with an increase in laser power density. It is due to the fact that the increase of laser power density leads to the enhancement of peak intensity. The increase of laser power density reduces the film transmission in the visible range of the spectra. The optical band gap value is found to be in the range from 3.42 to 3.39 eV. It shows that the optical band gap value decreases with an increase in laser power density. FTIR analysis shows that the hydrated oxide content in the deposited films decreases with an increase in laser power density.     

Modeling and analysis of birefringence in magneto-optical thin film made by SiO2/ZrO2 doped with ferrite of cobalt

We report the device characteristics of the metal–dielectric high-reflectivity (HR) coated 1.55 μm laterally coupled distributed feedback (DFB) laser with metal surface gratings by using holographic lithography. The HR coating films are composed of Au/Ti/SiO₂. It provides a variety of advantages compared to the uncoated DFB laser on the same processed wafer while there is no degradation on current–voltage characteristics. For 3 μm wide and 300 μm long HR coated DFB laser, it exhibits a maximum output power of ∼17 mW and a threshold current of 14.2 mA at 20°C under continuous-wave mode. It is clear that the threshold current and slope efficiency are improved by 36% and 96%, respectively, due to the reduction of mirror loss. The metal–dielectric HR coating on one facet of DFB laser is found to have significantly increased characteristic temperature (i.e., T ₀∼88 K). Furthermore, the stable single-mode operation with an increased single-mode suppression ratio was achieved.