Pulsed laser deposition of oriented barium ferrite (BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript>) thin films

Barium ferrite (BaFe₁₂O₁₉) thin films have been deposited by pulsed laser deposition at 900 °C in 250 mTorr oxygen on Si substrates with Pt(111) underlayers. The barium ferrite films contained platelet grains and a small amount of acicular grains, with sizes of 300 nm and 80×300 nm, respectively, and had a surface roughness of 11 nm. Vibrating-sample magnetometer measurements indicated that the BaFe₁₂O₁₉ films have some perpendicular orientation, with a perpendicular squareness of 0.64 and an in-plane squareness of 0.28. The saturation magnetization is about 190 emu/cc. The perpendicular and in-plane coercivities are 2.1 kOe and 1.6 kOe, respectively. PACS 75.50.Ss; 75.60.Ej; 75.70.Ak; 68.55.Ik     

Reactive pulsed laser deposition and laser induced crystallization of SnO2 transparent conducting thin films

Transparent conducting SnO₂ thin films with a thickness between 1000–2000 Å were deposited on glass, quartz and silicon substrates using standard pulsed laser deposition techniques with two different targets (Sri and SnO₂) and with three different laser wavelengths (1.06, 0.532 and 0.266 ) from a Q-switched Nd: YAG laser. Tin dioxide films with optical transmission over most of the visible spectrum exceeding 80% were obtained using a Sn target and a background oxygen pressure of 20 Pa. The electrical resistivity () depended strongly on the substrate temperature during deposition, with the lowest values of of about 10^–2 -cm obtained when the substrate was maintained at 400°C during deposition. Using SnO₂ targets, predominantly amorphous phase SnO₂ films were deposited on Si substrates and then transformed into polycrystalline Sn₃O₄ by laser induced crystallization ( = 1.06 m). Whereas these later films were essentially non-conducting as deposited ( > 400 -cm), the electrical resistivity was permanently reduced after laser induced crystallization by a factor greater than 1000 to a value of approximately 4 × 10^–1 -cm.     

Oxidation of Ni3Al–Ni3Nb alloys

Conclusions The Ni₃Al–Ni₃Nb alloys are oxidized as a result of the diffusion of oxygen ions toward the interface between the alloy and the oxidation product. This diffusion produces a relatively thick inner layer of complex composition; in addition, diffusion of nickel ions toward the interface between the oxidation product and the gas results in the formation of a thin outer layer of NiO. At any temperature, NiO in the inner oxide is reduced to Ni by niobium atoms. During the initial stages of the oxidation, the reduction occurs at the oxide-alloy inter face; during the later stages, it occurs at the interface between the oxide and the suboxide layer. Protective double oxides of NiO · Nb₂O₅ (t = 700–725 °) and NiO · Al₂O₃ (t = 800–850 °) form in the oxidation product. An -Nb₂O₅ conversion occurs at 825–900 ° and considerably reduces the oxidizability of the alloys. The -Nb₂O₅ lattice probably contains fewer oxygen vacancies than the -Nb₂O₅ lattice and thus has better protective properties.Translated from Izvestiya VUZ. Fizika, No. 12, pp. 75–83, December, 1969.     

A Mössbauer effect study of barium ferrite ball-milled in air

The effects of dry-milling BaFe₁₂O₁₉ in air for periods of 190, 360, 590, 690 and 1000 h have been investigated by X-ray diffraction and Mössbauer effect measurements. The sizes of the BaFe₁₂O₁₉ particles decrease on milling, as expected, although a partial decomposition of BaFe₁₂O₁₉ to -Fe₂O₃ is found to take place on extended milling (1000 h). The room temperature Mössbauer spectra are consistent with superparamagnetic relaxation associated with the fine BaFe₁₂O₁₉ and -Fe₂O₃ particles. The X-ray diffraction patterns of all the milled samples exhibit features indicative of a disordered structural state, consistent with the nanoscale particles and a nanostructured state.     

Crystalline growth of cubic (Eu, Nd):Y2O3 thin films on α -Al2O3 by pulsed laser deposition

In this paper we report on the growth of crystalline, europium- and neodymium-doped cubic yttria ((Eu,Nd):Y₂O₃) thin films on hexagonal corundum (-Al₂O₃ ) substrates using the pulsed laser deposition (PLD) technique. A KrF excimer laser was used to ablate material from ceramic (Eu, Nd):Y₂O₃ targets. The yttria films were deposited on the -Al₂O₃ (0001) substrates. X-ray diffractometry (XRD) revealed that the films grew in the Y₂O₃[111]-direction. The surface topography of the films was investigated using atomic force microscopy (AFM). PACS 81.15.Fg; 42.70.hj; 68.55.Jk     

Y1Ba2Cu3O7-δ thin films from KrF laser ablation with substrate heating and in situ patterning by CO2 laser radiation

Y₁Ba₂Cu₃O_7– thin films were deposited by KrF laser ablation while replacing conventional contact heating by cw CO₂ laser irradiation of the substrate front surface. The HTSC films obtained on (100)ZrO₂ showed T _c(R=0)=90 K, T(90–10%)=0.5 K, j _c=2.5 × 10⁶ A/cm², a sharp transition in the ac susceptibility X(T), and pure c-axis orientation. Micrographs of thin films (< 0.5 m) showed a smooth morphology while thick films (>1 m) contained many crystallites sticking in the bulk material. Furthermore, in situ patterning was achieved during deposition by local laser heating of a selected substrate surface area. The resulting planar films contained amorphous, semiconducting parts only 1 mm or less apart from crystalline material showing the above HTSC quality.Presented at LASERION '91, June 12–14, 1991, München (Germany)     

Textured thin films grown at room temperature by laser ablation

Thin films of SrFe₁₂O₁₉, BaFe₁₂O₁₉, Pb_0.76La_{0.16 0.08}Zr_0.53Ti_0.47O₃and Sr_0.3Ba_0.7Nb₂O₆ were grown on monocrystalline silicon substrates by pulsed laser deposition using a 20-ns Nd:YAG laser (1064 nm). The deposited thin films were analyzed by X-ray diffraction in the grazing incidence configuration. The analysis showed evidence of textured growth even though the films were grown at room temperature. Emission spectroscopy was used to establish the time of flight of the species within the plasma plume. Velocities of the order of 10⁶ cm/s were obtained. The high kinetic energy of the species is thought to be responsible for the film texture, as it is released in the substrate–film system, favoring a preferential growth. For all the ablated ceramics, singly ionized species were shown to expand at higher velocities than neutrals. For ions, no consistency in the mass–speed relation was obtained, suggesting both the presence of electric fields during the plasma formation and an evaporation of the target that depends on the vapor pressure of the elements. In this way species that are firstly evaporated will be attracted strongly by fast electrons, allowing heavy ions to acquire higher velocities than lighter ones. PACS 81.15.Fg; 52.38.Mf; 68.55.Jk; 52.38.Kd; 52.70.Kz     

Growth of polycrystalline LaNi<Subscript>1-x</Subscript>Co<Subscript>x</Subscript>O<Subscript>3</Subscript> (<Emphasis Type="BoldItalic">x</Emphasis> =0.3,0.5) thin films on Si(100) by pulsed laser deposition

Polycrystalline LaNi_1-xCo_xO₃ (x=0.5,0.3) thin films have been deposited on polished Si(100) substrates by pulsed laser deposition. The films are grown at 650 °C in ambient oxygen pressure of 0.4 mbar with an incident laser fluence of 1.5 J/cm² delivered by a KrF excimer laser. The lattice parameters of the as-grown films are slightly larger (0.05–0.4%) than those of the powders used to prepare the targets. The films exhibit weak texturing along the (012) direction. The low-temperature magnetic properties of the films, i.e. the coercive force, the remanence and the saturation magnetization, are enhanced compared to the powders. Furthermore, the x=0.3 film exhibits a low, almost temperature-independent resistivity above 200 K [(300 K)30 cm] and thus we propose it as a potential candidate material for electrode applications, e.g. in ferroelectric devices. PACS 68.55.-a; 73.61.-r; 81.15.Fg     

Polarization Characteristics of He–Ne Laser Radiation Reflected by Glass‐Reinforced Plastic

We have measured the Stokes parameters of the He–Ne laser radiation ( = 0.63 m) reflected at angles of incidence from 5 to 70° by glassreinforced plastic based on a siliconorganic polymer binder before and after its heating to 1200 K by CO₂ laser radiation. The probe radiation from the He–Ne laser is linearly polarized parallel or perpendicular to the incidence plane. It is shown that the flux reflected in the mirror direction by samples illuminated at a Brewster angle ( 56°) by He–Ne laser radiation linearly polarized in the plane of incidence contains a component with elliptical polarization.     

Microstructure of aluminium-copper thin films and its relation to electromigration

The microstructure of polycrystalline aluminium — 7·6 wt % copper thin films evaporated from the starting Al-Cu alloy was studied using electron microscopy and microanalysis. The structural properties of films were confronted with electromigration lifetime measurements of Al-Cu thin film conductors. In the films Al₂Cu precipitates were observed. Thermodynamically stable -Al₂Cu precipitates were found at grain boundaries, triple points and on the film surface. Within the grains -Al₂Cu precipitates were detected. When the temperature of deposition and/or the time of annealing of the films at 480 °C in nitrogen increased, the growth of grains and of the total volume of the precipitate phase was observed. Under these conditions precipitates tended to grow preferentially at the film surface and they ceased to influence the grain size distribution. The distribution approached then the log-normal distribution function. With regard to the structural investigations it is anticipated that the best electromigration resistance among the studied samples should possess conductors deposited at 250 °C as well as conductors deposited at 150 °C and 250 °C and annealed 10 min at 480 °C. The lifetimes of conductors having this type of microstructure and tested at the current density of 3×10⁶ A/cm² had values of 210÷3500 hrs, corresponding to the testing temperature of 150 °C. Higher lifetimes were observed with wider (20 m) and shortest (120 m) conductors encapsulated in packages filled with nitrogen. The activation energy for the failure process was 0·65 eV in this case.     

Pulsed laser deposition of bioceramic thin films from human tooth

The possibility of pulsed laser deposition of thin films from human tooth targets was studied, since bioceramic thin film coatings on dental and orthopaedic implants may have their surface characteristics for biointegration improved. Pellets were pressed from tooth powder at different pressures and ablated with pulses of ArF (=193 nm) and KrF (=248 nm) excimer lasers with fluences up to 4.5 and 12 J/cm², respectively. Layers were deposited onto heated (250 °C) titanium, glass, and KBr substrates. The increase of the pellet pressing pressure from 150 to 450 MPa enhanced the roughness of the deposited films. IR spectroscopic measurements showed that the chemical composition of the films were close to that of original tooth material under appropriate fluence. The adherence of the layers to the substrates could be significantly improved by post annealing at 550 °C. PACS 81.15.Fg; 68.55.Jk; 87.68.+z     

Structure and physical properties of ceramics in a section of the system Mg-Cu-Fe-O

The concentration dependences of the crystal lattice parameter and the Curie temperature of the magnetic ceramic, obtained in air at a calcination temperature of 1100°C from charges with the composition (1–x)MgFe₂O₄+x(0.5 CuO × 1.25 Fe₂O₃), where 0x1, were studied. The dependences of the magnetic parameters of the hysteresis loop as well as the resistivity on the composition of the charge were investigated. The single-phase ceramic, having the structure of spinel, is formed for x < 0.5, and in samples with x > 0.5 a tetragonal phase and -Fe₂O₃ are present. The maximum squareness ratio of the hysteresis loop (SHL) is observed in the region x=0.1–0.4. The region of high values of the squareness ratio is also the region of solid solutions containing defects, when -Fe₂O₃ quasiparticles, having the structure of imperfect spinel, are present in the solution.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 84–86, December, 1990.     

Surface Sol–gel Synthesis of Ultrathin Titanium and Tantalum Oxide Films

TiO₂, Ta₂O₅, and mixed TiO₂/Ta₂O₅ ultrathin films were grown layer-by-layer using a surface sol–gel deposition technique. The technique allows one to prepare smooth films of mixed composition with ångstrom-level control of thickness. The thickness increases per adsorption/hydrolysis cycle were 4.5, 2.1, and 2.5, respectively, for TiO₂, Ta₂O₅, and mixed TiO₂/Ta₂O₅ (1.6sol;1) films. By combining X-ray diffraction and ellipsometric analysis, it was determined that the as-deposited TiO₂ films are less dense than bulk TiO₂, and do not adhere persistently to Si/SiO₂ or Au/2-mercaptoethanol substrates. These green films were annealed at 400°C to produce denser and highly adherent films. Patterning the surface by microcontact printing of siloxane polymer thin films allows one to prepare patterned sol–gel oxide thin films.     

Studies of the promising material CoSi2 on GaAs substrates

The thermal stability of CoSi₂ thin films on GaAs substrates has been studied using a variety of techniques. The CoSi₂ thin films were formed by depositing Co(500 Å) and Si(1800 Å) layers on GaAs substrates by electron-beam evaporation followed by annealing processes, where the Si inter-layer was used as a diffusion/reaction barrier at the interface. The resistivity of CoSi₂ thin films formed is about 30 cm. The Schottky barrier height of CoSi₂/n-GaAs is 0.76 eV and the ideality factor is 1.14 after annealing at 750° C for 30 min. The CoSi₂/GaAs interface is determined to be thermally stable and the thin film morphologically uniform on GaAs after 900° C/30 s anneal. The CoSi₂ thin films fulfill the requirements in GaAs self-aligned gate technology.     

Mosaic Structure of (001)YBa2Cu3O7-δ/(10.2)Al2O3 Epitaxial Films and Millimeter Waveband Properties of Microstrip Resonators

The c-axis single-phase YBa₂Cu₃O_7- films ( = 0-0.15) on sapphire substrates prepared by the laser ablation technique and the band-pass stripline resonators for 34 GHz-range have been investigated. Increasing disorientation of mosaic block structure of YBa₂Cu₃O_7- films is related to increasing surface resistance R_s at 135 GHz-range and decreasing unloaded quality factor Q_o of linear stripline resonators. The linear dependence between the YBa₂Cu₃O_7- film mosaicity (M) and half-width B₁ of 00.13 reflecting component is determined. The reflection spreading is due to microstrains resulted mainly from the coherent adjustment of the YBa₂Cu₃O_7- film lattice to GdBa₂Cu₃O_7- sub-layer and sapphire substrate. Increasing number of the block characterized by a weak radial lattice adjustment () is demonstrated by spreading of 00.13 reflection. It is found out that depends on the Bragg angle of reflection due to inhomogenity of YBa₂Cu₃O_7- mosaic structure, which resulted from the gradual mosaicity decreasing with the depth.     

Synthesis of epitaxial γAl<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films by thermal oxidation of AlN/sapphire(0001) thin films

The synthesis of epitaxial Al₂O₃ films by oxidizing AlN/sapphire(0001) films was investigated in a synchrotron X-ray scattering experiment. Porous Al₂O₃ nucleates on the surface of the AlN film when annealed above 700 °C in oxygen ambient. As the annealing temperature increases above 900 °C, the entire AlN film is oxidized into an epitaxial Al₂O₃ film that has a cubic spinel structure. With increasing oxidation temperature, more oxygen atoms are incorporated into the oxide structure, resulting in denser oxide films with a larger lattice constant. The crystal domain size increases from 50 Å to 210 Å, suggesting that the initial nucleation of the Al₂O₃ crystalline domains is followed by gradual grain growth. PACS 61.10.Eq; 81.65.Mq; 68.55.Jk; 68.35.Ct     

Effect of substitution of vanadium on the structure and electrical properties of Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films

The ferroelectric and dielectric properties of Bi_4-xLa_xTi₃O₁₂ (BLT) and Bi_4-xLa_xTi_2.97V_0.03O₁₂ (BLTV) thin films deposited on (111)Pt/Ti/SiO₂/Si substrates using a chemical solution method were investigated. The BLTV thin films showed a larger remanent polarization (9.6 C/cm²) than the BLT thin films (6.5 C/cm²), while the coercive field for both thin films was nearly the same. The capacitance of the films as a function of a small ac driving field was measured, and the data were processed using Rayleighs law. The results show that the Rayleigh constant of the BLT films was smaller than that of the BLTV films, indicating that the defect concentration was lower in the latter case. The superior ferroelectricity of the BLTV films was attributed to a decrease of both the (001) orientation and the defect concentration. PACS 77.80.Bh; 77.55.+f     

Rapid thermal processing of lithium tantalite thin films prepared by a diol-based sol–gel process

Lithium tantalite (LiTaO₃) thin films have been deposited on Pt(111)/SiO₂/Si(100) substrates by means of sol–gel spin-coating technology. Using a diol-based precursor solution and rapid thermal processing (RTP), highly c-axis oriented LiTaO₃ thin films are obtained and the degree of orientation is increased with an increase of the heating rate. By changing the heating rate (600–3000 °C/min) and heating temperature (500–800 °C), the effects of various processing parameters on the growth of films are investigated. With the increase of heating rate, the grain size of LiTaO₃ thin films decreases markedly, and the relative dielectric constant (_r) increases from 28 up to 45.6. It was found that the dielectric loss factor (cos) decreased, and the ferroelectric properties were improved by the increase of heating rate. The figures of merit (F_v and F_m) indicate that the LiTaO₃ thin film with a heating rate of 1800 °C/min is suitable for application as a high-performance pyroelectric thin-film detector. PACS 81.20.Fw; 81.40.-z; 61.10.Eq; 77.84.-s     

Preparation of Nanoparticles of Barium Ferrite from Precipitation in Microemulsions

Magnetic nanoparticles of barium ferrite (BaFe₁₂O₁₉) have been synthesized using a microemulsion mediated process. The aqueous cores of water-in-oil microemulsions were used as constrained microreactors for the precipitation of precursor carbonate and hydroxide particles. These precursors were then calcined at 925°C for 12h, during which time they were transformed to the hexagonal ferrite. The pH of reaction was varied between 5 and 12, and it was found that the fraction of non-magnetic hematite (-Fe₂O₃) in the particles varied with the pH of reaction, thus affecting the magnetic properties of the particles. The same precursor particles were also prepared by bulk co-precipitation reaction for comparison. It was found that the microemulsion derived nanoparticles of barium ferrite had both higher intrinsic coercivity (H_c) and saturation magnetization (_s) than the particles derived from bulk co-precipitation. Particles were analyzed by electron microscopy, X-ray diffraction, differential thermal analysis (DTA), thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM). The best barium ferrite particles produced by the microemulsion synthesis method yielded an intrinsic coercivity of 4310Oe and a saturation magnetization of 60.48emu/g.     

Highly (100)-oriented Eu-doped PZT thin films on sol-gel derived (100)-textured LaNiO<Subscript>3</Subscript>/Si substrates

(100)-oriented LaNiO₃ (LNO) thin films were grown on Si substrates by a sol-gel method followed by a rapid thermal process at temperatures ranging from 650 °C to 800 °C. The films produced at 700 °C had a resistivity of 1.79 mcm and could be used as bottom electrodes in the fabrication of ferroelectric capacitors on Si. Subsequently, a sol-gel derived Eu-doped Pb(Zr_0.52,Ti_0.48)O₃ (PEZT) thin film with a thickness of 130 nm prepared on the LNO electrode was found to have a (100)-oriented texture. Possible reasons for the high degree of (100) orientation in PEZT thin films are given. Good ferroelectric performance was obtained for Au/PEZT/LNO capacitors. The remnant polarization (2P_r) was found to be 22 C/cm² at a coercive electric field (E_c) of 134 kV/cm. After 10¹¹ polarization reversals, P_r decreased by only 15%. PACS 68.37.Yz; 68.37.Hk