Structure and thermal stability of MOCVD ZrO2 films on Si (1 0 0)

The structure and thermal stability of ZrO₂ films grown on Si (1 0 0) substrates by metalorganic chemical vapor deposition have been studied by high-resolution transmission electron microscopy, selected area electron diffraction and X-ray energy dispersive spectroscopy. As-deposited films consist of tetragonal ZrO₂ nanocrystallites and an amorphous Zr silicate interfacial layer. After annealing at 850°C, some monoclinic phase is formed, and the grain size is increased. Annealing a 6 nm thick film at 850°C in O₂ revealed that the growth of the interfacial layer is at the expense of the ZrO₂ layer. In a 3.0 nm thick Zr silicate interfacial layer, there is a 0.9 nm Zr-free SiO₂ region right above the Si substrate. These observations suggest that oxygen reacted with the Si substrate to grow SiO₂, and SiO₂ reacted with ZrO₂ to form a Zr silicate interfacial layer during the deposition and annealing. Oxygen diffusion through the tetragonal ZrO₂ phase was found to be relatively easier than through the monoclinic phase.     

Epitaxial growth of the CoFe2O4 film on SrTiO3 and its characterization

Cobalt ferrite (CoFe₂O₄) thin film is epitaxially grown on (0 0 1) SrTiO₃ (STO) by laser molecular beam epitaxy (LMBE). The growth modes of CoFe₂O₄ (CFO) film are found to be sensitive to laser repetition, the transitions from layer-by-layer mode to Stranski–Krastanov (SK) mode and then to island mode occur at the laser repetition of 3 and 5 Hz at 700 °C, respectively. The X-ray diffraction (XRD) results show that the CFO film on (0 0 1) SrTiO₃ is compressively strained by the underlying substrate and exhibits high crystallinity with a full-width at half-maximum of 0.86°. Microstructural studies indicate that the as-deposited CFO film is c-oriented island structure with rough surface morphology and the magnetic measurements reveal that the compressive strained CoFe₂O₄ film exhibits an enhanced out-of-plane magnetization (190 emu/cm³) with a large coercivity (3.8 kOe).     

Formation of LiNbO3 films by hydrolysis of metal alkoxides

Homogeneous, crack-free, thin films of crystalline LiNbO₃ were synthesized above 250°C on Si(100) substrates by the dip-coating method using a double alkoxide solution. The coating solution, which was prepared by the controlled partial hydrolysis of the double alkoxide, gave stoichiometric LiNbO₃ crystalline films at temperatures as low as 250°C. The concentration of the alkoxide solution influenced both of thickness and quality of films. Crystallinity of thin film top-coated directly on the substrate affected the crystallization state of films coated on the film remarkably. Films crystallized on -Al₂O₃(0001) showed preferred orientation along the c-axis, while the preferred orientation could not be observed on Si(100) substrates.     

CrO2 (1 0 0) and TiO2 (1 0 0) film heteroepitaxy on a BaF2 (1 1 1)/Si (1 0 0) substrate

Multi-domained heteroepitaxial rutile-phase TiO₂ (1 0 0)-oriented films were grown on Si (1 0 0) substrates by using a 30-nm-thick BaF₂ (1 1 1) buffer layer at the TiO₂–Si interface. The 50 nm TiO₂ films were grown by electron cyclotron resonance oxygen plasma-assisted electron beam evaporation of a titanium source, and the growth temperature was varied from 300 to 600 °C. At an optimal temperature of 500 °C, X-ray diffraction measurements show that rutile phase TiO₂ films are produced. Pole figure analysis indicates that the TiO₂ layer follows the symmetry of the BaF₂ surface mesh, and consists of six (1 0 0)-oriented domains separated by 30° in-plane rotations about the TiO₂ [1 0 0] axis. The in-plane alignment between the TiO₂ and BaF₂ films is oriented as [0 0 1] TiO₂ || BaF₂ or [0 0 1] TiO₂ || BaF₂ . Rocking curve and STM analyses suggest that the TiO₂ films are more finely grained than the BaF₂ film. STM imaging also reveals that the TiO₂ surface has morphological features consistent with the BaF₂ surface mesh symmetry. One of the optimally grown TiO₂ (1 0 0) films was used to template a CrO₂ (1 0 0) film which was grown via chemical vapor deposition. Point contact Andreev reflection measurements indicate that the CrO₂ film was approximately 70% spin polarized.     

Effect of NH3 on the growth characterization of TiN films at low temperature

Titanium nitride (TiN) films were obtained by the atmospheric pressure chemical vapor deposition method of the TiCl₄–N₂–H₂ system with various flow rates of NH₃ at 600°C. The growth characteristics, morphology and microstructure of the TiN films deposited were analyzed by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Without NH₃ addition, no TiN was deposited at 600°C as shown in the X-ray diffraction curve. However, by adding NH₃ into the TiCl₄–N₂–H₂ system, the crystalline TiN was obtained. The growth rate of TiN films increased with the increase of the NH₃ flow rate. The lattice constant of TiN films decreased with the increase of the NH₃ flow rate. At a low NH₃ flow rate, the TiN (2 2 0) with the highest texture coefficient was found. At a high NH₃ flow rate, the texture coefficient of TiN (2 0 0) increased with the increase of the NH₃ flow rate. In morphology observation, thicker plate-like TiN was obtained when the NH₃ flow rate was increased. When the flow rate of NH₃ was 15 sccm, Moiré fringes were observed in the TiN film as determined by TEM analysis. The intrinsic strain was found in the TiN film as deposited with 60 sccm NH₃.     

Effect of CaO on the surface morphology and strength of water soaked Na2O–B2O3–Al2O3–SiO2 vitrified bond

The surface morphology of Na₂O–B₂O₃–Al₂O₃–SiO₂ vitrified bond with and without calcium oxide was studied by soaking vitrified bonded microcrystalline alumina composites in water. The content of water introduced to the vitrified bond was determined by thermal gravity analysis, and the effects of water and calcium on the phase separation and nucleation of the vitrified bond were investigated using scanning electron microscope and energy-dispersive X-ray spectrometer. Soaked in water for 72 h, the Na₂O–B₂O₃–Al₂O₃–SiO₂ vitrified bond presented a porous surface, and its bending strength declined with increasing sintering temperature. However, the Na₂O–CaO–B₂O₃–Al₂O₃–SiO₂ vitrified bond was more durable against aqueous coolant even needle-shape crystals were found clustered on the surface of the vitrified bond. The crystals were enriched with aluminosilicate tested by energy-dispersive X-ray spectrums. The appearance of crystals lessened the dissolution of the vitrified bond and made the bending strength increase in the sintering temperature region between 870 °C and 930 °C.     

Effects of SiO2 overlayer at initial growth stage of epitaxial Y2O3 film growth

We investigated the dependence of the Y₂O₃ film growth on Si surface at initial growth stage. The reflection high-energy electron diffraction, X-ray scattering, and atomic force microscopy showed that the film crystallinity and morphology strongly depended on whether Si surface contained O or not. In particular, the films grown on oxidized surfaces revealed significant improvement in crystallinity and surface smoothness. A well-ordered atomic structure of Y₂O₃ film was formed on 1.5 nm thick SiO₂ layer with the surface and interfacial roughness markedly enhanced, compared with the film grown on the clean Si surfaces. The epitaxial film on the oxidized Si surface exhibited extremely small mosaic structures at interface, while the film on the clean Si surface displayed an island-like growth with large mosaic structures. The nucleation sites for Y₂O₃ were provided by the reaction between SiO₂ and Y at the initial growth stage. The SiO₂ layer known to hinder crystal growth is found to enhance the nucleation of Y₂O₃, and provides a stable buffer layer against the silicide formation. Thus, the formation of the initial SiO₂ layer is the key to the high-quality epitaxial growth of Y₂O₃ on Si.     

Growth and properties of (Pb0.90La0.10)TiO3 thick films prepared by RF magnetron sputtering with a PbO buffer layer

The (Pb_0.90La_0.10)TiO₃ [PLT] thick films (3.0 μm) with a PbO buffer layer were deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by RF magnetron sputtering method. The PLT thick films comprise five periodicities, the layer thicknesses of (Pb_0.90La_0.10)TiO₃ and PbO in one periodicity are fixed. The PbO buffer layer improves the phase purity and electrical properties of the PLT thick films. The microstructure and electrical properties of the PLT thick films with a PbO buffer layer were studied. The PLT thick films with a PbO buffer layer possess good electrical properties with the remnant polarization (P_r=2.40 μC cm⁻²), coercive field (E_c=18.2 kV cm⁻¹), dielectric constant (ε_r=139) and dielectric loss (tan δ=0.0206) at 1 kHz, and pyroelectric coefficient (9.20×10⁻⁹ C cm⁻² K⁻¹). The result shows the PLT thick film with a PbO buffer layer is a good candidate for pyroelectric detector.     

Effect of the substrate temperature on the crystallization of TiO2 films prepared by DC reactive magnetron sputtering

Titanium oxide (TiO₂) films were deposited on silicon substrates at the temperature in the range 50–600 °C by DC reactive magnetron sputtering. It was found that the anatase and rutile phases co-existed in the TiO₂ films deposited at 450–500 °C, while only the anatase phase existed in those deposited at other temperatures. The mechanism of such a crystallization behavior of TiO₂ films is preliminarily explained.     

Microstructure and ferroelectric properties of BaTiO3 films on LaNiO3 buffer layers by rf sputtering

We have fabricated LaNiO₃ and BaTiO₃ films using the rf sputtering method. The LaNiO₃ were deposited on Si substrates, demonstrating a (1 0 0) highly oriented structure and nanocrystalline characteristic with a grain size of 30 nm. The BaTiO₃ thin films were deposited on the LaNiO₃ buffer layers, and have exhibited a (1 0 0) texture with a thickness of 400 nm. A smooth interface is obtained between the LaNiO₃ bottom electrode and the BaTiO₃ film from cross-section observations by scanning electron microscopy. The bi-layer films show a dense and column microstructure with a grain size of 60 nm. Ferroelectric characterizations have been obtained for the BaTiO₃ films. The remnant polarization and coercive field are 2.1 μC/cm² and 45 kV/cm, respectively. The leak current measurements have shown a good insulating property.     

Electronic traps in mixed Si1−xGexO2 films

Thermally stimulated luminescence (TSL) and infrared (IR) spectroscopy were measured in plasma grown Si_1−xGe_xO₂ (x=0, 0.08, 0.15, 0.25, 0.5) with different thicknesses (12–40 nm). A comparison with the TSL properties of thermally grown SiO₂ and GeO₂ was also performed. A main IR absorption structure was detected, due to the superposition of the peaks related to the asymmetric O stretching modes of (i) Si–O–Si (at ≈1060 cm⁻¹) and (ii) Si–O–Ge (at 1001 cm⁻¹). Another peak at ≈860 cm⁻¹ was observed only for Ge concentrations, x>0.15, corresponding to the asymmetric O stretching mode in Ge–O–Ge bonds. A TSL peak was observed at 70°C, and a smaller structure at around 200°C. The 70°C peak was more intense in all Ge rich layers than in plasma grown SiO₂. Based on the thickness dependence of the signal intensity we propose that at Ge concentrations 0.25x0.5 TSL active defects are localised at interfacial regions (oxide/semiconductor, Ge poor/Ge rich internal interface, oxide external surface/atmosphere). Based on similarities between TSL glow curves in plasma grown Si_1−xGe_xO₂, thermally grown GeO₂ and SiO₂ we propose that oxygen vacancy related defects are trapping states in Si_1−xGe_xO₂ and GeO₂.     

Synthesis, thermal and magnetic properties of new metal iodate: (LiFe1/3)(IO3)2

This paper reports the detail synthesis of a new kind of metal iodate, anhydrous (LiFe_1/3)(IO₃)₂, from aqueous solutions. The synthesized compound shows spinal morphology and is chemical stable up to 400°C. The iodate shows paramagnetic behavior from room temperature down to 4.2 K. At room temperature, the new compound has a hexagonal structure with the lattice parameters a=5.4632(2) Å, c=5.0895(6) Å, Z=1, space group of P6₃.     

Stability and formation of pyrochlore phase in doped Sr0.8Bi2.3Ta2O9 thin films

Ferroelectric thin films of bismuth-containing layered perovskite Sr_0.8Bi_2.3Ta_2−xM_xO₉ (SBTM), where M is V, Ti, W, and Zr, have been prepared on Pt/Ti/SiO₂/Si substrates using the metal-organic decomposition method. The effect of the incorporated B-site cations on pyrochlore phase formation and microstructure evolution of SBTM films was investigated. The pyrochlore phase formation has been identified due to out-diffusion of titanium from underneath platinum layer to participate in the reaction with the films. Furthermore, the formation of pyrochlore phase in the SBTM films has been observed strongly dependent on the characteristics of incorporated M cation. The substitution of both W and V for Ta leads to the formation of pyrochlore phase at lower annealing temperature (750–800 °C). On the other hand, the addition of Zr can retard the formation of pyrochlore phase from 850 to 900 °C. A model based on the binding energy of octahedral structure is used to elucidate the formation and stability of the pyrochlore phase present in the SBT film.     

Growth of NaBi(WO4)2 crystal by modified-Bridgman method

NaBi(WO₄)₂ (NBW) crystals have been grown for the first time by modified-Bridgman method. Influences of some factors on the crystal growth process are discussed. X-ray powder diffraction experiments show that the unit cell parameters of NBW crystal are a=b=0.5284 nm, c=1.1517 nm, and V=0.3215 nm³. The differential thermal analysis shows that the NBW crystal melts at 923°C.     

A study of growth and morphological features of TiOxNy thin films prepared by MOCVD

The growth and morphological features of MOCVD TiO_xN_y films have been characterized to evaluate the effect of various process parameters on film growth. XRD analysis of the films deposited at 600°C on Si(1 1 1) and mica show a TiN(1 1 1) peak at 2θ=36.6°, but only anatase peaks are detected below 550°C. Above 650°C, both anatase and rutile peaks are detected. The presence of ammonia is not effective below 550°C as the deposited film is mostly TiO₂. Also, ammonia does not play any role in homogeneous nucleation in the gas phase, as evident by the deposition of anatase/rutile particles above 650°C. The following changes in the morphological features are observed by varying process parameters. By increasing the ratio of titanium-isopropoxide to ammonia flow, the cluster shape changes from angular to rounded; dilution of the flow results in larger elongated clusters; increase in flow rate at constant precursor to ammonia ratios, changes the cluster shape from rounded to elongated and the cluster size deceases. Deposition at higher temperatures results in finer clusters with a slower growth rate and eventually results in a very thin film with particle deposition at 650°C and above.     

The effect of oxygen pressure on the microstructures of Co-doped rutile TiO2 thin films grown by pulsed laser deposition

Comprehensive microstructures of 7% cobalt-doped rutile TiO₂ thin films grown on c-plane sapphire by pulsed laser deposition were characterized using transmission electron microscopy (TEM). The effects of oxygen pressure during growth on the Co distribution inside the films were investigated, and the detailed growth mechanism of both TiO₂ and TiO₂+Co was discussed. The similar oxygen sublattices and low mismatch between (1 0 0) rutile and c-plane sapphire favors the rutile phase. However, the three-fold symmetry of the substrate surface resulted in three rutile domain orientation variants, and they grow adjacent to each other. Cobalt was found to precipitate out as nanocrystals inside the TiO₂ matrix as the growth pressure of oxygen was decreased. At 0.05 mTorr oxygen pressure, almost all of the Co segregates into crystallographically aligned nanocrystals with a particle size of 4.4±0.15 nm. All the samples have magnetic coercivity at room temperature. The magnetic moment per Co atom increased with decreased oxygen pressure, suggesting that the Co that replaced the Ti²⁺ in the TiO₂ lattice does not have a large magnetic moment.     

Study on the Ce substitution effects of BiFeO3 films on ITO/glass substrates

Ce substituted Bi_1−xCe_xFeO₃ (BCFO) films with x=0–0.15 were deposited on indium tin oxide (ITO)/glass substrates by sol–gel process annealed at 500 °C. Rhombohedral phase was confirmed by XRD study and no impure phases were observed till x=0.15. Substantially enhanced ferroelectricity was observed at room temperature due to the substitution of Ce. In the films with x=0.05 and 0.10, the double remnant polarization are 75.5 and 57.7 μC/cm² at an applied field 860 kV/cm. Moreover, the breakdown field was enhanced in the films with Ce substitution.     

Characteristic crystal growth from amorphous WO3 film by vacuum heating

Selective growth of WO₂, W and WO_3−x crystals from amorphous WO₃ film by vacuum heating at 400–900°C was clarified. The grown WO_3−x crystals were incommensurate structure based on crystallographic share structure. The growth process of WO₂ crystal in the amorphous film was directly observed at high temperature in the electron microscope. The growth front of the WO₂ crystal consumes WO₃ microcrystallites with various orientations. The growth speed of the WO₂ depended on WO₃ microcrystallites orientation. The origin of the wavy growth front of WO₂ was due to an orientation dependence of the WO₃ microcrystallites.     

Growth of epitaxial thin films of scandium nitride on 100-oriented silicon

A series of 100-oriented ScN films was grown under N-rich conditions on 100-oriented Si using different Sc fluxes. The ScN films grew in an epitaxial cube-on-cube orientation, with [0 0 1]_ScN//[0 0 1]_Si and [1 0 0]_ScN//[1 0 0]_Si, despite the high (11%) lattice mismatch between ScN and Si. The film grain size increases and the film ω-FWHM decreases with increasing Sc flux, but the film roughness increases. Films grown under similar conditions on 111-oriented Si resulted in mixed 111 and 100 orientations, indicating that the 100 orientation is favoured both due to texture inheritance from the substrate and due to the growth conditions used.     

Growth, dielectric, ferroelectric and optical properties of Ca0.28Ba0.72Nb2O6 single crystals

Calcium barium niobate Ca_0.28Ba_0.72Nb₂O₆ (CBN-28) crystals were grown by the Czochralski method. The effective segregation coefficients of Ca, Ba, Na elements in CBN-28 crystal growth were measured, and the rocking curve from 0 0 2 reflection of CBN-28 wafer was also measured by the high-resolution X-ray diffractometer D5005, and the full-width at half-maximum value was measured to be 70.6″. The measured dependence of dielectric constants on temperature showed the Curie temperature of the CBN-28 crystals is between 246.8 and 260 °C. Typical polarization–electric field (P–E) hysteresis loops were measured at room temperature. Ferroelectric 180° domains were observed by scanning electron microscopy (SEM) on the etched (0 0 1) surface of the CBN-28 crystals. The transmittance of [0 0 1]-oriented CBN-28 crystals was measured and the result shows that optical properties of CBN-28 crystal are almost the same as those of SBN for wavelengths between 2500 and 7500 nm.