Chuanbin Wang

Ferroelectric BaTi2O5 thin film prepared by laser ablation

Ferroelectric b-axis oriented BaTi2O5 thin film was successfully prepared on MgO (100) substrates by laser ablation. The effects of substrate temperature (Tsub) and oxygen partial pressure (PO2) on the crystal structure, surface morphology, and dielectric property of the film were investigated. BaTi2O5 thin films were obtained at Tsub=923–973K and PO2=vacuumto17.5Pa on MgO (100) substrates. The orientation of the films changed from (710) to (020) depending on Tsub and PO2. The optimum conditions for preparing film with a dense and elongated texture were Tsub=973K and PO2=12.5Pa. The permittivity of the ferroelectric b-axis oriented BaTi2O5 thin film showed a sharp peak (∼2000) at 750K.

Preparation of rutile TiO2 thin films by laser chemical vapor deposition method

TiO2 thin films were prepared on Pt/Ti/SiO2/Si substrate by laser chemical vapor deposition (LCVD) method. The effects of laser power (PL) and total pressure (ptot) on the microstructure of TiO2 thin films were investigated. The deposition temperature (Tdep) was mainly affected by PL, increasing with PL increasing. The single-phase rutile TiO2 thin films with different morphologies were obtained. The morphologies of TiO2 thin films were classified into three typical types, including the powdery, Wulff-shaped and granular microstructures. ptot and Tdep were the two critical factors that could be effectively used for controlling the morphology of the films.

Dielectric properties of Ba4Ti13O30 film prepared by laser chemical vapor deposition

Compounds in the BaO–TiO2 system have attracted great attention due to their excellent dielectric properties, which can be applied to microwave devices [1–6]. Among them, Ba4Ti13O30 ceramics were prepared 60 years ago [7]. However, Rase and Roy reported the improper stoichiometry, BaTi3O7. The correct structure of Ba4Ti13O30 was later solved by Tillmanns and Negas et al. [8, 9]. Since, Ba4Ti13O30 compound has low dielectric constant (er) and high-quality factor (Q), it is often used to improve microwave dielectric property of the other compounds as additive [10, 11]. To the best of our knowledge, there was no literature reported on preparation and dielectric property of single-phase Ba4Ti13O30 ceramics and film. Laser chemical vapor deposition (LCVD) is considered to be a promising process to prepare high-quality films at high deposition rate (Rdep) [12–15]. In this study, Ba4Ti13O30 film was prepared on Pt/Ti/SiO2/Si substrate by LCVD. The effect of frequency and temperature on dielectric properties of Ba4Ti13O30 film was investigated. Experimental

Effect of Mo substitution on ferroelectric properties of Bi3.6Ho0.4Ti3O12 thin films prepared by sol-gel method

The series of (Bi0.9Ho0.1)4−2x/3Ti3−xMoxO12 (BHTM) (x=0, 0.9%, 1.5%, 3.0%, and 6.0%) thin films on Pt/Ti/SiO2/Si substrates is prepared by sol-gel method, and the effect of Mo content on the microstructure and ferroelectric properties of these films are investigated. When the Mo content is not excessive, the BHTM films consisted of the single phase of Bi-layered Aurivillius phase. The B-site substitution with high-valent cation of Mo6+, in Bi3.6Ho0.4Ti3O12 films, enhanced the 2Pr (remanent polarization) and reduced the 2Ec (coercive field) of these films. The BHTM thin film with x=1.5% exhibited the best electrical properties with 2Pr of 48.4 μC/cm2, 2Ec of 263.5 kV/cm, dielectric constant of 391 (at 1 MHz), good insulting behavior, as well as the fatigue-free characteristic.

Strain-induced Curie temperature variation in La0.9Sr0.1MnO3 thin films

In this paper, La0.9Sr0.1MnO3 thin films were grown epitaxially on SrTiO3, LaAlO3 and MgO substrates, and their structural, electrical and magnetic properties were investigated, aiming at revealing and explaining the strain effects on the physical properties of La0.9Sr0.1MnO3 films. Compared with the compressive strained film on LaAlO3, the tensile strained films show a higher or lower Curie temperature when grown on SrTiO3 or MgO. The films on SrTiO3 and LaAlO3 show ferromagnetic metallic state at low temperature, while a ferromagnetic insulating state is observed in that on MgO. More valuably, significant enhanced magnetoresistance around room temperature is observed in the films grown on SrTiO3 and LaAlO3. The strain-induced TC variation in La0.9Sr0.1MnO3 films could not be explained by double-exchange mechanism alone, and the strong electron-phonon coupling originating from Jahn–Teller distortion of the MnO6 octahedra should be also taken into consideration. Based on this, we successfully derive a simplified equation for TC to explain quantitatively such an anomalous strain effect.

Pressureless sintering of silicon nitride ceramics with porous gradient structure for gas filter application

In the present study, Si3N4 ceramics with high porosity and porous gradient structure are prepared by pressureless sintering technique. Si3N4 ceramics with porosity of 34–47% are prepared by using ZrP2O7 as a binder material and heat treated at 1000°C in a nitrogen atmosphere. Si3N4 ceramics with porosity of 50–70% are prepared by using ZrP2O7 as a binder material, starch or naphthalene as a pore–forming agent and then heat treated at 1000°C in a nitrogen atmosphere. Si3N4 ceramics with porous gradient structure are then formed by laminating the Si3N4 porous ceramics with ordered porosity, followed by sintering at 1000°C. The phase compositions are analysed by X–ray diffraction (XRD), and the microstructure of the sintered samples is observed by scanning electronic microscope (SEM). The results show that the obtained Si3N4 ceramics exhibit a good porous–graded structure from high porosity to low porosity. The major phase of Si3N4 ceramics is still α phase.

Stoichiometric controlling of boron carbide thin films by using boron-carbon dual-targets

The stoichiometry of boron carbide thin films was controlled in the range of 0.1–8.9 via pulsed laser deposition by using boron-carbon dual-targets. The amorphous films sized 50 nm in thickness. The reaction rate of boron and carbon atoms increased with the increasing of target rotating speed. Carbon atoms preferentially substituted boron atoms within the chain site as sp2 hybridization at lower carbon concentrations and then within the icosahedrons site as sp3 hybridization at higher carbon concentrations.

Stoichiometric controlling of boroncarbonitride thin films with using BN-C dual-targets

High carbon-rich boroncarbonitride thin films have been grown by pulsed laser deposition (PLD) technique with using BN-C dual-targets. Fourier-transform infrared (FTIR) spectroscopy results presented B-N, B-C and C-N bonds, indicating the as-deposited thin films were new ternary compounds. B-N, B-C and C-N bonding structures were also detected by X-ray photoelectron spectroscopy (XPS), and carbon content fell into a large range of 45.8 to 85.9%. The films exhibited good thermalstability in vacuum, whereas were oxidized at 600 oC in air.

Understanding the deposition mechanism of pulsed laser deposited B-C films using dual-targets

Boron carbide thin films with stoichiometry (boron-carbon atomic ratio) range of 0.1 ∼ 8.9 were fabricated via pulsed laser deposition by using boron-carbon dual-targets. However, this experimental data on stoichiometry were smaller than the computer simulation values. The discrepancy was investigated by studies on composition and microstructure of the thin films and targets by scanning electron microscopy, excitation laser Raman spectroscopy, and X-ray photoelectron spectroscopy. The results indicate that the boron liquid droplets were formed by phase explosion after laser irradiation on boron sector. Part of the boron droplets would be lost via ejection in the direction of laser beam, which is tilted 45° to the surface of substrate.

Epitaxial Integration of (100) Bi4Ti3O12 with (0001) ZnO through Long-Range Lattice Matching

We report on an epitaxial relationship with a long-range lattice matching between the (100) plane of Bi-layered structure Bi4Ti3O12 (BiT) and the (0001) plane of wurtzite structure ZnO: BiT(100)[001] ∥ ZnO(0001) . Epitaxial (100)-oriented Ho-doped BiT thin film with the composite of Bi3.6Ho0.4Ti3O12 (BHT) was integrated with (0001)-oriented Al-doped ZnO (AZO) layer buffered c-sapphire substrate by pulsed laser deposition. X-ray diffraction and transmission electron microscopy characterizations validated the epitaxial orientation relationship, which was BHT(100)[001] ∥ AZO(0001) . The heteroepitaxy of (100) BiT with (0001) ZnO through long-range lattice matching opens the way to the study of novel BiT/ZnO-based ferroelectric wide-band-gap semiconductor heterostructure.