Showed C-axis Orientation Research Articles

Flexible, Piezoelectric Aluminum-Doped Zinc Oxide Energy Harvesters with Printed Electrodes for Wearable Applications

Aims: Recent advancements in sensing technology and wireless communications have accelerated the development of the Internet of Things (IoT) which promote the usage of wearable sensors. An emerging trend is to develop self-sustainable wearable devices, thus eliminating the necessity of the user to carry bulky batteries. In this work, the development of a flexible piezoelectric energy harvester that is capable of harvesting energy from low frequency vibrations is presented. The target application of this energy harvester is for usage in smart shoes. Objectives: The objectives of this research is to design, fabricate and test an energy harvester on PET substrate using Aluminum Zinc Oxide as its piezoelectric layer. Methods: The energy harvester was designed as a cantilever structure using PET/AZO/Ag layers in d33 mode which can generate large output voltages with small displacements. The electrodes were designed as an interdigitated structure in which two significant design parameters were chosen, namely the effect of gap between electrodes, g and number of interdigital electrodes (IDE) pairs, N to the output voltage and resonant frequency. Results: The sputtered AZO on PET showed c-axis orientation at 002 peak with 2 values of 34.45° which indicates piezoelectric behaviour. The silver IDE pairs were screen-printed on the AZO thin film. Functionality of the device as an energy harvester was demonstrated by testing it using a shaker. The energy harvester was capable of generating 0.867 Vrms output voltage when actuated at 49.6 Hz vibrations. Conclusion: This indicates that the AZO thin films with printed silver electrodes can be used as flexible, d33 energy harvesters.

Enhanced structural, optical and morphological properties of ZnO thin film using green chemical approach

In this work, ZnO thin film is fabricated by a green chemical approach using Uncaria gambir leaf extract on a glass substrate. The hexagonal wurtzite structure of ZnO does not change with the use of extracts. While ZnO fabricated without extract does not show preferred orientation, the ZnO prepared with extract shows c-axis orientation. The crystallite size is also significantly reduced from 41 nm to 32 nm. The visible transmittance increases from 71% to 76%, while the bandgap energy increases from 3.66 eV to 3.70 eV. The intensity of infrared transmission of ZnO with extract is lower than ZnO without extract because of the smaller crystallite size. The surface morphology of the film with extract is smoother, flatter, more homogeneous, and has smaller grain sizes, and uniform distribution.

Fabrication of Mg-Al Layered Double Hydroxide Thin Membrane for All-Solid-State Alkaline Fuel Cell Using Glass Paper as a Support

Layered double hydroxides (LDHs) are promising solid electrolytes for all solid-state alkaline fuel cells (AFCs) because of inorganic clay-like materials. However, LDHs were usually obtained as powder, and the formation of thin membranes as a separator of a fuel cell is rather difficult. In this study, a glass paper, non-woven fabric of fine glass fibers with more than 90% porosity, was used as a support for Mg-Al LDH powder, and self-standing, thin membranes for all solid-state AFCs were fabricated. Crystals of Mg-Al LDH were deposited in the inside of the glass paper by repeated immersion in Mg-Al LDH-dispersed solution and drying. Thickness of the obtained Mg-Al LDH thin membrane was about 150 µm, and LDH layer showed c-axis orientation because of the plate-like structure. The H2-O2 fuel cell using the Mg-Al LDH thin membrane as an electrolyte showed open circuit voltage of more than 0.9 V, indicating that the Mg-Al LDH thin membrane is dense and has high gas barrier property. The H2-O2 fuel cell using the Mg-Al LDH thin membrane showed higher power density compared with that using pelletized Mg-Al LDH powder as the electrolyte. The glass paper is proved to be very effective support for making thin Mg-Al LDH electrolyte membrane.

Structural and electrical properties of AlN thin films on GaN substrates grown by plasma enhanced-Atomic Layer Deposition

Aluminum nitride (AlN) thin films have been deposited by Plasma Enhanced Atomic Layer Deposition (PE-ALD) onto GaN-Sapphire substrates. The morphological, structural and electrical properties of AlN films with different thickness (from 5 to 15 nm) have been investigated. They uniformly cover the underlying GaN substrate without pinholes and cracks. All the AlN thin films show c-axis orientation and their in-plane crystalline arrangement perfectly matches the hexagonal structure of GaN substrate. In particular, the cross-sectional TEM analysis demonstrated that the first AlN layers are well aligned with respect to the GaN (0001) substrate, while stacking faults formation is observed in the upper part of the films. Finally, electrical measurements by Hg-probe on as-deposited AlN showed very low current leakage across these layers and the presence of a high density two-dimensional electron gas (>2 × 1013 cm−2) at the AlN/GaN interface.

Magnetoelectric properties of NiFe2O4/0.65BaTiO3–0.35Na0.5Bi0.5TiO3 bilayer thin films deposited via pulsed laser deposition

Lead-free magnetoelectric (ME) NiFe2O4/0.65BaTiO3–0.35Na0.5Bi0.5TiO3 (NFO/BT–NBT) bilayer thin films grown on (001)-SrRuO3/SrTiO3 (SRO/STO) substrates were prepared via pulsed laser deposition. Different deposition sequences of the BT–NBT and NFO layers on the substrates yielded the following layered structures: NFO/BT–NBT/SRO/STO and BT–NBT/NFO/SRO/STO. Structural characterization via X-ray diffraction indicated that all of the samples are good crystallization and show c-axis orientation. Physical properties testing indicated that such heteroepitaxial composite thin films simultaneously exhibit excellent ferroelectric, dielectric, ferromagnetic, and ME coupling properties. Meanwhile, the ME coupling behavior of the bilayer thin films is influenced by growth sequences of the composite films. The ME coupling coefficient of the BT–NBT/NFO/SRO/STO (αE ∼ 120 mV cm─1 Oe─1) thin film is smaller than that of the NFO/BT–NBT/SRO/STO (αE ∼ 140 mV cm─1 Oe─1) thin film, which may be due to the different substrate clamping effect.

Synthesis, structure and optics properties of Ba(Fe1/2Nb1/2)O3 thin film by pulsed laser deposition

The Ba(Fe1/2Nb1/2)O3 (BFNO) thin films have been successfully deposited on (1 0 0) SrTiO3 substrates by pulsed laser deposition. The structural characteristics, micro-topography and optical properties have been investigated. X-ray diffraction patterns suggest that all the films are good crystallization and show c-axis orientation. The X-ray photoelectron spectra analyses confirm the successful synthesis of BFNO material, and reveal the existence of the oxygen vacancies. The photoluminescence (PL) measurement is used to analyze the optical properties and carriers recombination mechanisms. The BFNO films have a narrow band gap of 1.37 eV, which show potential roles in solar cells and other photoelectric devices. According to the PL measurement, carriers recombination mechanisms are related with excitonic radiative recombination in our samples. This research not only lays a solid foundation on further researching BFNO thin films, but also opens an avenue to design various multifunctional devices.

Effects of Deposition Pressure and Target-Substrate Distance on Growth of ZnO by Femtosecond Pulsed Laser Deposition

Undoped Zinc oxide (ZnO) was successfully deposited on silicon (100) substrate by femtosecond pulsed laser deposition. A mode-locked femtosecond laser operating at 790 nm wavelength, 100 fs pulse duration and 80 MHz repetition rate was used as an excitation source. The depositions were carried out at vacuum pressures of 10-10 mbar and oxygen background gas pressures of 10 -10 mbar. Energy dispersive spectroscopy of samples grown without oxygen background gas shows higher zinc composition on deposited material as compared to oxygen that leads to off stoichiometric ZnO films. Scanning electron microscopy (SEM) images shows that increasing oxygen gas pressure increased the particle size of the deposited ZnO. The material deposited at 2x10 mbar oxygen pressure revealed clustering of nanorods forming a flower-like structure that has an average length of 2700 nm and an average diameter of 450 nm. The X-ray diffraction spectra show c-axis orientation of the deposited ZnO with (002) and (110) reflection.

Fabrication of sandwich-type MgB2/Boron/MgB2 Josephson junctions with rapid annealing method

Sandwich-type MgB2/Boron/MgB2 Josephson junctions were fabricated using magnetron sputtering system. The rapid-anneal process was adopted to replace traditional way of annealing, trying to solve the problem of interdiffusion and oxidation with multilayer films. The boron film was used as barrier layer to avoid the introduction of impurities and improve reproducibility of the junctions. The bottom MgB2 thin films deposited on c-plane sapphire substrate exhibits a critical temperature TC of 37.5 K and critical current density JC at 5 K of 8.7 × 106 A cm−2. From the XRD pattern, the bottom MgB2 thin film shows c-axis orientation, whereas the top MgB2 became polycrystalline as Boron barrier layer grown thicker. Therefore, all junction samples show lower TC than single MgB2 thin film. The junctions exhibit excellent quasiparticle characteristics with ideal dependence on temperature and Boron barrier thickness. Subharmonic gap structure was appeared in conductance characteristics, which was attributed to the multiple Andreev reflections (MAR). The result demonstrates great promise of this new fabrication technology for MgB2 Josephson junction fabrication.

Improvement of critical current densities in SmBa2Cu3Oy, films with BaHfO3 nano-rods using low temperature growth technique

We studied growth substrate temperature dependent morphologies of BaHfO3 (BHO) nano-rods for SmBa2Cu3Oy, (SmBCO) films with BHO fabricated by pulsed laser deposition (PLD) method. The morphology of BHO nano-rods within the SmBCO matrix could be controlled by changing substrate temperatures adoping a Low Temperature Growth (LTG) technique. Using the LTG technique, we could fabricate SmBCO films showed c-axis orientation even at low substrate temperature during deposition without a degradation of superconducting properties, which is one of the most advantages of the LTG technique. In this study, we found an optimal morphology of the BHO nano-rods and the morphology was fine, straight and various growth directions. The BHO nano-rods were more effective to improve the Jc in a magnetic field than other morphologies of the BHO nano-rods.

Preparation of Epitaxial MgO Films Deposited by RF Magnetic Sputtering on the IBAD-MgO Substrate

We deposited epi-MgO films on the textured ion beam assisted deposition (IBAD)-MgO substrates by RF magnetic sputtering at different substrate temperatures (600–850 °C), RF powers (110–224 W) and oxygen partial pressures (19.5–58.6 mTorr). The microstructure and surface morphology of epi-MgO films were characterized by X-ray diffraction (XRD) and atom force microscope (AFM). It was found that epi-MgO films with c-axis orientation could be easily fabricated for broad parameter ranges. But the in-plane full width half maximum (FWHM) of the epi-MgO film was dependent on the parameters, and the epi-MgO film with the smallest FWHM value of 5.22° was obtained at the optimum parameters. What’s more, the GdBa2Cu3O7 films deposited on the epi-MgO/IBAD-MgO substrate by RF magnetic sputtering showed c-axis orientation.

Anomalous second ferromagnetic phase transition as a signature of spinodal decomposition in Fe-doped GeTe diluted magnetic semiconductor

Structural and magnetic properties of diluted magnetic semiconductor Ge1-xFexTe thin films are investigated. The conventional structure analysis shows c-axis orientation with columnar growth of the films and no indication of Fe clusters or second phase. Magnetic measurements combined with theory models reveal that two ferromagnetic phase transitions occur. We consider that the second ferromagnetic phase transition in high Fe content thin film is from a ferromagnetic phase with long range exchange interaction to a superparamagnetic phase with dipole interaction between Fe clusters, which can be viewed as a signature of spinodal decomposition in Ge1-xFexTe material.

Thickness dependence of Ic and Jc of LTG-SmBCO coated-conductor on IBAD-MgO tapes

We have reported SmBa2Cu3Oy (SmBCO) films on single crystalline substrates prepared by low-temperature growth (LTG) technique. The LTG-SmBCO films showed high critical current densities in magnetic fields compared with conventional SmBCO films prepared by pulsed laser deposition (PLD) method. In this study, to enhance critical current (Ic) in magnetic field, we fabricated thick LTG-SmBCO films on metal substrates with ion-beam assisted deposition (IBAD)-MgO buffer and estimated the Ic and Jc in magnetic fields.All the SmBCO films showed c-axis orientation and cube-on-cube in-plane texture. Tc of the LTG-SmBCO films were 93.1–93.4K. Jc and Ic of a 0.5μm-thick SmBCO film were 3.0MA/cm2 and 150A/cm-width at 77K in self-field, respectively. Those of a 2.0μm-thick film were 1.6MA/cm2 and 284A/cm-width respectively. Although Ic increased with the film thickness increasing up to 2μm, the Ic tended to be saturated in 300A/cm-width. From a cross sectional TEM image of the SmBCO film, we recognized a-axis oriented grains and 45° grains and Cu–O precipitates. Because these undesired grains form dead layers, Ic saturated above a certain thickness. We achieved that Ic in magnetic fields of the LTG-SmBCO films with a thickness of 2.0μm were 88A/cm-width at 1T and 28A/cm-width at 3T.

Flux-pinning Properties and Microstructure in SmBa2Cu3Oy Thin Films with BaZrO3 Nanorods

Self-organized BaZrO3 (BZO) nanorods in REBa2Cu3Oy superconducting films are known as promising artificial pinning centers. Previously, we have reported high-Jc Sm1+xBa2-xCu3Oy (SmBCO) films fabricated by a low-temperature growth (LTG) technique. The LTG technique expands the range of the deposition temperature in which the REBCO films show c-axis orientation, and makes it possible to control the crystal grain size and number density. In this study, in order to tune the pinning properties, we fabricated SmBCO films with BZO nanorods (LTG-SmBCO + BZO films) using the LTG technique and investigated the influence of the LTG technique on the growth of BZO nanorods and pinning properties in SmBCO films. With decreasing deposition temperature of the upper layer in the LTG-SmBCO + BZO films, the diameter of the films was decreased and the number density of BZO nanorods was increased, producing a high matching field, Bφ. Additionally, remarkable upturn shifts in the irreversibility field line and plateau regions in the magnetic-field dependence of Jc were observed in the range of Bφ/3 B Bφ. These results indicate that the nature of the Bose-glass-like state of vortices localized on c-axis-correlated pinning centers emerges in the range of Bφ/3 B Bφ.

Nanocrystal Assembled TiO2 Particles Prepared from Aqueous Solution

Anatase TiO2 particles, 100−200 nm in diameter, were developed in aqueous solution at 50 °C. The particles were assemblies of nano TiO2 crystals covered with nanorelief surface structures. The crystals grew anisotropically along the c-axis to form acicular crystals. The particles showed c-axis orientation due to high-intensity X-ray diffraction from the (004) planes. The particles had a BET specific surface area of 270 m2/g. BJH and DFT/Monte-Carlo analysis of adsorption isotherm indicated the existence of pores ∼3 nm and ∼1 nm in diameter. Crystallization and self-assembly of nano TiO2 were effectively utilized to fabricate nanocrystal assembled TiO2 particles having a high surface area and nanorelief surface structure.

Liquid phase epitaxy of YBa2Cu3O7-δ film on single crystalline MgO and NdGaO3 substrate

YBa2Cu3O7-δ (YBCO) films were deposited by a liquid phase epitaxy (LPE) method on MgO single crystalline substrates that were covered by thin film of pulsed-laser-deposited (PLD) YBCO as a seed layer. The 990°C-deposited LPE film showed c-axis orientation perpendicular to the substrate surface and in-plain two -dimensional alignment. The LPE film contained twin structure with good crystalline perfection and the PLD film showed broad in-plain alignment, meaning lattice constant distribution or lattice distortion.

SUPERCONDUCTING PROPERTIES AND ORIENTATION BEHAVIOR OF REBa2Cu3Oy (RE = Yb, Er, Sm, Nd and La) FILMS BY METAL-ORGANIC DEPOSITION

We have investigated superconducting properties and orientation behavior of RE123 ( RE = Yb , Er , Sm , Nd and La ) films on MgO and SrTiO 3 substrates by metal-organic deposition technique using metal naphthenates. On MgO substrates, only Yb123 films showed superconducting transition with Tc( zero ) of 77.0 K and c-axis orientation with in-plane alignment. On SrTiO3 substrates, Yb123 , Er123 , Sm123 , Nd123 and La123 films showed c-axis orientation with in-plane alignment, and Tc( zero ) of 89.5 K, 89.7 K, 80.5 K, 85.0 K and 47.6 K, respectively. Sm123 and La123 films showed square and plate-like grains on MgO substrates, and relatively flat surface covered with well-grown grains on SrTiO 3 substrates.

Large second-harmonic kerr rotation in GaFeO 3 thin films on YSZ buffered silicon

Epitaxial thin films of gallium iron oxide (GaFeO 3) are grown on (0 0 1) silicon by pulsed laser deposition (PLD) using yttrium-stabilized zirconia (YSZ) buffer layer. The crystalline template buffer layer is in situ PLD grown through the step of high-temperature stripping of the intrinsic silicon surface oxide. The X-ray diffraction pattern shows c-axis orientation of YSZ and b-axis orientation of GaFeO 3 on Si (1 0 0) substrate. The ferromagnetic transition temperature ( T C ∼ 215 K ) is in good agreement with the bulk data. The films show a large nonlinear second harmonic Kerr rotation of ∼15° in the ferromagnetic state.

Manipulation of crystal orientation and microstructure of barium ferrite thin film

Pt, Pd, and Pt–Pd alloy underlayers were used to deposit c-axis oriented barium ferrite (BaM) thin films by a facing target sputtering system. All of the BaM thin films grown on these three underlayers show c-axis orientation normal to the film plane. But the grain size of BaM layer is strongly manipulated by the underlayer grain size. It is found that Pt–Pd alloy underlayer is effective to achieve c-axis oriented barium ferrite films with small grain size.

Platinum-assisted phase transition in bismuth-based layer-structured ferroelectric CaBi4Ti4O15 thin films

The phase transition of nonferroelectric pyrochlore to ferroelectric perovskite in CaBi4Ti4O15 thin films depends on platinum bottom electrodes. Rather than the strain and crystallinity of the bottom electrode, matching of the atomic arrangement to the Ca–Bi–Ti–O thin films is predominant. CaBi4Ti4O15 thin films crystallized on (200)-oriented platinum at 650 °C showed c-axis orientation. In contrast, thin films crystallized on highly crystalline (111)-oriented platinum at the same temperature contained pyrochlore grains which were about several tens of nanometers in diameter and located in the interface region. They showed P–V hysteresis loops. The remanent polarization and coercive electric field depended on platinum top electrode size.

Platinum-Accelerated Phase Transition in Bismuth-Based Layer-Structured Ferroelectric Thin Films

ABSTRACTThe phase transition of non ferroelectric pyrochlore to ferroelectric perovskite in CaBi4Ti4O15 thin films depended on matching of the atomic arrangements in platinum bottom electrodes to the Ca-Bi-Ti-O thin films. CaBi4Ti4O15 thin films crystallized on (200)-oriented platinum at 650°C showed c-axis orientation. In contrast, thin films randomly crystallized on highly crystalline (111)-oriented platinum at the same temperature contained pyrochlore phase and showed P-V hysteresis loops. The ferroelectric properties improved with the degrees of (h00) orientation.