Surface Review and Letters

Samples of lead zirconate titanate Pb(Zr_0.53Ti_0.47)O₃ with europium (Eu) doping concentration of 0, 0.5, 1.5, 3 mol% (PEZT) were fabricated by sol–gel method. XRD spectra showed that the introduction of Eu into PZT favored the growth of (100) orientation. With 3% Eu content, the preferential orientation of the film converted from (111) to (100) orientation. The Eu-doped PZT films exhibited lower leakage current less than 10^-9 A/cm² and the behavior of leakage current was discussed in terms of defect chemistry theorem. When Eu content was 1.5%, the remanent polarization (P_r) increased to 28 μ C/cm² which was much higher than that of undoped PZT film.

Ferroelectric/ferromagnetic (ME) biphase composite thin films with the type of (1–x)PbTiO₃(PT)–xNiFe₂O₄ (NFO) (x = 1–9) were successfully formed in situ by sol–gel process. The dielectric and ferroelectric behaviors of the composite thin films were investigated. The asymmetrical hysteresis loops of the composite arise from the leak current due to low resistivity of NFO. The stronger stress in the thin films due to the strong conjunction between PT and the substrate contributes to the increase (decrease) of the coercive force (the remanent polarization) with increasing the content of PT. The ME composites exhibit slight percolation effect. The high dielectric constant near the percolation threshold is attributed to the "micro-capacitors" in the composite thin films.

A series of (Pb_0.4Sr_0.6)_1-xLa_2x/3TiO₃ (PSLT) thin films were deposited on ITO/glass substrates by sol–gel technique. Their phase status, surface morphology, and dielectric properties were studied by X-ray diffraction, scanning electron microscope, and impedance analyzer, respectively. Results show that the PSLT thin films were consisted of tetragonal perovskite phase PSLT thin films for x < 0.4, and cubic perovskite phase PSLT thin films for x > 0.4. Dielectric properties such as dielectric constants, dielectric tunabilitis, and inharmonic coefficient were characterized as a function of the film composition.

A novel three-phase film with conductive acetylene black (AB) and ferroelectric phase (BaTiO₃) introduced intoβ-polyvinylidene fluoride (β-PVDF) was prepared by using dip-coating method. The high dielectric constant of 650 can be obtained in the AB–PVDF/BaTiO₃ composite film when AB content approached the percolation threshold (3.3 vol%), which is 40 times more than that of (PVDF + BaTiO₃) matrix. The dielectric constant of the composite film is almost independent of frequency.

The relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ compositions are of interest owing to their excellent dielectric, electromechanical, electro-optical, and other properties. In this paper, the 0.80Pb(Mg_1/3Nb_2/3)O₃–0.20PbTiO₃ (PMN–PT 80/20) films with pure perovskite structure were synthesized by a single step at 150°C. The corresponding oxides were used as starting materials, namely PbO, MgO, Nb₂O₅, and TiO₂. By using oxides as precursors, we simplified the hydrothermal process, allowing the process to be more economical. The influences of the Ti metal substrate on the PMN–PT 80/20 films are investigated. By surveying the variations of films, it was suggested that the substrate reacted with the ions in the solution. The films were smooth and homogeneous. There were no cracks and abnormity crystals on the surface of the films. The thickness was about 20 μm. The frequencies dependence of the dielectric properties of PMN–PT 80/20 films was stable even at a high frequency range over 1 MHz.

Ba(Zr_0.2Ti_0.8)O₃ (BZT) and 2 mol% Mn additional doped BZT (Mn-BZT) thin films were deposited by pulsed laser deposition technique under the same growth conditions on LaAlO₃ substrates with the bottom electrodes of LaNiO₃. The microstructure of the films was characterized by X-ray diffraction (XRD) in the mode of θ–2θ scan and Φ-scan. The results indicated that BZT film was (001)-oriented_with an in-plane relationship of BZT[100]//LNO[100]//LAO[100]. The Mn-BZT film exhibited higher dielectric constant of 225 at zero electric field, larger dielectric tunability of 59.4%, and lower dielectric loss of 1.8% under an applied electric field of 720 kV/cm. The figure of merit for BZT thin film increased from 19.8 to 33 by Mn doping. The enhanced dielectric behavior by Mn doping could be mainly attributed to the decrease of oxygen vacancies and the reorientation of the dipolar defect complex of .

In order to investigate the electrochemical properties of Li/FeS cell, FeS powder was fabricated by using a high-energy ball milling method. Then, surface of FeS powder was coated with metallic nickel. Nickel coating was conducted by using electroless nickel plating method. Nickel chloride (NiCl₂ · 6H₂O) was used as the nickel ion source for electroless nickel plating. The effects of nickel coating on the electrochemical properties of FeS electrode for Li/FeS cell were investigated by CV measurement and charge/discharge tests. Then, cells for electrochemical tests were assembled by stacking a lithium anode, separator containing liquid electrolyte, and FeS cathode in turn. From the results, electroless nickel plated FeS electrode showed very high initial discharge capacity of 581 mAh/g-FeS. And also, it showed higher discharge capacity than that of bare FeS electrode until the 29th cycle. Therefore, it is found that metallic nickel gives beneficial effects on enhancing the electrical conductivity of FeS cathode material. 82.47.Cb.

Ferroelectric PbZr_0.6Ti_0.4O₃ (PZT) thick films were fabricated using a combination of screen-printing method and PZT precursor sol coating process (M. Koch, N. Harris, R. Maas, A. G. R. Evans, N. M. White and A. Brunnschweiler, Meas. Sci. Technol.8 (1997) 49; Y. S. Yoon, J. Korean. Phys. Soc.47 (2005) 321). Structural and electrical properties of the PZT thick films with the treatment of sol coating were investigated. The porosity decreased and the densification was enhanced with increasing the number of sol coatings. All PZT thick films showed the typical X-ray diffraction patterns of a perovskite polycrystalline structure. The thickness of all thick films was approximately 60–61 μm. The relative dielectric constant increased and dielectric loss decreased with increasing the number of sol coatings, and the values of the six-layer PZT-6 film were 167.8, 0.78% at 1 kHz, respectively. The remanent polarization and coercive field of the 6-coated PZT-6 thick films were 14.1 μC/cm² and 20.3 kV/cm, respectively.

The oxidation of Ti₁₉Al₁₈La₄N₅₇ coating was studied at 600°C, 700°C, and 800°C for up to 30 h in air. The coating consisted of fine Ti₃Al₃N₂ polycrystals. The oxides formed were an amorphous mixture of Al₂O₃, TiO₂, and La₂O₃. During oxidation, nitrogen diffused out from the coating. The addition of 4 at.%La to the TiAlN coating deteriorated the soundness of the oxide film formed.

Gas-atomized amorphous Cu₅₄Zr₂₂Ti₁₈Ni₆ powders were sprayed onto a steel substrate by the kinetic spraying method to make an amorphous Cu₅₄Zr₂₂Ti₁₈Ni₆ coating. The oxidation behavior of the coating was studied over the temperature range 573–769 K in air. The oxidation products were primarily Cu₂O, CuO, β-ZrO₂, ZrTiO₄, and Cu. Copper oxides were the major oxides. Preferential oxidation of Cu occurred around the surface of the coating.

Polycrystalline vanadium oxide (VO_x) thin films with mixed phases of V₆O₁₃ + VO₂ (M) are deposited onto p-doped Si (100) substrates at 430°C using magnetron sputtering. By vacuum annealing on as-deposited VO_x thin films at 450°C, at different annealing times we obtained nanoscale polycrystalline VO_x thin films with two or more mixed phases. With the annealing time increasing, the phases of the films underwent the following transformation: V₆O₁₃ + VO₂ (M) → VO₂ (M) + VO₂ (B) → VO₂ (B) + VO₂ (M) + V₅O₉ → V₄O₇ + V₅O₉. The surface of VO_x thin films prepared in different conditions is of high quality with mean grain size ranging from 80 to 300 nm and the R_a being about 20nm. The lowest temperature coefficient of resistance at ambient temperature (20°C) of -2% K^-1 is found in the VO_x thin film annealed at 450°C for 8 h with mixed phases of VO₂ (M) + VO₂ (B), which can meet the needs of microbolometer materials.

Effect of pre-heating temperature on the properties of Lead zirconate titanate (PZT) powders and films was investigated. PZT powders and films were prepared via a triol-based sol–gel route. The PZT powders prepared at various heating temperatures were characterized. The preheating temperature range of 200°C–400°C and annealing temperature of 600°C were chosen to make the films. AFM micrograph revealed the thin films with homogeneous, dense, and crack-free properties. The pre-heating temperature was found to have a significant effect on phase formation, prefer orientation, and dielectric properties of the films. Higher dielectric constant and dielectric loss were observed at higher pre-heating temperature. However, all films showed the dielectric loss less than 0.04.

Co-ferrite films were prepared using pulsed laser deposition with both post-annealing and in situ heating processes. Magnetic properties of these films were studied in the function of temperature, film thickness, and substrate. The films using post-annealing processes exhibited isotropic microstructure, and the coercivity showed no obvious magnetic anisotropy and no strong dependence on film thickness. Co-ferrite films using in situ heating exhibited (111) highly textured structure and possessed perpendicular anisotropy as well as large coercivity. The preferential texture and magnetic anisotropy were closely associated with substrate temperature and thickness. Perpendicular Hc over 12.5 kOe was obtained in the 33 nm Co-ferrite film deposited on single crystal quartz substrate at 550°C. The high coercivity and perpendicular coercivity may be attributed to the nanocrystalline grain, textured orientation, and large residual strain in these films since large residual strain may induce strong stress anisotropy.

InSb films on GaAs (001) substrates have been grown using a two-step method by molecular beam epitaxy (MBE). The Kinetic Monte Carlo (KMC) method, based on solid-on-solid (SOS) model has been introduced to simulate the Volmer–Weber growth of InSb buffer layer on GaAs substrate. The buffer surface becomes rough obviously and produces an undulating profile during the last coverage of the substrate. The undulating buffer surface would play an adverse role in the surface morphology of the following InSb epilayer. Therefore, the growth of InSb epilayer before the formation of undulating buffer surface would get a better surface, which has been convinced by the results of atomic force microscope (AFM) observations.

The properties of Cu-, Al-, and Li-doped ZnO dilute magnetic semiconductor (DMS) have been analyzed and compared. Zincite with wurtzite structures have been synthesized successfully on SiO₂ (101) and SiO₂ (110) substrates in both the Cu–ZnO and Li–ZnO DMS. The highly textured ZnO (002) peaks were able to form in the Cu–ZnO system at 400°C. However, it formed at even much lower temperature in the Li–ZnO system, that is only 25°C. ZnO (002) peaks in both systems were formed without any impurity phases. However, no crystalline structure is synthesized in the Al–ZnO system. The thin films formed are amorphous. The structural and related magnetic properties of the films were analyzed by XRD, AFM, and VSM. The films were found to be at their highest magnetism at the value of 3.1 emu/cm³ for Co–ZnO and 2.5 emu/cm³ for Li–ZnO, synthesized at 400°C, and under 1 × 10^-4 Torr oxygen partial pressure.

In this study, resonance enhancement of giant magneto-impedance (GMI) effect in Fe-based Fe_73.5Cu₁Nb₃Si_13.5B₉ glass-coated microwires was investigated. A new method was adopted by sputtering a copper layer in the outside of the Fe-based glass-coated wire. A capacitance forms between the ferromagnetic core and outer copper layer, where the glass insulator works as a dielectric layer. Therefore, the composite wire forms an LC resonance circuit (which consists of an inductor, represented by the letter L, and a capacitor, presented by the letter C) itself, resulting in an increase of GMI ratio from 250% to 330%. Meanwhile, the influence of resonance frequency on the GMI effect was discussed.

Ferromagnetic (Ni, Co, Fe) nanowires were electrodeposited using AAO template. XRD analysis indicated that the ferromagnetic wires had preferred orientation. For longer deposition time, the nanowires with textured structure changed to single crystal. The investigation on the growth mechanism showed that in the initial stage, the nanowires were polycrystalline. Our TEM analysis revealed the transition from polycrystalline structure to single crystal from the bottom to the top. The growth mechanisms are probably due to the competition growth of the adjacent grains and the confinement of growth in the nano-sized hole of the AAO template.

Porous NiTi shape memory alloy (SMA) with 48% porosity and an average pore size of 50–800 μm was synthesized by capsule-free hot isostatic pressing (CF-HIP). To enhance the surface bioactivity, the porous NiTi SMA was subjected to H₂O₂ and subsequent NaOH treatment. Scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses revealed that a porous sodium titanate (Na₂TiO₃) film had formed on the surface of the porous NiTi SMA. An apatite layer was deposited on this film after immersion in simulated body fluid at 37°C, while no apatite could be found on the surface of the untreated porous NiTi SMA. The formation of the apatite layer infers that the bioactivity of the porous NiTi SMA may be enhanced by surface chemical treatment, which is favorable for its application as bone implants.

Cr/SmCo₅/Cr films were fabricated by a DC facing targets magnetron sputtering. The influences of sputtered Ar pressure and substrate temperature on their microstructure and magnetic properties were investigated. Magnetic measurements indicate that the optimal substrate temperature was 450°C, and the film deposited at 2 Pa Ar pressure had the largest in-plane coercivity (2403.54 Oe). No SmCo₅ diffraction peaks except Cr (110) peak with body-centered-cubic structure were seen in all the samples by X-ray diffusion. The Needle-like grains of the film deposited at low Ar pressure were observed by atomic force microscope. The domain pattern of the film fabricated at 2 Pa Ar pressure showed more uniform. When the sputtered Ar pressure was 2 Pa, the narrowest switching field distribution (0.57) was obtained, indicating a narrower grain size distribution. The δM value was nearly zero for the film deposited at 2 Pa Ar pressure, and this indicated that there was almost noninteraction between grains.

A numerical study is needed to gain insight into the growth mechanism and improve the reactor design or optimize the deposition condition in chemical vapor deposition (CVD). In this study, we have performed a numerical analysis of the deposition of gallium arsenide (GaAs) from trimethyl gallium (TMG) and arsine in a vertical CVD reactor. The effects of operating parameters, such as the rotation velocity of susceptor, inlet velocity, and inlet TMG fraction, are investigated and presented. The three-dimensional model which is used in this investigation includes complete coupling between the thermal-fluid transport and species transport with chemical reaction.

Ag nanoparticle deposition on the surface of spherical SiO₂ nanoparticles was studied to achieve hybrid structure of Ag–SiO₂ nanocomposite. SiO₂ nanoparticles were served as seeds for continuous Ag metal deposition. The ratio of elements and morphology was studied with scanning electron microscope energy dispersive X-ray and transmission electron microscope. The antibacterial properties of Ag–SiO₂ nanocomposite were examined. The homogeneously formed Ag nanoparticles on the surface of SiO₂ nanoparticles without aggregation of Ag nanoparticles showed excellent antibacterial abilities.

Nanocrystalline cerium oxide (CeO₂) particles prepared by the novel two-stage precipitation method were used for the catalysis of CO oxidation. Firstly, two shapes, i.e. particulate (P-) and needle-like (N-), CeO₂ nanoparticles were formed via proposed temperature-arranged routes. The crystalline structure, morphology, particle size, and surface area of samples were characterized by using XRD, TEM, HRTEM, and BET techniques. Furthermore, the morphological effect of the CeO₂ samples on the catalytic activity of CO oxidation was investigated. From the experimental results, it indicated that the prepared samples were all nonporous and fcc-structured CeO₂. The CeO₂ particles, as precipitating at 90°C for 5 min and then aging at 90°C, were particulate, whereas they were needle-like by aging at 0°C. The CO oxidation reaction showed that the catalytic activity of N-CeO₂ nanoparticles was higher than that of P-CeO₂, attributing from the exposed higher-energy {100} and {110} facets for N-CeO₂ nanoparticles. Moreover, the calcined samples with higher degree of crystallinity showed further promotion in catalytic activity. It was also worthy to note, that by replacing the CeO₂ catalyst by Pd/CeO₂, a large increase in the CO conversion was found, especially catalyzed by Pd/N-CeO₂.

Carbon-coated lithium ion phosphate was synthesized from a gel precursor with ferric iron and a carbon source of organic chelating agent via a sol–gel method. The dependence of the microstructure and electrochemical performance of the synthesized LiFePO₄/C on the pH value of the precursor solution during gel formation and the sintering time was investigated. The obtained LiFePO₄/C particles were characterized by X-ray diffraction, field-emission scanning electron microscopy, and element analysis. The results show that the pH value has little effect on the phase purity. At a sintering temperature of 700°C, the discharge capacity of LiFePO₄/C under 0.1 C (1 C = 170 mA/g) regime decreased from 152.8 to 62.5 mAh/g with decreasing the sintering time from 12 h to 8 h. Appropriate sintering time can lead to well-crystallized LiFePO₄/C, which improves the electrochemical performance.

GaAs/InGaP and AlGaAs/GaAs/InAlGaP npn heterostructural optoelectronic switches (HSOSs) have been fabricated to demonstrate the bulk-barrier and potential-spike height effects on the switching. It is seen that the illumination decreases the switching voltage V_S and increases the switching current I_S in the GaAs/InGaP HSOS characteristics. But in the AlGaAs/GaAs/InAlGaP HSOS, the V_S and I_S present contrary trends. These characteristic variation differences in the two HSOSs are mainly due to the photogenerated carriers that affect the bulk-barrier and potential-spike heights.

Three new asymmetric photochromic diarylethenes bearing fluorine atoms at the ortho-, meta-, or para-position of one terminal phenyl group were synthesized, and their photochromism and kinetics of the photochromic cyclization/cycloreversion both in different solvents and in PMMA films were investigated. The results showed that the cyclization/cycloreversion process of these compounds were determined to be zeroth/first order reaction, and the reaction rates (k) were obtained from the slope of every line. The substituent position effect on the cycloreversion process of the three compounds was remarkable and the solvent polarity enhanced this effect. The values of reaction rates in PMMA films were quite different from those in solvents indicating that the kinetics processes of the three compounds taking place in PMMA films differs from the same processes occurring in common solvent.

The effect of various laser processing parameters on the kerf width and cut quality of Si wafer as well as encapsulated Si wafer is investigated. The parameters are then optimized to minimize the heat affect zone and obtain the best possible cut quality. It has been found that oxygen is the most suitable assist gas for laser dicing and that the highest gas pressure may not produce the best cut quality. The effect of laser repetition rate, pump energy, feed rate, and number of passes are also studied. Under optimized parameters, the cut quality of Si wafer using laser dicing is found to be comparable to diamond saw dicing.

In this work, nanocrystalline TiO₂/ITO electrodes were prepared by sol–gel method starting from tetrabutyl orthotitanate (Ti(OBuⁿ)₄) reacted with hydrogen peroxide in the ice-water bath. The sol–gel derived TiO₂ films were characterized by XRD, SEM, BET, and UV/Vis absorption spectroscopic techniques. The preparation conditions, including the number of coats and calcination temperature, were also investigated. Furthermore, PEC cells were constructed for testing the activities of prepared TiO₂/ITO photoelectrodes. The photo-currents for hydrogen production via the PEC reaction were measured under UV irradiation (λ_max = 253.7 nm). The experimental results showed that the sol–gel derived TiO₂ films calcined at 300°C–600°C were anatase structure and they showed a maximum UV/Vis absorption at about 380 nm. Moreover, from the result of PEC reactions, it was found that the TiO₂/ITO photoelectrode (calcined at 600°C, with the thickness of TiO₂ layer of about ~0.2 μm) demonstrated a large saturation current (0.326 mA/cm²) with a quite high photoelectrochemical conversion efficiency of 2.39%.

Three different electrode films of highly crystallized LiCoO₂, nano-crystalline LiMn₂O₄ as cathode and amorphous LiNiVO₄ as anode were grown on stainless steel substrates by pulsed laser deposition. Microbatteries were assembled using liquid electrode of LiPF₆. The microbatteries were electrochemically tested by charge/discharge cycling and cyclic voltammetry. Both LiCoO₂/LiPF₆/LiNiVO₄ and LiMn₂O₄/LiPF₆/LiNiVO₄ cells showed smooth charge/discharge curves. Although the cells faced a fast capacity loss in the first 10 cycles, about 20 μA/cm² μm of discharge capacity was attainable after 20 cycles.

The Poly(vinylidene) fluoride (PVDF) thin films with a high content of β-phase were prepared by controlling heat-treatment temperature using casting from the poled solvents. The crystallite microstructure of thin films was depicted by the techniques of X-ray diffraction and FTIR. The results showed that heat treatment was favorable for inducing the β- and γ-phase formation of PVDF. The β phase films were obtained with heat treatment at temperatures ranging from 60°C to 120°C and annealing at 120°C after casting from DMF. The thermo-optical effect of β phase PVDF films was investigated using a spectroscopic ellipsometer. At temperatures ranging from 20°C to 100°C, the refractive index of PVDF was negatively correlated with the temperature between 350 and 1500 nm. The value of the t.o. coefficient of PVDF films was calculated at all temperatures. The maximum value of the t.o. coefficient was about 3.3 × 10^-4/°C at the ascending stage of temperature and 3.0 × 10^-4/°C at the descending stage of temperature. Therefore, it is possible to use the thermo-optic effect of the β phase PVDF for long wavelength infrared imaging.

The development of PCR chip shortens the reaction time of DNA amplification, reduces the bulk of reaction reagents; therefore, it is widely applied to biomedicine and other related fields. Since PCR reaction is completed through three different precise temperature zones periodically, the sensitivity of temperature measurement and the heating property of the metal membrane must be highly regarded. In this paper, three kinds of membranes, Ni, Pt, and Ni–Cr, were fabricated on silicon substrates; their resistance–temperature characteristics and heating properties are discussed. The results show that Ni and Pt films have good linear resistance–temperature relationship; the heating property of Pt film is superior to that of Ni–Cr film. The PCR chip with Pt film microheater can reach 150°C in a short time with 25 V voltage.

The nanostructure of p-type AlGaN/GaN strained-layer superlattice (SLS) cladding in a GaN-based violet laser diode (LD) has been investigated by high-angle annular dark-field (HAADF) scanning-transmission electron microscopy (STEM). The pairs of the AlGaN and GaN layers in SLS cladding are observed, where the AlGaN and GaN layers appear as dark and bright bands. It is also found that the threading dislocations disappeared within the SLS; this evidence manifests the role of SLS in suppressing threading dislocation propagation.

Ba_0.6Sr_0.4TiO₃ (BST) and Ba_0.6Sr_0.4TiO₃/Ba(Zr_0.2Ti_0.8)O₃/Ba_0.6Sr_0.4TiO₃ (BST/BZT/BST) multilayer (ML) films were prepared by pulsed laser deposition on the LaNiO₃-coated LaAlO₃ substrate. X-ray diffraction analysis revealed that the two kinds of films could be epitaxially grown in pure single-oriented perovskite phases and atomic force microscopy showed that the grain size of ML films was similar to BST films in size. The dielectric properties of the BST and ML thin films were measured at 10 kHz and 300 K with a parallel-plate capacitor configuration. The results revealed that the dielectric tunability for ML films slightly decreased, while the loss decreased synchronously. The figure-of-merit factor value increases from 17.32 for BST films to 42.14 for ML films under an applied electric field of 300 kV/cm. The leakage current density of the BST thin films at a positive bias field of 300 kV/cm decreases from 3.76 × 10^-6 to 1.25 × 10^-7 A/cm² for ML films. This work clearly reveals the highly promising potential of BST/BZT/BST multilayer films compared with BST films for application in tunable microwave devices.