The application with protocatechualdehyde to improve anticoagulant activity and cell affinity of silk fibroin

Protocatechualdehyde (PCA) is one of the effective ingredients extracted from Danshen (Radix Salviae Miltiorrhizae) and was employed to modify the silk fibroin (SF) by graft polymerization and surface adsorption. The surface composition of modified SF was characterized by attenuated total reflectance Fourier-transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and UV spectrophotometer. The anticoagulant activity of modified SF was assessed by in vitro coagulation test and platelet adhesion measurement. The endothelial cell affinity was evaluated by a parallel plate flow chamber. The test results indicated that with the introduction of PCA into SF, the anticoagulant activity has been improved obviously. And the SF surface composition altered by PCA, but did not disturb its β-sheet conformation. Moreover, the adsorbed PCA on SF surface can enhance the endothelial cell affinity.     

Retardation of enzymatic degradation of microbial polyesters using surface chemistry: effect of addition of non-degradable polymers

The effects of addition of non-degradable polymers on the rate of enzymatic erosion for the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] have been studied at 37 °C and pH 7.4 in the aqueous solution of an extracellular PHB depolymerase from Alcaligenes facalis. Polystyrene (PS) or poly(methyl methacrylate) (PMMA) was selected as a minor component (5 wt%) in a blend because of their non-enzymatic activity. Enzymatic degradation behaviors of the “as-cast” and “annealed” blend films were investigated using atomic force microscopy and weight loss measurements. Although the spherulites of P(3HB-co-3HV) cover all blend film surfaces throughout, the retardation of biodegradation in the P(3HB-co-3HV)/PS blend films was detected from morphological observation and weight loss measurement for both as-cast and annealed blend films while there was little difference between the P(3HB-co-3HV)/PMMA blend and pure P(3HB-co-3HV). Since the enzymatic degradation of P(3HB-co-3HV) initially occurs by a surface erosion process, these degradation behaviors were explained by the surface structure of blend films measured by X-ray photoelectron spectroscopy. The surface of P(3HB-co-3HV)/PS blend films revealed an excess of PS, whereas the surface of P(3HB-co-3HV)/PMMA blend films was nearly covered by P(3HB-co-3HV). It was concluded, therefore, that the PS, which exists within P(3HB-co-3HV) spherulites at surface acts as a retardant of enzymatic attack to the surface of the blend film.     

Optical characterization of thermal-stress induced by spin waves in thin-film ferrimagnetic structures

It is shown that intense spin-dipole waves (SDWs) excited in thin yttrium iron garnet (YIG) films induce an in-plane thermal stress (σ) of 1-2 MPa in a YIG/GGG structure (where GGG is gadolinium gallium garnet). In YIG/GGG with normal magnetization, σ shifts its ferromagnetic resonance frequency by ≈1 MHz, which is comparable to the linewidth of the absorption curve of YIG/GGG resonators. The effect was characterized by an optical technique that detects σ in the GGG substrate. It was also demonstrated that this effect can be used for the optical-microwave spectroscopy of spin waves in thin ferromagnetic films, by using thermal mapping of SDWs in the substrate. We have shown that this opens up the possibility of determining the contribution of the two-particle magneto-elastic interaction to the microwave heating of the sample.     

Microstructural,dielectric and magnetic behavior of spin-deposited nanocrystalline nickel–zinc ferrite thin films for microwave applications

Nanocrystalline nickel ferrite and zinc doped nickel ferrite thin films with general composition Ni_1−xZn_xFe₂O₄; x=0.0, 0.2 and 0.5 were fabricated by the spin-deposition technique. Citrate precursor method was adopted to prepare coating solution used for film deposition. This method resulted in single phase, transparent, homogeneous and crack-free nanocrystalline ferrite thin films at annealing temperature as low as 400 °C. The substrates used for film deposition were ITO-coated 7059 glass, fused quartz and Si (1 0 0). The thickness of films was found to be in the range ∼1000–5500 Å. The surface microstructure and morphology investigated by atomic force microscopy (AFM) confirmed the grain size of nickel–zinc ferrite films to be in nanometer range indicating nanocrystalline nature of the films. Dielectric properties such as the real (∈′) and imaginary parts (∈″) of complex permittivity were measured in the X-band microwave frequency region (8–12 GHz) by employing extended cavity perturbation technique. The M–H hysteresis measurements on the films annealed at 650 °C revealed narrow hysteresis curves with H_c and M_s varying for different compositions.     

Influence of grain growth on the high-frequency behaviour of ferromagnetic Fe-Co-(M)-N (M=Ta, Hf) nanocomposite films

The CMOS compatible ferromagnetic Fe-Co-(M)-N (M=Ta, Hf) films were investigated with regard to their grain size-dependent frequency behaviour. Predominantly Fe₃₃Co₄₀Ta₁₀N₁₇ films were deposited by reactive r.f. magnetron sputtering. These films were compared to Fe₃₆Co₄₄Hf₉N₁₁ films. In order to induce an in-plane uniaxial anisotropy H_u as well as to investigate the grain growth behaviour, the films were annealed in a static magnetic field. The in-plane uniaxial anisotropy field of around 4 mT as well as a good soft magnetic behaviour with a saturation polarisation of approximately 1.2-1.4 T could be observed after heat treatment. Ferromagnetic resonance frequencies (FMR) of approximately up to 2.4 GHz could be achieved according to the Kittel theory. Depending on the heat treatment, high-frequency losses through energy dissipation was made conspicuous by means of the full-width at half-maximum (FWHM) Δf_eff of the imaginary part of the frequency-dependent permeability which was between 0.4 and 1 GHz. This FWHM was basically discussed in terms of two-magnon scattering theories, in combination with the Herzer random anisotropy model. In order to correlate the resonance line broadening with a phenomenological damping parameter α_eff, which ranged from about 0.0125 to 0.028, the modified Landau-Lifschitz-Gilbert equation was used to fit and describe the permeability spectra of the ferromagnetic films.     

Ferromagnetism in MnxGe1−x films prepared by magnetron sputtering

Mn_xGe_1−x thin films were prepared by magnetron sputtering with a substrate temperature of 673 K and subsequently annealed at 873 K. The X-ray diffraction (XRD) measurements showed that all samples had a single Ge cubic structure. No films showed clear magnetic domain structure under a magnetic force microscope (MFM). Atom force microscope (AFM) measurements showed that the films had an uniform particle size distribution, and a columnar growth pattern. X-ray photoelectron spectroscopy (XPS) measurements indicated that the valences of both Mn and Ge atoms increase with the Mn concentration. The resistance decreased with increasing temperature, suggesting that the films were typical semiconductors. Magnetic measurements carried out using a Physical Property Measurement System (PPMS) showed that all samples exhibited ferromagnetism at room temperature. There was a small concentration of Mn₁₁Ge₈ in the films, but the ferromagnetism was mainly induced by Mn substitution for Ge site.     

Photosensitivity of nanocrystalline ZnO films grown by PLD

We have studied the properties of ZnO thin films grown by laser ablation of ZnO targets on (0 0 0 1) sapphire (Al₂O₃), under substrate temperatures around 400 °C. The films were characterized by different methods including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and atomic force microscopy (AFM). XPS analysis revealed that the films are oxygen deficient, and XRD analysis with θ-2θ scans and rocking curves indicate that the ZnO thin films are highly c-axis oriented. All the films are ultraviolet (UV) sensitive. Sensitivity is maximum for the films deposited at lower temperature. The films deposited at higher temperatures show crystallite sizes of typically 500 nm, a high dark current and minimum photoresponse. In all films we observe persistent photoconductivity decay. More densely packed crystallites and a faster decay in photocurrent is observed for films deposited at lower temperature.     

C-V studies on metal-ferroelectric bismuth vanadate (Bi2VO5.5)-semiconductor structure

Ferroelectric bismuth vanadate Bi₂VO_5.5 (BVO) thin films have been successfully grown on p-type Si(100) substrate by using chemical solution decomposition (CSD) technique followed by rapid thermal annealing (RTA). The crystalline nature of the films has been studied by X-ray diffraction (XRD). Atomic force microscopy (AFM) was used to study the microstructure of the films. The dielectric properties of the films were studied. The capacitance-voltage characteristics have been studied in metal-ferroelectric-insulator-semiconductor (MFIS) configuration. The dielectric constant of BVO thin films formed on Si(100) is about 146 measured at a frequency of 100 kHz at room temperature. The capacitance-voltage plot of a Bi₂VO_5.5 MFIS capacitor subjected to a dc polarizing voltages shows a memory window of 1.42 V during a sweep of ±5 V gate bias. The flatband voltage (V_f) shifts towards the positive direction rather than negative direction. This leads to the asymmetric behavior of the C-V curve and decrease in memory window. The oxide trap density at a ramp rate of 0.2 V/s was estimated to be as high as 1.45×10¹² cm⁻².     

Orbital currents and charge density waves in a generalized Hubbard ladder

We study a generalized Hubbard model on the two-leg ladder at zero temperature, focusing on a parameter region with staggered flux (SF)/d-density wave (DDW) order. To guide our numerical calculations, we first investigate the location of a SF/DDW phase in the phase diagram of the half-filled weakly interacting ladder using a perturbative renormalization group (RG) and bosonization approach. For hole doping δ away from half-filling, finite-system density-matrix renormalization-group (DMRG) calculations are used to study ladders with up to 200 rungs for intermediate-strength interactions. In the doped SF/DDW phase, the staggered rung current and the rung electron density both show periodic spatial oscillations, with characteristic wavelengths 2/δ and 1/δ, respectively, corresponding to ordering wavevectors 2k_F and 4k_F for the currents and densities, where 2k_F = π (1 − δ). The density minima are located at the anti-phase domain walls of the staggered current. For sufficiently large dopings, SF/DDW order is suppressed. The rung density modulation also exists in neighboring phases where currents decay exponentially. We show that most of the DMRG results can be qualitatively understood from weak-coupling RG/bosonization arguments. However, while these arguments seem to suggest a crossover from non-decaying correlations to power-law decay at a length scale of order 1/δ, the DMRG results are consistent with a true long-range order scenario for the currents and densities.     

Structure, magnetic and magnetostrictive properties of as-deposited Fe-Ga thin films

Polycrystalline Fe_100−xGa_x (19?x?23) films were grown on Si(1 0 0) substrates at different partial pressures of sputtering gas ranging from 3 to 7 μbar. Microstructural, magnetic and magnetostrictive properties were studied using X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and magneto-optic Kerr effect (MOKE) magnetometry respectively. X-ray diffraction showed that all films have the body-centered cubic (bcc) Fe-Ga phase with the 〈1 1 0〉 direction out of the film plane. Magnetic characterization of the films showed that the films prepared at 3 μbar had weak uniaxial anisotropy whereas films grown at Ar pressures in the range 4-7 μbar were magnetically isotropic. The effective saturation magnetostriction constants (λ_eff) of the films were measured using the Villari effect. It was found that effective saturation magnetostriction constants were almost constant over the Ga composition range achieved by varying the sputtering pressure. The measured effective magnetostriction constants fit closely to the calculated saturation magnetostriction constants of 〈1 1 0〉 textured polycrystalline films with the 〈1 1 0〉 directions slightly canted with respect to the normal to the sample surface. It was found that a high pressure of the sputtering gas effected the magnetic softness of the films. The saturation field increased and remanence ratio decreased with increase in pressure.     

Conductance and EPR study of the endohedral fullerene Li@C60

Thin films and bulk samples of endohedral fullerenes Li@C₆₀ are studied using current-voltage (I-V) measurements and electron paramagnetic resonance (EPR). Electrical measurements show a linear behaviour for the I-V curves and give an average resistivity of ca. 1.5 kΩcm for thin Li@C₆₀ films deposited in vacuum, four orders of magnitude lower than C₆₀ samples. A drastic effect on the conductance, lowering it to the values typical for C₆₀, is observed when the Li@C₆₀ samples are exposed to ambient atmosphere. No additional paramagnetic centres (PCs) are found for the Li@C₆₀ compared to C₆₀ that can be related to the formation of dimers or trimers of the endohedral fullerene molecules. However, the presence of the Li atoms in the fullerene cages contributes to a change of the spin-spin and spin-lattice relaxation times. The spin-lattice relaxation time becomes four orders of magnitude longer compared to the spin-spin relaxation time.     

Efficient field emission from well-oriented Cu2O film

Well-oriented Cu₂O films comprising of octahedral-shaped crystals were grown directly on copper foil via an hydrothermal treatment. The well-oriented films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Field emission from the film showed good emission properties, and, the electron emission turn-on field (E_to) and threshold field (E_thr) are about 9.6 and 13.4 V/μm respectively, which is similar to the values reported for CuO nanofiber, although the latter has a much larger size. The corresponding Fowler-Nordheim (F-N) plots showed a linear behavior. The sharp corners of the tips are considered as main electron emitters and account for its good performance.     

Pulsed laser deposition of polyhydroxybutyrate biodegradable polymer thin films using ArF excimer laser

We demonstrated the pulsed laser deposition (PLD) of high quality films of a biodegradable polymer, the polyhydroxybutyrate (PHB). Thin films of PHB were deposited on KBr substrates and fused silica plates using an ArF (λ = 193 nm, FWHM = 30 ns) excimer laser with fluences between 0.05 and 1.5 J cm⁻². FTIR spectroscopic measurements proved that at the appropriate fluence (0.05, 0.09 and 0.12 J cm⁻²), the films exhibited similar functional groups with no significant laser-produced modifications present. Optical microscopic images showed that the layers were contiguous with embedded micrometer-sized grains. Ellipsometric results determined the wavelength dependence (λ ∼ 245-1000 nm) of the refractive index and absorption coefficient which were new information about the material and were not published in the scientific literature. We believe that our deposited PHB thin films would have more possible applications. For example to our supposal the thin layers would be applicable in laser induced forward transfer (LIFT) of biological materials using them as absorbing thin films.     

High Curie temperature in B-site ordered Sr2CrWO6 epitaxial thin films

Epitaxial and c-axis oriented double perovskite Sr₂CrWO₆ thin films were prepared on SrTiO₃ (100) and LaAlO₃ (100) substrates by pulsed-laser deposition. Structural, magnetic and transport properties were found to be sensitive to the gas conditions employed during the deposition. A small amount of oxygen along with Ar during the deposition was found to be essential for B-site ordering; such films displayed lattice parameters close to the bulk value and display ferromagnetic metallic behavior. The Curie temperature observed above 500 K in these films is higher than bulk Sr₂CrWO₆ samples. Films grown without oxygen were observed to have long c-parameter and no B-site ordering; they were non-magnetic and semiconducting.     

Low-frequency excess noise characterizations of laser-assisted de-bonded GaN films

Systematic characterization of flicker noise was conducted on GaN-based metal-semiconductor-metal (MSM) interdigitated devices. The devices were fabricated on both the regular GaN-on-sapphire (type A) and laser de-bonded films followed by layer transfer of hydride vapor phase epitaxy-grown GaN films to Si substrates (type B). Experimental results indicated no significant degradation in the I-V characteristics for Schottky MSM devices fabricated on type B films compared to those fabricated on type A films. However, substantial increase in the flicker noise level, particularly in the low-temperature regime, is observed among the ohmic MSM devices fabricated on type B films. The experimental data suggest that material degradation occurs at the vicinity of the GaN-sapphire interface, while in regions close to the GaN film surface there is practically no change in the film quality. This is supported by finite element simulation of the temperature of the film during laser irradiation. The results indicate that the temperature dropped from 1400 K at the GaN-sapphire interface to about 1000 K within 0.5 μm away from the interface stipulating that material degradation occurs only within 0.5 μm from the GaN-sapphire interface.     

Damping and ferromagnetic resonance linewidth broadening in nanocrystalline soft ferromagnetic Fe–Co–Hf–N films

In order to describe high-frequency damping mechanisms of ferromagnetic films by means of the imaginary part of the frequency-dependant permeability, CMOS compatible ferromagnetic Fe₃₆Co₄₄Hf₉N₁₁ films were deposited by reactive r.f. magnetron sputtering on oxidised 5×5 mm²×380 μm (1 0 0)-silicon substrates with a 6-in. Fe₃₈Co₄₇Hf₁₅ target, as well as magnetic field annealing between 300 and 600 °C. An in-plane uniaxial anisotropy of around 4.5 mT as well as an excellent soft magnetic behaviour with a saturation polarisation of approximately 1.4 T could be observed after heat treatment at the above-mentioned temperatures, which drives these films to a high-frequency suitability. Ferromagnetic resonance frequencies of approximately up to 2.4 GHz could be obtained. The frequency-dependant permeability was measured with a broadband permeameter. Depending on the heat treatment, an increase of the full-width at half-maximum (FWHM) of the imaginary part of the frequency-dependant permeability is discussed in terms of two-magnon scattering, anisotropy-type competition and local resonance generation through predominant grain growth causing magnetisation and anisotropy inhomogeneities in the magnetic films. The grain size of the films was determined by (HRTEM) imaging and amounts from a few nanometres for films heat treated at 300 °C to more than 10 nm at 600 °C where the FWHM Δf_eff and the Landau–Lifschitz–Gilbert equation damping parameter α_eff increases with d_nm² and d_nm (e.g. d_nm is the grain diameter of the nonmagnetic Hf–N phase), respectively.     

On the relation between the effective ferromagnetic resonance linewidth Δfeff and damping parameter αeff in ferromagnetic Fe-Co-Hf-N nanocomposite films

Ferromagnetic Fe-Co-Hf-N nanocomposite films were investigated concerning their microstructure-dependent frequency behaviour. To modify the composition, the films were deposited by reactive RF magnetron sputtering by using three different 6 in. targets with various Hf fractions. The films were post-annealed up to 600 °C in a static magnetic field to induce an in-plane uniaxial anisotropy and to obtain different crystal sizes. Depending on the annealing temperature, high-frequency losses were investigated by considering the full-width at half-maximum (FWHM) Δf_eff of the imaginary part of the frequency-dependent permeability which showed a resonance frequency f_FMR of 2.3 GHz for an in-plane uniaxial anisotropy field H_u of 4 mT. The FWHM in correlation with the damping parameter α_eff is discussed, e.g., in terms of two-magnon scattering. Damping occurs due to film inhomogeneity in magnetisation and uniaxial anisotropy caused by a magnetocrystalline anisotropy H_a and/or non-magnetic phases. This will result in homogenous or even inhomogeneous resonance line broadening if additional and resonance as well as precession frequencies of independent grains arise.     

Microstructures and coercivities of SmCox and Sm(Co,Cu)5 films prepared by magnetron sputtering

We have investigated the influence of composition and annealing conditions on the magnetic properties and microstructural features of SmCo_x films that were prepared by sputtering and subsequent annealing. A huge in-plane coercivity of 5.6 T was obtained from an optimally annealed Sm–Co film, which was attributed to the nanometer sized polycrystalline microstructure of the highly anisotropic SmCo₅ phase. Although a high density of planar defects were observed in the films that were annealed at high temperatures, they did not act as strong pinning sites for domain wall motion. The effect of Cu on [SmCo_4.5(9 nm)/Cu(xnm)]₁₀ multilayer thin films was also studied. An appropriate Cu content increased the coercivity.     

Temperature-dependent ferroelectric and dielectric properties of Bi3.25La0.75Ti3O12 thin films

To investigate temperature-dependent ferroelectric and dielectric properties of ferroelectric films, Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were prepared on Pt-coated silicon substrates by pulsed laser deposition. The ferroelectric and dielectric behaviors have been studied in a wide temperature range from 80 K to room temperature. The saturated polarization (P_sat) decreases with decreasing temperature and decreasing electric field, whereas remnant polarization (P_r) shows a more complex temperature dependence. These results, which can be well explained based on a temperature-dependent charged defects-domain wall interaction model, might be helpful for further understanding the domain switching behavior. Based on these results, an alternative way to investigate temperature-dependent ferroelectric fatigue is proposed and experimentally carried out. The measured fatigue rate is found to be linearly dependent on temperature, consistent with the report on Pb(Zr,Ti)O₃ films. Temperature-dependent dielectric measurements of the films further confirm the above explanation.     

Microstructure and interfacial properties of HfO2-Al2O3 nanolaminate films

High-k HfO₂-Al₂O₃ composite gate dielectric thin films on Si(1 0 0) have been deposited by means of magnetron sputtering. The microstructure and interfacial characteristics of the HfO₂-Al₂O₃ films have been investigated by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and spectroscopic ellipsometry (SE). Analysis by XRD has confirmed that an amorphous structure of the HfO₂-Al₂O₃ composite films is maintained up to an annealing temperature of 800 °C, which is much higher than that of pure HfO₂ thin films. FTIR characterization indicates that the growth of the interfacial SiO₂ layer is effectively suppressed when the annealing temperature is as low as 800 °C, which is also confirmed by spectroscopy ellipsometry measurement. These results clearly show that the crystallization temperature of the nanolaminate HfO₂-Al₂O₃ composite films has been increased compared to pure HfO₂ films. Al₂O₃ as a passivation barrier for HfO₂ high-k dielectrics prevents oxygen diffusion and the interfacial layer growth effectively.