Storage moduli, loss moduli and damping factor of GaAs and Ga1-xMnxAs thin films using DMA 2980

The spin injector part of spintronic FET and diodes suffers from fatigue due to rising heat on the depletion layer. In this study the stiffness of Ga1-xMnxAs spin injector in terms of storage modulus with respect to a varying temperature, 45 degrees C <= T <= 70 degrees C was determined. It was observed that the storage modulus for MDLs (Manganese Doping Levels) of 0%, 1% and 10% decreased with increase in temperature while that with MDLs of 20% and 50% increase with increase in temperature. MDLs of 20% and 50% appear not to allow for damping but MDLs <= 20% allow damping at temperature range of 45 degrees C <= T <= 70 degrees C. The magnitude of storage moduli of GaAs is smaller than that for ferromagnetic Ga1-xMnxAs systems. The loss moduli for GaAs were found to reduce with increase in temperature. Its magnitude of reducing gradient is smaller than Ga1-xMnxAs systems. The two temperature extremes show a general reduction in loss moduli for different MDLs at the study temperature range. From damping factor analysis, damping factors for ferromagnetic Ga1-xMnxAs was found to increase with decrease in MDLs contrary to GaAs which recorded the largest damping factor at 45 degrees C <= T <= 70 degrees C Hence, MDL of 20% shows little damping followed by 50% while MDL of 0% has the most damping in an increasing trend with temperature. (C) 2013 Elsevier Ltd. All rights reserved.

Structural, dielectric, ferroelectric and optical properties of PBCT, PBST and PCST complex thin films on LaNiO3 metallic conductive oxide layer coated Si substrates by the CSD technique

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Determination of carrier mobility in MEH-PPV thin-films by stationary and transient current techniques

Charge transport and shelf-degradation of MEH-PPV thin-films were investigated through stationary (e.g. current versus voltage - JxV) and transient (e.g. Time-of-Flight - ToF, Dark-Injection Space-Charge-Limited Current - DI-SCLC, Charge Extraction by Linearly Increasing Voltage - CELN) current techniques. Charge carrier mobility in nanometric films was best characterized through JxV and DI-SCLC. It approaches 10(-6) cm(2)Ns under a SCLC regime with deep traps for light-emitting diode applications. ToF measurements performed on micrometric layers (i.e. - 3 mu m) confirmed studies in 100 nm-thick films as deposited in OLEDs. All results were comparable to a similar poly(para-phenylene vinylene) derivative, MDMO-PPV. Electrical properties extracted from thin-film transistors demonstrated mobility dependence on carrier concentration in the channel (similar to 10(-7)-10(-4) cm(2)/Vs). At low accumulated charge levels and reduced free carrier concentration, a perfect agreement to the previously cited techniques was observed. Degradation was verified through mobility reduction and changes in trap distribution of states. (C) 2011 Elsevier B.V. All rights reserved.

Concentration quenching and thermal activation of the luminescence from terbium-doped a-SiC:H and c-AlN thin films

The effect of terbium (Tb) doping on the photoluminescence (PL) of crystalline aluminum nitride (c-AlN) and amorphous hydrogenated silicon carbide (a-SiC:H) thin films has been investigated for different Tb atomic concentrations. The samples were prepared by DC and RF magnetron reactive sputtering techniques covering the concentration range of Tb from 0.5 to 11 at.%. The Tb-related light emission versus the Tb concentration is reported for annealing temperatures of 450 °C, 750 °C and 1000 °C. In the low concentration region the intensity exhibits a linear increase and its slope is enhanced with the annealing temperature giving an activation energy of 0.106 eV in an Arrhenius plot. In the high concentration region an exponential decay is recorded which is almost independent on the host material, its structure and the annealing process.

As-deposited near-single crystalline high Tc and Jc superconducting thin films by a pulsed lased deposition process

As-deposited high Tc superconducting Y1Ba2Cu3O7−x films with zero resistance temperatures of similar, equals89 K and critical current densities about 0.7×106 A/cm2 at 77 K have been reproducibly fabricated at a substrate holder temperature at 650°C, using pulsed laser deposition, without post-annealing. One key to these results is the injection of gaseous oxygen into laser produced plume just in front of the target. In this way, the correct amount of oxygen is incorporated into the as-grown film so that post-deposition treatment becomes unnecessary. Axial ion channeling in these as-deposit high Tc superconducting films on (100) SrTiO3 and X-ray photoelectron spectroscopy (XPS) on the film surfaces were performed. Angular yield profile near the film surface for Ba, and the surface peak intensity were measured using 3 MeV He ions. For channeling normal to the substrate a minimum yield of 7%, compared to similar, equals3% for single crystals, was obtained. The results of ion channeling and XPS studies indicate that the as-deposited films have good crystallinity as well as toichiometry to within similar, equals1 nm of the film surface. The in-situ growth of such high Tc and Jc films is an important step in the use of the laser deposition technique to fabricate multilayer structures and the surface perfection is of importance in tunneling devices such as Josephson junctions.

Anisotropic electrical transport property in La4BaCu5O13+δ and La4BaCu4NiO13+δ epitaxial thin films

Epitaxial films of La4BaCu5O13+δ and La4BaCu4NiO13+δ oxides are grown with a-b plane parallel to (100) of LaAlO3 and SrTiO3 by pulsed-laser deposition. The conductivity measurements performed along the c direction using LaNiO3 as the electrode show metallic behavior whereas they show semiconducting behavior in the a-b plane. Anisotropic transport property of these thin films is explained on the basis of nearly 180° connected Cu–O–Cu chains with an average Cu–O distance of 1.94 Å along the c direction and nearly 180° and 90° connected Cu–O–Cu chains in the a-b plane with short and long Cu–O distances ranging from 1.863 to 2.303 Å. YBa2Cu3O7−x has been grown along (00l) on La4BaCu5O13+δ and shows a Tc of 88 K.

Room-temperature ferromagnetism in zinc-blende and deformed CrAs thin films

We try to clarify the controversy about the origin of room-temperature ferromagnetism in a CrAs compound. Two kinds of CrAs thin films were grown on GaAs by molecular-beam epitaxy. Structural analyses confirm that the as-grown CrAs film is a pure zinc-blende phase. Magnetic measurements suggest that room-temperature ferromagnetism exists in zinc-blende CrAs. In contrast, the CrAs film turns into a mixture of zinc-blende and deformed CrAs after annealing. A ferromagnetic signal measured at room temperature demonstrates that zinc-blende CrAs remains room-temperature ferromagnetism even when it is partly deformed into a non-zinc-blende phase. (c) 2006 American Institute of Physics.

Tribocorrosion behavior of Ti-C-O-N nanostructured thin films (black) for decorative applications

Abstract: In the past few years, tribocorrosion has become a focus of research because of its relevance in terms of the future in-service degradation mechanisms of materials. In the particular case of decorative coatings, tribocorrosion is certainly one of the most important issues, and sweat corrosion and human contact wear are two other factors that may act as material selection tools. Thus, the current study aimed to investigate the tribocorrosion behavior of a new class of thin films, the Ti-C-O-N system, which is being developed to be used as a surface decorative material due to its relatively dark appearance. The films were prepared by reactive magnetron sputtering. The influence of the structural features on the tribocorrosion behavior is discussed. Crown Copyright © 2013.

Patterning optically clear films: co-planar transparent and color-contrasted thin films from interdiffused electrodeposited and solution-processed metal oxides

Transparent thin films can now be site-selectively patterned and positioned on surface using mask-defined electrodeposition of one oxide and overcoating with a different solution-processed oxide, followed by thermal annealing. Annealing allows an interdiffusion process to create a new oxide that is entirely transparent. A primary electrodeposited oxide can be patterned and the secondary oxide coated over the entire substrate to form high color contrast coplanar thin film tertiary oxide. The authors also detail the phase formation and chemical state of the oxide and how the nature of the electrodeposited layer and the overlayer influence the optical clearing of the patterned oxide film.

Study of in situ laser deposited YBCO thin films

YBCO thin films were fabricated by laser deposition, in situ on MgO substrates, using both O2 and N2O as process gas. Films with Tc above 90 K and jc of 106 A/cm2 at 77 K were grown in oxygen at a substrate temperature of 765 °C. Using N2O, the optimum substrate temperature was 745 °C, giving a Tc of 87 K. At lower temperatures, the films made in N2O had higher Tc (79 K) than the films made in oxygen (66 K). SEM and STM investigations of the film surfaces showed the films to consist of a comparatively smooth background surface and a distribution of larger particles. Both the particle size and the distribution density depended on the substrate temperature.

Complex permittivity measurements of RF plasma polymerized polyterpenol organic thin films employing split post dielectric resonator

In the fields of organic electronics and biotechnology, applications for organic polymer thin films fabricated using low-temperature non-equilibrium plasma techniques are gaining significant attention because of the physical and chemical stability of thin films and the low cost of production. Polymer thin films were fabricated from non-synthetic terpinen-4-ol using radiofrequency polymerization (13.56 MHz) on low loss dielectric substrates and their permittivity properties were ascertained to determine potential applications for these organic films. Real and imaginary parts of permittivity as a function of frequency were measured using the variable angle spectroscopic ellipsometer. The real part of permittivity (k) was found to be between 2.34 and 2.65 in the wavelength region of 400–1100 nm, indicating a potential low-k material. These permittivity values were confirmed at microwave frequencies. Dielectric properties of polyterpenol films were measured by means of split post dielectric resonators (SPDRs) operating at frequencies of 10 GHz and 20 GHz. Permittivity increased for samples deposited at higher RF energy – from 2.65 (25 W) to 2.83 (75 W) measured by a 20-GHz SPDR and from 2.32 (25 W) to 2.53 (100 W) obtained using a 10-GHz SPDR. The error in permittivity measurement was predominantly attributed to the uncertainty in film thickness measurement.

Enhancement of uniaxial magnetic anisotropy in Fe thin films grown on GaAs(001) with an MgO underlayer

The understanding and control of anisotropy in Fe films grown on cubic systems such as GaAs and MgO has been of interest from the point of view of applications in devices. We report magnetic anisotropy studies on Fe/GaAs(001) and Fe/MgO/GaAs(001) prepared by pulsed laser deposition. In Fe/GaAs(001), magneto optical Kerr effect (MOKE) measurements revealed a dominant uniaxial anisotropy for Fe thickness less than 20 monolayers (ML) and this was confirmed by ferromagnetic resonance (FMR) studies. Multiple steps in the hysteresis loops were observed for Fe films of thickness 20 and 25 ML. Whereas, in Fe/MgO/GaAs(001), even at 25 ML of Fe, the uniaxial anisotropy remained dominant. The anisotropy constants obtained from FMR spectra have shown that the relative strength of uniaxial anisotropy is higher as compared to the cubic anisotropy constant in the case of Fe/MgO/GaAs(001). (C) 2011 American Institute of Physics. doi:10.1063/1.3556941]

ac transport studies of La-modified antiferroelectric lead zirconate thin films

In recent times antiferroelectric thin-film material compositions have been identified as one of the most significant thin films for development of devices such as high charge storage, charge couplers/decouplers, and high strain microelectromechanical systems. Thus, understanding the dielectric and electrical properties under an ac signal drive in these antiferroelectric thin-film compositions, such as lead zirconate thin films, and the effect of donor doping on them is very necessary. For this purpose, thin films of antiferroelectric lead zirconate and La-modified lead zirconate thin films with mole % concentrations of 0, 3, 5, and 9 have been deposited by pulsed excimer laser ablation. The dielectric and hysteresis properties have confirmed that with a gradual increase of the La content, the room-temperature antiferroelectric lead zirconate thin films can be modified into ferroelectric and paraelectric phases. ac electrical studies revealed that the polaronic related hopping conduction is responsible for the charge transport phenomenon in these films. With a La content of less than or equal to3 mole % in pure lead zirconate, the conductivity of the films has been reduced and followed by an increase of its conductivity for a greater than or equal to3% addition of La to lead zirconate thin films. The polaronic activation energies are also found to follow a similar trend as that of the conductivity.

Dielectric Studies of laser ablated Ca doped BaTiO3 thin films

Recently, there has been growing interest in Ca modified BaTiO3 structures due to their larger electro-optic coefficients for their use in optical storage of information over conventional BaTiO3 crystals. Barium Calcium Titanate (BCT) shows promising applications in advanced laser systems, optical interconnects and optical storage devices. BaTiO3 thin films of varied Ca (3 at. % - 15 at. %) doping were deposited using pulsed laser ablation (KrF excimer laser) technique over Pt/Si substrates. The stoichiometric and the compositional analysis were carried out using EDAX and SIMS. The dielectric studies were done at the frequency regime of 40 Hz to 100 kHz at different ambient temperatures from 200 K to 600 K. The BCT thin films exhibited diffuse phase transition, which was of a typical non lead relaxor behavior and had high dielectric constant and low dielectric loss. The phase transition for the different compositions of BCT thin films was near the room temperature, showing a marked departure from the bulk phase transition. The C - V and the hysteresis behavior confirmed the ferroelectric nature below the phase transition and paraelectric at the room temperature.

Dielectric Properties of Pulsed Excimer Laser Ablated BaBi2Nb2O9 Thin Films

The dielectric response of BaBi2Nb2O9 (BBN) thin films has been studied as a function of frequency over a wide range of temperatures. Both dielectric constant and loss tangent of BBN thin films showed a ‘power law’ dependence with frequency, which was analyzed using the Jonscher's universal dielectric response model. Theoretical fits were utilized to compare the experimental results and also to estimate the value of temperature dependence parameters such as n(T) and a(T) used in the Jonscher's model. The room temperature dielectric constant (ε') of the BBN thin films was 214 with a loss tangent (tanδ) of 0.04 at a frequency of 100 kHz. The films exhibited the second order dielectric phase transition from ferroelectric to paraelectric state at a temperature of 220 °C. The nature of phase transition was confirmed from the temperature dependence of dielectric constant and sponteneous polarization,respectively. The calculated Currie constant for BBN thin films was 4 × 105°C.