Changes In Film Structure Research Articles

Effect of Indium Mole Fraction on the Diode Characteristics of ZnO:In/p-Si(111) Heterojunctions

We investigated the effect of indium (In) doping (0.6, 1, 5, and 10 at. %) on the diode characteristics of heterostructures consisting of In-doped ZnO films on p-Si(111) substrates. In-doped ZnO films were deposited by pulsed laser deposition with an In-doped ZnO target, and heterojunction diodes were fabricated by photolithography and a lift-off method. The electrical properties of ZnO films were altered by In doping, with the In (10 at. %)-doped ZnO film having the highest electron concentration (3.0×1019 cm-3) and lowest resistivity (1.5×10-2 Ω·cm) of the analyzed ZnO films. In doping also had a strong effect on diode characteristics. In particular, In-doped ZnO/p-Si diodes show a very low reverse current density of approximately 2.8×10-6 A/cm2 (In 10 at. %) at -5 V and a high on–off ratio (In 10 at. %) of about 2.5×10-6 at ±5 V. The heterostructure diodes exhibited typical current–voltage characteristics with turn-on voltages in the range 1.2–2.4 V and series resistances in the range 37–99 Ω. The modified diode characteristics may be related to changes in the ZnO film structure induced by In doping. We also discuss the effect on diode characteristics of In doping of ZnO films.

Atomic-scale study of structural change of TiAl alloy film during the cooling process

Microstructural changes of molten TiAl films are investigated by using molecular dynamics simulations within the framework of embedded atom method in quenching and continuous cooling processes. Atomic local structures in these films are analyzed by using atom average energy, pair distribution functions, and pair analysis technique. The local structure changes in the TiAl films can be divided in to three stages on quenching, and they are divided in to two stages on continuous cooling.

Nucleation and Growth Mechanism of Electropolymerization of Methylene Blue: The Effect of Preparation Potential on Poly(methylene blue) Structure

AbstractNucleation and growth mechanism of electropolymerization of methylene blue (MB) in a basic medium and the effect of preparation potential on poly(MB) film structure were investigated by using cyclic voltammetry, potentiostatic current‐time transient, scanning tunneling microscopy (STM), atomic force microscopy (AFM), and UV‐vis. absorption spectroscopy techniques. Electropolymerization of MB has been achieved by potentiodynamic (cyclic voltammetry) and potentiostatic (constant potential) techniques. The potentiostatic current‐time transients fitted with a theoretical model and morphological studies indicate that nucleation and growth mechanism of poly(MB) starts with a progressive layer‐by‐layer nucleation and growth besides random adsorption. Nucleation and growth of poly(MB) follows a process between progressive layer‐by‐layer and 3‐D instantaneous mechanism resulting in highly‐oriented poly(MB) nanofibers with increasing poly(MB) film thickness. Cyclic voltammetry and morphological studies exhibit that poly(MB) film structure changes depending on the preparation potential. Poly(MB) films prepared at the potential values of 900 and 950 mV show a well‐ordered, smooth surface but at the potential values higher than 1000 mV, rough polymer surface arises as overoxidation takes place. UV‐vis. absorption spectra of poly(MB) film and MB monomer show three peaks. The peak at 410 nm for poly(MB) shows 100 nm blue shift when compared to the MB monomer and is attributed to poly(MB) formation on the electrode.

Study of gas film quality in electrochemical discharge machining

Electrochemical Discharge Machining (ECDM) has been demonstrated to be an alternative spark-based micromachining method for fabricating microholes and microchannels in non-conductive brittle materials. However, the mechanism for attaining accurate control of the contour shape and dimensions remains to be explored. In ECDM process, the gas film on the electrode surface is used as the dielectric medium required for discharge generation. Quality of gas film is the dominant factor that determines the machining qualities such as geometric accuracy, surface roughness and repeatability. Nevertheless, it is difficult to assess the gas film quality of ECDM. In this study, current signals and machined contours were taken as indexes of gas film quality. Experimental results showed that a stable and dense gas film could be obtained when the applied voltage exceeded the critical voltage and reached a specific level, which is called the “transition voltage” in this study. At the transition voltage, a stable electrochemical discharge activity could be generated, thus producing the smallest deviation of contour dimensions. Moreover, when the drilling process reached a certain critical depth, bubbles inside the hole could not easily escape. In order to reduce the interface energy between bubbles, a thicker gas film is formed at the hole entrance, resulting in unstable discharge performance that undermined machining results. In summary, information provided by current signals can shed light on the changes in gas film structure, which serve as useful reference for varying process parameters to achieve better efficiency and accuracy.

Optically induced magnetization dynamics and variation of damping parameter in epitaxialCo2MnSiHeusler alloy films

All-optical pump-probe measurements of magnetization dynamics have been performed upon epitaxial ${\text{Co}}_{2}\text{MnSi}(001)$ Heusler alloy thin films annealed at temperatures of 300, 400, and $450\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$. An ultrafast laser-induced modification of the magnetocrystalline anisotropy triggers precession which is detected by time-resolved magneto-optical Kerr effect measurements. From the damped oscillatory Kerr rotation, the frequency and relaxation rate of the precession is determined. Using a macrospin solution of the Landau-Lifshitz-Gilbert equation the effective fields acting upon the sample magnetization are deduced. This reveals that the magnetization is virtually independent of the annealing temperature while the fourfold magnetocrystalline anisotropy decreases dramatically with increasing annealing temperature as the film structure changes between the B2 and $\text{L}{2}_{1}$ phases. From the measured relaxation rates, the value of the apparent Gilbert damping parameter is found to depend strongly upon the static field strength and in-plane static field orientation. The variation of the apparent damping parameter is generally well reproduced by an inhomogeneous broadening model in which the presence of B2 and $\text{L}{2}_{1}$ phases leads to a large dispersion of the magnetocrystalline anisotropy. However, for the sample annealed at a temperature of $300\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$, the lack of a detailed fit to the data suggests that the apparent anisotropy of the apparent damping parameter might alternatively arise due to a network of dislocations with fourfold symmetry.

Investigating polysilicon thin film structural changes during rapid thermal annealing of a thin film crystalline silicon on glass solar cell

Structural changes resulting from rapid thermal annealing were investigated in a thin film crystalline silicon on textured glass solar cell, in particular grain parameters and film modulus. Electron backscatter diffraction showed no significant change in grain dimensions post annealing and no preferred orientation. Columnar grains with large defect densities were visible in transmission electron microscopy with no qualitative change visible post annealing. A similar modulus obtained by nanoindenation, both pre and post annealing suggests no quantitative structural change. The film structure appears unchanged by rapid thermal annealing.

Raman investigation of ion-implanted ZnO films

ZnO thin films were implanted at room temperature with 80 keV N+ or 400 keV Xe+ ions. The implantation fluences of N+ and Xe+ ranged from 5.0×1014 to 1.0×1017/cm2, and from 2.0×1014 to 5.0×1015/cm2, respectively. The samples were analyzed using Raman spectroscopy and the Raman scattering modes of the N- and Xe-ion implanted samples varying with implantation fluences were investigated. It was found that Raman peaks (bands) at 130 and 578 cm-1 appeared in the spectra of ion-implanted ZnO samples, which are independent of the ion species, whereas a new peak at 274 cm-1 was found only in N-ion implanted samples, and Raman band at 470 cm-1 was found clearly in Xe-ion implanted samples. The relative intensity (peak area) increased with the increasing of the implantation fluences. From the comparison of the Raman spectra of N- and Xe-ion implanted ZnO samples and considering the damage induced by the ions, we analyzed the origin of the observed new Raman peaks (bands) and discussed the structure changes of ZnO films induced by N- and Xe-ion implantations.

S1108-2-4 DLC膜の構造変化に及ぼす熱および摺動の影響([S1108-2]卒業研究コンテスト(2))

Diamond-like carbon (DLC) films are expected to use in various applications such as cutting tool, steel mold, general machinery elements. On the other hands, there are some practical subjects for DLC films. Particularly, such as heat proof, deregulation of residual stress and improvement of adherence are focused on in general. In this study, we focused on the heat proof to utilize the DLC films which the surface becomes high temperature. Ball on disk tester and micro laser Raman spectroscopy are employed to research the effects of applied heat and sliding on structure changes on the DLC films. In this study, ball on disk test after heating at 300℃. 350℃, 400℃ are accomplished. Then, the structure changes of the DLC films are analyzed by micro laser Raman spectroscopy.

A High Corrosion and Wear Resistant Interior Surface Coating for Use in Oilfield Applications

A novel technique for depositing thick DLC based films on the inside of cylindrical substrates, like pipes, tubes and valves, has been developed. A plasma enhanced chemical vapour deposition (PECVD) technique has been used to engineer and optimize the above mentioned films for maximum coating performance. Of particular importance is the corrosion and wear resistant qualities of these films. Changes in film chemistry, structure and thickness are attributed to the improved corrosion and wear resistance. Details will be given of the corrosion testing which has taken place, such as exposure to HCL (hot and ambient temperature), NaCl and H2S environments. One such test is a very aggressive sour autoclave test where the film is exposed to an aqueous, organic and gas phase over a 30 day period and no damage to the film was found. In depth details of this sour autoclave test will be shown including photographs of the film before and after testing. Wear testing has also been carried out in dry and wet sand slurry environments where very low coefficient of friction (COF) and wear rates were found. It is believed that this thick DLC based film can increase the component life in applications where internal surfaces are exposed to highly corrosive and abrasive media, in particular the oil and gas industry. Examples of such applications are mud pump sleeves, deep well components, directional drilling, abrasive flow spools, pump barrels and in sour fields (H2S).

The application of the relaxation and simplex method to the analysis of data for glucose electrodes based on glucose oxidase immobilised in an osmium redox polymer

Data for a series of fully integrated glucose oxidase, osmium redox polyelectrolyte layers deposited on thiolated gold electrodes by layer-by-layer self assembly was analysed using the relaxation and simplex method described in our earlier work (Flexer et al., 2008) [12]. The layer-by-layer assembly method allows fine control over the film thickness, enzyme loading, osmium and glucose concentrations with good reproducibility from electrode to electrode. In the analysis we combine the use of approximate analytical expressions with digital simulation to fit the data from an extensive set of experiments. The analysis shows a thickness dependence of the fraction of “wired enzyme molecules” and second order enzyme re-oxidation rate constant for thin films (below 300 nm) following changes in the multilayer film structure. For films thicker than 300 nm the kinetic data approach that of a redox hydrogel.

Magnetic Properties of (Ni$_{83}$Fe$_{17}$)$_{1 - {\rm x}}$-Gd$_{\rm x}$ Thin Films with Diluted Gd Doping

(Ni83Fe17)1-x-Gdx thin films (30 nm) are deposited by sputtering at room temperature and studied using X-ray diffraction, vibrating sample magnetometer, and ferromagnetic resonance (FMR). The film structure changes from polycrystalline to amorphous when Gd content is around 5.7%. The magnetization is reduced almost linearly with the increase of the Gd content, while the high hysteresis squareness along the in-plane easy-axis, the low coercivity Hc of less than 10 Oe, and the high maximum permeability of around 1000 are all preserved. Theoretical fitting of angular dependences of FMR field yields the second and forth order perpendicular anisotropy constants Kperp1 and Kperp2 which show a spin reorientation with increasing Gd doping. The FMR linewidth is fitted by considering the contributions from Gilbert damping and inhomogeneous broadening. It is found that the damping coefficient alpha is tripled along with an enhancement of the gyromagnetic ratio gamma when the Gd content rises to 9.3%.

Effects of post-deposition surface treatment on the optical, structural and hydrogen sensing properties of TiO 2 thin films

TiO 2 thin films were prepared by DC reactive magnetron sputtering in a mixture of oxygen and argon on glass and oxidized silicon substrates. The effect of post-deposition annealing (300 °C, 500 °C and 700 °C for 8 h in air) on the structural and morphological properties of TiO 2 thin films is presented. In addition, the effect of Pt surface modification (1, 3 and 5 nm) on hydrogen sensing was studied. XRD patterns have shown that in the range of annealing temperatures from 300 °C to 500 °C crystallization starts and the thin film structure changes from amorphous to polycrystalline (anatase phase). In the case of samples on glass substrate, optical transmittance spectra were recorded. TiO 2 thin films were tested as sensors of hydrogen at concentrations 10,000–1000 ppm and operating temperatures within the 180–200 °C range. The samples with 1 nm and in particular with 3 nm of Pt on the surface responded to hydrogen fast and with high sensitivity.

Microstructure evolution of Ge+ implanted silicon oxide thin films upon annealing treatments

The structural evolution of silicon oxide films with Ge+ implantation was traced with a positron beam equipped with positron annihilation Doppler broadening and lifetime spectrometers. Results indicate that the film structure change as a function of the annealing temperature could be divided into four stages: (I) T<300°C; (II) 300°C⩽T⩽500°C; (III) 600°C⩽T⩽800°C; (IV) T⩾900°C. In comparison with stage I, the increased positron annihilation Doppler broadening S values during stage II is ascribed to the annealing out of point defects and coalescence of intrinsic open volumes in silicon oxides. The obtained long positron lifetime and high S values without much fluctuation in stage III suggest a rather stable film structure. Further annealing above 900°C brings about dramatic change of the film structure with Ge precipitation. Positron annihilation spectroscopy is thereby a sensitive probe for the diagnosis of microstructure variation of silicon oxide thin films with nano-precipitation.

From Nanoparticles to Nanoplates: Preferential Oriented Connection of Ag Colloids during Electrophoretic Deposition

The Ag nanostructured films are fabricated based on electrophoretic deposition (EPD) in the Ag colloidal solution produced by laser ablation in water, under a constant current deposition mode. It has been found that the obtained films are of tunable and controllable morphologies and structures depending on EPD parameters. Importantly, there exists significant crystal growth for the building blocks of the film during EPD, in addition to normal particles’ coagulation. With increasing the current density of EPD, the size of the building blocks in the film decreases, and the shape evolves from polyhedral particles to regular nanoplates, and to irregular equi-axial particles. Correspondingly, the film structure changes from discontinuous film, consisting of the isolated aggregates of the building blocks, to the homogeneous and dense film, consisting of equi-axial particles. Further experiments have revealed that formation of the regularly shaped single crystal building blocks is attributed to the crystal growt...

Investigation of the Interaction between Three-Block Copolymers with Phospholipid Monolayers and foam Films

ABSTRACTThe interaction of three-block copolymers (poloxamers) with dimiristoyl-phosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) is investigated experimentally at one (monolayer) and two interacting air/water interfaces (foam film). The poloxamers selected are F-88 and F-98. Both of them possess two hydrophilic polyoxyethylene (POE) and one hydrophobic polyoxypropylene moiety but differ in molecular weight. These substances and their interfacial behaviour are interesting for the development of targeted drug delivery systems. Monolayer tensiometry revealed the degree of poloxamer penetration in PC monolayers and the changes in monolayer compression/decompression behaviour. Foam film experiments showed the effect of steric disjoining pressure increase in presence of F-88 and F-98. It resulted in changes of film structure and equivalent water thickness. It was found that the interaction between poloxamers and PC molecules in monolayers and foam films depends both on copolymer size and on the acyl chain length of phosphatidylcholines.

Formation of Atomistic Island in Al Film Growth by Kinetic Monte Carlo

Kinetic Monte Carlo (KMC) method realizes the millisecond or second order atomistic thin film growth. Twenty five kinds of events which may occur on Al(111) surface were classified. An attempt frequency and an activation energy of each event were defined using vibration analyses and nudged elastic band (NEB) method by which the minimum energy path (MEP) can be reasonably predicted. Temperature and deposition rate dependences of Al(111) film growth were intensively investigated in the present paper. The higher temperature and the lower rate drive the layer-by-layer film structural change. Two types of islands (fcc and hcp) were seen by modeling without considering the events of diffusion of dimer and trimer, while only fcc islands remain with considering such events. Thus, we find that the primitive events of diffusion of dimer and trimer take important roles in determination of surface morphology.

Influences of partial melting and overheating on amorphization of Ge2Sb2Te5 during the reset process

AbstractIt is very important to observe the change in the atomic structure of melt‐quenched amorphous Ge2Sb2Te5 (GST) to discover the failure mechanism of phase‐change random access memory (PRAM) devices during the reset process. We fabricated the phase‐change devices and measured the initial resistance changes with various reset pulse amplitudes. For the observation of the atomic structure changes of GST thin films, we designed the specimens for transmission electron microscopy (TEM) and annealed them below and above the melting temperature of GST (Tm = 650 °C) before quenching. The annealed‐and‐quenched GST at 630 °C has a hexagonal structure with a grain size of about 10 nm after the partial melting. The annealed‐and‐quenched GST at 750 °C also has a hexagonal structure because of the latent heat. The observed atomic structures of GST are in accordance with the resistance changes inferred from the fabricated edge‐contact type of PRAM cell. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Effect of deposition temperature on the structure and electrical properties of thin barium strontium titanate films

We have studied the properties of thin ferroelectric films of barium strontium titanate (Ba,Sr)TiO3 (BSTO) obtained by RF ion-plasma deposition at various substrate temperatures in the 700–900°C range. It is established that BSTO films deposited at 700–800°C exhibit a polycrystalline structure. Beginning with 800°C, the film structure changes so that an (111)-oriented phase appears and becomes predominating. The effect of the deposition temperature on the grain size and the relationship between the structural features and electrical properties of the films are considered.

Correlation between metal-insulator transition characteristics and electronic structure changes in vanadium oxide thin films

We correlate electron transport data directly with energy band structure measurements in vanadium oxide thin films with varying V-O stoichiometry across the ${\text{VO}}_{2}$ metal-insulator transition. A set of vanadium oxide thin films were prepared by reactive dc sputtering from a V target at various oxygen partial pressures (${\text{O}}_{2}$ p.p.). Metal-insulator transition (MIT) characteristic to ${\text{VO}}_{2}$ can be seen from the temperature dependence of electrical resistance of the films sputtered at optimal ${\text{O}}_{2}$ p.p. Lower and higher ${\text{O}}_{2}$ p.p. result in disappearance of the MIT. The results of the near edge x-ray absorption fine structure spectroscopy of the $\text{O}\text{ }K$ edge in identical VO films are presented. Redistribution of the spectral weight from ${\ensuremath{\sigma}}^{\ensuremath{\ast}}$ to ${\ensuremath{\pi}}^{\ensuremath{\ast}}$ bands is found in the vanadium oxide films exhibiting stronger ${\text{VO}}_{2}$ MIT. This is taken as evidence of the strengthening of the metal-metal ion interaction with respect to the metal-ligand and indirect V-O-V interaction in vanadium oxide films featuring sharp MIT. We also observe a clear correlation between MIT and the width and area of the lower ${\ensuremath{\pi}}^{\ensuremath{\ast}}$ band, which is likely to be due to the emergence of the ${d}_{||}$ band overlapping with ${\ensuremath{\pi}}^{\ensuremath{\ast}}$. The strengthening of this ${d}_{||}$ band near the Fermi level only in the vanadium oxide compounds displaying the MIT points out the importance of the role of the ${d}_{||}$ band and electron correlations in the phase transition.

Effects of postdeposition annealing on the structure and optical properties of YOxNy films

High-k gate dielectric YOxNy films were prepared by reactive sputtering. The effects of postdeposition annealing on the structure and optical properties of YOxNy films have been investigated. The x-ray diffraction result shows that the crystallization starts at the annealing temperature of 500°C. Spectroscopic ellipsometry was employed to determine the optical properties of a set of YOxNy films annealed at various temperatures. It was found that the refractive index (n) of YOxNy films decreased with the increase of annealing temperature below 600°C, whereas it increased with increasing annealing temperature above 600°C. The annealing-temperature dependence of the optical band gap of YOxNy films was also discussed in detail. It has indicated that the optical band gap of YOxNy films shifts to higher energy after higher temperature annealing, which is likely due to the reduction of N content and the change of crystalline structure in YOxNy films.