Dependence Of Film Composition Research Articles

Thickness and temperature dependences of dielectric properties of {111}-oriented epitaxial Pb(Mg1/3Nb2/3)O3 and 0.6Pb(Mg1/3Nb2/3)O3–0.4PbTiO3 films

The effects of film thickness and composition on crystal structure and dielectric properties were investigated for {111}-oriented epitaxial Pb(Mg1/3Nb2/3)O3 (PMN) and 0.6Pb(Mg1/3Nb2/3)O3–0.4PbTiO3 (0.6PMN–0.4PT) films of various thicknesses grown on (111)cSrRuO3//(111)SrTiO3 substrates by pulsed metal organic chemical vapor deposition (MOCVD). When the film thickness of {111}-oriented PMN films increased from 500 to 1300 nm, the relative dielectric constant at room temperature increased from 1600 to 2800 at 10 kHz. This tendency was similar to our previous result for {100}-oriented PMN films. On the other hand, the relative dielectric constant at room temperature slightly increased from 2500 to 2700 at 10 kHz with the increase in film thickness from 750 to 2500 nm in the case of {111}-oriented 0.6PMN–0.4PT films. PMN films show strong frequency dependences of maximum relative dielectric constant against temperature, εr(max), and the temperature of εr(max), T(max), together with a strong thickness dependence. On the other hand, 0.6PMN–0.4PT films show small frequency dependences of εr(max) and T(max) together with a small film thickness dependence. These results show a strong film composition dependence of the dielectric properties of the films in a PMN–PT system such as frequency and thickness.

Enhanced half-metallicity of off-stoichiometric quaternary Heusler alloy Co2(Mn,Fe)Si investigated through saturation magnetization and tunneling magnetoresistance

We investigated the factors that critically affect the half-metallicity of the quaternary Heusler alloy $\mathrm{C}{\mathrm{o}}_{2}(\mathrm{Mn},\mathrm{Fe})\mathrm{Si}$ (CMFS) by examining the film composition dependence of the saturation magnetization per formula unit, ${\ensuremath{\mu}}_{s}$, of CMFS thin films and the tunneling magnetoresistance (TMR) ratio of CMFS/MgO/CMFS magnetic tunnel junctions (MTJs). We also investigated the origin of the giant TMR ratio of up to 2610% at 4.2 K (429% at 290 K) obtained for CMFS MTJs with Mn-rich, lightly Fe-doped CMFS electrodes. Co antisites at the nominal Mn/Fe sites ($\mathrm{C}{\mathrm{o}}_{\mathrm{Mn}/\mathrm{Fe}}$ antisites) can consistently explain the ${\ensuremath{\mu}}_{s}$ for (Mn + Fe)-deficient CMFS thin films being lower than the half-metallic ${Z}_{\mathrm{t}}\ensuremath{-}24$ value and the TMR ratio for MTJs with (Mn + Fe)-deficient CMFS electrodes being lower than that for MTJs with (Mn + Fe)-rich CMFS electrodes. It was revealed that the $\mathrm{C}{\mathrm{o}}_{\mathrm{Mn}/\mathrm{Fe}}$ antisite is detrimental to the half-metallicity of the CMFS quaternary alloy, as it is in the ${\mathrm{Co}}_{2}\mathrm{MnSi}$ (CMS) ternary alloy. It was also shown that $(\mathrm{Mn}+\mathrm{Fe})$-rich compositions are critical to suppressing these harmful antisites and to retaining the half-metallic electronic state. In addition, a relatively small Fe ratio, rather than a large one, in the total $(\mathrm{Mn}+\mathrm{Fe})$ composition led to a more complete half-metallic electronic state. Half-metallicity was more strongly enhanced by increasing the Mn composition in Mn-rich, lightly Fe-doped CMFS than in Mn-rich CMS. This phenomenon is the cause of the giant TMR ratio recently reported for CMFS MTJs. Our findings indicate that the approach to controlling off-stoichiometry and film composition is promising for fully utilizing the half-metallicity of quaternary CMFS thin films as spin source materials.

Yet another poor man's green bulk heterojunction photocells: Annealing effect and film composition dependence of photovoltaic devices using poly(3-hexylthiophene):C70 composites prepared with chlorine-free solvent

Chemically modified fullerenes and chlorinated solvents have been predominantly chosen in the recent studies of the photovoltaic devices based on polymer bulk heterojunction composites. However, these items seem to be undesirable because of their potential impacts on the environment as well as the consumption of resources. In this context, a systematic study on the annealing effect and film composition dependence of bulk heterojunction photovoltaic devices based on composites consisting of poly(3-hexylthiophene) (P3HT) and neat C70 prepared with a chlorine-free solvent 1,2,4-trimethylbenzene has been carried out. For the device using P3HT:C70 composite (2:1 by weight) film as an active layer, power conversion efficiency of 1.47%, with open-circuit voltage of 0.52V, short-circuit current density of 6.2mA/cm2 and fill-factor of 45%, has been obtained after post-production annealing at 160°C. The combination of neat fullerenes with naturally obtained solvents will open up a new way to produce cost-effective and environmentally-friendly photovoltaic devices based on polymer:fullerene bulk heterojunction composites.

Atomic Layer Deposition of Amorphous Niobium Carbide-Based Thin Film Superconductors

Niobium carbide thin films were synthesized by atomic layer deposition (ALD) using trimethylaluminum (TMA), NbF5, and NbCl5 precursors. In situ quartz crystal microbalance (QCM) measurements performed at 200 and 290 °C revealed controlled, linear deposition with a high growth rate of 5.7 and 4.5 A/cycle, respectively. The chemical composition, growth rate, structure, and electronic properties of the films were studied over the deposition temperature range 125–350 °C. Varying amounts of impurities, including amorphous carbon (a-C), AlF3, NbFx, and NbClx, were found in all samples. A strong growth temperature dependence of film composition, growth rate, and room temperature DC resistivity was observed. Increasing film density, decreasing total impurity concentration, and decreasing resistivity were observed as a function of increasing deposition temperature for films grown with either NbF5 or NbCl5. Superconducting quantum interference device (SQUID) magnetometry measurements down to 1.2 K revealed a superc...

The influence of nitrogen incorporation on the optical properties of anodic Ta 2O 5

Anodic oxides were grown on sputter-deposited Ta in different aqueous solutions. A photoelectrochemical investigation was performed in order to estimate the band gap of the films as a function of the anodizing bath composition and formation voltage, i.e. thickness. Photoelectrochemical results provided evidence of sub-band gap photocurrent for films formed in a bath containing ammonium ions at pH 9. Elemental depth profiles obtained by glow discharge optical emission spectroscopy revealed the presence of nitrogen species in the outer part of the anodic films, which is bonded to Ta according to XPS analysis. A mechanism of nitrogen incorporation is proposed in order to account for the pH dependence of film composition.

Molecular beam epitaxy of metamorphic InyGa1−yP solar cells on mixed anion GaAsxP1−x/GaAs graded buffers

The authors have grown metamorphic InyGa1−yP on optimized GaAsxP1−x/GaAs graded buffers via solid source molecular beam epitaxy (MBE) for multijunction solar cell applications. In this work, the authors show that a previously developed kinetic growth model can be used to predict the composition of mixed anion GaAsxP1−x alloys on GaAs as a function of substrate temperature and group-V flux. The advantages of using a high growth temperature of 700 °C are then described, including the minimized dependence of composition on small temperature variations, a linear dependence of film composition on incident group-V flux ratio, and the ability to attain low threading dislocation densities of ≤106 cm−2. The authors then discuss the effect of faceted trenches, a morphological defect specific to tensile strain relaxation, on minority carrier properties, as well as strategies to eliminate them. Growth temperature effects, phase separation, and difficulties encountered in n-type doping of InAlP:Si are then described in the context of InyGa1−yP solar cell growth. The MBE growth techniques presented here have enabled the demonstration of 2.00 eV band gap metamorphic In0.39Ga0.61P solar cells, exhibiting open-circuit voltages as high as 1.42 V. These results indicate that metamorphic InyGa1−yP is a promising material for future multijunction solar cells.

Small amplitude reciprocating wear performance of diamond-like carbon films: dependence of film composition and counterface material

Small amplitude (50 μm) reciprocating wear of hydrogen-containing diamond-like carbon (DLC) films of different compositions has been examined against silicon nitride and polymethyl-methacrylate (PMMA) counter-surfaces, and compared with the performance of an uncoated steel substrate. Three films were studied: a DLC film of conventional composition, a fluorine-containing DLC film (F-DLC), and silicon-containing DLC film. The films were deposited on steel substrates from plasmas of organic precursor gases using the Plasma Immersion Ion Implantation and Deposition (PIIID) process, which allows for the non-line-of-sight deposition of films with tailored compositions. The amplitude of the resistive frictional force during the reciprocating wear experiments was monitored in situ, and the magnitude of film damage due to wear was evaluated using optical microscopy, optical profilometry, and atomic force microscopy. Wear debris was analyzed using scanning electron microscopy and energy dispersive spectroscopy. In terms of friction, the DLC and silicon-containing DLC films performed exceptionally well, showing friction coefficients less than 0.1 for both PMMA and silicon nitride counter-surfaces. DLC and silicon-containing DLC films also showed significant reductions in transfer of PMMA compared with the uncoated steel. The softer F-DLC film performed similarly well against PMMA, but against silicon nitride, friction displayed nearly periodic variations indicative of cyclic adhesion and release of worn film material during the wear process. The results demonstrate that the PIIID films achieve the well-known advantageous performance of other DLC films, and furthermore that the film performance can be significantly affected by the addition of dopants. In addition to the well-established reduction of friction and wear that DLC films generally provide, we show here that another property, low adhesiveness with PMMA, is another significant benefit in the use of DLC films.

Amorphous aluminum silicate films by metal-organic chemical vapor deposition using aluminum- tri-sec-butoxide and tetraethyl orthosilicate

Amorphous aluminum silicate films with film thickness of 0.5–2.7 μm were prepared on glass and silicon substrates by metal-organic chemical vapor deposition using a mixture of tetraethyl orthosilicate (TEOS), aluminum tri-sec-butoxide (ATSB), and argon. These films were studied by choosing different substrate temperatures and reactant inputs. The apparent activation energy of the aluminum silicate films is related to surface reaction between reactive ATSB and less reactive TEOS. Microstructure was examined by scanning electron microscopy and atomic force microscopy. The Al content in films increased with increasing the ATSB content and with decreasing deposition temperature, while the Si content increased with the increase in the TEOS content. The dependence of film composition on deposition temperature can be related to the values of activation energy of the two systems. Mechanical properties, such as internal stress, hardness, and adhesion, of the aluminum silicate films were evaluated. Optical properties, such as refractive index and optical transmittance, were also measured.

Growth and microstructure of In xGa 1− xN films grown on SiC substrates via low pressure metalorganic vapor phase epitaxy

The growth and microstructures of In x Ga 1− x N films ( x≤0.23) grown on α(6H)–SiC(0001) wafer/AIN buffer layer/GaN heterostructures by low pressure metalorganic vapor phase epitaxy have been investigated. The system deposition pressure limited the InN content in these films. The maximum InN contents achievable at the deposition pressures of 45 and 90 torr were ∼13 and ∼23%, respectively. Kinetic phenomena based on the rates of adsorption and desorption of the In growth species off the growth surface are presented to explain the film composition dependence on the system pressure. The surface morphologies and microstructures of the In x Ga 1− x N films were analyzed using several techniques, and the formation of pinhole defects in the films was investigated. Most of the pinhole defects were associated with threading dislocations with a c-component Burgers vector. Edge-type dislocations were never observed to terminate in pinholes in the samples observed here. Indium segregation to areas around the defect areas was observed, as was an In compositional gradient in the growth direction. Based on experimental observations, the strain field around dislocations with a c-component Burgers vector could result in the increase of In atoms at the dislocation sites in the film, which result in a change to the local growth mode of the film and causes the pinhole defects to form.

XPS study of TiOx thin films prepared by d.c. magnetron sputtering in Ar-O2 gas mixtures

Titanium oxide films have been deposited, at a pressure of 5 mTorr and a discharge current of 500 mA, on borosilicate glass substrates. We have studied in situ by XPS the dependence of film composition on oxygen partial pressure. All the experiments have been performed under high vacuum; there is no air contamination of film surfaces before XPS analysis. The ions produced in the plasma have been analysed by glow discharge mass spectrometry (GDMS). The stoichiometry of the films is compared to the plasma composition. The XPS results show that for an increasing oxygen partial pressure four regimes are observed. At very low oxygen concentration (< 2%), the film is mainly metallic (zone I). For an oxygen concentration between 2% and 6%, a mixture of Ti, TiO, Ti2O3 and TiO2 is observed (zone II). In this zone the concentration of Ti decreases but the concentration of the three titanium oxides grows. In zone III (6% < O2 < 15%) the TiO2 concentration in the film increases. Finally, for O215% (zone IV) a pure TiO2 film is obtained. When zone IV starts, the Ti+ mass spectrometric signal is still higher than the TiO+ signal, showing that a pure TiO2 phase is occurring at the substrate while the sputtering mode is still partially metallic. Copyright © 2000 John Wiley & Sons, Ltd.

Formation of thin Bi(Pb)-Sr-Ca-Cu-O films by ex situ magnetron sputtering

Thin Bi(Pb)-Sr-Ca-Cu-O films with higher than 100 K were prepared by ex situ planar magnetron sputtering on substrates. Films are c-axis oriented and present a mixture of 2212 and 2223 phases. The film composition dependence or the substrate temperature during deposition, target composition, and oxygen content in the Ar/ mixture was studied. Addition of silver resulted in decrease of resistance of the films and increase of by 5 K on average.

Electronic characteristics of the SrBi2Ta2O9–Pt junction

The voltage and film composition dependence of leakage currents of ferroelectric SrBi2Ta2O9 thin films, sandwiched between Pt has been studied. Schottky emission dominated the leakage current at voltages above the ohmic conduction regime, while space charge limited currents (SCLC), for which the observed temperature dependence is correctly predicted in Rose’s theory, appeared to dominate the leakage current in high conductivity SrBi2Ta2O9 thin films including bismuth-excess samples. A consequence of the latter was the observation of negative differential resistivity in high conductivity SrBi2Ta2O9 thin films. X-ray photoemission spectroscopy depth profiling indicated that Bi has diffused into the ferroelectric–metal interface and also influenced the electronic conduction mechanism of the ferroelectric capacitors. Confirmation of this was found through the current–voltage dependence of Pt/SrBi2Ta2O9/Bi, which is compatible with space charge limited currents. The theory of Rose was successfully applied to the temperature and voltage dependencies of leakage currents in Bi-excess SBT; this is the first application of such theories to ferroelectric films and results in a generalization of the Child’s Law approximation for space-charge-limited currents. A single fitting parameter T*=315±20 K satisfied data at the voltages 3&amp;lt;V&amp;lt;4 and temperatures 300 K&amp;lt;T&amp;lt;400 K most useful for engineering device applications.

Dependence of film composition and thicknesses on optical and electrical properties of ITO–metal–ITO multilayers

ITO–metal–ITO (IMI) multilayers have been prepared by DC-magnetron reactive sputtering in an vertical Inline sputtering system. AgCu films with different film thicknesses were used as metallic layers. The transmission and the reflection of the multilayers were measured, as well as the film thickness and the sheet resistance. The complex indices of refraction both of ITO and of AgCu were calculated from the measured data. By theoretical simulations an optimization of material composition and of film thicknesses has been carried out. With the IMI multilayer a sheet resistance of 5.7 Ω/sq. and a maximum transmission of about 83% was achieved. The performance of the multilayers as transparent conducting materials was compared by using a figure of merit proposed by Haacke.

The influence of the discharge power on film composition obtained by reactive magnetron sputtering

The preparation of the binary nitrides or oxides with narrow homogeneity range at low substrate temperatures is considered. An attempt is made to establish the analytical dependence of film composition on both discharge power and ratio of argon and reactive gas pressures. It is shown that under the increase of the discharge power up to a certain limit, the increase of target sputtering rate is compensated by the proportional growth of the number of active nitrogen particles. Starting from some discharge power, the rate of arrival of these particles is steadily decreased and metal excess appears in the film. The metal/reactive gas ratio grows proportional to the discharge power at its high values. The aforementioned is illustrated by the data obtained for magnetron sputtering of aluminium target in the gas mixture Ar-N 2.

Reduced protein adsorption on plastics via direct plasma deposition of triethylene glycol monoallyl ether.

The direct plasma-induced deposition of tri(ethylene glycol) monoallyl ether is reported. RF plasma polymerization of this monomer was carried out under both continuous wave (CW) and pulsed plasma operation. The major focus of this work was optimization of the degree of retention of the C-O-C bonds of the starting monomer during the deposition process. This successfully was accomplished using low RF power during the CW runs and low RF duty cycles during the pulsed plasma experiments. Spectroscopic analysis of the plasma films revealed a strong dependence of film composition on the RF power and duty cycles employed. In particular, an unusually high level of film chemistry compositional control was demonstrated for the pulsed plasma studies, with film composition varying in a steady, progressive fashion with sequential changes in the ratios of plasma on to plasma off times. This film chemistry controllability is demonstrated despite the relatively low volatility of the starting monomer. The utility of this plasma deposition approach in introducing polyethylene oxide (PEO) structures on solid substrates was evaluated via protein adsorption studies. Radiolabeled bovine albumin adsorption was studied on plasma-modified poly(ethylene teraphthalate) (PET) substrates. Dramatic reductions in both initial adsorption and retention of this protein were observed on PET samples having maximal PEO content relative to its adsorption on untreated PET surfaces. Good stability and adhesion of the plasma films to the underlying PET substrates were observed, as evidenced from prolonged immersion of plasma-treated surfaces in aqueous solution. Overall, the results obtained from the present work provide additional support for the utility of one-step plasma process to reduce biological fouling of surfaces via deposition of PEO surface units.

Effects of target presputtering on stoichiometry of sputtered Bi–Sr–Ca–Cu–O thin films

We have studied the target presputtering effects on the stoichiometry of Bi–Sr–Ca–Cu–O (BSCCO) thin films prepared from a single composite target using rf magnetron sputtering in a vacuum system with a pressure of 10−6 Torr. A strong dependence of film composition on the target presputtering time has been found under pure argon discharge. A rather long time (∼20 h) is needed to bring the target to a steady state condition. The oxygen out-diffusion under the aid of energetic particle bombardment is believed to be the cause of this effect, a physical process similar to that observed in the Y–Ba–Cu–O system. It has been further demonstrated that introduction of oxygen into the sputtering chamber can effectively prevent this process from taking place and therefore preserve the BSCCO target surface in its initial state.

Silicon nitride films prepared using a SiH4/NH3 microwave multipolar plasma

Silicon nitride films have been prepared at room temperature using a microwave multipolar plasma chemical vapor deposition system. In situ kinetic ellipsometry during deposition and ex situ measurements such as infrared absorption or spectroscopic ellipsometry have been used to investigate the dependence of film composition and properties on the flow ratio SiH4/NH3 and on the total pressure. Depending on the silane partial pressure, the films contain a variable amount of oxygen or amorphous silicon which directly affects the electrical properties.

Optimization of thin-film YBa/sub 2/Cu/sub 3/O/sub 7/ deposition by DC sputtering onto sapphire substrates

A report is presented on the deposition of YBa/sub 2/Cu/sub 3/O/sub 7/ thin films onto epitaxial magnesia-coated single-crystal sapphire substrates at deposition temperatures in the range of 600 degrees C-850 degrees C. The dependence of film composition on sputtering parameters was investigated using a UHV DC magnetron sputter deposition system with both composite metal and ceramic oxide targets. Films deposited onto epitaxial magnesia are compared to those deposited directly onto sapphire and yttria-stabilized zirconia. The degree of control required for the sputter deposition of YBaCuO thin films at elevated temperatures is shown.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Chemical Kinetics of Silicon-Rich Oxide Growth in an LPCVD Reactor

ABSTRACTThe chemical kinetics of Silicon Rich Oxide (SRO) growth in a N2O-SiH4 LPCVD reactor has been studied at deposition temperatures from 610 to 680°C and pressures from 0.4 to 0.5 torr. We can produce SRO films with a wide spectrum of input reactant ratios γ = [N2O]/[SiH4] = 1 to 40. The dependence of film composition on γ changes dramatically in a region around γ = 2.Growth for γ &lt; 2 is consistent with the chemical kinetics of SIPOS growth. Growth for γ &gt; 20 can be explained by oxidation of silicon in the bulk of the growing SRO film. We can explain growth from γ ≈ 4 to 20 by considering the chemical kinetics of possible binary surface reactions which may produce Si-Si or Si-O bonds. This allows us to accurately model the dependence of SRO growth rate in this region as a function of γ, pressure, and deposition temperature.

Preparation of silicon nitride films at room temperature using double-tubed coaxial line-type microwave plasma chemical vapor deposition system

Silicon nitride films were prepared at room temperature using the double-tubed coaxial line-type microwave plasma chemical vapor deposition system. The dependence of film composition and properties on the flow rate of SiH4 gas and on the partial pressure of N2 gas in the deposition chamber has been investigated. A new simple method was suggested and employed to determine the film composition from the refractive index and nitrogen concentration. The flow rate of SiH4 gas was varied between 1 and 10 ml/min. The flow rate of N2 gas was at 50 ml/min and the partial pressures of N2 gas in the deposition chamber were set at 0.015 and 0.0036 Torr by changing the size of the substrate table. With an increasing flow rate of SiH4 gas, the following effects upon the films were obtained: proportional increases in the deposition rate, shifts to lower energy of the absorption edge, decreases in the film density, and decreases in the concentration of N and the N–H bond. Increases in the refractive index, the Si/N ratio, and the concentrations of Si and the Si–H bond were also observed. In the case of low partial pressure of N2 gas, the deposition rate decreases, the absorption edge shifts to higher energy, the N concentration increases, and the films become denser. The optical properties of the film vary slowly with the flow rate of SiH4, and these properties can be determined more precisely by varying the flow rate of SiH4.