Diffusion Of Oxygen Atoms Research Articles

Diffusion of oxygen atom near Zr(0001) surface

Based on the density functional theory calculations， the diffusion of oxygen atoms near the Zr（0001）surface is studied by using the nudged elastic band method. Firstly， the active energy of diffusion of oxygen atoms from the surface face-centred cubic （SFCC） sites into surface hexagonal close-packed sites in Zr（0001） surface is calculated. The active energy for the diffusion is 0.77 eV. Secondly， the active energy of diffusion of oxygen atoms from the SFCC into octahedral interstitial sites between the second and third layers Octa（2，3） via octahedral interstitial sites between the first and second layers Octa（1，2） is calculated too. There are two energy barriers for oxygen atom to overcome. The active energies are 2.14 and 2.57 eV， respectively. As a result， the diffusion of oxygen atom above the Zr（0001） surface is easier than the diffusion into the subsurface.

High Mobility Channel Materials and Novel Devices for Scaling of Nanoelectronics beyond the Si Roadmap

AbstractHigh mobility channel materials and new device structures will be needed to meet the power and performance specifications in future technology nodes. Therefore, the use of Ge and III/V materials and novel devices such as heterojunction TunnelFET’s is investigated for future CMOS applications. High-performance CMOS can be obtained by combining Ge pMOS devices with nMOS devices made on III/V compounds such as InGaAs. In all cases the key challenge is the electrical passivation of the interface between the high-k dielectric and the alternative channel materials. Recent studies have demonstrated good electrical properties of the GeO2/Ge interface. Since the GeO2 layer is very hygroscopic, full in-situ processing of GeO2 formation and high-k deposition must be performed or other methods must be employed to stabilize the GeO2 layer. One of the most successful passivation techniques for Ge MOS gate stacks is a thin, epitaxial layer of Si. A lot of attention went into better understanding of this passivation and the effects of its optimization on various device characteristics. It was found that mobility and Vt trends in both pMOS and nMOS transistors can be explained based on defects located at the Si/SiO2 interface. Unfortunately, III-V/oxide interfaces are not quite as robust and most interfaces present rather high densities of interface states. Although, considerable improvements have been realized in the reduction of the interface state density, further developments are required to obtain high performance MOS devices. To this purpose various passivation methods were critically evaluated. Simulations using Density Functional Theory reveal the possibility of using a thin amorphous layer made of GeOX to obtain an electrically unpinned gap. The major challenge resides in the control of the c-Ge thickness and the oxidation of this layer to avoid the diffusion of oxygen atoms at the Ge/GaAs(001) interface. Promising results are obtained by optimizing the surface preparation, high-k deposition and annealing cycle on In0.53Ga0.47As-Al2O3 interfaces. Self-aligned inversion channel n-MOSFETs fabricated on p-type In0.53Ga0.47As demonstrate inversion-mode operation with high drive current and a peak electron mobility of 3000 cm2/Vs. Since ultimately the major showstopper on the scaling roadmap is not device speed, but rather power density, the introduction of these advanced materials will have to go together with the introduction of new device concepts. Novel structures such as heterojunction TunnelFET’s can fully exploit the properties of these new materials and provide superior performance at lower power consumption by virtue of their improved subthreshold behaviour. Vertical surround gate devices produced from nanowires allow the introduction of a wide range of materials on Si. This illustrates the possibilities that are created by the combination of new materials and devices to allow scaling of nanoelectronics beyond the Si roadmap.

Oxygen vacancy configuration of δ‐Bi2O3: an ab initio study

AbstractThe oxygen vacancy configurations and electronic structures of δ‐Bi2O3 have been studied using the ab initio calculation full‐potential linearized augmented plane‐wave (FPLAPW) method and considering the relativistic effect in Bi atoms in terms of spin–orbital coupling. Three vacancy structures, 〈111〉, 〈110〉 and 〈100〉, were analysed. It was found that the layered δ‐Bi2O3 with 〈110〉 vacancy alignment is the most stable. An indirect band gap of 0.46 eV was observed for this structure. Additionally, the role of lone‐pair electrons as well as polarization during the diffusion of oxygen atoms have been investigated. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural properties of Al2O3 dielectrics grown on TiN metal substrates by atomic layer deposition

We investigated on the structural properties of Al2O3 dielectrics grown on TiN metal substrates using an atomic layer deposition technique with tri-methyl-aluminum and either O3 or H2O as the precursor and oxidant, respectively. The structural and morphological features of these films were examined by atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy measurements. We find that Al2O3 dielectric films with the O3 oxidant exhibit a rough morphology, a thick TiO2 film, and a small amount of contaminants such as carbon and hydrogen. The reason for the rapid diffusion of oxygen atoms into the TiN lattice leads to the formation of TiO2 layer on the TiN substrate. This is due to the higher oxidation potential of the O3 compared to the H2O.

Al-induced reduction of the oxygen diffusion inHfO2: an ab initio study

Using first-principles calculations we have studied the effect of Aladdition on the diffusion of interstitial oxygen atoms and ions inHfO2.Calculated results show that interstitial oxygen ions in the singly negatively charged state easily diffusein HfO2 via exchange with lattice oxygen atoms, due to the lower diffusion barrier as compared to thosefor neutral interstitial oxygen atoms and interstitial oxygen ions in the doubly negativelycharged state. The addition of Al raises the diffusion barrier for interstitial oxygen becausethe interstitial oxygen is strongly attracted by its neighboring Al atoms. The electronicstructure analysis further reveals that the bonding between interstitial oxygen andlattice oxygen atoms is strengthened for each charge state of interstitial oxygen inHfO2 with the addition of Al.

Oxygen Diffusion in Superconducting Oxides

Since the discovery of high-temperature superconductivity of cuprate oxides, it has been clear that it is strongly affected by the oxygen content, which is also a crucial factor to determine other physical properties of high Tc superconductors. Non-stoichiometric (interstitial) oxygen strongly influences the physical properties of various superconducting oxides, in particular by creating conducting holes. It is now ascertained that the amount of holes injected depends not only on the content of interstitial oxygen, but also on its ordering. Rearrangement of the oxygen ordering may occur even below room temperature due to the unusual high mobility of these atoms. This way, mechanical spectroscopy is one of the most adequate techniques for the study of the mobility (diffusion) of oxygen atoms. This technique allows the determination of the jump frequency of an atomic species precisely, regardless of the model or the different possible types of jumps. In order to evaluate the mobility and the effect of oxygen content on these oxides, ceramic samples we prepared and submitted to several oxygen removal cycles alternately with mechanical relaxation measurements. As for SBCO, it was assumed that the peak was due to O(1)-O(5) jumps of oxygen atoms at the chain terminals or in chain fragments in the orthorhombic phase. In the case of BSCCO, the results showed complex anelastic relaxation structures, which were attributed to interstitial oxygen atom jumps between two adjacent CuO planes.

Diffusion of atoms on an fcc(111) surface

The motion of adatoms on an fcc(111) surface is modeled. In light of recently revealed specific features of the potential energy surface, a new empirical potential taking into account the nonequivalence of fcc and hcp adsorption sites was proposed. The modeling was performed by the method of stochastic cycles, a new variety of MDM. Calculations were performed for the diffusion of oxygen atoms over a platinum surface. The potential energy surface was constructed based on experimental data and DFT calculations. An analysis demonstrated that the diffusion activation energy coincides with the static barrier while the preexponential factor is weakly temperature-dependent. Note, however, that the degree of asymmetry of the potential produces a significant effect on the preexponential factor: the changeover from a symmetric two-well potential to a strongly asymmetric single-well potential causes an increase in the preexponential factor by an order of magnitude.

A kinetic study of oxygen reduction reaction on La 2NiO 4 cathodes by means of impedance spectroscopy

The oxygen reduction reaction has been investigated at the La 2NiO 4+ δ /YSZ interface by impedance spectroscopy. The study has been performed in the temperature range 600–800 °C under different oxygen partial pressures under zero dc conditions. The analysis of the impedance diagrams revealed at least the presence of three processes involved in the reduction reaction. The first process at high-frequency was assigned to transport of oxide ions and/or oxygen intermediates within the electrode structure and the electrode/electrolyte interface. The second one at medium-frequency arc was associated to atomic oxygen diffusion within the electrode followed by a charge transfer. This is the rate limiting step in the overall oxygen reduction reaction at oxygen partial pressure ⩾0.2 atm and temperature >600 °C under zero dc conditions. Finally, the third arc at low-frequency could be related to molecular oxygen dissociation and adsorption phenomena. This last process disappears under 100% O 2 and becomes more important at low oxygen partial pressure pO 2 < 0.2 atm.

Long range diffusion noise in platinum microwires with metallic adhesion layers

Voltage fluctuations of platinum wires hosted by silicon nitride beams were investigated. The authors considered four variants of the wires: three with an adhesion layer and one without an adhesion layer. They found that the presence of an adhesion layer changes the nature of the power spectrum which is 1∕f for wires with no adhesion layers and 1∕f3∕2 for wires with an adhesion layer. They attribute the value of the exponent α=3∕2 found in wires with adhesion layers to the long range diffusion of oxygen atoms along the interface between the adhesion layer and the platinum layer.

An improved model to evaluate the oxidation kinetics of uranium dioxide during dry storage

During dry air storage, the oxidation of the spent fuel in case of cladding and container failure (accidental scenario) could be detrimental for further handling of the spent fuel rod and for the safety of the facilities. Recently, the phase transition sequence during the first step of parabolic oxidation kinetic has been challenged again and two well-distinguished intermediate products, U4O9 and U3O7 have been identified. Moreover, these observations have shown that the three phases (UO2, U4O9 and U3O7) occur together. Starting from a previous model of grain oxidation based on finite difference approach, a new model, describing the parabolic oxidation kinetic, has been developed based on the oxygen atom diffusion. This model allows in one hand to take into account the occurrence of the three phases and in another hand to describe accurately the plateau behaviour. A comparison between the model and literature data obtained on non-irradiated powders has been carried out and shows that this model can describe the weight gain evolution as a function of time for different temperatures. The diffusion coefficients of oxygen in the two phases (U4O9 and U3O7) were obtained by fitting the model results to experimental data. The comparison with the values given in literature is quite good.

Effects of plasma treatment on the high frequency characteristics of Cu/Ta/hydrogen silsesquioxane (HSQ) system and electrical behaviors of Cu/Ta/HSQ/Pt MIM capacitors

With the increasing of the operating frequencies, insertion loss, signal propagation delay, and parasitic coupling capacitance become the significant problems. Small capacitance ( C) between interconnects is required to reduce the crosstalk, insertion loss, and RC delay associated with the metal interconnect system. Therefore, the interconnect with low dielectric constant ( k) material is required. Implementation of Cu/low- k dielectric is used for reducing insertion loss, RC delay, crosstalk noises, etc. In this work, Cu–hydrogen silsesquioxane (HSQ) systems are studied. Ammonia (NH 3) plasma is employed for the nitridation of HSQ. The effects of NH 3 plasma treatments on the high frequency characteristics (100 MHz to 20 GHz) of the interconnect structure Cu/Ta/HSQ and electrical behaviors of Cu/Ta/HSQ/Pt MIM capacitors are evaluated. Auger electron spectroscopy (AES) results suggest the diffusion of oxygen and copper atoms during copper annealing. This raises resistance of Cu interconnect and increases the conductance of the HSQ films. Hence, 400 °C-annealed Cu/Ta/HSQ interconnect systems become lossy at high frequencies (>2 GHz). Ammonia (NH 3) plasma bombardments break some of the Si–H bonds and the resulting dangling Si bonds increase the moisture absorption. Meanwhile, NH 3 plasma treatments reduce the leakage current by passivating the Si dangling bond and forming silicon nitride. The absorption of moisture and/or the formation of SiN x result in high dielectric constant of HSQ after prolonged NH 3 plasma bombardment. The dielectric constant of HSQ decreases and then increases with the increase of NH 3 plasma treatment time and a minimum dielectric constant of 2.2 is obtained after 50 s NH 3 plasma treatment at 200 W. Among various specimens in this study, the smallest insertion loss is 1.97 dB/mm at 20 GHz for the 400°C-annealed Cu/Ta/HSQ (NH 3-plasma-treated for 50 s). Appropriate NH 3-plasma bombardment helps to form a thin SiN x barrier layer which prevents the diffusion of oxygen without increasing the dielectric constant of the Cu–HSQ interconnect system. The leakage currents versus electric field characteristics suggest that a Schottky emission dominate conduction mechanism.

Comparative Analysis of Process of Diffusion of Interstitial Oxygen Atoms and Interstitial Hydrogen Molecules in Silicon and Germanium Crystals: Quantumchemical Simulation

AbstractA theoretical modeling and comparative analysis of the process of diffusion of the interstitial oxygen atoms and interstitial hydrogen molecules (H2) in silicon and germanium crystals at normal and hydrostatic pressure (HP) have been performed. The process of diffusion of particle with a strong interaction with a crystal lattice (interstitial oxygen atom) is a cooperative process. Three nearest Si (Ge) atoms of crystal lattice are involved in an elementary oxygen jump from a bond-center site to another bond-center site along a path in the (110) plane. It is precisely their optimum position (corresponding to a local minimum of the crystal total energy) determines the value of the diffusion parameters of an interstitial oxygen atom in silicon and germanium crystals. In a sense, the diffusion process may be considered as a diffusion process of qwasiparticle – (Oi+3Si). In the case of a particle weakly interacting with a crystal lattice (interstitial hydrogen molecules) we come up against the opposite case – the diffusion of H2 is not a cooperative process. The calculated values of the activation energy and pre-exponential factor for an interstitial oxygen atom δE(Si) = 2.59 eV, δE(Ge) = 2.05 eV, D0 (Si)= 0.28 cm2 s−1, D0 (Ge)= 0.39 cm2 s−1 and interstitial hydrogen molecule δE(Si) = 0.79 – 0.83 eV, δE(Ge) = 0.58 – 0.62 eV D0 (Si)= 7.4 10−4 cm2 s−1, D0 (Ge)= 6.510−4 cm2 s−1 are in an excellent agreement with experimental ones and for the first time describe perfectly an experimental temperature dependence of an interstitial oxygen atom and hydrogen molecules diffusion constant in Si crystals.

Microscopic Grinding Effects on Fabrication of Ultra-fine Micro Tools

A developed grinding system employing super-fine abrasive wheels was used to fabricate ultra-fine microtools having a variety of shapes. The machine successfully produced a cylindrically shaped micro-tool having a tip diameter of less than 1 μm. The surfaces of the produced micro-tools were investigated by advanced analytical methods. Fracture strength of the micro-tools was evaluated by nano-indentation testing, and their surface chemical properties were analyzed by XPS. The results suggest that the surface of processed microtools might have been strengthened by allowing the penetration and diffusion of oxygen atoms into the material, and allowing oxidation.

Simulations of heat and oxygen diffusion in UO 2 nuclear fuel rods

We present finite-element simulations of coupled heat and oxygen atom diffusion for UO 2 fuel pellets. The expressions for thermal conductivity, specific heat and oxygen diffusivity for the fuel element are obtained directly from previously published correlations, or from analysis of previously published data. We examine the temperature and non-stoichiometry distributions for a varying range of conditions. Simulations are performed for steady-state and transient regime in one-dimensional (purely radial) configurations. For steady-state conditions we perform parametric studies that determine the maximum temperature in the fuel rod as a function of non-stoichiometry and heat generation rate intensity. For transient simulations, we examine the time lag in the response of the temperature and non-stoichiometry distributions with respect to sudden changes in heat generation rate intensity and oxygen removal rate. All simulations are performed with the commercial code COMSOL Multiphysics™.

Kinetics of laser-induced oxidation of silicon near room temperature

The growth of ultra-thin (<6 nm) silicon-dioxide films on Si(100):H, Si(111):H, and a-Si:H surfaces in a dry oxygen atmosphere (0.1–10 Pa) at low temperatures (35–200 °C) was investigated. Oxidation was induced by pulsed F2-laserradiation at 157 nm. The thickness and composition of the growing films were monitored in real time by spectroscopic ellipsometry in the photon energy range of 1.15–4.75 eV. The kinetics of low-temperature oxidation was similar for the Si surfaces investigated and differs from that of high-temperature thermal oxidation (900–1200 °C) that can be described by the Deal–Grove model. To explain the faster growth at the initial stage, it is proposed that oxidation occurs by diffusion of oxygen atoms O and/or ions O-rather than oxygen molecules. The recombination of diffusive species to oxygen molecules limits their penetration into the bulk. A diffusion model is developed for low-temperature oxidation which takes into account the recombination process of the diffusive species. Good agreement between theory and experiment is found. The activation energy of diffusion of the active species was found to be 0.15 eV, in agreement with previous results and recent calculations for O- ions.

Measurement of oxygen atom diffusion in Nb and Ta by anelastic spectroscopy

Impurity interstitial atoms present in metals with BCC structure can diffuse in the metallic matrix by jumps to energetically equivalent crystallographic sites. Anelastic spectroscopy (internal friction) is based on the measurement of mechanical loss or internal friction as a function of temperature. Due to its selective and nondestructive nature, anelastic spectroscopy is well suited for the study of diffusion of interstitial elements in metals. Internal friction measurements were made using the torsion pendulum technique with oscillation frequency of a few Hz, temperature interval from 300 to 700 K, heating rate of about 1 K/min, and vacuum better than 10-5 mbar. The polycrystalline Nb and Ta samples used were supplied by Aldrich Inc. The results obtained showed thermally activated relaxation structures due to stress-induced ordering of oxygen atoms around the Nb (or Ta) atoms of the metallic matrix. The results were interpreted by three methods and led to activation enthalpy values for the diffusion of oxygen in Nb and Ta of 1.15 eV and 1.10 eV, respectively.

Kinetic Model of Si Oxidation at HfO2/Si Interface with Post Deposition Annealing

The oxidation mechanism at the HfO2/Si interface is discussed by investigating oxidation kinetics on the basis of experimental results that were obtained using the technique of grazing incidence X-ray reflectivity (GIXR) in combination with spectroscopic ellipsometry (SE) measurements. In a relatively thick HfO2 region, the interface layer growth shows a logarithmic dependence on annealing time, while the activation energy of oxidation is very small compared with that of conventional oxidation. These results clearly indicate that the oxidation mechanism at the HfO2/Si interface is different from that at the Si surface. Moreover, it is also reported that the oxidation at the HfO2/Si interface has no surface orientation dependence, no HfO2 thickness dependence and a slight O2 pressure dependence. All of the results obtained in this work suggest that atomic oxygen is involved in the oxidation at the HfO2/Si interface and the diffusion of oxygen atoms in the interface layer limits oxidation rate in a relatively thick HfO2 region. On the other hand, in an ultra-thin HfO2 region, HfO2 thickness dependence and Si surface orientation dependence are observed. These results suggest that both atomic oxygen and molecular oxygen are involved in the interface oxidation in an ultra-thin HfO2 region. On the basis of the results, we propose a kinetic model for the oxidation associated with both atomic oxygen and molecular oxygen at the HfO2/Si interface.

Removal of volatile organic compounds in atmospheric pressure air by means of direct current glow discharges

A nonthermal plasma with an electron density on the order of 10/sup 12/ cm/sup -3/ and a gas temperature of 2000 K was generated in atmospheric pressure air, using a microhollow cathode discharge as plasma cathode. The plasma was sustained in a /spl sim/1 mm/sup 3/ micro reactor, by a voltage of 470 V between the plasma cathode and a planar anode, and at currents ranging from 12 to 22 mA. This direct current glow discharge has been used to study the remediation of methane and benzene, two of the most stable volatile organic compounds (VOCs). The removal fraction for 300-ppm methane in atmospheric pressure air, flowing through the 0.5-mm thick plasma layer, with a residence time of the gas in the plasma of less than 0.5 ms, was measured at 80% with an energy density of 4 kJ/L. For benzene, the remediation rate is as high as 90%, comparable to results obtained with low pressure glow discharges. The energy efficiency for benzene remediation is 0.9 g/kWh, higher than that obtained for benzene remediation in low pressure glow discharges in noble gases. However, the VOC fraction remaining was found to be limited to values of approximately 0.1 and 0.05 for methane and benzene, respectively. In addition to experimental studies, the VOC dissociation mechanism in a VOC/dry air mixture plasma was modeled using a zero-dimensional plasma chemistry code. The modeling results have shown that atomic oxygen impact reactions are the dominant dissociation reactions for VOC destruction in this kind of glow discharge. Diffusion of atomic oxygen to the dielectric walls of the reactor is assumed to cause the observed limitation in the VOC destruction rate and efficiency.

Thermal treatment effects on interfacial layer formation between ZrO 2 thin films and Si substrates

This paper describes the growth condition of stoichiometric ZrO 2 thin films on Si substrates and the interfacial structure of ZrO 2 and Si substrates. The ZrO 2 thin films were prepared by rf-magnetron sputtering from Zr target with mixed gas of O 2 and Ar at room temperature followed by post-annealing in O 2 ambient. The stoichiometric ZrO 2 thin films with smooth surface were grown at high oxygen partial pressure. The thick Zr-free SiO 2 layer was formed with both Zr silicide and Zr silicate at the interface between ZrO 2 and Si substrate during the post-annealing process due to rapid diffusion of oxygen atoms through the ZrO 2 thin films. After post annealing at 650–750 °C, the multi-interfacial layer shows small leakage current of less than 10 −8 A/cm 2 that is corresponding to the high-temperature processed thermal oxidized SiO 2.

Laser-induced diffusion of oxygen on a stepped Pt(1 1 1) surface

Laser-induced diffusion of atomic oxygen on a stepped Pt(1 1 1) surface has been studied using ultrashort pulses of near-infrared light for the generation of a hot electron distribution at the surface. The dissociative adsorption of molecular oxygen at steps on the Pt(1 1 1) surface has been used to generate a nonequilibrium distribution of an adsorbate by decorating the step edges selectively with chemisorbed atomic oxygen. The coverage at the step edges during adsorption and induced diffusion has been monitored by exploiting the sensitivity of optical second-harmonic generation (SHG) on surface symmetry, which is macroscopically broken by regular steps. The diffusion rate shows a strong nonlinear dependence on the absorbed laser fluence indicating that the diffusion process can be understood in the same framework as the well studied phenomena of desorption induced by multiple electronic transitions (DIMET). Description within an electronic friction model reveals a temperature-dependent friction coefficient which we attribute to an indirect excitation mechanism of the frustrated translations.