Oxides Thin Films

The aim of this work is to study the thermal reactions of thin films of gold and titanium vacuum deposited on GaAs including semi-insulating type GaAs(SI). We have examined Au/Ti/GaAs by the use of different techniques: X-Ray diffraction (XRD), scanning electron microscopy (SEM) and Rutherford backscattering (RBS) analysis in Tandem type accelerator. The deposition of Ti and Au films on (100) surfaces was carried out by thermal evaporation under a relative pressure of 8⋅10–5 torr, and then the samples were annealed in a furnace at low vacuum. The SEM image of Ti/GaAs interface presents a clear delimitation without a thermal reaction. For Au/Ti/GaAs (SI) samples Ti signal is interfered with GaAs signal, so it appears an interlayer diffusion process as in literature. The characteristic XRD pattern presented the main peaks for Au, Ti and GaAs. From this stage of experiments, further studies are in progress on the interlayer diffusion phenomenon in the two layers of Au-Ti on GaAs(SI) su...

This article presents the results of a study of the composition of oxides formed on surface of the laser impact zone (LIZ) in air of 9KhS, R6М5 and R9K5 tool steels, differing in chemical composition and degree of alloying. Using X-ray photoelectron spectroscopy, it was found that the formed oxide films have a qualitatively matching "layered" structure and differ significantly from each other both in overall thickness and in the thicknesses of the oxide films of different phase composition included in them. It is shown that the formed film is largely multilayered and multicomponent. For alloyed tool steels, a significant redistribution of alloying element concentrations along the LIZ depth was found, which determines the composition of the formed oxides and their location relative to the base material. It is noted that, regardless of the steel composition, the oxide film outer layer on the LIZ surface consists mainly of a mixture of FeO and Fe 2 O 3 oxides; deeper towards the base metal, there is a Fe 3 O 4 layer and a mixture of higher oxides of alloying elements located in the following sequence deep from the LIZ surface: WO 3 , V 2 O 5 , MoO 2 , Cr 2 O 3 , and CoO. For R9K5 steel, the selective enrichment of the surface in W and Mo atoms was found, leading to strengthening of grain boundaries and the appearance of a local hardened layer at a depth of 90 nm. It was found that the oxide film integral thickness on the LIZ surface of the studied steels does not exceed 200-250 nm.

The surface versus bulk composition, electronic and physical structure of polycrystalline Cu(In,Ga)Se 2 thin-film interfaces have been characterized using X-ray photoemission spectroscopy (XPS) and positron annihilation spectroscopy (PAS). Angle-resolved high resolution photoemission measurements on the valence band electronic structure and Cu 2p, In 3d, Ga 2p and Se 3d core lines were used to evaluate the surface and near surface chemistry of CuInSe 2 and Cu(In,Ga)Se 2 device grade thin films. XPS compositional depth profiles were also acquired from the near surface region. PAS was used as a nondestructive, depth-sensitive probe for open-volume-type defects. Device efficiencies are correlated with these results to show the effects of compositional variations and defect concentrations in the near surface region on device performance.

Single crystal GaAs substrates implanted with 70 MeV 120 Sn have been investigated by X-ray diffraction (XRD) and electrical resistance measurements after annealing in the temperature range 373-823 K. XRD measurements for the samples annealed up to 723 K show two peaks, one due to the substrate and another due to the implant damaged layer. The strain parameter from the measured separation between the substrate and layer peaks of several symmetric and asymmetric reflections after each annealing step has been calculated. Strain recovery occurs in two predominant annealing stages, one at about 500 K and the other at about 700 K. Temperature dependence (100-300 K) of resistance of these samples indicates that electrical conduction in the samples annealed up to 723 K, is dominated by variable range hopping. Localized states density at the Fermi level N(E F ), estimated from temperature dependence of sample resistance after each annealing step, shows two annealing stages similar to those observed from XRD measurements. Isothermal annealing carried out at two different annealing temperatures (523 and 573 K) indicates the activation energy E a = 0.16 eV for the first annealing stage.

Anodic and spontaneous corrosion of different types of stainless steel (AISI 304L, AISI 316L and 2205 DSS) in phosphate-buffered saline solution (PBS, pH = 7.4) at 37 °C (i.e., in simulated physiological solution in the human body) were examined using open circuit potential measurements, linear and cyclic polarization, and electrochemical impedance spectroscopy methods. After the anodic and spontaneous corrosion, the surface of the tested samples was investigated by light and scanning electron microscopy (SEM) with EDS analysis. It has been established that the tendency of the examined steel materials towards local corrosion decreases in the order: AISI 304L < AISI 316L < 2205 DSS. Namely, the possibility of repassivation and the resistance to local corrosion increases in the same order. The corrosion resistance of steel samples at open circuit potential is a consequence of forming a natural oxide film with a bi-layer structure and consists of an inner barrier and an outer por...

Untangling the cerium and iron contributions to the magnetism of Ce-doped yttrium iron garnet G. HERRANZ, B. CASALS, R. CICHELERO, J. FONTCUBERTA, Institute for Materials Science of Barcelona ICMAB-CSIC, H.B. VASILI, P. GARGIANI, M. VALVIDARES, J. HERRERO-MARTIN, E. PELLE-GRIN, ALBA Synchrotron Light Source, Spain, J. GESHEV, Univ Fed Rio Grande do Sul, Brazil -Due to their large magneto-optic responses, rare-earth-doped yttrium iron garnets, Y 3 Fe 5 O 12 (YIG), are highly regarded for their potential in photonics and magnonics. Here we consider the case of Ce-doped YIG (Ce-YIG), in which substitutional Ce 3+ ions are magnetic because of their 4f 1 ground state. Hence, it is expected that Ce substitution can remarkably impact on the magnetization of YIG. However, it is not completely understood how exactly the Ce ions contribute to the macroscopic magnetic properties. Having this in mind, we have carried out magneto-optical and soft x-ray spectroscopy measurements on Ce-YIG thin films. In particular, we have used the element-specificity of XMCD to extract the individual magnetic hysteresis loops linked to Ce 3+ and Fe 3+ ions, respectively. Our results show that the doping of YIG with Ce causes a disruption of the electronic and magnetic properties of the parent compound, which results into a reduction of the magnetic coupling between the Ce and Fe magnetic moments, especially at low magnetic fields. Our results are relevant for the understanding of magnetism in rare-earth doped YIG and, eventually, may enable a quantitative evaluation of the magneto-optic properties of rare earth incorporation into YIG.

Anodic and spontaneous corrosion of different types of stainless steel (AISI 304L, AISI 316L and 2205 DSS) in phosphate-buffered saline solution (PBS, pH = 7.4) at 37 • C (i.e., in simulated physiological solution in the human body) were examined using open circuit potential measurements, linear and cyclic polarization, and electrochemical impedance spectroscopy methods. After the anodic and spontaneous corrosion, the surface of the tested samples was investigated by light and scanning electron microscopy (SEM) with EDS analysis. It has been established that the tendency of the examined steel materials towards local corrosion decreases in the order: AISI 304L < AISI 316L < 2205 DSS. Namely, the possibility of repassivation and the resistance to local corrosion increases in the same order. The corrosion resistance of steel samples at open circuit potential is a consequence of forming a natural oxide film with a bi-layer structure and consists of an inner barrier and an outer porous film. The inner barrier film has a small thickness and extremely high resistance, while the outer porous film is much thicker but also has significantly lower resistance. The inner barrier layer mainly prevents corrosion of examined steel samples in order: AISI 304L < AISI 316L < 2205 DSS. Light microscopy and SEM/EDS analysis after pitting and spontaneous corrosion showed damage on the AISI 304L and AISI 316L surface, while the surface of 2205 DSS was almost undamaged by corrosion.

We report giant magnetoelectric coupling at room temperature in a self-assembled nanocomposite of BiFeO3-CoFe2O4 (BFO-CFO) grown on a BaTiO3 (BTO) crystal. The nanocomposite consisting of CFO nanopillars embedded in a BFO matrix exhibits weak perpendicular magnetic anisotropy due to a small out-of-plane compression (∼0.3%) of the magnetostrictive (CFO) phase, enabling magnetization rotation under moderate in-plane compression. Temperature dependent magnetization measurements demonstrate strong magnetoelastic coupling between the BaTiO3 substrate and the nanocomposite film, which has been exploited to produce a large magnetoelectric response in the sample. The reorientation of ferroelectric domains in the BTO crystal upon the application of an electric field (E) alters the strain state of the nanocomposite film, thus enabling control of its magnetic anisotropy. The strain mediated magnetoelectric coupling coefficient α=μodM/dE  calculated from remnant magnetization at room temperatur...

Pressure is shown to have a drastic effect on the annealing characteristics of ptype, nitrogen-doped ZnSe. Samples annealed in vacuum show decreased carrier concentrations and simultaneous formation of deep-donor-related luminescence, while samples annealed under pressure show suppression of this compensating donor. The results are interpreted as an increase in the formation energy of the compensating deep donor under pressure. In addition the samples annealed under pressure show emergence of a new, intense, green luminescence band centered at 2.44 eV. The magnitude of the shift of this peak under applied stress suggests that it results from a recombination involving a deep acceptor.

WNx/GaAs Schottky contacts formed by reactive sputtering were found to be thermally stable up to an annealing temprature of . . . . . . . . 900 DC. The interface morphology and structure of this contact under high temperature annealing conditions ( > 700 DC ) have been investigated by transmission electron microscopy (TEM) and x-ray diffractometry techniques. For the as-deposited samples, the thin film had an amorphous structure. Mter annealing at high temperatures, the amorphous phase transformed to (Y-W and WzN phases. However, the contact interface remained thermally stable up to 850 DC. Cross-sectional TEM micrographs revealed that annealing at temperatures above 850 DC resulted in the formation of 'pockets' beneath the interface. This phenomenon has been correlated with the electrical properties of the contacts, e. g., an enhancement of the barrier height of the contact. Comparisons between the interface morphology of this system and other refractory metal nitride contacts (e. g., TiN/GaAs) are also presented.

Aluminum is very sensitive to oxidation reactions. If a fresh surface of melt is exposed to air, it oxidizes quickly and an oxide layer covers the melt surface. New oxide films formed in a very short time during casting are thin and folded. The metal surface can be folded and create a double-oxide film as a result of the melt turbulence. The entrance of this double-oxide film into the melt is one of the most important reasons for the formation of crack-like defects during casting. In this work, the characteristics of these new oxide films have been investigated based on the oxide-metal-oxide sandwich technique. To study the futures of new oxide film, the contact area between two adjacent and entrapped bubbles have been examined using scanning electron microscope (SEM). Results showed that the short time oxide films formed in pure aluminum have a thickness less than 100 nanometer.

Magnesium alloys in liquid-phase condition form surface oxide films due to their high rate of oxidation. Oxide films enter the melt as a result of surface turbulence, and remain inside the workpiece after solidification. The incoherent nature of their interface causes decreases in mechanical properties and reliability of castings. The effect of critical velocity and greater velocities of entering the melt into the die cavity on fracture toughness has been studied in this research. Results indicated that an increase in the velocity decreases the fracture toughness, e.g. an increase of the velocity from 0.4 m/s (critical gate velocity of magnesium alloys) to 3.0 m/s decreases the fracture toughness for about 40%. Furthermore, increasing the velocity of melt entering the mold from 0.4 m/s to 1.0 and 3.0 m/s resulted in a decrease in the Weibull modulus from 13.34 to 7.28 and 4.93, respectively, and consequently, caused the results to be more scattered. SEM micrographs showed that increasing the velocity beyond the critical value increases significantly the quantity and size of the oxide films. Moreover, for the case of speeds greater than the critical value, double-layer films are observable due to considerable surface turbulence of the melt. Analysis of the fractured surfaces also showed that the failure mode of specimens produced using velocities greater than the critical value is of brittle type, whereas it was found to be ductile for the case of critical velocity.

Although the solubility of oxygen in molten aluminum alloys is said to be negligible, the fresh surface of the melt oxidizes quickly in the air and an oxide film is formed on the melt surface. Oxide-metal-oxide sandwich technique is a method for the study of short-time surface oxide films. In this research, air was blown at 0.5 atmosphere into the melts of Al-1Mg and Al-6Mg alloys by means of a compressor in order to form air bubbles within the melts. The sandwiches of oxide-metal-oxide were formed at locations where these bubbles reach each other. Some of the characteristics of these films inside the bubbles were evaluated using the scanning electron microscope. In Al-1Mg alloy, the formation of crystalline aluminum oxide as well as the granules of magnesium oxide at the same time was confirmed whereas the magnesium oxide in the form of layer and granule was detected for the case of Al-6Mg alloy.

The magnetic and magneto-optic properties of epitaxial CeY 2 Fe 5 O 12 (Ce∶YIG) and Y 3 Fe 5 O 12 (yttrium iron garnet or YIG) thin films grown by pulsed laser deposition on gadolinium gallium garnet substrates are determined. An enhanced Faraday effect is known to result from Ce substitution into the yttrium iron garnet lattice, and here we characterize the magneto-optic Kerr effect, as well as the magnetic hysteresis and ferromagnetic resonance response that result from the Ce substitution. X-ray diffraction analysis reveals a high crystallographic quality for the Ce∶YIG films. Measurements of the magneto-optic Kerr effect for two different wavelengths demonstrate that the Ce∶YIG exhibits an up-to-tenfold increase in Kerr rotation compared to YIG. The Ce∶YIG has a slightly larger magnetic moment, as well as increased magnetic damping and higher magnetic anisotropy compared to YIG with a dependence on the crystalline orientation. By specific cerium substitution in YIG, our results show that the engineering of a large Kerr effect and tailored magnetic anisotropy becomes possible as required for magneto-optically active spintronic devices.

This study investigated the surface hardening of AISI 4340 steel by linear oscillation scanning with a fibre laser. Various frequencies and amplitudes of oscillation were used under laser power of 2020 and 3020 W. Microscopic evaluation was done, and the effect of oscillation frequency on the hardened depth was examined. Hardness profiles were measured along the centre of the irradiated track toward the feeding direction of the laser, across the irradiated width and into the depth below the irradiated surface. The homogeneity of hardness and hardened depth with different processing parameters was investigated. The hardness profiles were compared with the results obtained with conventional single track hardening.

Various models have been developed to address the problem of &quot;Fermi level pinning,&quot; i.e., why the barrier height varies much less than the Schottky metal work function limit. The most widely accepted mechanism is some variant of the metal-induced gap state model. However, recent experimental data on (lOO)In, Gal _ x As surfaces and interfaces (O&lt;x&lt; 1) suggest that the surface or interface Fermi level can assume values which lie welt outside the variance associated with Fermi level pinning; in fact, recent data suggest the achievement of the Schottky limit. Furthermore, studies of epitaxially grown layers where dopant incorporation is dependent on an interface Fermi level suggest that such Fermi level positions are not always pinned. In order to account for these recent results, along with the pinned values, we introduce the concept of an insulating layer like surface reconstruction. Recent calculations suggest thd reconstructions of the GaAs(100) surface are insulati...

ABSTRACTRecent studies of interface states and band bending at metal / III-V compound semiconductor interfaces reveal that these junctions are much more controllable and predictable than commonly believed. Soft x-ray photoemission spectroscopy studies demonstrate a wide range of band bending for metals on many III-V compounds, including GaAs. Cathodoluminescence spectroscopy measurements show that discrete states form at the microscopic junction which can have a dominant effect on the band bending properties. Internal photoemission measurements confirm the bulk barrier heights inferred by photoemission methods. After separating out surface chemical and bulk crystal quality effects, one finds simple, predictive barrier height variations which follow classical Schottky behavior.

Cathodoluminescence spectroscopy is used to identify diffusion-associated III-V semiconductor defects and establish their role in AlGaAs/GaAs intrinsic and n-type impurity induced interdiffusion (Si, Ge, S, and Se) for various ambient conditions, As- and Ga-rich. These identifications involves the study of the temperature and composition dependence of these deep levels and their correlation with theoretical calculations. Our results reveal Column III vacancies and their complexes as the sole mediators of diffusion.

We have used soft x-ray photoemission spectroscopy measurements to demonstrate that metalGaAs interfaces can exhibit relatively unpinned Fermi level (Ef ) movements. For dean GaAs ( 100) surfaces obtained by molecular-beam epitaxy (MBE) growth and thermal decapping of a protective As overlayer, the metals Au, AI, Cu, and In produce a O.6-0.7-eV range of Ef stabilization. For a given metal, this stabilization occurs at the same energies for n-type and p-type GaAs. Furthermore, Ef movements are metal-dependent and can evolve over multimonolayer coverages. These results are examined with respect to pronounced differences in semiconductor quality between MBE versus melt-grown GaAs and in the context of previous GaAs Ef&#39; measurements. A self-consistent analysis of the junction electrostatics accounts for the functional dependence of barrier height on metal work function. The results highlight the importance of bulk quality as well as interface specific phenomena in controlling the Sc...

The sensitivity of luminescent Boltzmann thermometers is restricted by the energy difference between the thermally coupled excitement levels of trivalent lanthanides, and their values further decrease with increases in temperature, rendering their use at high temperatures difficult. Here, we demonstrate how to overcome this sensitivity limitation by employing multiparameter and multilevel cascade temperature readings. For this purpose, we synthesized Dy3+:Y2SiO5, a phosphor whose emission is known to begin quenching at very high temperatures. Its photoluminescence-emission features, later used for thermometry, consisted of two blue emission bands centered around 486 nm and 458 nm, and two bands centered around 430 nm and 398 nm, which were only visible at elevated temperatures. Next, we performed thermometry using the standard luminescence-intensity ratio (LIR) method, which employs the 4F9/2 and 4I15/2 Dy3+ levels’ emissions and the multilevel cascade method, which additionally use...

The sensitivity of luminescence thermometry is enhanced at high temperatures when using a three-level luminescence intensity ratio approach with Dy3+- activated yttrium aluminum perovskite. This material was synthesized via the Pechini method, and the structure was verified using X-ray diffraction analysis. The average crystallite size was calculated to be around 46 nm. The morphology was examined using scanning electron microscopy, which showed agglomerates composed of densely packed, elongated spherical particles, the majority of which were 80–100 nm in size. The temperature-dependent photoluminescence emission spectra (ex = 353 nm, 300–850 K) included Dy3+ emissions in blue (458 nm), blue (483 nm), and violet (430 nm, T 600 K). Luminescence intensity ratio, the most utilized temperature readout method in luminescent thermometry, was used as the testing method: a) using the intensity ratio of Dy3+ ions and 4I15/2→6H15/2/4F9/2→6H15/2 transitions; and b) employing the third, higher ...

Determining vacancy in complex crystals or nanostructures represents an outstanding crystallographic problem that has a large impact on technology, especially for semiconductors, where vacancies introduce defect levels and modify the electronic structure. However, vacancy is hard to locate and its structure is difficult to probe experimentally. Reported here are atomic vacancies in the InAs/GaSb strained-layer superlattice (SLS) determined by atomic-resolution strain mapping at picometre precision. It is shown that cation and anion vacancies in the InAs/GaSb SLS give rise to local lattice relaxations, especially the nearest atoms, which can be detected using a statistical method and confirmed by simulation. The ability to map vacancy defect-induced strain and identify its location represents significant progress in the study of vacancy defects in compound semiconductors.

We have developed a Josephson vortex-flow transistor based on a parallel array of 440 YBa2Cu3O7−δ bicrystal grain boundary Josephson junctions. The array&#39;s critical current Ic was measured as a function of the control current Ictrl through a control line that is inductively coupled to the array. The device has a highly asymmetric Ic(Ictrl) curve with several regions where a switching behaviour is observed characterized by a maximum current gain gmax = ∂Ic/∂Ictrl of 19 and a significant dynamic range of 20 μA at 77 K. In the range 4.7–92 K gmax versus temperature is non-monotonic with a maximum recorded at 77 K.

The redistribution of titanium during the growth of epitaxial CoSi2 from the reaction of Co(20nm)/Ti(lOnm)/Si&lt;100&gt; structures has been investigated. The concentration of Ti in the CoSi2 layers versus annealing temperature has been determined. Emphasis is placed on the formation of inhomogeneities in the epitaxial CoSi2 layers, and the role of Ti with respect to the thermal stability of the layers. The fundamental mechanism for the development of inhomogeneities in the epitaxial CoSi2 layers will be discussed.

Semiempirical potential energy functions have been utilized for a variety of calculations in the_Ga-Al-As system: (1) surface energies have been calculated for several orientations of GaAs; (2) ledge energies for the GaAs(001) (As terminated) surface show long range interaction effects with the ledge energy increasing with spacing; (3) GaAs(001)/A1As(001) superlattices have been simulated for a range of interlayer spacings with the excess interfacial energy per interlayer increasing from 5 erg/cm 2 at an interlayer spacing of I molecular layer (5.8 A) to 50 erg/cm2 at an interlayer spacing of 18 molecular layers (103.8 A).

Chemistry, crystal structure, interfacial microstructure and electrical characteristics of novel Cu-Ge alloyed ohmic contacts to n-type GaAs with a very low specific contact resistivity ((4–6)×10−7 Ω·cm2 for n∼1×1017 cm−3) were investigated by various methods. The Cu-Ge alloys with a wide range of Ge concentration, from 15 to 40 at %, were prepared by depositing sequentially Cu and Ge layers (or vise versa) onto GaAs substrates at room temperature followed by annealing at 400°C. It is shown that Cu reacts only with Ge to form the ξ and ε1-Cu3Ge phases. The latter has an orthorhombic structure with average lattice parameters: a = 5.301 Å, bo = 4.204 Å, co = 4.555 Å, arising from the parent hexagonal ξ-phase by Cu-Ge ordering along ao. The interface with GaAs is atomically sharp and free from secondary phases. The ε1-Cu3Ge ordered phase which is chemically inert with respect to GaAs, is believed to be responsible for high thermal stability (up to 450°C), interface sharpness, high cont...

The microstructure and tribological properties of the modified surface of 12Kh2N4A (its equivalent is E3310) and 38Kh2MYuA (its equivalent is A290C1M) structural alloy steels after laser treatment (LT) are studied using an ytterbium continuous-wave fiber laser. The laser surface treatment is carried out in air at a laser power of 75 and 100 W and a laser beam scanning velocity varying in the range of 2 to 14 mm/s. The micro-and macrostructures of the steels are examined using metallography and durometry; the structure of the laser-affected areas (LAZ) and steel constituents are determined. The scanning velocity at a laser power of 100 W is shown to have the most significant effect on the LAZ dimensions. The maximum depth of the LAZ during LT without surface melting in the studied modes is 310 μm for 12Kh2N4A steel and 170 μm for 38Kh2MYuA steel. According to the hardening mode, the microhardness in the LAZ increases from 1.36 to 1.97 times for 12Kh2N4A steel and by 2.0-2.6 times for 38Kh2MYuA steel. The tribotests performed using a pin-on-disk configuration show that the reduction of linear wear and wear rate in the 12Kh2N4A and 38Kh2MYuA steels at a hardened layer depth of ~100 μm is 26.6 and 43.9%, respectively.

In order to simulate the environment experienced by spacer grids in a boiling water reactor (BWR), specimens of the Ni-based Alloy X-750 were exposed to a water jet in an autoclave at a temperature of 286 C and a pressure of 80 bar. The oxide microstructure of specimens exposed for 2 h, 24 h, 168 h and 840 h has been investigated mainly using electron microscopy. The specimens suffer mass loss due to dissolution during exposure. At the same time a complex layered oxide develops. After the longest exposure the oxide consists of two outer spinel layers consisting of blocky crystals, one intermediate layer of nickel oxide interspersed with Ti-rich oxide needles, and an inner layer of oxidized base metal. The evolution of the oxide leading up to this structure is discussed and a model is presented.

ABSTRACTThe oxygen behaviour and its influence on the annealing properties of the TiO2/Si and Ti/TiO2/Si systems have been investigated. For the TiO2/Si system no reaction at all could be evidenced after vacuum annealing up to 900°C for 30&#39;. In the Ti/TiO2/Si system metallic Ti reacts with the TiO2 film above 400°C and at 600°C a uniform oxygen solid solution at the solubility limit was obtained without any Si reaction. Silicide formation occurs for annealing temperatures higher than 650°C and causes oxygen expulsion from the reacted layer and consequently a rise in its concentration at the surface where Ti oxide precipitation takes place. This surface oxide layer prevents a further growth of the silicide up to 850°C. The reaction of the whole metal film is attained only by annealing at 900°C or above, when the oxide is completely reduced and an important oxygen loss takes place. A model explaining this behaviour is proposed.

ABSTRACTA microscopic strain distribution across commensurate interfaces between GaAs layers grown on semi-insulating GaAs substrates was observed by means of convergent beam electron diffraction (CBED) and large angle convergent beam methods (LACBED). Strain relaxation at a specific distance from the interface was observed in these layers without formation of misfit dislocations. It was proposed that specific point defects distributed close to the interface can explain the asymmetric broadening of high-order Laue zone (HOLZ) lines in the CBED patterns.

The redistribution of titanium during the growth of epitaxial CoSi2 from the reaction of Co(20nm)/Ti(lOnm)/Si&lt;100&gt; structures has been investigated. The concentration of Ti in the CoSi2 layers versus annealing temperature has been determined. Emphasis is placed on the formation of inhomogeneities in the epitaxial CoSi2 layers, and the role of Ti with respect to the thermal stability of the layers. The fundamental mechanism for the development of inhomogeneities in the epitaxial CoSi2 layers will be discussed.

The Scanning Transmission Electron Microscopy, when used in the Electron Beam Induced Current mode (STEM-STEBIC), can allow the correlation, at high spatial resolution, of structural and electrical properties of individual defects in semiconductor materials. In this paper we describe the STEM-STEBIC defect analysis in gallium arsenide (bulk and epitaxial) and polycrystalline silicon with both p-n and Schottky barriers, in order to put in light some spurious effects associated to multiple scattering of the primary beam and to assess the potentiality of this technique. A proper device for a JEOL 200 kV transmission electron microscope was set up with facilities of double tilting and applying bias voltages. This apparatus allowed us to study correlations between diffraction contrast, at different orientation conditions, and conductive contrast, at different junction barrier amplitudes. The typical black recombination contrast at the electrical defects was not observed in poly-Si, unless very thick regions were examined or a direct bias voltage was applied. Recombining electrical defects were easily detected, on the contrary, in GaAs, also near the thinnest region of the specimen.

In the present work, the fabrication of a hydrophobic surface was carried out by thermal oxidation of thin layers of Zn deposited by electrodeposition on an aluminum substrate under air atmosphere at different temperatures between 400 C and 500 C. Structural analysis by XRD and Raman spectroscopy shows that increasing the annealing temperature leads to the formation of a considerable amount of ZnO on the aluminum substrate. ZnO-bound XRD peaks appear and Zn-and Al-bound peaks decrease. For TS  400 C and 500 C, the films treated at are polycrystalline with a hexagonal structure of the Wurtzite type due to the existence of the more intense peak relating to the orientation (100) located around the angle 31.75 . EDX analysis gives the chemical composition of these films and confirms the presence of zinc and oxygen in an almost stoichiometric composition. The morphological study of thin layers treated at 500 C shows the coexistence of nanostructures in the form of deformed flowers, which leads to their hydrophobicity. The contact angle values measured are  90 for the films treated at 400 C and 500 C, which confirms the hydrophobic nature with a high value obtained equal to 135.

To ensure good adhesion between a 200 nm thick silicon dioxide layer and a 4.5 μm thick hardcoat polymeric coating, a better understanding of mechanisms of adhesion at this interface is needed. To reach this purpose, focus is placed on two axes: characterizing mechanical properties of materials composing the system and in parallel, finding an applicable and effective method to quantify adhesion. Small dimension of SiO 2 thin film makes it challenging to accurately characterize it. Hence the use of both nano-indentation and AFM to attempt assessment of SiO 2 thin film elastic modulus Ef; taking into account limitations and uncertainty associated with each technique. Elastic modulus of SiO 2 thin film determined by nanoindentation is roughly 50 GPa on a wafer substrate and 15 GPa on a lens substrate. As for AFM, modulus measured is approximately 56 GPa on a wafer substrate and 22 GPa on a lens substrate. This highlights significant influence of substrate for both techniques. Impact on mechanical properties between SiO 2 thin films under different intrinsic stresses was also investigated. Results suggest that higher density of SiO 2 thin film leads to higher elastic modulus. To quantify adhesion, micro-tensile and micro-compression tests were performed. Micro-tensile experiments give ultimate shear strengths of hardcoat-substrate interface ranging from 9 to 14 MPa. Values of energy release rates of SiO 2 / Hardcoat, range from 0.1 J/m² to 0.5 J/m², depending on moduli values found on wafer or lens substrate.

Simultaneous wet-thermal oxidation of MBE and MOCVD grown AlxGal_xAs layers (x = 0.1 to 1.0) showed that the epitaxial growth method does not influence the oxidation rate. Nearly identical oxidation depths were measured for samples grown by both techniques. It was found, however, that the oxidation rate is very sensitive to non-uniformities in the Al concentration in the AlxGaixAs layers, and that maintaining consistent and uniform Al concentrations is critical to achieving reproducible oxidation rates. The study also showed that the oxidation rate was not affected by the V/Ill ratio during growth nor by impurities at concentrations less than or equal to 10 ppm.

The measurement of high temperatures in oxides and oxide-based structures in practical applications often presents challenges including steep thermal gradients, the presence of flames or chemically aggressive environments, and the transparency or translucency of most oxides. For turbine engines, oxide coatings are of great commercial importance, and the rapid motion of parts prohibits contact thermometry. Luminescence thermometry offers a number of advantages for measuring temperature in such systems and has been the subject of ongoing study for many years. Recent work on rare-earth-doped thermal barrier coatings, environmental barrier coatings, and related oxides has demonstrated the feasibility of luminescence thermometry to temperatures well in excess of 1000°C. The luminescent properties of these materials and the analytical techniques used to extract reproducible temperature measurements from the measured luminescence are reviewed.

ABSTRACTHigh-resolution transmission electron microscopy has been used to study formation of interfacial defects related to misfit strain accommodation in Ge/Si heterostructures (mismatch 4%) grown in the two-dimensional mode. Special emphasis is placed on the conditions leading to a two-dimensional (layer-by-layer) growth mode. We discuss general features of a dislocation tangle resulted from glide-limited plastic relaxation, typical for highly mismatched (001)-diamond and zinc-blende heterostructures. The evolution of the dislocation network as a function of film thickness and thermal annealing is controlled by growth instabilities and dislocation interactions. The observed correlation in distribution of parallel misfit dislocations including pairing (at &lt;2 nm) of misfit segments from intersecting glide planes and rearrangements in a nonequilibrium dislocation network driven by elastic interaction between 60° dislocation segments in the almost relaxed heterostructures are discu...

A self-consistent model is developed to describe the formation of misfit dislocation loops in hemispherical epilayers of finite size grown on thick substrates. The lattice mismatch between the substrate and the epilayer is described by virtual interfacial dislocation loops situated in the interface. The free surface boundary conditions are satisfied by the surface dislocation loops situated on the surface of the hemispherical island. A misfit dislocation loop is nucleated and the changes in the energy of the configuration are used to determine if a lowering in the total energy of the configuration can occur. The model consisting of the prismatic dislocation loops in the epilayer is replaced by a simpler dislocation model consisting of glide dislocation loops so that the stress fields and interaction energy terms between dislocations in a two-phase medium could be evaluated. The energy associated with the coherent epilayer and that with the misfit dislocation are evaluated by the minimization of the total energy of the configuration with respect to the Burgers vectors of the surface dislocation loops. The position of the misfit dislocation loop from the interface is changed for a given size of the hemispherical island and the energy terms are determined. The formation of a misfit dislocation loop is considered favorable when the energy of the configuration in the presence of the misfit dislocation is lower than that of the coherent epilayer. The numerical analysis is carried out for hemispherical islands of GaAs grown on (100) Si with a misfit dislocation of Burgers' vector 3.84A. It has been found energetically favorable to nucleate a misfit dislocation loop at a distance of 3/i from the interface when the radius of the hemispherical island is equal to or greater than 40/~. In addition, a misfit

ABSTRACTRapid thermal annealing (RTA) (800–1000°C, 1–60 s) was performed on capless and silicon nitride (SixNy) capped GaAs samples implanted with Si (30 keV, 4.5×1013cm−2 ) and SiF+ (50 keV, 4.5×1013cm−2 ). The maximum activation for the Si+ implants saturated at 25% (capless) and 42% (capped) and that for the SiF+ implants saturated at 20% (capless) and 35% (capped). The activation degraded at temperatures &gt; 825°C due to surface decomposition in the capless annealing case and at &gt; 925°C due to the cap failure in the capped annealing case. For all the RTA conditions studied here, higher activation always occurred with the Si+ rather SiF+ implants. An activation energy of 0.48 eV for the annealing process was determined from the electrical data. It was also observed that the heating and/or cooling rates can significantly influence the electrical activation.

interfaces, are studied and lattice images of their interfaces are given. The lattice images reveal interfacial defects as, e.g., misfit dislocations and interface steps, which cannot always be observed with conventional TEM. The interpretation of lattice images of interfaces is discussed and a systematic classification of interface defects and their appearance on lattice images is given for the case of the Si-Pd,Si interface. The results can be generalized for all coherent interfaces, including grain boundaries. >fit Hilfe yon QuerschnittsprLparaten werden direkte Abbildungen des Kristallgitters an Silizium-Silizid-GrenzflLchen erhalten. Die Si-Nisi,-, Si-Nisi-und Si-Pd,Si-Grenzflachen werden untersucht, und Gitterabbildungen dieser Grenzflachen werden gezeigt. Die Gitterabbildungen lassen Grenzfliichendefekte wie z. B. Fehlanpassungsversetzungen und St.ufen erkennen, die niit konvent,ioneller TEM nicht immer erfadbar sind. Die Interpretation von Gitterabbildungen an Grenzflachen wird diskutiert. Bur den speziellen Fall der Si-Pd,Si-Grenzflache wird eine systematische Klassifikation von Grenzfliichendefekten sowie ihres Aussehens auf Gitterabbildungen gegeben. Die Ergebnisse konnen fur alle koharenten Grenzflachen (inklusive Korngrenzen) verallgemeinert werden.

Due to their large magneto-optic responses, rare-earth-doped yttrium iron garnets, Y 3 Fe 5 O 12 (YIG), are highly regarded for their potential in photonics and magnonics. Here, we consider the case of Ce-doped YIG (Ce-YIG) thin films, in which substitutional Ce 3+ ions are magnetic because of their 4f 1 ground state. In order to elucidate the impact of Ce substitution on the magnetization of YIG, we have carried out soft x-ray spectroscopy measurements on Ce-YIG films. In particular, we have used the element specificity of x-ray magnetic circular dichroism to extract the individual magnetization curves linked to Ce and Fe ions. Our results show that Ce doping triggers a selective charge transfer from Ce to the Fe tetrahedral sites in the YIG structure. This, in turn, causes a disruption of the electronic and magnetic properties of the parent compound, reducing the exchange coupling between the Ce and Fe magnetic moments and causing atypical magnetic behavior. Our work is relevant for understanding magnetism in rare-earth-doped YIG and, eventually, may enable a quantitative evaluation of the magneto-optical properties of rare-earth incorporation into YIG.

The influence of low-temperature (40 K) e-beam irradiation on the cathodoluminescence (CL) spectrum reconstruction of MOVPE ZnSe : N epilayers was studied. The maximum of the initial wide emission band shifted from 466 to 459 nm and the LO phonon structure appeared at a total exposure dose greater than 10" cm-'. Neither Hg lamp nor N2 laser irradiation produced any spectral change. The observed reconstruction was attributed to an acceptor activation by a destruction of N-H complexes followed by a removal of free H atoms from the epilayer. This was initiated by ionization processes under the e-beam irradiation.

Alloy 690 is a high-chromium nickel alloy widely used for steam generator tubes in pressurized water reactors. We have applied an optimized thermal oxidation treatment to alloy 690 consisting of 4 h at 500 C (0.6 at% O 2 in Ar) to make an improved diffusion barrier layer limiting the release of Ni during processing. The efficiency of such a treatment was tested by immersion in simulated pressurized water reactor primary water for 9 weeks. This work also explores the use of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to characterize the oxidized films formed after different treatments. Reference spectra were acquired by analyzing thermally oxidized Ni, Cr, and Ni-30Cr samples as well as hydroxides and spinel powders [Ni(OH) 2 and NiFe 2 O 4 ]. ToF-SIMS spectra of model oxides have allowed the selection of a set of ionic intensity ratios to be used for data processing of the spectra and profiles, obtained after the different oxidation steps applied on alloy 690. Thus, the following information was obtained: (i) the oxide layer structure is triplex; (ii) an intermediate layer is composed of Cr 2 O 3 , on which surface coverage depends on treatment; (iii) the outer layer is Ni-and Fe-rich, whereas the inner layer is most probably constituted by a NiCr spinel oxide; and (iv) the total oxide layer grown during thermal oxidation is thinner than the one directly formed in primary water. If similar in thickness, the thermally grown oxide layer has a different composition once exposed to primary water. This ToF-SIMS strategy was very fruitful in such a surface tube characterization.