Thick Amorphous Films Research Articles

Multiple scattering effects of MeV electrons in very thick amorphous specimens

Multiple scattering has an important influence on the analysis of microns-thick specimens with MeV electrons. In this paper, we report on effects of multiple scattering of MeV electrons on electron transmission and imaging of tilted and thick amorphous film specimens by experiment and theoretical analysis. Electron transmission for microns-thick epoxy-resin and SiO 2 specimens calculated by the multiple elastic-scattering theory is in good agreement with measurements in the ultrahigh voltage electron microscope (ultra-HVEM) at Osaka University. Electron transmission and electron energy are then presented in an approximate power law. The bright-field ultra-HVEM images of gold particles on the top or bottom surfaces of 5 and 15 μm thick specimens further illustrate the effect of multiple scattering on image quality. The observed top‐bottom effect for the very thick specimens appears to be mainly caused by multiple elastic scattering. With increase in the accelerating voltage from 1 to 2 MV, image blurring, contrast, the signal-to-noise ratio, and the top‐bottom effect are improved because of reduction in the influence of multiple scattering. However, the effect of specimen thickness on image blurring is shown to be stronger than that of accelerating voltage. At the 2 MV accelerating voltage, the 100 nm gold particle can be imaged with less blurring of ∼4 nm when located at the bottom surface of a 15 μm thick epoxy-resin specimen.

The formation of carbon nanostructures by in situ TEM mechanical nanoscale fatigue andfracture of carbon thin films

A technique to quantify in real time the microstructural changes occurring duringmechanical nanoscale fatigue of ultrathin surface coatings has been developed. Cyclicnanoscale loading, with amplitudes less than 100 nm, is achieved with a mechanical probeminiaturized to fit inside a transmission electron microscope (TEM). The TEM tribologicalprobe can be used for nanofriction and nanofatigue testing, with 3D control ofthe loading direction and simultaneous TEM imaging of the nano-objects. It isdemonstrated that fracture of 10–20 nm thick amorphous carbon films on sharpgold asperities, by a single nanoscale shear impact, results in the formation of<10 nm diameter amorphous carbon filaments. Failure of the same carbon films after cyclicnanofatigue, however, results in the formation of carbon nanostructures with a significantdegree of graphitic ordering, including a carbon onion.

Amorphous film thickness dependence for epitaxy of perovskite oxide films under excimer laser irradiation

We have studied the epitaxial growth of perovskite manganite LaMnO 3 (LMO) on SrTiO 3(1 0 0) in the excimer laser assisted metal organic deposition process. The LMO was preferentially grown from the substrate surface by the KrF laser irradiation. The study of amorphous LMO film thickness dependence on epitaxial growth under the excimer laser irradiation revealed that the photo-thermal heating effect strongly depended on the amorphous film thickness due to a low thermal conductivity of amorphous LMO: the ion-migration for chemical bond-forming at the reaction interface would be strongly enhanced in the amorphous LMO film with the large film thickness about 210 nm. On the other hand, the photo-chemical effect occurred efficiently for the amorphous film thickness in the range of 35–210 nm. These results indicate that the epitaxial growing rate was dominated by the photo-thermal heating after the photo-chemical activation at the growth interface.

Effects of Postmetallization Oxygen Annealing on Electrical Properties of 25 nm Thick Amorphous BaSm2Ti4O12 Film

The effects of postmetallization oxygen annealing on the electrical properties of a thick amorphous (BSmT) thin film have been investigated. The radio frequency sputtered BSmT film was well-developed on a substrate. A BSmT film that was postmetallization-annealed at oxygen pressure exhibited a high capacitance density of at . It still showed a high capacitance density of and a high Q value of 67, even at , along with a relatively high of 30. Its leakage current density was significantly improved to at , and the conduction mechanism is considered to be a Poole–Frenkel mechanism. In addition, better quadratic voltage and temperature coefficients of capacitance were obtained, which were as low as approximately and , respectively, at . Therefore, it is thought that the oxygen during the annealing process significantly improves the electrical properties of the BSmT films for high-performance metal–insulator–metal capacitors.

Study on the amorphous Ta–Zr films as diffusion barrier in Cu metallization

An amorphous Ta–Zr binary alloy diffusion barrier was studied in the Cu metallization. A Cu∕Ta50Zr50∕Si stack with 50nm thick amorphous film was prepared by cosputtering can effectively suppress the penetration of Cu atoms into substrate upon annealing up to 650°C. Examining the thermal stability of the barrier revealed that the crystallization of these amorphous Ta50Zr50 films occurred at 800°C, higher than its failure temperature. The results show that the existence of Cu layer first induced the formation of TaSi2 and ZrSi2 crystalline phases at 650°C, followed by the formation of Cu3Si. A failure mechanism of the diffusion barrier is proposed based on the relation between the thermal stress and the activation energy of barrier/substrate interface reaction.

Diffusion barriers performance of amorphous Ta–Zr films in Cu metallization

An amorphous Ta–Zr binary alloy diffusion barrier was studied in the Cu metallization. A Cu/Ta50Zr50/SiO2/Si stack with 50 nm thick amorphous film was prepared by co-sputtering can effectively suppress the penetration of Cu atoms into substrate upon annealing up to 650 °C. Examining the thermal stability of the barrier revealed that the crystallization of these amorphous Ta50Zr50 films occurred at 800 °C, higher than its failure temperature. The results show that the existence of Cu layer first induced the formation of TaSi2 and ZrSi2 crystalline phases at 650 °C, followed by the formation of Cu3Si. A failure mechanism of the diffusion barrier is proposed based on the relation between thermal stress and the activation energy of barrier/substrate interface reaction.

Anodic behavior and pore growth of n-InP in acidic liquid ammonia

Abstract In this paper, we report on the anodic behavior of n -InP (100) in acidic liquid ammonia at 223 K. Electrochemical, morphological and optical characterizations have been performed on InP after galvanostatic polarizations in different ranges. Prior to any dissolution processes, the formation of a stable anodic passivating thin film with a chemical composition close to “HN P–NH 2 ” (phosphinimidic amide) is observed. Depending on the current, two different phenomena occur: at low current density a thick amorphous film is formed, while tortuous current line oriented pores are grown when a high current is applied. For high coulometric charges, this last porous film can exhibit a multilayered structure. A decrease of the photoluminescence intensity without any peak shifts is observed whatever the applied current. This has been ascribed to the absorbent property of the layers.

5 - nm -thick TaSiC amorphous films stable up to 750°C as a diffusion barrier for copper metallization

Ultrathin TaSiC amorphous films prepared by magnetron cosputtering using TaSi2 and C targets on Si(100), in a sandwiched scheme Si(100)∕TaSiC(5nm)∕Cu, were evaluated for barrier performance in copper metallization. Optimizing carbon content maximizes thermal stability of the films as depicted by sheet-resistance, x-ray diffraction, and transmission electron microscopy examination. The stability temperatures of 700°C (24at.% C) and 750°C (34at.% C) have been systematically verified and discussed. Since Ta, Si, and C are compatible with integrated circuit (IC) processing, the TaSiC films are readily applicable for sub-65-nm IC production.

Mechanical properties of alternating high-low sp 3 content thick non-hydrogenated diamond-like amorphous carbon films

Thick non-hydrogenated DLC films (∼ 1μm), consisting of alternating sub-layers of high/low sp 3 content, were deposited onto n++ Si substrates using the filtered cathodic vacuum arc method. These films were systematically studied to determine how the changes in composition of the sub-layers would affect the mechanical properties such as intrinsic stress, hardness, friction coefficient, wear rate and surface roughness. Variations of both the ratio of hard to soft layers (from 1:3 to 3:1) and thickness of individual layers (from 12.5nm to 75nm) were studied in detail. The stress of the film was sufficiently lowered (7.8GPa–2.4GPa) by the multilayer approach. The results indicated that although hardness has some correlations with the internal composition of the film, the reduced Young's modulus is largely not affected. Wear and frictional characterizations also showed that the multilayer was a good candidate for many mechanical applications.

VORTEX STATES AND PEAK EFFECT AT LOW TEMPERATURE IN THICK AMORPHOUS FILMS WITH WEAK PINNING

We report on the dynamic as well as static properties of vortices in the low-temperature (T) solid phase of a thick amorphous Mo x Ge 1-x film with weak pinning. The vortex-solid state is considered to be a weakly disordered vortex lattice, which is inferred from the mode-locking resonance over the broad field region. The peak effect of the critical current Ic with magnetic field is clearly visible down to the lowest T measured (0.2 K), which corresponds to 3.3% of the superconducting transition temperature. We find that largest voltage noise originating from current-driven vortices appears in the field region just prior to the peak field at which Ic takes a peak. This is in accord with the result reported in NbSe 2 single crystals.

Vortex dynamics detected by voltage noise in the quantum-liquid phase of thick amorphous films

We measure the fluctuations of the vortex-flow voltage in the low-temperature liquid phase of a thick amorphous Mo x Si 1− x film. The anomalous vortex flow with the asymmetric distribution of (real-time) voltage fluctuations is visible in the QVL phase, where we observe noise spectra indicative of shot noise, whose origin is attributed to the vortex bundles that are depinned and pinned randomly in the stationary flow of QVL.

Phase Transformations of Metallorganic Chemical Vapor Deposition Processed Alumina Coatings Investigated by In Situ Deflection

Phase transformations of films, deposited by metallorganic chemical vapor deposition from aluminium tri-isopropoxide on AISI 301 stainless steel, were investigated using an original technique of deflection associated with X-ray diffraction and electron microscopy. The samples were first oxidized at in air to obtain a thick protective oxide film on one side of the samples. Then, thick amorphous films were deposited on the opposite side at and . The deflection of such dissymmetrical samples was recorded during anisothermal treatments, consisting in slow heating to in Ar atmosphere. The coefficient of thermal expansion of both the and the amorphous films was determined to be and , respectively. Crystallization kinetics of amorphous to mainly become significant at temperatures equal or greater than . Transformation of metastable to is initiated below . It is demonstrated that deflection is a powerful tool for investigating the behavior of thin films deposited on a substrate and especially to reveal transformations occurring in these films during heat-treatments.

Investigation on the Electrical Properties of the Ba2Ti9O20 Thin Films for Metal-Insulator-Metal Capacitor Application

Homogeneous crystalline phase was formed for the films grown at 700 and annealed at . However, second phase was also developed for the films grown at temperatures lower than and annealed at . A high capacitance density of along with a leakage current density of at were obtained for a thick crystalline BT film. This film had small quadratic and linear voltage coefficients of capacitance (VCC) of and , respectively, and a small temperature coefficient of capacitance (TCC) of at . A thick amorphous BT film grown at showed a high capacitance density of with a very low leakage current density of at . This amorphous film also showed small quadratic and linear VCCs of and , respectively, with a low TCC of at . These results demonstrate that BT films, particularly amorphous BT films, are good candidate materials for metal-insulator-metal capacitors.

Structural and optical properties of as‐deposited and annealed SrTiO3 films prepared by laser ablation

AbstractIn order to clarify the large band gap energy reported for thin SrTiO3 film (of which thickness is smaller than 200 nm) and to examine the optical properties reported for bulk SrTiO3 crystals, different thick SrTiO3 films were prepared by a pulsed laser ablation method. The morphology and structure of the as‐deposited and annealed films were studied with the optical‐ and scanning electron microscopes and with an x‐ray diffraction method. The optical absorption and photoluminescence properties of the films are then measured at temperatures between 6.5 and 300 K. A large band gap energy (about 4.0 eV) has been observed even for thick amorphous SrTiO3 films (of which thicknesses are approximately 1.3 μm). (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Vortex flow and shot noise in the quantum-liquid phase of thick amorphous superconducting films

We measure the fluctuations (noise) of the vortex-flow voltage in the low-temperature liquid phase of thick amorphous $(a\text{\ensuremath{-}}){\mathrm{Mg}}_{x}{\mathrm{B}}_{1\ensuremath{-}x}$ and $a\text{\ensuremath{-}}{\mathrm{Mo}}_{x}{\mathrm{Si}}_{1\ensuremath{-}x}$ films with different transition temperatures and widths of the quantum-vortex-liquid (QVL) phase. An anomalous vortex flow with an asymmetric distribution of (real-time) voltage fluctuations is commonly observed in the QVL phase, independent of material as well as strength of quantum fluctuations. In the QVL phase we observe the Lorentzian-type noise spectra indicative of shot noise, whose origin is attributed to the vortex bundles that are depinned and pinned randomly in the stationary flow of QVL.

Flux-flow noise driven by quantum fluctuations in a thick amorphous film

We measure the voltage-noise spectrum SV(f) (where f is a frequency) as well as the time (t)-dependent component δV(t) of the flux-flow voltage in the low temperature liquid phase of a thick amorphous MoxSi1−x film. In the quantum-liquid phase both the amplitude ∣δV∣ of voltage fluctuations and the asymmetry of the probability distribution of δV(t) show an anomalous increase; the spectral shape of SV(f) is of a Lorentzian type, suggesting the shot-noise-like vortex motion with a large “vortex-bundle size” and short characteristic time.

Nanoscale Dynamics at Reactive Wetting Front on SiC

Nanoscale singularity at the reactive wetting front on SiC (0006) was studied using video recorded in situ to clarify the dynamic atomistic behaviours of the brazing and the molten tip spreading on a high-temperature stage of a high-resolution transmission electron microscope. An atomistic process controls the wetting at the front of the spreading film where the classical macroscopic phenomenon never holds true and the singularities are observed in a precursor film. A 0.5-nm-thick precursor film spreading ahead of the main molten alloy on SiC (0006) at 1073 K and continuous spreading of the molten alloy were clearly observed on the SiC (0006) surface with a less than 1-nm-thick amorphous layer. Molten Ti and TiC nanolayers preceded the Ti5Si3 nanolayer at the tip and they traveled continuously at a velocity of 14 nm/sec on the plane perpendicular to SiC (0006). Since Ti atoms in the molten alloy diffuse sufficiently rapidly on the SiC surface to the tip, the formation of these layers may be the rate-determining step of spreading. Discontinuous spreading of the precursor tip on SiC (0006) with a thick amorphous film was observed in contrast to the continuous spreading on SiC with a thin film. This suggests that the spreading of the Ti molten alloy on SiC is also controlled by the dissolution of the amorphous layer.

High Resolution Imaging with an Aberration Corrected JEOL 2200FS-AC STEM/TEM

A new JEOL 2200FS 200kV field emission STEM/TEM with a hexapole Cs-corrector (CEOS GmbH) for the probe-forming lens and an in-column Omega-type energy filter has recently been installed at the Advanced Microscopy Laboratory (AML) at Oak Ridge National Laboratory (ORNL). The microscope is intended primarily for high-resolution imaging of catalyst systems that are of interest to the U.S. Department of Energy for increased energy efficiency and energy security. In this paper we report on the high-resolution imaging characteristics of our microscope for both conventional high-resolution TEM and STEM imaging. The TEM Scherzer point resolution for our objective lens polepiece (C{sub s} = 0.5 mm) is 0.19 nm, but more significantly the information limit has been demonstrated to be better than 0.09 nm, as shown in Fig. 1. This figure shows a Young's fringe experiment carried out on an amorphous Ge specimen which was estimated to be 10 nm thick. The thickness of the sample damps out the Thon rings to some extent, but the information transfer to sub 0.1 nm resolution is clearly evident. The electron wave at the specimen exit surface with resolution out to the information limit of a microscope may be reconstructed via computational processing of amore » focal or tilt series of images. The extension of the TEM information limit to the sub-0.1 nm range in our microscope can be attributed primarily to the improved objective lens and high tension power supply stabilities provided by JEOL Co. to satisfy our instrument specifications. A contrast transfer function (CTF) calculated using the parameters for our microscope is shown in Fig. 2, computed at the alpha-null defocus condition used for FSR processing. The CTF closely matches the demonstrated Young's fringe pattern, indicating the ability of the microscope to achieve ultimate performance in TEM mode. Characterization of catalyst systems will be a primary focus of the aberration-corrected JEOL 2200FS and therefore high-resolution STEM high-angle annular dark field (HA-ADF) imaging will be applied to understand the atomic-scale arrangement of supported catalyst clusters. By correcting for the primary resolution-limiting aberration of a round electromagnetic lens - the third-order spherical aberration - smaller electron probes with greater probe current can be formed, with resulting improvements in both the point-to-point resolution for HA-ADF imaging and the signal-to-noise ratio. Both benefits are important for the study of the atomic arrangement of catalyst clusters. Figure 3 shows initial HA-ADF imaging images of very small Pt clusters on a 1.1 nm thick amorphous carbon film. Individual Pt atoms are clearly visible with a high signal-to-noise, as is shown in Fig. 4.« less

Macro- to Atomic-Scale Tailoring of Si&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt; Ceramics to Enhance Properties

Silicon nitride ceramics are finding uses in numerous engineering applications because of their tendency to form whisker-like microstructures that can overcome the inherent brittle nature of ceramics. Studies now establish the underlying microscopic and atomic-scale principles for engineering a tough, strong ceramic. The theoretical predictions are confirmed by macroscopic observations and atomic level characterization of preferential segregation at the interfaces between the grains and the continuous nanometer thick amorphous intergranular film (IGF). Two interrelated factors must be controlled for this to occur including the generation of the elongated reinforcing grains during sintering and debonding of the interfaces between the reinforcing grains and the matrix. The reinforcing grains can be controlled by (1) seeding with beta particles and (2) the chemistry of the additives, which also can influence the interfacial debonding conditions. In addition to modifying the morphology of the reinforcing grains, it now appears that the combination of preferential segregation and strong bonding of the additives (e.g., the rare earths, RE) to the prism planes can also result in sufficiently weakens the bond of the interface with the IGF to promote debonding. Thus atomic-scale engineering may allow us to gain further enhancements in fracture properties. This new knowledge will enable true atomic-level engineering to be joined with microscale tailoring to develop the advanced ceramics that will be required for more efficient engines, new electronic device architectures and composites.

Effect of Y 2O 3–Al 2O 3 ratio on inter-granular phases and films in tape-casting α-SiC with high toughness

Silicon carbide (SiC) ceramics prepared from liquid phase sintering after aqueous-tape-casting can yield high toughness when appropriate amount of Y 2O 3–Al 2O 3 are added, even though no elongated grains are present. Grain boundaries (GB), second-phases and hetero-phase boundaries (HB) in 2 samples with additive mole ratios of 3:5 and 3:7 are investigated using high-resolution and analytical electron microscopy (HREM and AEM). The meta-stable YAlO 3 (YAP) was nucleated from SiC surfaces in the sample with Y/Al = 3:5 as revealed by crystallographic relations across the HB, whilst relatively thick amorphous films were found at GB. In contrary, the higher level of Al 2O 3 additives decreases the GB film thickness in the sample with Y/Al = 3:7, and the homogeneous nucleation of Y 3Al 5O 12 (YAG) occurs at triple pockets accompanying with thick HB films. The strong variation of GB widths is a result of GB wetting in the sample with Y/Al = 3:5 and HB wetting in the sample of Y/Al = 3:7, both by liquid Al 2O 3. The energy of GB in the former sample is higher than the energy of HB as exhibited by the preferential nucleation of meta-stable YAP on SiC surfaces, which results in wetting of GB by the liquid; the situation is opposite in the latter sample as the wetting of HB occurs, leading to de-wetting of GB. The thermal mismatch between SiC and YAP or YAG as well as the presence of amorphous films facilitate the creation of micro-crack to promote inter-granular fracture and result in high toughness in both SiC ceramics.