Effect of sample bending on diffracted intensities observed in CBED patterns of plan view strained samples

Convergent beam electron diffraction is used to study the effect of the sample bending on diffracted intensities as observed in transmission electron microscopy (TEM). Studied samples are made of thin strained semiconductor Ga(1-)(x)In(x)As epitaxial layers grown on a GaAs substrate and observed in plan view. Strong variations of the diffracted intensities are observed depending on the thinning process used for TEM foil preparation. For chemically thinned samples, strong bending of the substrate occurs, inducing modifications of both kinematical and dynamical Bragg lines. For mechanically thinned samples, bending of the substrate is negligible. Kinematical lines are unaffected whereas dynamical lines have slightly asymmetric intensities. We analyse these effects using finite element modelling to calculate the sample strain coupled with dynamical multibeam simulations for calculating the diffracted intensities. Our results correctly reproduce the qualitative features of experimental patterns, clearly demonstrating that inhomogeneous displacement fields along the electron beam within the substrate are responsible for the observed intensity modifications.     

Microstructure of homoepitaxial strontium titanate films grown by pulsed laser deposition

Homoepitaxial strontium titanate (SrTiO₃) thin films have been grown by pulsed laser deposition in order to identify those defects which are intrinsic to the growth of SrTiO₃. The pulse rate and oxygen annealing pressure were varied, although the oxygen pressure had no effect under these conditions. Columnar growth was common. The nature of the columns is described, but the reason for their presence is not fully understood. They can be suppressed using a high laser pulse rate.     

Phase transformation in κ- and γ-Al2O3 coatings on cutting tool inserts

The phase transformation in as-deposited, metastable κ- and γ-alumina coatings on cutting inserts has been studied by a combination of X-ray diffraction, scanning electron microscopy and cathodoluminescence. In the case of κ-alumina, mechanical forces during metal cutting lower the transformation temperature of the metastable phases to the thermodynamically stable α-alumina phase from 1050 °C to 930 °C. This is the reason why that coating has a similar performance during metal cutting when compared to the stable α-alumina phase. The transformation temperature in γ-alumina coated cutting tools is found to be as low as 950-975 °C. Cathodoluminescence (CL) has been demonstrated as a possible method for differentiation between the various alumina phases. Specifically, both κ- and γ-alumina films have revealed a strong room temperature CL with different peak energies depending on the phase. CL of the metastable alumina coatings annealed at the transformation temperatures corresponds to the stable α-alumina phase.     

The influence of structure changes in the properties of TiCxOy decorative thin films

The main purpose of this work consists in the preparation of titanium oxycarbide, TiC_xO_y, thin films, in which the presence of oxygen changed the film properties between those of titanium carbide and those of titanium oxide. Varying the oxide/carbide ratio allowed to tune the structure of the films between titanium oxide and carbide and consequently electronic, mechanical and optical properties of the films. The depositions were carried out from a TiC target by direct current, dc, reactive magnetron sputtering, varying the oxygen flow rate. The obtained results showed that the film's properties can be divided into 3 different regimes — i) carbide, ii) a transition zone and iii) an oxide one. X-ray diffraction results revealed the occurrence of a face-centered cubic phase (TiC-type) for low oxygen content, also obtained in the TiC_1.6(O) film, with a clear tendency towards amorphization with the increase of the oxygen flow rate. For the highest oxygen contents, the results revealed the development of a mixture of poorly crystallized TiO₂ phases. The colour results indicated a strong dependence on the O/Ti ratio. A progressive reduction of hardness and residual stresses with the increase of the O/Ti ratio was also observed. The residual stresses, as well as the film structure, seem to play an important role on the adhesion of the coatings. The static friction coefficient revealed also some correlation with the mechanical properties, but mainly with the surface roughness.     

Oxygen plasma treatment effects of indium-tin oxide in organic light-emitting devices

The effects of oxygen plasma treatment on the surface properties of indium-tin oxide (ITO) substrates and its aging were investigated by X-ray photoelectron spectroscopy (XPS), contact angle, surface energy and polarity measurements. Experimental results demonstrate that the oxygen plasma treatment improves the stoichiometry of the surface and enhances the ITO wetting, so as to improve the surface properties of ITO substrates, due to the introduction of oxygen and the partial removal of hydrocarbon contaminants from the ITO surfaces. With the increment of aging time, however, the improved ITO surface properties are observed to tend to decay. Furthermore, the aging effect of treated ITO substrates on the performance of organic light-emitting devices (LEDs) was studied with respect to the driving voltage, brightness and efficiency. It is found that the device performance is subjected to the ITO surface properties and the ITO substrates aged for various times result in significant differences in electrical and optical characteristics which become worse as the aging time increases. The results indicate that the performance of organic LEDs is closely related to the surface properties of ITO substrates and the interface characteristics of ITO/organic layer.     

Irradiation-induced gold silicide formation and stoichiometry effects in ion beam-mixed layer

The irradiation-induced silicide formation in ion beam-mixed layer of Au/Si(1 0 0) system was investigated by using 200 keV Kr⁺ and 350 keV Xe⁺ ions to fluences ranging from 8×10¹⁴ to 1×10¹⁶ ions/cm² at room temperature. The thickness of Au layer evaporated on Si substrate was ∼500 Å. Rutherford backscattering spectrometry (RBS) experiments were carried out to study the irradiation effects on the mixed layers. We observed that at the fluence of 1×10¹⁶ Kr⁺/cm² and starting from the fluence of 8×10¹⁴ Xe⁺/cm², a total mixing of the deposited Au layer with Si was obtained. RBS data corresponding to the fluences of 1×10¹⁶ Kr⁺/cm² and 8×10¹⁴ Xe⁺/cm² clearly showed mixed layers with homogenous concentrations of Au and Si atoms which can be attributed to gold silicides.The samples irradiated to fluences of 1×10¹⁶ Kr⁺/cm² and 1×10¹⁶ Xe⁺/cm² were also analyzed by X-ray photoelectron spectroscopy (XPS). The observed chemical shift of Au 4f and Si 2p lines confirmed the formation of gold silicides at the surface of the mixed layers. Au₂Si phase is obtained with Kr⁺ irradiation whereas the formed phase with Xe⁺ ions is more enriched in Si atoms.     

Compositional studies on Transylvanian gold nuggets: Advantages and limitations of PIXE-PIGE analysis

Minute fragments from nine gold nuggets from Transylvania - two belonging to placer deposits and seven to primary deposits - were analyzed by PIXE and PIGE at the AGLAE tandem accelerator of the Centre de Recherche et de Restauration des Musées de France (C2RMF) with a 3 MeV proton beam extracted into air. This study was triggered by some archaeological provenance issues for which the elemental characterization of the Transylvanian gold source, exploited from the Antiquity, was required. All analyzed Transylvanian gold nuggets are characterized by a consistently high amount of Ag (18% on average). Au and Ag add up to roughly 99%, the other elements - Cu, Fe, Te, Pb - being detected only at a trace level. The obtained results are in good agreement with the previous analyses of Transylvanian gold.     

Low-energy heavy-ion TOF-ERDA setup for quantitative depth profiling of thin films

Low-energy heavy-ion time-of-flight elastic recoil detection analysis (TOF-ERDA) is becoming a mature technique for accurate characterization of thin films. In combination with a small tandem accelerator (∼2 MV terminal voltage) and beam energies below 20 MeV, it is suitable for routine analysis of key materials in semiconductor technology. In this paper we discuss advantages and drawbacks of low-energy ERDA, compared to high-energy ERDA, in terms of depth and mass resolution, detection efficiency for light elements, sample irradiation damage and quantification accuracy.The results presented are obtained with the time-of-flight telescope recently developed at IMEC. The time-of-flight is measured with timing gates based on electrostatic mirrors and is acquired in coincidence with the energy signal measured by a planar Si detector.     

Interfacial Fe(III)-hydroxide formation during Fe-Pt alloy deposition

Fe-Pt films with an Fe/Pt ratio close to one can be electrodeposited from an FeSO₄-H₂PtCl₆-Na₂SO₄electrolyte. At the deposition potential, the hydrogen evolution and the reduction of the Pt complex are diffusion limited, and Fe overpotential deposition has not yet set in. The sources of the Fe incorporation are iron hydroxide formation together with Fe underpotential deposition due to Fe-Pt alloy formation. Mössbauer measurements show that the iron in the iron hydroxide is predominantly Fe(III). For stoichiometry reasons, a Pt-rich Fe-Pt phase must be present in addition to the Fe(III)-hydroxide. The Fe³⁺ that takes part in the hydroxide formation is produced in the electrolyte by the oxidation of Fe²⁺ by the complexed Pt ion. This exchange reaction results in a significantly higher Fe³⁺ content in the FeSO₄-H₂PtCl₆-Na₂SO₄ electrolyte in comparison to the same electrolyte without H₂PtCl₆. Fe(III)-hydroxide formation can be depressed by adding citric acid, that acts as buffering and complexing agent. This leads to a lower iron content of the deposits. The Fe/Pt ratio close to one that is needed for hard magnetic properties can, however, only be achieved with a significant incorporation of iron hydroxide.