Papers by Keyword: FIB

Abstract: This work presents the results of process development for trench formation in SiC power devices to increase the trench depth by improving SiC/SiO₂-selectivity of the dry etch process. Motivation behind this development is to further improve the electrical properties of conventional devices like SiC MOSFETs by implementing a trench geometry, allowing the cell pitch to be increased, leading to a reduced on-resistance of SiC TrenchMOS devices. Trench etching was performed on 4H-SiC substrates by utilizing an oxide hard mask, patterned by photolithography and dry etching. The SiC trench profile was analyzed by cross-section preparation via FIB and SEM imaging. The highest SiC/SiO₂-selectivity achieved was 7.9, with SiF₄ gas flow being the most decisive parameter for it. With that, the selectivity of the standard SiC trench etch process was increased by nearly five times. SiC trenches with depths of 5 µm could be demonstrated. However, then the structural fidelity was deteriorated, with micro-trenching and sidewall bowing being the largest limitations regarding applicable trench depth in SiC power devices.

Abstract: Accommodation processes are crucial for grain boundary sliding in superplasticity though few have been reported on their positive experimental evidences. The present study achieved two-dimensional grain boundary sliding in ODS ferritic steel which had elongated and aligned grain structure and got direct observations of accommodation processes without the surface effect of floating grains: 1) In Region II, diffusional accommodation was confirmed through observing the change in marking-line spacing, which indicates volume inflow and outflow at grain boundaries. 2) Between Regions II and III, dislocation accommodation inside of the mantle region, as proposed by Gifkins, was confirmed through observing curves of marking lines near grain boundaries. 3) In Region III, dislocation accommodation inside of the core region, as proposed by Ball and Hutchison, was confirmed through observing slip bands and sub-boundaries passing through a grain. It is, then, derived that superplasticity relies not on a single mechanism but on several diffusional and dislocation accommodations contributing depending on strain rate condition.

Abstract: The microstructure of physical vapour deposition (PVD) coatings deposited by duplex technology was investigated by Dual Beam FIB/SEM system (focused ion beam / scanning electron microscope), which allows one to examine cross sections of specimens from their surface down to the substrate. Examined were PVD coatings of nanocomposite type: duplex AlXN3 (X=Cr) and duplex nACRo3, deposited by LARC and CERC technologies. Duplex coating is a modern technology, which combines plasma nitriding and PVD coating in one cycle. The FIB analysis can be widely used in the field of study of basic materials and technological applications as it is based on highly focused ion beam which enables accurate machining of the investigated specimens and flexible processing at a micro/nanometric level. Cross sections of specimens obtained by FIB-SEMs document the arrangement of individual deposited nanomultilayers within the nanocomposite coatings and their EDS analysis in specific locations.

Abstract: 100nm thin Mg/B precursor films were prepared on SiC substrates in ZZSX-500 vacuum coating machine. They were annealed by electron-beam(EB) which only took fractions of a second. In this paper the best annealing duration to fabricate the superconducting MgB₂ thin films was investigated. Under the optimized annealing condition(accelerating voltage 15kV, electron beam current 5mA, annealing duration 0.7s), the superconducting MgB₂ thin film with critical temperature Tc^onset~35.3 K and transition width ∆Tc~1K was fabricated. Besides that, a nano-bridge (about 100×200nm²) was etched on the superconducting MgB₂ thin film by Focused Ion Beam (FIB). It’s a relative simple and efficient method. The nano-bridge exhibited the effect of Josephson junction with RSJ characteristics. At the same time a little loss of superconducting property was detected.

Abstract: Cast iron is an iron alloy mainly composed of carbon and silicon, the amount of carbon is more than 2.1 mass%. Cast irons, gray cast iron and ductile cast iron, have been used as industrial parts and automobile parts widely because they have a good wear resistance and an excellent machinability. Graphite formation mechanism have been proposed, but, it is not established clearly yet. In this study, the microstructure of flake graphite was investigated to reveal the graphite formation mechanisms using FC250 alloy. Transmission electron microscopy (TEM) samples were prepared using focused ion beam (FIB). In the case of a cross section of flake graphite taken perpendicular to its elongated direction using TEM, internal microstructure of flake graphite was observed layered structure. In the case of a cross section of flake graphite taken parallel to its elongated direction, clear microstructure was not observed. Selected area electron diffraction (SAED) from flake graphite showed <0001> direction of graphite are mostly parallel to their thickness.

Abstract: A micro-scale interface strength evaluation technique is essential for evaluating cold-sprayed materials. A focused ion beam (FIB) micro strength test enables the micro-scale evaluation of the interface mechanical properties. However, this technique cannot be used to measure the strain in a specimen. This work discusses the possibility of strain measurement by combining this technique with image analysis in a newly designed test setup. Moreover, the micro stress-strain curve for cold-sprayed copper was obtained. This improved method enables us to measure stress with a precision of 5 MPa and strain with a precision of 0.015. It was determined that some local regions can deform plastically, which could not be determined with conventional micro-and macro-scale evaluation methods. These results proved that the coating is non-uniform, while also revealing various microstructure and mechanical properties.

Abstract: X-Ray analysis was performed on copper-clad aluminum wires at 423 K and 673 K to follow their microstructural evolution and understand their strain behavior under creep deformation, potential operating load in automotive industry. The lifetime of the wires is found to be strongly dependent on the existence of an initial heat treatment and on the applied stress. Annealed drawn wires verify a traditional Norton law in the overall range of the stress level. Raw drawn wires exhibit a distinct two stage behavior with a breakdown around an applied stress of 0.7 times the yield stress. It is shown in this work that the intermetallic compounds between copper and aluminum play only the role of a mechanical bounding without affecting the strain rate of the wires.

Abstract: Gas-atomised spherical powders of Ti-45Al-5Nb and Ti-45Al-10Nb alloys were produced using the plasma melting induction guided gas atomisation (PIGA) technique. The phase composition was determined by X-ray diffraction at the synchrotron beamline HEMS at PETRA III (DESY), as well as by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), two dimensional and focused ion beam (FIB) based three dimensional electron back scatter diffraction (EBSD) measurements. Due to the high cooling rates the alloy composition of both alloys consists of hexagonal-close-packed α- and body-centred-cubic β-phase. The α-phase is dominant in the larger powder size fractions. Considerable amounts of the β phase were only found in the powder particle size fractions smaller than 32 μm for the Ti-45Al-5Nballoy and smaller than 45 μm for the Ti-45Al-10Nb. A pronounced dendritic cauliflower-like structure was observed in bigger powder particles of the Ti-45Al-10Nb alloy. This gives proof that diffusion took place during the initial β-grain formation, even though there is no orientation relation between the final grain and the dendrite structure in the powder particles. The presence of dendritic structures showed that the cooling rate during powder atomization was still too low to reach the critical growth rate for a planar solidification. The absence of preferred misorientation angles between α-grains indicates that α-grains are not formed out of already solidified β-grains by a solid state phase transformation.

Abstract: X-B-C (X=Mo, Ta) layers prepared by magnetron sputtering were tested. Mechanical properties were characterized by means of nanoindentation experiments in both the static and the dynamic loading regime. The results were correlated with observations of the microstructure under indentation prints by means of scanning and transmission electron microscopy on cross sections prepared using a focussed ion beam. An excellent fracture resistance of prepared nanostructured coatings was found.

Abstract: Two-dimensional grain movements were microscopically observed in high-temperature shear deformation of an oxide-dispersion-strengthened ferritic steel with an elongated and aligned grain structure that was sheared in a direction perpendicular to the grain long axis. The microstructure was analyzed using electron back-scattered diffraction and electron channeling contrast imaging techniques before and after the shear deformation. Clear grain switching events, which are assumed to occur via grain-boundary sliding (GBS), were observed and the switching mechanism was characteristic of the core–mantle superplasticity model proposed by Gifkins; dislocation densities got much higher in narrow areas near the grain boundaries (mantles) than the grain interiors (cores). The mantle regions typically appeared in protruding portions of grains that was likely resistant to GBS, and low-angle boundaries were found to emerge at the core–mantle boundaries via slipping of dislocations within the mantle regions.