Papers by Keyword: Scanning Transmission Electron Microscopy

Abstract: Modest channel carrier mobility in SiC-MOSFETs with NO annealed gate oxides has been the main factor hampering development of low power devices (300 – 650 V). A very fast interface trap, noted as NI, has been suggested to be the main culprit for poor inversion channel carrier mobility. The origin of the NI trap is unknown, but it is likely a property of the SiO₂ and it is enhanced during post nitridation. In this study we show that the NI trap is also detected in 4H-SiC/AlN and 4H-SiC/Al₂O₃ MIS-capacitors. Observations are done using conductance spectroscopy and capacitance voltage measurements at cryogenic temperatures. This strongly suggests that the NI trap is a property of the SiC surface and not the dielectric used to form the SiC/dielectric interface. Furthermore, a scanning transmission electron microscopy (STEM) was performed to confirm that there are no SiO₂ layers or islands present at the 4H-SiC/AlN and 4H-SiC/Al₂O₃ interfaces.

Abstract: Cu-Pd-Ag alloy is widely used in electronic device applications due to its relatively low electric resistance. To obtain higher strength wire, age-hardening is usually conducted to this alloy wire. However, the detailed hardening mechanism of Cu-Pd-Ag alloy was not clarified enough. In the present paper, we investigated the microstructure and hardness of the Cu-Pd-Ag alloy wire with aging treatment. Original alloy contained many rods with an Ag-rich α phase extended along the wire direction in a Cu-rich α phase matrix. After heat treatment of 623K with 1 hour, the matrix was transformed to the β phase contained many elongated α₂ phases as nanolamellar structure. Many β’ phase precipitated in the rods. Hardness measured with nanoindentation test showed that the matrix had a higher value than that of the rods. In the Cu-Pd-Ag alloy wire, the nanolamellar structure of the matrix was revealed to contribute to the hardening of the wire.

Abstract: The dislocation analysis of latent scratch induced chemical mechanical polishing process on 4H-silicon carbide (SiC) using the multi directional scanning transmission electron microscopy (STEM) method and elastic stain measurement were performed. A scanning electron microscope image shows that a latent scratch extended toward the [30] direction and the width is about 50 nm. Cross sectional STEM images shows that the depth of latent scratch due to distortion is about 20 nm. From the result of plan view STEM observation along [000] direction, it was observed that a latent scratch had two defect lines toward the [30] direction, which were a loop type on upper side and a linear type on the lower side. The Burgers vector of each defect have a component in basal plane. Elastic strain mapping was performed using transmission electron microscope equipped with a procession diffraction system. Inside the latent scratch indicates stain-free field, however around latent scratch indicates compressive strain field. About 1.5 % compressive strain field x, y direction and shear strain along latent scratch exists on typical area. As a results of STEM and elastic strain analysis, the atomic arrangement in basal plane seems to be related with the compressive strain around latent scratch.

Abstract: Cu₆Sn₅ is an important intermetallic compound in soldering and electronic packaging. It is formed at the interface between molten solder and substrate during the soldering process, and the evolution of microstructure and properties also occurs in service. Previous studies revealed that Au and Ni are stabilization alloying elements for hexagonal η-Cu₆Sn₅ intermetallic. For better understanding of stabilization mechanisms at atomic resolution level, in this work, we made an attempt atomic structure analysis on a stoichiometric (Cu, Au, Ni)₆Sn₅ intermetallic prepared by direct alloying. High-angle annular dark-field (HAADF) imaging and atomic-resolution chemical mapping were taken by the aberration-corrected (Cs-corrected) scanning transmission electron microscopy (STEM). It is found that Au and Ni doped Cu₆Sn₅ has hexagonal structure. The atom sites of Cu1 and Sn can be distinguished in atomic-resolution images after being observed from orientation [2110], which is also confirmed by atomic-resolution chemical mapping analysis. Importantly, atomic-resolution about distribution of alloying Au atom was directly observed, and Au atoms occupy the Cu1 sites in η-Cu₆Sn₅.

Abstract: The detailed microstructural analysis of HCM12 steel after long time (100 000 hours) exposure at service temperatures around 600°C was investigated by means of scanning transmission electron microscopy. The results show, that the recovery processes of the martensite lath structure and δ ferrite are significantly different. Moreover are differences in particles precipitating at the martensite and δ ferrite. The intensive process intragranular M₂₃C₆ and Laves particles precipitating is observed at the martensite/ δ ferrite interfaces.

Abstract: A shape memory alloy with a nominal composition of 84.68 wt.% Cu-11.25 wt.%Al-4.07 wt.%Ni, has been studied. Polycrystalline specimens have been quenched into water at room temperature, after heat treatment of 15 minutes at a high temperature of 1123 K. Two successive cycles from room temperature to 923 K and inversely have been performed on the non equilibrium samples. The microstructural study presented in this work has been performed using TEM (Transmission Electron Microscopy) analysis, STEM (Scanning Transmission Electron Microscopy) analysis, X-ray diffraction analysis at a variable temperature. Nanometric phase precipitation of AlNi type was observed to appear in this alloy.

Abstract: This paper covers the analysis of amorphous alloys CoP-CoNiP system by means of high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy and electron tomography. The last years have seen a sufficient progress in the analysis of nanomaterials structure with the help of high resolution tomography. This progress was motivated by the development of microscopes equipped with aberration correctors and specialized sample holders which allow reaching the tilts angles up to ±80°. The opportunities delivered by the method of electron tomography sufficiently grow when producing high resolution images and using chemical analysis, such as X-Ray energy-dispersive microanalysis and electron energy loss spectroscopy (EELS).

Abstract: We have been studying the microstructure change of B2 cubic precipitates into an A2+B2 complex structure in Fe-Al-Ni alloy. In this study, we carried out detailed observation using focused ion beam (FIB) and scanning transmission electron microscopy (STEM). First, Fe-14.3at%Al-10.3at%Ni solid solution was prepared. Secondly, the specimens were heated at 1173 K, at which they formed B2 cubic precipitates (ordered bcc) dispersed in an A2 matrix (disordered bcc). After that, the B2/A2 two-phase specimen was annealed at 973 K. Then we fabricated STEM specimens using FIB, followed by high-resolution secondary electron imaging. We repeated this slice-and-observation procedure to determine the detailed microstructure of this heat-treated alloy. At the early stage of the 973 K annealing, the A2 phase appeared in the original B2 precipitates and showed a spongelike structure, whereas small nanometer-order B2 particles appeared in the A2 matrix. The A2/B2 interface at this stage showed no anisotropic morphology. Therefore, the main driving force of this process may not be strain energy, but chemical and interface energies. Further annealing at 973 K decreased the number of small B2 particles in the A2 matrix, and these particles dissolved into the matrix eventually. The annealing also changed the A2/B2 spongelike structure, which was observed in the original B2 precipitates, into simple structures such as the A2 core and B2 crust. Then the B2 phase showed ordinal coarsening behavior. When B2 precipitates, which had hollow cubic morphology, were observed to be very close to each other, the face-centered area of the B2 crust tended to dissolve and only large B2 precipitates remained.

Abstract: In this work, different ferrocene concentration (1.0-8.0 wt%) of bio-hydrocarbon palm oil precursor were utilized to investigate its effect on the characteristics of the produced carbon nanotubes (CNT). The palm oil-ferrocene mixture was vaporized at 450°C and pyrolyzed at 800°C for 30 min time in argon ambient. The CNT were analyzed using field emission scanning electron microscopy, scanning transmission electron microscopy, fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis. The analysis confirmed different diameter and morphologies of CNT were formed when different ferrocene concentration were used. FTIR spectra show the prominent peak at ~1445, 1736, 2851 and 2925 cm^-1 that are identified as CNT and C–H_x respectively.

Abstract: In this study we report the effect of various synthesis temperatures of 600 - 1000°C for the synthesis of carbon nanotubes (CNT). Bio-hydrocarbon precursor namely palm oil was utilized as a starting material by thermal vapor deposition method. Ferrocene at 5.33 wt% was directly mixed with palm oil precursor for 30 mins synthesis time. The prepared CNT was collected from the furnace wall and then characterized by field emission scanning electron microscopy, scanning transmission electron microscopy, fourier transform infrared spectroscopy and thermogravimetric analysis. The density, diameter and the purities of the CNT were found to be highly dependent on the temperature changes. The synthesis temperature of 800°C was considered to be the optimum temperature for higher quality and quantity of CNT production.