Papers by Keyword: Transmission Electron Microscopy

Abstract: This research investigated the impact of Ag content supported on ZnO catalysts regarding the oxidation activity of DPM. The catalyst was synthesised through the doping of varying Ag concentrations on ZnO (e.g., 2, 4, 8, and 16 wt%) employing the incipient wetness impregnation technique. Characterisation of the synthesised catalyst was conducted utilising XRD, SEM, TEM, and H₂-TPR. The evaluation of oxidation activity and stability was performed through TGA. The characterisation findings substantiated the successful integration of Ag onto ZnO across all experimental conditions investigated. H₂-TPR profiles revealed two distinct regions of H₂ consumption: 1) at 200-400 °C, and 2) at 400-700 °C. These regions were attributed to the reduction of Ag₂O to Ag⁰ and the liberation of lattice oxygen from ZnO, respectively. An increase in Ag concentrations resulted in enhanced reduction reactions within the temperature spectrum of 400 to 700 °C, demonstrating a favourable trend towards improved reaction efficiency. The oxidation performance of DPM was markedly augmented by the Ag content, particularly at 16 wt%. Stability assessments indicated a consistent capability in facilitating DPM oxidation across five cycles. The concentration of oxygen exhibited a significant influence on the oxidation activity of DPM.

Abstract: In this paper, we investigate the electrical and structural characteristics of Al₂O₃-based high-k gate dielectrics, which were integrated into a gate-first, high-temperature manufacturing process having comparable thermal budget as needed in 4H-SiC metal-oxide-semiconductor field-effect transistor (MOSFET) production. MOS capacitors were chosen as test devices to examine the electrical performance in terms of current-voltage (I-V) and capacitance-voltage (C-V) behavior. Remarkably, even after processing temperatures of up to 1,000 °C for ohmic contact formation, the Al₂O₃ layers revealed highly uniform breakdown characteristics, low C-V hysteresis and a flat-band voltage (V_FB) that closely aligns with the theoretical value. Time-dependent dielectric breakdown (TDDB) measurements of the Al₂O₃ MOS capacitors, however, showed a clear reliability disadvantage concerning the intrinsic dielectric lifetime when comparing with the SiO₂ counterpart from commercial SiC production. Finally, to better understand the electrical behavior, transmission electron microscopy (TEM) analysis was conducted, pointing out that high-temperature processing causes the Al₂O₃ films to transition from an amorphous state to an ordered, polycrystalline structure.

Abstract: One of the most important challenges of modern materials engineering is to improve the efficiency and durability of materials, which directly translates into reducing the consumption of raw materials. In many applications, these goals are achieved by strengthening and functionalizing the surface, especially in the case of nanocoatings. The material for the study is the Ta/TaN multilayer systems obtained with the ALD technique (Atomic Layer Deposition, R200 by Picosun). For their structure characterisation electron microscopy (HR STEM, electron diffraction, EDS, EELS) was used. Geometrical parameters (thickness of the constituent Ta and TaN layers, ratio of thicknesses of metallic and ceramic layers) were determined, and their chemical and phase compositions were verified. The obtained results will be used to model mechanical properties and interpret the results of experimental nanoindentation measurements.

Abstract: Today, Atomic Layer Deposition (ALD) sets the limits for achieving nanometer precision of thin, yet almost dense films. However, the initial growth process, determining possible film thinness, is poorly understood. A better understanding can be obtained with the help of in-situ characterization during film growth with high spatial and chemical resolution. Transmission Electron microscopy (TEM) would be a suitable and widely available technique to accomplish this objective. However, standard instruments have differing vacuum requirements than those necessary for ALD. During ALD, TEM detectors could be damaged as they are being exposed to corrosive volatile chemical compounds. Here we present a dedicated TEM holder design, where ALD deposition occurs inside a microchip containing a large area cavity surrounded by thin film Al₂O₃ membranes. These membranes act as windows for TEM characterization while decoupling the ALD process from the TEM environment. The microchip consists of longitudinal large overhang shell structures, themselves made by ALD and etched in an HF vapor etch processes. The set-up, which includes controlled heating, was tailored to ALD requirements, and passed a vacuum-pressure test. Post-mortem inspection of film growth on a silicon sample chip demonstrates the successful formation of an ALD Al₂O₃ film with 40 nm thickness inside the cavity. These results demonstrate the potential of the system to enable a range of experiments on growth phenomena that may lead to even thinner films and better control of interfaces than previously possible.

Abstract: The paper deals with changes in the stoichiometry of nanopowders obtained under staged irradiation of a brass ingot placed in a graphite crucible. Composite core-shell CuO/ZnO nanoparticles, copper nanoparticles, and copper and zinc oxides were obtained. The use of a relativistic electron accelerator is necessary to produce nanopowders on an industrial scale. Transmission electron microscopy and energy-dispersive analysis of the obtained nanoparticles were carried out. Thermodynamic calculation of the temperature dependence of the equilibrium content of copper and zinc is presented for the condensed and gas phases. The formation mechanism of CuO/ZnO composite nanoparticles is discussed.

Abstract: Increasing durability of catalysts used in fuel cells is a necessary condition for their widespread commercialization. Fulfilling this condition requires understanding the catalyst degradation mechanism to propose how to reduce it. Transmission electron microscopy can help solve this problem thanks to the fact that it enables direct observation and thus unambiguous interpretation of the processes taking place. For this purpose, Identical Location Transmission Electron Microscopy (IL-TEM) was applied for observations of a commercial catalyst (platinum nanoparticles with a diameter of about 2 nm deposited on Vulcan carbon black) before and after durability tests. Obtained results may contribute to the development of better models of phenomena occurring during cell operation.

Abstract: Double-rhombic shaped single Shockley stacking faults (1SSFs) were considered to have a converted threading edge dislocation (TED) on the shallower side of the initial basal plane dislocation segments. However, the structural analysis using transmission electron microscopy (TEM) revealed other possible configuration of the double-rhombic 1SSFs expanded from basal plane dislocations (BPDs) of which both ends were connected with two TEDs.

Abstract: In photovoltaic system the major challenge is the cost reduction of the solar cell module to compete with those of conventional energy sources. Evolution of solar photovoltaic comprises of several generations through the last sixty years. The first generation solar cells were based on single crystal silicon and bulk polycrystalline Si wafers. The single crystal silicon solar cell has high material cost and the fabrication also requires very high energy. The second generation solar cells were based on thin film fabrication technology. Due to low temperature manufacturing process and less material requirement, remarkable cost reduction was achieved in these solar cells. Among all the thin film technologies amorphous silicon thin film solar cell is in most advanced stage of development and is commercially available. However, an inherent problem of light induced degradation in amorphous silicon hinders the higher efficiency in this kind of cell. The third generation silicon solar cells are based on nano-crystalline and nano-porous materials. Hydrogenated nanocrystalline silicon (nc-Si:H) is becoming a promising material as an absorber layer of solar cell due to its high stability with high V_oc. It is also suggested that the cause of high stability and less degradation of certain nc-Si:H films may be due to the improvement of medium range order (MRO) of the films. During the last ten years, organic, polymer, dye sensitized and perovskites materials are also attract much attention of the photovoltaic researchers as the low budget next generation PV material worldwide. Although most important challenge for those organic solar cells in practical applications is the stability issue. In this work nc-Si:H films are successfully deposited at a high deposition rate using a high pressure and a high power by Radio Frequency Plasma Enhanced Chemical Vapor Deposition (RF PECVD) technique. The transmission electron microscopy (TEM) studies show the formations of distinct nano-sized grains in the amorphous tissue with sharp crystalline orientations. Light induced degradation of photoconductivity of nc-Si:H materials have been studied. Single junction solar cells and solar module were successfully fabricated using nanocrystalline silicon as absorber layer. The optimum cell is 7.1 % efficient initially. Improvement in efficiency can be achieved by optimizing the doped layer/interface and using Ag back contact.

Abstract: This paper reports on the synthesis of copper selenide (CuSe) and tin selenide (SnSe) powders by high energy planetary ball milling, starting from elemental powders. Synthesis time and milling speed have been optimized to produce single phase CuSe and SnSe materials. The structural, compositional, morphological and optical properties of the synthesized samples have been analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM), Field Emission Scanning Electron Microscopy (FESEM) and UV-Vis. The low-temperature phase selection of the binary compound in this system is seen as a direct consequence of the thermodynamic facilitation, coupled with the capability of mechano-chemical synthesis to aid in overcoming kinetic constraints.

Abstract: In this study, amorphous Fe₇₈Si₉B₁₃ alloy was successfully synthesized by mechanical alloying (MA) of pure elemental powders which were milled under an argon gas atmosphere. Effects of milling time on the phase transformation, microstructure and morphological evolution were studied by X-ray diffraction (XRD), laser diffraction (Granulometry), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Results showed that by increasing the milling time, the nanocrystalline and amorphous phase content increases and alloys with good properties are obtained at 100 h of milling.