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Crystal Morphology and Phase Transformation of LiAlO <sub/>2</sub> : Combined Experimental and First-Principles Studies
摘要： Layered α-LiAlO2 matrix often suffers from detrimental structural and morphological changes during its lifetime, especially under H2 containing fuel inlet environments of molten carbonate fuel cell systems. However, the underlying mechanism of this phase and morphological transformations has rarely been explored. In this study, transmission electron microscopy (TEM) techniques were used to determine the changes in structure and morphology of LiAlO2 samples lifted by a focused ion beam (FIB). In accordance with X-ray diffraction (XRD) analysis, TEM images show that under H-rich conditions the rhombohedral α-LiAlO2 transforms to tetragonal γ-LiAlO2 phase with the appearance of the (101) terminated octahedral shaped γ-LiAlO2 crystallites. We further support, and plausibly rationalize, the observed transformations using density functional theory (DFT) calculation. The DFT computed surface energies of γ-LiAlO2 reveal that the {101} surface becomes the lowest energy surface upon H-adsorption, thus leading to formation of observed octahedral geometry. Contrary to stabilization of γ-LiAlO2 surfaces upon H passivation, DFT revealed H-adsorption on α-LiAlO2 surfaces to be energetically unfavorable. This contrasting behavior of α-LiAlO2 and γ-LiAlO2 under H-rich environments could be a potential driving force for the observed α-LiAlO2 to γ-LiAlO2 phase transformation.
关键词： morphology,phase transformation,TEM,DFT,LiAlO2,XRD
更新于2025-09-10 09:29:36
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Tailoring of highly porous SnO2 and SnO2-Pd thin films
摘要： Tin oxide is a material that attracts attention due to varieties of technological applications. The main parameters that influence its properties are morphology, crystalline structure and stoichiometry. To influence these parameters researchers try to develop nanostructured thin films that would conform technological application. Here, we report the preparation and characterization of highly porous SnO2 and Pd doped SnO2 thin films. The films were deposited in form of nanorods with controllable geometry. Such morphology was achieved by utilizing glancing angle deposition (GLAD) with assisted magnetron sputtering. This arrangement allowed preparation of slanted pillars, zig-zag structure, vertically standing posts, spiral posts and “bush”-like structures. We calculated that slanted pillars possess highest surface area among the films listed. Then, sets of slanted pillars were deposited and studied in more details. The influence of substrate annealing during the film deposition and Pd doping on the morphology, crystalline structure and stoichiometry of the films are discussed. Characterizations of the tin oxide films were performed by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoelectron spectroscopy (SRPES). GLAD with assisted magnetron sputtering allowed us to deposit broad range of SnO2 nanostructures while annealing of the substrate during deposition affects the films crystallinity. Also, we find that doping of the SnO2 films with Pd leads to alloy phase formation. These findings can be applied in variety of applications including gas sensing, catalysis, optics and electronics.
关键词： XPS,SRPES,SnO2,tin oxide,glancing angle deposition,TEM,HRTEM,GLAD,highly porous
更新于2025-09-10 09:29:36
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Dislocations behavior in highly mismatched III-Sb growth and their impact on the fabrication of <i>top-down</i> n?+?InAs/p?+?GaSb nanowire tunneling devices
摘要： We study in this work the growth and fabrication of top-down highly doped n + InAs(Si)/p + GaSb(Si) Esaki tunneling diodes on (001) GaAs substrates. A careful investigation on the highly mismatched GaSb/GaAs growth is first conducted by means of Reflection High-Energy Electron Diffraction (RHEED), Atomic Force Microscopy (AFM), and X-Ray Diffraction (XRD) analyses. These results are expected to pave the way to methods for III-Sb buffer layer’s integration with low threading dislocation (TD) densities. A comparison between AFM, XRD, defect revealing by chemical etching and transmission electron microscopy (TEM) is then presented to calculate the precise TD density and its influence on the device structure. In the last part, we report on first operating sub-30 nm III-V vertical NW tunneling devices on (001) commercial GaAs substrates.
关键词： III-Sb growth,AFM,dislocations,TEM,nanowire tunneling devices,XRD,RHEED,GaAs substrates
更新于2025-09-10 09:29:36
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Photophysical insights and in vitro cytotoxicity of dyes-gold nanostars system towards MCF-7 and A-549 cancer cells
摘要： In this paper, the interaction of phenothiazine (PHZ) dyes (Azure A (AZA) and thionine (TH)) with gold nanostars (Au NSs) were studied using absorption spectroscopy, steady state emission spectroscopy, high resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS), Zetapotential measurements and Fourier transform infrared (FT-IR) spectroscopy. Absorption spectral studies of Au NSs in the presence of dyes resulted in a slight red shift on the surface plasmon resonance band (SPR) of Au NSs, suggesting the changes in the Au NSs surface owing to the adsorption of dyes. The phenomena of hypochromism and the appearance of coupled localized surface plasmon resonance (LSPR) bands in the absorption spectral studies of the AZA-Au NSs and TH–Au NSs systems suggested the vital role of electrostatic interactions between PHZ dyes and Au NSs. The formation of the ground state complex between dyes and Au NSs were evident from the outcome of the steady-state emission titration experiments of the dyes-Au NSs system. Further, the cytotoxic activity of AZA, TH, AZA-Au NSs and TH-Au NSs complexes on breast cancer (MCF-7) and A-549 cell lines were also investigated. These studies revealed that AZA-Au NSs, TH-Au NSs complexes showed the higher level of cytotoxicity than PHZ dyes treated cells.
关键词： A-549 and MCF-7 cells,Goldnanostars,Thionine,DLS,Azure A,HR TEM
更新于2025-09-09 09:28:46
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In-doped Sb nanowires grown by MOCVD for high speed phase change memories
摘要： We investigated the Phase Change Memory (PCM) capabilities of In-doped Sb nanowires (NWs) with diameters of (20-40) nm, which were self-assembled by Metalorganic Chemical Vapor Deposition (MOCVD) via the vapor-liquid-solid (VLS) mechanism. The PCM behavior of the NWs was proved, and it was shown to have relatively low reset power consumption (~ 400 μW) and fast switching capabilities with respect to standard Ge-Sb-Te based devices. In particular, reversible set and reset switches by voltage pulses as short as 25 ns were demonstrated. The obtained results are useful for understanding the effects of downscaling in PCM devices and for the exploration of innovative PCM architectures and materials.
关键词： In-Sb,Nanowires,Phase change memories,XRD,TEM,MOCVD
更新于2025-09-09 09:28:46
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bilayers
摘要： Magnetic exchange coupling behavior was investigated in MnBi/FeCo bilayer system at the hard/soft magnetic interface. We performed a combined study of cross-sectional high resolution transmission electron microscopy (HR-TEM), DFT calculations, and micromagnetic simulations to elucidate effect of interface structure on exchange coupling. Exchange spring MnBi/FexCo1?x (x = 0.65 and 0.35) bilayers with various thicknesses of the soft magnetic layer were deposited in a dc magnetron sputtering unit from alloy targets. According to magnetic measurements, using a Co-rich layer leads to a more coherent exchange coupling with optimum soft layer thickness of about 1 nm. Our DFT calculations predicted formation of a polycrystalline FeCo layer with coexisting crystalline and disordered (110) phases. The indexed FFTs from HR-TEM images con?rmed a crystalline FeCo(110) layer, with slight misorientation in some areas, and a disordered region close to the interface which deteriorates interface exchange coupling. Moreover, our micromagnetic simulations showed how the thickness of the FeCo layer and the interface roughness both control the effectiveness of exchange coupling in MnBi/FeCo bilayer.
关键词： Magnetic exchange coupling,micromagnetic simulations,HR-TEM,MnBi/FeCo bilayer,DFT calculations
更新于2025-09-09 09:28:46
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Transformation of the Anion Sublattice in the Cation-Exchange Synthesis of Au <sub/>2</sub> S from Cu <sub/>2-x</sub> S Nanocrystals
摘要： Cation exchange is a versatile post-synthetic technique that has been exploited in the synthesis of metastable nanocrystals through preservation of the anion sublattice. Here we report on the mechanistic details of the synthesis of metastable Au2S via cation exchange with Cu2-xS nanocrystals. This conversion requires a transformation of the anion sublattice, from hcp in Cu2-xS to bcc Au2S accompanied by an expansion of the unit cell. The ligand environment plays a key role in the driving force of the reaction as the presence of oleylamine allows the conversion to proceed at room temperature while the addition of trioctylphosphine hinders the reaction. By employing transmission electron microscopy (TEM) on faceted nanocrystals and partial cation exchange of nanocrystals, it was demonstrated that the reaction proceeds in a highly directional manner through the pyramidal facets. Since cation exchange produces high quality nanocrystals as seen through XRD and TEM, UV-Vis and Raman spectroscopy were used to characterize the optoelectronic properties of the metastable Au2S nanocrsytals. A Tauc plot analysis revealed a band gap of 2.6 eV, while two intrinsic Raman modes were identified at 265 cm-1 and 329 cm-1. Density functional theory (DFT) calculations of structures, energy bands, optical spectra, and phonon spectra were performed and combined with the experimental data to provide additional insights into the characterization of Au2S nanocrystals.
关键词： XRD,Raman spectroscopy,UV-Vis,trioctylphosphine,nanocrystals,TEM,Cation exchange,DFT,Cu2-xS,anion sublattice transformation,Au2S,oleylamine
更新于2025-09-09 09:28:46
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Synthesis of Curved CuIn1-xGax(S1-ySey)2 Nanocrystals and Complete Characterization of their Diffraction Contrast Effects
摘要： Herein, we report the synthesis and complete structural characterization of curved CuIn1-xGax(S1-ySey)2 (x = y = 0.5) nanocrystals, which adopt a 2D nanoplate morphology and crystallize in the hexagonal wurtzite phase. A detailed transmission electron microscopy (TEM) analysis reveals that the 2D nanoplates are predominately [001]-oriented and exhibit a unique bend contour pattern, due to curvature on the (001) basal plane. The contrast behavior of bend contours in this system is further supported through specimen tilting experiments inside the TEM, in combination with dark-field (DF) imaging in both TEM and scanning TEM (STEM) modes. This bending is believed to originate from the proximity effect of the top and bottom (001) surfaces.
关键词： bend contours,CuIn1-xGax(S1-ySey)2,hexagonal wurtzite phase,TEM,nanocrystals
更新于2025-09-09 09:28:46
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Annealing effects on the properties of tin thin films
摘要： The structure, absorption coefficient and electrical resistivity studies on TiN thin films are presented. The film of thickness 240 nm was grown on Si (100) substrate by DC reactive sputtering at an average deposition rate of ～8 nm/min. After deposition the samples were annealed for 1 h at 600 °C and 2 h at 700 °C in nitrogen ambient and vacuum furnace, respectively. Structural characterizations were performed by Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The optical properties were investigated by spectroscopic ellipsometry while a four point probe was used for electrical characterization. It was found that the post-deposition annealing of the films did not cause any variation in stoichiometry, but strongly affects the structural parameters such as lattice constant, micro-strain and grain size. The observed increase in the grain size after annealing leads to significantly lower value of the coefficient of absorption. These changes could be directly correlated with variation of electrical properties of TiN thin films.
关键词： RBS,annealing,sputtering,thin film,XRD,titanium nitride,TEM
更新于2025-09-09 09:28:46
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Recrystallization Phase in He-Implanted 6H-SiC
摘要： The evolution of the recrystallization phase in amorphous 6H-SiC formed by He implantation followed by thermal annealing is investigated. Microstructures of recrystallized layers in 15 keV He+ ion implanted 6H-SiC (0001) wafers are characterized by means of cross-sectional transmission electron microscopy (XTEM) and high-resolution TEM. Epitaxial recrystallization of buried amorphous layers is observed at an annealing temperature of 900°C. The recrystallization region contains a 3C-SiC structure and a 6H-SiC structure with different crystalline orientations. A high density of lattice defects is observed at the interface of different phases and in the periphery of He bubbles. With increasing annealing to 1000°C, 3C-SiC and columnar epitaxial growth 6H-SiC become unstable, instead of [0001] orientated 6H-SiC. In addition, the density of lattice defects increases slightly with increasing annealing. The possible mechanisms for explanation are also discussed.
关键词： Recrystallization,lattice defects,He-implanted 6H-SiC,annealing,TEM
更新于2025-09-09 09:28:46