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Item type:Publication, Thickness dependence of the room-temperature ethanol sensor properties of Cu2O polycrystalline films(Institute of Physics, 2024-08-05)This study investigates the fabrication process of copper thin films via thermal evaporation, with precise control over film thickness achieved through Z-position adjustment. Analysis of the as-fabricated copper films reveals a discernible relationship between grain size (〈D〉) and Z-position, characterized by a phenomenological equation 〈 D 〉 XRD n ( Z ) = 〈 D 〉 0 n 1 + 3 2 r Z 2 + 15 8 r Z 4 , which is further supported by a growth exponent (n) of 0.41 obtained from the analysis. This value aligns well with findings in the literature concerning the growth of copper films, thus underlining the validity and reliability of our experimental outcomes. The resulting crystallites, ranging in size from 20 to 26 nm, exhibit a resistivity within the range of 3.3-4.6 μΩ · cm. Upon thermal annealing at 200 °C, cuprite Cu2O thin films are produced, demonstrating crystallite sizes ranging from ∼9 to ∼24 nm with increasing film thickness. The observed monotonic reduction in Cu2O crystallites relative to film thickness is attributed to a recrystallization process, indicating amorphization when oxygen atoms are introduced, followed by the nucleation and growth of newly formed copper oxide phase. Changes in the optical bandgap of the Cu2O films, ranging from 2.31 to 2.07 eV, are attributed mainly to the quantum confinement effect, particularly important in Cu2O with size close than the Bohr exciton diameter (5 nm) of the Cu2O. Additionally, correlations between refractive index and extinction coefficient with film thickness are observed, notably a linear relationship between refractive index and charge carrier density. Electrical measurements confirm the presence of a p-type semiconductor with carrier concentrations of ∼1014 cm−3, showing a slight decrease with film thickness. This phenomenon is likely attributed to escalating film roughness, which introduces supplementary scattering mechanisms for charge carriers, leading to a resistivity increase, especially as the roughness approaches or surpasses the mean free path of charge carriers (8.61 nm). Moreover, ab-initio calculations on the Cu2O crystalline phase to investigate the impact of hydrostatic strain on its electronic and optical properties was conducted. We believe that our findings provide crucial insights that support the elucidation of the experimental results. Notably, thinner cuprite films exhibit heightened sensitivity to ethanol gas at room temperature, indicating potential for highly responsive gas sensors, particularly for ethanol breath testing, with significant implications for portable device applications. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Structural, morphological, and magnetic characterizations of (Fe0.25Mn0.75)2O3 nanocrystals: A comprehensive stoichiometric determination(Elsevier Ltd, 2024-12-01)This report aims to investigate in depth FeMnO3, a material of interest due to its fascinating magnetic and multiferroic properties and its many applications in fields including lithium-ion batteries, microwave devices, and catalysis. However, understanding the precise stoichiometry of the material is crucial for a better comprehension of its physical properties. A cheap, simple, and repeatable sol-gel process was used to fabricate the FeMnO3 nanocrystals. Comprehensive multi-technique characterization of the as-fabricated FeMnO3 indicates that the main phase (94 wt%) is Fe0.5Mn1.5O3, although hematite appears as the minority phase (6 wt%). Magnetic characterization shows core-shell spin-glass like behavior, as well as paramagnetic-ferrimagnetic transitions and a Griffiths phase regime. EPR measurements revealed a strong and broad resonance line across the temperature range of 4.3 K–300 K, primarily influenced by the majority phase. The g-value decreases monotonically from 2.93 at 50 K to 2.18 at 300 K. There is a notable change in the resonance field and linewidth between 40 and 50 K, attributed to surface spin glass behavior. The EPR data below 50 K are in line with the core-shell model of (Fe0.25Mn0.75)2O3 nanoparticles. Below 50 K, the shell's spin system undergoes a transition from paramagnetic to spin-glass-like, with a critical temperature around 43 K. Above 50 K, the superparamagnetic minority phase significantly affects the temperature dependence of the resonance linewidth. These results hold particular importance as they advance our understanding of the intricate magnetic interactions present in FeMnO3. For the best possible use of this material platform in new technologies, such insights are essential. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Impact of the thickness on the optical, electronic, and structural properties of sputtered Cu2S thin films(American Institute of Physics Inc., 2024-02-14)A successful hexagonal Cu 2 S p-type semiconductor thin film using DC magnetron sputtering is reported. Films with thickness gradients were deposited by taking advantage of deposition geometry and target dimensions. X-ray diffraction (XRD) analysis confirmed the exclusive formation of the hexagonal Cu 2 S phase. Elemental composition and thickness dependence with the sample position were determined using energy-dispersive x-ray spectroscopy. Optical properties, including the optical bandgap, refractive index, and extinction coefficient, were assessed by modeling transmittance spectra. The Tauc-Lorentz oscillator and Drude models were employed for this purpose. XRD data analysis successfully determined the film thickness ( t X R D ) as a function of the sample position, aligning well with thickness values ( t T ) derived from transmittance spectra analyses. These results were further supported by film thickness values ( t S E M ) obtained from cross-sectional SEM images. Charge carrier density and mobility, extracted from the optical models, were found to be consistent with DC electrical measurements. AC impedance curves were effectively modeled with RL-RC parallel circuits. The results indicate that the inductance (L) and capacitance (C) components of the films increase with decreasing film thickness. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Enhancing the Photoconductivity and Gas Sensing Performance of TiO2/SnO2 Heterostructures Tuned by the Thickness of the SnO2 Upper Layer(Elsevier B.V., 2023-03-15)In this report, polycrystalline TiO2/SnO2 heterostructures with variable SnO2 film thickness were deposited by DC sputtering. Scanning electron microscopy images show a cracked surface in all films. The latter gets more widespread as the SnO2 layer thickness increases with deposition time. Optical transmittance measurements were used to determine the thickness of the TiO2 and SnO2 polycrystalline films. Photocurrent measurements of pure SnO2 films using UVA irradiation revealed a good response for thinner SnO2 films, however, these decrease as film thickness increases. Besides, photocurrent response is enhanced for the TiO2/SnO2 heterostructures over pure SnO2 film. It is thought that a high photocurrent response can be produced due to the improved ability to separate the photoinduced electrons and holes, as well as due to suitable charge management at the TiO2 and SnO2 interface. Additionally, the large amount of active sites for the thinner SnO2 upper layer favors better room temperature gas response to ethanol than that obtained for single SnO2 films. These features make the TiO2/SnO2 heterostructure a promising candidate for room temperature gas sensors and photosensitivity applications.