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Item type:Publication, Enhancing the photoconductivity and gas sensing performance of TiO2/SnO2 heterostructures tuned by the thickness of the SnO2 upper layer(RELX Group (Netherlands), 2022-01-01)In this report, polycrystalline TiO2/SnO2 heterostructures with variable SnO2 film thickness were deposited by DC sputtering. Mean crystallite size of 4-6 nm was estimated for the upper SnO2 films. SEM 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 decreasing as film thickness increases. Besides, photocurrent response is enhanced for the TiO2/SnO2 heterostructures with respect to the 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 a 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. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Indirect excitation and luminescence activation of Tb doped indium tin oxide and its impact on the host's optical and electrical properties(IOP Publishing Ltd, 2022-05-26)The effect of adding terbium to indium tin oxide (ITO) thin films on the electrical, optical and light emission properties was investigated. The films were prepared by radio frequency dual magnetron sputtering, maintaining a high optical transmittance in the ultraviolet and visible spectral regions, and a low electrical resistivity ranging from 5 × 10 − 3 Ω ⋅ cm to 0.3 Ω ⋅ cm . Terbium-related luminescence is achieved after annealing at 470 ∘C in air at atmospheric pressure. Electrical resistivity and optical transmittance were measured after each annealing step to evaluate the compromise between the achieved light emission intensity, electrical and optical properties. Additionally, temperature dependence of Tb-related luminescence quenching was assessed by temperature-dependent photoluminescence measurements, from 83 to 533 K, under non-resonant excitation. Thermal quenching activation energies suggest an effective energy transfer mechanism from the ITO host to the rare-earth (RE) ions. This indirect excitation mechanism was modeled using a spherical potential-well and a tight-binding one-band approximation approaches, describing a short-range charge trapping process and subsequent formation of bound excitons to RE ion clusters. - Some of the metrics are blocked by yourconsent settings
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, TL, EPR, and optical properties of undoped and Eu-, Ce-, Tb-, Sm-, Cu-, Mn-, and Li-doped MgSiO3 phosphors, synthesized by sol-gel combustion technique(Elsevier Ltd, 2024-11-01)Polycrystalline MgSiO3 samples, undoped or doped with rare earth- (Eu, Tb, Ce, Li, Sm), transition- (Mn and Cu), and alkali metal- (Li) elements, were prepared by the sol-gel combustion method and characterized by thermoluminescence, electron spin resonance, and optical properties. Enstatite and protoenstatite phases are observed in undoped and doped MgSiO3. Better TL results have been observed for phosphors doped with Tb, Ce, and Li (0.5 % mol). Fading experiments and the GCD method have been performed. EPR signals of gamma-irradiated phosphors indicate the formation of radiation-induced defect centers. Cu-doped MgSiO3 shows an unusual feature of the Cu2+ ion. The Cu2+ ion occupies a tetragonally compressed octahedral site, presenting an unconventional attribute. Optical bandgap value Eg is higher for the Ce, Tb, Mn, Li, Sm, and Cu-doped MgSiO3 phosphors. Ce, Li, and Tb dopant ions were found suitable for the MgSiO3 sample regarding its thermoluminescent response and its possible application in radiation dosimetry. - 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, Tailoring structural, electrical, and optical properties of ITO thin films via vacuum-pressure annealing: An experimental and theoretical study(Elsevier BV, 2025-02-25)This study explores the structural, optical, and electronic properties of polycrystalline Sn-doped In2O3 (ITO) thin films deposited via DC sputtering method and annealed at 600∘ C for 2 h under different vacuum pressures (VPs) ranging from 1 to 10−6 mbar. The bandgap energy increases from 3.8 eV to 4.1 eV with the vacuum, driven by the Burstein-Moss effect, accompanied by the reduction of Urbach energy, crystallinity improvement and reduction of disorder. This reduction is likely due to enhanced migration of interstitial oxygen ions with vacuum during the annealing. The electrical resistivity decreases significantly when the carrier concentration increases, meanwhile, the effective mass increases (from 0.3 to 0.5me), which is linked to a transition from parabolic to non-parabolic density of states. Near-infrared optical analysis reveals higher optical mobility than Hall mobility, particularly in samples annealed under lower vacuum, which was assigned to the predominant grain boundary scattering process. Photocurrent generation correlates with photoabsorption, Urbach energy, and crystallite size, which decrease as the vacuum is increased. Impedance analysis shows a reduction of the resistance and inductance, with an increase of the capacitance and carrier concentration with the vacuum of the annealing. DFT calculations confirm oxygen vacancies enhance charge density and widen the bandgap, aligning with experimental findings. These results highlight the role of oxygen vacancies in tuning ITO properties for optoelectronic applications.7 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Structural, hyperfine, and magnetic evolution of a natural magnetite–serpentine composite: Effects of magnetic separation and thermal treatment(Elsevier BV, 2026-08-15)In this work, the structural, hyperfine, and magnetic evolution of a natural magnetite–serpentine composite was systematically investigated in its as-collected state, after magnetic separation, and following thermal treatments. X-ray diffraction combined with Rietveld refinement reveals a lizardite-dominated matrix containing magnetite as the primary magnetic phase. Mössbauer spectroscopy identifies Fe2＋ and Fe3＋ cations distributed over distinct octahedral and tetrahedral sites in both lizardite and magnetite, providing insight into cation distribution and oxidation state evolution. Magnetic measurements reveal ferrimagnetic behavior dominated by magnetite, with a saturation magnetization of ∼79 emu g−1 at room temperature. The transition temperature was estimated from the derivative of the ZFC–FC magnetization curve with respect to temperature, which exhibits a relatively broad peak associated with the Verwey transition (118 K). This feature suggests the presence of relatively preserved magnetite within the ultramafic matrix, although the broad character of the transition may reflect structural disorder, particle-size effects, or magnetic interactions. In addition, the magnetic data indicate the coexistence of superparamagnetic behavior and possible spin-glass-like contributions, likely associated with surface disorder and nanoscale magnetic interactions. Water-assisted magnetic separation enhances the magnetic fraction, confirming that magnetite particles are embedded within the lizardite matrix. Thermal treatments at 500 °C and 1000 °C induce progressive dehydroxylation, oxidation of iron-bearing phases, and the formation of hematite, forsterite, silica, and clinoenstatite, leading to significant modifications in both hyperfine parameters and magnetic behavior. The results establish clear structure-hyperfine-magnetic correlations and demonstrate how magnetic separation and thermal processing govern the phase stability and functional magnetic response of natural magnetite–serpentine systems. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Spatially controlled sputtering of Mo1?xHfx thin films: Composition-tuned structure, electronic transport, and room-temperature CO2 sensing(Elsevier BV, 2026-09-30)Mo1−xHfx thin films with a compositional gradient were deposited by a co-sputtering process. Structural characterization by XRD, supported by Rietveld refinement, suggests that at low Hf concentrations the films exhibit an fcc-like structure, with a systematic increase in the lattice parameter as Hf content increases, consistent with Vegard's law. At higher Hf concentrations, the diffraction patterns evolve and are better described by a mixed-phase system involving hcp-Hf and bcc-Mo contributions, indicating the onset of phase coexistence. EDS confirms the compositional gradient and the effective incorporation of Hf into the Mo matrix, while scanning electron microscopy reveals position-dependent variations in morphology and thickness arising from different sputtering rates. XPS identifies the formation of native surface oxide layers and provides their chemical composition. Impedance spectroscopy measurements exhibit pronounced spatial variations in the electrical response, which are well described using equivalent electrical circuits and are consistent with the presence of these oxide layers. At Mo-rich regions, an inductive response is attributed to enhanced charge transport and current inertia effects in highly conductive areas. Finally, room-temperature gas-sensing measurements demonstrate an electrical response to CO2, revealing two distinct regimes: Hf-rich films exhibit an n-type-like response, whereas Mo-rich films show a p-type-like behavior. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Room-temperature ferromagnetism and anomalous electrical transport in Fe-doped ITO thin films(Institute of Physics, 2026-06-26)Here, we report the structural, optoelectronic, and magnetic properties of sputtered Fe-doped ITO thin films. X-ray diffraction analysis confirms the formation of a single-phase cubic bixbyite structure, indicating effective diffusion and substitution of Fe ions into the ITO lattice without evidence of secondary phases. The incorporation of Fe ions introduces localized magnetic moments into the ITO host matrix. Increasing the annealing temperature reduces the defect density and enhances the optical transmittance, consistent with the observed decrease in Urbach energy. Temperature-dependent resistivity measurements reveal an anomalous semiconducting behavior strongly influenced by the annealing conditions. Magnetic characterization demonstrates the coexistence of paramagnetic and ferromagnetic contributions, with room temperature ferromagnetism reaching a saturation magnetization up to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>∼</mml:mo> </mml:mrow> </mml:math> 0.64 emu g <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> (1.4 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>μ</mml:mi> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> /Fe) after annealing at 400 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mo/> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> C. The observed ferromagnetism in the Fe-doped ITO samples is attributed to oxygen vacancies, which promote the formation of bound magnetic polarons near Fe ions. The resistivity-temperature curve shows a Kondo-like upturn at low temperatures, suggesting scattering of conduction electrons by localized Fe ions. Photocurrent measurements confirm n-type conductivity, which is significantly enhanced upon annealing at 700 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mo/> <mml:mo>∘</mml:mo> </mml:msup> </mml:mrow> </mml:math> C.