Increase In Band Gap Energy Research Articles

Dielectric Characteristics of Iridium Substituted Co0.05-xTi0.95O2 Dilute Magnetic Semiconductors for Electrical Device Applications

In the current study, a cost effective solid-state method have been used to prepare iridium (Ir) substituted and cobalt doped titanium dioxide (TiO2) dilute magnetic semiconductors (DMS) materials {i.e.; IrxCo0.05-xTi0.95O2; 0.00 ≤ x ≤ 0.05 DMS}. The impact of Ir substitution on structural, optical and dielectric properties for the prepared IrxCo0.05-xTi0.95O2; 0.00 ≤ x ≤ 0.05 DMS samples have been investigated using X-ray diffractometer, ultraviolet-visible spectroscopy and LCR (inductor, capacitor and resistor) meter, respectively. The structural analysis confirms the tetragonal rutile phase formation with space group p42/mnm-136, while the values of band gap energy increase with increasing Ir concentrations in prepared DMS materials and band gap value approaches the band gap energy of void band gap materials for large applications. The dielectric constant and tangent loss have been studied as a mapping of frequency (20Hz - 20MHz) at room temperature. Both the dielectric constant and tangent loss linearly decrease with increase in applied frequency and become stable at high frequency values, therefore, these DMS materials could be beneficial for storage and electrical device applications.

Investigation of the optical and radiation shielding parameters of erbium-doped zinc sodium tungsten borate glass using MCNP5 simulations

Abstract This study explores the potential of (20Na2O+25ZnO+10WO3+(60-x)B2O3+xEr2O3 where x = 0.1, 0.5, 0.7, and 1 mol%) glass for optical and radiation shielding applications, fabricated using the melt quenching method. Optical, structural, and radiation shielding properties were analyzed using UV–visible spectroscopy, XRD, FTIR, MCNP5, and Phy-X/PSD software. Results show a 9.01% decrease in refractive index from 2.22 to 2.02 and a significant increase in band gap energy from 2.29 eV to 3.12 eV with increasing Er2O3 content. The addition of Er3+ ions convert BO3 units into BO4 units, creating a denser glass network. The linear attenuation coefficient ( LAC ) increased in BTEr1 glass to 0.676 cm−1, compared to 0.607 cm−1 for BTEr0.1 glass, reflecting an approximate rise of 11.5% in LAC . The BTEr1 glass shows enhanced radiation shielding, with a 10.25% reduction in the half-value layer (HVL) from 1.15 cm in BTEr0.1 to 1.03 cm in BTEr1 at 0.284 MeV, and a further reduction of 8.17% from 4.77 cm in BTEr0.1 to 4.42 cm in BTEr1 at 2.506 MeV for 0.1 and 1 mol% Er2O3 level in the BTEr glass. The BTEr glass enhances light transmission in the visible spectrum and increases glass stability with Er2O3 addition , making it suitable for advanced optical applications. Additionally, its improved photon radiation shielding properties make it a promising candidate for radiation protection.

Enhanced UV photodetector using Mg-doped ZnO sub-micro tube films synthesized through laser-assisted chemical bath growth

This study presents the fabrication of MgxZn(100-X)O thin films (TFs) with Mg concentration levels (x) of 0.5 at%, 1.0 at%, 1.5 at%, and 2.0 at% on glass substrates using the novel laser-assisted chemical bath growth (LACBG) method, aimed at investigating their photo-response for potential UV photodetector applications. Utilizing a continuous wave semiconductor laser with a 444.5 nm wavelength, 1 W power, and 6 min of irradiation, the LACBG method successfully produced high-quality Mg-doped ZnO TFs. These films were deposited on glass substrates coated with silver (Ag) to serve as electrode contacts for constructing a metal-semiconductor-metal (MSM) UV photodetector. The structural, optical, and electrical properties of the TFs were thoroughly analyzed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to examine the crystal microstructures and surface morphologies, revealing vertically aligned hexagonal symmetrical sub-micro tubes. In contrast, energy dispersive X-ray (EDX) analysis confirmed successful Mg incorporation into the ZnO lattice. UV–visible absorbance spectra indicated a blue shift in the absorption edge and increased band gap energy from 3.24 eV to 3.67 eV with rising Mg content. The UV photodetectors, particularly those with 2.0 at% Mg-doped ZnO TFs, demonstrated significantly enhanced UV responsiveness attributed to optical confinement, high surface-to-volume ratio, and superior structural quality. Performance metrics for the 2.0 at% Mg-doped ZnO TFs included a responsivity of 10.60 A/W, external quantum efficiency of 34.10, specific detectivity of 2.25 × 107 Jones, noise equivalent power of 5.34 × 10−11 W, rise time of 86.9 ms, and decay time of 324.4 ms. These findings underscore the potential of Mg-doped ZnO TFs for high-performance UV photodetection applications. The novelty of this study lies in utilizing LACBG to achieve high-quality Mg-doped ZnO TFs, offering a cost-effective, low-temperature method that enhances UV photodetector performance.

Enhancement of supercapacitor efficiency by Fe3+ doping in hydrothermally synthesized NiO nanoparticles

This study examines the physicochemical and electrochemical characteristics of hydrothermally produced, 800°C-annealed pure and Fe3+ doped (0.02, 0.04, and 0.06 M) NiO nanoparticles(NPs).The face-centred cubic structure of NiO NPs was verified by XRD analysis, and doping resulted in a decrease in crystallite size from 43.92 nm to 19.67 nm.FE-SEM revealed dense and irregularly arranged granular morphologies, while EDAX confirmed successful Fe3+ incorporation into NiO matrix. UV–Vis DRS showed an increase in bandgap energy from 3.15 eV to 3.71 eV. XPS confirmed the presence of Ni2+ and Fe3+ with their elemental compositions. According to BET analysis, Fe3+ doping increases pore size and specific surface area, which raises specific capacitance.VSM analysis of pure and Fe3+ doped NiO NPs demonstrated a transition from a weak ferromagnetic to a distinctive ferromagnetic behaviour, which is beneficial for energy storage as well as data storage applications.The electrochemical studies showed that 0.06 M Fe3+ doped NiO had the maximum specific capacitance of 360.96 F g−1 at the scan rate of 10 mV s−1and EIS Nyquist plots showed enhanced electrical conductivity. These results highlight the possibility of Fe3+ doped NiO NPs as excellent electrode materials for high-efficiency supercapacitors.

Efek Pendoping Nd3+ Pada Senyawa BaBi2-xNdxNb2O9 Terhadap Struktur, Sifat Dielektrik Dan Optik

The Aurivillius compound with formula BaBi2-xNdxNb2O9 (x = 0.05, 0.1, 0.2, and 0.4) has been successfully synthesized using the molten salt method, showing potential as a ferroelectric material. The impact of Nd3+ substitution on the structure, morphology, dielectric, and optical properties has been systematically analyzed. XRD data refinement confirms that BaBi2-xNdxNb2O9 (BBNN) exhibits an orthorhombic structure with an A21am space group. Anisotropic plate-like grains were observed across all samples, decreasing their size as Nd3+ content increases. The ferroelectric transition temperature (Tc) decreases due to structural distortion caused by the reduction of the lone pair 6s2 electron effect of Bi3+ when substituted with Nd3+. Moreover, this structural distortion also contributes to an increase in bandgap energy (Eg). The diffuse ferroelectric phase transition is characterized by a broadened Tc peak induced by Nd3+ substitution due to increased cationic disruption in the bismuth layers. The ferroelectric phase with a lower and broader Tc suggests that the x = 0.4 sample has the potential for electrocaloric applications.

Effects of fluorine atom numbers on electrochromic properties of the benzothiadiazole-based D-A polymers

In this work, two fluorinated D-π-A-π-D type monomers, F-EDOT and FF-EDOT, were facilely synthesized by donor-acceptor-donor method via Stille coupling reaction, with monofluorinated benzothiadiazole and difluorinated benzothiadiazole as the acceptor units and 3,4-ethylenedioxythiophene (EDOT) as the donor units. The electrochemical polymerization behavior of the fluorinated monomers, electrochemical and electrochromic properties of the corresponding fluorinated D-A polymers were compared to study the effects of different fluorine atom numbers on the optoelectronic properties of the monomers and their resultant D-A polymers. The results show that the introduction of more F atoms into the conjugated backbone increases the oxidation potential of monomers, both of them have low initial oxidation potential (0.65 V/0.70 V). As in the case of monomers, the substitution of more F atoms also leads to the decreased HOMO energy level of the polymers, thus leading to the increased band gap energy of P(FF-EDOT) (1.39 eV). This result can be attributed to the deviation of planarity and the reduced effective conjugate length. As prepared fluorinated D-A polymers also have good adhesion on the electrode surface, favorable redox activity, and outstanding redox stability (the redox activity of P(F-EDOT) remains 99 % after 1000 cycles). At the same time, the fluorinated D-A polymers also show distinguish electrochromic properties under various external potentials; both the optical contrast and coloration efficiency decreased with the increase of F atom numbers, and the corresponding response time increased. As a result, both the fluorinated D-A polymers show light green in the neutral state, P(F-EDOT) shows more obvious electrochromic performance in the near infrared region (optical contrast: 35.02 %, coloration efficiency: 159.94 cm2 C−1, and quick response time: 0.2 s), accompanied with excellent discoloration stability and optical memory effect. The study of novel fluorinated-based electrochromic materials further expands the selection of acceptor units and the application prospect of electrochromic materials.

Impact of titanium modification on the performance improvement and phase change mechanism of ZnSb thin film

Phase change memory has emerged as a promising option for neuro-inspired and data-intensive AI applications, attracting significant attention from the semiconductor field recently. The performance of the device relies on the phase change material, aiming for enhanced thermal stability along with low power consumption. Nanocomposite ZnSb thin films with titanium dopant were prepared and their crystallization properties and mechanisms were investigated. Compared to pure ZnSb material, the addition of titanium can significantly enhance the temperature of crystallization and the 10-year data retention ability, both of which surpassing 16 °C. The obvious enhancement in thermal stability may be ascribed to the ionic bond formation between titanium and antimony elements, as indicated by differential charge calculations. Also, phase change memory cells with a diameter of 190 nm were fabricated using standard CMOS technology. The Ti-doped ZnSb thin film demonstrates rapid crystallization and amorphization within 50 ns while consuming low power at approximately 1.5 × 10−10 J. The decrease in power consumption may stem from the increase in band gap energy and a decrease in electrical conductivity, as confirmed by first-principles calculations. Both experimental and theoretical results prove that titanium doping can remarkably improve the physical properties of ZnSb thin film, facilitating the exploration and design of novel phase change materials with high thermal stability, low power consumption, as well as fast switching speed.

Interface and Size Effects of Amorphous Si/Amorphous Silicon Oxynitride Multilayer Structures on the Photoluminescence Spectrum

A room-temperature photoluminescence (PL) study of amorphous Si/amorphous silicon oxynitride multilayer films prepared by plasma-enhanced chemical vapor deposition is reported. The PL peak position can be tuned from 800 nm to 660 nm by adjusting the oxygen/nitride ratio in the a-SiOxNy:H sublayer. The Fourier transform infrared (FTIR) absorption spectra indicate that the shift of the PL peak position is accompanied by an increase in the Si-O-Si absorption peak’s intensity, which induces the structural disorder at the interface, resulting in an increase in band gap energy. The effects of size on the photoluminescence spectrum have been studied. As a result, it has been observed that the addition of oxygen atoms introduces a large number of localized states at the interface, causing a blue shift in the emission peak position. With an increase in oxygen atoms, the localized states tend to saturate, and the quantum phenomenon caused by the a-Si sublayer becomes more pronounced. It is found that, as the thickness of the a-Si sublayer decreases, the increase in the [O/N] ratio is more likely to cause an increase in disordered states, leading to a decrease in luminescence intensity. For a-Si/a-SiOxNy:H samples with thinner a-Si sublayers, an appropriate value of [O/N] is required to achieve luminescence enhancement. When the value of [O/N] is one, the enhanced luminescence is obtained. It is also suggested that the PL originates from the radiative recombination in the localized states’ T3- level-related negatively charged silicon dangling bond in the band tail of the a-Si:H sublayer embedded in an a-Si/a-SiOxNy:H multilayer structure.

Simulation and analysis of the single event transient characteristics of SiGe HBT at low-temperature environment

This study investigates the temperature dependence of single event transient (SET) effects in silicon germanium heterojunction bipolar transistors (SiGe HBTs). Using Silvaco TCAD simulations, we analyze the influence of linear energy transfer (LET), emitter bias voltage, and striking angle across a temperature range from 100 K to 300 K. The results reveal that temperature significantly affects emitter pulse current and charge collection induced by heavy ions. Higher temperatures increase charge collection, while lower temperatures correspond to higher emitter current and shorter pulse width. The study also observes an increase in bandgap energy (from 1.12 eV to 1.16 eV) and electrostatic potential (from 1.19 V to 1.25 V) with decreasing temperature. The study highlights the crucial role of temperature in SiGe HBT performance under radiation threats and emphasizes drift and diffusion mechanisms as dominant for charge collection.

Impact of stacking sequence and sulfurization duration on the growth of pyrargyrite Ag3SbS3 absorber layers

Pyrargyrite Ag3SbS3 is a promising absorber for thin-film solar cells. In this study, the impact of precursor stacking sequence and sulfurization duration on the growth and properties of Ag3SbS3 films was investigated. Initially, the Ag3SbS3 films produced by depositing Sb/Ag and Ag/Sb/Ag metal stacks and then sulfurizing at 300 °C crystallized in rhombohedral structure with (113) preferred orientation. The film produced from the Sb/Ag stack had a uniform and large-grained morphology up to a thickness of 1150 nm, and a direct bandgap of 1.65 eV; whereas the film prepared with the Ag/Sb/Ag stack exhibited nonuniform grain morphology with decreased film thickness, and increased bandgap energy (1.70 eV). Secondly, the Ag3SbS3 films produced from the Sb/Ag stack by increasing sulfurization duration from 10 to 90 min increases the crystallite size from 26 to 27 nm, enhances the grain compactness and uniformity, varies the bandgap in the range of 1.65–1.69 eV, and electrical resistivity. The solar cells fabricated using the films produced by sulfurizing the Sb/Ag stack for 30 min duration exhibited a maximum power conversion efficiency of 0.52% with an VOC of 471.6 mV, JSC of 2.0 mA/cm2, and FF of 55.0%. This study offers a pathway for the advancement of Ag3SbS3 thin-film solar cells.

Novel zinc and gallium nanocomposites for protecting against green laser radiation

In the present communication, binary (ZnO:Ga2O3- 1:1 (ZGO), ZnO:Ga2O3- 2:1 (GaZn))/ternary (EZG (Eu2O3: ZnO: Ga2O3 (1:1:1)), MZG (MgO: ZnO: Ga2O3 (1:1:1)) NCs are synthesized by Piperbetle leaves extract as a reducing agent followed by calcination at 600 °C for 3 h. The Bragg reflections confirms the formation of single phase cubic symmetry with Fd3m space group in ZGO NCs whereas reflections related individual metal oxides are observed in the GaZn, EZG and MZG NCs. The irregular size and shaped nanoparticles are observed in all the synthesized NCs. The tuned band gap was found to be in the range of 3.08 to 3.11 eV. The optical nonlinearity of the specimens was analyzed using the open aperture Z-scan technique. The material demonstrated reverse saturable absorption attributed to a two-photon absorption (2PA) process. The non linear absorption coefficient follows the order MZG > GaZn > ZGO > EZG. However, the optical limiting threshold follows the order ZGO > GaZn > MZG > EZG NCs with increase in energy band gap. These outcomes distinctly indicate the superior potential of GaZn binary NCs for optical limiting applications. This characteristic is advantageous for shielding sensors and the human eye, safeguarding them against the detrimental effects of intense green laser radiation.

Localized surface plasmon resonance properties of green synthesized Ag/rGO composite nanoparticles utilizing Amaranthus viridis extract for biosensor applications

The green synthesized Ag/rGO composite nanoparticles were successfully synthesized using the Hummers' method with Amaranthus viridis extract. The localized surface plasmon resonance (LSPR) behavior of the Ag/rGO was studied using the Kretschmann configuration consisting of prism/Au/Ag/rGO/air. The addition of the Ag/rGO composite to the prism system aims to determine the effect of rGO on the SPR angle. X-ray diffraction results showed that there were four diffraction peaks with the presence of lattice planes (111), (200), (220), and (311), proving the face-centered cubic crystal structure of silver. The characterization results showed that the size of Ag NPs was 23.1 nm, and that of Ag/rGO composite was 16.7 nm. The EDX results of the Ag/rGO composite showed the presence of several elements such as C, O, Ag, and N. Fourier transform infrared analysis showed the presence of O–H, C–H, CO, CC, and C–O–C functional groups confirming the formation of Ag/rGO. The UV–Vis spectra showed an absorption peak at 257 nm and 346–412 nm with an increase in band gap energy from 3.27 eV to 3.40 eV. Meanwhile, the LSPR measurements demonstrate a shift in the SPR angle due to the addition of rGO, in which the angle shifts from 0.33 ° to 0.96 °. In conclusion, the addition of rGO can optimize the plasmonic properties of Ag, so that it potentially could be applied to enhance the performance of SPR-based biosensor applications.

Fabrication of rare earth (Tb+3) and alkaline earth metal (Mg+2) Co-doped CdAl2O4@MXene composite: A unique approach to tune bandgap energy through quantum confinement effect for photocatalytic applications

The present work includes the use of effective strategy to improve the photocatalytic degradation activity of CdAl2O4 via dopant assimilation to enhance the bandgap energy (Eg) and to influence the light-sensitive activity of this spinel mixed oxide. In this study, CdAl2O4 (CA), Mg–CdAl2O4 (MCA), and Tb-doped Mg–CdAl2O4 (TMCA) were fabricated by the facile co-precipitation route and an ultra-sonication approach was used to prepare a composite of Tb-doped Mg–CdAl2O4 with MXene (TMCA@MXene). The obtained results from UV–Visible analysis deduce that there is an increase in Eg of MCA (2.51 eV) and TMCA (2.67 eV) as compared to pure CA (2.45 eV) which follows the quantum confinement effect accompanying the decrease in crystallite sizes of doped samples as compared to CA. The significant increase in bandgap energy of TMCA is due to the confinement of electrons in a small area and also due to the conversion of continuous energy levels into discrete energy levels. Moreover, UV–Visible spectroscopic analysis was made to evaluate the catalytic performance of fabricated photocatalysts against harmful organic pollutants. The photocatalytic study showed that the co-doped CdAl2O4 (TMCA) is a better photocatalyst than MCA and CA for the degradation of selected pollutants. Among all synthesized catalysts i.e. CA, MCA, TMCA, and TMCA@MXene, the highest photocatalytic activity was shown by MXene based nanocomposite. TMCA@MXene showed ∼86 % degradation of Rhodamine B (RhB) and 79.6 % degradation of Aspirin (acetylsalicylic acid). The outstanding photocatalytic efficacy of TMCA@MXene could be accredited to the quantum confinement effect produced by co-doping of alkaline earth metal (Mg+2) and rare earth metal (Tb+3) and large surface area, high conductivity, and excellent light harvesting capability provided by MXene sheets. Hence, TMCA@MXene could be an effective photocatalyst in future for the removal of toxic organic pollutants.

Development of pyrargyrite Ag3SbS3 absorber films through sulfurization of Ag–Sb stacks for thin-film photovoltaics

Pyrargyrite Ag3SbS3, which consists of naturally abundant and non-toxic elements, has attracted attention as a promising solar cell material. A two-stage fabrication method has been developed to synthesize Ag3SbS3 thin films through a solid-state reaction between Sb and Ag metallic layers by sulfurizing at 250–350 oC. The Ag3SbS3 film prepared at a sulfurization temperature of 250 °C contained Ag2S and Sb2S3 secondary phases with non-stoichiometric composition, distinct grain growth, a bandgap energy of 1.4 eV, and an electrical resistivity of 5.74 × 10−4 Ω cm. Through sulfurization of the stacks at 300 °C, the Ag2S and Sb2S3 secondary phases disappeared, and dominant Ag3SbS3 films were obtained with a minor AgSbS2 secondary phase. A compact and uniform near-stoichiometric Ag3SbS3 composition with large grains was obtained with an increased bandgap energy of 1.64 eV and electrical resistivity of 6.19 × 104 Ω cm. A further increase in the sulfurization temperature to 350 °C resulted in an increase in the crystallite and grain sizes of Ag3SbS3 with a decreased bandgap energy of 1.62 eV and electrical resistivity of 2.90 × 104 Ω cm. AgSbS2 remained as a minor secondary phase in this film. Thin-film solar cells prepared with the Ag3SbS3 absorber synthesized at a sulfurization temperature of 300 °C exhibited an open-circuit voltage of 473.85 mV, short-circuit current density of 1.47 mA/cm2, fill factor of 41.6 %, and an efficiency of 0.3 %. These results demonstrate that Ag3SbS3 is a potential candidate for thin-film solar cells.

Tuning magnetic and optical properties in Mn x Zn1−x PS3 single crystals by the alloying composition

The exploration of two-dimensional (2D) antiferromagnetic (AFM) materials has shown great promise and interest in tuning the magnetic and electronic properties as well as studying magneto-optical effects. The current work investigates the control of magneto-optical interactions in alloyed Mn x Zn1−x PS3 lamellar semiconductor single crystals, with the Mn/Zn ratio regulating the coupling strength. Magnetic susceptibility results show a retention of AFM order followed by a decrease in Néel temperatures down to ∼40% Mn concentration, below which a paramagnetic behavior is observed. Absorption measurements reveal an increase in bandgap energy with higher Zn(II) concentration, and the presence of Mn(II) d-d transition below the absorption edge. DFT + U approach qualitatively explained the origin and the position of the experimentally observed mid band-gap states in pure MnPS3, and corresponding peaks visible in the alloyed systems Mn x Zn1‒x PS3. Accordingly, emission at 1.3 eV in all alloyed compounds results from recombination from a 4T1g Mn(II) excited state to a hybrid p-d state at the valence band. Most significant, temperature-dependent photoluminescence (PL) intensity trends demonstrate strong magneto-optical coupling in compositions with x > 0.65. This study underscores the potential of tailored alloy compositions as a means to control magnetic and optical properties in 2D materials, paving the way for advances in spin-based technologies.

Microstructures and Dielectric Permittivity Properties of Fe3O4/Cdots Nanocomposites Synthesized by Green Route Utilizing Moringa Oleifera Extract and Watermelon Peel

Dielectric materials are beneficial for storing electrical energy due to their insulating and polarization properties in response to external electric fields. Magnetite has shown promise as a dielectric material among other materials due to its good magnetic properties, low toxicity, and biocompatibility. However, the weakness of Fe3O4, which has low stability and easy agglomeration, requires a modification on its surface by using Carbon dots (Cdots). This research investigates the dielectric properties of Fe3O4/Cdots obtained through the green synthesis method. Fe3O4 nanoparticles were synthesized using the co-precipitation method with Moringa oleifera leaf extract as a reducing and stabilizing agent. In contrast, Cdots were synthesized using the hydrothermal method with watermelon peel waste as a carbon source. The Fe3O4 composite nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), ultraviolet-visible spectroscopy (UV-Vis), and impedance spectroscopy. The XRD spectra revealed the existence of cubic inverse spinel and a reduction in crystal size as the concentration of Cdots increased, measuring 7.8 and 7.1 nm, respectively. SEM-EDX revealed that the sample is composed of Fe, O, and C elements and has a spherical shape with Cdots distributed on the surface of Fe3O4. The UV-Vis spectrum showed the absorption peak of Cdots at 282 nm. The Fe3O4 absorption peak is identical to the Fe3O4/Cdots absorption peak at 193 nm. The increase in band gap energy from 2.96 to 3.33 eV is related to the increase in Cdots concentration. In the 10-900 kHz frequency range, dielectric property tests demonstrated peak dielectric permittivity values (real and imaginary). A substantial decrease was observed between 10 kHz and 200 kHz, followed by a relatively stable pattern up to 900 kHz. The loss tangent value obtained has a tanδ value <0.5, which means that the addition of Cdots affects reducing the energy loss stored in Fe3O4.

Mössbauer, optical and structural properties of [formula omitted] ion in borate glass

Lanthanum-bearing iron lithium borate glass is a quaternary system for oxide glasses and was prepared via the melt-quenching method. The present article correlates the structure, optical, ligand field and Mössbauer data on iron lithium borate glass containing La3+. The density was measured, while the molar volume was calculated. Other physical parameters are well-described. With increasing the La2O3 content within the glass network, infrared spectra analysis reveals structural modifications such as the increase in BO4 units and the decline in both BO3 units and NBO bonds content. Furthermore, optical absorption spectra were measured. The absorption spectra disclose a plethora of electronic transitions that are related to Fe3+ in tetrahedral and octahedral sites, however, Fe2+ phase is not observed in optical spectra, but it has a clear signature in Mössbauer spectra. Besides, the glass absorption edges undergo a clear blue shift, reflecting an increased band gap energy (1.96–2.28 eV). The decline in NBO bonds justifies this trend. Bewitchingly, the values of crystal field splitting are increased, while the values of Racah parameters are decreased. This trend is justified by the decline in NBO bonds and increases electron localization around Fe cations. Mössbauer spectra confirm the existence of Fe3+ in tetrahedral and octahedral sites, while Fe2+ exists in only a tetrahedral state. With increasing La2O3 content, the isomer shift of Fe3+ in tetrahedral sites changes to be 0.312–0.329 mm/s, while the isomer shift of octahedral Fe3+ is 0.424–0.456 mm/s. These findings coincide with optical data. While the isomer shift of tetrahedral Fe2+ is 0.902–0.911 mm/s. Our results of structural, optical and ligand field associated with Mössbauer spectra open more vistas toward the utility of these samples in the optics realm.

Enhanced mechanical, optoelectronic and thermoelectric properties of binary CdO by under pressure: An ab initio study

AbstractThis manuscript presents, under the effect of different pressures (0–60 GPa), the structural, mechanical, electronic, optical, and thermoelectric properties of CdO with NaCl type structure by using the FP‐LAPW (Full Potential Linearized Augmented Plane Wave method) with Generalized Gradient Approximation (GGA) whose basis is the Density Functional Theory (DFT). PBE‐GGA was used to compute the structural, elastic, optical, electronic, and thermoelectric properties using Tran‐Blaha modified Becke‐Johnson (TB‐mBJ) potential. Different terms like formation energy, cohesive energy, and phonon were used for the computation of thermal stability and that is further confirmed by elastic properties. Bulk moduli and pressure‐dependent lattice constants were achieved by using the optimization method. From the results, we can say that the increase in pressure is directly related to the band gap and inversely related to the lattice constant. The mechanical properties show that CdO is highly ductile and mechanically stable and ductility is directly related to pressure. The minimum conduction band goes to a higher energy level when the pressure increases while the maximum valance band goes to a lower energy level ultimately the energy band gap increases. The optical parameter curve does not change by increasing pressure but the peaks start moving towards the higher energies slightly. Calculations reveals that band gap increases by increasing pressure which shows the blue shift in optical properties. The optical properties spectrum was studied, including reflectance, dielectric coefficient, and absorption coefficient. The optical constants show that the phase of CdO with NaCl structure was translucent. In the end, the thermoelectric feature in terms of thermal conductivity (K), power factor (PF), Seebeck coefficient (S), and electrical conductivity (σ) were studied by using the BoltzTrap code as a function of temperature. Thermoelectric and optical aspects revealed that pressure induces the possible use of CdO material for various TE and optical applications.

Structural, mechanical, and electronic properties of armchair and zigzag germanene nanotubes

This computational study investigated germanene nanotubes (GeNTs) using density functional theory (DFT) simulations to comprehend their structural, mechanical, and electronic properties. The analysis includes armchairs and zigzag GeNTs with diameters from ∼7 to ∼221 Å. It explores their relative stabilities, band structures, density of states, effective mass carriers, and piezoelectric and elastic constants. As a result, it is highlighted that smaller nanotube diameters exhibit higher instability than larger ones due to increased structural strain produced by higher curvature. An intriguing behavior is observed for diameters greater than 25 Å, with negative strain energies. The quantum confinement effect significantly influences the electronic properties of GeNTs, leading to increased band gap energy for smaller nanotubes. The band gap energy of armchair nanotubes has a decreasing behavior as the diameter increases. In contrast, for zigzag nanotubes, the band gap energy increases to ∼13 Å diameter and then decreases, reaching a band gap energy of 0.08 eV. Regarding mechanical properties, smaller GeNTs exhibit significantly lower elastic constants (C11). As the diameter increases, C11 values converge around 114 GPa for both armchair and zigzag GeNTs. Only the zigzag GeNTs exhibit piezoelectricity. Carrier effective masses decrease with increasing diameter, enhancing carrier mobility for larger-diameter GeNTs. The herein-reported findings provide valuable insights into the properties of germanene nanotubes, demonstrating their promising potential for nanoscale device applications and inspiring further research and synthesis of germanene-related systems.

Rapid thermal annealing of chalcogenide thin films for mid-infrared sensing and nonlinear photonics

The influence of rapid thermal annealing (RTA) onto chalcogenide Ge-Sb-Se thin films is reported, focusing on changes in optical properties. These materials possess broad mid-infrared transparency covering the most critical absorption bands for (bio)chemical sensing and high third-order optical nonlinearities for potential applications in nonlinear photonics. The parameters of the RTA process within this study include the annealing temperature, heating rate, and the two sample processing methods – one by placing the sample inside the graphite susceptor and the other by simply laying the sample onto the silicon wafer. Selenide thin films were found to undergo a shift of the absorption edge upon the RTA, resulting in an optical bandgap energy increase (bleaching effect) and a notable refractive index decrease. As a result of structural relaxation, such changes show a great potential of RTA in fine-tuning of optical performance of chalcogenide thin films and planar chalcogenide waveguides. The authors acknowledge the IBAIA (101092723) Horizon Europe project, the ANR AQUAE (ANR-21-CE04-0011-04) project of the French National Research Agency (ANR), and project No. 22-05179S of the Czech Science Foundation (GAČR) for financial support.