Direct Transition Research Articles

Morphological and Optical Characterization of Hydrothermally-Synthesized Two-Dimensional MoS2 Nanosheets

Transition metal dichalcogenides (TMDs) are extensively utilized in optoelectronics, sensors, and battery storage due to their versatile properties. Among the TMDs, Molybdenum disulfide (MoS2) nanosheets possess remarkable optical, electronic, and chemical properties. This study employed a cost-effective hydrothermal method to synthesize high-quality 2D MoS2 nanosheets. Different characterization techniques such as XRD, SEM, EDS, FTIR, Raman, UV–vis, and photoluminescence (PL) spectroscopy were utilized to evaluate the structural, morphological, chemical, and optical characteristics of the nanosheets. The XRD analysis revealed that the MoS2 nanosheets have a hexagonal crystal structure, with an average crystallite size of 27.76 nm. Furthermore, SEM images confirmed the formation of thin MoS2 nanosheets, with an estimated thickness ranging from 20–30 nm. The growth mechanism of the formation of MoS2 is discussed in detail. Different functional groups present in the material were analyzed using FTIR spectra. The difference in vibration modes analysed by Raman spectroscopy indicated the presence of layered nanosheets. The optical bandgap (2.20 eV) of the material was determined by analyzing its UV–vis spectroscopy data using the Tauc plot. PL analysis indicates a direct transition between the upper valence and lower conduction bands, suggesting that the nanosheets were synthesized with high quality. These findings have opened new possibilities for the use of MoS2 nanosheets in various applications such as optoelectronics and sensing devices.

An Analytical Model of Material Deformation During Friction Welding of Alloy 718

A new model of the material flow in rotary friction welding of tubes is proposed. The material flow proposed is based on 3D microcomputer tomography scans of welds performed with tungsten tracers. The tracers indicate a bifurcation of flow into two deformation paths. The material in Path 1 interacts with the weld interface and exhibits large azimuthal flow. The material in Path 2 transitions from axial to primarily radial flow with little or no azimuthal flow. The directional transition in this path is compared to orthogonal machining and equal channel angular pressing. The process to estimate the variables needed to calculate strain and strain rates using the equations from orthogonal machining and equal channel angular pressing is defined. Strain and strain rate in Path 2 are dependent upon feed rate and upset and decrease throughout the welding process. The strain rate is higher than previously reported for rotary friction welding as a result of the deformation model proposed.

A photodetector based on p-GaN/N-MoS2 QDs heterojunction with high responsivity

Molybdenum disulfide (MoS2) is the most thoroughly investigated for photodetection applications with direct bandgap transition in low-dimensional structures, high light–matter interaction, and good carrier mobility. In this work, MoS2 quantum dots was synthesis by liquid exfoliation and characterized using scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Fluorescence emission spectra (FES), UV–vis spectroscopy, and Photoluminescence (PL). The average size is ∼ 3.6 nm with strong absorption in the UV region and a band gap of 4.49 eV. Moreover, a novel structure of N- MoS2 QDs \\ p-GaN heterojunction photodetector was deposited by spray coating. The PL of N- MoS2 QDs \\ p-GaN emission spectra expanded from UV to visible light with high responsivity to the visible light of 7.06 mA W−1 and detectivity of 1.24 × 1010 jones.

Facile synthesis and physical properties of magnesium dititanate nanoparticles for antibacterial applications

AbstractThe modified aqueous co-precipitation approach was used to successfully manufacture magnesium dititanate (MgTi2O5) nanoparticles. Thermogravimetric analysis/differential scanning calorimetry (TG/DSC) was used to clearly reveal the thermal stability. Moreover, pseudobrookite structure, and surface morphology of MgTi2O5 nanoparticles were determined using X-ray diffraction (XRD), transmission electron microscope (TEM), and Fourier-transform infrared (FT-IR), and scanning electron microscope (SEM) techniques, respectively. The average size of the crystallites calculated by Scherer approach was compared to Williamson-Hall and TEM images results. The optical band gap of MgTi2O5 nanoparticles was found to be 3.81 eV for direct transitions. The effect of temperature on the conductivity of DC electricity was tested between the rages 303–503 K. The data on antibacterial activity showed that MgTi2O5 nanoparticles were antimicrobial and stopped the test microorganisms from growing. These findings revealed that MgTi2O5 will be extensively promising in environmental pollution control and antibacterial research.

Temperature and power-dependent photoluminescence spectroscopy in suspended WSe2 monolayer

This work, the photoluminescence (PL) of a suspended monolayer of WSe2 was investigated to avoid the substrate effect, and its evolution with temperature and excitation energy. Raman spectroscopy and PL demonstrated the monolayer characteristic of the sample due to the absence of the B1 2g peak along with a symmetric PL peak centered at approximately 1.65 eV. The PL spectrum exhibited two main emission bands attributed to a neutral exciton (X0) and a trion (X T ), where X0 showed a redshift with temperature variation from 10 K to 310 K, and the intensity ratio between the bands varied from 2.68 to 3.96 eV. The energy evolution of the bands as a function of temperature was analyzed using the modified Varshni equation, yielding an electron–phonon coupling constant with a value of 1.54 (2.11) for X0 (X T ). The intensity behavior was studied using the multi-level model, which provided activation energies of 58.0 meV for X0 and 94.6 meV for X T . The redshift of the mentioned bands is explained by the Urbach formalism, attributing this shift to an increase in phonon density in the material. Computational calculations demonstrated an increase in the material’s lattice parameter with rising temperature, resulting in an increase in the W–Se bond length and a decrease in the distance between Se atoms from different sublattices, causing the direct transition to decrease with temperature. In conclusion, this study showed that the observed evolution in the PL spectrum of the suspended WSe2 monolayer could be related to the increase of phonon density in the material which is important for the future applications of 2D materials in optoelectronics.

Effect of annealing temperature on the structural and optical properties of vacuum evaporated Cu13Se52Bi35 thin films

Thermal evaporation technique was used to prepare Cu13Se52Bi35 thin films. The asdeposited and annealed samples were investigated by using the X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical transmission and reflection. The XRD showed that the as-deposited film is crystalline in nature, and the crystalline size of samples increased with increasing the annealing temperature. SEM images showed that the morphology of the sample changes with the annealing temperature. The direct transition of the optical band gap (Eg) of Cu13Se52Bi35 films was observed and the values of Eg decreased with increasing the annealing temperature. Other optical parameters were also investigated.

Impact of annealing temperature on optical, morphological, and surface characteristics of PC/PBT blend exposed to alpha particles

The induced modifications of the optical and surface characteristics in the annealed α-irradiated polycarbonate/polybutylene terephthalate (PC/PBT) blend have been studied in the temperature annealing range from 100 to 200 °C for 15 min. Several techniques have been used to study the changes in chemical composition, optical-electronic transitions, photoemission, contact angle, surface roughness, and hardness of annealed samples comparable to the pristine one. The FTIR spectra exhibit aggregate changes in the band intensities after annealing, indicating the scission and cross-linking of the polymer chains. The intensity of the peaks reduced with α-irradiation but began to increase with increasing annealing temperature. The trend of the function groups found in the annealed samples with the rise in annealing temperature supports the crosslinking mechanism. The UV/Vis spectra revealed that the absorption edges of annealed samples were shifted toward lower photon energy (red shift), reflecting the decrease of optical energy gap from 4 eV to 3.6 eV for direct transition and from 3.8 eV to 3.5 eV for indirect transition at the highest temperature. Further, the number of carbon atoms and the number of carbon clusters increases with the increase in the annealing temperature. The refractive index of the samples decreases from 1.5479 for the pristine sample to 1.4008 for the sample at the highest temperature. Moreover, the dielectric parameters and optical conductivity of the annealed samples were modified after thermal annealing. The PL emission yields are decreased with the increase in annealing temperatures that indicating an enhancement in the non-radiative recombination rate relative to the radiative recombination, which may be due to the increasing in the surface density states. The α-irradiated samples showed a notable increase in contact angle and a notable decrease in surface tension values with increasing the annealing temperatures. The side chain induction, which readily bundles and recombines the annealed parts by raising temperatures, also causes the surface roughness of annealed samples to decrease from 1.099 μm for the pristine sample to 0.696 μm for the annealed sample at the highest temperature. It is noteworthy that there is an increase in the hardness from 10.49 ΜPa for the pristine sample to 41.98 ΜPa for the annealed sample at the highest temperature. This is related to the results of changes in the polymer chains due to the active sites or branching points created by scission, which can lead to cross-linking.

Computational and experimental approach for investigation of optical properties of single-crystal MnGa2Se4

In the presented work, we propose a systematic investigation of the electronic and optical properties of MnGa2Se4 by combining the spectroscopic ellipsometry carried out at room temperature in the spectral range of 1–4 eV and density functional theory (DFT) calculations. Ellipsometric measurements were collected at an incidence angle between 60° and 75° with a 5° step. The optical direct gap energies of MnGa2Se4 were estimated from the linear extrapolation of the absorption coefficients that were verified by band structure calculation. DFT calculation of the imaginary part ɛ shows that first critical point occurs at 2.46 eV and represents the direct optical transition at Γ point. The total magnetic moment of compound is 3.38 mB. The major contribution in total magnetic moment is due to 3 d state of Mn atoms.

Effect of high concentration of ZnO on the structural and optical properties of silicate glass system

An investigation was conducted to explore the optimum composition to fabricate a zinc silicate glass substrate for optoelectronic device applications. The composition was determined based on the empirical formula (ZnO)x-(SiO2)1-x, where x = 0.40, 0.50, 0.60 and 0.70 wt%, which was prepared by the conventional melt quenching technique. The focus is on characterizing the physical and structural aspects as well as the optical properties of the glass substrate. The physical properties of zinc silicate samples were assessed using the densitometer and their physical appearance. In addition, the materials' amorphous and glassy characteristics were verified using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) techniques. Finally, ultraviolet–visible (UV–Vis) spectroscopy and photoluminescence spectrometer were used to study the optical properties of samples. The density of the samples was observed to increase from 2805 to 3878 kg/m3 as the percentage of ZnO in the glass composition increased. X-ray diffraction analysis indicated the absence of sharp peaks in the samples containing up to 0.60 wt% of ZnO, suggesting the presence of an amorphous phase. Furthermore, the results of this study indicate that ZnO-SiO2 glass substrate samples favor direct forbidden transitions, with an increase in ZnO leading to higher absorption and consequently a lower band gap. The photoluminescence spectrum showed blue light emissions at 422 nm, associating with the variation of band gaps in the ZnO phase. Overall, from the interesting results achieved, this zinc silicate-based composite material at 0.60 wt% ZnO can be a potent candidate in optoelectronic applications, among other concentrations used in this study.

Role of triethanolamine complexing agent in chemical bath deposition of tin sulfide thin films: Microstructural and optical properties

This paper reports the experimental results studying the structure, optical and dielectric properties of tin monosulfide thin films. Tin monosulfide (SnS) films were deposited on glass substrate by chemical bath deposition to study the role of triethanolamine (TEA: complexing agent) concentration on the film properties. X-ray diffraction spectra reveal that the films exhibit mainly cubic phase which remain stable over the range of TEA concentration (3.0 M − 5.0 M). FTIR spectra indicate the S-Sn bond stretching in all films. Raman spectroscopy analysis shows the presence of minor trace of secondary SnS2 phase (along with main cubic π-SnS phase) in all films. SEM micrographs show cauliflower-like surface morphology of all films. Optical results reveal that the films possess high value of absorption coefficient (≥105 cm−1) in the visible region. Direct optical transition behavior is observed in all films. From Tauc plots, the calculated optical band gap (Eg) varies from 1.79 eV to 1.91 eV with the variation in TEA concentration. The dielectric constant, refractive index and an extinction coefficient are also calculated and observed to decrease with increasing TEA concentration. Experimental results suggest that an appropriate concentration of a complexing agent (TEA) can be chosen to obtain crystalline films without deterioration of crystalline structure and phase, not effecting Eg significantly.

Damping effect of longitudinal optical phonon—plasmon coupling on thermal radiation from surface micro-gratings on direct and indirect electronic transition type semiconductors

Thermal radiation properties of surface micro-Au-line and space structures on direct and indirect electronic transition-type semiconductors of n-type (n-) GaAs and GaP, respectively, are studied. The electron densities range from 0.62 to 1.0 × 1018 cm−3. The emission spectra of samples on n-GaAs wafers show peak energies significantly shifted from the longitudinal optical (LO) phonon energy due to the LO-phonon−plasmon coupling (LOPC) at 630 K, while partial decoupling is observed. The thermal emission from the sample on n-GaP is peaked at 395.9 cm−1, shifted only by 1.5 cm−1 from the LO-phonon energy, with a linewidth of 12.5 cm−1 at 630 K. The effect of LOPC on the emission from the sample on n-GaP is mostly suppressed because of the electron localization in the X-valley, suggesting an advantage of indirect transition-type semiconductors in LO-phonon resonant infrared emitters using the phonons generated via the electron energy relaxation.

Graphenyldiene: A new sp2-graphene-like nanosheet

The race and the discovery of novel two-dimensional (2D) carbon-based materials have been intensified because many are suitable for energy storage systems, thermoelectric devices, and catalysis applications. Therefore, this study introduces to the scientific community a novel 2D nanosheet named graphenyldiene (GPD), which is formed by arranging cyclobutadiene and bi-phenyl groups to create a monolayer with octadecagonal, hexagonal and tetragonal rings. The cohesive energy of GPD is only 1.37 and 0.65 eV/atom higher than graphene and biphenylene, respectively. Molecular dynamics simulations confirmed its structural and thermal stability. The GPD monolayer remains stable, with no significant deformations at around 1000 K, and the disintegration of the geometry occurs only at a temperature of 1500 K, which is characterized by the formation of an amorphous graphdiyne. The GPD electronic structure shows a direct band gap transition, 1.26 eV, at the Γ point. GPD is a promising alternative to electronic devices due to its carrier mobility of around 103.cm2/V.s. Also, the GPD satisfies the Born-Huang criterion for mechanical stability with elastic constants C11 = 157.62 N/m, C12 = 53.66 N/m and C66 = 51.98 N/m. The Bader's topological analysis indicated that all bonds have strong shared shell characteristics. Finally, the vibrational analysis identified 54 modes, where 21 are Raman active, with A1g and E2g modes dominating the spectrum at 1347, 1685 and 1697 cm−1.

Study on Microstructure and Properties of Additive-Manufactured TC4ELI+TC21 Titanium Alloy Gradient Composite Structures

TC4ELI+TC21 titanium gradient composite structures with direct transition (TD1) and cross transition (TD2) were prepared using laser deposition manufacturing technology. The microstructure of the gradient interface was observed, and the distribution of alloying elements was detected. The tensile properties of the two alloys at room temperature were tested, and the effects of different heat treatment regimens on the microstructure and mechanical properties were investigated. The results show that there is no obvious defect at the gradient interface of the two alloys. Compared with direct transition alloys, the alloying elements of TD2 alloys change less at the interface, the structure of the transition zone is more closely bound, and the elongation is higher. After heat treatment, the α phase in the alloy is coarsened, and the alloy elements at the interface are fully diffused, so that the gradient interface of the alloy is eliminated to a certain extent, the tensile strength of the alloy decreases, and elongation increases. The strength and plasticity of the alloy reached their best match at a solution temperature of 930 °C.

Determining the Structural Properties and Vibrational Modes of Annealed Lead Composite Material Deposit

Techniques for effectively harnessing lead (Pb) deposits for optimum utilization have attracted a lot of research interest. Results obtained from investigating the elemental composition, vibrational modes, and structural properties of a fired Pb composite deposit, which is purified using an electric kiln furnace and further annealed in palladium‐diffused hydrogen ambient, are reported in the present study. Both atomic force microscopy and scanning electron microscopy analysis on the deposit indicate that the Pb composite is composed of crystal‐like morphology. The vibrational modes obtained from the material are identical to the Raman spectrum reported for PbSO4. Also, data acquired from the energy‐dispersive X‐ray analysis of the annealed Pb composite material confirm the presence of zinc, carbon, silicon, sulfur, and oxygen in the material. At the same time, Pb appears to be the primary constituent with reference to its weight percentage composition compared to other elements. The findings from the present study may be vital for providing an improved understanding of the electronic and structural properties of the annealed Pb composite deposit while promoting the development of a feasible approach for the recovery and recycling of Pb for future related applications.

Diffusive and displacive phase transitions in Fe-Ga alloys

Phase transitions between structurally ordered phases in Fe–Ga alloys have been studied upon their heating to 850 °C and subsequent cooling to room temperature by neutron diffraction in real-time mode. The transitions between four types of phases have been analyzed: D03 → L12 (both cubic phases), L12 ↔ D019 (cubic – hexagonal), D019 ↔ A2 (hexagonal – cubic). It has been established that all phase transitions include stage of the formation of a disordered state and have a combined, diffusive-displacive nature. The diffusion stages are necessary for the disordering and ordering of the structure, the displacive stage provides a change in the type of the crystal lattice. It can be concluded that the formation of an intermediate disordered state followed by a transition to the final equilibrium state is less energy-consuming than the direct transition to the final state. During the observed transformations, no traces of predicted intermediate structurally ordered tetragonal phases were found. These results may provide new insight into the microscopic basis for the formation of enhanced magnetostriction in Fe–Ga alloys.

Using Recycled Tetrapak and Doped Titanyl/Vanadyl Phthalocyanine to Make Solid-State Devices.

In this work we studied the semiconductor behavior of titanyl phthalocyanine (TiOPc) and vanadyl phthalocyanine (VOPc), doped with anthraflavic acid and deposited on Tetrapak/graphite as flexible electrodes. The molecular structure was approached using the density functional theory and astonishingly, it was found that the structure and electronic behavior can change depending on the metal in the phthalocyanine. Experimentally, the Root Mean Square was found to be 124 and 151 nm for the VOPc-Anthraflavine and TiOPc-Anthraflavine films, respectively, and the maximum stress was 8.58 MPa for the film with VOPc. The TiOPc-Anthraflavine film presents the smallest fundamental gap of 1.81 eV and 1.98 eV for indirect and direct transitions, respectively. Finally, the solid-state devices were fabricated, and the electrical properties were examined. The tests showed that the current-voltage curves of the devices on Tetrapak and VOPc-Anthraflavine on a rigid substrate exhibit the same current saturation behavior at 10 mA, which is achieved for different voltage values. Since the current-voltage curves of the TiOPc-Anthraflavine on a rigid substrate presents a defined diode model behavior, it was approximated by nonlinear least squares, and it has been determined that the threshold voltage of the sample for the different lighting conditions is between 0.6 and 0.8 volts.

Effects of physicochemical characteristics on natural durability of eucalypts woods to wood-decaying fungi

This study aimed to relate the biological resistance of seven eucalypt woods to wood-decaying fungi with physicochemical characteristics of wood. Two 12-year-old trees per species were randomly sampled, removing disks at 0 (base), diameter to breast height - DBH, 25, 50, 75, and 100% of the commercial height to determine the wood specific gravity. One basal log of 2.20 m of each wooden species was obtained for chemical analysis and biological tests with brown and white rot fungi (Gleophyllum trabeum, Rhodonia placenta, and Trametes versicolor). For these tests, wood samples were taken in two positions in the radial direction of the trunk in the pith-bark direction (median heartwood and transition region; containing heartwood and sapwood), and the relation between wood natural resistance and physicochemical characteristics was established. Wood specific gravity ranged of 0.51 g cm−3 to 0.73 g cm−3, total lignin of 27.34–32.18%, and holocellulose of 53.39–66.18, not being influenced by pith-bark direction. The extractive and ash contents were affected by the pith-bark direction, in which, in general, the transition region exhibited the highest values contents. The extractive showed a negative relation (−0.67) regarding the loss of mass caused by the fungus Rhodonia placenta. For the holocellulose content, it showed positive relations (0.61; 0.54) to the degradation by Rhodonia placenta and Gleophyllum trabeum, respectively. Independently of the analyzed wood and tested fungus, the median heartwood region was more resistant to wood decay fungi than the transition region.

Molybdenum Based Manganese Oxides as Optoelectronic Nanomaterials: Synthesis, Structural & Optical Characterization

AbstractThis work reports the synthesis of molybdenum based manganese oxide nanomaterials named as (CH1‐CH5) via a facile hydrothermal approach. Nanomaterials were characterized through Powder XRD, SEM, BET, UV‐Vis, Photoluminescence, and FTIR analysis. Structural characterization revealed triclinic crystal structure of nanomaterials having particle sizes in the range of 23.08–52.7 nm with very low levels of microstrain levels (<0.05) and dislocation densities. Surface areas were found to be in the range of 42.37–52.32 m2/g with mesoporous structures and solid bar and cross surface morphology. Optical band gaps (Eg) calculated from absorption data was found to be in the range of 4.65–4.75 eV for direct transitions whereas 4.60–4.74 eV for indirect transitions. The Eg calculated from emission data was found to be in the range of 2.42–2.67 eV. Absorption edge broadening was investigated by urbach energy (EU) calculated to be in the range of 1.23–1.51 eV whereas fermi energy (Ef) were obtained as 4.66–4.72 eV. Refractive index (n) was calculated to be in the range of 0.13–0.21 whereas high values obtained for real and imaginary parts of dielectric constants (ϵ) indicating polarization relaxation in synthesized materials. The calculated structural and optical characteristics indicates that these materials can be potential candidates for optoelectronic and catalytic applications.

SYNTHESES, CHARACTERIZATION, CRYSTAL STRUCTURES AND ANTIMICROBIAL PROPERTIES OF A NEW ORGANIC−INORGANIC HYBRID [4FBzTPP]2[CuBr4

This article presents a study on the synthesis and character of a new organic-inorganic hybrid [4FBzTPP]2[CuBr4](1) ([4FBzTPP]+ is 4-fluorobenzyltriphenylphosphinium) by XRD, SEM, FT-IR and UV-Vis. The XRD analysis showed that the hybrid 1 belongs to the triclinic space group P21 with b = 8.8600(10) Å, c = 16.4867(17) Å, α = 16.639(2) °, β = 96.342(4) °, V = 2415.6(5) Å3, and Z = 2. The hybrid consists of two [4FBzTPP]+ cations and one [CuBr4]2– anion, and the [CuBr4]2– exhibits a twisted tetrahedral coordination geometry with the average bond length between Cu−Br is 2.393 Å. The 3D network structure of 1 is formed by electrostatic terms and other intermolecular interactions. The hybrid material undergoes a direct optical transition and has energy gap values of 1.66 eV and 2.18 eV, indicating its potential as a semiconductor material for optical research. The hybrid material undergoes a direct optical transition and has energy gap values of 1.66 eV and 2.18 eV, showing that the hybrid material is a potential semiconductor material for optical research. In addition, the compound exhibited good antibacterial activity against E. coli and S. aureus.

Structure, optical and visible-light photocatalytic performance of Mo1-xCoxS2 (0 ≤ x ≤ 0.1) nanoparticles synthesized by facile hydrothermal method for methylene blue dye degradation

Mo1-xCoxS2 (0 ≤ x ≤ 0.1) nanoparticles were successfully synthesized by using a hydrothermal route. The crystal structure of the prepared samples was investigated by Xray diffraction (XRD), emphasizing that all the prepared samples had a hexagonal structure of MoS2, and revealed an increment in the average particle size from 5 to 8 nm with increasing the cobalt ratio. The morphology was examined using scanning electron microscopy (SEM), and the recorded images of pure and cobalt-doped MoS2 show flowerlike architecture clusters. FT-IR spectroscopy was carried out to detect functional groups and stretching and bending vibrations of chemical bonds existing in all the prepared samples, confirming the presence of Mo-O and Co-O-Co characteristic peaks. The chemical composition of the synthesized samples was determined by energy dispersive Xray (EDX) analysis. The results confirmed the presence of Mo, S, and Co, which are consistent with the proposed formation of Mo1-xCoxS2 nanosystems. Optical properties were examined by UV–Visible spectrophotometry, reflecting allowed direct transitions with an energy band gap that decreases from 1.9 eV to 1.53 eV with increasing cobalt concentration. The photocatalytic degradation efficiency of methylene blue (MB) using pure and different ratios of cobalt-doped MoS2 as catalysts was tested under visible light radiation, and it was noticed that the MB degradation increased with increasing cobalt concentration.