A1g Vibrational Modes Research Articles

Effect of 10 MeV electron irradiation on structural and magnetic properties of Ti- and Al- substituted strontium hexaferrite SrFe11.3Ti0.4Al0.3O19

The irradiation stability of Ti- and Al-substituted SrFe11.3Ti0.4Al0.3O19 strontium hexaferrite to 10 MeV electron irradiation with the fluences of 1014 and 2·1017 cm−2 was investigated using various characterization techniques such as scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectrum microanalysis, atomic force microscopy, Raman spectroscopy, vibrating sample magnetometry and magnetic force microscopy. Notable changes in lattice vibrations, magnetic domain microstructure and magnetization behavior were obtained after the electron irradiation with the fluence of 2·1017 cm−2. Phonon hardening observed by Raman spectroscopy confirms the increasing disorder in crystalline structure and the presence of spin-phonon coupling in the samples after electron irradiation with the fluence 2·1017 cm−2. It was found that the strongest spin-phonon interactions correspond to A1g vibration modes at trigonal bipyramidal 2b, 2a octahedral, 4f1 tetrahedral sites and E1g mode at 4f2 octahedral site in electron-irradiated SrFe11.3Ti0.4Al0.3O19 hexaferrite, while the most radiation-resistant phonon mode is A1g vibration of the Fe–O bonds at the 4f2 octahedral site. No significant change was observed in magnetic saturation magnitude after electron irradiation. The increase in coercivity and significant decrease of magnitude of the dM/dH derivative of magnetization curves with increasing radiation fluence is attributed to the increase in uniaxial magnetic-crystalline anisotropy. It is found that the fractal dimension of hierarchical magnetic domain structure in SrFe11.3Ti0.4Al0.3O19 continuously decreases with increasing fluence of 10 MeV electron irradiation, which can be caused by the distortion in uniaxial magnetocrystalline anisotropy and irradiation-induced defects.

Enhancing photodetector performance of MoS2 thin films by nitrogen ion irradiation

In this work, MoS2 thin films were grown on a Si substrate using RF sputtering, and subsequently subjected to nitrogen ion irradiation with varying ion fluence. The Raman spectroscopy observed the oxygen doping into MoS2 lattice and induced shift in E2g and A1g vibration modes, along with a decrease in the interdefect distance (LD) after ion irradiation. The evolution of oxygen into MoS2 sample after ion irradiation was confirmed by XPS. The incorporation of oxygen in the MoS2 is due to the bond breaking of the surface layers of the material due to ion irradiation, which creates dangling bonds. These bonds in the MoS2 are more reactive with the oxygen and lead to the formation of MoOx species on the surface of the material. The Field Emission Scanning Electron Microscopy (FESEM) provides the morphological study of post-irradiation samples. As ion fluence increases, the optical bandgap decreases from 1.46 eV to 1.33 eV. Using current-voltage (I–V) characteristics, the electrical properties of the irradiated films were characterized, along with photodetector measurements. This combined analysis provided a comprehensive understanding of the film's electrical behaviour, shedding light on their post-irradiation performance. Our results demonstrate that due to oxygen doped into MoS2/Si thin film significantly affects the barrier height, ideality factor, and carrier concentration in I–V characteristics. Taking silicon-based and n-type MoS2 heterojunction photodetectors, its photoresponsivity can reach ∼14.7 mA/W at 7.19 × 1016 ion-cm−2 ion fluence. Our findings provide insights into the tunability of the electrical properties of MoS2/Si thin films through ion irradiation, which has implications for the development of novel electronic and optoelectronic devices based on MoS2/Si thin film.

Dynamic strain coupling driven by structural phase transition in mixed-dimensional 2H-MoS2/VO2 van der Waals heterointerfaces

Mixed-dimensional van der Waals (vdW) heterostructures, integrated two-dimensional (2D) atomic crystals with three-dimensional (3D) functional materials, offer a powerful means to manipulating physical properties and generating unprecedented functionalities. Understanding interfacial couplings at those hetero (homo)-interfaces is indispensable for exploring new optical and electronic devices. Herein, we investigated dynamically phase-transition-driven strain coupling across a vdW heterointerface through integrating 2D layered 2H-MoS2 nanoflakes onto 3D phase-change VO2 epitaxial thin films. The Raman peak positions of the in-plane and out-of-plane vibration modes E2g1 and A1g from the 2H-MoS2 nanoflakes show a phonon softening and reversible hysteresis loop as a function of temperature in this mixed-dimensional vdW 2H-MoS2/(1¯11)-VO2/(11¯02)-Al2O3 heterostructure, originating from the co-action of temperature-dependent anharmonicity in 2H-MoS2 and reversible structural phase transition (SPT)-induced in-plane tensile strain from the VO2 thin film. Accordingly, the integrated Raman scattering intensity of these two feature peaks of the 2H-MoS2 nanoflakes increased (decreased) as the temperature increased (decreased), exhibiting a hysteresis loop in the SPT and metal–insulator transition region of VO2. Additionally, the peak integrated intensity enhancement ratio of the E2g1 and A1g vibration modes was approximately 2.3 and 2.8, respectively. These results indicate that the dynamically SPT-driven in-plane tensile strain from the bottom VO2 layer interfacially couples with the adjacent 2H-MoS2 nanoflakes and results in a reduction in the electronic transition energy, leading to an enhancement in the Raman scattering intensity of 2H-MoS2. Our work holds promise for dynamic strain control of lattice dynamics and electron–phonon interaction of 2D materials for functional electronic and photoelectronic devices.

One-step sputtering of MoSSe metastable phase as thin film and predicted thermodynamic stability by computational methods

We present the fabrication of a MoS2−xSex thin film from a co-sputtering process using MoS2 and MoSe2 commercial targets with 99.9% purity. The sputtering of the MoS2 and MoSe2 was carried out using a straight and low-cost magnetron radio frequency sputtering recipe to achieve a MoS2−xSex phase with x = 1 and sharp interface formation as confirmed by Raman spectroscopy, time-of-flight secondary ion mass spectroscopy, and cross-sectional scanning electron microscopy. The sulfur and selenium atoms prefer to distribute randomly at the octahedral geometry of molybdenum inside the MoS2−xSex thin film, indicated by a blue shift in the A1g and E1g vibrational modes at 355 cm−1 and 255 cm−1, respectively. This work is complemented by computing the thermodynamic stability of a MoS2−xSex phase whereby density functional theory up to a maximum selenium concentration of 33.33 at.% in both a Janus-like and random distribution. Although the Janus-like and the random structures are in the same metastable state, the Janus-like structure is hindered by an energy barrier below selenium concentrations of 8 at.%. This research highlights the potential of transition metal dichalcogenides in mixed phases and the need for further exploration employing low-energy, large-scale methods to improve the materials’ fabrication and target latent applications of such structures.

Hydrophobic polymer nano hybrid ternary composite electrode for nanomolar tracing of Cd2+ ions

AbstractIn the present study, we reported the successful synthesis of a ternary nano hybrid polymer composite system obtained by solution casting. Composing carbon nanotubes (CNTs) and molybdenum disulfide (MoS2) in ethylene vinyl acetate (EVA) derived ECM ternary electrode. It demonstrated an excellent electrochemical sensor performance and a more efficient supercapacitor. Chemical structure of hybrid electrode Fourier transform Infrared Spectroscopy (FTIR) illustrated the CS and CN stretching with MoS2 and CNT new bands (at 1368 and 1032 cm−1). FE‐SEM and Atomic force microscopy (AFM) 3D topographic image identified the decreased rough morphology of the hybrid electrode. Whereas contact angle measurements revealed the enhanced wettability of electrode system. Microporous nature of the hybrid electrode was observed through SEM investigation. Transmission electron microscopy (TEM) revealed the nano hybrid entity in a hybrid electrode system. XRD and TEM investigation confirmed semicrystalline phase of the hybrid electrode system due to the presence of MoS2. D band, G bands, E12g and A1g vibrational modes in Raman spectroscopy revealed the occupied hybrid filler CNTs and MoS2. An electroactive site for the Cd2+ ion sensor was confirmed by the ECM/PGE hybrid electrode. It comply the desirable sensor qualities, such as excellent selectivity, reproducibility and repeatability with a high accuracy and lower detection limit of 15 nM. Additionally, the ECM/PGE electrode demonstrated a capacitive nature with an aerial capacitance of 73 μF/cm2 at an applied current density of 3 μA/cm2. Furthermore, it exhibited a power density of 44 mW/cm2 and an energy density of 148 μWh/cm2 over a wide potential range of 1 V.

Divergent interfacial thermal transport in MoS2/Si heterostructure over optical phonon modes

Thermal transport within nanostructures is highly confined by interfaces, and non-trivial physics can emerge at boundaries. Theoretical studies have shown that different phonon modes can exhibit varying thermal resistances at interfaces. Experimental observation of these variations, however, is lacking. Using the steady-state Raman thermometry, the E2g1 and A1g vibrational modes of MoS2 were utilized to characterize the thermal transport properties across the MoS2/Si interface. Our results revealed distinct temperature rises associated with different modes, indicating various mode contributions in the interfacial thermal conductance. Combining experimental and numerical simulations, the out-of-plane mode in MoS2 was found to contribute less to the interfacial transport, by 21.5%, attributed to the less variational mode mismatch of the in-plane phonon, compared to the in-plane mode. Furthermore, our results confirmed a 26.9% higher thermal conductivity from the out-of-plane mode than the in-plane one.

Abnormal Out-of-Plane Vibrational Raman Mode in Electrochemically Intercalated Multilayer MoS2.

Raman spectroscopy is a powerful technique to probe structural and doping behaviors of two-dimensional (2D) materials. In MoS2, the always coexisting in-plane (E2g1) and out-of-plane (A1g) vibrational modes are used as reliable fingerprints to distinguish the number of layers, strains, and doping levels. In this work, however, we report an abnormal Raman behavior, i.e., the absence of the A1g mode in cetyltrimethylammonium bromide (CTAB)-intercalated MoS2 superlattice. This unusual behavior is quite different from the softening of the A1g mode induced by surface engineering or electric-field gating. Interestingly, under a strong laser illumination, heating, or mechanical indentation, an A1g peak gradually appears, accompanied by the migration of intercalated CTA+ cations. The abnormal Raman behavior is mainly attributed to the constraint of the out-of-plane vibration due to intercalations and resulting severe electron doping. Our work renews the understanding of Raman spectra of 2D semiconducting materials and sheds light on developing next-generation devices with tunable structures.

Green synthesis of Cr2O3 nanoparticles by Cassia fistula, their electrochemical and antibacterial potential

Chromium oxide (Cr2O3) nanoparticles (NPs) find applications in modern science and technology due to their chemical stabilities, high-density corners and magnetic/electrical/catalytic properties. Current studies were performed to produce the (Cr2O3)aq and (Cr2O3)et NPs by treating chromium acetate with the aqueous and ethanolic extracts, respectively of Cassia fistula leaves; the same reaction was also performed in the presence of NaOH to yield the (Cr2O3)aqNa and (Cr2O3)etNa NPs, respectively. The synthesized NPs were characterized by XRD, FTIR, Raman spectroscopy,UV–Vis spectroscopy, SEM, TGA and DSC analysis and examined for their electrochemical properties. Their antibacterial potential was tested by biofilm inhibition and agar well diffusion methods. XRD studies revealed that Cr2O3 NPs possessed hexagonal crystal structures with the crystallite sizes of 14.85 to 23.90 nm; the lowest size (14.85 nm) was possessed by (Cr2O3)et. FTIR and Raman spectroscopies verified the +3-oxidation state of chromium and corresponding Cr-O and Cr=O vibrations. Raman spectroscopy determined A1g vibration modes (540.50–557.07 cm−1) with rhombohedral Cr2O3 structure, high degree of crystallinity and existence of Cr3+ ions in octahedral coordination whereas Eg vibration modes were displayed at 306.04–350.87 cm−1 and 602.47–613.81 cm−1. UV–Visible spectroscopy has shown band gaps in the range of 4.06–4.40 eV. The SEM images demonstrated the spherical morphology with a high degree of agglomeration between fine particles. The synthesized NPs exhibited good thermal stabilities up to 600 °C. The CV curves displayed the oxidation–reduction peaks and reversible behavior whereas GCD curve indicated the possible energy storage applications of NPs. (Cr2O3)aqNa NPs showed the highest specific capacitance (234.35 mAhg−1) at 1 mA current density. The biofilm inhibitions of the investigated NPs were comparable to those of the standard antibacterial drug (ciprofloxacin); the activity of (Cr2O3)etNa was found even better than that of ciprofloxacin. The NPs were more active against Escherichia coli (Gram-negative) as compared to those against Staphylococcus aureus (Gram-positive).

Photocatalytic and Antimicrobial Performance Evaluation of Reusable MoS2 Nanoflowers under Visible Light

2D semiconductor material, Molybdenum Disulfide (MoS2), with unique properties similar to that of graphene, is considered as a potential candidate for photocatalytic and antimicrobial applications. In the current work, MoS2 was prepared by a simple hydrothermal method using sodium molybdate and thiourea as precursors. The calculated band gap values of MoS2 grown at 200 °C and 180 °C were 2.1 eV and 1.98 eV, respectively. Flower like morphology was observed from FESEM analysis. Multi layered structure of MoS2 was confirmed from the difference the peak value obtained for A1g and E1 2g vibrational modes observed from Raman spectra. The reusability of the synthesized MoS2 was analyzed against MB dye degradation. The pristine MoS2 removed ∼98% of the dye molecules from the water under the minimum wattage (20 W) of visible light in 180 min. The catalyst retained good stability even after the third degradation, confirming the reusability of MoS2. The disk diffusion method was used to evaluate the antimicrobial activity of the grown MoS2 nanostructures. The gram-positive and gram-negative bacteria used in present study were Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli and Bacillus serius. Investigation of the antibacterial activity of MoS2 against these four different pathogens was carried out in detail and the resistance function was measured.

Self-powered photodetectors based on InxMo1-xS2 crystals

Transition metal dichalcogenides (TMDCs) have attracted global interest in recent years due to their optoelectronic characteristics and tunable bandgap energies. Due to their potential use in photovoltaic devices, photodetectors, and field effect transistor (FET) recording systems, single crystalline semiconductors of TMDC family have attracted a lot of attention. In the present article, the direct vapour transport technique was used to synthesis the InxMo1-xS2 (x = 0, 0.05, and 0.1) crystals. The purity and distribution of all the elements were investigated by EDAX mapping. The power X-ray diffraction technique examine the grown crystals have hexagonal lattice structure. The structure of all the crystals was investigated by scanning electron microscopy (SEM). The in-plane E2g and outer-plane A1g vibration modes were studied through Raman spectra. Photodetectors based on InxMo1-xS2(x = 0, 0.05, and 0.1) crystals show the self-powered photoresponse under white light source at 100 mW/cm2power intensity.

Enhanced thermoelectric properties of 2H–MoS2 thin film by tuning post sulfurization temperature

Two-dimensional transition metal dichalcogenide semiconductors (TMDCs) like MoS2 are becoming more popular as thermoelectric materials because they are abundant, nontoxic, and have good performance. In the study, the MoS2 thin films have prepared by the sputtering and post-sulfurization process at various temperatures 450 °C, 550 °C, 650 °C, and 750 °C. The XRD data exhibits the formation of the 2H phase of MoS2 thin film with (002), (004), and (006) planes. The Raman spectroscopy has confirmed the 2H–MoS2 thin films with 2LA (M), A1g, E2g, and Eg vibrational modes. The SEM images have shown the thin MoS2 flakes. The Seebeck and electrical conductivity data indicated an enhancement in Seebeck coefficient and electrical conductivity from 20 to 31 μV/°C and 26–53 S/m, respectively, as the post sulfurization temperature increased from 450 °C to 750 °C. The enhancement of the Seebeck coefficient and electrical conductivity have been linked to the perfection of the 2H phase of MoS2 film. The improved crystal structure has increased carrier mobility, leading to a high power factor of the 5.09 μWm−1C−2.

Controlling transition metal atomic ordering in two-dimensional Mo1−x W x S2 alloys

The unique optical and electronic properties of two-dimensional transition metal dichalcogenides (2D TMDs) make them promising materials for applications in (opto-)electronics, catalysis and more. Specifically, alloys of 2D TMDs have broad potential applications owing to their composition-controlled properties. Several important challenges remain regarding controllable and scalable fabrication of these alloys, such as achieving control over their atomic ordering (i.e. clustering or random mixing of the transition metal atoms within the 2D layers). In this work, atomic layer deposition is used to synthesize the TMD alloy Mo1−x W x S2 with excellent composition control along the complete composition range 0 ⩽ x ⩽ 1. Importantly, this composition control allows us to control the atomic ordering of the alloy from well-mixed to clustered while keeping the alloy composition fixed, as is confirmed directly through atomic-resolution high-angle annular dark-field scanning transmission electron micrography imaging. The control over atomic ordering leads to tuning of the bandgap, as is demonstrated using optical transmission spectroscopy. The relation between this tuning of the electronic structure and the atomic ordering of the alloy was further confirmed through ab-initio calculations. Furthermore, as the atomic ordering modulates from clustered to well-mixed, the typical MoS2 and WS2 A1g vibrational modes converge. Our results demonstrate that atomic ordering is an important parameter that can be tuned experimentally to finely tune the fundamental properties of 2D TMD alloys for specific applications.

Synthesis of bismuth oxychloride nanoparticles via co-precipitation method: Evaluation of photocatalytic activity

Bismuth oxychloride (BiOCl) nanoparticles were synthesized via chemical co-precipitation process at room temperature. The structural, optical and morphological features of synthesized BiOCl nanoparticles were characterized by using different analytical techniques such as XRD, UV-DRS, Raman and SEM. The XRD pattern of BiOCl NPs shows tetragonal phase having on average crystalline size was found to be 21 nm. The UV-DRS spectrum of BiOCl NPs exhibiting the energy band gap of 3.5 eV. The Raman spectroscopy was used to identify the characteristic A1g and Eg vibrational normal modes of BiOCl NPs. SEM micrograph of BiOCl NPs reveals the agglomeration of the particles with effect of reducing agent. Furthermore, the photocatalytic degradation of methylene blue dye using BiOCl NPs under UV light is investigated and found to be effective. The synthesis of BiOCl nanoparticles is very simple, inexpensive, and environmentally friendly and it’s exhibiting the possibility of finding novel properties.

Molybdenum(IV) dithiocarboxylates as single-source precursors for AACVD of MoS2 thin films.

Tetrakis(dithiocarboxylato)molybdenum(IV) complexes of the type Mo(S2CR)4 (R = Me, Et, iPr, Ph) were synthesized, characterized, and prescreened as precursors for aerosol assisted chemical vapor deposition (AACVD) of MoS2 thin films. The thermal behavior of the complexes as determined by TGA and GC-MS was appropriate for AACVD, although the complexes were not sufficiently volatile for conventional CVD bubbler systems. Thin films of MoS2 were grown by AACVD at 500 °C from solutions of Mo(S2CMe)4 in toluene. The films were characterized by GIXRD diffraction patterns which correspond to a 2H-MoS2 structure in the deposited film. Mo-S bonding in 2H-MoS2 was further confirmed by XPS and EDS. The film morphology, vertically oriented structure, and thickness (2.54 μm) were evaluated by FE-SEM. The Raman E12g and A1g vibrational modes of crystalline 2H-MoS2 were observed. These results demonstrate the use of dithiocarboxylato ligands for the chemical vapor deposition of metal sulfides.

Feasibility of ZrSiO4 as reference signature in naturally-occurring radioactive elements for the application of radioactivity monitoring

Radioactivity monitoring post-cold war has become more complex due to the nuclear fallout and the surge in use of radioactive materials. This requires novel methods to detect, trace and distinguish natural and anthropogenic radioactive sources in the environment. We explored the feasibility of using ZrSiO4 (Zircon), as a reference signature for radioactivity monitoring due to the unique phenomenon of metamictization. We investigated the variations in microstructural properties of Zircon samples collected from a proposed Uranium site to identify these signatures using analytical techniques such as Gamma-ray Spectroscopy, XRD and Raman spectrum analysis. Besides elevated levels of radioactivity, the samples exhibited distinct properties such as increased lattice parameters observed from the XRD analysis and dramatic broadening of A1g (439 cm−1) and B1g (1008 cm−1) vibrational modes in the Raman spectrum. Structural parameters were further analyzed by modeling the crystal from experimentally observed lattice parameters. Ab-initio calculations were then performed on the modeled structure providing more insight into the microstructural variations. Samples collected from proposed Uranium mines indicate an increase of 1.226% and 0.9389% in Si–O and Zr–O bond lengths of the Zircon crystal signifying the ongoing process of metamictization from radiation damage. By correlating radioactivity levels with the lattice parameters variations of the collected samples, the study establishes a linear relation between the degree of damage to a mineral's crystal structure and the amount of radioactivity. We propose to use the variations in damage found in a mineral's structure as a nuclear forensic signature for advanced assessment of accumulated radioactivity in a particular geographical location.

Raman spectroscopy of the Al-doping induced structural phase transition in LaCrO3 perovskite

It has been well established that LaCrO3 exhibits an orthorhombic structure (Pnma) and undergoes a structural phase transition to rhombohedral (R-3c) when submitted to physical or chemical pressure. The doping-induced structural phase transition in the LaCr1-xAlxO3 solid solution is carefully investigated by Raman Spectroscopy in this communication. Spectral band analysis of the experimental results strongly indicates that solid solution with low Al-content (x = 0.0 and 0.05) displays an orthorhombic structure characterized by the Ag, B1g, B2g, and B3g vibrational modes, whereas the solid solution with high Al-content (x = 0.5 and 0.95) displays a rhombohedral structure with A1g and Eg vibrational modes. Particularly, the decrease of intensity and the displacement of some vibrational modes with increasing of Al-content indicates that the structural phase transition from orthorhombic to rhombohedral in the LaCr1-xAlxO3 solid solution is accompanied by a freezing of the (Cr/Al)O6 octahedron vibrations. It is therefore postulated that the Al-doping in LaCrO3 above a threshold leads to instability and structural distortions that induce a structural phase transition.

Synthesis, characterization of DMS Pb0.8Fe0.2I2 and influence study to EPR structure and properties of magneto-optical glass

Transition metal ions doped PbI2 is strongly anisotropic material having high molecular weight, high polarizability and strong spin-orbit coupling. Dilute magnetic semiconductor doped glasses are attractive to magneto-optical and nonlinear applications due to the sp-d exchange interaction between semiconductor carriers and magnetic ions in glass matrix. This study reports the synthesis, characterization of Pb1−xFexI2 nano-plate and its influence to structure and properties of sol-gel borosilicate glass. 50 nm Pb0.8Fe0.2I2 hexagonal nano-plates presented characteristic Raman Eg, A1g and A2u vibrational modes, the reduced optical band gap and a complex magnetization. Sol-gel fabricated transparency borosilicate glasses containing 5%, 10% and 15% Pb0.8Fe0.2I2 presented progressively changed color and reduced band gap because of Pb2+, Fe2+ and Fe3+ ions absorption in the ultraviolet and visible range. Third nonlinearity performance was double enhanced due to the high polarized doping ions. All studied glasses had diamagnetic properties and the magnetization increased with doping amount. XPS and EPR measurement revealed the co-existence of Fe ions and the change of environment of matrix. Verdet constant glasses was significantly improved. 15% Pb0.8Fe0.2I2 doped sol-gel SBZPF15 glass showed promising optical linear and nonlinear, magnetic and Faraday rotation performance.

Layered WS2 thin films prepared by sulfurization of sputtered W films

We present structural, optical and electrical investigations of layered WS2 films prepared on tungsten. A two-step technique has been used to synthesize layered WS2 films using sulfurization of W films sputtered with thinner (1 and 2 nm) and thicker (14 and 28 nm) thicknesses at 800 °C. XRD analysis revealed that the examined films are polycrystalline with texture and have a 2H-WS2 hexagonal microstructure. Using Raman spectroscopy with the 532 nm laser excitation, the presence of E12g and A1g vibration modes was observed and the layered nature of WS2 was confirmed. FE SEM observations showed two different surface morphologies. The samples grown on thinner W films were not compact over the surface and agglomeration of nanosize grains in combination of triangles and flakes was visible. In another group the surface was lamellar and contained plenty of nanorods embedded vertically and/or inclined at different angles to the surface. Layered WS2 films exhibited a direct band gap in the range of 2.1–2.5 eV and they were n-type semiconductors with the sheet resistance in the order of several MΩ at room temperature.

Temperature effect on structural, morphological and optical properties of 2D-MoS2 layers: An experimental and theoretical study

In this work, we present experimental and theoretical studies of the effect of temperature on the structural, morphological and optical performance of 2D-MoS2 nanosheets. We have used X-ray diffraction, Raman, photoluminescence spectroscopies and electron transmission microscopy to study the structural, morphologic and optical properties of MoS2 synthesized by hydrothermal method. The results indicate that, the structuraland optical properties are significantly temperature-dependent. The number of MoS2-layers has been estimated from the Raman frequencies of the E12g and A1g vibration modes. For the theoretical study we have used k.p and density matrix to calculate the band structure and optical gain for the 2D-MoS2. It is found that the nanosheets exhibit a significant enhancement in the TE-polarized optical gain at room temperature. These results show that 2D-MoS2 layered is promoters for laser device.

Mechanism of Cu dopant in transition metal oxide Mn1.56Co(0.96-x)Ni0.48CuxO4+δ (0 ≤ x ≤ 0.2) thin films

To identify the substitution of Cu element for cations in transition metal oxide AB2O4 structure, we propose to investigate the structural, optical and magnetic properties of Cu-doped Mn1.56Co(0.96-x)Ni0.48CuxO4+δ films with 0 ≤ x ≤ 0.2. The X-ray diffraction of Mn1.56Co(0.96-x)Ni0.48CuxO4+δ films indicates good crystallization and cubic spinel structure. Raman spectra show two peaks of F2g and A1g vibration modes, and the peak position changes with Cu dopant. The transition temperatures TP1, TP2 shift towards lower temperature by Cu doping, and the saturation magnetization MS decreases monotonously. The results show that the substitution of Cu ions does not vary the crystal structure but changes the ratio of Mn3+/Mn4+. Our proposed way overcomes the difficulties to directly observe the atoms of Mn, Co, Ni, and Cu with closed sizes in microstructure, and it is instructive to further understand the conduction mechanism of doped manganese cobalt nickel oxides in theory.