Raman Modes Research Articles

Study on the structural and electrical transport properties of YMn0.9Cr0.1O3

In this work, the structural, micro-structural, dielectric, AC conductivity of rare earth manganite YMn0.9Cr0.1O3 have been reported. The compound is synthesized by sol–gel auto-combustion route. The X-ray diffraction study confirms the formation of hexagonal structure along with the onset of few orthorhombic peaks. The morphological study using scanning electron micrographs shows homogeneous distribution of particles with average particle size of 185 nm. Raman spectroscopy shows the A1Raman scattering line at ∼ 676 cm−1to be much stronger than the other Raman modes. The nature of frequency dependence of dielectric constant has been described by Maxwell-Wagner model. The frequency dependence of the conductivity at different temperatures as described by Jonscher’s plot suggests that the conduction phenomenon in the material obeys the correlated barrier hopping (CBH) model. The activation energy of the intrinsic charge carriers has been calculated by using the Arrhenius equation at different frequencies.

Enhanced upconversion luminescence and optical temperature sensing performance in Er3+ doped BaBi2Nb2O9 ferroelectric ceramic

A series of BaBi 2- x Nb 2 Er x O 9 ceramic compositions with different Er 3+ concentration ( x = 0.0–8 mol %) is synthesized by a conventional solid-state reaction method. The upconversion (UC) light emission under 980 nm excitation with different pump powers and luminescence-based temperature sensing ability of BaBi 2- x Nb 2 Er x O 9 composition have been examined. The formation of a Bi-layered perovskite phase of BaBi 2 Nb 2 O 9 is confirmed having an orthorhombic geometry and Fmmm space group. Shifts in the Raman modes indicate reduced interaction of Bi 3+ ions with NbO 6 octahedron leading to relaxation of structural distortion with increasing Er 3+ content. The maximum value for remnant polarization and coercive field of doped BaBi 2- x Nb 2 Er x O 9 ceramic for ( x = 0.08) Erbium concentration comes out to be 2.9524 μC/cm 2 and 49.8980 kV/cm. For an optimum content of x = 0.04, two strong UC green emission bands were observed at 549 nm via 4 S 3/2 → 4 I 15/2 transition and 527 nm via 2 H 11/2 → 4 I 15/2 transitions, and a weak red emission appears at 657 nm attributed to the 4 F 9/2 → 4 I 15/2 transition. Pump power dependence suggests that UC emission is a two-photon mechanism for red and green emission bands. Temperature sensing evaluated by the change in the fluorescence intensity ratio (I 527 /I 549 ) indicates the highest sensitivity to be 0.00996 K −1 at 483 K for an optimum concentration of Er 3+ at x = 0.04 in BaBi 2- x Nb 2 Er x O 9 composition and is useful for non-contact optical thermometry.

Improving the microwave dielectric properties of Ga2[LiGa3]O8 inverse spinel by enhancing B-site ordering degree

A series of inverse spinel ceramics, Ga 2 [Li 1+ x Ga 3 ]O 8+δ (0.05 = x ≤ 0.125), were synthesized by the conventional solid-phase reaction. The addition of Li ( x ≤ 0.1) increased the order degree of octahedra cations and caused an expansion in cell volume, and the maximum solution was located at 0.1–0.125. The dielectric constant of Ga 2 [Li 1+ x Ga 3 ]O 8+δ ceramics increased with the ionic polarizability of primitive unit cell, and the optimum microwave dielectric performances were obtained at x = 0.1 sample sintered at 1260 °C with ε r = 10.78 ± 0.1, Q × f = 171,171 ± 500 GHz, and τ f = −56.47 ± 1.0 ppm/°C. The τ f showed an opposite variation trend to that of the Ga1 bond valence and octahedron distortion. The Q × f was determined by the packing fraction and FWHM of 424 cm −1 Raman mode. In addition, the intrinsic dielectric properties of Ga 2 [Li 1+ x Ga 3 ]O 8+δ ceramics were evaluated by infrared reflectivity spectra. The results show that Ga 2 [Li 1+ x Ga 3 ]O 8+δ ceramic is a promising substrate material.

Thickness dependent optical properties of sputtered Bi2Se3 films on mica

The Bi2Se3 thin films of different thicknesses (100, 200 and 400 nm) were deposited on mica substrates by magnetron sputtering technique and their structural and optical properties have been studied. The X-ray diffraction analysis revealed the crystalline nature of Bi2Se3 films with preferred orientation along the c-axis. The presence of three well-pronounced Raman modes i.e. A11g, E2g, and A21g confirms the formation of pure Bi2Se3 compound on mica substrates. The field emission scanning electron microscopy and elemental analysis measurements showed the growth of Bi2Se3 film with varying grain sizes with thickness while maintaining the stoichiometric ratio of 2:3 of Bi and Se. Surface roughness was analysed using atomic force microscopy and it revealed that the roughness increases from 2.16 to 28.3 nm when the film thickness increases from 100 to 400 nm. The optical bandgap analysed with broadband absorption spectroscopy showed a decrease in bandgap from 1.3 to 1.08 eV with increasing film thickness. The sputtered Bi2Se3 films on mica possess good crystalline and structural quality with tunable bandgap that can be used for futuristic optoelectronic applications.

1.7 μm laser with a low frequency shifted Raman mode cascade connection

1.7 μm laser with a low frequency shifted Raman mode cascade connection

Structural and optical properties of Ce1-xGdxO2 Nanoparticles

We report on systematic study of structural and optical properties of Ce1-xGdxO2 (x = 0 to 0.2) nanoparticles (NPs). Solution combustion method was used for the synthesis of NPs. Rietveld analysis of X-ray diffraction (XRD) data confirms single-phase cubic fluorite structure of all considered compositions. Lattice expansion also observed as Gd concentration is increased. Scanning electron microscopy (SEM) confirmed the porous and spongy nature of the NPs. Raman spectroscopy shows the presence of F2g Raman mode, confirming the fluorite cubic structure of the considered NPs. The peak shifting and asymmetric broadening behaviour of Raman peaks demonstrate the phonon confinement effect. Band-edge absorption peak show the blue shifts along with direct bandgap and change in the bandgap, observed as increases the Gd content.

Piezochromic Luminescence of Dicoronylene: Key for Revealing Hidden Raman Modes at High Pressure

Piezochromic Luminescence of Dicoronylene: Key for Revealing Hidden Raman Modes at High Pressure

Stability of rhombohedral structure and improved dielectric and ferroelectric properties of Ba, Na, Ti doped BiFeO3 solid solutions

A study of the (1-x)BiFeO 3 -(x)Ba 1/2 Na 1/2 TiO 2.75 (BFO-BNT) solid solutions obtained using the solid state reaction method, for different molar relative concentration of Ba 1/2 Na 1/2 TiO 2.75 in the 0.0 ≤ x ≤ 0.12 composition range, is presented. The crystal structure and the dielectric and ferroelectric properties are studied in detail. Results of the Rietveld refinement of the X-ray diffraction data demonstrate that the system is single phase with R3c symmetry up to x = 0.09 while for x = 0.12, a small quantity of a secondary phase with P4mm symmetry appears. Scanning electron microscopy demonstrates that BNT presence promotes grain growth resulting in larger grains. Raman spectroscopy shows that, with increasing x, some of the A and E Raman modes slightly reduce their intensity while shifting in frequency, evincing the structural changes caused by the Ba, Na, and Ti incorporation on the BFO lattice. The X-ray photoelectron spectroscopy study confirms the successful substitution and gradual structural distortion in the samples. The improvement in dielectric properties with increasing BNT concentration can be attributed to stable dipole moment formation. Compared with pure BFO ceramics, doped BFO samples exhibit remarkably enhanced ferroelectric properties.

Superparamagnetism of potassium-doped tris(diphenacyl) iron

Synthesis and exploration of intriguing physical properties of alkali-metal-doped aromatic hydrocarbons have been the important research topics in the fields of physics, chemistry and materials science. In this work, a powder sample of potassium-doped tris(diphenacyl) iron molecular crystal is prepared by the high-vacuum annealing method. The X-ray diffraction results show that the crystal structure of the synthesized sample is different from that of pristine tris(diphenacyl)iron. The direct current (DC) magnetic susceptibilitiy shows a pronounced hump structure near 8.0 K, which is distinct from the paramagnetism of pristine material in the whole temperature range of 1.8–300 K. The alternating current (AC) magnetic susceptibility shows that the hump has a significant frequency dependence, which can safely rule out the possibility of antiferromagnetism. The combination of the Vogel-Fulcher law, the Néel-Brown model and the critical slowing down model reveals that the hump originates from superparamagnetism with a blocking temperature (<i>T</i><sub>B</sub>) of about 8.0 K. According to the results of Raman spectroscopy, it can be confirmed that the 4s electrons of potassium in the doped material are transferred to the benzene ring of tris(diphenacyl)iron, causing the characteristic Raman modes to be red-shifted and the local magnetic moment to form. Our work is of great significance in exploring alkali-metal-doped aromatic hydrocarbons, and provides a new route for searching organic magnetic materials.

Ultrasensitive and label-free detection of prognostic and diagnostic biomarkers of sepsis on a AgNP-laden black phosphorous-based SERS platform

Rapid and early detection of sepsis biomarkers using AgNP@BP SERS substrate and identification of signature Raman modes of sepsis biomarkers (IL-3 and PCT).

Isotopomeric Elucidation of the Mechanism of Temperature Sensitivity in 59Co NMR Molecular Thermometers.

Understanding the mechanisms governing temperature-dependent magnetic resonance properties is essential for enabling thermometry via magnetic resonance imaging. Herein we harness a new molecular design strategy for thermometry─that of effective mass engineering via deuteration in the first coordination shell─to reveal the mechanistic origin of 59Co chemical shift thermometry. Exposure of [Co(en)3]3+ (1; en = ethylenediamine) and [Co(diNOsar)]3+ (2; diNOsar = dinitrosarcophagine) to mixtures of H2O and D2O produces distributions of [Co(en)3]3+-dn (n = 0-12) and [Co(diNOsar)]3+-dn (n = 0-6) isotopomers all resolvable by 59Co NMR. Variable-temperature 59Co NMR analyses reveal a temperature dependence of the 59Co chemical shift, Δδ/ΔT, on deuteration of the N-donor atoms. For 1, deuteration amplifies Δδ/ΔT by 0.07 ppm/°C. Increasing degrees of deuteration yield an opposing influence on 2, diminishing Δδ/ΔT by -0.07 ppm/°C. Solution-phase Raman spectroscopy in the low-frequency 200-600 cm-1 regime reveals a red shift of Raman-active Co-N6 vibrational modes by deuteration. Analysis of the normal vibrational modes shows that Raman modes produce the largest variation in 59Co δ. Finally, partition function analysis of the Raman-active modes shows that increased populations of Raman modes predict greater Δδ/ΔT, representing new experimental insight into the thermometry mechanism.

Magnetic polaronic and bipolaronic excitons in Mn(II) doped (TDMP)PbBr4 and their high emission

If we introduce transition metal ions with spins into an organic-inorganic halide perovskite compounds, interesting spin dependent optical properties may be seen in this system. This paper reports an organic-inorganic hybrid manganese ion doped lead halide crystal incorporated by TDMP (trans-2,5-dimethylpiperazinium), it gives not only the STE1 (polaronic exciton), usually brought up by the enhanced electron-phonon coupling in the amine incorporated compound, but also give a novel bipolaronic exciton (STE2) for the paired charge state formation due to the incorporation of bi-amine cationic molecules, a excitation by the polaronic molecule due to enhanced electron-phonon coupling and neighboring correlation out of the Mn ion ferromagnetic spin coupling in the lattice at slightly high doping. Such magnetic bipolaron state could often be accompanied by several multiphonon Raman modes and ferromagnetism. It is even interesting that this state can give super-high red emission with PLQY at ~92.5% at room temperature. Moreover, the emission color and intensity could also be modulated by the Mn doping concentration, temperature, and laser excitation power. The low doping products can give green emission out of single Mn d-d transition at very low temperature or high laser excitation power. The intermediately doped products can give white emission out of STE1 and STE2. The highly doping products give red emission out of STE2 (bipolaron states) at room temperature or low laser power. These interesting phenomena reflected the microscopic interactions between spins, carriers and phonons in the products, which can be found applications in the future fields of photonics and spintronics.

Studies of Optical, Dielectric, Ferroelectric, and Structural Phase Transitions in 0.9[KNbO3]-0.1 [BaNi1/2Nb1/2O3−δ

The compound 0.9[KNbO3]-0.1[(BaNi1/2Nb1/2O3−δ] (KBNNO), a robust eco-friendly (lead-free) ferroelectric perovskite, has diverse applications in electronic and photonic devices. In this work, we report the dielectric, ferroelectric, and structural phase transitions behavior in the KBNNO compound using dielectric, X-ray diffraction, and Raman studies at ambient and as a function of temperature. Analyses of X-ray diffraction (XRD) data at room temperature (rtp) revealed the orthorhombic phase (sp. Gr. Amm2) of the compound with a minor secondary NiO cubic phase (sp. Gr. Fm3m). A direct optical band gap Eg of 1.66 eV was estimated at rtp from the UV–Vis reflectance spectrum analysis. Observation of non-saturated electric polarization loops were attributed to leakage current effects pertaining to oxygen vacancies in the compound. Magnetization studies showed ferromagnetism at room temperature (300 K) in this material. XRD studies on KBNNO at elevated temperatures revealed orthorhombic-to-tetragonal and tetragonal-to-cubic phase transitions at 523 and 713 K, respectively. Temperature-dependent dielectric response, being leaky, did not reveal any phase transition. Electrical conductivity data as a function of temperature obeyed Jonscher power law and satisfied the correlated barrier-hopping model, indicating dominance of the hopping conduction mechanism. Temperature-dependent Raman spectroscopic studies over a wide range of temperature (82–673 K) inferred the rhombohedral-to-orthorhombic and orthorhombic-to-tetragonal phase transitions at ~260, and 533 K, respectively. Several Raman bands were found to disappear, while a few Raman modes such as at 225, 270, 289, and 831 cm−1 exhibited discontinuity across the phase transitions at ~260 and 533 K.

Investigated coherent anti-Stokes Raman scattering in the process of cascaded stimulated Raman scattering in liquid and ice-Ih D2O.

Stimulated Raman scattering (SRS) of liquid and ice-Ih D2O was investigated using a pulsed Nd:YAG laser with a wavelength of 532nm. The high-order Stokes peaks and corresponding anti-Stokes SRS [Coherent Anti-Stokes Raman Spectroscopy (CARS)] peaks were obtained. Two symmetric and antisymmetric Raman modes of stretching vibrations were observed in liquid D2O, while only a symmetric stretching vibration mode was observed in ice-Ih D2O. Pure Stokes SRS is always collinear with the pump beam along the axial direction. Some ring-like Stokes SRS and CARS shifts, which originate from four-wave mixing processes, can also be observed only in the forward direction along with different angles meeting the phase-matching criteria, respectively. Simultaneously, the temporal behavior of SRS in liquid and ice-Ih D2O was examined, and the temporal waveforms of the pump laser pulse, transmitted pump pulse, and the forward SRS pulse were measured. In both cases, SRS was the dominant contributor to stimulated scattering. However, the efficiency values drastically decreased due to the self-termination behavior of SRS in liquid D2O, which arose from the thermal self-defocusing of both the pump beam and the SRS beam, owing to the Stokes shift-related opto-heating effect. In contrast, for the SRS process in ice-Ih D2O, the thermal self-defocusing influence was negligible, benefitting from a much greater thermal conductivity and a higher conversion efficiency of SRS generation retained under both of the conditions.

Quantitative Surface-Enhanced Spectroscopy.

Surface-enhanced Raman scattering (SERS), a powerful technique for trace molecular detection, depends on chemical and electromagnetic enhancements. While recent advances in instrumentation and substrate design have expanded the utility, reproducibility, and quantitative capabilities of SERS, some challenges persist. In this review, advances in quantitative SERS detection are discussed as they relate to intermolecular interactions, surface selection rules, and target molecule solubility and accessibility. After a brief introduction to Raman scattering and SERS, impacts of surface selection rules and enhancement mechanisms are discussed as they relate to the observation of activation and deactivation of normal Raman modes in SERS. Next, experimental conditions that can be used to tune molecular affinity to and density near SERS substrates are summarized and considered while tuning these parameters is conveyed. Finally, successful examples of quantitative SERS detection are discussed, and future opportunities are outlined.

Substrate surface effects on electron-irradiated graphene

Chemical, mechanical, thermal and/or electronic properties of bulk or low-dimensional materials can be engineered by introducing structural defects to form novel functionalities. When using particles irradiation, these defects can be spatially arranged to create complex structures, like sensing circuits, where the lateral resolution of the defective areas plays a fundamental role. Here, we show that structural defects can be patterned by low-energy electrons in monolayer graphene sheets with lateral resolution strongly defined by the surface of the supporting substrate. Indeed, two-dimensional micro-Raman mapping revealed that the surroundings of irradiated areas contain unintentional defects of the graphene lattice, whose density depends on the methods exploited to clean the supporting surface. By combining Monte Carlo simulations with the analysis of the graphene Raman modes, we attributed these structural modifications mainly to the action of back-scattered electrons and back-scattered electrons-created secondaries. The latter create reactive radicals at the interface between graphene and the supporting surface that affect the lateral resolution of the defective areas. Hence, defects pattern can be produced with high lateral resolution by removing any organic contaminants from the supporting surface and by reducing the thickness of the substrate, in order to minimize the number of back-scattered and secondary electrons.

Investigating the correlation between the Urbach energy and asymmetry parameter of the Raman mode in semiconductors

A quantitative correlation between the Urbach energy $({E}_{u})$ and asymmetry parameter $q$ of Raman spectra has been derived. For this purpose, the effect of electronic disorder $(\ensuremath{\sim}{E}_{u})$ on the possible interference between the electronic continuum states and discrete phononic states is reinvestigated. The equation of the form $\frac{I}{{q}^{2}}\ensuremath{\propto}\ensuremath{\xi}{E}_{u}\ifmmode\pm\else\textpm\fi{}\ensuremath{\lambda}$ ($I$: intensity of phonon mode $;\phantom{\rule{0.28em}{0ex}}\ensuremath{\xi},\ensuremath{\lambda}:$ some material-dependent parameters) has been obtained and verified experimentally on different semiconductors. The experimental results reveal an offset which has been understood as intrinsic or disorder-induced contribution to electron-phonon interactions in the system. The obtained equations quantitatively explain the changes in the Raman line shape due to disorder induced by atomic substitutions, temperature, etc., and provide understanding of the superposition between electronic and phononic states and of electron-phonon coupling in semiconductors with disorder.

Lattice defects and oxygen vacancies formulated ferromagnetic, luminescence, structural properties and band-gap tuning in Nd3+ substituted ZnO nanoparticles

ZnO and Zn1-xNdxO nanoparticles synthesized using the microwave assisted co-precipitation method were probed using XRD, HRTEM, UV–Vis spectroscopy, Raman spectroscopy, Photoluminescence spectroscopy and SQUID for robust and sufficient optical, structural, and magnetic profiles. The Hexagonal wurtzite structure of all the nanoparticles with a spherical shape and size in the 20-14 nm range was confirmed by XRD and HRTEM. The lower angle shift of the diffraction peaks indicated the interstitial addition of Nd3+ and collated to the lattice expansion. Urbach energy with its tail slope was used to define structural disorder in materials, and it increased with doping and decreased the optical band gap due to band-tail and tail-tail transitions. Broadening and asymmetry of the first-order E2 (high) phonon Raman mode identified structural disorder. The Spatial correlation model with changes in line center position, line width, and asymmetry of the E2 (high) phonon mode gave dopant created disorder. PL studies were used to determine the oxygen vacancy concentration, other defects, and excitation wavelength in all the nanoparticle samples that could be used as white light display devices. Magnetic studies with the BMP model were employed to confirm that Nd3+ doping leads to an increase in RTFM. Oxygen vacancies were considered to have a critical role in generating weak FM behavior in Zn1-xNdxO nanoparticles.

Fabrication of DSSCs using ferroelectric photoanodes of co-substituted (1 − x)BiFeO3-(x)BaFe1/2Nb1/2O3: Structural correlation to bandgap reduction and its impact on power conversion efficiency

In this letter, a series of A site and B site substituted (1 − x)BiFeO3-(x)BaFe1/2Nb1/2O3 (x = 0.05 to 0.20) (BFO-BFN) ferroelectric materials are designed to serve as photoanode in dye-sensitized solar cells (DSSCs). The formation of mixed structural phase from R3c to R3c + Pm-3m on substitution is confirmed by Rietveld refinement of powder X-ray diffraction data and Raman mode. Tuning the bandgap of BiFeO3 through A and B site substitution is a possible route for improving the power conversion efficiency (PCE). Improvement on the PCE is because of narrowing of bandgap as the function of increase in Fe-O-Fe bond angle and Fe-O bond length along with the decrease in octahedral tilt. The results have shown that the x = 0.20 sample has a maximum of 5.38% PCE. The novel photoanode based on BFO-BFN material could be a specific component of DSSC devices.

Sulfurization temperature dependent properties of tin mono-sulfide thin films

Tin mono-sulfide thin films were prepared using a two-step process consisting of DC sputtered deposition of Sn precursors over glass substrate held at 150 oC, followed by sulfurization for 1 hour at different temperatures ranging from 250 oC to400 oC. The influence of the sulfurization temperature on resultant films was studied in terms of its structure, morphology and opto-electronic properties. X-ray diffraction study revealed that the films sulfurized at lower temperature (~250 oC) had prominent SnS2 phase in addition to SnS. A single-phase tin mono-sulfide planes corresponding to orthorhombic structure has been observed at 300 oC and found to be highly crystalline at 350 oC. Further, three distinct Raman modes observed at 95, 190 and 218 cm-1 for Sn precursors sulfurized at 350 oC, strongly supporting the formation of single phase SnS. The optimized SnS film showed a direct band gap of 1.35 eV with an absorption coefficient of 5 x 104 cm-1. The valence states of Sn (+2) and S (-2) determined from X-ray photoelectron spectroscopy analysis for Sn precursors sulfurized at 350 oC, indicating the existence of SnS. These films had stoichiometric atomic ratio of Sn/S ~ 1 with surface roughness of 20 nm. All the films have shown p-type conductivity and the Sn precursors sulfurized at 350 oC exhibited relatively high conductivity of 0.947 x 10-2 (Ω cm)-1. The optoelectronic properties of SnS films reported in the present work would be highly suitable for device fabrication and promising as an alternative absorber for thin film solar cells. Copyright © 2017 VBRI Press.