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We describe a simple experiment on the diffraction of monochromatic light by interfering liquid surface waves. The surface wave profile, which acts as a reflection phase grating for incident light, is generated by electrically driven vertical oscillations of two or more slightly immersed exciters. The theoretical intensity of the diffracted light agrees well with observations. In particular, we show the relation between the intensity and the amplitude (height) of the surface wave. Although invisible to the naked eye, the interference of liquid surface waves can be optically detected from the characteristic features of the diffraction pattern. In addition, we can measure the amplitude, wavelength, and phase velocity of the surface wave that propagates along the line joining the exciters. [ABSTRACT FROM AUTHOR]

Results of an in-situ extended X-ray absorption fine-structure study of photostructural changes in films of amorphous selenium are reported. It is shown that at first the average coordination number decreases by about 10%. As time elapses, the initial coordination number is restored. This change is attributed to breaking of ring-like structural fragments with subsequent formation of longer chains. This model is supported by a Raman scattering experiment demonstrating the disappearance upon photoexcitation of a peak at about 112 cm -1 characteristic of rings. [ABSTRACT FROM AUTHOR]

We report electron transmission and Raman spectroscopy study of InAs nanowires. We demonstrate that the temperature dependent behavior of optical phonon energies can be used to determine the relative wurtzite fraction in the InAs nanowires. Furthermore, we propose that the interfacial strain between zincblende and wurtzite phases along the length of the wires manifests in the temperature-evolution of the phonon linewidths. From these studies, temperature-dependent Raman measurements emerge as a non-invasive method to study polytypism in such nanowires. [ABSTRACT FROM AUTHOR]

Resonance Raman measurements are carried out on defect-free wurtzite GaP nanowires over the excitation energy range between 2.19 and 2.71 eV. Resonances of the E1(LO) and A1(LO) modes demonstrate the existence of energy states with Γ9hh and Γ7V (Γ7C) symmetries of the valence (conduction) band and enable us to measure wurtzite phase GaP band energies. In addition, we have performed temperature dependent resonant Raman measurements, which allowed us to extrapolate the zero temperature values of Γ point energies. Our results provide the necessary feedback required for refining the available theoretical calculations to derive the correct wurtzite III-V semiconductor band structure. [ABSTRACT FROM AUTHOR]

Human serum albumin (HSA), the most abundant plasma protein in the human body is known to form fibrils under partial denaturing conditions. Natural polyphenols are known to interact with HSA and some polyphenols have been shown to be potent inhibitors of amyloid fibrillation. (−)-Epigallocatechin gallate (EGCG), the major component of green tea is known to inhibit amyloid fibrillation. In this report, we have investigated the effect of EGCG on native HSA as well as on the fibrillation process of HSA from amide III band analysis of their respective visible Raman spectra. The differential role of the tryptophan (Trp214) residue present in domain II of HSA in the absence and presence of EGCG has been pointed out using fluorescence anisotropy and visible Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Microwave radiations from various electronic devices are of serious health concern. In this article, using spectroscopic measurements, we show that the microwave radiation of strength 22 dBm and frequency 10 GHz facilitates protein fibrillation. However, this adverse effect of low-field radiation can be restricted by the presence of biocompatible citrate-capped gold nanoparticles. The dissipative field by metallic particles is able to disrupt the fibrillar network. We believe that the obtained results paved a way to find a therapeutic measure to combat fibrillation related diseases. [ABSTRACT FROM AUTHOR]

Optical properties of nanocrystalline red-emitting phosphor, europium-doped yttria (Y2O3:Eu3+), of average particle size of 15 nm are investigated. The intensity of the strongest emission line at 612 nm is found to be highest in the nanocrystalline sample with 4 at. wt % of europium. The narrow electronic emission spectrum suggests a crystalline surrounding in this nanomaterial. We have estimated the strength of the crystal-field parameter at the dopant site, which plays a crucial role in determining the appearance of the intense emission line. The equilibrium temperature of this system has also been calculated from the intensity ratio of Stokes and anti-Stokes Raman scattering. Though known for the bulk samples, our approach and consequent results on the crystalline nanomaterial of Y2O3:Eu3+ provide a unique report, which, we believe, can be of considerable significance in nanotechnology. [ABSTRACT FROM AUTHOR]

Single crystals of the iron-pnictide compound BaFe 2 (As 1 − x P x) 2 for x ∼ 0.23, with a doping concentration near quantum criticality and enhanced nematic fluctuating state in the doping-temperature phase diagram, have been studied. Transport measurements confirm the presence of a magneto-structural transition at 60 K from the tetragonal to the orthorhombic phase, followed by a superconducting transition below 16 K. Micro-Raman spectra of the compound exhibit a phonon mode at 211 cm−1 and two broad modes (BMs) at 515 cm−1 and 635 cm−1, which corresponds to an energy difference of 15 meV. The temperature dependent Raman measurements reveal that the intensity of these BMs drop over the temperature range between 80 K and 300 K. In the non-superconducting state, strong anisotropic behaviour is observed for these BMs in polarization dependent Raman scattering. Electronic structure calculations for doped and undoped BaFe 2 As 2 show that while Fe d x z and d y z orbitals do not split in the tetragonal phase, the splitting energy is 13.5 meV in the orthorhombic phase of the doped system, which is reasonably close to the experimentally observed value of the energy separation of the BMs. We believe that the reported BMs are consistent with the signature of electronic Raman scattering involving the crystal field levels of d -orbitals of Fe2＋ due to local breaking of the C 4 symmetry in the doped system. • Local symmetry breaking in tetragonal phase of P doped BaFe 2 As 2 near quantum critical point. • Signature of crystal field splitting using temperature dependent micro Raman spectroscopy. • Calculation of Fe d orbitals split energies in local orthorhombic phase using DFT. [ABSTRACT FROM AUTHOR]

In this article, we report negative thermal expansion and spin frustration in hexagonal GdInO3. Rietveld refinements of the x-ray diffraction patterns reveal that the negative thermal expansion in the temperature range of 50-100 K stems from the triangular lattice of Gd3+ ions. The downward deviation of the low-temperature inverse susceptibility (χ-1) versus T plot from the Curie-Weiss law and the large value of the ratio, 0CW|/TN>28, where θCW and TN are respectively Curie-Weiss and Neel temperature, indicate a strong spin frustration, which inhibits long-range magnetic ordering down to 1.8 K. Magnetostriction measurements clearly demonstrate a spin-lattice coupling in the system. Low-temperature anomalous phonon softening, as obtained from temperature-dependent Raman measurements, also reveals the same. Our experimental observations are supported by first-principles density functional theory calculations of the electronic and phonon dispersion in GdInO3. The calculations suggest that the GdInO3 lattice is highly frustrated at low temperature. Further, the calculated normal mode frequencies of the Gd-related G point phonon modes reveal significant magnetoelastic coupling in this system. The competitive role of magnetic interaction energy and thermal stabilization energy in determining the change in interatomic distances is the possible origin for the negative thermal expansion in GdInO3 over a limited range of temperature. [ABSTRACT FROM AUTHOR]

In this study, we attempt to find the origin of atypical doping concentration dependant electrical properties of group III element (Al, Ga, In) doped ZnO thin films. The carrier density and mobility of these films are measured and compared for a wide range of doping concentrations. It is found that donor density determines the electrical properties of the films for a low level of doping, whereas lattice defects play a dominant role beyond a certain level of doping concentration. We also demonstrate an interrelationship between the electrical properties and the structural/optical properties of the films. We find 2% as optimum doping concentration for Al-, Ga- or In-doped ZnO for obtaining highest conducting layers and Ga emerges as the most effective dopant among all. [ABSTRACT FROM AUTHOR]

In vitro fibrillation of hen egg white lysozyme (HEWL) causes complete reduction of Cu(II) to Cu(I) at pH 7. Here in the present article, we have shown the presence of both Cu(II) and Cu(I) at pH 11 during fibrillation of HEWL using electron paramagnetic resonance and Raman spectroscopy. Our results suggest the existence of a partially reducing environment during fibrillation of hen egg white lysozyme at pH 11. The fibrillation process is governed by the pH of the solution and maximum fibrillation is found to occur at pH 11. Fibrils formed in the absence of Cu(II) were also found to cause significant hemolysis of RBC. [ABSTRACT FROM AUTHOR]

Abstract: Copper is known to exert diverse effects on the self-association of proteins and has been found in amyloid deposits that are involved in neurodegenerative disease processes. The effects of the metal ion on the protein during fibrillation were investigated by fluorescence, circular dichroism spectroscopy and fluorescence microscopy. We report for the first time, the complete reduction of Cu(II)→Cu(I) in vitro during fibrillation of hen egg white lysozyme at pH 7. This was confirmed by the lack of any signal for Cu(II) in electron paramagnetic resonance spectroscopy and quantification of Cu(I) was achieved by a bathocuproine disulfonate based assay. [Copyright &y& Elsevier]

Abstract: In this article, we discuss metal–protein interactions in the Ag–lysozyme complex by spectroscopic measurements. The analysis of the variation in relative intensities of SERS bands reveals the orientation and the change in conformation of the protein molecules on the Ag surface with time. The interaction kinetics of metal–protein complexes has been analyzed over a period of 3h via Raman measurements. Our analysis indicates that the Ag nanoparticles most likely interact with Trp123 which is in close proximity to Phe34 of the lysozyme molecule. [ABSTRACT FROM AUTHOR]

The phase stability of zirconia (ZrO 2) under external perturbation draws the attention of researchers, as it governs the practical use of this material in technological applications. In this article, the phase transition in zinc oxide (ZnO) doped ZrO 2 is addressed by exploiting complementary methodologies, X-ray diffraction, and Raman spectroscopic measurements. We have observed a pressure-induced partial phase transformation in the doped ZrO 2 system for a compacting pressure of less than 1 GPa. It is noteworthy that the level of compacting pressure used in this study is much lower than the range of pressure, reported in the literature, for observing phase transition in pure and doped ZrO 2 using other high-pressure experiments. To understand the underlying dynamics of low pressure-induced phase transformation, we carried out density functional theory calculations for the doped supercell. We have discussed the local bonding environment around the dopant metal ion (Zn2+ in the present case), which, we believe, leads to the phase evolution in a real system. [ABSTRACT FROM AUTHOR]

We have investigated the nonthermal effect of 10 GHz/22 dBm microwave radiation on hen egg-white lysozyme (HEWL) over different irradiation times, ranging from 2 min to 1 h. To ensure a control over the radiation parameters, a pair of microwave rectangular waveguides is used to irradiate the samples. Optical spectroscopic measurements, which include UV-visible absorption spectroscopy, Raman spectroscopy, and far UV CD spectroscopy, reveal the exposure of the buried tryptophan (Trp) residues of the native molecule between 15 and 30 min of radiation. The higher duration of the perturbation leads to a compact structure of the protein and Trp residues are buried again. Interestingly, we do not find any change in the secondary structure of the protein even for 1 h duration of radiation. The relaxation dynamics of the irradiated molecules also has been discussed. We have shown that the molecules relax to their native configuration in 7-8 h after the radiation field is turned off. The structural rearrangement over the above timescale has further been probed by a model calculation, based on a modified Langevin equation. Our coarse-grained simulation approach utilizes the mean of atomic positions and net atomic charge of each amino acid of native HEWL to mimic the initial conformation of the molecule. The modified positions of the residues are then calculated for the given force fields. The simulation results reveal the nonmonotonous change in overall size of the molecule, as observed experimentally. The radiation parameters used in our experiments are very similar to those of some of the electronic devices we often come across. Thus, we believe that the results of our studies on a simple protein structure may help us in understanding the effect of radiation on complex biological systems as well. [ABSTRACT FROM AUTHOR]

Phonon modes and their association with the electronic states have been investigated for the metallic EuCu 2 As 2 system. In this work, we present the Raman spectra of this pnictide system which clearly shows the presence of seven well defined peaks above 100 cm -1 that is consistent with the locally non-centrosymmetric P4/nmm crystal structure, contrary to that what is expected from the accepted symmorphic I4/mmm structure. Lattice dynamics calculations using the P4/nmm symmetry attest that there is a commendable agreement between the calculated phonon spectra at the Γ point and the observed Raman mode frequencies, with the most intense peak at∼232 cm -1 being ascribed to the A1gmode. Temperature dependent Raman measurements show that there is a significant deviation from the expected anharmonic behaviour around 165 K for the A1gmode, with anomalies being observed for several other modes as well, although to a lesser extent. Attempts are made to rationalize the observed anomalous behavior related to the hardening of the phonon modes, with parallels being drawn from metal dichalcogenide and allied systems. Similarities in the evolution of the Raman peak frequencies with temperature seem to suggest a strong signature of a subtle electronic density wave instability below 165 K in this compound., (© 2024 IOP Publishing Ltd.)

Various electronic devices, which we commonly use, radiate microwaves. Such external perturbation influences the functionality of biomolecules. In an ultralow field, the cumulative response of a molecule is expected only over a time scale of hours. To study the structural dynamics of biomolecules over hours, we adopt a simple methodology for constructing the coarse-grained structure of the protein molecule and solve the Langevin equation under different working potentials. In this approach, each amino acid residue of a biomolecule is mapped onto a number of beads, a few for the backbone, and few for the side chain, depending on the complexity of its chemical structure. We choose the force field in such a way that the dynamics of the protein molecule in the presence of ultralow radiation field of microvolt/nm could be followed over the time frame of 2 h. We apply the model to describe a biomolecule, hen egg white lysozyme, and simulate its structural evolution under ultralow strength electromagnetic radiation. The simulation revealed the finer structural details, like the extent of exposure of bioactive residues and the state of the secondary structures of the molecule, further confirmed from spectroscopic measurements [details are available in Phys. Rev. E 97, 052416 (2018)10.1103/PhysRevE.97.052416 and briefly described here]. Though tested for a specific system, the model is quite general. We believe that it harnesses the potential in studying the structural dynamics of any biopolymer under external perturbation over an extended time scale.

Rare earth indates are an interesting class of compounds with rich crystallography. The present study explores the crystallographic phases observed in REInO3 (RE: La-Yb) systems and their dependence on synthesis routes and annealing temperature. All REInO3 compositions were synthesized by a solid state route as well as gel-combustion synthesis (GC) followed by annealing at different temperatures. The systems were well characterized by powder XRD studies and were analysed by Rietveld refinement for the structural parameters. The cell parameters were observed to decrease in accordance with the trend in ionic radii on proceeding from lighter to heavier rare earth ions. Interestingly, the synthesis route and the annealing temperature had a profound bearing on the phase relationships observed in the REInO3 series. The solid state synthesized samples depicted an orthorhombic phase (Pbnm) field for LaInO3 to SmInO3, followed by a hexagonal-type phase (P63cm) for GdInO3 to DyInO3. However, the phase field distribution was greatly influenced upon employing gel-combustion (GC) wherein both single-phasic hexagonal and orthorhombic phase fields were found to shrink. Annealing the GC-synthesized compositions to still higher temperatures (1250 °C) further evolved the phase boundaries. An important outcome of the study is observance of polymorphism in SmInO3 which crystallized in the hexagonal phase when synthesized by GC and orthorhombic phase by solid state synthesis. This reveals the all-important role played by synthesis conditions. The existence and energetics of the two polymorphs have been elucidated and discussed with the aid of theoretical studies.

The structural and magnetic properties of the Y 1-x Tb x MnO 3 (0.1  ⩽  x  ⩽  0.3) compounds were investigated. Neutron diffraction patterns for all three samples, recorded at room temperature (RT), were fitted to the nuclear structure confirming the paramagnetic nature of the compounds. At 2.8 K, for the x  =  0.1 sample magnetic moments of the Tb 3+ ionic as well as Mn 3+ ionic were ordered. At 5 K for the x  =  0.2 sample only the Mn 3+ ionic magnetic moments were ordered. There were six sites for Mn atoms. Three on the z  =  0 plane and three on the z  =  0.5 plane (where z corresponds to  +c axis).The Mn 3+ ionic moments were confined to the a-b plane with a net magnitude of 2.78(3) µ B , and 2.90(3) µ B for the x  =  0.1 and the x  =  0.2 samples. The Tb 3+ ionic moments had a magnitude of 1.36(4) µ B at 2.8 K and were aligned antiferromagnetically along the crystallographic c-axis for the x  =  0.1 sample. The low moment in comparison with Mn 3+ free ions has been attributed to crystalline electric fields similar to that found in the parent compound YMnO 3 and also in another rare earth manganite viz HoMnO 3 . The x  =  0.3 sample was found to be a canonical spin glass. To investigate the role of the above spin ordering in Y 1-x Tb x MnO 3 in governing the phonon dynamics, temperature dependent Raman measurements were carried out. We observed the deviation of the phonon frequency near 685 cm -1 and its line-width from the expected anharmonic behaviour around magnetic ordering temperature for Tb substituted compounds with x  =  0.1 and 0.2. This was attributed to the spin-phonon coupling in these systems. The anomalous behaviour of this phonon mode in the canonical spin glass compound with x  =  0.3, indicated that the coupling sustained even in the presence of only local magnetic ordering.

Herein, we report the graded electronic band gap along the axis of individual heterostructured WZ-ZB InAs/InSb 0.12 As 0.88 nanowires. Resonance Raman imaging has been exploited to map the axial variation in the second excitation gap energy (E 1 ) at the high symmetry point (L point) of the Brillouin zone. We relate the origin of the observed evolution of the gap energy to the fine tuning of the alloy composition from the tip towards the interface of the nanowire. The electronic band structures of InAs, InSb and InSb x As 1-x alloy systems at x = 0.125, 0.25, 0.50, 0.75 and 0.875, using the all electron density functional theory code Wien2k, are reported. The measured band gap along the axis of the InAs/InSb 0.12 As 0.88 nanowire is correlated with the calculated gap energy at the A point and the L point of the Brillouin zone for InAs and InSb 0.125 As 0.875 , respectively. We draw a one-to-one correspondence between the variation of the E 1 gap and the fundamental E 0 gap in the calculated electronic band structure and propose the graded fundamental gap energy across the axis of the nanowire.

In this article we demonstrate type-II band alignment at the wurtzite/zinc-blende hetero-interface in InAs polytype nanowires using resonance Raman measurements. Nanowires were grown with an optimum ratio of the above mentioned phases, so that in the electronic band alignment of such NWs the effect of the difference in the crystal structure dominates over other perturbing effects (e.g. interfacial strain, confinement of charge carriers and band bending due to space charge). Experimental results are compared with the band alignment obtained from density functional theory calculations. In resonance Raman measurements, the excitation energies in the visible range probe the band alignment formed by the E 1 gap of wurtzite and zinc-blende phases. However, we expect our claim to be valid also for band alignment near the fundamental gap at the heterointerface.

Knowing the distribution of Ramachandran angles helps in understanding peptide and protein backbone conformation. Empirical relations are proposed to correlate the spectral profile of the amide III3 band, obtained from ultraviolet resonance Raman measurements (UVRR), with the Ramachandran dihedral psi angle distribution in small peptide and protein molecules, in different environmental conditions (Mikhonin et al. J. Phys. Chem. B 2006, 110, 1928-1943). It has also been used for more complicated structures, like large globular proteins and protein fibrils. In our work here, we use visible Raman spectra and available empirical relations to obtain similar correlations for human serum albumin, hen egg white lysozyme, and human gamma crystallin. We also report the dihedral angle distribution in fibrils and a denatured protein in an ethanol environment using the same spectroscopic technique.

The interaction of lysozyme (Lyz)-conjugated silver (Ag) nanoparticles with (-)-epigallocatechin gallate (EGCG), one of the major components of green tea, has been investigated. Interaction of a protein with ligand/drug molecules perturbs the conformation of secondary and tertiary structures of the protein. We have demonstrated the conformational changes in the tertiary structures of the Lyz molecules on EGCG binding using surface-enhanced Raman scattering (SERS) and circular dichroism (CD) spectroscopic measurements. From the analysis of the amide I band of Lyz in SERS and CD spectra, the site of interaction of EGCG with protein molecules in Lyz-conjugated Ag particles has been identified. Spectroscopic evidence for the conformational response of Trp62 and Trp63, in the β-domain of the protein, to the binding of EGCG has been discussed.

In this article, the dipolar response of gold nanorods on the adsorbed organic molecule, benzonitrile, has been investigated. We estimate the average aspect ratio of nanorods using TEM measurements. The longitudinal and transverse plasmon modes of nanorods are measured and analyzed using theoretical estimates. Well characterized gold nanorods are further used to establish the effect of plasmon coupling on the characteristics of the ligand molecule. Making use of the dipolar response function model we are able to match the experimental and theoretical values of the frequencies of vibrational modes of ad-molecules upon adsorption on the rod surface. We believe that our studies using optical probes can explain the effect of the metallic nanorod, as a whole, on the ad molecules and can thereby serve as a sensitive tool to understand metal-ligand interactions for such metallic nanostructures.

Adsorption of acetonitrile (Ac) molecules on gold (Au) nanorods has been investigated by Raman spectroscopic measurements and density functional theory (DFT) calculations. DFT calculations provide a valuable insight into the underlying structure of the metal-molecule complex. From the best agreement between the observed and the calculated Raman frequencies and also from other spectroscopic observations, we propose that Ac molecules interact with Au nanorods and form an [Ac+2Au](0)-like complex on the surface of nanostructures. The environmental effect has also been taken into consideration to explain the Raman activity of the complex.