Comparative Raman Study Research Articles

Complexities in the structural evolution with pressure of water-ammonia mixtures.

The structural evolution with pressure of icy mixtures of simple molecules is a poorly explored field despite the fundamental role they play in setting the properties of the crustal icy layer of the outer planets and of their satellites. Water and ammonia are the two major components of these mixtures, and the crystal properties of the two pure systems and of their compounds have been studied at high pressures in a certain detail. On the contrary, the study of their heterogeneous crystalline mixtures whose properties, due to the strong N-H⋯O and O-H⋯N hydrogen bonds, can be substantially altered with respect to the individual species has so far been overlooked. In this work, we performed a comparative Raman study with a high spatial resolution of the lattice phonon spectrum of both pure ammonia and water-ammonia mixtures in a pressure range of great interest for modeling the properties of icy planets' interiors. Lattice phonon spectra represent the spectroscopic signature of the molecular crystals' structure. The activation of a phonon mode in plastic NH3-III attests to a progressive reduction in the orientational disorder, which corresponds to a site symmetry reduction. This spectroscopic hallmark allowed us to solve the pressure evolution of H2O-NH3-AHH (ammonia hemihydrate) solid mixtures, which present a remarkably different behavior from the pure crystals likely to be ascribed to the role of the strong H-bonds between water and ammonia molecules characterizing the crystallites' surface.

Comparative Raman study on the molecular structure and IN VIVO wear of poly(methyl methacrylate)-based devices used as temporary knee prostheses: Effect of the antibiotic

The infection rate of total knee arthroplasty is still high, in spite of the high success of this surgical procedure. The use of an antibiotic-loaded temporary spacer made of poly(methyl methacrylate) (PMMA) has been proposed to treat infected knee arthroplasties.This study was aimed at comparatively investigating, on a molecular scale, two types of spacers from the same manufacturer (Spacer K and Vancogenx-space knee, Tecres, Italy), which differ for the added antibiotic (gentamicin sulphate in Spacer K and gentamicin sulphate + vancomycin hydrochloride in Vancogenx). Raman spectroscopy was used to gain more insights into the possible effects of the antibiotic on the spacer composition and polymer structure both in the new components and after in vivo use. Vancogenx was found to contain a lower residual MMA content than Spacer K (about 0.15% versus 0.4%). The former contained a higher amount of isotactic stereosequences than the latter, while the syndiotactic content (the prevailing component) was not significantly different in the two prostheses. The presence of vancomycin hydrochloride influenced not only the degree of polymerization and PMMA tacticity and crystallinity, but in turn also the wear behavior. Actually, Spacer K retrievals were found more affected by in vivo implantation than Vancogenx-space knee ones, revealing slight variations in polymer tacticity and crystallinity and relative radiopacifier content, besides release of MMA and additives of polymerization. However, these changes did not appear worrisome, due to the temporary nature of the prosthesis. In view of these results, the addition of vancomycin hydrochloride could offer an advantage, in spite of the higher costs requested and the potential risks of its unselective use.

Raman Spectroscopy Study of Structurally Uniform Hydrogenated Oligomers of α-Olefins.

The expansion of the range of physico-chemical methods in the study of industrially significant α-olefin oligomers and polymers is of particular interest. In our article, we present a comparative Raman study of structurally uniform hydrogenated dimers, trimers, tetramers, and pentamers of 1-hexene and 1-octene, that are attractive as bases for freeze-resistant engine oils and lubricants. We found out that the joint monitoring of the disorder longitudinal acoustic mode (D-LAM) and symmetric C–C stretching modes allows the quantitative characterization of the number and length of alkyl chains (i.e., two structural characteristics), upon which the pour point and viscosity of the hydrocarbons depend, and to distinguish these compounds from both each other and linear alkanes. We demonstrated that the ratio of the contents of CH2 and CH3 groups in these hydrocarbons can be determined by using the intensities of the bands in the spectra, related to the asymmetric stretching vibrations of these groups. The density functional theory (DFT) calculations were applied to reveal the relations between the wavenumber and bandshape of the symmetric C–C stretching mode and a conformation arrangement of the 1-hexene and 1-octene dimers. We found that the branched double-chain conformation results in the splitting of the C–C mode into two components with the wavenumbers, which can be used as a measure of the length of branches. This conformation is preferable to the extended-chain conformation for hydrogenated 1-hexene and 1-octene dimers.

Fabrication of Ag/ZnO nanostructures for SERS applications

A novel and effective approach is suggested for fabrication of composite Ag/ZnO nanostructures for surface-enhanced Raman scattering (SERS) by combining laser and ion implantation techniques. The study explores the relation between the nanoscopic features of the prepared Ag/ZnO nanocomposites and their effectiveness as SERS active substrates. The ZnO thin films are grown by pulsed laser deposition (PLD). Ag+-ion implantation is used for surface synthesis of Ag nanoparticles (NPs) in the ZnO matrix. The implanted samples are annealed by a Nd:YAG laser at various parameters. The surface morphology, composition and optical properties of the nanocomposites are studied before and after the ion and laser modifications. The possibility to apply these structures to ammonium nitrate detection is investigated by identifying the most suitable conditions for laser annealing of the implanted Ag/ZnO structures in view of producing the strongest SERS signal. A comparative Raman study is performed at two laser excitation wavelengths. New results are obtained for different ammonium nitrate (AN) concentrations. The strongest Raman signal of ammonium nitrate is detected for the Ag/ZnO substrate annealed at 532 nm and characterized by a high surface roughness and a wide nanoparticles’ size distribution, where a low surface electron density of silver was obtained.

The intrinsic temperature-dependent Raman spectra of graphite in the temperature range from 4K to 1000K

Temperature-dependent (T-dependent) Raman scattering can provide valuable informations on thermal properties, phonon anharmonicity and electron-phonon coupling of graphene-based materials. Graphene are found to exhibit extrinsic T-dependent Raman behavior at low temperature in vacuum or N2 gas, showing a behavior of heavily doped graphene. To obtain intrinsic properties of graphene-based materials, we focused on the comparative T-dependent Raman study on graphite and silicon in the temperature range of 4 K∼1000 K by different excitation lasers and different hot-stages or cryogenic stations. In contrast to the monotonic increase of full width at half maximum (FWHM) with temperature for the Si mode in silicon, FWHM for the G mode in graphite exhibits a minimum when T∼700K, which can be explained by the contributions from phonon anharmonicity and electron-phonon coupling. The result shows that the previous theoretical works underestimate the contribution from phonon anharmonicity above ∼ 600 K. The electron-phonon coupling strength of 0.026 is revealed, smaller than that of graphene. The peak position of G peak of graphite shows a nonlinear decrease with increasing temperature, which agrees well with the previous theoretical calculation. Our results find that the contribution of phonon anharmonicity to both peak position and FWHM is more prominent for the G mode in graphite than the Si mode in silicon.

Comparative Raman study of two laterally fluorinated LC compounds having different terminal chains

ABSTRACTIn this article, we present the Raman study of two laterally fluorinated liquid crystal compounds, namely, C3PP(23F)P-NCS and C3PP(23F)PC3. The two compounds have different terminal groups, one with NCS which is more polar than the other which has an alkyl group. The Raman bands were deconvoluted with Lorentzian profiles to get the values of spectral parameters. The main feature of the work is the temperature-dependent behaviour of the spectra profiles of the C–H bending mode, C–F stretching modes and aromatic C–C stretching mode in the vicinity of the phase transitions. The effect on the charge distribution over different bonds of the molecule and the vibrational energy of the bonds due to the presence of the more polar group on the terminal chain is well observed. The contrasting behaviours of the spectral profiles at the Cr–N and N–I transitions were also observed which we have ascribed to some pre-transitional effect associated with the breaking of the orientational order near the N–I transition. Density functional theory using B3LYP exchange correlation with the 6-31G (d,p) basis set was also used to generate a theoretical spectra which were found to be matching with the experimental spectra.

A comparative Raman study between PrMnO3, NdMnO3, TbMnO3 and DyMnO3

In this paper, we present a detailed Raman study of the non-multiferroic compounds PrMnO3 and NdMnO3 and the multiferroic compounds TbMnO3 and DyMnO3 as a function of temperature and magnetic field. All studied systems show anomalous phonon shifts close to the Néel transition TN. In PrMnO3 and NdMnO3, the frequency softenings are partly attributed to an orbital-spin-phonon coupling whereas in TbMnO3 and DyMnO3, the relatively weak frequency shifts are rather attributed to an expansion of the Mn−O bond lengths. On the other hand, the frequencies of TbMnO3 phonons are shifted as a function of magnetic field, while those of PrMnO3 remain unaffected. These frequency shifts are interpreted in terms of local oxygen rearrangements under magnetic field that could play an important role in the multiferroicity of TbMnO3 and DyMnO3.

Comparative Raman study of Weyl semimetals TaAs, NbAs, TaP and NbP

We report a comparative polarized Raman study of Weyl semimetals TaAs, NbAs, TaP and NbP. The evolution of the phonon frequencies with the sample composition allows us to determine experimentally which atoms are mainly involved for each vibration mode. Our results confirm previous first-principles calculations indicating that the A1, B1(2), E(2) and E(3) modes involve mainly the As(P) atoms, the B1(1) mode is mainly related to Ta(Nb) atoms, and the E(1) mode involves both kinds of atoms. By comparing the energy of the different modes, we establish that the B1(1), B1(2), E(2) and E(3) become harder with increasing chemical pressure. This behaviour differs from our observation on the A1 mode, which decreases in energy, in contrast to its behaviour under external pressure.

Comparative Raman study of transparent and turbid materials: models and experiments in the remote sensing mode

The influence of turbidity on the Raman signal strengths of condensed matter is theoretically analyzed and measured with laboratory - scale equipment for remote sensing. The results show the quantitative dependence of back- and forward-scattered signals on the thickness and elastic-scattering properties of matter. In the extreme situation of thin, highly turbid layers, the measured Raman signal strengths exceed their transparent analogs by more than a factor of ten. The opposite behavior is found for thick layers of low turbidity, where the presence of a small amount of scatterers leads to a decrease of the measured signal. The wide range of turbidities appearing in nature is experimentally realized with stacked polymer layers and solid/liquid dispersions, and theoretically modeled by the equation of radiative transfer using the analytical diffusion approximation or random walk simulations. Graphical abstract Spatial Raman emission profiles in transparent and turbid materials.

Comparative Raman study of photo-oligomer stability in the donor-acceptor fullerene complex {Pt(dbdtc)2}•C60 and pristine C60

Comparative Raman study of photo-oligomer stability in the donor-acceptor fullerene complex {Pt(dbdtc)2}•C60 and pristine C60

Comparative Raman study of four plant metallothionein isoforms: Insights into their Zn(II) clusters and protein conformations

Four Metallothioneins (MTs) from soybean (Glycine max) were heterologously synthesized and comparatively analysed by Raman spectroscopy. The participation of protein donor groups (S-thiol and N-imidazol) in Zn(II) chelation, as well as the presence of secondary structure elements was comparatively analysed. Metal clusters with different geometry can be hypothesised for the four GmMTs: a cubane-like or an adamantane-like metal cluster in Zn-GmMT1, and dinuclear Zn–S clusters in Zn-GmMT2, Zn-GmMT3 and Zn-GmMT4. The latter have also a similar average Cys/Zn content, whereas a lower ratio is present in Zn-GmMT1. This is possible thanks to the involvement in metal coordination of a greater number of bridging Cys, as well as of some carboxylate groups. As regards secondary structure elements, a large content of β-turn segments is present in all four Zn-GmMTs, especially for isoforms 1 and 4. β-strands give a contribution to the folding of three GmMTs isoforms, and the highest percentage was found in Zn-GmMT2 (~45%). Conversely, the α-helix content is negligible in all the GmMTs except in Zn-GmMT3, where this peculiar feature coincides with the possible involvement of the two His residues in metal coordination. Conversely, His is predominantly free and present as tautomer I in Zn-GmMT4. In conclusion, this work illustrates the attractive potential of Raman spectroscopy, combined with other techniques, to be a very informative tool for evidencing structural differences among in vivo synthesized metal-MT complexes.

Raman spectra for characterization of defective CVD multi‐walled carbon nanotubes

Curved graphene fragments can be considered as building blocks of carbon nanotubes. Thus, the size of graphene fragments may be considered as one of the most important characteristics of their structural disorder. In this paper, we have performed a comparative Raman study of CVD multi‐walled carbon nanotubes (MWCNTs) and graphene flakes deposited on MWCNTs. Raman data have been considered in combination with HRTEM characterization of nanotubes. The basic attention has been paid to the behavior of D (disorder‐induced), G (tangential mode), and 2D (two‐phonon scattering) bands in Raman spectra in order to use them for MWCNT characterization. A ratio of intensities of 2D and D bands (I2D/ID) demonstrates almost a linear dependence on the mean diameter of MWCNTs produced with two different types of catalysts (see abstract figure). It should be mentioned that each type of catalyst provides the linear dependence with its own specific slope. The graphene fragments have been proposed to form a mosaic structure of nanotube walls. I2D/ID ratio depends on the amount of graphene flakes deposited on nanotube surface via ethylene decomposition.A dependence of intensity ratio I2D/ID on the diameter of nanotubes produced with different types of catalysts.

Structural, electrical and piezoelectric properties of V-, Nb- and W-substituted CaBi4Ti4O15 ceramics

The equimolar substitution of V5+, Nb5+ and W6+ ions in the B-site of CaBi4Ti4O15 (CBT) ceramics was performed, and their sintering characteristics and microstructures were investigated. The results indicated that V2O5 has a substantial effect on the structure and properties of CaBi4Ti4O15 ceramics compared to Nb2O5 and WO3. The V-substituted sample exhibited the lowest sintering temperature, the best sinterability and the lowest conductivity among all of these samples. The comparative Raman study of the V5+, Nb5+ and W6+ doping indicated that the Bi ions in the [Bi2O2]2+ layers are more stable than those at the A sites in the pseudo-perovskite blocks, and the volatilisation of Bi during sintering preferentially occurs at A sites in the pseudo-perovskite blocks. The decrease in the volatilisation of Bi in the V-doped sample helps to maintain the amount of Bi atoms in the pseudo-perovskite blocks and the stoichiometric composition of the ceramics resulting in excellent properties. In addition, the increase in Bi ions in the pseudo-perovskite structure and the dense microstructure with a closed-packed arrangement of small grains, which result from sintering of the ceramics at a low temperature, also contributed to the notable reduction in the electrical conductivity. In comparison to the Nb- and W-doped CBT ceramics, the V-doped samples exhibited a dual slope transition in the conductivity-temperature curves, a minimum conductivity over the measured temperature range and optimum piezoelectric properties.

Comparative Raman Study of Organic-Free and Surfactant-Capped Rod-Shaped Anatase TiO<SUB>2</SUB> Nanocrystals

Comparative Raman Study of Organic-Free and Surfactant-Capped Rod-Shaped Anatase TiO<SUB>2</SUB> Nanocrystals

Single‐Cell Investigations of Silver Nanoparticle–Bacteria Interactions

Interaction of bacteria with citrate‐reduced silver nanoparticles (AgNPs) of size 25 nm ± 8.5 nm is studied using Raman spectroscopy in conjunction with plasmon resonance imaging of single bacterial cells. Distribution of isolated nanoparticles (NPs) inside Escherichia coli (ATCC 25922; E. coli) is observed by hyperspectral imaging (HSI) as a function of incubation time. Time‐dependent degradation of bacterial DNA upon incubation of AgNPs with E. coli is proven by Raman spectroscopic studies. While attachment of NPs is evident in HSI, molecular changes are evident from the surface‐enhanced Raman spectra of adsorbed DNA and its fragments. Distinct enhancement of DNA features is observed upon interaction of AgNPs and the number of such distinct features increases with incubation time, reaches a maximum, and decreases afterwards. This systematic interaction of DNA with the NPs system and its gradual chemical evolution is proven by investigating isolated plasmid DNA. A comparative Raman study with silver ions has shown that DNA features are observable only when bacteria are incubated with AgNPs. Energetics of interaction examined with microcalorimetry suggests the exothermicity of −1.547 × 1010 cal mol−1 for the NP–bacteria system. Specific interaction of AgNPs with exocyclic nitrogen present in the bases, adenine, guanine, and cytosine, leads to the changes in DNA.

Comparative computational IR, Raman and phosphorescence study of Ru- and Rh-based complexes

We report density functional theory (DFT) calculations providing the infrared and Raman spectra of [Ru(II)(bpy)3-n (dcbpy) n ]2+ and [Rh(III)(bpy)3-n (dcbpy) n ]3+ complexes, where bpy = 2,2′-bipyridyl, dcbpy = 4,4′-dicarboxy-2,2′-bipyridyl, and n = 0, 1, 2, 3, studied in the context of dye-sensitised solar cells. We compare and contrast the role of the metallic ion and of the COOH groups on the vibration and phosphorescence properties of these complexes. The vibrational spectra are not very sensitive to the replacement of the metal ion, but the presence of carboxyl groups leads to a richer spectrum due to the additional bands caused by the COOH groups. Comparison with the limited experimental data available allowed the assignment of the Raman bands. The calculated phosphorescence lifetimes suffer only modest changes when the COOH groups are introduced but vary significantly when changing the metal ion, being two orders of magnitude larger for Rh(III) than for the Ru(II) complexes.

Possibility of VOx/SiO2 Complexes Speciation: Comparative Multi-wavelength Raman and DR UV-vis Study

Raman spectroscopy is one of the very often used spectroscopic methods for characterization of vanadium surface species. However, Raman spectra of VOx-silica systems are more complex and interpretation is more difficult in comparison with other supports (like Al2O3, ZrO2, TiO2 or Nb2O5) because there is strong vibrational coupling between the vanadia species and the silica support. Therefore, assignment and interpretation of some vibrational bands is still subject of controversy. This fact results in incongruity of suggested molecular structure and population of individual vanadium surface complexes. In this contribution, we present systematic comparative study of diffuse reflectance UV-vis spectra and Raman spectra excited by 325 and 514.5 nm lasers obtained on set of dehydrated vanadium modifed hexagonal mesoporous silica (VOx-HMS) samples with vanadium loading from 2 up to 12 wt. %. We prove that changes in population of oligomeric and monomeric VOx species in individual samples are not manifested by significant changes in the character of Raman signals. On the other hand it is evident that with increasing of vanadium loadings the UV-vis spectra show systematic changes. Raman spectroscopy is useful characterization technique for detection presence of very small amount of V2O5 microcrystallites, especially if suitable wavelength of laser is used for remarkable resonant enhancement of Raman intensity of its bands (e.g. 514.5 nm).

Comparative Raman Study of Individual Double-Walled Carbon Nanotubes and Single-Walled Carbon Nanotubes

Comparative Raman Study of Individual Double-Walled Carbon Nanotubes and Single-Walled Carbon Nanotubes

Effect of deuteration on hydrogen bonding: A comparative concentration dependent Raman and DFT study of pyridine in CH3OH and CD3OD and pyrimidine in H2O and D2O

The relative effect of hydrogen bonding of pyrimidine (Pyr) in H2O/D2O and pyridine (Py) in CH3OH/CD3OD has been analyzed using Raman Difference Spectroscopic (RDS) technique and DFT calculations. This study is focused on analyzing the concentration dependent variation of linewidth, peak position and intensity of ring breathing mode of Py and Pyr. The ring breathing mode of Pyr in H2O and D2O has three components; due to free Pyr, lighter complexes of mPyr+nH2O/D2O and heavier complexes of mPyr+nH2O/D2O. The pyridine molecules, however, show only two components in CH3OH and CD3OD. Of these two components, one corresponds to free Py and the other inhomogeneously broadened profile corresponds to all mPy+nCH3OH/CD3OD complexes. The variation of peak position and linewidth establishes the role of dipole moment of complexes and the diffusion in the mixture. In case of CD3OD solution splitting was observed in ∼1030cm−1 band of Py, where an additional band at ∼1034cm−1 appears at x(Py)⩽0.4. However, this band remains single at all concentrations in case of CH3OH solvent.

The spin dynamics in distorted kagome lattices: a comparative Raman study

Despite the conceptional importance of realizing spin liquids in solid states only few compounds are known. On the other hand the effect of lattice distortions and anisotropies on the magnetic exchange topology and the fluctuation spectrum is an interesting problem. We compare the excitation spectra of the two s = 1/2 kagome lattice compounds, volborthite and vesignieite, using Raman scattering. We demonstrate that even small modifications of the crystal structure may have a huge effect on the phonon spectrum and low-temperature properties.