Raman study on pentacene:C60 bulk heterojunction films

We measured 785 nm excited Raman and infrared spectra of pentacene-d₁₄. The observed spectra were assigned on the basis of the Raman and infrared spectra calculated by the density functional theory (DFT) method at the B3LYP/6⬜311 + G** level. We measured 785 nm excited Raman spectrum of a pentacne-d₁₄:C₆₀ bulk heterojunction film. The spectrum was assigned on the basis of the wavenumber shifts upon deuteration of pentacene. The assignments of the 1462 and 493 cm^↙1 A_g bands of C₆₀ were confirmed. The 511, 453, and 256 cm^↙1 bands, which were observed only in pentacene:C₆₀ bulk heterojunction films, did not show large deuteration shifts. This result indicates that the 511, 453, and 256 cm^↙1 bands are attributed to activation of the silent modes of C₆₀ due to symmetry lowering_.     

Regularity modes in Raman spectra of polyolefins: Part I. Propylene/olefin copolymers

Behavior of the regularity modes of isotactic polypropylene is analyzed in Raman spectra of a number of random propylene/olefin copolymers. The regularity modes at 809, 841, 973, 998, and 1220 cm⁻¹ decrease in intensity with growth of the content of the incorporated monomer. For the lines at 809, 973, and 1220 cm⁻¹ the rate of intensity damping varies depending on the structure of the incorporated monomer. The type of the incorporated monomer has inconsiderable effect on the evolution of intensity of the regularity bands at 841 and 998 cm⁻¹. Anomalous behavior of the mode at 1220 cm⁻¹ was observed for the propylene/1-butene copolymers.     

A Raman spectroscopic study of the antimonite mineral peretaite Ca(SbO)4(OH)2(SO4)2·2H2O

Raman spectra of mineral peretaite Ca(SbO)₄(OH)₂(SO₄)₂·2H₂O were studied, and related to the structure of the mineral. Raman bands observed at 978 and 980 cm^?1 and a series of overlapping bands observed at 1060, 1092, 1115, 1142 and 1152 cm^?1 are assigned to the SO₄^2? ν₁ symmetric and ν₃ antisymmetric stretching modes. Raman bands at 589 and 595 cm^?1 are attributed to the SbO symmetric stretching vibrations. The low intensity Raman bands at 650 and 710 cm^?1 may be attributed to SbO antisymmetric stretching modes. Raman bands at 610 cm^?1 and at 417, 434 and 482 cm^?1 are assigned to the SO₄^2? ν₄ and ν₂ bending modes, respectively. Raman bands at 337 and 373 cm^?1 are assigned to O–Sb–O bending modes. Multiple Raman bands for both SO₄^2? and SbO stretching vibrations support the concept of the non-equivalence of these units in the peretaite structure.     

Vibrational spectroscopic study of syngenite formed during the treatment of liquid manure with sulphuric acid

Syngenite (K₂Ca(SO₄)₂·H₂O), formed during treatment of manure with sulphuric acid, was studied by infrared, near-infrared (NIR) and Raman spectroscopy. C_s site symmetry was determined for the two sulphate groups in syngenite (P2₁/m), so all bands are both infrared and Raman active. The split ν₁ (two Raman+two infrared bands) was observed at 981 and 1000 cm⁻¹. The split ν₂ (four Raman+four infrared bands) was observed in the Raman spectrum at 424, 441, 471 and 491 cm⁻¹. In the infrared spectrum, only one band was observed at 439 cm⁻¹. From the split ν₃ (six Raman+six infrared) bands three 298 K Raman bands were observed at 1117, 1138 and 1166 cm⁻¹. Cooling to 77 K resulted in four bands at 1119, 1136, 1144 and 1167 cm⁻¹. In the infrared spectrum, five bands were observed at 1110, 1125, 1136, 1148 and 1193 cm⁻¹. From the split ν₄ (six infrared+six Raman bands) four bands were observed in the infrared spectrum at 604, 617, 644 and 657 cm⁻¹. The 298 K Raman spectrum showed one band at 641 cm⁻¹, while at 77 K four bands were observed at 607, 621, 634 and 643 cm⁻¹. Crystal water is observed in the infrared spectrum by the OH-liberation mode at 754 cm⁻¹, OH-bending mode at 1631 cm⁻¹, OH-stretching modes at 3248 (symmetric) and 3377 cm⁻¹ (antisymmetric) and a combination band at 3510 cm⁻¹ of the H-bonded OH-mode plus the OH-stretching mode. The near-infrared spectrum gave information about the crystal water resulting in overtone and combination bands of OH-liberation, OH-bending and OH-stretching modes.     

Vibrational and electronic properties of single-walled and double-walled boron nitride nanotubes

We calculated IR, nonresonance Raman spectra and vertical electronic transitions of the zigzag single-walled and double-walled boron nitride nanotubes ((0,n)-SWBNNTs and (0,n)@(0,2n)-DWBNNTs). In the low frequency range below 600 cm⁻¹, the calculated Raman spectra of the nanotubes showed that RBMs (radial breathing modes) are strongly diameter-dependent, and in addition the RBMs of the DWBNNTs are blue-shifted reference to their corresponding one in the Raman spectra of the isolated (0,n)-SWBNNTs. In the high frequency range above ∼1200 cm⁻¹, two proximate Raman features with symmetries of the A_1g (∼1355 ± 10 cm⁻¹) and E_2g (∼1330 ± 25 cm⁻¹) first increase in frequency then approach a constant value of ∼1365 and ∼1356 cm⁻¹, respectively, with increasing tubes’ diameter, which is in excellent agreement with experimental observations. The calculated IR spectra exhibited IR features in the range of 1200–1550 cm⁻¹ and in mid-frequency region are consistent with experiments. The calculated dipole allowed singlet–singlet and triplet–triplet electronic transitions suggesting a charge transfer process between the outer- and inner-shells of the DWBNNTs as well as, upon irradiation, the possibility of a system that can undergo internal conversion (IC) and intersystem crossing (ISC) processes, besides the photochemical and other photophysical processes.     

Electronic structure and Raman spectroscopy study of dibarium magnesium orthoborate,Ba2Mg(BO3)2

The samples of dibarium magnesium orthoborate Ba₂Mg(BO₃)₂ were synthesized by solid-state reaction. The X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Electronic structure and vibrational spectroscopy of Ba₂Mg(BO₃)₂ were systematically investigated by first principle calculation. A direct band gap of 4.4 eV was obtained from the calculated electronic structure results. The top valence band is constructed from O 2p states and the low conduction band mainly consists of Ba 5d states. Raman spectra for Ba₂Mg(BO₃)₂ polycrystalline were obtained at ambient temperature. The factor group analysis results show the total lattice modes are 5E_u + 4A_2u + 5E_g + 4A_1g + 1A_2g + 1A_1u, of which 5E_g + 4A_1g are Raman-active. Furthermore, we obtained the Raman active vibrational modes as well as their eigenfrequencies using first-principle calculation. With the assistance of the first-principle calculation and factor group analysis results, Raman bands of Ba₂Mg(BO₃)₂ were assigned as E_g (42 cm⁻¹), A_1g (85 cm⁻¹), E_g (156 cm⁻¹), E_g (237 cm⁻¹), A_1g (286 cm⁻¹), E_g (564 cm⁻¹), A_1g (761 cm⁻¹), A_1g (909 cm⁻¹), E_g (1165 cm⁻¹). The strongest band at 928 cm⁻¹ in the experimental spectrum is assigned to totally symmetric stretching mode of the BO₃ units.     

A Raman spectroscopic study of the mineral coquandite Sb6O8(SO4)·(H2O)

Raman spectra of coquandite Sb₆O₈(SO₄)·(H₂O) were studied, and related to the structure of the mineral. Raman bands observed at 970, 990 and 1007 cm^?1 and a series of overlapping bands are observed at 1072, 1100, 1151 and 1217 cm^?1 are assigned to the SO₄^2? ν₁ symmetric and ν₃ antisymmetric stretching modes respectively. Raman bands at 629, 638, 690, 751 and 787 cm^?1 are attributed to the SbO stretching vibrations. Raman bands at 600 and 610 cm^?1 and at 429 and 459 cm^?1 are assigned to the SO₄^2? ν₄ and ν₂ bending modes. Raman bands at 359 and 375 cm^?1 are assigned to O–Sb–O bending modes. Multiple Raman bands for both SO₄^2? and SbO stretching vibrations support the concept of the non-equivalence of these units in the coquandite structure.     

Vibrational spectroscopy of lapachol, α- and β-lapachone: Theoretical and experimental elucidation of the Raman and infrared spectra

Raman and infrared spectroscopy were applied for the vibrational characterization of lapachol and its pyran derivatives, α-lapachone and β-lapachone. Experimental spectra of solid state samples were acquired between 4000 and 100 cm⁻¹ in Raman experiments, and between 4000 and 600 cm⁻¹ (mid-infrared) and 600–100 cm⁻¹ (far-infrared) with FTIR spectroscopy, respectively. Full structure optimization and theoretical vibrational wavenumbers were calculated at the B3LYP/6-31 + + G(d,p) level. Detailed assignments of vibrational modes in an experimental and theoretical spectra were based on potential energy distribution analyses, using Veda 4.1 software. Clear differentiation between the three compounds was verified in the region between 1725 and 1525 cm⁻¹, in which the ν(CO) and ν(CC) modes of the quinone moiety were assigned.     

Investigation of the phonon band gap effect on Raman-active optical phonons in SrMoO4 crystal

The phonon dispersions of SrMoO₄ crystal are calculated using the lattice dynamical calculations approach. Spontaneous Raman spectra in the SrMoO₄ were measured in the temperature range from 10 K to 295 K, and the temperature dependence of the linewidth of the B_g (95 cm⁻¹) and A_g (888 cm⁻¹) Raman modes was analyzed using the lattice dynamical perturbative approach. We found that different behaviors of these two modes in the case of temperature broadening could be attributed to the large energy band gap in the phonon spectrum resulting in different anharmonic interactions. The calculated temperature dependence of the linewidth of A_g (888 cm⁻¹) mode was well accounted for the experimental one by including both down-conversion by the cubic term and the dephasing by quartic term. The dephasing processes are increased only at high temperatures and the effect of dephasing is related to the size of a large phonon band gap.     

Structure formation of random isotactic copolymers of propylene and 1-hexene or 1-octene at rapid cooling

The effect of variation the cooling rate in a wide range between 10^?2 and 10³ K s^?1 on solidification the relaxed melt of random isotactic copolymers of propylene with low amount of 1-hexene or 1-octene has been studied. Emphasis has been placed on the structure formation at rapid cooling and an evaluation of the conditions required to permit crystallization, mesophase formation, or suppression of any ordering. The presence of low amount of either 1-hexene or 1-octene co-units in the propylene chain decreases drastically the critical cooling rate required for suppression of crystallization from about 150–200 K s^?1 in the homopolymer to about only 10 K s^?1 in the copolymers; increasing the cooling rate beyond these limits allowed mesophase formation or even generation of fully amorphous samples. The study of the kinetics of formation of specific structures is completed by a complementary analysis of the X-ray structure, morphology and superstructure of the ordered phase. The hindrance of non-isothermal crystallization and mesophase formation of random copolymers of propylene with 1-hexene or 1-octene is compared with that in propylene–1-butene copolymers; addition of only 2–3 mol% 1-hexene or 1-octene into the propylene chain leads to even larger hindrance of the ordering process than the addition of more than 10 mol% 1-butene.     

Vibrational spectroscopic characterization of the phosphate mineral series eosphorite–childrenite–(Mn,Fe)Al(PO4)(OH)2·(H2O)

The phosphate mineral series eosphorite–childrenite–(Mn,Fe)Al(PO₄)(OH)₂·(H₂O) has been studied using a combination of electron probe analysis and vibrational spectroscopy. Eosphorite is the manganese rich mineral with lower iron content in comparison with the childrenite which has higher iron and lower manganese content. The determined formulae of the two studied minerals are: (Mn_0.72,Fe_0.13,Ca_0.01)(Al)_1.04(PO₄, OHPO₃)_1.07(OH_1.89,F_0.02)·0.94(H₂O) for SAA-090 and (Fe_0.49,Mn_0.35,Mg_0.06,Ca_0.04)(Al)_1.03(PO₄, OHPO₃)_1.05(OH)_1.90·0.95(H₂O) for SAA-072. Raman spectroscopy enabled the observation of bands at 970 cm⁻¹ and 1011 cm⁻¹ assigned to monohydrogen phosphate, phosphate and dihydrogen phosphate units. Differences are observed in the area of the peaks between the two eosphorite minerals. Raman bands at 562 cm⁻¹, 595 cm⁻¹, and 608 cm⁻¹ are assigned to the ν₄ bending modes of the PO₄, HPO₄ and H₂PO₄ units; Raman bands at 405 cm⁻¹, 427 cm⁻¹ and 466 cm⁻¹ are attributed to the ν₂ modes of these units. Raman bands of the hydroxyl and water stretching modes are observed. Vibrational spectroscopy enabled details of the molecular structure of the eosphorite mineral series to be determined.     

Raman scattering study of the geometrically frustrated pyrochlore Y2Ru2O7

Geometrically frustrated pyrochlore Y₂Ru₂O₇, which shows a spin-glass-like transition at T_G ∼ 80 K, were investigated by temperature-dependent Raman scattering. Three discernable phonons appear around 315, 410, and 510 cm⁻¹ without any abrupt change in the number of Raman active modes within the temperature range of 10–300 K. Fitting each phonon with Lorentz oscillators, we analyzed the effects of temperature on the phonon frequencies and the linewidths. The temperature-dependence of the mode near 510 cm⁻¹ shows abnormal behavior below T_G, while the other two phonons follow the usual thermal effect of lattice vibration. This behavior can be understood in terms of spin–phonon coupling. Considering the atomic modulations of each phonon mode, it is conjectured that the 510 cm⁻¹ phonon mode is isotropically coupled to the spin degree of freedom, while the other modes are not.     

Investigation of anharmonicity in rotational phonon mode for BaWO4 crystal

Spontaneous Raman spectra in the BaWO₄ were measured in the temperature range from 4 K to 280 K, and the temperature dependence of the linewidth of the A_g (191 cm⁻¹) Raman mode was analyzed using the lattice dynamical perturbative approach and one-phonon density of states (PDOS). The linewidth slope for the 191 cm⁻¹ peak for an external mode is 7.2 times larger than that for the 926 cm⁻¹ peak for a breathing mode. The different behaviors of these two modes in the case of temperature broadening could be attributed to the large energy band gap in the one-phonon density of states (PDOS) resulting in different anharmonic interactions. The origin may be that the ratio of up-conversion TDOS to down-conversion TDOS for Eg mode (191 cm⁻¹) is more than that for A_g (926 cm⁻¹). The peak of the Eg mode (191 cm⁻¹) is attributed to the coupling mode both a rotation of the Barium and an out-of-phase rotation of the oxygen in x–y plane as a librational mode.     

The spectroscopic characterization of the sulphate mineral ettringite from Kuruman manganese deposits,South Africa

The mineral ettringite has been studied using a number of techniques, including XRD, SEM with EDX, thermogravimetry and vibrational spectroscopy. The mineral proved to be composed of 53% of ettringite and 47% of thaumasite in a solid solution. Thermogravimetry shows a mass loss of 46.2% up to 1000 °C. Raman spectroscopy identifies multiple sulphate symmetric stretching modes in line with the three sulphate crystallographically different sites. Raman spectroscopy also identifies a band at 1072 cm⁻¹ attributed to a carbonate symmetric stretching mode, confirming the presence of thaumasite. The observation of multiple bands in the ν₄ spectral region between 700 and 550 cm⁻¹ offers evidence for the reduction in symmetry of the sulphate anion from T_d to C_2v or even lower symmetry. The Raman band at 3629 cm⁻¹ is assigned to the OH unit stretching vibration and the broad feature at around 3487 cm⁻¹ to water stretching bands. Vibrational spectroscopy enables an assessment of the molecular structure of natural ettringite to be made.     

Pressure-tuning Raman and infrared spectra of N-thiocyanato[tris(o-tolyl)]tin(IV), (o-CH3C6H4)3SnNCS

The effect of high external pressures on the Raman and IR spectra of the title compound (I) has been examined at ambient temperature. A pressure-induced phase transition was observed at 13–16 kbar, which is most likely second-order, resulting from slight rotations of the phenyl rings and/or the CH₃ groups under the influence of pressure. No new peaks were observed in the spectra with increasing pressure indicating that no pressure-induced linkage isomerism or SnNCS⋯Sn bridging took place. The average pressure sensitivity (dν/dP) of the Raman-active vibrational modes is lower in the low-pressure region (0.23 cm⁻¹/kbar) than in the high-pressure one (0.47 cm⁻¹/kbar). In general, the IR-active modes are less sensitive to increasing pressure than are the Raman-active modes and the average dν/dP value for the IR-active modes in the low-pressure region is quite similar to that in the high-pressure region, i.e., about 0.23 cm⁻¹/kbar.     

In-plane chemical pressure in (U1−yCey)O2 studied by Raman spectroscopy

We investigate the nature of bonding and charge states in (U_1−yCe_y)O₂ (y = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) by Raman spectroscopy. Raman spectrum of UO₂ exhibits two prominent bands below 1000 cm⁻¹, a F_2g mode at 446 cm⁻¹ and a F_1u LO mode at 578 cm⁻¹. As y is increased from 0 to 0.6, the F_1u exhibits a large blue shift of 90 cm⁻¹, and from y = 0.6 to 1.0, a red shift of 54 cm⁻¹. We show that our results can be interpreted as arising from anisotropic compression/relaxation of the lattice under Ce substitution and this can give an indication of its charge states. Alternate interpretations have been given in the literature on the effect of substituents and dopants to the Raman spectra of UO₂ and CeO₂. The present interpretation of chemical stress effects can be taken as another plausible explanation.     

Polarized Raman study on the lattice structure of BiFeO3 films prepared by pulsed laser deposition

Polarized Raman spectroscopy was used to study the lattice structure of BiFeO₃ films on different substrates prepared by pulsed laser deposition. Interestingly, the Raman spectra of BiFeO₃ films exhibit distinct polarization dependences. The symmetries of the fundamental Raman modes in 50–700 cm⁻¹ were identified based on group theory. The symmetries of the high order Raman modes in 900–1500 cm⁻¹ of BiFeO₃ are determined for the first time, which can provide strong clarifications to the symmetry of the fundamental peaks in 400–700 cm⁻¹ in return. Moreover, the lattice structures of BiFeO₃ films are identified consequently on the basis of Raman spectroscopy. BiFeO₃ films on SrRuO₃ coated SrTiO₃ (0 0 1) substrate, CaRuO₃ coated SrTiO₃ (0 0 1) substrate and tin-doped indium oxide substrate are found to be in the rhombohedral structure, while BiFeO₃ film on SrRuO₃ coated Nb: SrTiO₃ (0 0 1) substrate is in the monoclinic structure. Our results suggest that polarized Raman spectroscopy would be a feasible tool to study the lattice structure of BiFeO₃ films.     

Infrared and Raman spectra of magnesium ammonium phosphate hexahydrate (struvite) and its isomorphous analogues. IX: Spectra of protiated and partially deuterated cubic magnesium caesium phosphate hexahydrate

Infrared and Raman spectra of cubic magnesium caesium phosphate hexahydrate, MgCsPO₄·6H₂O (cF100), and its partially deuterated analogues were analyzed and compared to the previously studied spectra of the hexagonal analogue, MgCsPO₄·6H₂O (hP50). The vibrational spectra of the cubic and hexagonal dimorphic analogues are similar, especially in the regions of HOH stretching and bending vibrations. In the difference IR spectrum of the slightly deuterated analogue (<5% D), one distinctive band appears at 2260 cm⁻¹ with a small shoulder at around 2170 cm⁻¹, but only one band is expected in the region of the OD stretchings of isotopically isolated HDO molecules. The small weak band could possibly result from second-order transitions (a combination of HDO bending and some libration of the same species) rather than statistical disorder of the water molecules. By comparing the IR spectra in the region of external vibrations of water molecules of the protiated compound recorded at RT (room temperature) and at LNT (liquid nitrogen temperature) and those in the series of the partially deuterated analogues, it can be stated with certainty that the bands at 924 and 817 cm⁻¹ result from librations of water molecules, rocking and wagging respectively. And the band at 429 cm⁻¹ can be safely attributed to a stretching Mg–O_w mode. In the ν₃(PO₄) and ν₄(PO₄) region in the infrared spectra, one band in each is observed, at 995 and 559 cm⁻¹, respectively. In the region of the ν₁ modes, in the Raman spectrum of the protiated compound, one very intense band was observed at 930 cm⁻¹ which is only insignificantly shifted to 929 cm⁻¹ in the spectrum of the perdeuterated compound. The band at 379 cm⁻¹ in the Raman spectrum could be assigned to the ν₂(PO₄) modes. With respect to the phosphate ion vibrations, the comparison between the two polymorphic forms of MgCsPO₄·6H₂O and their deuterated compounds shows that ν₁(PO₄) and ν₃(PO₄) appear at lower wavenumbers in the cubic phase than in the hexagonal phase. These data are in full agreement with the lower repulsion potential at the cubic lattice sites compared with that for the hexagonal lattice sites.     

Near-infrared spectroscopy as an effective tool for monitoring the conformation of alkylammonium surfactants in montmorillonite interlayers

Application of near-infrared (NIR) spectroscopy to probing the arrangement of trimethylalkylammonium cations in montmorillonite interlayers has been demonstrated. Detailed analysis of the mid-IR (MIR) and NIR spectra of montmorillonite from Jelšový Potok (JP, Slovakia) saturated with surfactants with varying alkyl chain length (even numbers of carbon atoms from C6 to C18) was performed to show the advantages of the NIR region in characterizing surfactant conformations. The position of the ν_as(CH₂), (∼2930–2920 cm⁻¹), ν_s(CH₂) (∼2860–2850 cm⁻¹), 2ν_as(CH₂) (∼5810–5785 cm⁻¹), (ν + δ)_as(CH₂) (∼4340–4330 cm⁻¹) and (ν + δ)_s(CH₂) (∼4270–4250 cm⁻¹) signals was used as an indicator of the gauche/trans conformer ratio. For all bands, a shift toward lower wavenumber on increasing the alkyl chain length from 6 to 18 carbons suggests a transition from disordered liquid-like to more ordered solid-like structures of the surfactants. The magnitude of the shift was significantly higher for 2ν_as(CH₂) (28 cm⁻¹) than for ν_as(CH₂) (8 cm⁻¹) or ν_s(CH₂) (10 cm⁻¹), showing the NIR region to be a useful tool for examining this issue. Comparison of the IR spectra of crystalline alkylammonium salts and the corresponding organo-montmorillonites demonstrated a confining effect of montmorillonite layers on surfactant ordering. For each alkyl chain length the CH₂ bands of the organo-montmorillonites appeared at higher wavenumbers than for the unconfined surfactant, thus indicating a higher disorder of the alkyl chains. The wavenumber difference between corresponding samples was always higher in the NIR than in the MIR region. All these findings show NIR spectroscopy to be useful for conformational studies.     

A Raman scattering study of structural changes in LaMn1−xCoxO3+δ system

We present results of Raman scattering studies on LaMn_1−xCo_xO_3+δ over a wide range of doping content (x = 0.1–0.75) and temperature range of 20–300 K. Powder X-ray diffraction patterns show that there is a structural change from orthorhombic to rhombohedral at x = 0.5 as x increases. Raman spectra of all LaMn_1−xCo_xO_3+δ samples show peaks near 260, 500, and 650 cm⁻¹. However, the Raman spectra are not drastically different from each other across the structural phase transition at x = 0.5. On the other hand, the peak frequencies of the modes near 260 and 500 cm⁻¹ as functions of Co content (x) show slope changes at x = 0.5. The full-width at the half-maximum (FWHM) of the mode near 650 cm⁻¹ as a function of Co content (x) shows minimum at x = 0.5. Normally, larger values of FWHM are expected at near x = 0.5, if the mode were affected by the structural disorder at the phase boundary. Therefore, it is likely due to lowest charge concentration at x = 0.5, which results in lowest screening effect. This is consistent with the fact that the intensity of the phonons is strongest at x = 0.5. As the temperature decreases, the two peaks near 500 and 650 cm⁻¹ of different Co contents, related with octahedral distortions, are found to shift to lower frequencies unlike the usual temperature behavior. However, no abrupt change in the peak frequencies and the FWHM is observed across measured temperature range, regardless of the Co content.