B2 Modes Research Articles

Raman spectra of CuGa3Te5 ordered‐defect compound

Raman spectra of CuGa3Te5 that has a chalcopyrite‐related structure with space group P2c were obtained at room temperature from measurements performed under parallel (z|xx|z) and perpendicular (z|xy|z) polarization dependent configurations. A tentative assignment of the observed lines was made by comparison with the reported phonon modes for ZnTe, which is the binary analogue of CuGaTe2, and also by using theoretical models reported in the literature for multinary compounds. The main lines observed at 129, 144, and 187 cm−1 were assigned to the three A1‐symmetry modes for P2c ternary compounds predicted by group theory, and other lines at 91 and 277–285 cm−1 to the B1 modes. Also, lines at 55, 64, 102, 172, 224, 265–269, and 333–334 cm−1 and lines at 78, 172, 224, 205–209, 242–249, and 342 cm−1 were assigned to E and B2 modes, respectively. The higher‐phonon frequencies observed at 291–297, 303–310, and 319–323 cm−1 are attributed to an overtone of the A1 mode at 144 cm−1, and a combination of A1 and E modes, respectively.

Charge-Transfer-Induced Enantiomer Selective Discrimination of Chiral Alcohols by SERS

In our previous study, we proposed a label-free enantioselective discrimination methodology for chiral alcohols based on surface-enhanced Raman scattering (SERS) spectroscopy. This method does not use either chiral reagents or circularly polarized light (chiral light). In the present study, a series of SERS experiments were carried out with an achiral SERS probe molecule, p-aminobenzenethiol (PATP), as the chiral selector molecule to develop this method further and to explore the possible mechanism of enantioselective discrimination. The relative intensities of the nontotally symmetric (b2 mode) bands in the SERS spectra of PATP change depending on the presence of different enantiomeric environments, which is a manifestation of charge transfer (CT) processes. From laser excitation wavelength-dependent and concentration-dependent SERS experiments, we have further verified that this CT-induced chiral discrimination magnifies the differences between two chiral alcohol enantiomers interacting with PATP by SER...

Influence of Capping Ligand and Synthesis Method on Structure and Morphology of Aqueous Phase Synthesized CuInSe2 Nanoparticles

A facile route to synthesize copper indium diselenide (CuInSe2) nanoparticles in aqueous medium was developed using mercaptoacetic acid (MAA) as capping agent. Two different mole ratios (5 and 10) of MAA were used to synthesize CuInSe2 nanoparticles at room temperature, as well as hydrothermal (high temperature) method. Powder x-ray diffraction analysis reveals that the nanoparticles exhibit chalcopyrite phase and the crystallinity increases with increasing the capping ratio. Raman analysis shows a strong band at 233 cm−1 due to the combination of B2 (E) modes. Broad absorption spectra were observed for the synthesized CuInSe2 nanoparticles. The effective surface capping by MAA on the nanoparticles surface was confirmed through attenuated total reflection–Fourier transform infrared spectral analysis. The thermal stability of the synthesized samples was analyzed through thermogravimetric analysis–differential scanning calorimetry. The change in morphology of the synthesized samples was analyzed through scanning electron microscope and it shows that the samples prepared at room temperature are spherical in shape, whereas hydrothermally synthesized samples were found to have nanorod- and nanoflake-like structures. Transmission electron microscope analysis further indicates larger grains for the hydrothermally prepared samples with 10 mol ratio of MAA. Comparative analyses were made for synthesizing CuInSe2 nanoparticles by two different methods to explore the role of ligand and influence of temperature.

Plastic deformation induced nano-scale twins in Ti-6Al-4V machined surface with high speed machining

High speed machining (HSM) is one of the plastic deformation processes in which deformation twinning is generated. The mechanism of deformation twinning formation and its effects on the work hardening of Ti-6Al-4V machined surface are revealed. First, transmission electron microscope (TEM) and electron backscattered diffraction (EBSD) experiments are conducted to observe the twinning behaviors of machined surface with different cutting speeds (50–600m/min). Then, the distributions of deformation variables including stress, strain rate and temperature in Ti-6Al-4V machined surface are analyzed to disclose the factors on the formation of deformation twinning under different cutting speeds. A simple model is established to illustrate the formation mechanism of {101¯1} twin of Ti-6Al-4V. Finally, nanoindentation technique in conjunction with x-ray diffraction and light microscopy are used to elucidate the effect of deformation twinning on the hardness evolution of Ti-6Al-4V machined surface. The TEM experimental results show that {101¯1} nano-scale twins of b1 mode generate on the machined surface under the cutting speed higher than 200m/min. High stress and strain rate are the main factors in promoting the formation of {101¯1} twin of Ti-6Al-4V machined surface. Nanoindentation experiments show that the appearance of nano-twins can enhance the hardness of machined surface. This paper proves that HSM can be applied as an efficient approach to prepare nano-twinned material by selecting appropriate cutting speed to control the emergence of deformation modes. It also reveals that nano-twins make a significant contribution to the work hardening of Ti-6Al-4V machined surface at higher cutting speed.

Electrostatic Assemblies of Well-Dispersed AgNPs on the Surface of Electrospun Nanofibers as Highly Active SERS Substrates for Wide-Range pH Sensing.

Surface-enhanced Raman scattering (SERS) has shown high promise in analysis and bioanalysis, wherein noble metal nanoparticles (NMNPs) such as silver nanoparticles were employed as substrates because of their strong localized surface plasmon resonance (LSPR) properties. However, SERS-based pH sensing was restricted because of the aggregation of NMNPs in acidic medium or biosamples with high ionic strength. Herein, by using the electrostatic interaction as a driving force, AgNPs are assembled on the surface of ethylene imine polymer (PEI)/poly(vinyl alcohol) (PVA) electrospun nanofibers, which are then applied as highly sensitive and reproducible SERS substrate with an enhancement factor (EF) of 10(7)-10(8). When p-aminothiophenol (p-ATP) is used as an indicator with its b2 mode, a good and wide linear response to pH ranging from 2.56 to 11.20 could be available, and the as-prepared nanocomposite fibers then could be fabricated as excellent pH sensors in complicated biological samples such as urine, considering that the pH of urine could reflect the acid-base status of a person. This work not only emerges a cost-effective, direct, and convenient approach to homogeneously decorate AgNPs on the surface of polymer nanofibers but also supplies a route for preparing other noble metal nanofibrous sensing membranes.

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.

Structure, Raman and infrared spectroscopic properties of new nonlinear optical material Na3VO2B6O11

In this paper we report on the structure of Na3VO2B6O11 (NVBO) single crystals which were investigated by XRD, polarized Raman spectra in the range from 10 to 1600 cm−1 and infrared spectrum (IR) in the range from 100 to 1600 cm−1. Factor group analysis has been used to study the full vibrational representation of the crystal. More than 120 phonon modes have been obtained, which are related to BO and VO vibration in the trigonal planar BO3 triangle groups and tetrahedral BO4/VO4 groups. The high frequency bands located at 1300–1415 cm−1 are assigned to stretching modes of the trigonal planar BO3 groups. Moreover, intense Raman modes located at 631 cm−1 is related to BO3 bending vibration as well. The weak band at 1158 cm−1 (A1 mode) and strong band at 431 cm−1 (A1 mode) are attributed to asymmetric stretching and bending vibration mode of tetrahedral BO4 groups respectively. The vibrational band at 765–738 cm−1 in the Raman spectra of NVBO crystal maybe related to the breathing vibration of the boroxol ring consisting of two BO4 tetrahedra. In addition, we assigned the intense band 900 (A1 mode) and 831 cm−1 (B2 mode) are relative to the v1 symmetric stretching vibration of VO4 tetrahedra. And the middle intense band at 382 (A1 mode) and 385 (A2 mode) are due to OVO vibration in VO4 tetrahedra.

Effect of the Molecule–Metal Interface on the Surface-Enhanced Raman Scattering of 1,4-Benzenedithiol

The influence of the number of molecule–metal interactions on the surface-enhanced Raman scattering (SERS) spectroscopy of 1,4-benzenedithiol (BDT) was investigated. For this purpose, a series of SERS-active samples were prepared featuring one or two molecule–metal interfaces. Molecules were adsorbed on the surface of a rough Au substrate, or sandwiched between Au nanoparticles (NPs) and a flat Au(111) substrate in a “sphere–plane” disposition. In the presence of the Au surface(s), vibrational energy and intensity of the SERS spectra differs significantly from the bulk. Molecule–metal charge transfer upon chemisorption weakens intramolecular bonds, resulting in the observed red shift of the breathing and C═C stretching modes. This effect was found to be more pronounced for samples with multiple molecule–metal interfaces. In addition, the SERS spectra of BDT featured additional b2 signals not present in the bulk spectra. Chemical enhancement of the b2 modes takes place by means of photoinduced charge transfer from an occupied molecular orbital to an unoccupied metal orbital. Analysis of the normalized SERS intensity revealed a larger scattering enhancement for the samples with a sphere–plane disposition arising from the stronger electromagnetic enhancement effect via plasmonic localization of optical fields. Complementary studies on 4-aminobenzenethiol support these findings.

Raman Spectroscopy Investigation of the Polar Vibrational Modes in CuB2O4

We report results of polarized Raman spectroscopy of piezoelectric copper metaborate CuB2O4 (space group I ¯42d, Z = 12) in the range from 80 to 1300 cm-1. Due to the dense population of the phonon spectra we carried out angular-dependent measurements by rotating the sample in different crystallographic planes thus performing gradual transitions from one polarization configuration to another. The different angular dependence of the scattering intensities of vibrational modes of different symmetries allowed us to obtain Raman signal from some transversal optical (TO) modes of E-symmetry and to demonstrate the singlemode behavior of the B2 modes by means of transition from TO character to longitudinal optical (LO) character of these phonons.

Mg doping induced high structural quality of sol–gel ZnO nanocrystals: Application in photocatalysis

Undoped and Mg doped ZnO nanocrystals (NCs) ZnO:x%Mg (x=1, 2, 3, and 5) were synthesized using sol–gel method. The structural and optical properties were investigated by X-ray diffraction (XRD), Raman spectroscopy, diffuse reflectivity, and photoluminescence (PL). XRD analysis demonstrates that all prepared samples present pure hexagonal wurtzite structure without any Mg related phases. The NCs size varies from 26.82nm to 42.96nm with Mg concentrations; it presents an optimal value for 2% of Mg. The Raman spectra are dominated by the E2high mode. For highly Mg doping (5%), the occurrence of silent B1(low) mode suggested that the Mg ions do substitute at Zn sites in the ZnO lattice The band gap energy was estimated from both Tauc and Urbach methods and found to be 3.39eV for ZnO:2%Mg. The PL spectra exhibit two emission bands in the UV and visible range. Their evolution with Mg doping reveals the reduction of defect density in ZnO at low Mg doping by filling Zn vacancies.In addition, it was found that further Mg doping, above 2%, improves the photocatalytic activity of ZnO NCs for photodegradation of Rhodamine B (RhB) under sunlight irradiation. The efficient electron–hole separation is the main factor responsible for the enhancement of photocatalytic performance of Mg doped ZnO NCs.Through this work, we show that by varying the Mg contents in ZnO, this material can be a potential candidate for both optoelectronic and photocatalytic applications.

Applied quantum chemistry: Spectroscopic detection and characterization of the F2BS and Cl2BS free radicals in the gas phase.

In this and previous work [D. J. Clouthier, J. Chem. Phys. 141, 244309 (2014)], the spectroscopic signatures of the X2BY (X = H, halogen, Y = O, S) free radicals have been predicted using high level ab initio theory. The theoretical results have been used to calculate the electronic absorption and single vibronic level (SVL) emission spectra of the radicals under typical jet-cooled conditions. Using these diagnostic predictions, the previously unknown F2BS and Cl2BS free radicals have been identified and characterized. The radicals were prepared in a free jet expansion by subjecting precursor mixtures of BF3 or BCl3 and CS2 vapor to an electric discharge at the exit of a pulsed molecular beam valve. The B̃(2)A1-X̃(2)B2 laser-induced fluorescence spectra were found within 150 cm(-1) of their theoretically predicted positions with vibronic structure consistent with our Franck-Condon simulations. The B̃(2)A1 state emits down to the ground state and to the low-lying Ã(2)B1 excited state and the correspondence between the observed and theoretically derived SVL emission Franck-Condon profiles was used to positively identify the radicals and make assignments. Excited state Coriolis coupling effects complicate the emission spectra of both radicals. In addition, a forbidden component of the electronically allowed B̃-X̃ band system of Cl2BS is evident, as signaled by the activity in the b2 modes in the spectrum. Symmetry arguments indicate that this component gains intensity due to a vibronic interaction of the B̃(2)A1 state with a nearby electronic state of (2)B2 symmetry.

A two-layer linear piezoelectric micromotor.

A first bending (B1) mode two-layer piezoelectric ultrasonic linear micromotor has been developed for microoptics driving applications. The piezo-vibrator of the micromotor was composed of two small Pb(Zr,Ti)O3 (PZT-5) plates, with overall dimensions and mass of only 2.0 × 2.0 × 5.0 mm(3) and 0.2 g, respectively. The proposed micromotor could operate either in single-phase voltage (standing wave) mode or two-phase voltage (traveling wave) mode to drive a slider via friction force to provide bidirectional linear motion. A large thrust of up to 0.30 N, which corresponds to a high unit volume direct driving force of 15 mN/mm(3), and a linear movement velocity of up to 230 mm/s were obtained under an applied voltage of 80 Vpp at the B1 mode resonance frequency of 174 kHz.

Intercalated 4-Aminobenzenethiol between Au and Ag Nanoparticles: Effects of Concentration and Nanoparticles Neighborhood on its SERS Response

In this work is reported the investigation of the 4-aminobenzenethiol (4-ABT) surface-enhanced Raman scattering (SERS) response for different 4-ABT concentrations as well as when this molecule is intercalated between Ag and Au nanoparticles (AgNP and AuNP). SERS substrates consisting of the individual AgNP or AuNP and bi-layer AgNP/4-ABT/AuNP or AuNP/4-ABT/AgNP were prepared on glass slides. It was observed a decreasing trend of the bands intensity ratios b2/a1 as a function of the 4-ABT solutions concentration. Since the b2 modes are enhanced through the charge transfer (CT) mechanism, this result indicates that this mechanism is less effective for low concentration of 4-ABT. Also, a dependence between a1 and b2-type bands intensities could be identified for the samples where 4-ABT molecules were intercalated between AgNP and AuNP. A significantly increase in the SERS intensities of the a1 mode around 1074 cm-1 and b2 mode around 1142 cm-1 is observed when AgNP are present in the samples. This result indicates that AgNP promote amplifications of the Raman signal thorough the CT and electromagnetic (EM) mechanisms, whereas for the AuNP the SERS effect is related manly to EM mechanism. These results show that the 4-ABT SERS response can provide more information than the SERS substrate activity. Its SERS signal pattern is rich in information, allowing investigations about the local where the molecule is, details about the substrate surface, and also on the mechanisms present in the system under study.

Mechanical and Vibrational Properties of ZnS with Wurtzite Structure: A First-Principles Study

We perform a first-principles study of the mechanical and vibrational properties of ZnS with a wurtzite structure. The calculated elastic constants by using a pseudopotential plane-wave method agree well with the experimental data and with the previous theoretical works. Based on the elastic constants and their related parameters, the crystal mechanical stability is discussed. Calculations of the zone-center optical-mode frequencies including longitudinal-optical/transverse-optical splitting, by using the density functional perturbation theory, are reported. All optical modes are identified, especially B1 modes, and agree with Raman measurements.

MnO2 doped PSN–PZN–PZT piezoelectric ceramics for resonant actuator application

Hard type piezoelectric ceramics of MnO2 modified 0.09Pb(Sn1/3Nb2/3)O3–0.09Pb(Zn1/3Nb2/3)O3–0.41PbZrO3–0.41PbTiO3 (PSN–PZN–PZT–M) are prepared by the traditional solid-state reaction method for power piezoelectric resonant actuator application. The optimal properties are obtained at MPB when MnO2 content is 1.5mol%, and the piezoelectric constant d33, electromechanical coupling factor kp, relative dielectric constant εr, the mechanical quality factor Qm and the Curie temperature Tc are found to be 325pC/N, 55.9%, 1311, 1250 and 313°C, respectively. A double B1 mode resonant actuator with dimensions of 15×15×2.0mm3 is then presented, and it can drive a slider moving linearly with a maximum speed of 170mm/s and a maximum load of 1.2N at resonance frequency of 89kHz under 100Vpp voltage drive. These results demonstrate that MnO2 modified PSN–PZN–PZT ceramics are promising candidates for piezoelectric resonant actuator applications.

Zero kinetic energy photoelectron spectroscopy of triphenylene.

We report vibrational information of both the first electronically excited state and the ground cationic state of jet-cooled triphenylene via the techniques of resonantly enhanced multiphoton ionization (REMPI) and zero kinetic energy (ZEKE) photoelectron spectroscopy. The first excited electronic state S1 of the neutral molecule is of A1' symmetry and is therefore electric dipole forbidden in the D3h group. Consequently, there are no observable Franck-Condon allowed totally symmetric a1' vibrational bands in the REMPI spectrum. All observed vibrational transitions are due to Herzberg-Teller vibronic coupling to the E' third electronically excited state S3. The assignment of all vibrational bands as e' symmetry is based on comparisons with calculations using the time dependent density functional theory and spectroscopic simulations. When an electron is eliminated, the molecular frame undergoes Jahn-Teller distortion, lowering the point group to C2v and resulting in two nearly degenerate electronic states of A2 and B1 symmetry. Here we follow a crude treatment by assuming that all e' vibrational modes resolve into b2 and a1 modes in the C2v molecular frame. Some observed ZEKE transitions are tentatively assigned, and the adiabatic ionization threshold is determined to be 63 365 ± 7 cm(-1). The observed ZEKE spectra contain a consistent pattern, with a cluster of transitions centered near the same vibrational level of the cation as that of the intermediate state, roughly consistent with the propensity rule. However, complete assignment of the detailed vibrational structure due to Jahn-Teller coupling requires much more extensive calculations, which will be performed in the future.

Vibrational modes and symmetry in a hexagonal-cross-section nanowire

We theoretically study acoustic phonon modes in hexagonal-cross-section nanowires with a wurtzite structure. As numerical examples, we examine the dispersion relations of solid and hollow GaN nanowires. The calculated dispersion curves are classified into six modes: A1, A2, B1, B2, E1, and E2 modes. It is found that the eigenfrequencies of the E2, B1, and B2 modes are particularly sensitive to the ratio of the inner side to outer side lengths of the hexagonal hollow nanowire.

Hydrothermal synthesis and characterization of CuInSe2 nanoparticles using ethylenediamine as capping agent

Ethylenediamine capped CuInSe2 nanoparticles were synthesized by wet chemical method at room temperature and hydrothermal method at 150°C for 2h at two different mole ratio of the capping agent. The effect of the synthesis method and ratio of the capping agent on the optical, structural, and morphology of the synthesized nanoparticles were analyzed. The optical property of the synthesized nanoparticles was estimated from the UV–Vis spectra and also from the emission spectra. The surface capping was confirmed through the FT-IR. Powder XRD analysis reveals that the nanoparticles exhibit wurtzite phase and the crystallinity increases while increasing the capping ratio and hydrothermally synthesized nanoparticles show higher crystallinity. Raman analysis shows that the hydrothermally synthesized samples exhibit B2 (LO) mode. The surface morphology was modified depending on the synthesis method and capping agent ratio (i.e.) rod like and cube like morphology were obtained for the hydrothermally synthesized nanoparticles with 5 and 10mol ratio of the capping agents respectively.

Exploring the Effect of Intermolecular H-Bonding: A Study on Charge-Transfer Contribution to Surface-Enhanced Raman Scattering of p-Mercaptobenzoic Acid

We report the significant effect of intermolecular hydrogen bonding (H-bonding) on surface-enhanced Raman scattering (SERS) spectra in which the vibrational frequencies and intensities of some characteristic peaks of p-mercaptobenzoic acid (MBA) change with varying concentrations of aniline. These changes can be attributed to modifications in the electronic structure of the MBA molecule and the conjugation of the system under the influence of H-bonding. Of remarkable note is that the nontotally symmetric (b2) mode of MBA is dramatically enhanced, which can be considered as a manifestation of the charge-transfer (CT) transition process in the system. By comparing SERS spectra obtained under normal and basic conditions, the effect caused by H-bonding can be further understood. These results manifest that the CT resonance between MBA and Ag NPs through Herzberg–Teller contributions can be promoted by H-bonding. The current work may, therefore, be instructive for studying the influence of H-bonding on the ele...

Phonon Deformation Potential Constants of Wurtzite ZnO: A First-Principles Study

ABSTRACTWe performed first-principles calculations to obtain the phonon deformation potential (PDP) constants of wurtzite ZnO. The results are in good agreement with available experimental data except for a few PDP constants. We also found that the phonon frequencies of the A1 and B2 modes have relatively stronger nonlinear characteristics than the other modes.