A facile strategy for the fabrication of uniform CdS nanowires with high yield and its controlled morphological growth with the assistance of PEG in hydrothermal route

A series of novel wurtzite cadmium sulphide (CdS) nanowires with uniform diameter were synthesized by using a rapid and simple solvothermal route. CdS nano structures with certain morphology could be selectively produced by only varying the concentration of poly ethylene glycol (PEG) as a surfactant in the reaction system with cadmium acetate, sulphur powder and ethelynediamine (EDA). We extensively studied UV-vis absorption spectra, photoluminescence spectra after confirming CdS nanowires with diameter 24-25 nm and length ranging up to several nano meters by field emission scanning electron microscopy (FE-SEM). Therefore we may definitely propose a new formation mechanism of CdS nanowires assisted by PEG with its illustrating optical properties.     

High‐pressure Raman and photoluminescence of highly anisotropic CdS nanowires

Raman and photoluminescence of CdS nanowires of diameter 80 nm and lengths up to several tens of micrometers were studied at pressure up to 60 kbar using a Jobin‐Yvon T64000 micro‐Raman system in conjunction with the diamond‐anvil cell technique. The phase transition pressure of wurtzite to rock salt was observed at 38 kbar, which is higher than that of bulk CdS. In contrast with the transition pressure of different‐sized CdS nanocrystal, this elevated phase transition pressure cannot be explained well by the size effect. Thus the contribution of particle morphology of such a system, which represents the low‐energy surface structure, should be considered. The pressure dependence of photoluminescence is also discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Raman spectroscopy of collective modes in charge‐density‐wave systems: the mean‐field microscopic theory

The electron‐mediated coupling of external electromagnetic fields and Raman‐active oscillations is derived for a general electronic model with multiple bands using the adiabatic approach and the explicit diagrammatic approach. The theory is illustrated on the quasi‐one‐dimensional (Q1D) quarter‐filled charge‐density‐wave (CDW) model. It is shown how the long‐range Coulomb forces and the single‐electron relaxation processes affect the Raman spectroscopy of the amplitude‐oscillation mode in clean CDW systems. It is also argued that the adiabatic treatment of the photon‐phonon coupling functions can be safely used in this case. Copyright © 2008 John Wiley & Sons, Ltd.     

Simple method to prepare size‐controllable gold nanoparticles in solutions and their applications on surface‐enhanced Raman scattering

We report here, for the first time, a simple method to prepare size‐controllable Au nanoparticles (NPs) in aqueous solutions from bulk Au substrates. First, chitosan (Ch)‐capped Au‐containing complexes were prepared by electrochemical oxidation–reduction cycles in 0.1 N NaCl and 1 g/l Ch solutions. Then the solutions were heated from room temperature to boiling at different heating rates to synthesize size‐controllable Au NPs. The particle sizes of the prepared Au(111) NPs could be controlled from 5 to 30 nm with an increase of the heating rate during preparation. Experimental results indicate that the prepared Au(111) NPs with diameters ranging from 10 to 30 nm can serve as surface‐enhanced Raman scattering active probes for molecules of rhodamine 6G. Copyright © 2010 John Wiley & Sons, Ltd.     

The importance of gold‐electrode‐adjacent stationary high‐field Böer domains for the photoconductivity of CdS

When the electron density decreases stronger than linearly with the electric field in photoconductive CdS due to field quenching, high‐field domains must occur that remain attached to either the cathode or anode in slit electrode geometry with blocking cathodes. These Böer domains¹ are easily seen by their shift in optical absorption due to the Franz‐Keldysh effect and offer unique opportunities to analyze field dependent parameters within the range of constant electron density and electric field, such as the carrier density or mobility as a function of the field, and give information of the light dependent work function. They also provide insight why a 200 Å thick cover layer of CdS on top of a CdTe solar cell increases its efficiency from 8 to 16% . The behavior of these Böer domains escapes conventional current voltage analyses except for their visual observation, while other high‐field domains with their current fluctuations or oscillations are easily observed and are the subjects of thousands of publications and many books. In this review we will exclude detailed discussion of dynamic domains, but include some new specifics that help to understand the mechanisms of the Böer domains and their applications. Only properties at low optical excitation intensities are discussed that exclude Joules heating. Within the p‐type regime of the anode‐adjacent domain extremely steep electronic quenching signal becomes visible that could signalize an intrinsic donor level slightly above the middle of the band gap that may be responsible for not allowing CdS to ever become p‐type by doping.

     

Excited‐state structural dynamics and vibronic coupling of 1,3‐dithiole‐2‐thione—resonance Raman spectroscopy and density functional theory calculation study

1,3‐Dithiole‐2‐thione (DTT) was synthesized and characterized using NMR, FT‐Raman, FT‐IR, UV spectroscopies. Resonance Raman spectra (RRs) were obtained with 341.5, 354.7 and 368.9 nm excitation wavelengths and density functional calculations were done to elucidate the electronic transitions and the RRs of DTT in cyclohexane solution. The RRs indicate that the Franck‐Condon region photodynamics is predominantly along the CS stretch+ H‐CC‐H scissor υ₄, accompanied by the H‐CC‐H scissor υ₃, S‐C‐S symmetric stretch υ₆, CC stretch υ₂, and overtone of the non‐totally symmetric SC‐S2 out‐of‐plane deformation 2υ₁₁. The excited‐state dynamics and the force constant of CS stretch calculated by the RRs were discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Evidences of the evolution from solid solution to surface segregation in Ni‐doped SnO2 nanoparticles using Raman spectroscopy

Ni‐doped SnO₂ nanoparticles, promising for gas‐sensing applications, have been synthesized by a polymer precursor method. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) data analyses indicate the exclusive formation of nanosized particles with rutile‐type phase (tetragonal SnO₂) for Ni contents below 10 mol%. The mean crystallite size shows a progressive reduction with the Ni content. Room‐temperature Raman spectra of Ni‐doped SnO₂ nanoparticles show the presence of Raman active modes and modes activated by size effects. From the evolution of the A_1g mode with the Ni content, a solubility limit at ∼2 mol% was estimated. Below that content, Raman results are consistent with the occurrence of solid solution (ss) and surface segregation (seg.) of Ni ions. Above ∼2 mol% Ni, the redshift of A_1g mode suggests that the surface segregation of Ni ions takes place. Disorder‐activated bands were determined and their integrated intensity evolution with the Ni content suggest that the solid‐solution regime favors the increase of disorder; meanwhile, that disorder becomes weaker as the Ni content is increased. Copyright © 2010 John Wiley & Sons, Ltd.     

Photodissociation effects on pulsed laser deposited silver oxide thin films: surface‐enhanced resonance Raman scattering

Temporal Raman scattering measurements with 488, 532 and 632 nm excitation wavelengths and normal Raman studies by varying the power (from 30 W/cm² to 2 MW/cm²) at 488 nm were performed on silver oxide thin films prepared by pulsed‐laser deposition. Initially, silver oxide Raman spectra were observed with all three excitation wavelengths. With further increase in time and power, silver oxide photodissociated into silver nanostructures. High‐intensity spectral lines were observed at 1336 ± 25 and 1596 ± 10 cm⁻¹ with 488 nm excitation. No spectral features were observed with 633 nm excitation. Surface‐enhanced resonance Raman scattering theory is used to explain the complex behavior in the intensity of the 1336/1596 cm⁻¹ lines with varying power of 488 nm excitation. Copyright © 2011 John Wiley & Sons, Ltd.     

Label‐free optical detection of type II diabetes based on surface‐enhanced Raman spectroscopy and multivariate analysis

Surface‐enhanced Raman scattering (SERS) spectroscopy was first employed to detect oxyhemoglobin (OxyHb, the common type of hemoglobin) variation in type II diabetic development without using exogenous reagents. Using silver nanoparticles as SERS‐active substrate, high‐quality SERS spectra are obtained from blood OxyHb samples of 49 diabetic patients and 40 healthy volunteers. Tentative assignment of the observed SERS bands indicates specific structural changes of OxyHb molecule in diabetes, including heme transformation and globin variation. Furthermore, partial least squares and principal component analysis combined with linear discriminate analysis diagnostic algorithms are employed to analyze and classify the SERS spectra acquired from diabetic and healthy OxyHb, yielding the diagnostic accuracies of 90.0% and 95.5%, respectively. This exploratory work suggests that the silver nanoparticles‐based OxyHb SERS method in combination with multivariate statistical analysis has great potential for the label‐free detection of type II diabetes. Copyright © 2014 John Wiley & Sons, Ltd.     

Observation of resonance electronic and non‐resonance‐enhanced vibrational natural Raman optical activity

Natural resonance electronic Raman optical activity (ROA) is observed for the first time. Coincidently, the first example of vibrational ROA enhanced by low‐lying electronic transition is reported. These new phenomena were measured using the rare‐earth complex Eu(tfc)₃ (+)‐tris[3‐trifluoroacetyl‐D ‐camphorato]europium(III), where electronic resonance occurs between the 532‐nm laser excitation and the ⁷F₁ → ⁵D₁ transition of the Eu³⁺ metal center. Electronic Raman spectra involve the Raman transitions terminating on the low‐lying electronic states of Eu(tfc)₃. The observed vibrational ROA spectra are enhanced relative to typical ROA spectra by the proximity of vibrational states of Eu(tfc)₃ to its low‐lying electronic states with significant magnetic‐dipole character, whereas the parent vibrational Raman spectra do not appear to be resonance‐enhanced since the 532‐nm vibrational Raman spectrum has similar relative intensities to the corresponding Raman spectrum measured with 1064‐nm laser excitation. Copyright © 2010 John Wiley & Sons, Ltd.     

Bichromophoric behavior of nitrophenyl‐triazene anions: a resonance Raman spectroscopy investigation

Highly delocalized molecular frameworks with intense charge transfer transitions, known as push‐pull systems, are of central interest in many areas of chemistry, as is the case of nitrophenyl‐triazene derivatives. The 1,3‐bis(2‐nitrophenyl)triazene and 1,3‐bis(4‐nitrophenyl)triazene were investigated by electronic (UV‐Vis) and resonance Raman (RR) spectroscopies. The bichromophoric behavior of 1,3‐bis(4‐nitrophenyl)triazene anion opens the possibility of tuning with visible radiation, two distinct electronic states. The RR profiles of nitrophenyl‐triazene derivatives clearly show that the first allowed electronic state can be assigned to a charge transfer from the ring π system to the NO₂ moiety (ca 520 nm), while the second, as a charge transfer from N₃⁻ to the aromatic ring (ca 390 nm). In the para‐substituted derivative, a more efficient electron transfer and a greater energy separation between the two excited states are observed. Copyright © 2008 John Wiley & Sons, Ltd.     

Studies on the resonance Raman spectra of polyaniline obtained with near‐IR excitation

The effects of near‐IR (NIR) laser power over the Raman spectra of poly(aniline) emeraldine salt (PANI‐ES) and base (PANI‐EB) were investigated. The reasons for the existence of several bands from 1324 to 1500 cm⁻¹ in the Raman spectra of poly(aniline) obtained at NIR region were also studied. The bands from 1324 to 1375 cm⁻¹ were associated to νC N of polarons with different conjugation lengths and the bands from 1450 to 1500 cm⁻¹ in Raman spectra of PANI emeraldine and pernigraniline base forms were correlated to νCN modes associated with quinoid units having different conjugation lengths. The increase of laser power at 1064.0 nm causes the deprotonation of PANI‐ES and the formation of cross‐linking segments having phenazine and/or oxazine rings. For PANI‐EB only a small spectral change is observed when the laser power is increased, owing to the low absorption of this form in the NIR region. Copyright © 2007 John Wiley & Sons, Ltd.     

Resonance Raman spectroscopic and density functional theory investigation of the excited state structural dynamics of 2‐mercapto‐1‐methylimidazole

The resonance Raman spectroscopy in conjunction with the density functional theory calculations were used to study the excited state structural dynamics of 2‐mercapto‐1‐methylimidazole (MMI). The experimental UV absorption bands were assigned according to the time‐dependent density functional calculations. The vibrational assignments were done for the A‐band resonance Raman spectra of MMI in water and acetonitrile on the basis of the Fourier transform infrared (FT‐IR) and FT‐Raman measurements in solid, in water and in acetonitrile and the corresponding B3LYP/6‐311+G(d, p) computations. The dynamic structures of MMI were obtained by analysis of the resonance Raman intensity pattern and normal mode analysis. The differences in the dynamic structures of MMI and thiourea were revealed and explained. The structural dynamic of MMI was found to be similar to that of 2‐thiopyrimidone in terms of major reaction coordinates and thus favored the intra‐molecular proton transfer reaction. Copyright © 2012 John Wiley & Sons, Ltd.     

DFT simulations and vibrational analysis of FTIR and FT‐Raman spectra of 2‐amino‐4,6‐dihydroxypyrimidine

This work deals with the vibrational spectroscopy of 2‐amino‐4,6‐dihydroxy pyrimidine (ADHP) by means of quantum chemical calculations. The mid‐ and far FTIR and FT‐Raman spectra were measured in the condensed state. The fundamental vibrational wavenumbers and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6‐311 + G** methods and basis set combinations, and were scaled using various scale factors, which yielded good agreement between the observed and calculated wavenumbers. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on the scaled density functional force field. The results of the calculations were applied to simulate the infrared and Raman spectra of the title compound, which showed excellent agreement with the observed spectra. Copyright © 2008 John Wiley & Sons, Ltd.     

UV resonance Raman study of TrpZip2 and related peptides: π‐π interactions of tryptophan

Aromatic interactions are important stabilizing forces in proteins but are difficult to detect in the absence of high‐resolution structures. Ultraviolet resonance Raman spectroscopy is used to probe the vibrational signatures of aromatic interactions in TrpZip2, a synthetic β‐hairpin peptide that is stabilized by edge‐to‐face and face‐to‐face tryptophan π‐π interactions. The vibrational markers of isolated edge‐to‐face π‐π interactions are investigated in the related β‐hairpin peptide W2W11. The bands that comprise the Fermi doublet exhibit systematic shifts in position and intensity for TrpZip2 and W2W11 relative to the model peptide, W2W9, which does not form aromatic interactions. Additionally, hypochromism of the B_b absorption band of tryptophan in TrpZip2 leads to a decrease in the relative Raman cross‐sections of B_b‐coupled Raman bands. These results reveal spectral markers for stabilizing tryptophan π‐π interactions and indicate that ultraviolet resonance Raman may be an important tool for the characterization of these biological forces. Copyright © 2012 John Wiley & Sons, Ltd.     

Changes in the vibrational modes of carbon nanotubes induced by electron‐beam irradiation: resonance Raman spectroscopy

Influence of electron‐beam (e‐beam) irradiation on multi‐walled (MW) and single‐walled (SW) carbon nanotube films grown by microwave chemical vapor deposition technique is investigated. These films were subjected to an e‐beam energy of 50 keV from a scanning electron microscope for 2.5, 5.5, 8.0, and 15 h, and to 100 and 200 keV from a transmission electron microscope for a few minutes to ∼2 h continuously. Such conditions resemble an increased temperature and pressure regime enabling a degree of structural fluidity. To assess structural modifications, they were analyzed prior to and after irradiation using resonance Raman spectroscopy (RRS) in addition to in situ monitoring by electron microscopy. The experiments showed that with extended exposures, both types of nanotubes displayed various local structural instabilities including pinching, graphitization/amorphization, and formation of an intramolecular junction (IMJ) within the area of electron beam focus possibly through amorphous carbon aggregates. RRS revealed that irradiation generated defects in the lattice as quantified through (1) variation of the intensity of radial breathing mode (RBM), (2) intensity ratio of D to G band (I_D/I_G), and (3) positions of the D and G bands and their harmonics (D* and G*) and combination bands (D + G). The increase in the defect‐induced D band intensity, quenching of RBM intensity, and only a slight increase in G band intensity are some of the implications. The MW nanotubes tend to reach a state of saturation for prolonged exposures, while the SW ones transform from a semiconducting to a quasi‐metallic character. Softening of the q = 0 selection rule is suggested as a possible reason to explain these results. Furthermore, these studies provide a contrasting comparison between MW and SW nanotubes. Copyright © 2006 John Wiley & Sons, Ltd.     

Beam‐size‐related phenomena and effective normalization in energy‐dispersive EXAFS for the study of heterogeneous catalysts,powder materials and the processes they mediate: observations and (some) solutions

The effects of focal spot size and the nature of powder samples (such as heterogeneous catalysts) on the quality of data obtainable from a dispersive EXAFS experiment are characterized at ID24 of the ESRF. Using examples of supported Pd catalysts, it is shown that, for a given photon flux, massive improvements in data quality can be achieved by increasing the size of the dispersive beam in the vertical, whilst concurrently applying a methodology to account for scattering effects emanating from the samples under study. These improvements are demonstrated using progressively practical and demanding examples. Questions regarding optimal beam dimensions for the study of such materials, how to counter undesirable effects that arise from the coherence of the source, how to obtain similar results consistently across the 5–30 keV bandwidth of ID24, and whether a methodology for simultaneous normalization in dispersive EXAFS is of significant utility in such circumstances are discussed.     

Experimental and theoretical FT‐IR and FT‐Raman spectroscopic analysis of N1‐methyl‐2‐chloroaniline

In this work, the experimental and theoretical vibrational spectra of N1‐methyl‐2‐chloroaniline (C₇H₈NCl) were studied. FT‐IR and FT‐Raman spectra of the title molecule in the liquid phase were recorded in the region 4000–400 cm^?1 and 3500–50 cm^?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method (B3LYP) with the 6‐311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT‐IR and FT‐Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. ¹³C and ¹H NMR chemical shifts results were compared with the experimental values. The optimized geometric parameters (bond lengths and bond angles) were given and are in agreement with the corresponding experimental values of aniline and p‐methyl aniline. Copyright © 2008 John Wiley & Sons, Ltd.     

Time‐resolved resonance Raman and density functional theory study of the photochemistry of 4‐benzoylpyridine in acetonitrile and 2‐propanol

A nanosecond time‐resolved resonance Raman (ns‐TR³) spectroscopic investigation of the intermolecular hydrogen‐abstraction reaction of the triplet state of 4‐benzoylpyridine (4‐BPy) in 2‐propanol solvent is reported. The TR³ results reveal a rapid hydrogen abstraction (<10 ns) by the 4‐BPy triplet state (nπ*) with the 2‐propanol solvent, leading to formation of a 4‐BPy ketyl radical and an associated dimethyl ketyl radical partner from the solvent. The recombination of these two radical species occurs with a time constant about 200 ns to produce a para‐N‐LAT (light absorbing transient). The structure, major spectral features, and identification of the ketyl radical and the para‐N‐LAT coupling complex have been determined and confirmed by comparison of the TR³ results with results from density functional theory (DFT) calculations. A reaction pathway for the photolysis of 4‐BPy in 2‐propanol deduced from the TR³ results is also presented. The electron‐withdrawing effect of the heterocyclic nitrogen for 4‐BPy on the triplet state makes it have a significantly higher chemical reactivity for the hydrogen abstraction with 2‐propanol compared to the previously reported corresponding benzophenone triplet reaction under similar reaction conditions. In addition, the 4‐BPy ketyl radical reacts with the dimethyl ketyl radical to attach at the para‐N atom position of the pyridine ring to form a cross‐coupling product such as 2‐[4‐(hydroxy‐phenyl‐methylene)‐4h‐pyridin‐1‐yl]‐propan‐2‐ol instead of attacking at the para‐C atom position as was observed for the corresponding benzophenone reaction reported in an earlier study. Copyright © 2008 John Wiley & Sons, Ltd.     

Density functional theory study and vibrational analysis of FT‐IR and FT‐Raman spectra of N‐hydroxyphthalimide

The Fourier transform infrared (FT‐IR) spectrum of N‐hydroxyphthalimide has been recorded in the range of 4000–400 cm⁻¹, and the Fourier transform Raman (FT‐Raman) spectrum of N‐hydroxyphthalimide has been recorded in the range of 4000–50 cm⁻¹. With the hope of providing more and effective information on the fundamental vibrations, the Density Functional Theory (DFT)‐Becke3‐Lee‐Yang‐Parr (B3LYP) level with 6‐31G* basis set has been employed in quantum chemical analysis, and normal coordinate analysis has been performed on N‐hydroxyphthalimide by assuming C_s symmetry. The computational wavenumbers are in good agreement with the observed results. The theoretical spectra obtained along with intensity data agree well with the observed spectra. Copyright © 2009 John Wiley & Sons, Ltd.