Order Raman Lines Research Articles

Wear performance of diamond coated WC-Co tools with a CrN interlayer

In this paper we report the wear performance of diamond coated WC-Co cutting tools with a CrN interlayer by machining Al-Si alloys. Diamond films were deposited on both WC-6%Co (Arno) and WC-10%Co (Sandvik) substrates with a CrN interlayer using the hot filament chemical vapor deposition technique. Adhesion assessment by the indentation technique shows that there was no major delamination of diamond coatings on any substrate at a load of 196N. The stress field image of the region close to the indentation marks using Raman spectral imaging shows the splitting of the first order Raman line as well as a shift in the peak position to a higher frequency. Machining experiments of diamond/CrN/WC-6%Co tools with the Al-Si alloy (AlSi17Cu4Mg) workpiece shows a wear performance of VBmax=0.1mm at tc=960s, however, their performance in impact tests was not as high. On the other hand, machining experiments of diamond/CrN/WC-10%Co tools with an Al-Si alloy workpiece showed an excellent wear performance (VBmax=0.17mm at tc=960s), alongside an improved coating-substrate interface fatigue strength. A combined study using indentation, turning and impact tests demonstrates the potential advantage of diamond coatings on WC-10%Co substrates with a CrN interlayer for machining of Al-Si alloys and other high impact applications.

TiO2/Ti1−xSnxO2 heterojunction nanowires: characterization, formation, and gas sensing performance

Tetragonal rutile TiO2/Ti1−xSnxO2 heterojunction nanowires were successfully fabricated through carbothermal reaction with hydrogen gas at 1050 °C. These heterojunction nanowires partially formed Ti1−xSnxO2 superlattice structures and SnO2 nanocrystals epitaxially grew on the TiO2 nanowire surfaces. Based on the evaluations of Gibbs free energy, all reaction processes were governed by spontaneous reactions with vapor–solid–liquid (VLS). The nanowires exhibited many defect states, such as dislocations, stacking faults, and vacancies, revealed by high-resolution transmission microscopy (HRTEM) and the cathodoluminescence spectrum. The Raman spectrum revealed obvious redshift and asymmetric broadening effects, especially in the position of A1g (604 cm−1) and Eg (427 cm−1) modes when compared with a previous study (J. M. Wu et al., J. Cryst. Growth, 2005, 281, 384.). The size-induced phonon confinement effect and the presence of dislocations with internal strain in the vicinity of the nanowire surfaces led to a downshift and broadening of the first order Raman line. The results are consistent with our observations from the HRTEM images. Operating temperatures of ∼160 °C with a gas sensitivity of ∼350% were achieved when detecting an ethanol concentration of ∼300 ppm. The material characterizations and formation mechanism are investigated in detail.

Raman spectral imaging—A nondestructive, high resolution analysis technique for local stress measurements in silicon

In this study, Raman spectral imaging is used to investigate the stress fields around Vickers indents produced with various load forces on a silicon sample. Raman spectroscopy, a chemically and structurally sensitive measuring technique, is combined with high resolution confocal microscopy, thus enabling the identification of different chemical compounds or polymorphs within a sample or in this case, the stress field around the indents. In Raman spectral imaging mode, a complete Raman spectrum is recorded at every confocal imaging point with integration times below 100 ms. The automated evaluation of spectral features (sum, peak position, width, etc.) from the large number of recorded spectra (typically 10,000–100,000 spectra) produces chemical images of the analyzed heterogeneous material, providing insight into the chemical composition of the samples studied. To demonstrate the capabilities of the Raman spectral imaging technique for semiconductor applications, Vickers indents in a crystalline silicon Si(1 1 1) wafer have been characterized by combining Raman spectral imaging with atomic force microscopy (AFM). AFM images provide the topographic structure of the indents, whereas Raman spectral images are used to generate the stress images around the Vickers indent by analyzing the shift of the first order Raman line of silicon at 520 cm −1. At load forces of 1–5 mN, only a very small deformation of the surface topography (Δ z < 30 nm) is observed. At higher load forces (10–100 mN), the depth of the indent increases to a maximum of 240 nm, leading to deformation of the silicon in the vicinity of the indent. This deformation forms a stress field around the indent. At a load force of 5 mN the compressive strain along the long edge of the indent extends over 1.5 μm from the center. With increasing load, this strain expands over several micrometers. The stress fields around the indents are composed of tensile stress at the corners of the indent and compressive strain along the edges.

Pressure Dependence of Raman Linewidth in Semiconductors

The pressure dependences of the phonon lifetimes of zone-center optical phonons of various group IV and III–V semiconductors are calculated from first principles using third-order density-functional perturbation theory. The microscopic mechanism responsible, i.e. the anharmonic decay of a phonon into phonons of different energy, is revealed and the sensitive dependence on pressure is studied in detail. The results are compared with recent measurements of the pressure dependence of the linewidths of the first order Raman lines of Si, Ge, and SiC.

Wear resistance of non-tungsten cemented carbides : Y. Pirso, P. Kallas. (Tallinn Technical Univerisity, Tallinn, Estonia)

In this paper we report the wear performance of diamond coated WC-Co cutting tools with a CrN interlayer by machining Al-Si alloys. Diamond films were deposited on both WC-6%Co (Arno) and WC-10%Co (Sandvik) substrates with a CrN interlayer using the hot filament chemical vapor deposition technique. Adhesion assessment by the indentation technique shows that there was no major delamination of diamond coatings on any substrate at a load of 196 N. The stress field image of the region close to the indentation marks using Raman spectral imaging shows the splitting of the first order Raman line as well as a shift in the peak position to a higher frequency. Machining experiments of diamond/CrN/WC-6%Co tools with the Al-Si alloy (AlSi17Cu4Mg) workpiece shows a wear performance of VBmax = 0.1 mm at tc = 960 s, however, their performance in impact tests was not as high. On the other hand, machining experiments of diamond/CrN/WC-10%Co tools with an Al-Si alloy workpiece showed an excellent wear performance (VBmax = 0.17 mm at tc = 960 s), alongside an improved coating-substrate interface fatigue strength. A combined study using indentation, turning and impact tests demonstrates the potential advantage of diamond coatings on WC-10%Co substrates with a CrN interlayer for machining of Al-Si alloys and other high impact applications.

Structurally ordered or disordered states in PbIn1/2Nb1/2O3studied by Raman spectroscopy

Abstract The first order Raman lines in the paraelectric phase for the ordered and disordered PIN crystals have been investigated. These lines disappear at a temperature where a change of thermal expansion takes place. Mechanism of this high temperature transition is related to the Pb-O chain transformation from the non-linear to the linear form.

The effects of microcrystal size and shape on the one phonon Raman spectra of crystalline semiconductors

Small physical dimensions of the scattering crystals lead to a downshift and broadening of the first order Raman line through a relaxation of the q = 0 selection rule. We consider the effect of the exact shape of the microcrystal and show that there are significant differences between spherical, columnar and thin slab microcrystals. The relationship between the width, shift and asymmetry of the Raman line is calculated and is in good agreement with available experimental data.

Defect induced fluctuations in Li:KTaO3

Abstract We present experimental results of dielectric and birefringence measurements on 3.5% and 8% Li:KTaO3 as a function of temperature. These results indicate that the 8% Li: KTaO3 sample undergoes a ferroelectric phase transition at 97K. The 3.5% sample seems to undergo a distortive transition at ∼75K. Preliminary measurements of the dependence of the dielectric constant on the electric field and temperature indicate that the distortive and ferroelectric domains are not identical. These results may explain the strange ferroelectric properties of this system. Raman experiments show that the splitting of the TO1 mode of the 8% Li sample extrapolates to zero at ∼97K supporting the conclusion that this sample undergoes a phase transition at this temperature. Raman spectra of both samples at temperatures above the phase transition or freezing temperatures exhibit in addition to second order Raman features first order Raman lines. These lines have the properties of fluctuation induced first order Raman sca...

Defect induced fluctuations in Li?KTaO3

We present experimental results of dielectric and birefringence measurements on 3.5% and 8% Li∶KTaO3 as a function of temperature. These results indicate that the 8% Li∶KTaO3 sample undergoes a ferroelectric phase transition at 97 K. The 3.5% sample seems to undergo a distortive transition at ∼75 K. Raman experiments show that the splitting of the TO1 mode of the 8% Li sample extrapolates to zero at ∼97 K supporting the conclusion that this sample undergoes a phase transition at this temperature. Raman spectra of both samples at temperatures above the phase transition or freezing temperatures exhibit in addition to second order Raman features first order Raman lines. These lines have the properties of fluctuation induced first order Raman scattering. Measurement of the integrated intensity of these lines is used to obtain the temperature dependence of the fluctuation intensity. The results are compared to the Halperin and Varma theory. The data obtained for the 3.5% Li sample partialy fits the theory. However the results for the 8% Li sample do not fit the theory. The misfit is attributed to the overlap of defect zones.

The second order Raman spectrum of liquid tetrachloroethylene

AbstractThe Raman spectrum of liquid tetrachloroethylene in a capillary cell of 20 m length was recorded and about 20 new second order Raman lines were detected in addition to the previously known ones. Using a rectangular cell the depolarization ratios of many of the second order lines were determined and an assignment is given.

Defect induced fluctuations in the paraelectric phase of KTa0.94Nb0.06O3

First order Raman lines observed in the paraelectric phase of KTa0.94Nb0.06O3 are shown to be the result of odd symmetry microdistortions or fluctuations with a correlation length that extends to several unit cells. The possibilities that the lines result from impurity induced or disorder induced Raman scattering are considered and discarded. From simple theoretical considerations it is shown that the integrated intensity of distortion induced first order Raman lines, normalized by the corresponding phonon occupation numbers, is proportional to the average distortion intensity. This proportionality is independent of the correlation length of the distortion field provided it is larger than a certain minimum.

Pressure dependence of the impurity soft modes in Li and Na : KTaO 3

Low energy Raman scattering measurements on samples of K 0.76Na 0.24TaO 3, K 0.9Na 0.1TaO 3 and K 0.75Li 0.25TaO 3 under hydrostatic pressures of up to 60 kbar supply confirming evidence to the hypothesis that the Na + ions in these crystals are displaced from the centers of the sites they occupy. The pressure Raman experiments also reveal another second order Raman line interpreted as Raman scattering by two TA phonons at M. A line induced by the substitution of Na for K is found to have an energy about equal to the energy of this new second order Raman line. It is shown that if this is a resonant mode it must be an even mode.

Observation of an anomolously sharp feature in the 2nd order Raman spectrum of graphite

The second order Raman spectrum of graphite is shown to exhibit an anomolously sharp feature at an energy higher than twice the energy of the first order Raman line. This feature is compared to the 2667 cm -1 band in the second order Raman spectrum of diamond and is discussed in terms of a two-phonon bound state and ordinary overtone scattering. Also this feature serves to discriminate between current lattice dynamics calculations of graphite.

Raman Effect in Selenium–Tellurium Mixed Crystals

AbstractThe Raman effect in selenium–tellurium mixed crystals has been studied. Four first order Raman lines have been observed and associated with long wavelength lattice modes of the alloy system. The experimental results together with existing infrared data indicate that the long wavelength modes from three of the six optical branches in these trigonal crystals show “multimode behaviour” while the other three branches show “one mode behaviour”. All the experimental data are compared to and discussed in connection with an existing random‐element‐isodisplacement model calculation of the eigenfrequencies of the lattice modes as a function of composition. The calculated frequencies and the predictions of the model for the behaviour of the long wavelength lattice modes are in, at least, qualitative agreement with the experimental data.

Line shape and temperature dependence of the first order Raman spectrum of diamond

It is shown that a modified Voigt profile best represents the first order Raman line shape of diamond. The temperature dependence of the peak position and the width of this spectrum has been measured in the temperature range of 25–1000 K. The shift of the peak position can be almost fully accounted for by thermal expansion alone. A small contribution due to anharmonic effects becomes evident for temperatures above 700 K. The half-width data agree well with a two-phonon decay process.

Raman Spectrum of Pure and Impurity Doped RbCl Crystals

In this paper we report results concerning the second order Raman spectrum in pure RbCl crystals and the impurity induced first order Raman spectra in these crystals. The impurities used were thallium and copper. The observed experimental results are compared with earlier theoretical and infrared work. Three first order Raman lines at 86,100 and 125 cm -1 arising due to the break of symmetry in the host lattice because of the presence of an impurity are reported.

Frequency shifts in the Raman lines due to the high-frequency Stark effect

Experimental observations are reported on the shifts of the first order Raman lines arising from the Stark effect produced by a large field. The effect was pointed out by Javan.

The First Order Raman Effect in Crystals, particularly in Diamond

The theory of the first order Raman effect in crystals is presented in a form which takes into account the finiteness of the wavelength of the incident radiation. The theory is applied to calculate the relative intensities of the first order Raman line and of the Brillouin components of diamond, which are interpreted as the Stokes and anti-Stokes Raman lines produced by those elastic vibrations, whose wave vector Q fulfils the condition Q=Q"-Q'. (Q' and Q" are the wave vectors of the incident and scattered radiation.) The calculated intensities are in good agreement with experiments of Krishnan. A formula derived by Leontowitsch and Mandelstamm is discussed and is shown to be inadequate to calculate the intensities of the Brillouin components

Raman spectra of the second order in crystals

The importance of the study of the second order Raman spectra in crystals for getting a deeper insight into dynamical and optical properties of crystals has been pointed out. The previous work on the Raman effect in calcite has been briefly reviewed. Using the 2536.5 A.U. mercury resonance radiation, the first and second order Raman spectra of calcite have been photographed. As has already been reported the first order spectrum consists of five lines. The frequency shifts and widths of these have been accurately measured. The second order spectrum exhibits a series of eleven lines of varying intensity and width. The frequency shifts of these lines are 221, 864, 1065, 1360, 1583, 1750,2147,2172.5,2220,2310 and 2500 cm -1 . Some of these appear also in the infra-red absorption spectrum of calcite with very nearly the same freequncies. On the basis of the group theoretical analysis given by Bhagavantam, the observed second order Raman lines have been assigned as some of the octaves and allowed combinations of the fundamental frequencies of vibration of the calcite lattice. The existence of Brillouin components along with the unmodified radiation in the light scattered by the crystal of calcite has been demonstrated in a very simple way. A complete bibliography on the Raman effect and infra-red studies in calcite is also included.

The second order Raman spectrum of diamond

Using an exceptional1y colourless plate of diamond of the ultra-violet transparent type and the λ2536.5 resonance radiation of mercury as exciter, the author has photographed the second order Raman spectrum of diamond with greatly increased intensity and much better resolved than any recorded hitherto. The spectrum exhibits ten distinct Raman lines with frequency shifts 2176, 2190, 2225, 22531 2299, 2330, 2430, 2460, 2502 and 2666 cm-1. The frequency shifts of the first five lines, in particular, correspond very closely with the positions of a set of five absorption peaks observed by Robertson, Fox and Martin while exploring the absorption band in the region 4-4.8 μ with the aid of a concave grating of the echelette type. Of the ten observed second order Raman lines, the more intense and prominent ones have been identified as octaves of the prominent lattice frequencies of diamond appearing in the luminescence and absorption spectra. These facts are irreconcilable with the consequences of the Born lattice dynamics. They can, however, be satisfactorily explained on the basis of the Raman dynamics of crystal lattices. The relative intensities of the second order Raman lines, as well as the ratios of the intensities of the Stokes, the anti-Stokes and the octave of the principal Raman shift of 1332 cm-1 have been estimated by photographic photometry.