Peak Wavenumber Research Articles

Mid infrared emission of quantum wire cascade structures

A novel mid infrared emitting GaAs/AlGaAs quantum wire cascade device is presented that is fabricated using the cleaved edge overgrowth technique. The samples are pumped electrically. Radiative electronic transitions between discrete energy levels in coupled quantum wires are calculated for such a structure. Operation current dependent mid infrared emission is observed at a peak wave number of 1200 cm −1 with a full-width at half-maximum of 300 cm −1 at a heat sink temperature of 20 K . The presented sample is an experimental proposal for an unipolar quantum wire intersubband laser.

Equilibrium ranges in surf zone wave spectra

Laboratory measurements of two wave trains breaking on a plane slope demonstrate dramatic changes in spectral shape in the surf zone. The higher‐frequency spectral peak is completely eliminated in the surf zone, and the resulting spectral shape is similar regardless of the peak frequency and relative energy content of the higher‐frequency peak. Examination of both laboratory and field data show that surf zone wave number (k) spectra evolve to contain two equilibrium ranges. The higher‐frequency range is similar to that proposed by Toba in deeper water with the form k−5/2 and is valid for approximately k > 1/depth. The second range falls between the peak wave number and k = 1/depth and has a wave number dependence of k−4/3, similar to that proposed by Zakharov on theoretical grounds. The equilibrium range coefficients, which are a function of wind speed in deep and finite water depths, are a function of the water depth in the surf zone. The laboratory and field data sets used in these analyses covered a broad range of conditions (unidirectional and multidirectional waves, plane and barred beaches, two orders of magnitude variation in wave height, and one order of magnitude variation in wave period), yet the equilibrium ranges identified were consistent and provide a robust parameterization of surf zone wave spectra.

Fictive temperature measurement of alumino-silicate glasses using IR spectroscopy

A simple IR reflection method was used in a previous study to determine the fictive temperature of silica glasses and a soda-lime glass. The IR method is based upon the fact that the silica structural band of a glass takes a unique wavenumber at a particular fictive temperature. When this method was applied to an alumino-silicate glass in this study, however, the IR reflection peak wavenumber of the glass surface was found to be strongly affected by the reaction of the glass with water vapor in the atmosphere. Still, it was possible to measure the fictive temperature of the alumino-silicate glass using IR spectroscopy by taking an IR reflection of the bulk sample after eliminating the surface layer affected by the reaction with water vapor. The IR peak wavenumber of the silica structural band decreased with increasing fictive temperature for the alumino-silicate glass, similar to silica glass.

Intermolecular interaction in liquid dimethylformamide and its manifestation in Raman spectra

AbstractThe wavenumbers of peaks of parallel and perpendicular polarized components of the CO vibration band for dimethylformamide in the Raman spectra differ by 14.5 cm−1. The difference in wavenumber values decreases and falls to zero on strong dilution with CCl4 and dimethyl sulfoxide. A doublet structure of the band is observed in solutions with CCl4 in the 0.2 mole fraction concentration region. The above‐mentioned non‐coincidence of CO vibration band wavenumbers in pure liquid is explained by the complexity of the band, i.e. the presence within the band of two close and overlapped lines with different magnitudes of depolarization ratio belonging to monomeric molecules (high wavenumber) and aggregate formation. In a mixture at strong dilution there remains only one type of formation, and the band acquires a simple shape of a separate line, and the above‐mentioned wavenumber difference falls to zero. The experimental results are supplemented by ab initio calculations of normal vibrational wavenumbers and of some parameters for monomeric and dimeric dimethylformamide molecules. Copyright © 2003 John Wiley & Sons, Ltd.

Field-effect-induced midinfrared electroluminescence of a quantum-wire-cascade structure by remote δ-doping

We present a quantum-cascade emitter in the galliumarsenide/aluminum–galliumarsenide (GaAs/AlGaAs) heterosystem whose emission properties are controlled by an additional electric field perpendicular to the transport direction. In our case, the additional field is established by remote δ-silicon doping, which is also responsible for charge carrier supply. The field originating from the δ-doping gives rise to an in-plane confinement creating a quantum-wire cascade. This field-effect quantum-cascade emitter is realized using the cleaved edge overgrowth method. Radiative electronic transitions between discrete energy levels in coupled quantum wires were calculated for such a structure. Without an additional electric field, no significant transport is observed. With a field applied, midinfrared emission is observed at a peak wave number of 1200 cm−1 with a full width at half maximum of 300 cm−1 for a heat-sink temperature of 20 K. The presented sample is an experimental proposal for a unipolar quantum-wire intersubband laser.

IR peak shift due to phase separation of Na 2O–SiO 2 system glasses

The IR reflection peak shift of a silica structural band was found to be a sensitive measure of phase separation in glasses. In order to examine the details of the origin of the peak shift, a model system glass, Na 2O–SiO 2, with a well-established immiscibility boundary was examined. Selected glasses in the system were heat-treated for phase separation and the IR reflection peak wavenumber was measured as a function of heat-treatment time and temperature. The IR peak wavenumber approached constant values, which varied systematically with the heat-treatment temperature. The observed constant values of the IR peak wavenumber were compared with the IR peak positions of the spectra synthesized by summing spectra of separated phase compositions at appropriate molar ratios. The peak wavenumbers obtained by the synthesis agreed reasonably well with the observed values. It appears that the main cause of the phase separation-related IR peak shift is the compositional shift weighted by the fractional contribution of the separated phases.

Preparation, physical properties, on-bead binding assay and spectroscopic reliability of 25 barcoded polystyrene-poly(ethylene glycol) graft copolymers.

Here we describe the preparation of 25 beaded polystyrene-poly(ethylene glycol) graft copolymers from six spectroscopically active styrene monomers: styrene, 2,5-dimethylstyrene, 4-methylstyrene, 2,4-dimethylstyrene, 4-tert-butylstyrene, and 3-methylstyrene. These polymers were thoroughly characterized by Raman, infrared, and (1)H/(13)C NMR spectroscopies, and differential scanning calorimetry. Determination of the swelling properties, peptide synthesis, and on-bead streptavidin-alkaline phosphatase (SAP) binding assay further established that their physical and chemical properties where not significantly altered by the diversity of their encoded polystyrene core. Each of the 25 resins displayed a unique Raman and infrared vibrational fingerprint, which was converted into a "spectroscopic barcode". The position of each bar matches the peak wavenumber in the corresponding spectrum but is independent of its intensity. From this simplified representation similarity maps comparing 35 000 resin pairs were generated to establish the spectroscopic barcoding as a reliable encoding methodology. In effect, in 99% of the cases, the highest similarity coefficients were obtained for resin pairs prepared from the same styrene derivatives even after SAP binding assay. We have also shown that a small but unique combination of a resin's vibrations (30-40%) is sufficient for its identification. However, in rare cases where a resin's vibrational signature has been severely compromised, both the Raman and infrared barcodes were synergistically and reliably utilized to unequivocally identify its chemical make up.

Thermally induced micro-domain formation in fatty acid Langmuir–Blodgett films observed by attenuated total reflectance infrared spectroscopy

We have utilized attenuated total reflectance infrared (ATR-IR) spectroscopy to study the temperature dependence of conformational transitions and micro-domain structure in single- and binary-component Langmuir–Blodgett (LB) films. The single-component films such as lignoceric (C24), stearic (C18), and perdeuterated stearic (C18-d 35 ) acids, as well as binary-component films of 4:1 H:D C24:C18-d 35 and 4:1 H:D C18:C18-d 35 were studied. For C24:C18-d 35 binary films, changes in the peak wavenumber of the ν a CH 2 band after heating above the main chain melting temperature ( T m ) reflect a thermally induced de-mixing and phase separation of the C24 component from C18-d 35 . For C18:C18-d 35 LB film, heating above T m shows that C18 and C18-d 35 components do not phase segregate and retain a degree of conformational flexibility, even at low temperatures. The carbonyl CO stretching region between 1800 and 1600 cm −1 showed that each LB film contained a mixture of cis – trans ring dimer conformations at all temperatures below T m . Above T m , the LB films converted to the higher energy cis isomer, while upon further cooling the more stable trans isomer predominated. The shorter chain length C18:C18-d 35 LB film more easily crystallized the trans ring dimer after heating above T m . The band splitting of the δ CH 2 vibration at ∼1470 cm −1 was used to monitor micro-domain phase separation in these samples. For the C24:C18-d 35 binary mixture, heating the sample above T m before cooling crystallizes the C24 chains into phase-separated micro-domains. In contrast, the C18:C18-d 35 binary mixture shows that a much smaller domain size is calculated, indicative of a higher degree of chain miscibility. The shorter C18 hydrocarbon chain length produces a smaller δ CH 2 band splitting in the binary C18:C18-d 35 sample, and hence is less ordered and less crystalline than the C24 binary LB film.

Phase contrast imaging interferometer for edge density fluctuation measurements on LHD

A phase contrast interferometer employing a CO2 laser (wavelength λi=10.6 μm) is designed and installed in order to study density fluctuations on a large helical device. A 250×50 mm slab beam passes the edge of the plasma, where ρ=r/a>0.65, and provides observations of edge density fluctuations. A spatial image of the integrated fluctuations is measured by a multichannel detector array, of which the effective spacing is 5 mm in the plasma. Measured wave number components are dominated by radial components, and within the range of 7.2×10−2⩽k⩽0.63 mm−1 and within the frequency range of 5–125 kHz. A clear difference in the fluctuation levels and peak wave numbers are observed between different discharges, which differ in the energy confinement.

Observation of Nonlinear Effects in Ocean Surface Wave Frequency Spectra

Abstract Nonlinearity and directionality of an evolving open-ocean surface wave field are investigated under increasing wind forcing. In addition to the frequency wave elevation spectrum, the frequency wave slope spectrum, the bicoherence of the wave elevation time series, and the peak wavenumber at a given frequency estimated by the maximum likelihood method are examined. As the wave field matures, an increasing portion of the high-frequency components of the wave elevation spectrum becomes phase correlated with the dominant wave component. This observation clearly suggests that the contribution to the frequency spectrum from the higher harmonics generated by steep dominant waves becomes increasingly important relative to the contribution from free waves that propagate at their own phase speed predicted by the dispersion relation. The observation therefore invalidates the common assumption that an ocean surface wave spectrum is a superposition of linear surface wave components of different frequencies. I...

Effect of Hydrophobic Surfactant Proteins SP-B and SP-C on Binary Phospholipid Monolayers: II. Infrared External Reflectance-Absorption Spectroscopy

In situ external reflection infrared spectroscopy at the air-water interface was used to study the influence on phospholipid structure of an endogenous mixture of the two hydrophobic surfactant proteins, SP-B and SP-C, which are thought to play pivotal roles in the adsorption and function of pulmonary surfactant. Mixtures studied were 1:1, 2:1, and 7:1 (mol:mol) DPPC-d 62:DPPG, and 7:1 DPPC-d 62:DOPG, alone and in the presence of 0.5–10 wt % mixed SP-B/C purified chromatographically from calf lung surfactant extract. Perdeuteration of DPPC produced a shift in vibrational frequencies so that it could be differentiated spectroscopically from the phosphoglycerol component in the surface monolayer. CH 2 antisymmetric and symmetric stretching bands (∼2920 and 2852 cm −1) along with the analogous CD 2 stretching bands (∼2194 and 2089 cm −1) were analyzed, and band heights and peak wavenumber positions were assessed as a function of monolayer surface pressure. Small, near-physiological contents of 1–2 wt % SP-B/C typically produced the maximum observed spectroscopic effects, which were abolished at high protein contents of 10 wt %. Analysis of CH 2 and CD 2 stretching bands and C-H/C-D band height ratios indicated that SP-B/C affected PC and PG lipids differently within the surface monolayer. SP-B/C had preferential interactions with DPPG in 1:1, 2:1, and 7:1 DPPC-d 62:DPPG films that increased its acyl chain order. SP-B/C also interacted specifically with DOPG in 7:1 DPPC-d 62:DOPG monolayers, but in this case an increase in CH 2 band heights and peak wavenumber positions indicated a further disordering of the already fluid DOPG acyl chains. CD 2 band height and peak wavenumber analysis indicated that SP-B/C had no significant effect on the structure of DPPC-d 62 chains in 7:1 films with DPPG or DOPG, and had only a slight tendency to increase the acyl chain order in 1:1 films of DPPC-d 62:DPPG. SP-B/C had no significant effect on DPPC-d 62 structure in films with DOPG. Infrared results also indicated that interactions involving SP-B/C and lipids led to exclusion of PC and PG lipids from the compressed interfacial monolayer, in agreement with our previous report on the phase morphology of lipid monolayers containing 1 wt % SP-B/C.

Higher Fourier Harmonics of the Directional Distribution of an Equilibrium Wave Field under Steady Wind Forcing*

Recently, directional wave spectra have been obtained by applying the two-dimensional fast Fourier transform (2D FFT) to the three-dimensional spatial topography of ocean surface waves collected by an airborne scanning laser ranging system during a quasi-equilibrium wind wave condition. The directional distributions show that most wave energy at wavenumbers larger than the peak wavenumber is in two sidelobes at directions symmetrically located about the wind direction. Presented in this study is an analysis of the Fourier harmonics derived from decomposition of the measured bimodal directional distributions. The similarity properties of the Fourier coefficients are analyzed. A nonlinear function is proposed to represent the similarity relation. A bimodal directional distribution model in the form of Fourier series expansion consisting of the first eight Fourier harmonics is developed. Application of this model to extend the directional distribution of buoy measurements is demonstrated.

First- and second-order Raman spectra of galena (PbS)

Raman spectra of cleaved, millimeter-sized single crystals of mineral galena (PbS) have been measured between 100 and 1200 cm−1 over the temperature range 80 to 373 K. Three low wave number bands are observed which can be reconciled with the results of earlier reports. However, changes in the peak wave numbers and in the relative intensities of these bands in response to changes in temperature do not conform with previous assignments for the observed bands. Detailed assignments are proposed which are based on resonance Raman processes. The observed bands are assigned to forbidden longitudinal optical excitations, which are allowed under resonance conditions by a Fröhlich interaction mechanism, and two-phonon excitations.

Raman imaging of stress‐induced phase transformation in transparent ZnSe ceramic and sapphire single crystals

AbstractIt is known that the polishing of a material can cause pressure‐induced phase transformation and modify its surface properties. Indentation was used to apply controlled perturbation on optically clear ZnSe ceramics and on α‐alumina single‐crystal wafers. New Raman bands are observed at the periphery and/or the centre of the indented area. Confocal Raman and Rayleigh imaging of the peak intensity, bandwidth and wavenumber shift show complex transformations of the indented area. Peak intensity can be used to map the surface geometry with approximately micrometre resolution. For ZnSe, the new bands (ca 235 and 248 cm−1) are assigned to the phases obtained above 5 and 34 GPa under hydrostatic pressure. Comparison is made with zirconia and corundum crystals. Stress‐induced modifications are observed on the α‐alumina wafer. They seem to be due to an unknown disordered phase rather than to a high remnant stress. The relationship between the Raman parameters and the applied stress is discussed. Copyright © 2002 John Wiley & Sons, Ltd.

INFRARED SPECTRA OF CHLOROFORM AT HIGH PRESSURES

ABSTRACT Infrared spectra of chloroform samples in diamond anvil cells at ambient temperature and at pressures up to 10 GPa are reported. The freezing pressure is determined to be 0.76 GPa. All six fundamental vibrational modes and several combination modes are observed, with some exhibiting several components as a result of crystal field effects, and the dependence of their peak wavenumbers on pressure is presented. Some minor changes in the spectra near 6 GPa may be indicative of a structural phase transition, postulated from previous Raman studies. No color changes are observed over this pressure range and molecular distortion appears to be minimal, although there is evidence of a moderate increase in Cl-C-Cl bending forces. A metastable crystal is formed when the liquid is superpressed and flash-frozen, and its spectra suggest that this is characterized by molecular orientational disorder, similar to that found in crystalline bromoform.

RAMAN AND INFRARED SPECTRA OF IODOFORM AT HIGH PRESSURES

ABSTRACT Raman and infrared spectra are reported for iodoform samples in diamond anvil cells at ambient temperature and at pressures up to 5 GPa (Raman) and 10 GPa (infrared). The spectra appear to evolve smoothly and no evidence of any structural phase transitions is found. The dependence on pressure of 7 Raman and 13 infrared peak wavenumbers is presented. A large increase in intermolecular bonding strengths is confirmed, together with a moderate increase in intramolecular I-C-I bending forces. Color changes in the samples at high pressures are found to be mostly reversible, but long exposure to high fluxes of visible photons causes some molecular dissociation, with the release of iodine.

The effect of temperature on hydrogen bonding in crystalline and amorphous phases in dihydropyrine calcium channel blockers.

To investigate the effect of temperature on hydrogen bonding in a series of structurally related amorphous and crystalline compounds to gain a better molecular-level understanding of structural differences in the various phases. FT-infrared spectra of seven 1,4-dihydropyridine calcium channel blockers were obtained at temperatures between 0 and 200 degrees C using a temperature-controlled attenuated total reflection accessory. Thermal behavior was characterized using differential scanning calorimetry. Hydrogen bonding was investigated by monitoring the position of the NH stretching vibration, where an increase in peak wavenumber was taken to indicate a weakening of hydrogen bonding. Heating resulted in a reduction in hydrogen bonding strength, which was greatest for liquids and less for glassy and crystalline phases. For the amorphous samples, a plot of NH peak position vs. temperature displayed a discontinuity in the region of the glass transition (determined using differential scanning calorimetry) indicating that hydrogen bonding weakened abruptly as the material passed through the glass transition. This effect was more pronounced for some samples than for others. The variation in the decrease in hydrogen-bonding interactions with increasing temperature for the different phases is consistent with greater configurational freedom as one moves from crystal to glass to liquid.

ARTIFICIAL NEURAL NETWORK FOR THE QUANTITATIVE ANALYSIS OF AIR TOXIC VOCs

A 23-6-10 artificial neural network system (ANNs) with three layers has been developed in this paper. The simultaneous concentration analysis of ten air toxic volatile organic compounds (VOCs) was resolved. The net was trained with a back- propagation algorithm. The input signals were the absorbance values at the selected peak wavenumbers and a series of equispaced wavenumbers. The output is the predicted concentration for each component in the prediction samples. Several parameters were optimized to ensure convergence and to speed up learning. The comparison of prediction results at the characteristic peak wavenumbers and the series of equispaced wavenumbers showed that results obtained at the peak absorption wavenumbers were superior to that at the equispaced wavenumbers. The results also showed that ANN can successfully resolve the concentration analysis problem when the FTIR spectra of several constituents in the mixture interfere with each other.

Horizontal wave number spectra of temperature in the unstably stratified oceanic surface layer

Horizontal wave number spectra of temperature in the unstably stratified oceanic surface layer were determined from measurements on a bow boom at a depth of 2 m. Spectra were estimated in the wavelength band from 2 m to 2 km, normalized in accordance with Monin‐Obukhov similarity theory, and averaged in groups with similar stability parameter and fractional mixed layer depth. The shapes of the wave number‐weighted oceanic spectra agree qualitatively with observed and modeled atmospheric spectra, including the wavelength of the peaks and the variation of peak wave number with stability. However, the peak spectral levels disagree by as much as a factor of two and the variation of spectral level with stability is in the opposite sense for the oceanic and atmospheric spectra. The wave number of the peak in the near neutral oceanic spectrum is similar to the wave number of the peak in the longitudinal velocity spectrum observed in the atmospheric surface layer, which is consistent with temperature acting as a passive tracer in near neutral conditions. The wave number of the peak in the free convection oceanic spectrum is similar to the wave number of the peak in the spectrum of vertical velocity observed in the atmospheric surface layer during free convection, which reflects the dynamical role played by temperature in a freely convecting boundary layer. The difference between oceanic and modeled near‐neutral spectral levels at a wavelength of 2 m suggests that dissipation could be enhanced (up to a factor of three) by surface wave breaking.

Crystallization temperature and activation energy of rf-sputtered near-equiatomic TiNi and Ti 50Ni 40Cu 10 thin films

Amorphous thin films of Ti 49.93Ni 50.07 and Ti 49.96Ni 40.09Cu 9.95 alloys were rf-sputtered onto a (1 0 0) Si-wafer and characterized by X-ray diffraction (XRD), DSC, and Auger electron spectrometer (AES) tests. The amorphous structure of the Ti 49.93Ni 50.07 films is found to be similar to that of Ti X Ni 1− X rapidly quenched ribbons and mechanically alloyed powders, but more stable than Ti 49.96Ni 40.09Cu 9.95 films, by comparing the wavenumbers ( Q P) of the broad XRD peaks. The crystalline activation energy, E a, and the onset crystallization temperature, T X, for a 30°C/min DSC heating rate of the Ti 49.96Ni 40.09Cu 9.95 and Ti 49.93Ni 50.07 films are 388 kJ/mol, 488°C, and 416 kJ/mol and 511°C, respectively. This also suggests that the amorphous Ti 49.96Ni 40.09Cu 9.95 thin film is less stable than the Ti 49.93Ni 50.07 film, and can be explained in terms of the enthalpy of mixing. The T X values of amorphous Ti X Ni 1− X materials fabricated by the sputtering technique, by rapid quenching and by mechanical alloying are also compared and discussed.