Change In Linewidth Research Articles

Softening of the radial breathing mode in metallic carbon nanotubes.

The softening of the radial breathing mode (RBM) of metallic single walled carbon nanotubes (m-SWNTs) due to electron-phonon coupling has been studied by observing the Fermi level [see text] dependence of the RBM Raman peak. In situ Raman spectra were obtained from several individual m-SWNTs while varying [see text] electrochemically. The RBM frequency of an intrinsic m-SWNT is shown to be down-shifted relative to highly doped tubes by approximately 2 cm(1). The down-shift is greatest for small diameter and small chiral angle SWNTs. Most tubes show no change in RBM linewidth. A comparison is drawn between the RBM and the G band (A(LO) phonon) with respect to the [see text] dependence of their frequencies and linewidths.

Probing antiphase boundaries in Fe3O4 thin films using micro-Raman spectroscopy

We present Raman study of Fe3O4 films of different thicknesses grown on single crystal Si and MgO substrates to investigate the presence of antiphase boundaries (APBs). X-ray diffraction and x-ray photoelectron spectroscopy measurements indicate that films are single phase Fe3O4 on both the substrates. The changes in frequency and linewidth of different Raman modes [A1g and T2g(3)] are monitored and the electron-phonon coupling parameter (λ) is computed. λ is correlated with the combined effect of strain and APBs present in the grown films and it is concluded that the films grown on Si substrates are free from APBs.

Spectral linewidth broadening from pair fluctuations in a frozen Rydberg gas

Spectral linewidth broadening in Rydberg gases, a phenomenon previously attributed to the many-body effect, was observed experimentally almost a decade ago. The observed linewidth was typically 80--100 times larger than the average interaction strength predicted from a binary interaction. The interpretation of such a phenomenon is usually based on the so-called diffusion model, where the linewidth broadening mostly originates from the diffusion of excitations. We present a model calculation to show that diffusion is not the main mechanism of the linewidth broadening. We find that the rare pair fluctuation at small separation is the dominant factor contributing to this broadening. Our results give a width of about 20--30 times larger than the average interaction strength. More importantly, by turning off the diffusion process, we do not observe an order-of-magnitude change in the spectral linewidth.

Estimating protein-ligand binding affinity using high-throughput screening by NMR.

Many of today's drug discovery programs use high-throughput screening methods that rely on quick evaluations of protein activity to rank potential chemical leads. By monitoring biologically relevant protein-ligand interactions, NMR can provide a means to validate these discovery leads and to optimize the drug discovery process. NMR-based screens typically use a change in chemical shift or line width to detect a protein-ligand interaction. However, the relatively low throughput of current NMR screens and their high demand on sample requirements generally makes it impractical to collect complete binding curves to measure the affinity for each compound in a large and diverse chemical library. As a result, NMR ligand screens are typically limited to identifying candidates that bind to a protein and do not give any estimate of the binding affinity. To address this issue, a methodology has been developed to rank binding affinities for ligands based on NMR screens that use 1D (1)H NMR line-broadening experiments. This method was demonstrated by using it to estimate the dissociation equilibrium constants for twelve ligands with the protein human serum albumin (HSA). The results were found to give good agreement with previous affinities that have been reported for these same ligands with HSA.

Change of Damping for Long-Chain Molecules during Solidification and Melting in Scattering Samples Studied by Raman Spectroscopy

We studied the solidification and melting of certain complex scattering substances by laser Raman spectroscopy. We used a modified laser Raman system to study the spectrum of certain long-chain organic substances (paraffin and candlewax) during solidification and melting, and found that there is a significant and discontinuous change in linewidth (by 4–5 times) during these processes. By measuring the linewidth of a certain line during solidification, we show that at a microscopic level, there is a large change in the immediate microscopic environment and damping of the molecular motions. This shows that Raman spectroscopy can be used as a sensitive probe of the change in the immediate environment of the molecular motions in these systems.

Phonon linewidths in YNi2B2C

Phonons in a metal interact with conduction electrons which give rise to a finite linewidth. In the normal state, this leads to a Lorentzian shape of the phonon line. Density functional theory is able to predict the phonon linewidths as a function of wave vector for each branch of the phonon dispersion. An experimental verification of such predictions is feasible only for compounds with very strong electron-phonon coupling. YN2B2C was chosen as a test example because it is a conventional superconductor with a fairly high T c (15.2 K). Inelastic neutron scattering experiments did largely confirm the theoretical predictions. Moreover, they revealed a strong temperature dependence of the linewidths of some phonons with particularly strong electron-phonon coupling which can as yet only qualitatively be accounted for by theory. For such phonons, marked changes of the phonon frequencies and linewidths were observed from room temperature down to 15 K. Further changes were observed on entering into the superconducting state. These changes can, however, not be described simply by a change of the phonon linewidth.

Patterned bilayer plate microstructures subjected to thermal loading: Deformation and stresses

We studied the deformation of a series of gold/polysilicon patterned plate microstructures fabricated by surface micromachining. The patterned plate microstructures were subjected to a uniform temperature change from 100 °C to room temperature that was intended to induce linear and geometrically nonlinear deformation. We used interferometry to measure full-field deformed shapes of the microstructures. From these measurements we determined the spatially-averaged curvature of the deformed microstructures within individual lines and across the entire plate. The deformation response of the patterned plates can be broadly characterized in terms of the average curvature as a function of temperature change and exhibits linear and geometrically nonlinear behavior. We modeled the deformation response of the patterned plates using geometrically nonlinear plate theory with the finite element method. Good agreement was obtained between predictions and measurements for both local curvature variations across lines and for the evolution of curvature of the entire plate with temperature change. Using a generalized plane strain approach with the finite element method we also modeled the spatial dependence of the stress distribution in the lines and substrate. For thick plates, our results agree with those of previous studies, showing a decrease in the von Mises stress in the metal lines with decreasing linewidth. For thinner substrates, though, we find the behavior with linewidth is opposite and there is a critical substrate thickness (about 10 μm for the system in our study) where the behavior with linewidth changes. These results have important implications in the design of patterned structures for micro-electro-mechanical systems (MEMS) applications where films are of comparable thickness to the underlying substrate.

Sodium and potassium monolayers on Be(0001) investigated by photoemission and electronic structure calculations

Photoemission spectra show that Be(0001) surface states shift to lower energy with increasing Na or K coverage in the monolayer range. At an intermediate monolayer coverage a quantum well state appears near the Fermi edge and shifts to lower energy reaching saturation energy at full monolayer coverage. At full monolayer coverage low energy electron diffraction shows $2\ifmmode\times\else\texttimes\fi{}2$ order for K while Na forms an incommensurate close-packed structure aligned with the substrate. As a result of the different structures, the photoemission spectra show qualitative differences that are explained by diffraction. First-principles calculations for Be(0001) and $p(2\ifmmode\times\else\texttimes\fi{}2)\text{K}/\text{Be}(0001)$ reproduce reasonably the measured energy shifts and dispersions. Spectra recorded for the shallow alkali-metal core levels show that the adlayer is inhomogeneous in an intermediate coverage range. While this is not noted when the valence state energies are measured a linewidth change observed for one of the surface states is ascribed to this inhomogeneity. It is suggested that the onset of inhomogeneity is associated with the occupation of states in the quantum well band. Occupation of these states, which are highly localized to the adlayer, gives metal character to the layer over an increasing area as the coverage is increased making the film homogeneous at high monolayer coverage. An anomalous emission line is observed for both Na and K as a low energy companion to the quantum well state line becoming increasingly separated from this as the coverage increases. We suggest that the satellite is due to an energy loss associated with collective oscillations in the overlayer.

Effect of indium on phase-change characteristics and local chemical states of In–Ge–Sb–Te alloys

We introduce single-phase In–Ge–Sb–Te (IGST) quaternary thin film (fcc structure when crystallized) deposited by cosputtering from Ge2Sb2Te5(GST) and In3Sb1Te2 targets. This film, compared with the GST ternary system, provides a significant increase of amorphous-to-crystalline transformation temperature. High-resolution x-ray photoelectron spectroscopy (HRXPS) revealed that, with increasing In amounts, the Sb 4d and Ge 3d core peaks shift toward lower binding energies (BEs), with negligible changes in spectral linewidths, whereas the In 4d and Te 4d core peaks show insignificant changes in BEs. HRXPS interpretation suggests that the Na site in IGST can be occupied by Te, Sb, In, and vacancy, whereas in GST it is occupied only by Te.

Mott Transition of Excitons in Coupled Quantum Wells

In this work we study the phase diagram of indirect excitons in coupled quantum wells and show that the system undergoes a phase transition to an unbound electron-hole plasma. This transition is manifested as an abrupt change in the photoluminescence linewidth and peak energy at some critical power density and temperature. By measuring the exciton diamagnetism, we show that the transition is associated with an abrupt increase in the exciton radius. We find that the transition is stimulated by the presence of direct excitons in one of the wells and show that they serve as a catalyst of the transition.

ChandraX‐Ray Grating Spectrometry of η Carinae near X‐Ray Minimum. I. Variability of the Sulfur and Silicon Emission Lines

We report on variations in important X-ray emission lines in a series of Chandra grating spectra of the supermassive colliding wind binary star Eta Carinae, including key phases around the X-ray minimum/periastron passage in 2003.5. The X-rays arise from the collision of the slow, dense wind of Eta Car with the fast, low-density wind of an otherwise hidden companion star. The X-ray emission lines provide the only direct measure of the flow dynamics of the companion's wind along the wind-wind collision zone. We concentrate here on the silicon and sulfur lines, which are the strongest and best resolved lines in the X-ray spectra. Most of the line profiles can be adequately fit with symmetric Gaussians with little significant skewness. Both the silicon and sulfur lines show significant velocity shifts and correlated increases in line widths through the observations. The R = forbidden-to-intercombination ratio from the Si XIII and S XV triplets is near or above the low-density limit in all observations, suggesting that the line-forming region is >1.6 stellar radii from the companion star. We show that simple geometrical models cannot simultaneously fit both the observed centroid variations and changes in line width as a function of phase. We show that the observed profiles can be fitted with synthetic profiles with a reasonable model of the emissivity along the wind-wind collision boundary. We use this analysis to help constrain the line formation region as a function of orbital phase, and the orbital geometry.

Optimization of resolution-enhancement technology and dual-layer bottom-antireflective coatings in hypernumerical aperture lithography

Resolution-enhancement technique (RET) and dual-layer bottom-antireflective coatings (DL-BARC) must be adopted in hypernumerical aperture (NA>1) lithography for a 45nm half-pitch device. However, interactions of RET, polarization effect, and the resist process significantly impact on lithography performance. An in-house program and PROLITH 9.0 were employed to perform comprehensive optimization of RET and DL-BARC structures in order to improve pattern fidelity with a reasonable process window (PW). High-fidelity resist patterns are obtained when we employed optimum DL-BARC structures in conjunction with optimum RET. An alternating phase-shift mask and a conventional illumination is one kind of optimum combination of RET. An attenuated phase-shift mask and a cross-dipole illumination is the other one. Line-width changes are controlled within 4nm. Sidewall angles are greater than 88°.

1H NMR Study on Pre-micellization of Quaternary Ammonium Gemini Surfactants

Two quaternary ammonium Gemini surfactant series, 12-s-12, ([C(12)H(25)N+ (CH(3))(2)](2)(CH(2))(s).(2)Br(-)) and 14-s-14 ([C(14)H(29)N(+)(CH(3))(2)](2)(CH(2))(s).(2)Br(-)), where s = 2, 3, and 4, have been studied by the use of (1)H NMR in aqueous solution at concentrations below their critical micelle concentrations (CMC) at 25 degrees C. The appearance of a second set of peaks for the 14-s-14 series and the changes in chemical shifts, line widths, and line shapes of the 12-s-12 series with increasing concentration below the CMC are interpreted as evidence for the formation of premicelle aggregates (oligomers) that appear at approximately one-half their CMC values. Self-diffusion coefficients (D) and transverse relaxation times (T(2)) have also been detected and support the results obtained by (1)H NMR.

Inkjet printing of single-walled carbon nanotubes and electrical characterization of the linepattern

Single-walled carbon nanotubes (SWCNTs) were patterned using inkjet printing. To makethe uniform networks of dropped SWCNTs, the effects of substrate heating, surfacehydrophilicity of the substrate and the jetting process were investigated. Circuit diagramsincluding holes, lines and curves were printed on glass and polymer substrates, and theconductive lines were printed on a glass substrate to characterize their electrical properties byI–V curveand impedance measurements. Lines 75 mm long were printed along with the number of overwriteswith 150 µm linewidth and width change with five overwrites. As for the results, we confirmed that thedc resistance of the SWCNT line was proportionally changed according to the linewidthand the number of overwrites, and the line feature possessed ohmic characteristics to 2 MHzeven after two overwrites.

Water-Soluble Thermoresponsive Polylactides

Novel glycolides with pendent oligo(ethylene oxide) monomethyl ether substituents were synthesized. Subsequent ring-opening polymerization using 4-tert-butylbenzyl alcohol as the initiator and Sn(2-ethylhexanote)2 as the catalyst yielded homogeneous oligo(ethylene oxide)-grafted polylactides with high molecular weights and low polydispersities. Polymers with short oligo(ethylene oxide) chains (1 or 2 ethylene oxide repeat units) are more hydrophilic than polylactide but insoluble in water, whereas polymers having 3 or 4 ethylene oxide repeat units are water-soluble. Aqueous solutions of polymers with 3 and 4 ethylene oxide repeat units in each pendent chain are thermoresponsive, with lower critical solution temperatures (LCSTs) at 19 and 37 °C, respectively. The LCST transitions were confirmed by cloud point measurements, variable temperature dynamic light scattering, and changes in line widths measured by variable temperature 1H NMR spectroscopy.

10 GHz regeneratively mode-locked semiconductor optical amplifier fiber ring laser and its linewidth characteristics

A 10 GHz regeneratively mode-locked semiconductor optical amplifier fiber ring laser with a picosecond pulse duration was newly constructed, and the linewidth change of a longitudinal mode was measured for various laser cavity lengths using a delayed self-heterodyne detection method. The detected line shape was approximately Gaussian for cavity lengths of 3.4-171 m. This result indicates that the laser linewidth depends strongly on thermal or acoustic cavity length fluctuations. The linewidth was proportional to the inverse square root of the cavity length, and a linewidth of 1.7 kHz was obtained for a cavity length of 171 m.

Improper hydrogen bonding and motional narrowing in binary mixtures of 2‐ and 3‐bromopyridine in methanol probed by polarized Raman study and DFT calculations

AbstractA concentration‐dependent Raman study of the ν(CBr) stretching and trigonal bending modes of 2‐ and 3‐Br‐pyridine (2Br‐p and 3Br‐p) in CH3OH was performed at different mole fractions of the reference molecule, 2Br‐p/3Br‐p, from 0.1 to 0.9 in order to understand the origin of blue/red wavenumber shifts of the vibrational modes due to hydrogen‐bond formation. The appearance of additional Raman bands in these binary systems at ∼617 cm−1in the case of 2Br‐p and at ∼618 cm−1 in the case of 3Br‐p compared to neat bromopyridine derivatives were attributed to specific hydrogen‐bonded complexes formed in the mixtures. The interpretation of experimental results is supported by density functional calculations on optimized geometries and vibrational wavenumbers of 2Br‐p and 3Br‐p and a series of hydrogen‐bonded complexes with methanol. The parameters obtained from these calculations were used for a qualitative explanation of the blue/red shifts. The wavenumber shifts and linewidth changes for the ν(CBr) stretching and trigonal bending modes as a function of concentration reveal that the caging effects leading to motional narrowing and diffusion‐causing line broadening are simultaneously operative, in addition to the blue shift caused due to hydrogen bonding. Copyright © 2007 John Wiley & Sons, Ltd.

Ferromagnetic resonance spectra in patterned and unpatterned NiFe/Pt films

AbstractThe ferromagnetic resonance in nanostructured Ni81Fe19 films comprising flim parts and wire parts covered with Pt has been investigated. In contrast to the systematic variation of the FMR linewidth for the film parts, the linewidth for the nanostructured wire parts shows an irregular change with changing the thickness of Pt. This irregular change indicates that the spin current absorption in the Pt layer cannot fully account for the linewidth change in the wire parts. This FMR‐linewidth variation can be argued in terms of the competition between the spin pumping and the roughness effect. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Paramagnetic NMR Relaxation in Polymeric Matrixes: Sensitivity Enhancement and Selective Suppression of Embedded Species (1H and 13C PSR Filter)

A study of the practical applications of the addition of paramagnetic spin relaxation (PSR) ions to a variety of polymers (PLL, PAA, PGA, PVP, and polysaccharides such as hyaluronic acid, chitosan, mannan, and dextran) in solution (D2O and DMSO-d6) is described. Use of Gd(III), Cu(II), and Mn(II) allows a reduction of up to 500% in the 1H longitudinal relaxation times (T1), and so in the time necessary for recording quantitative NMR spectra (sensitivity enhancement) neither an increase of the spectral line width nor chemical shift changes resulted from addition of any of the PSR agents tested. Selective suppression of the 1H and 13C NMR signals of certain components (low MW molecules and polymers) in the spectrum of a mixture was attained thanks to their different sensitivity [transverse relaxation times (T2)] to Gd(III) (PSR filter). Illustration of this strategy with block copolymers (PGA-g-PEG) and mixtures of polymers and low MW molecules (i.e., lactose-hyaluronic acid, dextran-PAA, PVP-glutamic acid) in 1D and 2D NMR experiments (COSY and HMQC) is presented. In those mixtures where PSR and CPMG filters alone failed in the suppression of certain components (i.e., PVP-mannan-hyaluronic acid) due to their similarity of 1H T2 values and sensitivities to Gd(III), use of the PSR filter in combination with CPMG sequences (PSR-CPMG filter) successfully resulted in the sequential suppression of the components (hyaluronic acid first and then mannan).

Annealing of dilute-nitride GaAsSbN∕InP strained multiple quantum wells

The thermal annealing of GaAsSbN∕InP strained multiple quantum wells (MQWs) grown by metal organic chemical vapor deposition was investigated. Photoluminescence peak intensity and linewidth changes indicate a significant improvement in optical quality of the GaAsSbN∕InP MQWs upon annealing. We find no significant annealing-induced blueshift of the optical transitions, which confirms the theoretical expectation that a change in the nearest-neighbor configuration nitrogen atoms has negligible effect on the band gap of GaAsSbN. The evolution of (400) x-ray diffraction rocking curves with thermal treatment of the samples was consistent with the constituent redistribution in the GaAsSbN QW.