Resulting Line Shapes Research Articles

Definition of a new (Doniach‐Sunjic‐Shirley) peak shape for fitting asymmetric signals applied to reduced graphene oxide/graphene oxide XPS spectra

The existence of asymmetry in X‐ray photoelectron spectroscopy (XPS) photoemission lines is widely accepted, but line shapes designed to accommodate asymmetry are generally lacking in theoretical justification. In this work, we present a new line shape for describing asymmetry in XPS signals that is based on two facts. First, the most widely known line shape for fitting asymmetric XPS signals that has a theoretical basis, referred to as the Doniach‐Sunjic (DS) line shape, suffers from a mathematical inconvenience, which is that for asymmetric shapes the area beneath the curve (above the x‐axis) is infinite. Second, it is common practice in XPS to remove the inelastically scattered background response of a peak in question with the Shirley algorithm. The new line shape described herein attempts to retain the theoretical virtues of the DS line shape, while allowing the use of a Shirley background, with the consequence that the resulting line shape has a finite area. To illustrate the use of this Doniach‐Sunjic‐Shirley (DSS) line shape, a set of spectra obtained from varying amounts of graphene oxide (GO) and reduced GO on a patterned, heterogeneous surface are fit and discussed.

Coherently displaced oscillator quantum states of a single trapped atom

Coherently displaced number states of a harmonically bound ion can be coupled to two internal states of the ion by a laser-induced motional sideband interaction. The internal states can subsequently be read out in a projective measurement via state-dependent fluorescence, with near-unit fidelity. This leads to a rich set of line shapes when recording the internal-state excitation probability after a sideband excitation, as a function of the frequency detuning of the displacement drive with respect to the ion’s motional frequency. We precisely characterize the coherent displacement based on the resulting line shapes, which exhibit sharp features that are useful for oscillator frequency determination from the single quantum regime up to very large coherent states with average occupation numbers of several hundred. We also introduce a technique based on multiple coherent displacements and free precession for characterizing noise on the trapping potential in the frequency range of 500 Hz–400 kHz. Signals from the ion are directly used to find and eliminate sources of technical noise in this typically unaccessed part of the spectrum.

Line shapes of the Zb(10610) and Zb(10650) in the elastic and inelastic channels revisited

The most recent experimental data for all measured production and decay channels of the bottomonium-like states $Z_b(10610)$ and $Z_b(10650)$ are analysed simultaneously using solutions of the Lippmann-Schwinger equations which respect constraints from unitarity and analyticity. The interaction potential in the open-bottom channels $B^{(*)}\bar{B}^{*}+\mbox{c.c.}$ contains short-range interactions as well as one-pion exchange. It is found that the long-range interaction does not affect the line shapes as long as only $S$ waves are considered. Meanwhile, the line shapes can be visibly modified once $D$ waves, mediated by the strong tensor forces from the pion exchange potentials, are included. However, in the fit they get balanced largely by a momentum dependent contact term that appears to be needed also to render the results for the line shapes independent of the cut-off. The resulting line shapes are found to be insensitive to various higher-order interactions included to verify stability of the results. Both $Z_b$ states are found to be described by the poles located on the unphysical Riemann sheets in the vicinity of the corresponding thresholds. In particular, the $Z_b(10610)$ state is associated with a virtual state residing just below the $B\bar{B}^{*}/\bar B{B}^{*}$ threshold while the $Z_b(10650)$ state most likely is a shallow state located just above the $B^*\bar{B}^{*}$ threshold.

Detecting dark-matter waves with a network of precision-measurement tools

Virialized Ultra-Light Fields (VULFs) are viable cold dark matter candidates and include scalar and pseudo-scalar bosonic fields, such as axions and dilatons. Direct searches for VULFs rely on low-energy precision measurement tools. While the previous proposals have focused on detecting coherent oscillations of the VULF signals at the VULF Compton frequencies at individual devices, here I consider a network of such devices. VULFs are essentially dark matter {\em waves} and as such they carry both temporal and spatial phase information. Thereby, the discovery reach can be improved by using networks of precision measurement tools. To formalize this idea, I derive a spatio-temporal two-point correlation function for the ultralight dark matter fields in the framework of the standard halo model. Due to VULFs being Gaussian random fields, the derived two-point correlation function fully determines $N$-point correlation functions. For a network of $N_{d}$ devices within the coherence length of the field, the sensitivity compared to a single device can be improved by a factor of $\sqrt{N_{d}}$. Further, I derive a VULF dark matter signal profile for an individual device. The resulting line shape is strongly asymmetric due to the parabolic dispersion relation for massive non-relativistic bosons. I discuss the aliasing effect that extends the discovery reach to VULF frequencies higher than the experimental sampling rate. I present sensitivity estimates and develop a stochastic field SNR statistic. Finally, I consider an application of the developed formalism to atomic clocks and their networks.

Coherent Rayleigh-Brillouin scattering measurement of atmospheric atomic and molecular gas temperature.

Broadband coherent Rayleigh-Brillouin scattering (CRBS) was used to measure translational gas temperatures for nitrogen, argon, and methane at the ambient pressure of 0.8 atm. Temperatures derived from spectral analysis were compared with experimentally-measured temperatures, with a maximum 5.2% difference for all gases at all temperatures; and with nitrogen, argon, and methane exhibiting average differences over the temperature range tested of 0.8%, 1.4% and -0.5%, respectively. These values are consistent with the 2% estimated, experimental error of the experiment. Improving upon the efficiency of previous line shape acquisition methods, CRBS data were spectrally de-convolved using a cost effective, purpose-designed, Fabry-Perot etalon spectrometer. The resulting line shapes were compared to models obtained from approximations to the 1D Boltzmann equation. Although this study employed broadband CRBS for explicit gas temperature measurement, similar line shape acquisition techniques could be used with broadband coherent Rayleigh scattering (CRS) to experimentally-measure gas temperatures, pressures and other transport properties in both the kinetic (CRBS) and rarefied (CRS) regimes.

Ligand Hyperfine Structure of EPR Spectra of Eu2+ Ions in Superionic CaF2 Crystals

The electron paramagnetic resonance (EPR) spectra of the Eu 2+ ion in CaF 2 crystals is investigated. In samples with Eu 2+ concentration equal to 0.1 and 0.01 mole %, additional splitting of the hyperfine structure lines is observed. The electron paramagnetic resonance spectrum is calculated with allowance for the ligand hyperfine interactions (LHFI), and the resulting line shape of the hyperfine structure is determined for the central fine-structure transition. Comparing the calculated spectrum with the experimental one, we have determined the principal values of the LHFI tensor T|| = 18.44 MHz and T⊥ = –12.98 MHz and have carried out a comparative analysis of the values obtained with the results of other authors. Using nonlinear least squares fitting, we have determined the parameters of the partially resolved lines in the spectra.

Disorder Influenced Absorption Line Shapes of a Chromophore Coupled to Two-Level Systems

We have carried out a theoretical and numerical study of disorder-induced changes in the absorption line shape of a chromophore embedded in a host matrix. The stochastic sudden jump model is employed wherein the host matrix molecules are treated as noninteracting two-level systems (TLSs) occupying points on a three-dimensional lattice with randomly oriented dipole moments. By systematically controlling the degree of positional disorder (α) attributed to them, a perfectly crystalline (α = 0) or a glassy environment (α = 1) or a combination of the two is obtained. The interaction between the chromophore and the TLSs is assumed to be of the dipole-dipole form. With an increase in α, the broadening of the absorption line shape was found to follow a power-law behavior. More importantly, it is revealed in the long-time limit that the resultant line shape is Gaussian in the absence of disorder but transforms to Lorentzian for a completely disordered environment. For an arbitrarily intermediate value of α, the resultant line shape can be approximately fitted by a linear combination of Gaussian and Lorentzian components. The Lorentzian profile for the disordered medium is attributed to the chomophore-TLS pairs with vanishingly small separation between them.

Quasi-dark modes in a five-bar plasmonic oligomer

We introduce a plasmonic oligomer that supports two quasi-dark modes. A double plasmon-induced transparency spectrum arises from the Fano interference between a bright mode and two quasi-dark modes. A coupling Lorentzian oscillator model is employed to explain the resulting line shape. It is found that the modulation depths and frequency of two Fano resonances can be tuned effectively by displacement of each component of the oligomer. The oligomer can be used as a sensitive plasmon ruler based on both frequency shift and radiance sensing. Furthermore, an artificial magnetic quadrupole is also introduced by one of the quasi-dark modes. We expect that the oligomer will be valuable for the design of plasmonic circuits and multiwavelength surface-enhanced Raman scattering.

Thermal bistability-based method for real-time optimization of ultralow-threshold whispering gallery mode microlasers

A method based on thermal bistability for ultralow-threshold microlaser optimization is demonstrated. When sweeping the pump laser frequency across a pump resonance, the dynamic thermal bistability slows down the power variation. The resulting line shape modification enables a real-time monitoring of the laser characteristic. We demonstrate this method for a functionalized microsphere exhibiting a submicrowatt laser threshold. This approach is confirmed by comparing the results with a step-by-step recording in quasi-static thermal conditions.

Interpretation of Glancing Angle and Bragg–Brentano XRD Measurements for CoCr Alloy and Austenitic Stainless Steel After PIII Nitriding

X-ray diffraction data taken in Bragg-Brentano and glancing angle geometries are compared for stainless steel AISI 304 and CoCr alloys HS188 after nitriding by plasma immersion ion implantation. A direct inferring of the nitrogen depth profile from the line shape for expanded austenite is precluded as additional stress is present. Furthermore, conventional stress analysis is rather complicated as highly textured material is present and only a very much reduced set of reflections is available for evaluation. Nevertheless, a strong dependence of the lattice expansion and the resulting line shape on the detailed process conditions was observed.

Removing a Wedge from a Metallic Nanodisk Reveals a Fano Resonance

A wide variety of complex, multicomponent plasmonic nanostructures have been shown to possess Fano resonances. Here we introduce a remarkably simple planar nanostructure, a single metallic nanodisk with a missing wedge-shaped slice, that also supports a Fano resonance. In this geometry, the Fano line shape arises from the coupling between a hybridized plasmon resonance of the disk and a narrower quadrupolar mode supported by the edge of the missing wedge slice. As a consequence, both disk size and wedge angle control the properties of the resonance. A semianalytical description of plasmon hybridization proves useful for analyzing the resulting line shape.

Growth and optical properties of Ag clusters deposited on poly(ethylene terephthalate)

The growth and concomitant evolution of the optical properties of Ag nano-clustersdeposited on biaxially extruded poly(ethylene terephthalate) films is studied by reflectancedifference spectroscopy. It is demonstrated by low energy ion scattering and simulatedoptical spectra that the clusters form a two-dimensional layer buried beneath the surface ofthe substrate. The experimental spectra are described by simulations in which differentconfigurations of the host such as anisotropy, amorphization, and dilution areconsidered in an effective medium approach. The contribution of the anisotropicsubstrate is used to explain the resulting line shapes. We also discuss the roleof the rate of change of the filling fraction with Ag coverage in the evolutionof the spectra and the detection of the onset of coalescence by optical means.

Effect of Precursor Molar Mass on the 2H NMR Line Shapes of End-Linked PDMS Elastomers

A series of end-linked PDMS networks synthesized with different molar mass precursor chains is examined using 2H NMR spectroscopy. The resulting line shapes for networks in the undeformed state show clear differences with precursor chain molar mass. Furthermore, samples uniaxially extended to high extension ratio show a clear shoulder in the line shape and two characteristic splittings (two doublets). Comparison with spectra for deuterated free chains dissolved in an unlabeled network confirms that the inner doublet results from excluded volume interactions between segments whereas the outer doublet is due to more highly aligned chain segments from chains with conformations trapped by the cross-linking reaction.

Collisional shifts and broadenings of doubly excited states of barium

Shift and broadening parameters for doubly excited states of 5d6d, 5d7d, 5d7s, 5d8s and 6p2 configurations in neutral barium atoms are presented. A tunable dye laser pumped by an excimer laser was used to populate the Rydberg states of Ba by two-photon absorption from the 6s2 1S0 ground state. Inert gases Ar, Kr and Xe at 100 mbar pressure were used as perturbing gases. The resulting line shapes were fitted to a Voigt line shape function, from which shift and broadening parameters were inferred.

Structure and Dynamics of Membrane-associated ICP47, a Viral Inhibitor of the MHC I Antigen-processing Machinery

To evade the host's immune response, herpes simplex virus employs the immediate early gene product ICP47 (IE12) to suppress antigen presentation to cytotoxic T-lymphocytes by inhibition of the ATP-binding cassette transporter associated with antigen processing (TAP). ICP47 is a membrane-associated protein adopting an alpha-helical conformation. Its active domain was mapped to residues 3-34 and shown to encode all functional properties of the full-length protein. The active domain of ICP47 was reconstituted into oriented phospholipid bilayers and studied by proton-decoupled 15N and 2H solid-state NMR spectroscopy. In phospholipid bilayers, the protein adopts a helix-loop-helix structure, where the average tilt angle of the helices relative to the membrane surface is approximately 15 degrees (+/- 7 degrees ). The alignment of both structured domains exhibits a mosaic spread of approximately 10 degrees . A flexible dynamic loop encompassing residues 17 and 18 separates the two helices. Refinement of the experimental data indicates that helix 1 inserts more deeply into the membrane. These novel insights into the structure of ICP47 represent an important step toward a molecular understanding of the immune evasion mechanism of herpes simplex virus and are instrumental for the design of new therapeutics.

A study of the headgroup motion of sphingomyelin using 31P NMR and an analytically soluble model

A 31P NMR investigation has been carried out of the headgroup dynamics of sphingomyelin molecules in bilayers for the L α and L β ′ phases. The resulting line shapes have been analysed in terms of a reduced-parameter model, using van Faassen's method for obtaining an analytic solution to first-order stochastic differential equations to simulate the line shapes of oriented and non-oriented samples. Our treatment results in good fits to measured data but using fewer parameters than traditional methods. Angles and correlation times ( τ | | and τ ⊥ ) describing the geometry and dynamics of the headgroup are obtained by optimising the agreement between simulated and experimental data. The results are contrasted with those obtained for the lecithins DMPC and DPPC using a similar analysis. Not only are τ | | and τ ⊥ now equal in value for the L α phase, but this value is also found to be nearly four times larger than the longest correlation time for the lecithins. We interpret this as evidence of inter- and intramolecular hydrogen bonding in the L α phase of sphingomyelin. In the L β ′ phase of sphingomyelin, however, although τ | | and τ ⊥ remain equal their value is now 32% smaller than that of the lecithins in the same phase. This indicates less difference between the fluidities in the headgroup region of the two phases of sphingomyelin as compared to that of the lecithins. Another significant difference between the L β ′ phases is that the tilt angle for sphingomyelin is found to be nearly twice as large as for the lecithins. We argue that these combined observations point to the existence of hydrogen bonding in this phase also. Again in contrast to our previous work on lecithins, our results provide evidence of a negative diamagnetic anisotropy in sphingomyelin molecules, even in the L β ′ phase. This is provided for in our model by the assumption that our unoriented samples consist of prolate ellipsoidal liposomes whose major axes are oriented parallel to the static magnetic field. The apparently different diamagnetic behaviour of sphingomyelin in the present work is due to the higher static field used rather than any intrinsic difference in this respect between sphingomyelin and the lecithins DMPC and DPPC.

Orientation dependence of the Landé factor in an inversion layer

The magneto-optical properties of a biased semiconductor inversion layer (GaAlAs–GaAs) are calculated for applied magnetic fields in the Faraday and Voigt configurations. Electric and magnetic dipole transitions for spin flip in an n-type inversion layer are investigated. Resulting line shapes and the orientation dependence of the effective Landé factor g*are discussed. The electric potential in the inversion layer is calculated self-consistently.

Does the Heisenberg Model Describe the Multimagnon Spin Dynamics in Antiferromagnetic CuO Layers?

We compute the absorption spectrum for multimagnon excitations assisted by phonons in insulating layered cuprates using exact diagonalization in clusters of up to 32 sites. The resulting line shape is very sensitive to the underlying magnetic Hamiltonian describing the spin dynamics. For the usual Heisenberg description of undoped Cu-O planes we find, in accordance with experiment, a two-magnon peak followed by high energy sidebands. However the relative weight of the sidebands is too small to reproduce the experiment. An extended Heisenberg model including a sizable four-site cyclic exchange term is shown to be consistent with the experimental data.

A PARTIALLY CORRELATED STRONG COLLISION MODEL FOR VELOCITY- AND STATE-CHANGING COLLISIONS APPLICATION TO Ar-BROADENED HF ROVIBRATIONAL LINE SHAPE

High-resolution tunable laser measurements of rovibrational line shapes in Ar-broadened HF [A.S. Pine, J. Chem. Phys., 1994, 101, 3444] have shown the need of partially correlated Dicke narrowing models to accurately describe the observed asymmetries. A strong collision model accounting for both velocity- and state-changing mechanisms (VCD) and phase-changing ones (D), is presented. The resulting line shape justifies, on a physical basis, the empirical model previously used to interpret the observed features. The present partially correlated strong collisional model leads to a clearer interpretation of the characteristic parameters determined from the experiment for HF–Ar. Further theoretical calculations and experiments show that the residual discrepancies for the first rovibrational lines cannot be attributed to the speed dependence of the collisional line shape parameters.

Self-assembled DNA–cationic-lipid complexes: Two-dimensional smectic ordering, correlations, and interactions

We report a synchrotron small-angle x-ray scattering (SAXS) study of the mutilayered, self-assembled structure (complex) that is formed by mixing DNA with cationic liposomes. In these complexes the DNA is confined between charged lipid bilayers and orders as a two-dimensional (2D) smectic liquid crystal. The power-law bilayer-bilayer correlations of the 3D multilayer smectic liquid crystal, which are coupled to the 2D lattice of DNA chains, are found to deviate significantly from those described by the standard Caill\'e model of smectic-$A$ phases. To model the DNA ordering, the 2D smectic correlation function and the corresponding structure factor are derived from the smectic Hamiltonian in harmonic approximation. The resulting line shape is then fitted to the DNA correlation peak. It is found that for samples of higher $d,$ short-range correlations between the DNA in adjacent sheets have to be assumed to explain the data. From the least-square fitting, the 2D DNA interchain compressibility modulus $B$ is extracted as a function of $d$ and discussed in view of different possible microscopic interactions responsible for the ordering.