Peak Broadenings Research Articles

Time-Resolved Pump-Probe Diffraction Experiment at SOLEIL Synchrotron: Photoinduced Spin Transition in the Molecular Crystal [TPA Fe(III) TCC] PF6

We present the first time-resolved pump-probe experiment performed at synchrotron SOLEIL at the CRISTAL diffraction beamline. The time-resolved setup will be used in the near future for sub-ns time resolution experiments. We studied spin state switching in a [TPA Fe(III) TCC] PF6 single crystal as induced by a ¼ 6 ns laser pulse (1064 nm), by measuring the 3D diffraction volume of the 002 Bragg reflection as a function of time after excitation. The intensity profiles (rocking curves) are found to evolve at two characteristic timescales, namely hundreds of ns and few ¹s, exhibiting subtle profile changes and peak broadenings. Consistently with previous studies, we interpret these features as due to structural inhomogeneities related to laser-induced deformation wave propagation and heat diffusion, which both start from the absorbing sites.

Raman spectrometry study of phase stability and phonon anharmonicity of Al3BC3 at elevated temperatures and high pressures

In situ Raman spectra of Al3BC3 have been measured at elevated temperatures of up to 1000 °C and high pressures of up to 32 GPa. It is shown that there are no abnormal phonon shifts when the measurement conditions were up to 1000 °C or up to 27 GPa, which indicates a good structural stability of Al3BC3 at high temperatures and pressures. The Raman active phonon modes were assigned comprehensively to the corresponding vibration modes by first-principles calculations. Interestingly, an abnormal softening of the E1g(559 cm–1) and E2g(578 cm–1) phonon modes were observed when the pressure was higher than 27 GPa. Correlating the results with previous theoretical predictions of polymorphism in Al3BC3, the mode softening at higher pressures might originate from the structural transformation (from hexagonal to tetragonal symmetry) involving changes of Al and C coordination numbers. In addition, the phonon anharmonicity has been investigated by studying the temperature and pressure dependence of the Raman peak shifts and broadenings. Finally, the present work has highlighted that in situ Raman spectrometry study is a sensitive method for investigating the structural stability and phonon anharmonicity of complex ceramics.

A Raman Spectrometry Study of Phonon Anharmonicity of Zirconia at Elevated Temperatures

Raman spectra of monoclinic zirconia (ZrO2) were measured at temperatures of up to 950 K. Temperature-dependent Raman peak shifts and broadenings were reported and compared with prior results on hafnia (HfO2). Lattice dynamics calculations were performed with both shell model and density functional theory to obtain Raman frequencies, and the total and partial phonon density of states. These calculations were also used to identify the individual motions of metal and oxygen atoms in the different Raman modes. By correlating these motions to the thermal peak shifts and broadenings, it was confirmed that modes involving changes in oxygen–oxygen bond length were the most anharmonic. The metal-dominated modes were found to be more quasiharmonic, and thus showed less broadening with temperature. Mass effects were evident by comparing the mode softening and shifting between zirconia and hafnia.

The Polar Phase of NaNbO3: A Combined Study by Powder Diffraction, Solid-State NMR, and First-Principles Calculations

A polar phase of NaNbO(3) has been successfully synthesized using sol-gel techniques. Detailed characterization of this phase has been undertaken using high-resolution powder diffraction (X-ray and neutron) and (23)Na multiple-quantum (MQ) MAS NMR, supported by second harmonic generation measurements and density functional theory calculations. Samples of NaNbO(3) were also synthesized using conventional solid-state methods and were observed to routinely comprise of a mixture of two different polymorphs of NaNbO(3), namely, the well-known orthorhombic phase (space group Pbcm) and the current polar phase, the relative quantities of which vary considerably depending upon precise reaction conditions. Our studies show that each of these two polymorphs of NaNbO(3) contains two crystallographically distinct Na sites. This is consistent with assignment of the polar phase to the orthorhombic space group P2(1)ma, although peak broadenings in the diffraction data suggest a subtle monoclinic distortion. Using carefully monitored molten salt techniques, it was possible to eradicate the polar polymorph and synthesize the pure Pbcm phase.

Raman spectrometry study of phonon anharmonicity of hafnia at elevated temperatures

Raman spectra of monoclinic hafnium oxide $({\text{HfO}}_{2})$ were measured at temperatures up to 1100 K. Raman peak shifts and broadenings are reported. Phonon dynamics calculations were performed with the shell model to obtain the total and partial phonon density of states, and to identify the individual motions of Hf and O atoms in the Raman modes. Correlating these motions to the thermal peak shifts and broadenings, it was found that modes involving changes in oxygen-oxygen bond length were the most anharmonic. The hafnium-dominated modes were more quasiharmonic and showed less broadening with temperature. Comparatively, the oxygen-dominated modes were more influenced by the cubic term in the interatomic potential than the hafnium-dominated modes. An approximately quadratic correlation was found between phonon-line broadening and softening.

XPS measurements for probing dynamics of charging

The technique of recording X-ray photoemission data while the sample rod is subjected to ±10.0 V (dc) or square-wave pulses (ac) with varying frequencies in the range of 10 −3 to 10 3 Hz for probing charging/discharging dynamics of dielectric materials, is reviewed. Application of this technique introduces charging shifts as well as broadening of the peaks, which depend non-linearly on the polarity, as well as on the frequency of the pulses applied. These changes have been measured on: (i) an artificially created dielectric sample consisting of a Au metal strip connected externally to a series resistor of 1 MΩ and a parallel capacitor of 56 nF, and two real dielectric films; (ii) a 20 nm organic polystyrene film spin-coated on a silicon substrate; (iii) a 10 nm SiO 2 inorganic layer thermally grown on silicon. A simple circuit model is introduced to simulate the charging shifts and the peak broadenings. Although this simple model faithfully reproduces the charging shifts in all three cases, and also some of the broadenings for the artificial dielectric and the polystyrene film, the additional broadening in the negatively charged peaks of the SiO 2 dielectric film cannot be accounted for. It is also claimed that these experimental findings can be used for extracting material-specific dielectric properties.

Dislocation structure and crystallite size distribution in lath martensite determined by X-ray diffraction peak profile analysis

Abstract X-ray diffraction peak profiles obtained from 18Ni lath martensite were analyzed in accordance with the modified Williamson – Hall and modified Warren – Averbach methodologies, aided by supplemental optical and transmission electron microscopy. After instrumental broadening removal, structural peak broadenings were determined for diffraction lines. Consequently, a log-normal size distribution with a mean size of about 156 nm was determined, corresponding reasonably to the lath width illustrated by means of transmission electron microscopy. Further, a dislocation density of 0.723 × 1016 m– 2 along with a near equal proportion of edge and screw dislocations were identified. Determination of the dislocation arrangement parameter revealed a weak dipole and thus, weak screening action of dislocation strain fields.

Domain-swapped dimerization of ZO-1 PDZ2 generates specific and regulatory connexin43-binding sites

PDZ domain scaffold proteins are capable of assembling macromolecular protein complexes in diverse cellular processes through PDZ-mediated binding to a short peptide fragment at the carboxyl tail of target proteins. How each PDZ domain specifically recognizes its target protein(s) remains a major conceptual question, as at least a few out of the several hundred PDZ domains in each eukaryotic genome share overlapping binding properties with any given target protein. Here, we show that the domain-swapped dimerization of zonula occludens-1 PDZ2 generates a distinct interface that functions together with the well-separated canonical carboxyl tail-binding pocket in each PDZ unit in binding to connexin43 (Cx43). We further demonstrate that the charge-charge interaction network formed by residues in the PDZ dimer interface and upstream residues of the Cx43 peptide not only provides the unprecedented interaction specificity for the complex but may also function as a phosphorylation-mediated regulatory switch for the dynamics of the Cx43 gap junctions. Finally, we provide evidence that such domain-swapped dimer assembly also occurs in other PDZ domain scaffold proteins. Therefore, our findings present a new paradigm for understanding how some PDZ domain proteins specifically bind to and regulate the functions of their target proteins.

Effects of rapid thermal annealing on the emission properties of highly uniform self-assembled InAs∕GaAs quantum dots emitting at 1.3μm

The authors report the effects of rapid thermal annealing (RTA) on the emission properties of highly uniform self-assembled InAs quantum dots (QDs) emitting at 1.3μm grown on GaAs substrate by metal organic chemical vapor deposition. Postgrowth RTA experiments were performed under N2 flow at temperatures ranging from 600to900°C for 30s using GaAs proximity capping. Surprisingly, in spite of the capping, large blueshifts in the emission peak (up to about 380meV at 850°C) were observed (even at low annealing temperatures) along with enhanced integrated photoluminescence (PL) intensities. Moreover, pronounced peak broadenings occurred at low annealing temperatures (<700°C), indicating that RTA does not always cause peak narrowing, as is typically observed with traditional QDs with large inhomogeneous PL linewidths. The mechanism behind the large peak blueshift was studied and found to be attributed to the as-grown QDs with large size, which cause a larger dot-barrier interface and greater strain in and near the QD regions, thereby greatly promoting Ga–In intermixing across the interface during RTA. The results reported here demonstrate that it is possible to significantly shift the emission peak of the QDs by RTA without any additional procedures, even at lower annealing temperatures.

粉末Ｘ線回折プロファイル関数の開発

A model peak profile function synthesized by multiple convolutions of the intrinsic peak profile with the instrumental functions of a conventional powder X-ray diffractometer has been developed. The general recipe for deriving accurate instrumental functions as well as an efficient numerical method for evaluating the convolutions are presented. The validity of the model function has been examined by comparing the experimental peak profiles measured in different conditions. The use of the convoluted model profile function provides a convenient and reliable way to estimate the integrated intensities, intrinsic peak positions and broadenings.

Dynamics of collagen hydration by quasielastic neutron scattering

QENS spectra from 52% H 2O-hydrated collagen fibres ( T=276–321 K) were modelled by three-component scattering laws including small central peak broadenings. These give diffusion coefficients for mobile H 2O of ∼5×10 −6 cm 2/s, with activation energy ∼2 kcal/mol. The broad components relate to localised modes.

Raman and Spectroscopic Ellipsometry Studies of P-Doped Poly-Si

ABSTRACTPhosphorus-doped poly-Si films were studied with Raman spectroscopy and spectroscopic ellipsometry. We determine strain and grain size and compare with a structural analysis using plan-view transmission electron microscopy and atomic force microscopy. We analyze the derivatives of our ellipsometry data (peak shifts and broadenings) using analytical lineshapes, which are affected by grain size, film thickness, doping, and inhomogeneity, but only minimally by macroscopic biaxial strain.

Raman study of the relationship between nanoparticles and photoluminescence in spark-processed silicon

Spark-processed silicon (sp-Si) that strongly photoluminesces (PL) in the blue and green regions of the visible spectrum has been analyzed by Raman scattering, in order to probe a possible relationship between the presence and size of Si nanoparticles and PL emission wavelengths. Spatially resolved Raman spectra were measured across spark-processed regions, scanning areas which vary in PL intensity but not wavelength. The observed small shifts and broadenings of the Raman signals indicate the presence of Si particles having diameters of about 15 nm in the central, photoluminescing section of the sp region. Slightly smaller Si crystallites with sizes of about 8–9 nm were found in the halo region which does not contribute to PL. Furthermore, the Raman peak shifts and broadenings are essentially identical for blue and green photoluminescing sp-Si. These results suggest that the PL of sp-Si is not caused by a quantum-size effect which is coupled to the presence of Si nanoparticles.

Triple-axis diffractometry on GaN/Al2O3(001) and AlN/Al2O3(001) using a parabolically curved graded multilayer as analyzer

X-ray Bragg diffraction profiles of epitaxial layers of A1N and GaN grown onc-plane sapphire were measured with a novel triple-axis diffractometer using a parabolically curved, graded multilayer mirror in the diffracted beam instead of an analyzer crystal. In addition, the intensity of the incident beam is enhanced by a parabolically graded multilayer mirror acting as condensor for a Ge(022) channel-cut monochromator. This novel diffractometer configuration provides a clear improvement in intensity at sufficiently high resolution for the study of angular peak broadening and peak shape functions of weak reflections from samples of poor structural quality and from thin layers. For AlN and GaN, the reason for peak broadening of symmetric rocking curves was found to be small coherence lengths parallel to the substrate surface and not distinct out-of-plane misorientations. Additionally, different peak broadenings of asymmetric reflections due to edge dislocations were observed for AlN and GaN.

Evaluation and measurement of the experimental gamma-ray peak broadenings and recovery times in a gain stabilized system

Peak broadenings induced by gain wander in a gain stabilized system were measured and found to approximate values determined from prediction techniques and a system simulation. An equation is derived for the recovery time of the system; its predictions are validated by experimental measurements.

Study of strain and disorder of InxGa1−xP/(GaAs, graded GaP) (0.25≤x≤0.8) using spectroscopic ellipsometry and Raman spectroscopy

The optical properties of InxGa1−xP/GaAs and InxGa1−xP/graded InGaP/GaP (0.25≤x≤0.8) epitaxial layers have been studied using spectroscopic ellipsometry and Raman spectroscopy. The (E1,E1+Δ1) critical points and the first-order phonon frequencies were determined as a function of In composition. The general behavior of the peak shifts and broadenings of both the E1 gaps and the optical phonons of InxGa1−xP/GaAs can be explained in terms of biaxial strain and strain relaxation caused by lattice-mismatch. The near-cancellation of E1 gap change due to the compensation effect between alloy composition and misfit strain is observed. As misfit strain increases, the E1 gap broadens whereas the phonon line shape does not change. In strain relaxed samples of InxGa1−xP/(GaAs, graded GaP) (0.3≤x≤0.8), the E1 gap linewidth shows upward bowing as a function of In composition.

Above-threshold ionization spectra for hydrogen atoms exposed to ultra-intense linearly polarized high-frequency laser pulses

The time evolution of H (1s) atoms in very intense (Io approximately=3.5*1018 W cm-2) high-frequency ( omega =1 au) laser fields is calculated by numerical integration of the time-dependent Schrodinger equation in the Kramers-Henneberger frame. ATI spectra are analysed as a function of pulse duration for a sin2 pulse shape and pulse durations in the sub-picosecond range. A prominent feature in these spectra is a combination of peak broadenings due to interaction time and laser power. For short pulses the spectra are dominated by ionization early during the pulse. For the longer pulses find an additional series of peaks that correspond to ionization from the Stark-shifted H(nl) levels (n)1) near the peak of the laser pulse. Such peak positions (for n=1) were predicted before by Pont et al. (1990) using a high-frequency Floquet theory,but have been calculated for the first time in an ab initio approach for finite laser pulses.

AES and XPS studies of oxygen stabilized alpha zirconium

In order to examine the effect of oxygen on AES and XPS spectra of zirconium, we have made AES and XPS studies of oxygen stabilized alpha zirconium (α-Zr(O)) with various oxygen contents. Both AES and XPS spectra of α-Z(O) are varied continuously with increasing oxygen content up to 25 at% and no evidence for the surface precipitation of the oxide or the surface depletion of oxygen is observed. The surface oxygen concentration of the α-Zr(O) determined by AES peak intensities shows a quite good agreement with the bulk oxygen concentration even after a prolonged Ar ion bombardment, whereas the depletion of oxygen is seen in ZrO 2 . In XPS spectra, the conduction band of α-Zr(O) remains for oxygen content up to 25 at%, while peak broadenings of Zr 4p and O 2p become notable above 15at% O. Such an electronic structure change should be taken into account for the investigation of the different behavior under Ar ion bombardment between α-Zr(O) and ZrO 2 .

A first order diffusion approximation to atomic redistribution during ion bombardment of solids, II. finite range approximation

Abstract An improved diffusion approximation, in which diffusion enhancement operates only over a finite depth, to model atomic redistribution resulting from recoil and cascade mixing during ion bombardment of solids is described, it is shown that this model correctly simulates the main results of the more complex linear cascade atomic collision calculations of positive mean depth shifts, negative peak shifts, broadenings and exponential tails in surface concentration of diffusant marker species during sputter erosion. The analytic method of generalisation to any arbitrary and more realistic diffusivity-depth profiles is also outlined.

Influence of the particle size (5–35 μm) of spherical silica on column efficiencies in high-pressure liquid chromatography

The preparation of spherical silica with sieve fractions between 5 and 35 μm is described. Permieabilities ( K) and relative peak broadenings ( h) have been determined experimentally to be a functionof the average particle size ( d p) of the narrow-sieve fractions ( h ??? d p 1.3). The average particle size can be calculated to a reasonable approximation from the permeability of the column packed by the balanced density method. Simple relationships are proposed for estimating the constants in the equation h = A + Cu as a function of d p . The maximum sample size is about 2·10 1 g of sample per gram of silica. Some consequences of the pressure limits in high-pressure liquid chromatography are discussed.