Evolution Of Line Shape Research Articles

Comparison of non-Hermitian three-dimensional quantization line shape in ion-doped microcrystals

In this paper, we studied the relationship between non-Hermitian quantization and line shape in ion-doped microcrystals. We depict the Eu3+: BiPO4 exhibited a broad line shape in contrast to Eu3+: NaYF4, and Dy3+: BiPO4. The line shape is controlled through angle quantization (constructive and destructive quantization) and phonon detuning effects. The Eu3+: BiPO4 and Eu3+: NaYF4 exhibits less sensitivity to line shape as compared to Dy3+: BiPO4. The more sensitivity of Dy3+: BiPO4 is supported by the presence of multiple levels, which disrupt the transition from destructive (out of phase de-phase rate Г) to constructive (in phase dressing Rabi frequency G) three-dimensional quantization. The line shape evolution from out of phase to in phase could be tuned by changing time gate position (the ratio of G and Г regulated largely) and time gate width (the ratio of G and Г regulated on a small scale). We observed that the line shape ratio in Dy3+: BiPO4 is significantly smallest (13.63 %) as compared to Eu3+: NaYF4 (61.29 %) and Eu3+: BiPO4 (85.18 %). Furthermore, the angle quantization affects the line shape evolution of fluorescence and Autler-Townes. However, spontaneous four-wave mixing line shape evolution can not be controlled by the angle quantization. Such results hold significant potential for applications in long band stop filter.

Dressing Stark splitting of time-resolved excitation spectra in Eu3+-doped BiPO4 micro-crystals

The Stark splitting of 5DJ-7FJ transitions has been investigated by time-resolved dressing excitation spectra in Eu3+-doped BiPO4 micro-crystals with different phase structures. The evolution of the Stark transition peaks significantly depends on the laser power, bandwidth, delay time, temperature, and phase structures of BiPO4 crystals. It is explained by photon-phonon coupling dressing effect. There is competition between the crystal field splitting and the dressing splitting alignment in the line-shape evolution. The time-resolved dressing excitation spectrum provides an effective method to investigate Stark splitting and modulate line-shape for applications in optical communication.

Localisation-to-delocalisation transition of moiré excitons in WSe2/MoSe2 heterostructures.

Moiré excitons (MXs) are electron-hole pairs localised by the periodic (moiré) potential forming in two-dimensional heterostructures (HSs). MXs can be exploited, e.g., for creating nanoscale-ordered quantum emitters and achieving or probing strongly correlated electronic phases at relatively high temperatures. Here, we studied the exciton properties of WSe2/MoSe2 HSs from T = 6 K to room temperature using time-resolved and continuous-wave micro-photoluminescence also under a magnetic field. The exciton dynamics and emission lineshape evolution with temperature show clear signatures that MXs de-trap from the moiré potential and turn into free interlayer excitons (IXs) for temperaturesabove 100 K. The MX-to-IX transition is also apparent from the exciton magnetic moment reversing its sign when the moiré potential is not capable of localising excitons at elevated temperatures. Concomitantly, the exciton formation and decay times reduce drastically. Thus, our findings establish the conditions for a truly confined nature of the exciton states in a moiré superlattice with increasing temperature and photo-generated carrier density.

Band bending and k -resolved band offsets at the HfO2/n+(p+)Si interfaces explored with synchrotron-radiation ARPES/XPS

$\mathrm{Hf}{\mathrm{O}}_{2}/\mathrm{Si}$ interface is among the most studied heterostructure materials due to the use of ${\mathrm{HfO}}_{2}$ in the mainstream Si microelectronic technology. Following the discovery of new functionalities in ${\mathrm{HfO}}_{2}$ such as ferroelectric and reversible resistance-switching properties, we study ultrathin ${\mathrm{HfO}}_{2}$ films grown on highly doped (${p}^{+}$ and ${n}^{+}$) Si by means of synchrotron-based soft-x-ray spectroscopy techniques, such as x-ray photoelectron spectrosopy (XPS) and angle resolved photoelectron spectroscopy (ARPES). With angular resolution, we directly obtain the electronic dispersions $E$(k) of the single-crystalline Si substrate in contact with the ${\mathrm{HfO}}_{2}$ overlayer, depending on the Si doping and heat treatment, and determine the k-resolved band offset at the interface. Analysis of the Hf and Si core-level energies and line shapes as a function of photon energy yields band bending in ${\mathrm{HfO}}_{2}$ and Si. The evolution of the Hf $4f$ linewidth upon annealing points to development of a potential distribution across ${\mathrm{HfO}}_{2}$ due to charged defects at the surface and interface with Si. The effect of intense x-ray beam on the $\mathrm{Hf}{\mathrm{O}}_{2}/\mathrm{Si}$ interfaces, distorting their pristine electronic structure, is evaluated from the time evolution of line shape and position under irradiation. We propose a model explaining the effects of both heat treatment and x-ray irradiation on the $\mathrm{Hf}{\mathrm{O}}_{2}/\mathrm{Si}$ electronic structure in terms of oxygen vacancies generated at the surface of ${\mathrm{HfO}}_{2}$ and its interface to Si, where the released O atoms react with Si to form ${\mathrm{SiO}}_{x}$ at the interface. The knowledge of the irradiation-dependent band bending is essential for precise determination of the k-dependent band offset locally at the $\mathrm{Hf}{\mathrm{O}}_{2}/\mathrm{Si}$ interface.

Precise dynamic characterization of microcombs assisted by an RF spectrum analyzer with THz bandwidth and MHz resolution.

The radio frequency (RF) spectrum of microcombs can be used to evaluate its phase noise features and coherence between microcomb teeth. Since microcombs possess characteristics such as high repetition rate, narrow linewidth and ultrafast dynamical evolution, there exists strict requirement on the bandwidth, resolution and frame rate of RF measurement system. In this work, a scheme with 1.8-THz bandwidth, 7.5-MHz spectral resolution, and 100-Hz frame rate is presented for RF spectrum measurement of microcombs by using an all-optical RF spectrum analyzer based on cross-phase modulation and Fabry Perot (FP) spectrometer, namely FP-assisted light intensity spectrum analyzer (FP-assisted LISA). However, extra dispersion introduced by amplifying the microcombs will deteriorate the bandwidth performance of measured RF spectrum. After compensating the extra dispersion through monitoring the dispersion curves measured by FP-assisted LISA, the more precise RF spectra of microcombs are measured. Then, the system is used to measure the noise sidebands and line shape evolution of microcombs within 2s temporal window, in which dynamic RF combs variation at different harmonic frequencies up to 1.96 THz in modulation instability (MI) state and soliton state are recorded firstly. Therefore, the improved bandwidth and resolution of FP-assisted LISA enable more precise measurement of RF spectrum, paving a reliable way for researches on physical mechanism of microcombs.

Mobility of Aromatic Guests and Isobutane in ZIF-8 Metal–Organic Framework Studied by 2H Solid State NMR Spectroscopy

Metal–organic framework ZIF-8 is renowned for its adsorption and separation properties influenced by the framework flexibility. Although much effort was put into understanding the molecular mechanism of such gate-opening (dynamical and static), the mobility of large guest themselves remained unclear. In this work, we present a detailed 2H solid-state NMR investigation of large guests (xylene isomers, benzene, toluene, and isobutane) confined inside the ZIF-8. Evolution of line shape and T1, T2 relaxation times with temperature were interpreted in terms of existence of three different motional states for diffusing guest molecules: (i) the highly mobile guest molecules located in the central part of the cage; (ii) the bound state for a guest located on the cage wall or near the window; and (iii) the guest squeezing through the window with a subsequent release to the next cage. We report detailed quantitative analysis of molecular dynamics in each of the states and the kinetics of exchange between the bound ...

Ultrafast to Ultraslow Dynamics of a Langmuir Monolayer at the Air/Water Interface Observed with Reflection Enhanced 2D IR Spectroscopy.

Monolayers play important roles in naturally occurring phenomena and technological processes. Monolayers at the air/water interface have received considerable attention, yet it has proven difficult to measure monolayer and interfacial molecular dynamics. Here we employ a new technique, reflection enhanced two-dimensional infrared (2D IR) spectroscopy, on a carbonyl stretching mode of tricarbonylchloro-9-octadecylamino-4,5-diazafluorenerhenium(I) (TReF18) monolayers at two surface densities. Comparison to experiments on a water-soluble version of the metal carbonyl headgroup shows that water hydrogen bond rearrangement dynamics slow from 1.5 ps in bulk water to 3.1 ps for interfacial water. Longer time scale fluctuations were also observed and attributed to fluctuations of the number of hydrogen bonds formed between water and the three carbonyls of TReF18. At the higher surface density, two types of TReF18 minor structures are observed in addition to the main structure. The reflection method can take usable 2D IR spectra on the monolayer within 8 s, enabling us to track the fluctuating minor structures' appearance and disappearance on a tens of seconds time scale. 2D IR chemical exchange spectroscopy further shows these structures interconvert in 30 ps. Finally, 2D spectral line shape evolution reveals that it takes the monolayers hours to reach macroscopic structural equilibrium.

Understanding the Different Exciton–Plasmon Coupling Regimes in Two-Dimensional Semiconductors Coupled with Plasmonic Lattices: A Combined Experimental and Unified Equation of Motion Approach

We study exciton–plasmon coupling in two-dimensional semiconductors coupled with Ag plasmonic lattices via angle-resolved reflectance spectroscopy and by solving the equations of motion (EOM) in a coupled oscillator model accounting for all the resonances of the system. Five resonances are considered in the EOM model: semiconductor A and B excitons, localized surface plasmon resonances (LSPRs) of plasmonic nanostructures, and the lattice diffraction modes of the plasmonic array. We investigated the exciton–plasmon coupling in different 2D semiconductors and plasmonic lattice geometries, including monolayer MoS2 and WS2 coupled with Ag nanodisk and bowtie arrays and examined the dispersion and line shape evolution in the coupled systems via the EOM model with different exciton–plasmon coupling parameters. The EOM approach provides a unified description of the exciton–plasmon interaction in the weak, intermediate, and strong coupling cases with correctly explaining the dispersion and lineshapes of the complex system. This study provides a much deeper understanding of light–matter interactions in multilevel systems in general and will be useful to instruct the design of novel two-dimensional exciton–plasmonic devices for a variety of optoelectronic applications with precisely tailored responses.

Observation of a Structure and Line Shape Evolution of Non-resonant Microwave Absorption in a SmFeAs(O, F) Polycrystalline Iron Pnictide Superconductor

We report on the non-resonant microwave absorption (NRMA) in a SmFeAsO0.88F0.12 polycrystalline sample measured at 9.45 GHz below T c (6.06−42 K). The NRMA line shape has a structure with, remarkably, two peaks, namely; a broad peak 1 and a narrow peak 2. The narrow peak 2 is a new feature in the NRMA line shape of iron pnictide superconductors, and it appears at both high (0−10000 G) and low field (−250 through 0 to +250 G) sweeps. We have observed that the structure and NRMA line shape evolves as a function of temperature and field modulation amplitude. Most importantly, we observed that this line shape evolution as a function of temperature does not show a crossover from ‘normal’ to ‘anomalous’ type of absorption.

Interface originated modification of electron-vibration coupling in resonant photoelectron spectroscopy

We present a comprehensive study of the photon-energy ($h\ensuremath{\nu}$)-dependent line-shape evolution of molecular orbital signals of large $\ensuremath{\pi}$-conjugated molecules by resonant photoelectron spectroscopy (RPES). A comparison to RPES data on small molecules suggests that the excitation into different vibrational levels on the intermediate-state potential energy surface of the electronic excitation is responsible for the observed effect. In this simplified picture of electron-vibration coupling the character of the potential energy surfaces involved in the RPES process determines the line shape of the molecular orbital signal for a particular $h\ensuremath{\nu}$. We use the sensitivity of this effect to probe the influence of different interfaces on the electron-vibration coupling in the investigated systems. The magnitude of the variation in line shape throughout the particular $h\ensuremath{\nu}$ region allows us to reveal significant differences within the physisorptive regime.

Study of the ion role in the magnetic properties of the AFM ring using Mössbauer spectroscopy

Abstract In recent years the synthesis of antiferromagnetic rings traced a path to the observation of interesting quantum coherence phenomena in heterometallic Single Molecule Magnets. Because of the presence of different magnetic centers, it is crucial to understand the distribution of the molecular spin on all the sites. 57Fe Mossbauer spectroscopy is an efficient and powerful technique to contribute to this knowledge in antiferromagnetic wheels containing iron ions. We analyze the Cr7FeII wheel: the Mossbauer line shape evolution of low temperature spectra (2.1 K) at different external fields is illustrated and the mean spin value of the iron ion is evaluated.

Evolution of infrared photoreflectance lineshape with temperature in narrow-gap HgCdTe epilayers

Temperature-dependent (11–290K) infrared photoreflectance (PR) measurements are performed on as-grown arsenic-doped HgCdTe epilayers in a midinfrared spectral region. Main PR features near bandedge manifest clear evolution of lineshape with temperature, of which the fittings identify besides a band-band process several below-gap processes. Analyses show that these features are due to photomodulation-induced screening of donor-acceptor pairs and photomodulation of band- impurity and band-band reflectance, their intensities correlate to the joint concentration of the involved energetic states. Temperature-dependent infrared PR may be a right optical spectroscopy for identifying impurity levels in semiconductors such as HgCdTe with high-density impurities.

Spin polarization of the magnetic spiral inNaCu2O2as seen by nuclear magnetic resonance spectroscopy

The incommensurate (IC) spin ordering in quasi-1D edge-shared cuprate NaCu_2O_2 has been studied by ^{23}Na nuclear magnetic resonance spectroscopy in an external magnetic field near 6 Tesla applied along the main crystallographic axes. The NMR lineshape evolution above and below T_N\approx12 K yields a clear signature of an IC static modulation of the local magnetic field consistent with a Cu^{2+} spin spiral polarized in the bc-plane rather than in the ab-plane as reported from earlier neutron diffraction data.

Structural evolution of ZnSe/ZnS quantum dots during growth interruptions under hydrogen flows

It was demonstrated that ZnSe/ZnS quantum dots (QDs) could undergo structural transitions from 3D islands to 2D layer during growth interruption (GI) under hydrogen flows. In addition to the structural transition, a complex ripening process of the ZnSe QDs were observed together. Temperature-dependent photoluminescence (PL) measurements show that the ZnSe QDs turned into a quasi-2D layer, when the GI reached 60 s. PL lineshape evolution through the GI suggests two ripening regimes for the ZnSe QDs, which are in striking agreement with those for CdSe QDs.

Microphotoluminescence spectroscopy of CdSe quantum dots grown on vicinal‐surface and exact‐orientation substrates

We investigated the optical properties of CdSe quantum dots (QDs) grown by molecular-beam epitaxy on GaAs substrates using micro-photoluminescence spectroscopy. Comparison was made between the QDs grown on a substrate with a vicinal tilt of 2° in the [111] direction and those on an on-axis substrate. We have studied the evolution of lineshapes of QD photoluminescence spectra under the improved condition of spatial resolution. It was found that the use of a substrate with the vicinal surface leads to the suppression of excitonic PL emitted from a wetting layer. The PL studies revealed that the thermo-stability up to 150 K was obtained in the sample on the on-axis substrate, whereas rapid temperature-induced quenching starting from 6 K was observed in that grown on the vicinal substrate. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Highly sensitive optical monitoring of molecular film growth by organic molecular beam deposition

Reflectance anisotropy spectroscopy (RAS) has been employed to study in situ the growth of thin α-sexithiophene films by organic molecular beam deposition onto an organic substrate. A large anisotropy can be detected by following the line shape evolution of the RAS spectrum; in addition, the signal variation at a fixed wavelength is used to monitor the film growth. The signal intensity scales with the deposited thickness, demonstrating a very high sensitivity of RAS to less than 1/50 of a monolayer. Evidence of the advantages of RAS to monitor in real time the growth of molecular films and to probe in situ their properties is therefore obtained.

Effect of growth conditions on optical properties of CdSe/ZnSe single quantum dots

In this work, we have investigated the optical properties of two samples of CdSe quantum dots by using submicro-photoluminescence spectroscopy. The effect of vicinal-surface GaAs substrates on their properties has been also assessed. The thinner sample, grown on a substrate with vicinal surface, includes only dots with a diameter of less than 10 nm (type A islands). Islands of an average diameter of about 16 nm (type B islands) that are related to a phase transition via a Stranski–Krastanow growth process are also distributed in the thicker sample grown on an oriented substrate. We have studied the evolution of line shapes of PL spectra for these two samples by improving spatial resolution that was achieved using nanoapertures or mesa structures. It was found that the use of a substrate with the vicinal surface leads to the suppression of excitonic PL emitted from a wetting layer.

Accuracy and convergence of parametric dislocation dynamics

In the parametric dislocation dynamics (PDD), closed dislocation loops are described as an assembly of segments, each represented by a parametric space curve. Their equations of motion are derived from an energy variational principle, thus allowing large-scale computer simulations of plastic deformation. We investigate here the limits of temporal and spatial resolution of strong dislocation interactions. The method is demonstrated to be highly accurate, with unconditional spatial convergence that is limited to distances of the order of interatomic dimensions. It is shown that stability of dislocation line shape evolution requires very short time steps for explicit integration schemes, or can be unconditionally stable for implicit time integration schemes. Limitations of the method in resolving strong dislocation interactions are established for the following mechanisms: dislocation generation, annihilation, dipole and junction formation, pileup evolution.

Magnetic rotation molecular spectroscopy using an oscillating field

The high resolution magnetic rotation spectrum of a diatomic molecule is considered. A procedure is described for calculation of the magnetic rotation signal in both first and second harmonic for an oscillating magnetic field in the low-field limit. The procedure is simpler than other methods available in the literature, and a more complete account is taken of the various possible contributions to the signal. Perturbations between electronic states that make it possible to observe magnetic rotation signals for high-J transitions are discussed, along with the associated evolution of line shape that complicates frequency measurements from magnetic rotation spectra. Examples are given from a recent magnetic rotation study of the A 3Π1u–X 1Σg+ system of Br279.

Core-level photoemission study of 2D ordered Bi/Si(100) interfaces

A high resolution core-level photoemission investigation of 2D ordered Bi layers grown on Si(100)-(2×1) is presented. We study the Si 2p and Bi 5d core-levels at room temperature as a function of coverage and in the reconstructed phases. The different Bi structural configurations around the monolayer coverage and in the (2× n)-reconstructed phase are derived from the core-level lineshape evolution. By following the Fermi level pinning, the presence of Bi-induced occupied electronic states close to the Si mid-gap is suggested.