Large Linewidth Research Articles

Structural Characterization of Electron Donors in Ziegler-Natta Catalysts.

Ziegler–Natta catalysis is a very important industrial process for the production of polyolefins. However, the catalysts are not well-understood at the molecular level. Yet, atomic-scale structural information is of pivotal importance for rational catalyst development. We applied a solid-state NMR/density functional theory tandem approach to gain detailed insight into the interactions between the catalysts’ support, MgCl2, and organic electron donors. Because of the heterogeneity of the samples, large line widths are observed in the carbon spectra. Despite this, good agreement between experimental and computational values was reached, and this shows that 1,3-diether based donors coordinate at (110) surface sites, while phthalates are less selective and coordinate at both (104) and (110) surface sites.

Domain wall oscillation in magnetic nanowire with a geometrically confined region

In conventional magnetic devices such as magnetic tunnel junctions, a steady oscillation of a soft layer magnetization could find its application in various electronic systems. However, these devices suffer from their low output signal and large spectral linewidth. A more elegant scheme based on domain wall oscillation could be a solution to these issues if DW dynamics could be controlled precisely in space and time. In fact, in DW devices, the magnetic configuration of domain wall and its position are strongly dependent on the device geometry and material properties. Here we show that in a constricted device with judiciously adjusted dimensions, a DW can be trapped within the central part and keep oscillating with a single frequency f. For 200 nm by 40 nm nanowire, f was found to vary from 2 GHz to 3 GHz for a current density between 4.8 × 1012 A/m2 and 5.6 × 1012 A/m2. More interestingly, the device fabrication is simply based on two long nanowires connected by adjusting the offset in both x and y directions. This new type of devices enables the conversion of dc-current to an ac-voltage in a controllable manner opening thus the possibility of a new nano-oscillators with better performance.

A Green Bank Telescope Survey of Large Galactic H ii Regions

As part of our ongoing HII Region Discovery Survey (HRDS), we report the Green Bank Telescope detection of 148 new angularly-large Galactic HII regions in radio recombination line (RRL) emission. Our targets are located at a declination greater than -45deg., which corresponds to 266deg. > l > -20deg. at b = 0deg. All sources were selected from the WISE Catalog of Galactic HII Regions, and have infrared angular diameters >260''. The Galactic distribution of these "large" HII regions is similar to that of the previously-known sample of Galactic HII regions. The large HII region RRL line width and peak line intensity distributions are skewed toward lower values compared with that of previous HRDS surveys. We discover 7 sources with extremely narrow RRLs <10 km/s. If half the line width is due to turbulence, these 7 sources have thermal plasma temperatures <1100 K. These temperatures are lower than any measured for Galactic HII regions, and the narrow line components may arise instead from partially ionized zones in the HII region photo-dissociation regions. We discover G039.515+00.511, one of the most luminous HII regions in the Galaxy. We also detect the RRL emission from three HII regions with diameters >100 pc, making them some of the physically largest known HII regions in the Galaxy. This survey completes the HRDS HII region census in the Northern sky, where we have discovered 887 HII regions and more than doubled the previously-known census of Galactic HII regions.

Innovative scheme for high-repetition-rate imaging of CN radical.

We have employed, to the best of our knowledge, a novel excitation scheme to perform the first high-repetition-rate planar laser-induced fluorescence (PLIF) measurements of a CN radical in combustion. The third harmonic of a Nd:YVO4 laser at 355nm due to its relatively large linewidth overlaps with several R branch transitions in a CN ground electronic state. Therefore, the 355nm beam was employed to directly excite the CN transitions with good efficiency. The CN measurements were performed in premixed CH4-N2O flames with varying equivalence ratios. A detailed characterization of the high-speed CN PLIF imaging system is presented via its ability to capture statistical and dynamical information in these premixed flames. Single-shot CN PLIF images obtained over a HMX pellet undergoing self-supported deflagration are presented as an example of the imaging system being applied towards characterizing the flame structure of energetic materials.

Imaging the molecular outflows of the prototypical ULIRG NGC 6240 with ALMA

Abstract We present 0.97 × 0.53 arcsec2 (470 pc × 250 pc) resolution CO (J = 2–1) observations towards the nearby luminous merging galaxy NGC 6240 with the Atacama Large Millimeter/submillimeter Array. We confirmed a strong CO concentration within the central 700 pc, which peaks between the double nuclei, surrounded by extended CO features along the optical dust lanes (∼11 kpc). We found that the CO emission around the central, a few kpc, has extremely broad velocity wings with full width at zero intensity ∼ 2000 km s−1, suggesting a possible signature of molecular outflow(s). In order to extract and visualize the high-velocity components in NGC 6240, we performed a multiple Gaussian fit to the CO data cube. The distribution of the broad CO components shows four extremely large line width regions (∼1000 km s−1) located 1–2 kpc away from both nuclei. Spatial coincidence of the large line width regions with H α, near-IR H2, and X-ray suggests that the broad CO (2–1) components are associated with nuclear outflows launched from the double nuclei.

Assembly of phospholipid nanodiscs of controlled size for structural studies of membrane proteins by NMR.

Suitable membrane mimetics are crucial to the performance of structural and functional studies of membrane proteins. Phospholipid nanodiscs (formed when a membrane scaffold protein encircles a small portion of a lipid bilayer) have native-like membrane properties. These have been used for a variety of functional studies, but structural studies by high-resolution solution-state NMR spectroscopy of membrane proteins in commonly used nanodiscs of 10-nm diameter were limited by the high molecular weight of these particles, which caused unfavorably large NMR line widths. We have recently constructed truncated versions of the membrane scaffold protein, allowing the preparation of a range of stepwise-smaller nanodiscs (6- to 8-nm diameter) to overcome this limitation. Here, we present a protocol on the assembly of phospholipid nanodiscs of various sizes for structural studies of membrane proteins with solution-state NMR spectroscopy. We describe specific isotope-labeling schemes required for working with large membrane protein systems in nanodiscs, and provide guidelines on the setup of NMR non-uniform sampling (NUS) data acquisition and high-resolution NMR spectra reconstruction. We discuss critical points and pitfalls relating to optimization of nanodiscs for NMR spectroscopy and outline a strategy for the high-resolution structure determination and positioning of isotope-labeled membrane proteins in nanodiscs using nuclear Overhauser enhancement spectroscopy (NOESY) spectroscopy, residual dipolar couplings (RDCs) and paramagnetic relaxation enhancements (PREs). Depending on the target protein of interest, nanodisc assembly and purification can be achieved within 12-24 h. Although the focus of this protocol is on protein NMR, these nanodiscs can also be used for (cryo-) electron microscopy (EM) and small-angle X-ray and neutron-scattering studies.

Strongly Coherent Single-Photon Emission from Site-Controlled InGaN Quantum Dots Embedded in GaN Nanopyramids

Group III-nitride materials have drawn a great deal of renewed interest due to their versatile characteristics as quantum emitters including room-temperature operation, widely tunable wavelengths from ultraviolet to infrared, and a high degree of linear polarization. However, most reported results for III-nitride-based quantum emitters show large inhomogeneous line width broadening in comparison to their lifetime-limited values, which is detrimental to achieving indistinguishability with high visibility. To overcome this, we propose an unprecedented InGaN quantum dot formation technique at the apex of GaN nanopyramid structures, which significantly suppresses inhomogeneous line width broadening. Using high-resolution transmission electron microscopy, a site-controlled InGaN quantum dot with small height (<2 nm) was estimated. No measurable screening effect or frequency jitter of the single-photon emission was observed, which leads to the narrow homogeneous emission line width (64 ± 8 μeV) beyond the spect...

Anomalously large ferromagnetic resonance linewidth in the Gd/Cr/Fe film plane

As an important parameter for characterizing the magnetization dynamics, Gilbert damping constant α in a thin film or a multilayer is generally extracted from the linear fitting of the frequency-dependence of the ferromagnetic resonance linewidth, sometimes accompanied with a tiny deviation of the linewidth to a smaller value at the low-frequency or high-frequency region due to the two-magnon scattering with an in-plane-field configuration, in which an in-plane magnetic field H perpendicular to a microwave field h was applied in film plane during measurement. In contrast, here we report, in ultrathin Gd/Cr/Fe multilayers, an anomalously large linewidth in the film plane at the low-frequency region. For the first time, we have successfully extracted the Gilbert damping constant from perfect theoretical fitting to the experimental data, by considering the effective direction of the magnetization around in precession staying out of the film plane when the in-pane H at which the precession starts is below the saturation field. This magnetization deviation from the film plane is found to have an obvious contribution to the enhanced linewidth caused by two magnon scattering, while slightly reduce the intrinsic linewidth. Under the same resonance frequency, the deviation angle reaches the maximum values at tCr = 1.0 nm while decreases when tCr increases to 1.5 nm, which coincides with the trend of the surface perpendicular anisotropy constant K⊥. A reduced intrinsic damping constant α is obtained as the introduction of Gd layer and Cr layer as a result of the competition between the spin pumping effect and the interfacial effects at the Fe/Gd and Fe/Cr interfaces. While the decreasing α for film with Cr layer thickness increasing to 1.5 nm might means the contribution of the electron density of states at the Fermi energy n(EF). This study offers an effective way to accurately obtain the intrinsic damping constant of spintronic materials/devices, which is essential for broad applications in spintronics.

Fano Resonances in Ultracompact Silicon‐on‐Insulator Compatible Integrated Photonic–Plasmonic Hybrid Circuits

AbstractA novel on‐chip Fano device is experimentally demonstrated operating at telecom wavelengths, which consists of an ultracompact plasmonic nanocavity integrated with two Si waveguides on a silicon‐on‐insulator substrate. It is observed that an Au symmetric split ring with a large linewidth can be coupled to an embedded Au nanorod with a narrow linewidth via excitation of an Si waveguide, contributing to a Fano resonance phenomenon. In addition, the relative precise control of the resonant properties, including the depth, lineshape, and central wavelength, is realized by varying the rotation angle of the Au nanorod. For further investigations, a coupled Lorentz oscillator model is applied to study the transmission peak arising within an absorption region in the nanocavity. Slow‐light effects and sensing characteristics are also verified with finite difference time domain simulations and numerical calculations. This device has achieved Fano resonance in integrated photonic–plasmonic hybrid circuits, which may find utility in optical communications, buffering, and sensing.

High sensitivity plasmonic sensor using hybrid structure of graphene stripe combined with gold gap-ring

Local surface plasmonic resonance (LSPR) produced by metallic nano-structures is often sensitive to the refractive index of the surrounding media and can be applied for sensing. However, it often suffers from large line width caused by large plasmonic radiative damping, especially in the infrared (IR) frequencies, which reduces the sensitivity. Here we propose a hybrid structure consists of a graphene stripe and a gold gap-ring at short-IR frequencies (1–3 µm). Due to the low loss and high plasmonic confinement of graphene, LSPR line width of 6 nm is obtained. In addition, due to the strong coupling of the gold gap-ring with graphene stripe, the intensity of graphene LSPR is enhanced by 100 times. Simulation results show that the sensitivity of the sensor is ~1000 nm/RIU (refractive index unit) and the figure of merit (FoM) can reach up to 383.

Super-Resolved Nuclear Magnetic Resonance Spectroscopy

We present a novel method that breaks the resolution barrier in nuclear magnetic resonance (NMR) spectroscopy, allowing one to accurately estimate the chemical shift values of highly overlapping or broadened peaks. This problem is routinely encountered in NMR when peaks have large linewidths due to rapidly decaying signals, hindering its application. We address this problem based on the notion of finite-rate-of-innovation (FRI) sampling, which is based on the premise that signals such as the NMR signal, can be accurately reconstructed using fewer measurements than that required by existing approaches. The FRI approach leads to super-resolution, beyond the limits of contemporary NMR techniques. Using this method, we could measure for the first time small changes in chemical shifts during the formation of a Gold nanorod-protein complex, facilitating the quantification of the strength of such interactions. The method thus opens up new possibilities for the application and acceleration of multidimensional NMR spectroscopy across a wide range of systems.

Impact of Interface Roughness Scattering on the Performance of GaAs/AlxGa1–xAs Terahertz Quantum Cascade Lasers

We investigate the impact of interface roughness (IFR) scattering on the performance of a series of the state-of-the-art GaAs/AlxGa1–xAs terahertz quantum cascade lasers (THz-QCLs) through a calculation of the induced inhomogeneous broadening and intersubband scattering rates. Our analysis includes two GaAs/Al0.15Ga0.85As THz-QCL devices with measured maximum operating temperatures at $T _{\mathrm {max}} =177$ K and 175 K, two GaAs/Al0.30Ga0.70As devices with $T _{\mathrm {max}} = 150$ K and 89 K, a GaAs/AlAs-Al0.15Ga0.85As device with $T _{\mathrm {max}} = 181$ K, and a GaAs/AlAs device that did not lase. The investigated QCL wafers were grown at the same solid-source molecular beam epitaxy facility and at fixed parameters, so that we expect a constant interface roughness quality for all devices. We find negligible impact of IFR scattering on the performance of devices that use $x =0.15$ barriers as well as for devices that use $x =0.30$ barriers with wide > 40 monolayers (ML) wells to support upper and lower laser levels. Fixing the barrier height to $x =0.30$ , we calculate a drastic increase of the IFR-induced linewidth broadening from ~0.66 meV to ~2 meV when the quantum wells thicknesses reduce from ~40 ML to ~30 ML and relate this effect to the observed reduction of $T _{\mathrm {max}}$ from 150 to 89 K. Furthermore, we calculate a large (~2 meV) IFR linewidth broadening and short (~1 ps) IFR intersubband scattering times for the device with pure AlAs layers and relate the consequent reduction of optical gain to the nonlasing of this device.

Gas kinematics in powerful radio galaxies at z ~ 2: Energy supply from star formation, AGN, and radio jets

We compare the kinetic energy and momentum injection rates from intense star formation, bolometric AGN radiation, and radio jets with the kinetic energy and momentum observed in the warm ionized gas in 24 powerful radio galaxies at z ~ 2. These galaxies are among our best candidates for being massive galaxies near the end of their active formation period, when intense star formation, quasar activity, and powerful radio jets all co-exist. All galaxies have VLT/SINFONI imaging spectroscopy of the rest-frame optical line emission, showing extended emission-line regions with large velocity offsets (up to 1500 km s-1) and line widths (typically 800–1000 km s-1) consistent with very turbulent, often outflowing gas. As part of the HeRGÉ sample, they also have FIR estimates of the star formation and quasar activity obtained with Herschel/PACS and SPIRE, which enables us to measure the relative energy and momentum release from each of the three main sources of feedback in massive, star-forming AGN host galaxies during their most rapid formation phase. We find that star formation falls short by factors 10−1000 of providing the energy and momentum necessary to power the observed gas kinematics. The obscured quasars in the nuclei of these galaxies provide enough energy and momentum in about half of the sample, however, only if both are transferred to the gas relatively efficiently. We compare with theoretical and observational constraints on the efficiency of the energy and momentum transfer from jet and AGN radiation, which favors the radio jets as main drivers of the gas kinematics.

Unified rule based correction for corners in proximity lithography mask using high resolution features

Printing industry and printing techniques are increasing its market value by new methodologies. The resolution and accuracy of the pattern transfer is always a challenge for the industry, especially for the proximity printing industries which use mask aligners. In this sector proximity correction structures which are printed at different proximity gap can play an important role. Different correction methods exist to increase the accuracy of pattern transfer, but most of them are defined for projection techniques in wafer steppers. Our main aim is to define a simple and universal rule based resolution enhancement, using the cost effective method of optical proximity correction for mask aligners. Our concept is based on the fact that today's mask fabrication allows for implementing amplitude structures on the mask with very high resolutions at competitive price. This gives the possibility to draw fine proximity correction structures operating in the resonance regime having Fresnel numbers larger than one. The most prominent problem that always exists is of corner rounding. Here, we have designed a correction structure to prevent corner rounding based on high resolution amplitude mask elements. We proceed to a detailed analysis of the results using simulation, optical characterization and printing. The main advantage of the new correction structure is that, both 10μm and larger line widths can be printed with precisions on the same wafer at the same proximity gap and in a single exposure.

Internally-loaded ring resonator configuration for optical filter applications

We study on-chip Wavelength Division Multiplexing (WDM) application of ring resonators on Silicon-on-Insulator (SOI) platform. Though WDM devices have been demonstrated earlier, there are certain challenges which are yet to be tackled. Large FSR and narrow line width requirement for a WDM device cannot be fulfilled in a conventional WDM device as the requirement for both the metrics demand opposing structural requirements from a ring resonator. A larger FSR demands for a smaller resonator length whereas smaller line width requires a large resonator length device. We overcome this using an embedded type ring resonator configuration. The structure is made of a racetrack type ring resonator with another ring embedded inside it (loading the external ring). Such structures are capable of showing coupled resonator induced transparency (CRIT) which can result in a very narrow line-width. We present initial experimental demonstration of CRIT in an internally loaded micro ring resonator fabricated on SOI material platform. The structures were optimized using 3D-FDTD analysis and coupling-matrix method.

Influence of the linewidth enhancement factor on the characteristics of the random number extracted from the optical feedback semiconductor laser

Random numbers play an important role in many fields, including information security, testing and engineering practice. Especially in information security, generation of secure and reliable random numbers, they have a significant influence on national security, financial stability, trade secrets and personal privacy. Generally, random number generators can be classified as two main types: pseudo random number generators and physical random number generators. Pseudo random numbers with high speed are generated by software algorithms, but the inherent periodicity will cause serious hidden dangers when they are used in information security. Random numbers based on physical entropy sources (such as electronic thermal noise, frequency jitter of oscillator, quantum randomness) can produce reliable random numbers. However, due to the limitation of traditional physical source bandwidth, their generation speeds are at a level of Mbit/s typically, which cannot meet the needs of the current high-speed and largecapacity communication. In 2008, Uchida et al. (2008 Nat. Photon. 2 728) realized the physical random number of 1.7 Gbit/s by using a wideband chaotic laser for the first time. The emergence of wideband physical entropy sources such as chaotic laser greatly promote the rapid development of the physical random number generators. As far as we know, a semiconductor laser can generate wideband chaotic signals under external disturbances such as optical feedback, optical injection or photoelectric feedback. However, compared with the structures of other two lasers, the structure of the optical feedback semiconductor laser is simple and easy to integrate. Therefore, chaotic signals have received great attention to produce high-speed physical random number extracted from the optical feedback semiconductor laser. In the reported schemes, a variety of post-processing methods are used to improve the speed and randomness of random numbers. Besides, optimizing the chaotic entropy source can also improve the performance of random number. So far, the influence of internal parameters on the dynamic characteristics of semiconductor lasers has attracted wide attention. The linewidth enhancement factor is one of the key parameters for a semiconductor laser. The values of linewidth enhancement factor are different, depending on the type of semiconductor laser. The existence of linewidth enhancement factor results in a large number of unstable dynamic characteristics of semiconductor lasers. Therefore, it is of great significance for studying the influence of the linewidth enhancement factor on performance of random numbers. In this paper, we focus on the influence of the linewidth enhancement factor on the randomness of the obtained random numbers. The time delay characteristics and complexity are two important parameters to measure the quality of chaotic signals. The simulation results show that with the increase of the linewidth enhancement factor, the time delay characteristic peak of the chaotic signal from an optical feedback semiconductor laser decreases gradually, meanwhile, the maximum Lyapunov exponent of chaotic signal increases gradually. The randomness of random numbers, generated by the chaotic signal from the optical feedback semiconductor laser under different linewidth enhancement factors, is tested by NIST SP 800-22. The test results show that semiconductor laser with larger linewidth enhancement factor is chosen as a physical entropy source to generate random numbers with high quality.

Continuous Gradient Temperature Raman Spectroscopy of Oleic and Linoleic Acids from -100 to 50°C.

We analyzed the unsaturated fatty acids oleic (OA, 18:1n-9) and linoleic (LA, 18:2n-3), and a 3:1 LA:OA mixture from -100 to 50°C with continuous gradient temperature Raman spectroscopy (GTRS). The 20Mb three-dimensional data arrays with 0.2°C increments and first/second derivatives allowed rapid, complete assignment of solid, liquid, and transition state vibrational modes. For OA, large spectral and line width changes occurred in the solid state γ to α transition near -4°C, and the melt (13°C) over a range of only 1°C. For LA, major intensity reductions from 200 to 1750cm-1 and some peak shifts marked one solid state phase transition at -50°C. A second solid state transition (-33°C) had minor spectral changes. Large spectral and line width changes occurred at the melt transition (-7°C) over a narrow temperature range. For both molecules, melting initiates at the diene structure, then progresses towards the ends. In the 3:1 LA:OA mixture, some less intense and lower frequencies present in the individual lipids are weaker or absent. For example, modes assignable to C8 rocking, C9H-C10H wagging, C10H-C11H wagging, and CH3 rocking are present in OA but absent in LA:OA. Our data quantify the concept of lipid premelting and identify the flexible structures within OA and LA, which have characteristic vibrational modes beginning at cryogenic temperatures.

Room-temperature exciton-polaritons with two-dimensional WS2.

Two-dimensional transition metal dichalcogenides exhibit strong optical transitions with significant potential for optoelectronic devices. In particular they are suited for cavity quantum electrodynamics in which strong coupling leads to polariton formation as a root to realisation of inversionless lasing, polariton condensation and superfluidity. Demonstrations of such strongly correlated phenomena to date have often relied on cryogenic temperatures, high excitation densities and were frequently impaired by strong material disorder. At room-temperature, experiments approaching the strong coupling regime with transition metal dichalcogenides have been reported, but well resolved exciton-polaritons have yet to be achieved. Here we report a study of monolayer WS2 coupled to an open Fabry-Perot cavity at room-temperature, in which polariton eigenstates are unambiguously displayed. In-situ tunability of the cavity length results in a maximal Rabi splitting of ħΩRabi = 70 meV, exceeding the exciton linewidth. Our data are well described by a transfer matrix model appropriate for the large linewidth regime. This work provides a platform towards observing strongly correlated polariton phenomena in compact photonic devices for ambient temperature applications.

Electron Spin Resonance Study of Co-doped ZnO System: Spin-Canted Magnetism and Sintering Effects

We report on the electron spin resonance (ESR) studies in the Mn:Ni and Mn:Gd co-doped ZnO system sintered at 500 and 800 °C. We found that sintering temperature has strong effect on the ESR line widths, with the Mn-Gd co-doped ZnO system showing the largest effect. Increasing sintering temperature has increased the line widths considerably, running into Kilo Oersted range. These large line widths indicate magnetic in-homogeneities and disorder and are consistent with the occurrence of secondary phases due to high-temperature sintering. Further analysing the asymmetry parameters, together with Δg/ g-values, we explain the weak ferromagnetism at low temperatures in 500°C sintered Mn:Gd-ZnO system to be due to spin canting which is the parasitic or the ‘spin-canted magnetism’. The ESR line intensity which is the spin susceptibility shows a paramagnetic behaviour in the range 300–100 K and shows a sharp rise and a peak around 40 K consistent with the magnetization data reported earlier. In the case of Mn:Ni–ZnO system, the Δg/ g and P asc parameters, which are proportional to spin canting and magneto-crystalline anisotropy, closely follow each other representing the classic picture of Moriya-Dzyaloshinsky.

Collective mode splitting in hybrid heterostructures

We report on a drastic change of the Ni collective magnetization dynamics when incorporated into a $\mathrm{Ni}\text{/}{\mathrm{V}}_{2}{\mathrm{O}}_{3}$ heterostructure. Two, unexpected, well-defined Ni ferromagnetic resonance (FMR) modes are observed in the coexistence region of the first-order ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ structural phase transition (SPT). The phase coexistence across the ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ SPT can explain the presence of the two resonance fields but not their anticrossing and large linewidth broadenings. Our results imply a strong coupling between the lattice dynamics of the strongly correlated oxide (${\mathrm{V}}_{2}{\mathrm{O}}_{3}$) and the magnon modes of the ferromagnet (Ni) in this hybrid. This and additional experiments on Ni grown on $\mathrm{SrTi}{\mathrm{O}}_{3}$, a prototypical second-order phase transition oxide, imply that these effects require the presence of first-order transitions in the oxides.