Similar Line Shapes Research Articles

“Green” Aqueous Synthesis, Structural, and Optical Properties of Quaternary Cu2ZnSnS4 and Cu2NiSnS4 Nanocrystals

Element substitution in Cu2ZnSnS4‐like chalcogenides offers the potential to create alternative low‐cost photovoltaic and thermoelectric materials with tunable properties. In this work, the “green” synthesis of colloidal cation‐substituted Cu–Ni–Sn–S nanocrystals (CNTS NCs) in aqueous solutions using thioglycolic acid as a stabilizer is reported for the first time. The structural and optical properties of CNTS NCs are studied in colloidal solutions and thin films, and are compared with those of Cu–Zn–Sn–S (CZTS) NCs obtained under similar conditions. The NC sizes of both compounds are estimated to be in the range of 1.5–2.5 nm. Both NCs exhibit strongly non‐stoichiometric composition and a structure corresponding to cationically disordered kesterite Cu2ZnSnS4, which are common features of such quaternary metal‐based chalcogenides. The phonon Raman spectra of CNTS and CZTS NCs exhibit very similar lineshapes, but the CNTS phonon band has a larger width and lower frequency, presumably due to stronger cation disorder. The absorption of both types of NCs extends continuously through the visible range with an estimated bandgap of ≈2.2 eV and sub‐bandgap absorption due to an Urbach tail. The absorption coefficient of CNTS is determined to be α > 102 cm−1 at 700 nm and α > 104 cm−1 at 400 nm.

Direct comparison of three-terminal and four-terminal Hanle effects in the persistent photoconductor Al0.3Ga0.7As:Si

The electronic rendition of the Hanle effect, which is interpreted as the ensemble dephasing of a spin accumulation in the semiconductor under a perpendicular magnetic field, has been one of the most widely utilized and effective methods of measuring spin lifetime, spin accumulation, and spin transport in semiconductors. However, the origin of the Hanle magnetoresistance in the three-terminal (3T) setup has been intensively questioned both theoretically and experimentally; this is in contrast to the nonlocal four-terminal (NL-4T) measurement, which is accepted as reflecting spin accumulation and its spatial decay in metals and semiconductors alike. Here, we present results from 3T and NL-4T Hanle measurements on the same spin injection and detection devices with an ${\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}:\mathrm{Si}$ semiconducting channel. The use of ${\mathrm{Al}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}:\mathrm{Si}$, a persistent photoconductor, enables examination of the evolution of both types of Hanle signals with varying carrier density in the channel on one and the same device via in situ photodoping. We observe that the 3T and NL-4T Hanle signals exhibit similar Lorentzian line shapes, and thus yield similar spin lifetimes at all carrier densities. Moreover, the amplitudes of both types of Hanle signals are found to be consistent with each other, showing a similar exponential decrease with carrier density and in agreement with the Valet-Fert theory, in contrast to devices with artificial oxide barriers. These observations provide compelling evidence that in devices in which the spin injectors and detectors are engineered to minimize the presence of localized states, the 3T Hanle measurements provide a reliable probe of the spin accumulation and its dynamics in the semiconductor channel.

Influence of Hyperfine Coupling Strain on Two-Dimensional ESEEM Spectra from I = 1/2 Nuclei

HYSCORE, a variant of two-dimensional ESEEM spectroscopy, is currently one of the most effective tools in high-resolution solid-state EPR spectroscopy. Our systematic studies of hydrogen bonds with semiquinones in 15N-labeled proteins have previously provided us with an extensive collection of 15N HYSCORE spectra produced by N–H…O nitrogen donors. Examination of these spectra has indicated in several cases lineshape distortions not described by available theoretical models. We were able to explain all observed artificial phenomena in the 15N spectra of semiquinones considering a single mechanism—strain of the isotropic hyperfine interaction. In this review article, we introduce the HYSCORE experiment and the theoretical background for spectra of I = 1/2 nuclei in orientation-disordered samples. We then present a description of the observed lineshape distortions and an explanation of the hyperfine strain’s influence on the experimental spectra. In the final part of the article, we discuss (i) similar lineshape distortions found in previously published spectra from 15N, 29Si, 31P, and 57Fe nuclei that can be explained using the approach applied for the analysis of the 15N spectra of semiquinones, and (ii) a recently published analysis of 31P spectra with a different type of lineshape distortion based on a more sophisticated method, where the strength of anisotropic coupling is correlated with the sign and value of the isotropic constant in different conformations of a Cu(II) complex.

Interfacial chemistry and electronic structure of epitaxial lattice-matched TiN/Al0.72Sc0.28N metal/semiconductor superlattices determined with soft x-ray scattering

Epitaxial lattice-matched TiN/(Al,Sc)N metal/semiconductor superlattices have attracted significant interest in recent years for their potential applications in thermionic emission-based thermoelectric devices, optical hyperbolic metamaterials, and hot-electron-based solar-energy converters, as well as for the fundamental studies on the electron, photon, and phonon propagation in heterostructure materials. In order to achieve high efficiency devices and for the quest to discover new physics and device functionalities, it is extremely important that the superlattices exhibit atomically sharp and abrupt interfaces with minimal interface mixing and surface roughness. Moreover, as the energy transport across the cross-plane direction of these superlattices depends on the interface-properties, it is important to characterize the interfacial electronic structure and the chemistry of bond formation. Employing a combination of soft x-ray scattering techniques such as x-ray diffraction and synchrotron-based x-ray reflectivity, in this article, we demonstrate sharp and abrupt TiN/(Al,Sc)N superlattice interfaces with an asymmetric interface roughness ranging from two-to-three unit cells. Synchrotron-based soft x-ray absorption analysis revealed similar peak positions, line shapes, and absorption edges of different atoms in the individual thin films and in the superlattices, which demonstrate that the oxidation state of the atoms remains unchanged and rules-out the secondary structure or phase formation at the interfaces. The x-ray scattering results were further verified by aberration-corrected high-resolution scanning transmission electron microscopy imaging and energy dispersive x-ray spectroscopy mapping analysis. These results will be important for understanding of the transport properties of metal/semiconductor superlattices and for designing superlattice-based energy conversion devices.

High-resolution x-ray scattering from epitaxial thin films of Y/Nb on Al2O3

During the 1990s, Roger Cowley had a strong interest in the crystal and magnetic structures of rare-earth superlattices as a means to understand the rich and exotic magnetic properties of the rare-earth metals. High-quality samples can be grown by molecular beam epitaxy on sapphire substrates by first depositing a thin epitaxial layer of niobium, then a layer of yttrium or lutetium as a seed. High-resolution x-ray scattering is an excellent probe to characterise the crystal quality and was used to study the structure of the niobium layer. However, relatively little attention was paid to the seed layer. This article summarises some of the x-ray experiments performed by the Cowley group to study the structure of epitaxial niobium on sapphire, and extends the work to report some results on the structure of thin yttrium seed layers. The structure of the yttrium films is shown to have a strong dependence on the thickness of the niobium buffer, with the buffer needing to be thicker than a critical value of ∼80 for the formation of misfit dislocations at the Nb/Al2O3 interface before highly coherent Y films can be grown. Yttrium films grown on Nb buffers thinner than ∼500 show a similar two-peak line shape in scans through their specular Bragg peaks to that seen in the specular Nb Bragg peaks, with a resolution-limited feature on a broader diffuse peak. The resolution-limited feature depends on the thickness of the yttrium film, becoming weaker and having a stronger decay with increasing as the film thickness increases, while the width of the yttrium broad peak evolves as the square root of the width of the niobium Bragg peak. The data are discussed within the context of theories describing the scattering from films with misfit dislocations.

Observation of the Stacking Faults in In0.53Ga0.47As by Electron Channeling Contrast Imaging

The observation and interpretation of Frank stacking faults, Shockley stacking faults, Lomer dislocations, and 60° misfit dislocations, which have similar line shapes in the (001) In0.53Ga0.47As crystalline surface, are performed with the electron channeling contrast imaging (ECCI) technique. To minimize the backscattered electron (BSE) contrast that resulted from the surface morphology, a relatively flat region is first selected and compared with an atomic force microscopy (AFM) image and then, subsequently, examining ECCI with transmission electron microscopy (TEM)‐like invisibility criteria. By orthogonally choosing the diffraction vector g between (220) and (2‐20), misfit dislocations seem to be always visible but partially faint in the g parallel to the line direction on the surface. With respect to the image contrast, Frank stacking faults and Lomer dislocations are likely to be completely invisible for parallel g. The criteria are further confirmed by cross‐sectional TEM analysis, which shows a preferred homogeneous surface nucleation.

Analysis of trap-assisted triplet exciton quenching by magneto- conductance in rubrene-based organic light-emitting diodes

In this work, we have fabricated the conventional organic light-emitting diodes which are based on the promising rubrene material and their magneto-conductances (MCs) of the device have been measured at various temperatures and injection currents. The experimental results demonstrate that the current- and temperature-dependent MC curves of the device mainly show three structures as the magnetic field increases. Specifically, at room temperature (300 K), under low magnetic field (| B | 1 shows a rapid enhancement with increasing magnetic field at low currents, slowly rises and then decreases at moderate currents, and slowly decreases at high currents; in the medium magnetic field range (6 mT B |<17 mT), as magnetic field increases, MC 2 shows a slow rise in each current range; in the high magnetic field range (17 mT B | 3 rapidly reduces with increasing applied magnetic field in each current range. In order to further research the temperature effect on the MC responses, we also take the current of 50 μA as an example and measure the MC curves at different temperatures. Surprisingly, we found that temperature dependences of MC curves possess similar line-shape with current-dependent MC curves at ambient temperature. That is, with decreasing temperatures, in the low magnetic field range (| B | 1 demonstrates a slow rise at 300 K, slowly rises and then decreases at 250 and 150 K, and then slows down gradually at 100 and 20 K; in the medium magnetic field range (6 mT B | 2 shows a slow rise in each temperature range; in the high magnetic field range (17 mT B | 3 rapidly reduces with increasing applied magnetic field in each temperature range. On the whole, the line-shapes of MC 2 and MC 3 curves remain almost unchanged with decreasing temperatures (or increasing injection currents) in the medium and high magnetic field ranges (| B |>6 mT), but the tendency of MC 1 curves corresponding to low magnetic field (| B |<6 mT) will change with injection currents and temperatures. Additionally, by further analyzing the double logarithmic and temperature-dependent current density-voltage curves, we find that some traps which were usually originated from the fabrication process of devices inevitably exist in the device at room temperature and small injection currents, and the number of traps increases with decreasing temperature. Therefore, in addition to the dissociation of the triplet excitons by free charges (T+Q ® e+h+Q) and the intersystem crossing between singlet and triplet polaron pairs (PP 1 ® PP 3 ), two kinds of trap-assisted triplet exciton quenching processes (that is, trapped triplet-free polaron interaction (T t +P ® S 0 +P t ) and free triplet-trapped polaron interaction (T+P t ® S 0 +P)) are also included in the device. The combined effects of these four microscopic mechanisms lead to a complicated structure of the MC curves at small field and could be well tuned by device current density and working temperature. But the line-shapes of high-field MC responses are mainly determined by the role of TQA process. This article not only deepens the mechanism understanding of triplet-charge interactions in rubrene devices, but also enriches the manifestations of organic magneto-conductance curves.

Comparison of Satellite-Observed XCO2 from GOSAT, OCO-2, and Ground-Based TCCON

CO2 is one of the most important greenhouse gases. Its concentration and distribution in the atmosphere have always been important in studying the carbon cycle and the greenhouse effect. This study is the first to validate the XCO2 of satellite observations with total carbon column observing network (TCCON) data and to compare the global XCO2 distribution for the passive satellites Orbiting Carbon Observatory-2 (OCO-2) and Greenhouse Gases Observing Satellite (GOSAT), which are on-orbit greenhouse gas satellites. Results show that since GOSAT was launched in 2009, its mean measurement accuracy was −0.4107 ppm with an error standard deviation of 2.216 ppm since 2009, and has since decreased to −0.62 ppm with an error standard deviation of 2.3 ppm during the past two more years (2014–2016), while the mean measurement accuracy of the OCO-2 was 0.2671 ppm with an error standard deviation of 1.56 ppm from September 2014 to December 2016. GOSAT observations have recently decreased and lagged behind OCO-2 on the ability to monitor the global distribution and monthly detection of XCO2. Furthermore, the XCO2 values gathered by OCO-2 are higher by an average of 1.765 ppm than those by GOSAT. Comparison of the latitude gradient characteristics, seasonal fluctuation amplitude, and annual growth trend of the monthly mean XCO2 distribution also showed differences in values but similar line shapes between OCO-2 and GOSAT. When compared with the NOAA statistics, both satellites’ measurements reflect the growth trend of the global XCO2 at a low and smooth level, and reflect the seasonal fluctuation with an absolutely different line shape.

Incoherent population mixing contributions to phase-modulation two-dimensional coherent excitation spectra.

We present theoretical and experimental results showing the effects of incoherent population mixing on two-dimensional (2D) coherent excitation spectra that are measured via a time-integrated population and phase-sensitive detection. The technique uses four collinear ultrashort pulses and phase modulation to acquire two-dimensional spectra by isolating specific nonlinear contributions to the photoluminescence or photocurrent excitation signal. We demonstrate that an incoherent contribution to the measured line shape, arising from nonlinear population dynamics over the entire photoexcitation lifetime, generates a similar line shape to the expected 2D coherent spectra in condensed-phase systems. In those systems, photoexcitations are mobile such that inter-particle interactions are important on any time scale, including those long compared with the 2D coherent experiment. Measurements on a semicrystalline polymeric semiconductor film at low temperatures show that, in some conditions in which multi-exciton interactions are suppressed, the technique predominantly detects coherent signals and can be used, in our example, to extract homogeneous line widths. The same method used on a lead-halide perovskite photovoltaic cell shows that incoherent population mixing of mobile photocarriers can dominate the measured signal since carrier-carrier bimolecular scattering is active even at low excitation densities, which hides the coherent contribution to the spectral line shape. In this example, the intensity dependence of the signal matches the theoretical predictions over more than two orders of magnitude, confirming the incoherent nature of the signal. While these effects are typically not significant in dilute solution environments, we demonstrate the necessity to characterize, in condensed-phase materials systems, the extent of nonlinear population dynamics of photoexcitations (excitons, charge carriers, etc.) in the execution of this powerful population-detected coherent spectroscopy technique.

1015 cm−3 eV−1 level detection of density of states of a p-type polymer by hν-dependent high-sensitivity ultraviolet photoemission spectroscopy

We propose a method, called hν-dependent high-sensitivity ultraviolet photoemission spectroscopy, to observe the density of states (DOS) in a very wide range from HOMO to extremely weak gap states (1022 to 1015 cm−3 eV−1 in density of states). The method was applied to a p-type semiconducting polymer. A series of spectra for hν = 4.4–7.7 eV were recorded, and the DOS was obtained by overlapping the spectral part with a similar line shape between adjacent photon energy spectra to eliminate the photon energy dependence of the photoionization cross section. This method can be applied to both organic and inorganic materials, providing useful information about the DOS of functional materials.

The magnetic field effects of electroluminescence in thermally activated delayed fluorescence devices

In device with the activation of delayed fluorescence (TADF), triplet excitons can be activated by the environment and then converted into singlet excitons through reverse intersystem crossing (RISC), leading to delayed fluorescence and internal quantum efficiency of 100%. To further reveal the underlying mechanism of electroluminescence based on TADF devices, this paper selected three types of high efficient TADF materials, 4CzTPN-Ph, 2CzPN, and PIC-TRZ2 to fabricate organic light emitting devices. Our results show that, although the TADF devices have RISC process, their magneto-electroluminescence (MEL) curves exhibited similar line-shapes with those in the ordinary devices. This is due mainly to the facts that magnetic field can only affect the intersystem crossing (ISC) and Reverse ISC of polaron pairs rather than exciton in the these devices. At the same time, we found that the magnitudes of magnetic field effects in TADF devices increase with increasing the injection current, which is contrary to those from ordinary exciton-based devices. The relative change between the triplet polaron to triplet exciton rate k t and the singlet Polaron to singlet excitons rate k s is used to interpret these abnormal experimental results.

Population physiologically-based pharmacokinetic model incorporating lymphatic uptake for a subcutaneously administered pegylated peptide.

PurposePhysiologically-based pharmacokinetic (PBPK) models provide a rational mechanistic approach for predicting the time course of macromolecules in plasma. Population PBPK models for large molecules necessitate incorporation of lymphatic circulation to mechanistically account for biodistribution. Moreover, characterization of subcutaneous absorption requires consideration of the microvascular transit from the injection site to the systemic circulation. A PBPK model for a pegylated peptide conjugate, previously developed for primates, was modified to describe the lymphatic uptake in a population of humans by incorporation of interindividual variability in the lymphatic circulation and a unique lymphatic drainage compartment (LDC). The model was then used to simulate the time course of the drug in a population of humans and compared to the same drug administered to a group of human subjects participating in a first-in-human study.MethodsOrgan, blood and lymph masses for the population were sampled from either normal or log-normal distributions. Blood flows were calculated for each organ based on mean organ perfusion per gram of organ tissue and lymphatic flow was set as a fixed fraction of blood flow. Interindividual variability in lymphatic volume was assumed to be similar to that of blood volume. The volume of the LDC was parameterzed as a fraction of the injection volume. Sensitivity analysis was performed to study uncertain parameters and distribution assumptions.ResultsThe population generator was capable of simulating a virtual population incorporating the lymphatic circulation. Incorporation of a LDC resulted in similar line shape relative to the observed data and incorporation of anthropometric variability accounted for individual differences in the absorption and elimination phases across all dose cohorts. Line shape was sensitive to the inclusion of LDC while peak and elimination portions of the time course were influenced by the magnitude of variance assumed for blood volume and renal clearance, respectively.ConclusionLymphatic circulation can be incorporated into a population PBPK model assuming similar interindividual variability as observed for blood volume. Incorporation of an LDC, where the volume of this transit compartment is proportional to the SC injection volume may be an important mechanistic means of predicting the transit from the SC depot to the systemic circulation.Electronic supplementary materialThe online version of this article (doi:10.1186/s40203-016-0018-5) contains supplementary material, which is available to authorized users.

Inorganic alkali lead iodide semiconducting APbI&lt;sub&gt;3&lt;/sub&gt; (A = Li, Na, K, Cs) and NH&lt;sub&gt;4&lt;/sub&gt;PbI&lt;sub&gt;3&lt;/sub&gt; films prepared from solution: Structure, morphology, and electronic structure

APbI3 alkali lead iodides were prepared from aqueous (A= Na, Cs, ammonium NH4+, and methyl­ammonium CH3NH3+) and acetone (A= Li, K) solutions by a self-organization low temperature process. Diffraction analysis revealed that the methylammonium-containing system (MAPbI3) crystallizes into a tetragonal perovskite structure, whereas the alkali and NH4+ systems adopt orthorhombic structures. Morphological inspection confirmed the influence of the cation on the growth mechanism: for A = Cs and NH4+, needle-like crystallites with lengths up to 3–4 mm; for A = K, thin stripes with lengths up to 5–6 mm; and for A = MA+, dodecahedral crystallites were observed. For A = Li and Na, the APbI3 systems typically resulted in polycrystalline aggregates. Optical absorption measurements demonstrated large energy band gaps for the alkali and ammonium systems with values between 2.19 and 2.40 eV. For electronic and chemical characterization by photoelectron spectroscopy, the as-prepared powders were dissolved in di-methylformamide and re-crystallized as thin films on F:SnO2 substrates by spin-coating. The binding energy differences between Pb4f and I3d core levels are highly similar in the investigated systems and close to the value measured for PbI2, indicating similar relative partial charges and formal oxidation states. The binding energies of the alkali ions are in accordance with oxidation state +1. The X-ray excited valence band spectra of the investigated APbI3 systems exhibited similar line shapes in the region between the valence band maximum and 4.5 eV higher binding energy due to common PbI6 octahedra which dominate the electronic structure. While the ionization energy values are quite similar (6.15 ± 0.25 eV), the Fermi-level positions of the unintentionally doped materials vary for different cations and different batches of the same material, which indicates that the position of the Fermi level can be influenced by changing the process parameters.

On-wafer magnetic resonance of magnetite nanoparticles

Magnetic resonance measurements of ferumoxytol and TEMPO were made using an on-wafer transmission line technique with a vector network analyzer, allowing for broadband measurements of small sample volumes (4nL) and small numbers of spins (1nmol). On-wafer resonance measurements were compared with standard single-frequency cavity-based electron paramagnetic resonance (EPR) measurements using a new power conservation approach and the results show similar line shape. On-wafer magnetic resonance measurements using integrated microfluidics and microwave technology can significantly reduce the cost and sample volumes required for EPR spectral analysis and allow for integration of EPR with existing lab-on-a-chip processing and characterization techniques for point-of-care medical diagnostic applications.

EPR Data Support the Existence of a Symmetric BH3-in-Groove Homodimer in Oligomeric BAK

The BAX or BAK oligomeric pore formation in the mitochondrial outer membrane is a critical step in apoptosis, yet their structures are not clearly understood. Czabotar et al. (Cell 2013, 152, 519) reported a crystal structure of a water-soluble tetramer of the BAX fragment (helices α2-α5) fused to the green-fluorescent protein (GFP), in which the α2-α3 extended helices and the α5 helix, respectively, were juxtaposed to each other, in an anti-parallel orientation, forming a symmetric “BH3-in-groove homodimer (BGH).” We have constructed a GFP-BAK fusion protein using the α2-α5 helices of mouse BAK, designated as GFP-BAKα2-α5, which also forms a soluble tetramer. To determine whether the BGH exists in the BAK oligomers in the membrane or not, we spin labeled the C-terminal hexahistidine-tagged soluble form of mouse BAK (helices α1-α8) at residues 84, 122, 128 and 135 and the corresponding residues in GFP-BAKα2-α5. We then compared the continuous wave (CW) EPR spectra of the spin-labeled residues from the tetrameric GFP-BAKα2-α5 with those from the oligomeric BAK in membrane. Spin labeled residue 122R1, located in the loop interconnecting helices α4 and α5 in the homology model of the GFP-BAKα2-α5 tetramer, displayed a mobile lineshape. The corresponding residue in the oligomeric BAK also had a remarkably similar lineshape, indicating that the two residues are in similar structural environments. Residues 84R1, 128R1 and 135R1, located at the anti-parallel helical interfaces in the BGH also had remarkably similar immobile lineshapes both in the GFP-BAKα2-α5 tetramer and in the oligomeric BAK in membrane, further strengthening the above conclusion. The intra-dimer distances between 84R1 spin label pairs in the GFP-BAKα2-α5 and the oligomeric BAK, determined by the double electron electron resonance (DEER) method, also support this interpretation.

Dependence of magnetic properties on the growth temperature of Mn0.04Ge0.96 grown on Si (001)

The structural and magnetic properties of Mn 0.04 Ge 0.96 thin films grown on Si (001) substrates at different growth temperatures were investigated. The films were grown by sequential deposition of MnGe and Ge multilayers using molecular beam epitaxy . It was found that the magnetic ordering and Curie temperature could be controlled by adjusting the distance between the Mn ions in the Ge spacer layer depending on growth temperature. We found that the samples grown below 130 °C contained highly disordered ferromagnetic Mn rich domains. Both structural and magnetic characterizations revealed that Mn 5 Ge 3 precipitates were formed in Mn clusters free Ge matrix when the samples were grown at 150 °C. Both the Mn rich domains and Mn 5 Ge 3 precipitates showed out of the plane magnetic anisotropy and similar ESR line shapes. • We investigated the effects of growth temperature on spin systems in Mn 0.04 Ge 0.96 . • The degree of ferromagnetic ordering increases with temperature. • Ferromagnetism occurs due to interaction of Mn 2+ ions in Mn rich clusters. • ESR reveals that the formation of magnetic phases depends on growth temperature.

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.

Interaction of single quantum emitter and dark plasmon supported by a metal nanoring.

We explore the interaction between a quantum emitter and a metal nanoring by numerical solution of coupled Maxwell-Liouville equations. When the quantum emitter and nanoring are subjected to an incident plane wave, coupling between the quantum emitter and a dark plasmon supported by the nanoring gives rise to a similar lineshape to the familiar Fano type. It results from the excitation of a dark plasmon via intermediary participation of the quantum emitter. The dark plasmon is characterized through the width and shift parameters of the emitter peak in the absorption spectrum of the nanoparticle. Our results are obtained with the help of finite-difference time-domain method and a recently proposed symmetry-adapted averaging approach.

Direct observation of substrate induced exciton in carbon nanotube

We have successfully measured the electroluminescence spectra of a single-walled carbon nanotube (CNT) grown to serpentine shape on quartz substrate. We observe two emission peaks: One locates at 0.85 eV and is identified as the usual E11 exciton peak, and the other locates at slightly higher energy of 0.94 eV with similar symmetrical line shape and comparable intensity. However, the extra peak is substantially wider and it broadens with increasing current at unusually faster speed. We show that the extra peak is not from interband transitions, and ascribe it to a type of exciton induced by the formation of substrate-CNT superlattice. The periodic surface potential of the substrate modulates the CNT band structure, causes degeneracy lifting and band flattering at the Brillouin zone, and generates the higher energy exciton. For confirmation, a similar device is fabricated using amorphous SiO2 substrate to avoid the formation of the superlattice. Indeed, the extra emission peak disappears.

Optical properties of fully and partially fluorinated rubrene in films and solution

We present the optical properties of fully (C42F28, PF-RUB) and half-fluorinated (C42F14H14, F14-RUB) rubrene, both in thin films and as monomers in solution and compare them to hydrogenated rubrene (C42H28, RUB). All three compounds show similar optical absorption bands and photoluminescence line shapes. The results are interpreted with density functional calculations of the orbital energies and time-dependent density functional theory for the HOMO-LUMO transition. Red shifts induced by the surrounding solvent or organic thin films remain much smaller than for polyacenes, in keeping with previous observations for rubrene and existing models for the solvatochromic shifts.