Influence of a dielectric decoupling layer on the local electric field and molecular spectroscopy in plasmonic nanocavities:a numerical study

In this Letter,we use electromagnetic simulations to systematically investigate the influence of a thin dielectric layer on the local electric field and molecular spectroscopy in the plasmonic junction.It is found that both the intensity and spatial confinement of the electric field and molecular spectroscopy can be significantly enhanced by applying a dielectric layer with large dielectric constant.We also discuss the optimal dielectric layer thickness to obtain the largest quantum efficiency of a dipole emitter.These results may be instructive for further studies in molecular spectroscopy and optoelectronics in plasmonic junctions.

The inelastic electron tunneling spectroscopy of edge-modified graphene nanoribbon-based molecular devices

The inelastic electron tunneling spectroscopy（IETS） of four edge-modified finite-size grapheme nanoribbon（GNR）-based molecular devices has been studied by using the density functional theory and Green＇s function method. The effects of atomic structures and connection types on inelastic transport properties of the junctions have been studied. The IETS is sensitive to the electrode connection types and modification types. Comparing with the pure hydrogen edge passivation systems, we conclude that the IETS for the lower energy region increases obviously when using donor–acceptor functional groups as the edge modification types of the central scattering area. When using donor–acceptor as the electrode connection groups, the intensity of IETS increases several orders of magnitude than that of the pure ones. The effects of temperature on the inelastic electron tunneling spectroscopy also have been discussed. The IETS curves show significant fine structures at lower temperatures. With the increasing of temperature, peak broadening covers many fine structures of the IETS curves.The changes of IETS in the low-frequency region are caused by the introduction of the donor–acceptor groups and the population distribution of thermal particles. The effect of Fermi distribution on the tunneling current is persistent.

Rapid Detection of Oil Pollution in Soil by Using Laser-Induced Breakdown Spectroscopy

Detection of oil pollution in soil has been carried out using laser-induced breakdown spectroscopy（LIBS）. A pulsed neodymium-doped yttrium aluminum garnet（Nd：YAG） laser（1,064 nm, 8 ns, 200 mJ） was focused onto pelletized soil samples. Emission spectra were obtained from oil-contaminated soil and clean soil. The contaminated soil had almost the same spectrum profile as the clean soil and contained the same major and minor elements. However, a C–H molecular band was clearly detected in the oil-contaminated soil, while no C–H band was detected in the clean soil. Linear calibration curve of the C–H molecular band was successfully made by using a soil sample containing various concentrations of oil. The limit of detection of the C–H band in the soil sample was 0.001 mL/g. Furthermore, the emission spectrum of the contaminated soil clearly displayed titanium（Ti） lines, which were not detected in the clean soil. The existence of the C–H band and Ti lines in oil-contaminated soil can be used to clearly distinguish contaminated soil from clean soil. For comparison, the emission spectra of contaminated and clean soil were also obtained using scanning electron microscope-energy dispersive X-ray（SEM/EDX） spectroscopy,showing that the spectra obtained using LIBS are much better than using SEM/EDX, as indicated by the signal to noise ratio（S/N ratio）.

Thermodynamics of the long range assembly of safranine T on molecular surfaces of nucleic acids

By making use of the fluorescence quenching properties of safranine T(ST) in its long range assembly on the molecular surfaces of nucleic acids, the assembly number and constant of ST with calf thymus DNA, fish sperm DNA and yeast RNA were determined at 12℃. The corresponding free energy change, enthalpy change and entropy change of the long range assembly were calculated at the same temperature. It was found the assembly complexes are very stable and the assembly is a spontaneous process characterized an entropy increase.

An Automated,Highly Selective Reaction Monitoring Instrument Using Molecular Rotational Resonance Spectroscopy

Online monitoring of chemical reactions by using analytical chemistry tools is a powerful way to maximize control over these processes.In this paper,we demonstrate the use of molecular rotational resonance,an emerging and extraordinarily selective spectroscopic technique,to perform automated reaction monitoring measurements.An interface using a six-port valve with a calibrated sample loop,coupled to a temperature controlled inlet for analyte volatilization,was developed and tested.Two reactions were chosen for initial characterization:an amine-aldehyde condensation reaction to form an imine product and an isotopic exchange reaction of aβ-ketoester with keto-enol tautomerization.The spectrometer was able to provide kinetic information about the reaction and determine reaction completion.In the future,this system can be extended to detect and quantify impurities and characterize reaction selectivity,in addition to the reaction progress.

Adsorption Reaction Dynamics of Systems Lysozyme and Nanodiamond/Nanosilica at pH=7-13

Adsorption reactions between surfaces of nanodiamond and nanosilica with diameter of 100 nm prepared as suspension solutions of 0.25μg/μL and lysozyme molecule with different concentrations of 7 mmol/L PPBS at pH=7, 9, 11, and 13 have been investigated by fluores- cence spectroscopy. Adsorption reaction constants and coverages of lysozyme with different concentrations of 0-1000 nmol/L under the influences of different pH values have been ob- tained. Helicities and conformations of the adsorbed lysozyme molecules, free spaces of every adsorbed lysozyme molecule on the surfaces of nanopartieles at different concentrations and pH values have been deduced and discussed. The highest adsorption capabilities for both sys- tems and conformational efficiency of the adsorbed lysozyme molecule at pH=13 have been obtained. Lysozyme molecules can be prepared, adsorbed and carried with optimal activity and helicity, with 2 and 10 mg/m2 on unit nanosurface, 130 and 150 mg/g with respect to the weight of nanoparticle, within the linear regions of the coverages at around 150-250 nmol/L and four pH values for nanodiamond and nanosilica, respectively. They can be prepared in the tightest packed form, with 20 and 55 mg/m2, 810-1680 and 580-1100 mg/g at threshold concentrations and four pH values for nanodiamond and nanosilica, respectively.

Precise measurement of the line width of the photoassociation spectra of ultracold molecules by using a frequency shifter

We propose a technique to precisely measure the line width of the photoassociation spectra of the excited cesium molecule by using a frequency shifter to generate two laser beams with a precise frequency difference. A series of photoassociation （PA） spectra are recorded with two laser beam induced molecular lines, whose peak separation serves as an accurate frequency ruler to measure the line width of the PA spectra. The full width half maximum line width was studied as a function of PA laser intensity. The extrapolated value at zero laser intensity is （34.8± 0.22） MHz. By analyzing other broadening mechanisms, a value of （32.02 ± 0.70） MHz was deduced. It is shown that this scheme is inexpensive, simple, robust, and is promising for applications in a variety of other atomic species.

Thermo-oxidative Oligomerization of Aromatic Diamine

Molecular spectroscopy(electronic,FT-IR,NMR),methods of thermal and elemental analysis were used for the first time to describe the process of thermo-oxidative oligomerization of 1,3-bis-(4-aminophenoxy)benzene.Introduction of this monomer into linear and network copolymers makes it possible to improve processability,mechanical strength and heat resistance of materials.The structures of copolymers obtained by thermo-oxidation of the diamine in various thermal regimes were studied.It was demonstrated that during prolonged heating of this diamine in air in the temperature range from 220 to 320°C,oligomeric aromatic diamines were formed;these products contained fragments of benzenoid and quinoid types.

Effects of urea,metal ions and surfactants on the binding of baicalein with bovine serum albumin

The interaction of baicalein with bovine serum albumin（BSA） was investigated with the help of spectroscopic and molecular docking studies.The binding affinity of baicalein towards BSA was estimated to be in order of 10~5 M^（-1） from fluorescence quenching studies.Negative ΔH°（-5.66 ＋ 0.14 kJ/mol） and positive（ΔS°）（＋ 79.96 ＋ 0.65J/mol K） indicate the presence of electrostatic interactions along with the hydrophobic forces that result in a positive ΔS°.The hydrophobic association of baicalein with BSA diminishes in the presence of sodium dodecyl sulfate（SDS） due to probable hydrophobic association of baicalein with SDS,resulting in a negative ΔS°（-40.65 ＋ 0.87 J/mol K）.Matrix-assisted laser desorption ionization/time of flight（MALDI-TOF） experiments indicate a 1：1 complexation between baicalein and BSA.The unfolding and refolding phenomena of BSA were investigated in the absence and presence of baicalein using steady-state and fluorescence lifetime measurements.It was observed that the presence of urea ruptured the non-covalent interaction between baicalein and BSA.The presence of metal ions（Ag~＋,Mg^（2＋）,Ni^（2＋）,Mn^（2＋）,Co^（2＋） and Zn^（2＋）） increased the binding affinity of ligand towards BSA.The changes in conformational aspects of BSA after ligand binding were also investigated using circular dichroism（CD） and Fourier transform infrared（FT-IR） spectroscopic techniques.Site selectivity studies following molecular docking analyses indicated the binding of baicalein to site 1（subdomain MA） of BSA.

Changes of the Molecular Mobility of Poly(ε-caprolactone) upon Drawing,Studied by Dielectric Relaxation Spectroscopy

Dielectric relaxation spectroscopy（DRS） of poly（ε-caprolactone） with different draw ratios showed that the mobility of polymer chains in the amorphous part decreases as the draw ratio increases. The activation energy of the α process, which corresponds to the dynamic glass transition, increases upon drawing. The enlarged gap between the activation energies of the α process and the β process results in a change of continuity at the crossover between the high temperature a process and the α and β processes. At low drawing ratios the a process connects with the β process, while at the highest drawing ratio in our measurements, the a process is continuous with the αprocess. This is consistent with X-ray diffraction results that indicate that upon drawing the polymer chains in the amorphous part align and densify upon drawing. As the draw ratio increases, the α relaxation broadens and decreases its intensity, indicating an increasing heterogeneity. We observed slope changes in the α traces, when the temperature decreases below that at which τα≈ 1 s. This may indicate the glass transition from the ‘rubbery＇ state to the non-equilibrium glassy state.

Novel and Validated Spectrophotometric Matrix Matching Method for Simple and Rapid Determination of Chromium in Oily Media

N,N'-bis(4-methoxysalicylidene)ethylenediamine is proposed as analytical reagent for the direct determination of chromium in original matrix of liquid oils.The method is based on the complexation of N,N'-bis(4-methoxysalicylidene)ethylenediamine and chromium in n-hexane∶acetone(1∶4)medium and spectrophotometric determination at 355 nm against reagent blank.Complexation of MSE and chromium is completed in20 seconds at molar ratio 1∶1.The molar absorptivity and the formation constant of the complex are determined as 9 740L·mol^(-1)·cm^(-1) and 3.6(±0.1)×10~5,respectively.Beer's law is obeyed in range 0.02~1.50mg·L^(-1) chromium concentration.Limits of detection and quantification of the suggested method were7.5 and 25.11μg·kg-,respectively.The accuracy and precision of the method was checked by finding mean recovery and relative standard deviation by oil-based chromium standard analysis as 96.4%±1.4%and 1.5%,respectively.The practical applicability of elaborate method was tested using oil-based chromium standard spiked and unspiked corn,sunflower,soybean,olive and canola oils.

Mid-infrared dual-comb spectroscopy with electro-optic modulators

Absorption spectroscopy of fundamental ro-vibrational transitions in the mid-infrared region provides a powerful tool for studying the structure and dynamics of molecules in the gas phase and for sensitive and quantitative gas sensing.Laser frequency combs permit novel approaches to perform broadband molecular spectroscopy.Multiplex dual-comb spectroscopy without moving parts can achieve particularly high speed,sensitivity and resolution.However,achieving Doppler-limited resolution in the mid-infrared still requires overcoming instrumental challenges.Here we demonstrate a new approach based on difference-frequency generation of frequency-agile near-infrared frequency combs that are produced using electro-optic modulators.The combs have a remarkably flat intensity distribution,and their positions and line spacings can be freely selected by simply dialing a knob.Using the proposed technique,we record,in the 3-μm region,Doppler-limited absorption spectra with resolved comb lines within milliseconds,and precise molecular line parameters are retrieved.Our technique holds promise for fast and sensitive time-resolved studies of,for example,trace gases.

Adaptive-sampling near-Doppler-limited terahertz dual-comb spectroscopy with a free-running single-cavity fiber laser

Dual-comb spectroscopy(DCS)is an emerging spectroscopic tool with the potential to simultaneously achieve a broad spectral coverage and ultrahigh spectral resolution with rapid data acquisition.However,the need for two independently stabilized ultrafast lasers significantly hampers the potential application of DCS.We demonstrate mode-resolved DCS in the THz region based on a free-running singlecavity dual-comb fiber laser with the adaptive sampling method.While the use of a free-running single-cavity dual-comb fiber laser eliminates the need for two mode-locked lasers and their frequency control,the adaptive sampling method strongly prevents the degradation of spectroscopic performance caused by the residual timing jitter in the free-running dual-comb laser.Doppler-limit-approaching absorption features with linewidths down to 25 MHz are investigated for low-pressure acetonitrile/air mixed gas by comb-mode-resolved THz spectroscopy.The successful demonstration clearly indicates its great potential for the realization of lowcomplexity,Doppler-limited THz spectroscopy instrumentation.

Scanning dual-microcomb spectroscopy

Dual-comb spectroscopy(DCS) is a powerful tool in molecular spectroscopy benefiting from the advantages of high resolution and short measurement time. The recently developed soliton microcomb(SMC) can potentially transfer the dual-comb method to an on-chip platform. In this paper, we demonstrate DCS using two frequency scanning SMCs, termed scanning dual-microcomb spectroscopy(SDMCS). The two SMCs are generated by an auxiliary-assisted thermal balance scheme, and the pump laser frequency sweeps over one free spectral range of the microresonator(~49 GHz) using a feedback control system. The proposed SDMCS has a spectral resolution of 12.5 MHz, which is determined by the minimum sweeping step of the pump laser. Using this SDMCS system, we perform three types of gas molecule absorption spectroscopy recognition and gas concentration detection.This study paves the way for integrated DCS with a high signal-to-noise ratio, high spectral resolution, and fast acquisition rate.

Wavelength modulation spectroscopy based on quasi-continuous-wave diode lasers

A modified wavelength modulation spectroscopy（WMS）based on the self-heating effect of the tunable diode laser when driven in quasi-continuous-wave（QCW）mode is investigated.A near-infrared distributed feedback（DFB）diode laser working at the QCW mode is employed as the QCW light source,and CO2 is selected as the target gas.The characteristic of the QCW second harmonic（2f）line profile is analyzed through a comparison with that of the traditional CW WMS with the same system.A noise-equivalent absorbance of 3.2×10-5 Hz-1/2 for CO2 at 1.58μm is obtained with 18-m optical path.The QCW WMS lowers the dependence on lasers and expands selectivity,thus verifying the feasibility of the method.

Surface plasma treatment effects on the molecular structure at polyimide/air and buried polyimide/epoxy interfaces

Polyimides are widely used as chip passivation layers and organic substrates in microelectronic packaging. Plasma treatment has been used to enhance the interfacial properties of polyimides, but its molecular mechanism is not clear. In this research, the effects of polyimide surface plasma treatment on the molecular structures at corresponding polyimide/air and buried polyimideJepoxy interfaces were investigated in situ using sum frequency generation （SFG） vibrational spectroscopy. SFG results show that the polyimide backbone molecular structure was different at polyimide/air and polyimideJepoxy interfaces before and after plasma treatment. The different molecular structures at each interface indicate that structural reordering of the polyimide backbone occurred as a result of plasma treatment and contact with the epoxy adhesive. Furthermore, quantitative orientation analysis indicated that plasma treatment of polyimide surfaces altered the twist angle of the polyimide backbone at corresponding buried polyimide/epoxy interfaces. These SFG results indicate that plasma treatment of polymer surfaces can alter the molecular structure at corresponding polymer/air and buried polymer interfaces.

Novel method for correcting light intensity fluctuation in the TDLAS system

A novel method for online correction of light intensity fluctuation in a practical tunable diode laser ab-sorption spectroscopy（TDLAS）system with wavelength modulation is presented.The proposed method is developed according to the linear relation between peaks at multiple frequencies of sine modulation in the power spectral density of the demodulated second-harmonic（2f）signal and the incident light intensity.Those peaks are demonstrated experimentally and explained as residual power at the first-harmonic and third-harmonic frequencies after 2f demodulation of the residual amplitude modulation signal due to the limited integrating time constant of the lock-in-amplifier.This method can achieve real-time correction of light intensity fluctuations with only little calculation.It can work well in a very large range of light intensity and has great potential applications in the wavelength modulation spectroscopy system.

Open-loop experiments of resonator micro-optic gyro

An open-loop resonator micro-optic gyro (R-MOG) with a 6 cm-long waveguide-type ring resonator is set up using the phase modulation spectroscopy technique. In the experiment, according to the test parameters of the resonator, the shot- noise-limited sensitivity is estimated to be 1.07×10-4 rad/s. From the test demodulation signal, the gyro dynamic range of ±7.0×103 rad/s is obtained. Using different phase modulation frequencies, the open-loop gyro output signal is observed when the equivalent gyro rotation ...

Spectroscopic study on the interaction between[Hg(SCN)_4]^(2-) and hemoglobin

The interaction between [Hg（SCN）4]^2- and hemoglobin （Hb） under conditions that simulate a physiological environment was investigated by UV-vis spectroscopy, fluorescence spectroscopy, resonance Rayleigh scattering （RRS） spectroscopy and circular dichroism （CD） spectroscopy. The results obtained from the change of UV-vis and CD spectra, the quenching of Hb fluorescence and the enhancement of RRS intensity proved that a 10：1 type complex was formed between [Hg（SCN）4]^2- and Hb. The possible mechanism suggested for the interaction was that ten Hg（SCN）4]^2- anions entered the four subunits of a Hb molecule to react with some residues to form an adduct by coordination and electrostatic forces. The coordination of [Hg（SCN）4]^2- with Trp was the major cause of the fluorescence quenching of Hb.