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Vibrational Energy Redistribution between CH Stretching Modes in Alkyl Chain Monolayers Revealed by Time-Resolved Two-Color Pump–Probe Sum Frequency Spectroscopy
摘要： The vibrational dynamics of the various CH stretching modes in a fatty acid Langmuir?Blodgett ?lm was studied using a resonant narrowband infrared (IR) laser pulse for pumping and a broadband femtosecond IR visible pulse pair for detection in a sum frequency spectroscopy setup. The resulting two-dimensional spectra indicate that pumping either the antisymmetric methyl or methylene stretch results in the transfer of energy to the other modes on a time scale faster than 2 ps. This rapid process is followed by energy redistribution to other modes, presumably the bending and internal rotational modes, with a time constant of approximately 85 ps. The formation of gauche defects is not observed within the ?rst 250 ps. The whole spectrum recovers on a time scale of several nanoseconds, indicating dissipation of the excitation energy into the substrate.
关键词： CH stretching modes,energy redistribution,vibrational dynamics,sum frequency spectroscopy,Langmuir?Blodgett ?lm
更新于2025-09-12 10:27:22
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Vibrational Spectra of Thiolate-Protected Gold Nanocluster with Infrared Reflection Absorption Spectroscopy: Size- and Temperature-Dependent Ordering Behavior of Organic Monolayer
摘要： Vibrational spectra of thiolate-protected gold nanoclusters, prepared in a monolayer manner using the Langmuir?Blodgett method, were measured by means of infrared re?ection absorption spectroscopy (IRAS). A transferred monolayer of gold nanoclusters ligated by dodecanethiolate or 2-phenylethane-1-thiolate onto a single-crystal gold (Au) surface of Au(111) exhibits worthy IRAS spectra that reveal temperature-dependent behaviors from 100 to 340 K as well as comprehensive peak assignments based on density functional theory calculations: the conformation change in ligands between all trans and gauche defect forms with temperature. In addition to the temperature dependence, the cluster size dependence of alkyl and phenyl moieties is discussed, compared with the IRAS spectra of the corresponding self-assembled monolayers (SAMs) on Au(111). Ligands spreading three-dimensionally from the Au core determine the coordination structure of the ligated Au nanoclusters.
关键词： self-assembled monolayers,density functional theory calculations,Langmuir?Blodgett method,thiolate-protected gold nanoclusters,Vibrational spectra,temperature-dependent behaviors,infrared re?ection absorption spectroscopy
更新于2025-09-12 10:27:22
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A model for real time, <i>in situ</i> estimation of cesium coverage on metal substrate using infrared imaging under vacuum
摘要： The present work is to develop an infra-red (IR) camera based in situ diagnostic tool for the determination of cesium (Cs) coverage suitable for ion source applications. Cs seeding is done to reduce the surface work function that enhances the surface assisted negative hydrogen ion production. The temporal Cs deposition on a metal surface (for, e.g., tungsten or molybdenum) follows Langmuir adsorption isotherm (LAI) kind of behavior. The surface temperature varies while the Cs deposition is reflected in the IR camera temperature measurements for a constant surface emissivity value. In this paper, a model on the relationship between Cs coverage in correlation with surface emissivity and temperature variation based on the theory of LAI is presented. A surface ionization probe (SIP) in the form of a cathode-anode assembly together with an IR camera viewing arrangement is designed to measure the Cs flux and the surface temperature simultaneously to test our model. In the present experiment, the Cs flux measurement using SIP is validated with a standard quartz crystal microbalance (QCM). The proposed model would be useful to correlate Cs coverage on plasma grid-like surface conditions under negative ion source relevant vacuum conditions.
关键词： surface ionization probe,infra-red camera,cesium coverage,quartz crystal microbalance,Langmuir adsorption isotherm
更新于2025-09-12 10:27:22
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Complementary Characterization of Laser-Induced Plasmas by Optical Emission Spectroscopy and Triple Langmuir Probe
摘要： In this article, we study the temporal evolution of the electron density and temperature of carbon laser-produced plasmas (LPP) using a combination of optical emission spectroscopy (OES) and the triple Langmuir probe (TLP) method. OES has been widely used to characterize LPPs but it is limited to distances relatively close to the target. On the other hand, the main advantage of TLP over the single-probe method is that it allows to obtain simultaneous measurements of electron temperature (Te) and density (Ne), without any voltage sweeping. In this article, we compare both techniques; measurements by OES were performed at distances from the target <1 cm, whereas the triple probe was employed for distances >5 cm. The plasma was generated by focusing nanosecond laser pulses onto a high purity graphite target placed inside a vacuum chamber. Our results show that the values of Te measured using both techniques predict decreasing exponential behavior. Ne determined by the spectral line Stark broadening in OES (<1 cm) was two orders of magnitude larger than that measured by the TLP (>5 cm). This difference in the electron density can be explained by radiative recombination and the presence of different kinds of plasma species detected by the TLP technique. The results show that both methods are complementary and their combination can be used to characterize LPP in a wide range of distances and timescales.
关键词： triple Langmuir probe (TLP),optical emission spectroscopy (OES),Laser-induced plasmas
更新于2025-09-11 14:15:04
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Negative ion characterization in a helicon plasma source for fusion neutral beams by Cavity Ring-Down Spectroscopy and Langmuir Probe laser photodetachment
摘要： Negative ions are characterized in the helicon plasma source RAID (Resonant Antenna Ion Device) at the Swiss Plasma Center by means of Cavity Ring-Down Spectroscopy (CRDS) and Langmuir Probe (LP)-assisted laser photodetachment. A high density and axially homogeneous plasma column is produced via a RF antenna able to sustain the propagation of helicon waves in a steady state regime. An electron density ne ≈ 2.0 × 1018 m?3 in H2 plasma at 0.3 Pa and 3 kW of input power is measured in the center of the plasma column by LP and microwave interferometry. The electron temperature pro?le is peaked on axis reaching Te ≈ 5 eV and decreasing to 1.5 eV at r = 0.05 m. Thus, a hot core region forms where H2 molecules are rovibrationally excited (H2(ν)), and a cold edge, where low energy electrons can attach to H2(ν) and produce H? ions by dissociative attachment. In this work we use LP-assisted laser photodetachment and CRDS diagnostics to measure H? and D? radial density pro?les and how they depend on source parameters. We show that negative ions are distributed on a shell of 0.06 m radius with a peak value of ～ 2.0 × 1016 m?3 in H2 plasma. These results suggest that, although substantial technical development is needed, helicon plasmas could be considered as a possible candidate as sources of negative ions for future NBIs.
关键词： laser photodetachment,Cavity Ring-Down Spectroscopy,helicon plasma source,Langmuir Probe,Negative ions
更新于2025-09-11 14:15:04
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Handbook of Graphene || Self‐Assembled Thin Films of Graphene Materials for Sensors
摘要： It is well known that graphene and its derivatives exhibit unique optical, electrical, mechanical, and chemical properties, which are valuable for sensing applications. However, the chosen methods to synthesize and process graphene to form the sensing unit are critical steps defining the real property of the final sensor. Instead of a physical mixture of graphene in a bulk support, different immobilization techniques have been investigated to take advantage of the outstanding properties of graphene and graphene-based materials, such as linkage to the self-assembled monolayers, layer-by-layer, and Langmuir–Blodgett techniques. Such techniques lead to a new concept of nanoarchitectonics allowing to take a synergistic effect on mixing distinct properties with various materials in a unique device. Examples of these approaches on developing electrochemical, electric, and optical sensors are discussed in an overview.
关键词： chemical synthesis,self-assembled monolayers,Sensors,layer-by-layer,Langmuir–Blodgett,biosensors
更新于2025-09-11 14:15:04
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Highly sensitive air stable easily processable gas sensors based on Langmuir-Schaefer monolayer organic field-effect transistors for multiparametric H <sub/>2</sub> S and NH <sub/>3</sub> real-time detection
摘要： A combination of low limit of detection, low power consumption and portability makes organic field-effect transistors (OFETs) chemical sensors promising for various applications in the areas of industrial safety control, food spoilage detection and medical diagnostics. However, the OFET sensors typically lack air stability and restoration capability at room temperature. Here we report on a new design of highly sensitive gas sensors based on Langmuir-Schaefer monolayer organic field-effect transistors (LS OFETs) prepared from organosilicon derivative of [1]benzothieno[3,2-b][1]-benzothiophene. The devices fabricated are able to operate in air and allows an ultrafast detection of different analytes at low concentrations down to tens ppb. The sensors are reusable and can be utilized in real-time air quality monitoring systems. We show that a direct current response of the LS OFET can be splitted into the alteration of various transistor parameters, responsible for the interactions with different toxic gases. The sensor response acquiring approach developed allows distinguishing two different gases, H2S and NH3, with a single sensing device. The results reported open new perspectives for the OFET-based gas-sensing technology and pave the way to easy detection of the other types of gases enabling the development of complex air analysis systems based on a single sensor.
关键词： Multiparametric detection,Sensing mechanism,Monolayer organic field-effect transistors,Langmuir-Schaefer monolayers,Chemical sensors
更新于2025-09-11 14:15:04
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Comparative study on the behaviour of Chitosan-Gelatin based Hydrogel and nanocomposite ion exchanger synthesized under microwave conditions towards photocatalytic removal of cationic dyes
摘要： The present work reports the comparison study of Chitosan-Gelatin based hydrogels with their nanocomposite ion exchangers synthesized under microwave conditions for the adsorption and photodegradation of the cationic dyes. In this report, the hydrogel based on Chitosan-Gelatin, more selective for anionic dyes is modified to nanocomposite ion exchanger by incorporating the zirconium (IV) selenophosphate1 to make it selective for cationic dyes. The nanocomposite was investigated with a tremendous hike in the degradation capacity (99% from 12%) of MB after being modified to nanocomposite ion exchanger. Adsorption process followed Langmuir adsorption (Qo = 10.46 mgg-1) and non linear PFO kinetic model with k1, qe (calculated), R2, RMSE = 0.011, 1.02 (mgg-1), 0.996, and 0.01709 respectively.
关键词： nonlinear PFO,ion exchanger,cationic dye,nanocomposite,Chitosan,Langmuir
更新于2025-09-10 09:29:36
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Linear Analyses of Langmuir and EM Waves in Relativistic Hot Plasmas
摘要： The linear Langmuir and electromagnetic (EM) waves in relativistic hot plasmas are discussed, and the dispersion relations are obtained based on the covariant Maxwell’s and ?uid equations. When kBT =mc2 > 1, the e?ective mass of electrons will be increased obviously. As the results, many other in?uences are induced, such as the decrease of the plasmas frequency and the critical frequency, the reduction of the electron sound velocity and the electrons’ oscillation velocity, and so on. Numerical results show that these in?uences can a?ect the dispersion relations of Langmuir and EM waves seriously even in linear regime.
关键词： relativistic hot plasmas,dispersion relation,Langmuir wave,electromagnetic wave
更新于2025-09-09 09:28:46
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Surface FTIR Techniques to Analyze the Conformation of Proteins/ Peptides in H2O Environment
摘要： Proteins/peptides, which are involved in various biochemical processes in biological systems, contain infrared (IR) active vibrations. Among all the IR absorption bands of proteins/peptides, the amide I band arises mainly from the stretching vibration of the carbonyls (C=O) in backbone amide bonds and is sensitive to the conformations (such as α–helix, β–sheet, unstructured conformation, and so on) in a protein/peptide. Therefore, the amide I band has been used to monitor the biophysical/biochemical behavior of proteins/peptides in biological samples (e.g., living cells or tissues). However, obtaining reproducible IR spectra of proteins/peptides in H2O solution was challenging by direct transmission measurement using a liquid cell with milli-meter level path length, due to the intensive IR absorption of H2O around 1620 cm-1 which overlaps the amide I band. Thus, lots of the IR spectra of proteins/peptides were accomplished in D2O, which has IR absorption around 1200 cm-1. Since D2O may not be a favorable solvent for biological samples, the position of the amide I band of various conformations was needed as a reference for biological samples. Consequently, various surface FTIR techniques (such as Infrared Reflection-Absorption Spectroscopy or IRRAS, and Attenuated Total Reflection or ATR) have been developed to obtain the IR spectra of proteins/peptides in H2O environment and have been reviewed here.
关键词： Amide I band,Langmuir monolayer,ATR,13C labels,IRRAS,PM-IRRAS
更新于2025-09-09 09:28:46