- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Dynamical distortions of structural signatures in molecular high-order harmonic spectroscopy
摘要： We study the signature of two-center interferences in molecular high-order harmonic spectra, with an emphasis on the spectral phase. With the help of both ab initio computations based on the time-dependent Schr?dinger equation and the molecular strong-field approximation (SFA) as developed by Chiril? et al. [Phys. Rev. A 73, 023410 (2006)] and Faria [Phys. Rev. A 76, 043407 (2007)], we observe that the phase behavior is radically different for the short and the long trajectory contributions. By means of Taylor expansions of the molecular SFA, we link this effect to the dynamics of the electron in the continuum. More precisely, we find that the value of the electric field at recombination time plays a crucial role in the shape of the destructive interference phase jump.
关键词： molecular spectroscopy,spectral phase,strong-field approximation,two-center interferences,time-dependent Schr?dinger equation,high-order harmonic generation
更新于2025-09-23 15:23:52
-
Importance of electron correlations in understanding photoelectron spectroscopy and Weyl character of
摘要： We study the role of electron correlations in the presumed type-II Weyl semimetallic candidate γ-MoTe2 by employing density functional theory (DFT) where the on-site Coulomb repulsion (Hubbard U) for the Mo 4d states is included within the DFT+U scheme. We show that pure DFT calculations fail to describe important features of the light-polarization dependence of the angular resolved photoemission intensity which can be accounted for by including the role of the Hubbard U. At the same time, while pure DFT calculations cannot explain the angular dependence of the Fermi surface as revealed by quantum oscillation experiments (a fact which had raised doubt about the presence of the Weyl physics in γ-MoTe2), inclusion of such on-site Coulomb repulsion can. We find that while the number of Weyl points (WPs) and their position in the Brillouin zone change as a function of U, a pair of such WPs very close to the Fermi level survive the inclusion of these important corrections. Our calculations suggest that the Fermi surface of γ-MoTe2 is in the vicinity of a correlations-induced Lifshitz transition, which can be probed experimentally and its interplay with the Weyl physics might be intriguing.
关键词： electron correlations,Lifshitz transition,angular resolved photoemission,MoTe2,DFT+U,Hubbard U,quantum oscillation,Weyl semimetal,photoelectron spectroscopy
更新于2025-09-23 15:23:52
-
Noise reduction for near-infrared spectroscopy data using extreme learning machines
摘要： The near infrared (NIR) spectra technique is an effective approach to predict chemical properties and it is typically applied in petrochemical, agricultural, medical, and environmental sectors. NIR spectra are usually of very high dimensions and contain huge amounts of information. Most of the information is irrelevant to the target problem and some is simply noise. Thus, it is not an easy task to discover the relationship between NIR spectra and the predictive variable. However, this kind of regression analysis is one of the main topics of machine learning. Thus machine learning techniques play a key role in NIR based analytical approaches. Pre-processing of NIR spectral data has become an integral part of chemometrics modeling. The objective of the pre-processing is to remove physical phenomena (noise) in the spectra in order to improve the regression or classification model. In this work, we propose to reduce the noise using extreme learning machines which have shown good predictive performances in regression applications as well as in large dataset classification tasks. For this, we use a novel algorithm called C-PL-ELM, which has an architecture in parallel based on a non-linear layer in parallel with another non-linear layer. Using the soft margin loss function concept, we incorporate two Lagrange multipliers with the objective of including the noise of spectral data. Six real-life dataset were analyzed to illustrate the performance of the developed models. The results for regression and classification problems confirm the advantages of using the proposed method in terms of root mean square error and accuracy.
关键词： Parallel layers,Constrained optimization,Regression,Near-infrared spectroscopy,Classification
更新于2025-09-23 15:23:52
-
Classification of pre-dyed textile fibers exposed to weathering and photodegradation by non-destructive excitation-emission fluorescence spectroscopy paired with discriminant unfolded-partial least squares
摘要： Undyed textile fabrics such as Acrylic 864, Nylon 361 and Cotton 400 were pre-dyed with Basic Green 4 (BG4), Acid Yellow 17 (AY17) and Direct Blue 1 (DB1) dyes, respectively; and then exposed to two extremely diverse weather conditions in the United States: desert and humid environmental settings in Arizona (AZ) and Florida (FL) respectively, for different time intervals of exposure, which included 0, 3, 6, 9 and 12 months. After every interval of a 3 months period, ten fibers were uniformly sampled from each cloth piece, and fluorescence microscopy was employed to collect two-dimensional excitation and fluorescence spectra (2-D spectra) and three-dimensional (3D) excitation-emission matrices (EEMs). A significant loss of fluorescence intensity was observed upon fiber exposure to outdoor weathering conditions. For a comprehensive statistical data analysis and to be able to discriminate between any two single fibers weathered under different conditions, a multiway calibration algorithm known as discriminant unfolded partial least-squares (DU-PLS) method was applied to the exposed fibers. Results indicate that fluorescence spectroscopy combined with DU-PLS has the ability to appropriately classify and differentiate between any two pairs of dyed cotton or nylon fibers (acrylic in some cases) exposed to dry versus humid weather environments under different time intervals of exposure. These results provide the foundation for future studies towards a non-destructive approach capable to provide information on the weathering history of the fiber.
关键词： Discriminant unfolded partial least squares,Fiber analysis,Photodegradation,Excitation emission matrices,Weathering,Fluorescence spectroscopy
更新于2025-09-23 15:23:52
-
[IEEE 2018 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - Saint Petersburg, Russia (2018.10.22-2018.10.23)] 2018 IEEE International Conference on Electrical Engineering and Photonics (EExPolytech) - Investigation of the Phase Composition and Morphology of Silicon Structures by Using the Raman Spectroscopy to Determine the Parameter of Crystallinity
摘要： This work aims to investigate the dependence of the phase composition of thin films of microcrystalline silicon deposition on process parameters. The films of microcrystalline silicon were obtained by plasma-chemical deposition method (PECVD). Phase composition and correlation between degree of crystallinity and structure of the obtained layers were analyzed by Raman Spectroscopy. The results show that the control of several technical parameters, e.g. pressure, discharge power and monosilane flow, allows to reach the crystallinity parameter in the range 50-70 %. Based on the conducted experiments, the recommendations for the control of the crystallinity parameter, which are planned to be implemented when working with silicon-based porous structures, were proposed.
关键词： Morphology,Semiconductors,Silicon,Por-silicon,Phase composition,Raman spectroscopy,Raman Crystallinity
更新于2025-09-23 15:23:52
-
Effect of Oxygen on Thermal and Radiation Induced Chemistries in a Model Organotin Photoresist
摘要： Organotin photoresists have shown promise for next generation lithography due to their high extreme ultraviolet (EUV) absorption cross sections, their radiation sensitive chemistries, and their ability to enable high-resolution patterning. To better understand both temperature and radiation induced reaction mechanisms, we have studied a model EUV photoresist, which consists of a charge-neutral butyl-tin cluster. Temperature programmed desorption (TPD) showed very little outgassing of the butyl-tin resist in ultrahigh vacuum, and excellent thermal stability of the butyl groups. TPD results indicated that decomposition of the butyl-tin resist was first order with a fairly constant decomposition energy between 2.4 and 3.0 eV, which was determined by butyl group desorption. Electron stimulated desorption (ESD) showed that butyl groups were the primary decomposition product for electron kinetic energies expected during EUV exposures. XPS was performed before and after low energy electron exposure to evaluate the compositional and chemical changes in the butyl-tin resists after interaction with radiation. The effect of molecular oxygen during ESD experiments was evaluated and it was found to enhance butyl group desorption during exposure, and resulted in a significant increase in the ESD cross section by over 20%. These results provide mechanistic information that can be applied to organotin EUV photoresists, where a significant increase in photoresist sensitivity may be obtained by varying the ambient conditions during EUV exposures.
关键词： X-ray photoelectron spectroscopy,electron stimulated desorption,Extreme ultraviolet lithography,organotin photoresist,temperature programmed desorption
更新于2025-09-23 15:23:52
-
Dual frequency-comb spectroscopy of chromophores in condensed phases
摘要： Femtosecond time-resolved spectroscopy and frequency-comb spectroscopy have been individually developed to achieve better time and frequency resolutions, respectively. The two spectroscopic techniques have been developed for different systems, even though they use mode-locked laser in common. Recently, there was an interesting merge of the two techniques into a dual frequency-comb (DFC) spectroscopy, resulting in a new femtosecond spectroscopy with simple instrumentation and high data acquisition speed compared to conventional femtosecond spectroscopic techniques. By slightly detuning the repetition rates of two phase-locked frequency-comb lasers, both automatic time-delay scanning and parallel data recording with single point detectors are possible. Thus, we anticipate that the DFC spectroscopy would allow one to expand the application limits of the conventional femtosecond spectroscopic methods. In this Perspective article, we provide reviews of linear and nonlinear DFC spectroscopy theory and applications with a perspective on the development of coherent multidimensional frequency-comb spectroscopy.
关键词： nonlinear spectroscopy,optical frequency-comb,time-resolved spectroscopy,coherent two-dimensional spectroscopy,solvation dynamics,dual comb spectroscopy
更新于2025-09-23 15:22:29
-
Transverse phonons and intermediate-range order in Sr-Mg fluorophosphate glasses
摘要： Vibrational and ultrasonic spectroscopies have been employed to study the composition and polarization dependence of the vibrational and elastic properties of the pseudo-binary mixed fluoride-phosphate glass-forming system xSr(PO3)2-(1-x)(0.62MgF2-0.38AlF3) with x: 0, 0.04, 0.06, 0.1, 0.15, 0.2, 0.3, 0.4, 0.8, 0.9 and 1. Composition-induced alterations in the short-range order have been quantitatively followed by means of Raman and IR spectroscopies. The analysis has shown that the incorporation of the phosphate groups in the fluoride network results in a less interconnected network with suppressed rigidity. The specific amorphous materials have been used as a model system in terms of wide glass-forming ability to elucidate the effect of variation in connectivity between the fluoride and phosphate sub-networks on the Boson peak nature. Emphasis has been given in the low-frequency Raman phenomenology, which in conjunction with the elastic properties allowed us to establish a possible link between the Boson peak and the transverse phonons in these glasses.
关键词： phonons,amorphous materials,oxide glasses,Boson peak,elastic properties,Raman spectroscopy,ATR spectroscopy
更新于2025-09-23 15:22:29
-
Peroxy radical detection for airborne atmospheric measurements using absorption spectroscopy of NO<sub>2</sub>
摘要： Development of an airborne instrument for the determination of peroxy radicals (PeRCEAS – peroxy radical chemical enhancement and absorption spectroscopy) is reported. Ambient peroxy radicals (HO2 and RO2, R being an organic chain) are converted to NO2 in a reactor using a chain reaction involving NO and CO. Provided that the amplification factor, called effective chain length (eCL), is known, the concentration of NO2 can be used as a proxy for the peroxy radical concentration in the sampled air. The eCL depends on radical surface losses and must thus be determined experimentally for each individual setup. NO2 is detected by continuous-wave cavity ring-down spectroscopy (cw-CRDS) using an extended cavity diode laser (ECDL) at 408.9 nm. Optical feedback from a V-shaped resonator maximizes transmission and allows for a simple detector setup. CRDS directly yields absorption coefficients, thus providing NO2 concentrations without additional calibration. The optimum 1σ detection limit is 0.3 ppbv at an averaging time of 40 s and an inlet pressure of 300 hPa. Effective chain lengths were determined for HO2 and CH3O2 at different inlet pressures. The 1σ detection limit at an inlet pressure of 300 hPa for HO2 is 3 pptv for an averaging time of 120 s.
关键词： peroxy radicals,NO2,cavity ring-down spectroscopy,airborne measurements,absorption spectroscopy,chemical amplification
更新于2025-09-23 15:22:29
-
Biodegradability of Disulfide-Organosilica Nanoparticles Evaluated by Soft X-ray Photoelectron Spectroscopy: Cancer Therapy Implications
摘要： Two kinds of organosilica nanoparticles (NPs) that were fabricated from thiol-containing precursors, (3-mercaptopropyl)trimethoxysilane and (3-mercaptopropyl)methyldimethoxysilane (MPDMS), are potential delivery vehicles of anticancer drugs. MPMS can form three siloxane bonds, but MPDMS forms two siloxane bonds as the maximum limit. Hence, disulfide bonds can be involved in the three-dimensional morphology of MPDMS NPs. In addition, NPs containing disulfide bonds are potentially degraded by a reduced form of glutathione (GSH). To examine reactions between the organosilica NPs and GSH, the NPs were incubated in 10 mM GSH aqueous solution at 37 °C for 7 d and the products were analyzed using field-emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and soft X-ray photoelectron spectroscopy (XPS). The Raman spectra showed the presence of disulfide bonds in the MPDMS NPs and the absence of disulfide bonds in MPMS NPs. The results of XPS measurements suggested that the disulfide bonds in the outer layer of MPDMS NPs were reduced to thiol groups. FE-SEM observations of MPDMS NPs detected changes in NP morphology after the GSH incubation. These results support the idea that MPDMS NPs contain disulfide bonds and are degradable by GSH. Therefore, MPDMS NPs possess a biodegradable feature that is advantageous for clinical translation, that is, nanomedicine.
关键词： (3-mercaptopropyl)methyldimethoxysilane,nanoparticles,(3-mercaptopropyl)trimethoxysilane,biodegradability,glutathione,X-ray photoelectron spectroscopy,Raman spectroscopy
更新于2025-09-23 15:22:29