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Effect of substrate bias and substrate/plasma generator distance on properties of a-C:H:SiOx films synthesized by PACVD
摘要： In this paper the a-C:H:SiOx films were synthesized on silicon (100) and glass substrates by plasma-assisted chemical vapor deposition combined with pulsed bipolar substrate bias from mixtures of argon and polyphenylmethylsiloxane vapor. The process of a-C:H:SiOx films formation was investigated by controlling processing conditions such as amplitude of negative pulse of substrate bias and the distance between the substrate and plasma generator. Physico-mechanical characteristics of a-C:H:SiOx films were studied by the nanoindentation technique, atomic force microscopy, Fourier transform infrared and Raman spectroscopy. The contact angle and surface free energy were determined by the sessile drop method using couple liquids (water and glycerin). It was found that the films’ properties are interrelated with the density of the ion current on the substrate, which was measured using a guarded planar probe. The obtained results show that film prepared at the smaller substrate/plasma generator distance and optimal substrate biasing has a higher content of sp3 bonded carbon and, accordingly, has higher hardness, Young's modulus and resistance to plastic deformation. At the same time the a-C:H:SiOx films show large hydrophobicity with a contact angle for water of about 91° and small total surface free energy of about 17.9 mN/m.
关键词： a-C:H:SiOx films,PACVD,Raman Spectroscopy,Substrate bias,Fourier Transform Infrared Spectroscopy,Wettability
更新于2025-09-23 15:21:21
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Evaluation of selected SERS substrates for trace detection of explosive materials using portable Raman systems
摘要： Raman spectroscopy has become an essential analytical technique for field detection and identification of illicit or dangerous materials such as explosives, but its main drawback is low signal intensity. This problem can be circumvented by using surface enhanced Raman spectroscopy (SERS), in which scattering signals increase significantly for analytes adsorbed onto or near nanostructured surfaces of the plasmonic materials. However, despite numerous studies, SERS has still not been widely used in real-world applications. The main goal of the studies describe herein was to investigate the possibility of detection of trace amounts of selected explosive materials on various commercial and non-commercial SERS substrates using portable Raman instruments. Our studies have shown that while portable systems suitable for SERS measurement of trace amounts of explosives are readily available, the problem remains in the selection of reliable and reproducible SERS substrates. Among five investigated SERS substrates only two, Klarite 312 and GaN-pillars allowed for trace analysis of all studied explosive materials. In both cases, detected concentrations of explosives ranged from single to hundreds of μg/cm2 depending on the explosive material and the Raman spectrometer used. Based on our findings, it could be concluded that the best SERS substrates for trace analysis of explosives are substrates with hot spots densely and evenly distributed over a whole active area of SERS substrate.
关键词： portable Raman spectroscopy,SERS,SERS substrates,trace detection,explosives
更新于2025-09-23 15:21:21
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Raman spectroscopy combined with advanced chemometric methods: A new approach for detergent deformulation
摘要： Deformulation of a commercial surfactant mixture using RAMAN spectroscopy and advanced chemometric tools have been investigated. Since the use of surfactants is drastically expanding, their fine identification and quantification are required for quality control and regulation. Dilution of the detergent mixtures combined with RAMAN spectroscopy for signal extraction tools allowed the extraction of the first information concerning the composition of the mixture. The raw materials identified were thus used in an experimental design to obtain a robust model for the determination of detergent composition. The combination of chemometric tools (Independent Component Analysis and Partial Least Square) and spectroscopic methods provided pertinent information for detergent composition. This methodology can easily be transposed to the industrial world.
关键词： detergents deformulation,RAMAN spectroscopy,surfactants characterization,design of experiments,Chemometrics,blind source separation methods
更新于2025-09-23 15:21:21
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Light scattering from the critical modes of the Verwey transition in magnetite
摘要： We present inelastic light scattering data on a single crystal of magnetite (Fe3O4) across the Verwey transition. We identify anomalies of the lattice vibrations that originate from strong coupling to electronic excitations. We reveal spectroscopic signatures of diffusive modes in the electronic contribution to the Raman response function. We thereby provide information on the critical dynamics and the hierarchy of the structural and electronic modes in the mechanism of the Verwey transition.
关键词： Raman spectroscopy,Verwey transition,critical dynamics,inelastic light scattering,magnetite
更新于2025-09-23 15:21:21
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Ultrathin Y <sub/>2</sub> O <sub/>3</sub> :Eu <sup>3+</sup> nanodiscs: spectroscopic investigations and evidence for reduced concentration quenching
摘要： Here, we report the synthesis and spectral properties of ultrathin nanodiscs (NDs) of Y2O3:Eu3+. It was found that the NDs of Y2O3:Eu3+ with a thickness of about 1 nm can be fabricated in a reproducible, facile and self-assembling process, which does not depend on the Eu3+ concentration. The thickness and morphology of these NDs were determined with small angle x-ray scattering and transmission electron microscopy. We found that the crystal field in these nanoparticles deviates from both the cubic and monoclinic characteristics, albeit the shape of the 5D0 → 7FJ (J = 0, 1, 2) transitions shows some similarity with the transitions in the monoclinic material. The Raman spectra of the non-annealed NDs manifest various vibration modes of the oleic acid molecules, which are used to stabilise the NDs. The annealed NDs show two very weak Raman lines, which may be assigned to vibrational modes of Y2O3 NDs. The concentration quenching of the Eu3+ luminescence of the NDs before annealing is largely suppressed and might be explained in terms of a reduction of the phonon density of states.
关键词： nanodiscs,small angle x-ray scattering,europium-doped yttrium oxide,Raman spectroscopy,concentration quenching,transmission electron microscopy,luminescence
更新于2025-09-23 15:21:21
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Controlling surface morphology and sensitivity of granular and porous silver films for surface-enhanced Raman scattering, SERS
摘要： The design of efficient substrates for surface-enhanced Raman spectroscopy (SERS) for large-scale fabrication at low cost is an important issue in further enhancing the use of SERS for routine chemical analysis. Here, we systematically investigate the effect of different radio frequency (rf) plasmas (argon, hydrogen, nitrogen, air and oxygen plasma) as well as combinations of these plasmas on the surface morphology of thin silver films. It was found that different surface structures and different degrees of surface roughness could be obtained by a systematic variation of the plasma type and condition as well as plasma power and treatment time. The differently roughened silver surfaces act as efficient SERS substrates showing greater enhancement factors compared to as prepared, sputtered, but untreated silver films when using rhodamine B as Raman probe molecule. The obtained roughened silver films were fully characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron (XPS and Auger) and ultraviolet–visible spectroscopy (UV–vis) as well as contact angle measurements. It was found that different morphologies of the roughened Ag films could be obtained under controlled conditions. These silver films show a broad range of tunable SERS enhancement factors ranging from 1.93 × 102 to 2.35 × 105 using rhodamine B as probe molecule. The main factors that control the enhancement are the plasma gas used and the plasma conditions, i.e., pressure, power and treatment time. Altogether this work shows for the first time the effectiveness of a plasma treatment for surface roughening of silver thin films and its profound influence on the interface-controlled SERS enhancement effect. The method can be used for low-cost, large-scale production of SERS substrates.
关键词： plasma treatment,sputtering,surface-enhanced Raman spectroscopy (SERS),silver,surface roughening
更新于2025-09-23 15:21:21
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Vapor-liquid-equilibria of fuel-nitrogen systems at engine-like conditions measured with Raman spectroscopy in micro capillaries
摘要： A fuel, here ethanol or decane, and nitrogen are fed at elevated pressure and temperature through a micro capillary of fused silica. The flow inside the capillary is characterized by alternating liquid- and vapor-phase segments that accommodate to thermodynamic equilibrium at the set temperature and pressure. The composition of the equilibrated liquid or vapor segments is measured in situ and remotely inside the micro capillary by Raman spectroscopy. Temperature-composition (Tx) vapor-liquid equilibria were measured for pressures between 3 MPa and 8 MPa and up to the highest mixture critical temperature of 593 K in this pressure range. Comparison to the scarce literature data for these conditions and to the GERG-2008 model, resembling the conditions in IC-engines at the time of injection, is shown.
关键词： Fuel,Solubility,Vapor,Liquid,Capillary,Raman spectroscopy,VLE
更新于2025-09-23 15:21:21
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[ASME ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems - San Francisco, California, USA (Monday 27 August 2018)] ASME 2018 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems - Analysis of Thermal Properties of Power Multifinger HEMT Devices
摘要： In this paper, several methods suitable for real time on-chip temperature measurements of power AlGaN/GaN based high-electron mobility transistor (HEMT) grown on SiC substrate are presented. The measurement of temperature distribution on HEMT surface using Raman spectroscopy is presented. We have deployed a temperature measurement approach utilizing electrical I-V characteristics of the neighboring Schottky diode under different dissipated power of the transistor heat source. These methods are verified by measurements with micro thermistors. The results show that these methods have a potential for HEMT analysis in thermal management. The features and limitations of the proposed methods are discussed. The thermal parameters of materials used in the device are extracted from temperature distribution in the structure with the support of 3-D device thermal simulation. The thermal analysis of the multifinger power HEMT is performed. The effects of the structure design and fabrication processes from semiconductor layers, metallization, and packaging up to cooling solutions are investigated. The analysis of thermal behavior can help during design and optimization of power HEMT.
关键词： thermal properties,Raman spectroscopy,thermal management,Schottky diode,power HEMT devices
更新于2025-09-23 15:21:21
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A noticeable effect of thickness on third order nonlinear properties of CBD grown CdS thin films investigated by Z-scan measurements
摘要： In current work, thin films of CdS with alike thickness were fabricated by chemical bath deposition by varying the deposition time. Thickness of films was measured to be ~ 200, 250 and 300 nm using Alfa step stylus profilometer. As thickness play significant role hence thickness dependent structural, vibrational, morphological, optical and third order nonlinear optical (TONLO) studies are exclusively explored. The XRD and FT-Raman studies revealed an enhancement in crystallinity with increasing thickness of films and also confirmed non existence of any impurity peak. Crystallite size evaluated from Scherrer's rule is found to be increased from 21 to 30 nm with increasing the thickness of films. Scanning electron microscopy images demonstrates the modification of spherical nanoparticles to nano needles with increase of thickness of films. Average size of grains are intuited to be in 30 to 65 nm range. Transmission spectra showed high transparency for films of 200 nm thickness and later reduced with increase of thickness. Direct energy gap was attained in range of 2.2 to 2.3 eV. Stable values of k and n indicates defect free films. The n2 and χ3 values are found to very high which are in range of 3.15 to 8.67 (×10-6) and 1.11 to 1.47 (×10-1), respectively. Such transparent films with higher TONLO susceptibility values are potential candidates for optoelectronic device applications.
关键词： CdS films,FT-Raman spectroscopy,Optical properties,X-ray diffraction,third order nonlinear properties
更新于2025-09-23 15:21:21
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Study of keratin hair of domestic cat under methionine and cystine experimental diet using FT-Raman spectroscopy
摘要： FT-Raman spectroscopy has been extensively used to study human keratotic biopolymers, such as skin, nail and hair, since the disulfide bonds of keratin protein is Raman-active vibrational mode. In this context, animal hair can also be evaluated by Raman spectroscopy, for the main protein is keratin. In this study, domestic cats were submitted to an experimental diet with different levels of methionine and cysteine; then their hair was evaluated by using FT-Raman spectroscopy on the first and on the last day of the diets. The results were compared with tensile rupture measurements. They showed that FT-Raman spectroscopy was able to monitor disulfide bonds (510 cm-1) and keratin protein conformation (amide I) in different sulfur amino acids levels, indicating that the levels above the minimum recommended were not efficient to improve the hair quality.
关键词： Raman spectroscopy,cat hair,cystine,keratin
更新于2025-09-23 15:21:21