4,077 research outputs found
Raman microspectroscopy interrogating 19th and 20th century painted trades union banners
No full textWe have previously developed protocols for the application of Raman microspectroscopy to studies on painted textiles. We have further assessed the value of such microanalyses in the identification of both inorganic and organic constituents, including original components and consolidants used in conservation treatments. This paper presents the results of a recent study on a number of 19th- and 20th-century trades union banners directed at collating a spectral database of inorganic pigments used in the illustrations and at probing the preparative process prior to painting. Such information will contribute to an understanding of the manufacture of such banners and their current condition, leading to the development of optimum conservation procedures.While Raman spectroscopy has the potential to be used in situ and, with the appropriate protocol, is non-destructive, nonetheless we have found that the analysis of resin-embedded cross-sections is to be preferred with microtoming providing the cleanest sample surface. The optimum methodology for acquiring good quality Raman spectra is described including operation in the confocal mode, with consideration of fluorescence, interference from resin, laser-induced photochemistry, and so on
Stimulated terahertz emission due to electronic Raman scattering in silicon
Get PDFSilicon-based semiconductors are intensively investigated over the past years as promising candidates for optoelectronic devices at terahertz (THz) frequencies [1]. Optically pumped intracenter silicon lasers, realized in the past decade in the THz range, are based on direct optical transitions between shallow levels of different shallow donors [2]. Recently, terahertz Raman laser emission has been demonstrated in silicon doped by antimony [3] and phosphorus [4].
We report on realization of terahertz lasers based on intracenter electronic Raman scattering in silicon doped by arsenic (Si:As, frequency range 4.8 – 5.1 THz and 5.9 – 6.5 THz) and silicon doped by bismuth (Si:Bi, 4.6 – 5.9 THz) under optical excitation by infrared frequency-tunable free electron laser at low lattice temperatures. The Stokes shift of the observed laser emission is equal to the Raman-active donor electronic transition between the ground 1s(A1) and the excited 1s(E) donor states. Raman terahertz gain of the lasers is similar to those observed for the donor-type terahertz silicon donor lasers
Design and analysis of dopingless charge-plasma-based ring architecture of tunnel field-effect transistor for low-power application
No full textThis chapter discusses the dopingless charge-plasma-based ring architecture of the tunnel field-effect transistor (CP-Ring-TFET). The operation of the TFET has been described in this chapter. The two- and three-dimensional structures of the CP-Ring-TFET with device specification are also described. For a simulation of the device, the Silvaco technology computer-aided design (TCAD) tool is used. This chapter also covers the methodology, device specification, and model specification used in the simulation of the CP-Ring-TFET device. The proposed CP-Ring-TFET device is a dopingless device and CP technique is used to operate the proposed device in the equilibrium operating region, OFF operating region, and ON operating region. For the performance analysis of the CP-Ring-TFET device, various parameters are examined like device and analog specification. The proposed CP-Ring-TFET structure shows the higher ON-state current (ION ), better subthreshold slope (SS), and lower threshold voltage (VTH ), which is beneficial for low-power applications
Infrared and Raman studies of thin polymer films
Get PDF[Keywords:- Waveguide; Raman; Attenuated Total Reflection; Infrared; Polymer Films; Barrier Films; Epoxy; Diffusion; Isocyanate; Crosslinking Agents; Cure Time; Kinetics; Urethane; Film Quality]This thesis describes the experimental work carried out between October l(^st), 1990 and 30th September, 1993, in the Chemistry Department of the University of Durham, in association with Courtaulds Coatings plc, m partial fulfilment of the requirements for the degree of Doctor of Philosophy. The thesis is divided into three sections, namely Theoretical Considerations (three Chapters), Experimental Results (three Chapters) and Discussion of Results (one Chapter). There are also three appendices. The theoretical section presents a working description of Paint Chemistry, Vibrational spectroscopy, Waveguide Raman Spectroscopy, Attenuated Total Reflection Fourier Transform Infrared Spectroscopy and Diffusion Processes. The experimental section is divided into three chapters. The first describes methods of film preparation and characterisation and includes methods of film thickness determination and the development of an off-line waveguiding rig at the University of Durham. Raman spectroscopic results are detailed in the second chapter, and include waveguide experiments on both single polymer films and laminate systems, some of which are reported for the first time, along with some FT-Raman results, also reported for the first time. The FT-IR ATR spectroscopic results are presented in the third chapter and include some barrier film studies on polymeric laminate systems, plus the study of certain diffusion processes, along with an estimation of the associated diffusion coefficients and some kinetic parameters, occurring in epoxy resins, which are reported for the first time. The discussion section concentrates on a full elucidation of the results, and conclusions that may be drawn from them, and ends with suggestions for future work. Refractive indices quoted, unless otherwise stated, refer to indices measured usmg 632.8 nm radiation, and have been estimated either using previous literature, or with the off-line rig. It is accepted that electric field calculations performed with these values will be slightly different to the actual fields observed in the Raman experiments, due to slightly different refractive indices at 514.5 nm. T in tables, unless otherwise stated, refers to band intensities in absorbance units. Finally, the attention of the reader is drawn to the fact that some of the materials used in the course of this project have no precise structure given. This is due to the fact that some of the substances used are of either a highly complicated and/or confidential nature
Towards objective endoscopic diagnosis of Barrett's associated early neoplasia using fibre-optic Raman Spectroscopy
Get PDFThis translational research evaluates a novel, custom-built Raman probe for potential
application as an in vivo diagnostic tool in the oesophagus. Raman spectroscopy (RS) is a
well established analytical technique which is capable of probing the biochemical changes
associated with neoplastic progression in oesophageal tissue. RS relies on measurement of
subtle inelastic scattering signals following monochromatic laser excitation.
Clinical utilisation of RS within hollow organs requires accurate collection and transmission
of signal through fibre-optic cables. This research aims to evaluate the ability of a custom
built fibre-optic Raman probe, in conjunction with multivariate classification models, to
differentiate between benign and neoplastic oesophageal pathologies ex vivo. The need for
spectral stability and reproducibility are addressed, as are difficulties associated with multisystem
reliability. In addition, the biochemical basis of spectral classification is evaluated and
discussed. Cont/d
layers using machine learning‐assisted low‐frequency interlayer Raman fingerprints
Get PDFThe investigation of twisted stacked few‐layer MoS2 has revealed novel electronic, optical, and vibrational properties over an extended period. For the successful integration of twisted stacked few‐layer MoS2 into a wide range of applications, it is crucial to employ a noninvasive, versatile technique for characterizing the layered architecture of these complex structures. In this work, we introduce a machine learning‐assisted low‐frequency Raman spectroscopy method to characterize the twist angle of few‐layer stacked MoS2 samples. A feedforward neural network (FNN) is utilized to analyze the low‐frequency breathing mode as a function of the twist angle. Moreover, using finite difference method (FDM) and density functional theory (DFT) calculations, we show that the low‐frequency Raman spectra of MoS2 are mainly influenced by the effect of the nearest and second nearest layers. A new improved linear chain model (TA‐LCM) with taking the twist angle into the consideration is developed to understand the interlayer breathing modes of stacked few‐layer MoS2. This approach can be extended to other 2D materials systems and provides an intelligent way to investigate naturally stacked and twisted interlayer interactions.CHE-1945364 - National Science FoundationFirst author draf
Raman microscopy of processed polyethylene particles
No full textRaman microscopy was applied to detect structural change within individual particles of low-density polyethylene following chemical and electrochemical processing steps that aimed to facilitate material decomposition. Probing at a depth of ~20 μm from the surface of the nominally 500 μm diameter particles, changes in vibrational bands sensitive to polyethylene crystallinity were evident following treatments and linked to the release of low molecular weight compounds present as additives and products of electrochemical processing. The rise of Raman scattering intensity in vibrational modes associated with polyethylene chains in a zig-zag (trans) conformation near 1128 cm-1, 1294 cm-1 and 1418 cm-1 signaled chain clustering and development of organized, crystalline-like assemblies. Multivariate statistical methods were adapted to aid in discerning spectral change. Principal component (factor) analysis was applied as a simple, rapid means to detect variation in datasets. Least-squares modeling was used to derive pure component spectra reflecting crystallinity change. The work lays a foundation for the use of confocal Raman microscopy coupled with multivariate statistical analysis techniques for quantitative probing of processed polymers.Embargo status: Restricted until 09/2028. To request the author grant access, click on the PDF link
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Raman spectroscopy of silicon with nanostructured surface
No full textWe compared the morphology and Raman response of nanoscale shaped surfaces of Si substrates versus monocrystalline Si. Samples were structured by reactive ion etching, and four of them were covered by a RuO2-IrO2 layer. Raman bands, centred at approx. 520 cm–1, belonging to samples processed by etching the Si surface have intensities higher by approximately one order of magnitude than those of reference non-etched samples. For nanostructured samples, the rise in the Raman signal was 12–14 ×, which is in agreement with the model of the electric field at the tips of Si due to their geometry. This phenomenon is related to the high absorption of excitation radiation. Nanostructured surfaces of samples containing a layer of RuO2-IrO2 give rise to the phenomenon of surface enhancement of the Raman response most likely due to the charge transfer at the interface between silicon and conductive oxides. The nanostructured surface of Si without a metal layer behaves as a SERS substrate and detects the analytes at a low concentration.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Photovoltaic Materials and DevicesElectrical Sustainable Energ
An investigative and evaluative study of factors affecting quality of agricultural and farm information services in Kerala
Get PDFAgriculture is not only a country’s backbone of food, livelihood and ecological security systems, but is also the very soul of its sovereignty. In Kerala population density is high and land is scarce. To achieve sustainable advancement in quality of human life, meeting the domestic food requirement is to be given foremost priority in development plans. As the area of cultivation cannot be increased and growth of population cannot be controlled growth in food production is to be achieved by qualitative improvement in farming. This requires improvements in material inputs, farming techniques, storage technology and research. Effective integration of these factors is tied closely to adequate information flow, which can be ensured only by an efficient information system for agricultural education, research, extension and development. So evaluation and improvement of existing information services is very crucial for sustainable agricultural growth. The study evaluates the existing information resources, facilities, services, possibilities for resource sharing, accessibility of external sources, and the factors that affect the quality and efficiency of information services in agricultural sector. Coverage is limited to the State of Kerala. Sample consist 105 institutions of different levels, and information users consisting of 426 scientists and 220 farmers. Different sets of questionnaires and interview schedule were used to elicit information. The study found that agricultural research conducted at various institutions in the region at huge public expense has generated knowledge for improving production. Along with these huge collections of acquired content is also stored in the sector. But when a farmer, an extension worker, a scientist or an administrator needs information it is not easily accessible. The study found that agricultural sector fails to effectively bank on information resources available due to the lack of an information system and network. Recommends an Agricultural and Farm Information System for Kerala. Suggests a model plan for a computer communication network for resource sharing between the agricultural institutions in the State, which will also ensure, smooth flow of results of research down to the grassroots level to achieve maximum productivity in agriculture
Revealing the nanogeometry of WS2 nanoflowersby polarization-resolved Raman spectroscopy
No full textRecent studies of transition metal dichalcogenides (TMDs) have revealed exciting optical properties, such as stable excitons and chiral light–matter interactions. Chemical vapor deposition techniques provide a platform for the fabrication of nanostructures with diverse geometries, ranging from horizontal flakes to flower-like structures. Raman spectroscopy is commonly used to characterize TMDs and their properties. Here, we use polarization-resolved Raman spectroscopy to probe the nanogeometry and orientation of WS 2 nanoflower petals.Exciting the nanoflowers with linearly polarized light, we observe an enhanced Raman response from flower petals oriented along the excitation polarization direction. Furthermore, the helicity-resolved Raman response of vertically oriented wall-like flower petals exhibits clear differences with horizontally oriented flakes. Although the photoluminescence from the nanoflowers is strongly reduced, the Raman response upon excitation in resonance with the WS 2 excitonic transition does reveal the presence of the exciton, which results in a distinct temperature dependence of the Raman response.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.QN/Kuipers LabQN/Conesa-Boj LabQN/Quantum Nanoscienc
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