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Investigation of Temperature Dependent Optical Modes in GexAs35-xSe65 Thin Films: Structure Specific Raman, FIR and Optical Absorption Spectroscopy  [PDF]
Pritam Khan,Arinjoy Bhattacharya,Abin Joshy,Vasant Sathe,Uday Deshpande,K. V. Adarsh
Physics , 2015,
Abstract: In this article, we present a comprehensive study of temperature and composition dependent Raman spectroscopy of GexAs35-xSe65 thin films to understand different structural units responsible for optical properties. Strikingly, our experimental results uncover the ratio of GeSe4/2 tetrahedral and AsSe3/2 pyramidal units in GexAs35-xSe65 thin films and their linear scaling relationship with temperature and x. An important notable outcome of our study is the formation of Se8 rings at lower temperatures. Our experimental results further provide interesting optical features, thermally and compositionally tunable optical absorption spectra. Detailed structure specific FIR data at room temperature also present direct information on the structural units in consistent with Raman data. We foresee that our studies are useful in determining the lightinduced response of these films and also for their potential applications in optics and optoelectronics.
Characterizing top gated bilayer graphene interaction with its environment by Raman spectroscopy  [PDF]
D. L. Mafra,P. Gava,L. M. Malard,R. S. Borges,G. G. Silva,J. A. Leon,F. Plentz,F. Mauri,M. A. Pimenta
Physics , 2011, DOI: 10.1016/j.carbon.2012.03.006
Abstract: In this work we study the behavior of the optical phonon modes in bilayer graphene devices by applying top gate voltage, using Raman scattering. We observe the splitting of the Raman G band as we tune the Fermi level of the sample, which is explained in terms of mixing of the Raman (Eg) and infrared (Eu) phonon modes, due to different doping in the two layers. We theoretically analyze our data in terms of the bilayer graphene phonon self-energy which includes non-homogeneous charge carrier doping between the graphene layers. We show that the comparison between the experiment and theoretical model not only gives information about the total charge concentration in the bilayer graphene device, but also allows to separately quantify the amount of unintentional charge coming from the top and the bottom of the system, and therefore to characterize the interaction of bilayer graphene with its surrounding environment.
Calculating Colimits Compositionally  [PDF]
R. Rosebrugh,N. Sabadini,R. F. C. Walters
Mathematics , 2007,
Abstract: We show how finite limits and colimits can be calculated compositionally using the algebras of spans and cospans, and give as an application a proof of the Kleene Theorem on regular languages.
Scanning rotational Raman lidar at 355 nm for the measurement of tropospheric temperature fields
M. Radlach, A. Behrendt,V. Wulfmeyer
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2008,
Abstract: For high-resolution measurements of temperature fields in the atmospheric boundary layer and the lower free troposphere a scanning eye-safe lidar which deploys the rotational Raman technique at 355 nm was developed. To optimize the filters of the receiver for both high nighttime and daytime performance, detailed simulation studies have been performed. The receiver is fiber-coupled to a sequential setup of multicavity interference filters used under small angles of incidence. Examples of nighttime and daytime measurements with the system which has a total power-aperture-efficiency product of 0.006 W m2 are presented. Noontime temperature measurements with a temporal resolution of 60 s result in 1-sigma statistical temperature uncertainty of <1 K up to 1 km height and <2 K up to 2 km height. With an integration time of 60 min and a gliding average of 750 m a 1-sigma statistical temperature uncertainty of <1 K up to 14 km height is achieved during night.
Scanning rotational Raman lidar at 355 nm for the measurement of tropospheric temperature fields
M. Radlach,A. Behrendt,V. Wulfmeyer
Atmospheric Chemistry and Physics Discussions , 2007,
Abstract: For high-resolution measurements of temperature fields in the atmospheric boundary layer and the lower free troposphere a scanning eye-safe lidar which deploys the rotational Raman technique at 355 nm was developed. To optimize the filters of the receiver for both high nighttime and daytime performance, detailed simulation studies have been performed. The receiver is fiber-coupled to a sequential setup of multicavity interference filters used under small angles of incidence. Examples of nighttime and daytime measurements with the system which has a total power-aperture-efficiency product of 0.006 W m2 are presented. Noontime temperature measurements with a temporal resolution of 60 s result in 1-sigma statistical temperature uncertainty of <1 K up to 1 km height and <2 K up to 2 km height. With an integration time of 60 min and a gliding average of 750 m a 1-sigma statistical temperature uncertainty of <1 K up to 14 km height is achieved during night.
STRUCTURE AND MAGNETIC PROPERTIES OF Fe/Pd COMPOSITIONALLY MODULATED FILMS
ZHANG Lin,LIU Yihua Shandong University,Jinan,China WANG Hao Dongnan University,Nanjing,China engineer,
ZHANG Lin
,LIU Yihua Shandong University,Jinan,China WANG Hao Dongnan University,Nanjing,China engineer

金属学报(英文版) , 1993,
Abstract: Metal Fe/Pd compositionally modulated films(CMFs) were prepared by vapour depo- sition from two sources onto glass substrate under vacuum.The modulation and crystal structures of the films were examined by X-ray diffraction.The magnetic properties were determined by vibrating sample magnetometer.The Pd layers in the Fe/Pd CMFs are of fcc structure,and the Fe layer structure transits from bcc into amorphous,state with decreasing thickness of Fe layer.The dependence of specific saturation magnetization on thickness of Fe layers has also been discussed.
Optimizing the Raman signal for characterizing organic samples: The effect of slit aperture and exposure time  [PDF]
Jo o Carlos Lázaro,Marcos Tadeu T. Pacheco,Kátia Calligaris Rodrigues,Carlos José de Lima,Leonardo Marmo Moreira,Antonio Balbin Villaverde,Landulfo Silveira Jr.
Spectroscopy: An International Journal , 2009, DOI: 10.3233/spe-2009-0377
Abstract: The present work is focused on the influence of the slit aperture and time exposure of the infrared light on the Charge Coupled Device (CCD) in relation to their physical effects, in order to improve the Raman spectrum characteristics. Indeed, the alterations in slit aperture and CCD time exposure affect significantly important spectral properties, such as the spectral intensity, Signal to Noise Ratio (SNR) and band width resolution of the Raman spectra. Therefore, the present proposal has the aim of to found the optimum conditions of instrumental arrangement, involving the minimum collection time and maximum signal quality in dispersive Raman spectrometers. Samples of dehydrated human teeth and naphthalene were evaluated with a Raman dispersive spectrometer employing excitation wavelength of 830 nm in several integration times and spectrometer slit apertures. The analysis of the spectral intensity, SNR and band width of selected Raman peaks allowed to infer that these properties of a dispersive Raman spectrum depend directly of the exposure time on the detector as well as spectrograph slit aperture. It is important to register that the higher SNR was obtained with higher exposure time intervals. To the samples evaluated in the present article, the band width has lower values for slit apertures of 100–150 μm, i.e., in this aperture range the spectral resolution is maximum. On the other hand, the intensity and SNR of the Raman spectra becomes optimal for slit apertures of 150–200 μm, since this aperture does not affect significantly the integrity of the Raman signal. In this way, we can to propose that in approximately 150 μm, it is possible to obtain an optimum condition, involving spectral resolution as well as SNR and spectral intensity. In any case, depending of the priorities of each spectral measurement, the instrumental conditions can be altered according with the necessities of each specific chemical analysis involving a determined sample. The present data are discussed in details in agreement with recent data from literature.
Geometric frustration in compositionally modulated ferroelectrics  [PDF]
Narayani Choudhury,Laura Walizer,Sergey Lisenkov,L. Bellaiche
Physics , 2011, DOI: 10.1038/nature09752
Abstract: Geometric frustration is a broad phenomenon that results from an intrinsic incompatibility between some fundamental interactions and the underlying lattice geometry1-7. Geometric frustration gives rise to new fundamental phenomena and is known to yield intriguing effects, such as the formation of exotic states like spin ice, spin liquids and spin glasses1-7. It has also led to interesting findings of fractional charge quantization and magnetic monopoles5,6. Geometric frustration related mechanisms have been proposed to understand the origins of relaxor behavior in some multiferroics, colossal magnetocapacitive coupling and unusual and novel mechanisms of high Tc superconductivity1-5. Although geometric frustration has been particularly well studied in magnetic systems in the last 20 years or so, its manifestation in the important class formed by ferroelectric materials (that are compounds exhibiting electric rather than magnetic dipoles) is basically unknown. Here, we show, via the use of a first-principles-based technique, that compositionally graded ferroelectrics possess the characteristic "fingerprints" associated with geometric frustration. These systems have a highly degenerate energy surface and exhibit original critical phenomena. They further reveal exotic orderings with novel stripe phases involving complex spatial organization. These stripes display spiral states, topological defects and curvature. Compositionally graded ferroelectrics can thus be considered as the "missing" link that brings ferroelectrics into the broad category of materials able to exhibit geometric frustration. Our ab-initio calculations allow a deep microscopic insight into this novel geometrically frustrated system.
COMPOSITION OF PIGMENTS ON HUMAN BONES FOUND IN EXCAVATIONS IN ARGENTINA STUDIED WITH MICRO-RAMAN SPECTROMETRY AND SCANNING ELECTRON MICROSCOPY  [PDF]
Larysa Darchuk,Elzbieta A. Stefaniak,Cristina Vázquez,Oscar M. Palacios
E-Preservation Science , 2009,
Abstract: Results on analysis of prehistoric pigments from excavationsand pigments on coloured child bones from NorthPatagonia, Argentina, are reported. To analyze their compositionwe used two micro-analytical techniques: micro-Raman spectrometr y (MRS) and scanning electronmicroscopy coupled with X-ray micro-analysis (SEM/EDX).Most investigated excavated pigments show red or yellowochres consistent with reddish or yellow minerals, such asα- and γ-goethite, haematite, er dite, haapalaite andjarosite. Raman spectra show also evidence of calciumoxalate monohydrate and calcite indicating lichen activity.Pigments covering human bones were identified ashematite and magnetite. This study allows us to infer thatpigments found in excavation were employed for burial ceremonies,even though distances between excavated pigmentarchaeological site and buried remains are quite far,more than 50 km in a straight line.
CHARACTERIZATION OF REFINED HEMP FIBERS USING NIR FT RAMAN MICRO SPECTROSCOPY AND ENVIRONMENTAL SCANNING ELECTRON MICROSCOPY  [PDF]
Siva Kumar Kovur,Karla C. Schenzel,Eckhard Grimm,Wulf Diepenbrock
BioResources , 2008,
Abstract: The research was focused on the separation of single hemp (Cannabis sativa L.) fibre cells with low fineness from mechanically extracted fibre bundles of high fineness. The fiber bundles were treated with enzymes, namely panzym, pectinase, hemicellulase, and cellulase, along with a combination of panzym and ultrasonic treatments. Changes in the fiber structure were followed at molecular and microscopic levels by means of NIR FT Raman spectroscopy and Environmental Scanning Electron Microscopy (ESEM). Buffer-panzym treatments of hemp fibers had a prominent effect in loosening of the fiber cells. The best of refining was achieved when the fiber bundles were treated with buffer-panzym solution in combination with ultrasonic treatment.
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