Browsing by Subject "Raman spectrometry"

Now showing 1 - 7 of 7

Open Access
Anharmonic line shift and linewidth of the Raman modes in TlInS2 layered crystals
(John Wiley & Sons Ltd., 2004) Yuksek, N. S.; Gasanly, N. M.; Aydınlı, Atilla
The temperature dependence of the unpolarized Raman spectra from TlInS 2 layered crystal was measured between 10 and 300 K. The analysis of the experimental data showed that the temperature dependences of wavenumbers and linewidths are well described by considering the contributions from thermal expansion and lattice anharmonicity. The purely anharmonic contribution (phonon-phonon coupling) was found to be due to three-phonon processes. This work demonstrates that the two Raman modes at 280.9 and 292.3 cm-1 exhibit changes toward high wavenumbers as the temperature is raised from 10 to 300 K.
Open Access
Dispersion of multi-walled carbon nanotubes in an aqueous medium by water-dispersible conjugated polymer nanoparticles
(2010) Baykal, B.; Ibrahimova, V.; Er, G.; Bengü, E.; Tuncel, D.
Vertically aligned multi-walled carbon nanotubes (MWCNTs) synthesized by the alcohol catalytic CVD (ACCVD) technique are dispersed in water with the aid of water-dispersible conjugated polymer nanoparticles (CPNs). The interactions between CPNs and CNTs are studied with spectroscopy (UV-Vis, fluorescence and Raman) and electron microscopy techniques are used to confirm attachment of CPNs to the CNT sidewalls.
Open Access
Electrochemical synthesis of mesoporous gold films toward mesospace-stimulated optical properties
(Nature Publishing Group, 2015) Li C.; Dag Ö.; Dao, T.D.; Nagao, T.; Sakamoto, Y.; Kimura, T.; Terasaki O.; Yamauchi, Y.
Mesoporous gold (Au) films with tunable pores are expected to provide fascinating optical properties stimulated by the mesospaces, but they have not been realized yet because of the difficulty of controlling the Au crystal growth. Here, we report a reliable soft-templating method to fabricate mesoporous Au films using stable micelles of diblock copolymers, with electrochemical deposition advantageous for precise control of Au crystal growth. Strong field enhancement takes place around the center of the uniform mesopores as well as on the walls between the pores, leading to the enhanced light scattering as well as surface-enhanced Raman scattering (SERS), which is understandable, for example, from Babinet principles applied for the reverse system of nanoparticle ensembles. © 2015 Macmillan Publishers Limited. All rights reserved.
Open Access
Generation of InN nanocrystals in organic solution through laser ablation of high pressure chemical vapor deposition-grown InN thin film
(Springer, 2012-07-27) Alkis, S.; Alevli, M.; Burzhuev, S.; Vural, H. A.; Okyay, Ali Kemal; Ortaç, B.
We report the synthesis of colloidal InN nanocrystals (InN-NCs) in organic solution through nanosecond pulsed laser ablation of high pressure chemical vapor deposition-grown InN thin film on GaN/sapphire template substrate. The size, the structural, the optical, and the chemical characteristics of InN-NCs demonstrate that the colloidal InN crystalline nanostructures in ethanol are synthesized with spherical shape within 5.9-25.3, 5.45-34.8, 3.24-36 nm particle-size distributions, increasing the pulse energy value. The colloidal InN-NCs solutions present strong absorption edge tailoring from NIR region to UV region.
Open Access
One-step synthesis of size-tunable Ag nanoparticles incorporated in electrospun PVA/cyclodextrin nanofibers
(Pergamon Press, 2014) Celebioglu A.; Aytac Z.; Umu, O. C. O.; Dana, A.; Tekinay, T.; Uyar, Tamer
One-step synthesis of size-tunable silver nanoparticles (Ag-NP) incorporated into electrospun nanofibers was achieved. Initially, in situ reduction of silver salt (AgNO3) to Ag-NP was carried out in aqueous solution of polyvinyl alcohol (PVA). Here, PVA was used as reducing agent and stabilizing polymer as well as electrospinning polymeric matrix for the fabrication of PVA/Ag-NP nanofibers. Afterwards, hydroxypropyl-beta-cyclodextrin (HPβCD) was used as an additional reducing and stabilizing agent in order to control size and uniform dispersion of Ag-NP. The size of Ag-NP was ∼8 nm and some Ag-NP aggregates were observed for PVA/Ag-NP nanofibers, conversely, the size of Ag-NP decreased from ∼8 nm down to ∼2 nm within the fiber matrix without aggregation were attained for PVA/HPβCD nanofibers. The PVA/Ag-NP and PVA/HPβCD/Ag-NP nanofibers exhibited surface enhanced Raman scattering (SERS) effect. Moreover, antibacterial properties of PVA/Ag-NP and PVA/HPβCD/Ag-NP nanofibrous mats were tested against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria.
Open Access
Plasmonic band gap structures for surface-enhanced Raman scattering
(Optical Society of American (OSA), 2008) Kocabas, A.; Ertas G.; Senlik, S.S.; Aydınlı, Atilla
Surface-enhanced Raman Scattering (SERS) of rhodamine 6G (R6G) adsorbed on biharmonic metallic grating structures was studied. Biharmonic metallic gratings include two different grating components, one acting as a coupler to excite surface plasmon polaritons (SPP), and the other forming a plasmonic band gap for the propagating SPPs. In the vicinity of the band edges, localized surface plasmons are formed. These localized Plasmons strongly enhance the scattering efficiency of the Raman signal emitted on the metallic grating surfaces. It was shown that reproducible Raman scattering enhancement factors of over 10 5 can be achieved by fabricating biharmonic SERS templates using soft nano-imprint technique. We have shown that the SERS activities from these templates are tunable as a function of plasmonic resonance conditions. Similar enhancement factors were also measured for directional emission of photoluminescence. At the wavelengths of the plasmonic absorption peak, directional enhancement by a factor of 30 was deduced for photoluminescence measurements. © 2008 Optical Society of America.
Open Access
Role of the environmental spectrum in the decoherence and dephasing of multilevel quantum systems
(The American Physical Society, 2005) Hakioǧlu T.; Savran, K.
We examine the effect of multilevels on decoherence and dephasing properties of a quantum system consisting of a nonideal two level subspace, identified as the qubit, and a finite set of higher energy levels above this qubit subspace. The whole system is under interaction with an environmental bath through a Caldeira-Leggett type coupling. The model that we use is an rf-SQUID under macroscopic quantum coherence and coupled inductively to a flux noise characterized by an environmental spectrum. The model interaction can generate dipole couplings which can be appreciable between the qubit and the high levels. The decoherence properties of the qubit subspace is examined numerically using the master equation formalism of the system's reduced density matrix. We calculate the relaxation and dephasing times as the spectral parameters of the environment are varied. We observe that, these calculated time scales receive contribution from all available frequencies in the noise spectrum (even well above the system's resonant frequency scales) stressing the dominant role played by the nonresonant transitions. The relaxation and dephasing and the leakage times thus calculated, strongly depend on the appreciably interacting levels determined by the strength of the dipole coupling. Under the influence of these nonresonant and multilevel effects, the validity of the two level approximation is dictated not by the low temperature as conveniently believed, but by these multilevel dipole couplings as well as the availability of the environmental modes.